MEDICAL MONITORING AND TREATMENT DEVICE WITH EXTERNAL
PACING
RELATED APPLICATIONS
This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional
Application Serial No. 61/653,889, titled "NONINVASIVE AMBULATORY
MONITORING AND TREATMENT DEVICE WITH EXTERNAL PACING," filed
on May 31, 2012, which is hereby incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is directed to noninvasive ambulatory medical devices,
and more particularly, to a non-invasive medical monitoring and treatment device that
is capable of externally pacing the heart of a patient wearing the device.
2. Discussion of the Related Art
Cardiac arrest and other cardiac health ailments are a major cause of death
worldwide. Various resuscitation efforts aim to maintain the body's circulatory and
respiratory systems during cardiac arrest in an attempt to save the life of the victim.
The sooner these resuscitation efforts begin, the better the victim' s chances of
survival.
To protect against cardiac arrest and other cardiac health ailments, some atrisk
patients may use a wearable defibrillator, such as the LifeVest® wearable
cardioverter defibrillator available from Zoll Medical Corporation of Chelmsford,
Massachusetts. To remain protected, the patient wears the device nearly continuously
while going about their normal daily activities, while awake, and while asleep.
SUMMARY OF THE INVENTION
Some aspects and embodiments of the present invention administer external
pacing to the heart using a non-invasive bodily-attached ambulatory medical
monitoring and treatment device (hereinafter referred to as a "medical monitoring and
treatment device"). As used herein, the term non-invasive means that the device does
not penetrate the body of a patient. This is in contrast to invasive devices, such as
implantable medical devices, in which at least a portion of the device is disposed
subcutaneously. The term bodily-attached means that at least a portion of the device
(other than its electrodes in the case of a defibrillator, cardioverter or pacer) is
removably attached to the body of a patient, such as by mechanical coupling (for
example, by a wrist strap, cervical collar, bicep ring), adhesion (for example, by a
adhesive gel intermediary), suction, magnetism, fabric or other flexible material (for
example, by straps or integration into a garment) or other body mounting features not
limited by the aforementioned examples. These coupling elements hold the device in a
substantially fixed position with respect to the body of the patient. The term
ambulatory means that the device is capable of and designed for moving with the
patient as the patient goes about their daily routine.
One example of a medical monitoring and treatment device is the LifeVest®
Wearable Cardioverter Defibrillator available from Zoll Medical Corporation of
Chelmsford, Massachusetts. A medical monitoring and treatment device can provide
life saving defibrillation treatment to a patient suffering a treatable form of cardiac
arrhythmia such as Ventricular Fibrillation (VF) or Ventricular Tachycardia (VT).
Applicants have appreciated that such a medical monitoring and treatment device can
be configured to perform a variety of different types of cardiac pacing to treat a wide
variety of different cardiac arrhythmias, such as bradycardia, tachycardia, an irregular
cardiac rhythm, and asystole (including asystole after a shock). Applicants have
further appreciated that, in other embodiments, a medical monitoring and treatment
device can be configured to perform pacing to treat pulseless electrical activity. In
accordance with an aspect of the present invention, the medical monitoring and
treatment device can be configured to pace the heart of the patient at a fixed energy
level (e.g., fixed current, fixed voltage, etc. . .) and pulse rate, to pace the heart of the
patient on demand with a fixed energy level and an adjustable rate responsive to the
detected intrinsic activity level of the patient's heart, or to pace the heart of the patient
using capture management with an adjustable energy level and adjustable rate
responsive to the detected intrinsic rate of the patient's heart and the detected response
of the patient's heart to pacing, including both on a beat-by-beat basis and as analyzed
over other various time intervals.
According to some embodiments, a medical monitoring and treatment device
is provided. The medical monitoring and treatment device includes a battery, at least
one therapy electrode coupled to the battery, a memory storing information indicative
of a patient's cardiac activity, and at least one processor coupled to the memory and
the at least one therapy electrode. The at least one processor is configured to identify
a cardiac arrhythmia within the information and execute at least one pacing routine to
treat the identified cardiac arrhythmia.
In the medical monitoring and treatment device, the cardiac arrhythmia that
the at least one processor is configured to identify may include bradycardia and the at
least one pacing routine may be configured to determine that a first interval has
passed without detection of a heart beat and apply, responsive to determining that the
first interval has passed, a pacing pulse via the at least one therapy electrode. The
first interval may be defined by a base pacing rate and a hysteresis rate. The at least
one pacing routine may be further configured to detect an intrinsic heart beat prior to
passage of a second interval; determine a third interval based on the base pacing rate,
the hysteresis rate, and a point where the intrinsic heart beat was detected; and
determine whether another intrinsic heart beat occurs within the third interval.
In the medical monitoring and treatment device, the cardiac arrhythmia that
the at least one processor is configured to identify may include tachycardia and the at
least one pacing routine may be configured to detect a plurality of intrinsic heart beats
prior to passage of a first interval, the plurality of intrinsic heart beats having an
intrinsic frequency, the first interval being defined by an anti-tachyarrhythmic pacing
rate and apply, responsive to detecting the intrinsic frequency, a series of pacing
pulses via the at least one therapy electrode, the series of pacing pulses having a
frequency above the intrinsic frequency. The at least one pacing routine may be
further configured to detect, after applying the series of pacing pulses, whether
another plurality of intrinsic heart beats occur within a second interval, the second
interval being defined by the anti-tachyarrhythmic pacing rate.
In the medical monitoring and treatment device, the cardiac arrhythmia that
the at least one processor is configured to identify may include an erratic heart rate
and the at least one pacing routine may be configured to identify a first series of heart
beats within the information, the first series having a lower frequency; identify a
second series of heart beats within the information, the second series a upper
frequency; and apply, responsive to identifying the erratic heart rate, a series of pacing
pulses via the at least one therapy electrode, the series of pacing pulses having a
frequency above the lower frequency and below the upper frequency.
In the medical monitoring and treatment device, the cardiac arrhythmia that
the at least one processor is configured to identify may include at least one of asystole
and pulseless electrical activity and the at least one pacing routine may be configured
to determine that a first interval has passed without detection of a heart beat; and
apply, responsive to determining that the first interval has passed, a pacing pulse via
the at least one therapy electrode. The at least on pacing routine may be further
configured to apply a defibrillating shock prior to applying the pacing pulse.
In the medical monitoring and treatment device, the at least one pacing routine
may be further configured to determine whether the at least one pacing routine
resulted in capture and adjust, responsive to determining that capture did not result,
the characteristics of pacing pulses applied during subsequent executions of the at
least one pacing routine. The characteristics of the pacing pulses subject to
adjustment may include a pulse energy level, a pulse rate, and a pulse width.
In the medical monitoring and treatment device, the at least one pacing routine
is further configured to determine whether the at least one pacing routine resulted in
capture; and adjust, responsive to determining that capture did result, the
characteristics of pacing pulses applied during subsequent executions of the at least
one pacing routine.
According to other embodiments, a non-invasive bodily-attached ambulatory
wearable defibrillator is provided. The non-invasive bodily-attached ambulatory
wearable defibrillator includes a battery, at least one therapy electrode coupled to the
battery, a memory storing information indicative of a patient' s cardiac activity, and at
least one processor coupled to the memory and the at least one therapy electrode. The
at least one processor is configured to identify a cardiac arrhythmia within the
information and execute at least one pacing routine to treat the identified cardiac
arrhythmia.
In the non-invasive bodily-attached ambulatory defibrillator, the cardiac
arrhythmia that the at least one processor is configured to identify may include
bradycardia and the at least one pacing routine may be configured to determine that a
first interval has passed without detection of a heart beat and apply, responsive to
determining that the first interval has passed, a pacing pulse via the at least one
therapy electrode. The first interval may be defined by a base pacing rate and a
hysteresis rate. The at least one pacing routine may be further configured to detect an
intrinsic heart beat prior to passage of a second interval; determine a third interval
based on the base pacing rate, the hysteresis rate, and a point where the intrinsic heart
beat was detected; and determine whether another intrinsic heart beat occurs within
the third interval.
In the non-invasive bodily-attached ambulatory defibrillator, the cardiac
arrhythmia that the at least one processor is configured to identify may include
tachycardia and the at least one pacing routine may be configured to detect a plurality
of intrinsic heart beats prior to passage of a first interval, the plurality of intrinsic
heart beats having an intrinsic frequency, the first interval being defined by an antitachyarrhythmic
pacing rate; and apply, responsive to detecting the intrinsic
frequency, a series of pacing pulses via the at least one therapy electrode, the series of
pacing pulses having a frequency above the intrinsic frequency. The at least one
pacing routine may be further configured to detect, after applying the series of pacing
pulses, whether another plurality of intrinsic heart beats occur within a second
interval, the second interval being defined by the anti-tachyarrhythmic pacing rate.
In the non-invasive bodily-attached ambulatory defibrillator, the cardiac
arrhythmia that the at least one processor is configured to identify may include an
erratic heart rate and the at least one pacing routine may be configured to identify a
first series of heart beats within the information, the first series having a lower
frequency; identify a second series of heart beats within the information, the second
series a upper frequency; and apply, responsive to identifying the erratic heart rate, a
series of pacing pulses via the at least one therapy electrode, the series of pacing
pulses having a frequency above the lower frequency and below the upper frequency.
In the non-invasive bodily-attached ambulatory defibrillator, the cardiac
arrhythmia that the at least one processor is configured to identify may include at least
one of asystole and pulseless electrical activity and the at least one pacing routine may
be configured to determine that a first interval has passed without detection of a heart
beat and apply, responsive to determining that the first interval has passed, a pacing
pulse via the at least one therapy electrode. The at least one pacing routine may be
further configured to apply a defibrillating shock prior to applying the pacing pulse.
In the non-invasive bodily-attached ambulatory defibrillator, the at least one
pacing routine may be further configured to determine whether the at least one pacing
routine resulted in capture and adjust, responsive to determining that capture did not
result, the characteristics of pacing pulses applied during subsequent executions of the
at least one pacing routine. The characteristics of the pacing pulses subject to
adjustment may include a pulse energy level, a pulse rate, and a pulse width.
In the non-invasive bodily-attached ambulatory defibrillator, the at least one
pacing routine may be further configured to determine whether the at least one pacing
routine resulted in capture and adjust, responsive to determining that capture did
result, the characteristics of pacing pulses applied during subsequent executions of the
at least one pacing routine.
According to another embodiment, a method of treating cardiac dysfunction
using a medical monitoring and treatment device with pacing is provided. The
medical monitoring and treatment device may include a non-invasive bodily-attached
ambulatory defibrillator. The method includes acts of identifying, by the medical
monitoring and treatment device, a cardiac arrhythmia within information indicative
of a patient' s cardiac activity; and executing, by the medical monitoring and treatment
device, at least one pacing routine to treat the identified cardiac arrhythmia.
In the method, where the cardiac arrhythmia includes bradycardia, the act of
executing the at least one pacing routine may include acts of determining that a first
interval has passed without detection of a heart beat and applying, responsive to
determining that the first interval has passed, a pacing pulse via the at least one
therapy electrode. The act of determining that the first interval has passed may
include an act of defining the first interval using a base pacing rate and a hysteresis
rate. The act of executing the at least one pacing routine may include acts of detecting
an intrinsic heart beat prior to passage of a second interval; determining a third
interval based on the base pacing rate, the hysteresis rate, and a point where the
intrinsic heart beat was detected; and determining whether another intrinsic heart beat
occurs within the third interval.
In the method, where the cardiac arrhythmia includes tachycardia, the act of
executing the at least one pacing routine may include acts of detecting a plurality of
intrinsic heart beats prior to passage of a first interval, the plurality of intrinsic heart
beats having an intrinsic frequency, the first interval being defined by an antitachyarrhythmic
pacing rate and applying, responsive to detecting the intrinsic
frequency, a series of pacing pulses via the at least one therapy electrode, the series of
pacing pulses having a frequency above the intrinsic frequency.
In the method, where the cardiac arrhythmia includes an erratic heart rate, the
act of executing the at least one pacing routine may include acts of identifying a first
series of heart beats within the information, the first series having a lower frequency;
identifying a second series of heart beats within the information, the second series a
upper frequency; and applying, responsive to identifying the erratic heart rate, a series
of pacing pulses via the at least one therapy electrode, the series of pacing pulses
having a frequency above the lower frequency and below the upper frequency.
In the method, where the cardiac arrhythmia includes at least one of asystole
and pulseless electrical activity, the act of executing the at least one pacing routine
may include acts of determining that a first interval has passed without detection of a
heart beat; and applying, responsive to determining that the first interval has passed, a
pacing pulse via the at least one therapy electrode. The act of executing the at least
one pacing routine may include an act of applying a defibrillating shock prior to
applying the pacing pulse.
In the method, the act of executing the at least one pacing routine may include
acts of determining whether the at least one pacing routine resulted in successful
capture and adjusting, responsive to determining that capture did not result, the
characteristics of pacing pulses applied during subsequent executions of the at least
one pacing routine. The act of adjusting the characteristics may include an act of
adjusting at least one of a pulse energy level, a pulse rate, and a pulse width.
Still other aspects, embodiments, and advantages of these exemplary aspects
and embodiments are discussed in detail below. Moreover, it is to be understood that
both the foregoing information and the following detailed description are merely
illustrative examples of various aspects and embodiments of the present invention,
and are intended to provide an overview or framework for understanding the nature
and character of the claimed aspects and embodiments. Any embodiment disclosed
herein may be combined with any other embodiment in any manner consistent with at
least one of the aspects disclosed herein, and references to "an embodiment," "some
embodiments," "an alternate embodiment," "various embodiments," "one
embodiment," "at least one embodiment," "this and other embodiments" or the like
are not necessarily mutually exclusive and are intended to indicate that a particular
feature, structure, or characteristic described in connection with the embodiment may
be included in at least one embodiment. The appearance of such terms herein is not
necessarily all referring to the same embodiment.
Furthermore, in the event of inconsistent usages of terms between this
document and documents incorporated herein by reference, the term usage in the
incorporated references is supplementary to that of this document; for irreconcilable
inconsistencies, the term usage in this document controls. In addition, the
accompanying drawings are included to provide illustration and a further
understanding of the various aspects and embodiments, and are incorporated in and
constitute a part of this specification. The drawings, together with the remainder of
the specification, serve to explain principles and operations of the described and
claimed aspects and embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are not intended to be drawn to scale. In the
drawings, each identical or nearly identical component that is illustrated in various
figures is represented by a like numeral. For purposes of clarity, not every component
may be labeled in every drawing. In the drawings:
Fig. 1 illustrates a medical monitoring and treatment device, such as a
wearable defibrillator;
Fig. 2 is a functional block diagram of one example of a portable treatment
controller that may be used in the medical monitoring and treatment device of Fig. 1;
Fig. 3 illustrates a number of different pacing waveforms that may be provided
by the medical monitoring and treatment device, including a 40ms constant current
pulse; and
Fig. 4 illustrates various aspects of demand pacing which can be adjusted in
connection with on demand pacing or capture management pacing.
DETAILED DESCRIPTION
This invention is not limited in its application to the details of construction and
the arrangement of components set forth in the following description or illustrated in
the drawings. The invention is capable of other embodiments and of being practiced
or of being carried out in various ways. Also, the phraseology and terminology used
herein is for the purpose of description and should not be regarded as limiting. The
use of "including," "comprising," "having," "containing," "involving," and variations
thereof herein is meant to encompass the items listed thereafter and equivalents
thereof as well as additional items.
Fig. 1 illustrates a medical monitoring and treatment device, such as a
LifeVest® Wearable Cardioverter Defibrillator available from Zoll Medical
Corporation of Chelmsford, Massachusetts. As shown, the medical monitoring and
treatment device 100 includes a harness 110 having a pair of shoulder straps and a belt
that is worn about the torso of a patient. The harness 110 is typically made from a
material, such as cotton, nylon, spandex, or antron that is breathable, and unlikely to
cause skin irritation, even when worn for prolonged periods of time. The medical
monitoring and treatment device 100 includes a plurality of electrocardiographic
(ECG) sensing electrodes 112 that are disposed by the harness 110 at various
positions about the patient's body and electrically coupled (wirelessly or by a wired
connection) to a portable treatment controller 120 via a connection pod 130. The
plurality of ECG sensing electrodes 112 are used by the portable treatment controller
120 to monitor the cardiac function of the patient and generally include a front/back
pair of ECG sensing electrodes and a side/side pair of ECG sensing electrodes. It
should be appreciated that additional ECG sensing electrodes may be provided, and
the plurality of ECG sensing electrodes 112 may be disposed at varying locations
about the patient's body. In addition, the plurality of ECG electrodes 112 may
incorporate any electrode system, including conventional stick-on adhesive
electrodes, dry-sensing capacitive ECG electrodes, radio transparent electrodes,
segmented electrodes, or one or more long term wear electrodes that are configured to
be continuously worn by a patient for extended periods (e.g., 3 or more days). One
example of such a long term wear electrode is described in co-pending Application
Serial No. 61/653,749, titled "LONG TERM WEAR MULTIFUNCTION
BIOMEDICAL ELECTRODE," filed 5/3 1/20 12, which is hereby incorporated herein
by reference in its entirety.
The medical monitoring and treatment devices disclosed herein may
incorporate sundry materials arranged in a variety of configurations to maintain a
proper fit with the patient's body. For example, some embodiments include a
garment as described in co-pending Application Serial No. 13/460,250, titled
"PATIENT-WORN ENERGY DELIVERY APPARATUS AND TECHNIQUES
FOR SIZING SAME," filed April 30, 2012, which is hereby incorporated herein by
reference in its entirety. Thus embodiments are not limited to the configuration and
materials described above with reference to Fig. 1.
The medical monitoring and treatment device 100 also includes a plurality of
therapy electrodes 114 that are electrically coupled to the portable treatment controller
120 via the connection pod 130 and which are capable of delivering one or more
therapeutic defibrillating shocks to the body of the patient, if it is determined that such
treatment is warranted. As shown, the plurality of therapy electrodes 114 includes a
first therapy electrode 114a that is disposed on the front of the patient's torso and a
second therapy electrode 114b that is disposed on the back of the patient's torso. The
second therapy electrode 114b includes a pair of therapy electrodes that are
electrically coupled together and act as the second therapy electrode 114b. The use of
two therapy electrodes 114a, 114b permits a biphasic shock to be delivered to the
body of the patient, such that a first of the two therapy electrodes can deliver a first
phase of the biphasic shock with the other therapy electrode acting as a return, and the
other therapy electrode can deliver the second phase of the biphasic shock with the
first therapy electrode acting as the return. The connection pod 130 electrically
couples the plurality of ECG sensing electrodes 112 and the plurality of therapy
electrodes 114 to the portable treatment controller 120, and may include electronic
circuitry. For example, in one implementation the connection pod 130 includes signal
acquisition circuitry, such as a plurality of differential amplifiers to receive ECG
signals from different ones of the plurality of ECG sensing electrodes 112 and to
provide a differential ECG signal to the portable treatment controller 120 based on the
difference therebetween. The connection pod 130 may also include other electronic
circuitry, such as a motion sensor or accelerometer by which patient activity may be
monitored.
In some embodiments, both the first therapy electrode 114a and the second
therapy electrode 114b are disposed on the front of the patient's torso. For example,
the first therapy electrode 114a may be located at external to the apex of the heart and
the second therapy electrode 114b may be located along the parasternal line. Thus
embodiments are not limited to a particular arrangement of therapy electrodes 114.
In some embodiments, the plurality of ECG sensing electrodes 112 are
positioned and paired such that artifacts generated from electrical activity are
decreased. In other embodiments, the electronic circuitry included in the portable
treatment controller 120 may equalize artifacts measured at electrodes by changing a
gain or impedance. Other techniques of decreasing or preventing artifacts within
measured electrical activity that may be used in conjunction the embodiments
disclosed herein are explained in U.S. Patent No. 8,185,199, titled "MONITORING
PHYSIOLOGICAL SIGNALS DURING EXTERNAL ELECTRICAL
STIMULATION," issued May 22, 2012, which is incorporated by reference herein in
its entirety.
As shown in Fig. 1, the medical monitoring and treatment device 100 may also
include a user interface pod 140 that is electrically coupled to the portable treatment
controller 120. The user interface pod 140 can be attached to the patient's clothing or
to the harness 110, for example, via a clip (not shown) that is attached to a portion of
the interface pod 140. Alternatively, the user interface pod 140 may simply be held in
a person's hand. The user interface pod 140 typically includes one or more actionable
user interface elements (e.g., one or more buttons, a fingerprint scanner, a touch
screen, microphone, etc. . .) by which the patient, or a bystander can communicate
with the portable treatment controller 120, and a speaker by which the portable
treatment controller 120 may communicate with the patient or the bystander. In
certain models of the LifeVest® Wearable Cardioverter Defibrillator, the
functionality of the user interface pod 140 is incorporated into the portable treatment
controller 120.
Where the portable treatment controller 120 determines that the patient is
experiencing cardiac arrhythmia, the portable treatment controller 120 may issue an
audible alarm via a loudspeaker (not shown) on the portable treatment controller 120
and/or the user interface pod 140 alerting the patient and any bystanders to the
patient's medical condition. Examples of notifications issued by the portable
treatment controller 120 are described in co-pending Application Serial No.
13/428,703, titled "SYSTEM AND METHOD FOR ADAPTING ALARMS IN A
WEARABLE MEDICAL DEVICE," filed March 23, 2012, which is incorporated by
reference herein in its entirety. The portable treatment controller 120 may also
instruct the patient to press and hold one or more buttons on the portable treatment
controller 120 or on the user interface pod 140 to indicate that the patient is conscious,
thereby instructing the portable treatment controller 120 to withhold the delivery of
one or more therapeutic defibrillating shocks. If the patient does not respond, the
device may presume that the patient is unconscious, and proceed with the treatment
sequence, culminating in the delivery of one or more defibrillating shocks to the body
of the patient.
The portable treatment controller 120 generally includes at least one processor,
microprocessor, or controller, such as a processor commercially available from
companies such as Texas Instruments, Intel, AMD, Sun, IBM, Motorola, Freescale
and ARM Holdings. In one implementation, the at least one processor includes a
power conserving processor arrangement that comprises a general purpose processor,
such as an Intel® PXA270 processor and a special purpose processor, such as a
Freescale™ DSP5631 1 Digital Signal Processor. Such a power conserving processor
arrangement is described in co-pending Application Serial No. 12/833,096, titled
SYSTEM AND METHOD FOR CONSERVING POWER IN A MEDICAL
DEVICE, filed July 9, 2010 (hereinafter the "'096 application") which is incorporated
by reference herein in its entirety. The at least one processor of the portable treatment
controller 120 is configured to monitor the patient's medical condition, to perform
medical data logging and storage, and to provide medical treatment to the patient in
response to a detected medical condition, such as cardiac arrhythmia.
Although not shown, the medical monitoring and treatment device 100 may
include additional sensors, other than the ECG sensing electrodes 112, capable of
monitoring the physiological condition or activity of the patient. For example,
sensors capable of measuring blood pressure, heart rate, heart sounds, thoracic
impedance, pulse oxygen level, respiration rate, and the activity level of the patient
may also be provided.
Fig. 2 illustrates a portable treatment controller 120 that is configured to perform
the critical functions of monitoring physiological information for abnormalities and
initiating treatment of detected abnormalities. As shown, the portable treatment
controller 120 can include the power conserving processor arrangement 200 described
in the '096 application, a sensor interface 212, a therapy delivery interface 202, data
storage 204, a communication network interface 206, a user interface 208 and a
battery 210. In this illustrated example, the battery 210 is a rechargeable 3 cell
2200mAh lithium ion battery pack that provides electrical power to the other device
components with a minimum 24 hour runtime between charges. Such a battery 210
has sufficient capacity to administer one or more therapeutic shocks and the therapy
delivery interface 202 has wiring suitable to carry the load to the therapy electrodes
114. Moreover, in the example shown, the battery 210 has sufficient capacity to
deliver up to 5 or more therapeutic shocks, even at battery runtime expiration. The
amount of power capable of being delivered to a patient during a defibrillating shock
is substantial, for example up to approximately 200 Joules.
The sensor interface 212 and the therapy delivery interface 202 are coupled to
the power conserving processor arrangement 200 and more particularly to the critical
purpose processor of the power conserving processing arrangement 200 as described
in the Ό 96 application. The data storage 204, the network interface 206, and the user
interface 208 are also coupled to the power conserving processor arrangement 200,
and more particularly to the general purpose processor of the power conserving
processing arrangement as also described in the Ό 96 application.
In the example shown, the data storage 204 includes a computer readable and
writeable nonvolatile data storage medium configured to store non-transitory
instructions and other data. The medium may, for example, be optical disk, magnetic
disk or flash memory, among others and may be permanently affixed to, or removable
from, the portable treatment controller 120.
As shown in FIG. 2, the portable treatment controller 120 includes several system
interface components 202, 206 and 212. Each of these system interface components
is configured to exchange, i.e., send or receive data, with specialized devices that may
be located within the portable treatment controller 200 or elsewhere. The components
used by the interfaces 202, 206 and 212 may include hardware components, software
components or a combination of both. In the instance of each interface, these
components physically and logically couple the portable treatment controller 200 to
one or more specialized devices. This physical and logical coupling enables the
portable treatment controller 120 to both communicate with and, in some instances,
control the operation of specialized devices. These specialized devices may include
physiological sensors, therapy delivery devices, and computer networking devices.
According to various examples, the hardware and software components of the
interfaces 202, 206 and 212 employ a variety of coupling and communication
techniques. In some examples, the interfaces 202, 206 and 212 use leads, cables or
other wired connectors as conduits to exchange data between the portable treatment
controller 120 and specialized devices. In other examples, the interfaces 202, 206 and
212 communicate with specialized devices using wireless technologies such as radio
frequency or infrared technology. The software components included in the interfaces
202, 206 and 212 enable the power conserving processor arrangement 200 to
communicate with specialized devices. These software components may include
elements such as objects, executable code and populated data structures. Together,
these hardware and software components provide interfaces through which the power
conserving processor arrangement 200 can exchange information with the specialized
devices. Moreover, in at least some examples where one or more specialized devices
communicate using analog signals, the interfaces 202, 206 and 212 can include
components configured to convert analog information into digital information, and
vice-versa.
As discussed above, the system interface components 202, 206 and 212 shown in
the example of Fig. 2 support different types of specialized devices. For instance, the
components of the sensor interface 212 couple the power conserving processor
arrangement 200 to one or more physiological sensors such as a body temperatures
sensors, respiration monitors and dry-capacitive ECG sensing electrodes. It should be
appreciated that other types of ECG sensing electrodes may be used, as the present
invention is not limited to any particular type of ECG sensing electrode. The
components of the therapy delivery interface 202 couple one or more therapy delivery
devices, such as capacitors and defibrillator electrodes, to the power conserving
processor arrangement 200. In addition, the components of the network interface 206
couple the power conserving processor arrangement to a computer network via a
networking device, such as a bridge, router or hub. The network interface 206 may
supports a variety of standards and protocols, examples of which include USB,
TCP/IP, Ethernet, Wireless Ethernet, Bluetooth, ZigBee, M-Bus, IP, IPV6, UDP,
DTN, HTTP, FTP, SNMP, CDMA, NMEA and GSM. To ensure data transfer is
secure, in some examples, the portable treatment controller 200 can transmit data via
the network interface 206 using a variety of security measures including, for example,
TSL, SSL or VPN. In other examples, the network interface 206 includes both a
physical interface configured for wireless communication and a physical interface
configured for wired communication.
The user interface 208 shown in FIG. 2 includes a combination of hardware and
software components that allow the portable treatment controller 200 to communicate
with an external entity, such as a user. These components are configured to receive
information from actions such as physical movement, verbal intonation or thought
processes. In addition, the components of the user interface 208 can provide
information to external entities. Examples of the components that may be employed
within the user interface 208 include keyboards, mouse devices, trackballs,
microphones, electrodes, touch screens, printing devices, display screens and
speakers.
The LifeVest® wearable cardioverter defibrillator can monitor a patient's ECG
signals, detect various cardiac arrhythmias, and provide life saving defibrillation
treatment to a patient suffering a treatable form of cardiac arrhythmia such as
Ventricular Fibrillation (VF) or Ventricular Tachycardia (VT).
Applicants have appreciated that such a medical monitoring and treatment device
can be configured to perform a variety of different types of cardiac pacing to treat a
wide variety of different cardiac arrhythmias, such as bradycardia, tachycardia, an
irregular cardiac rhythm, or asystole. Applicants have further appreciated that, in
other embodiments, a medical monitoring and treatment device can be configured to
perform pacing to treat pulseless electrical activity. In accordance with an aspect of
the present invention, the device can be configured to pace the heart of the patient at a
fixed energy level and pulse rate, to pace the heart of the patient on demand with a
fixed energy level and an adjustable rate responsive to the detected intrinsic activity
level of the patient's heart, or to pace the heart of the patient using capture
management with an adjustable energy level and rate responsive to the detected
intrinsic activity level of the patient's heart and the detected response of the patient's
heart. The various types of pacing may be applied to the patient externally by one or
more of the therapy electrodes 114a, 114b (Fig. 1). Various types of pacing that can
be performed by a medical monitoring and treatment device, such as the LifeVest®
wearable cardioverter defibrillator, can include asynchronous pacing at a fixed rate
and energy, pacing on demand at a variable rate and fixed energy, and capture
management pacing with an adjustable rate and adjustable energy level.
In some embodiments, the medical monitoring and treatment device is configured
to periodically assess the level of discomfort of the patient during pacing operation.
In these embodiments, responsive to determining that the patient' s discomfort level
exceeds a threshold, the device attempts to adjust the attributes of the pacing activity
to lessen the discomfort experienced by the patient.
In one embodiment, the medical monitoring and treatment device provides a user
interface through which the device receives information descriptive of the discomfort
level experienced by a patient. Should this information indicate that the level of
discomfort has transgressed a threshold level, the device adjusts characteristics of the
pacing operation in an attempt to decrease the level of discomfort.
In another embodiment, the medical monitoring and treatment device assesses the
level of discomfort of the patient by monitoring and recording the patient' s movement
before, during, and after administration of a pacing pulse. The device may monitor
the patient's movement using a variety of instrumentation including, for example, one
or more accelerators, audio sensors, etc. To assess the level of discomfort
experienced by the patient during pacing pulses, the device may analyze the recorded
history of the patient's movement and identify correlations between changes in the
patient's movement and the pacing pulse. Strong correlations between pacing pulses
and sudden patient movement, which may be representative of a flinch, and strong
correlations between pacing pulses and a sudden stoppage of movement, may indicate
that a patient is experiencing discomfort. Correlations having a value that
transgresses a threshold value may be deemed to indicate discomfort and may cause
the device to adjust the characteristics of a pacing pulse.
In other embodiments, the device adjusts the characteristics of the pacing
operation to lessen the discomfort level of the patient. The characteristics of the
pacing operation that may be adjusted include, for example, the energy level of pacing
pulses, the width of the pacing pulses, and the rate of the pacing pulses. In some
embodiments, the device monitors the cardiac activity of the patient during this
adjustment process to ensure that the pacing operation continues to effectively
manage cardiac function. In these embodiments, the device may revert the
characteristics of the pacing operation to their previous settings, should the pacing
operation become ineffective.
1. Fixed Rate and Energy Pacing
In accordance with an aspect of the present invention, a medical monitoring and
treatment device, such as the LifeVest® wearable cardioverter defibrillator, can be
configured to pace the heart of a patient at a fixed rate and fixed energy in response to
various types of cardiac arrhythmias. Examples of these cardiac arrhythmias include
bradyarrythmia, a lack of sensed cardiac activity (spontaneous or post shock asystole)
and pulseless electrical activity. In some cases, these cardiac arrhythmias may occur
before or after one or more defibrillation shocks. For example, the device may be
configured to provide pulses at a fixed energy level, a fixed pulse width, and a fixed
frequency in response to detection of any of the above-noted events by the ECG
sensing electrodes 112. The energy level of the pacing pulses may be set to a fixed
value by applying a desired current waveform for a determined duration of time by
one or more of the therapy electrodes 114a, 114b. The maximum current level of the
current waveform may be set to a value between approximately 0 mAmps to 200
mAmps, the pulse width may be set to a fixed value between approximately .05ms to
2ms, and the frequency of the pulses may be set to a fixed value between
approximately 30 pulses per minute (PPM) to approximately 200 PPM. In
accordance with one embodiment, a 40ms square wave pulse is used. Exemplary
pacing current waveforms, including a 40ms constant current pulse, a 5ms constant
current pulse, and a variable current pulse are shown in Fig. 3.
During pacing operation of the medical monitoring and treatment device, the
device may periodically pause for a period of time to evaluate the patient via the ECG
sensing electrodes to determine whether a normal sinus rhythm has returned. Where
the device detects a normal sinus rhythm, the device may discontinue the application
of pacing pulses and simply continue monitoring the patient's physiological signals,
such as the patient's ECG, temperature, pulse oxygen level, etc.
During an initial fitting of the medical monitoring and treatment device, the level
of current, the pulse width, and the frequency of the pulses may be set to an
appropriate level based on the input of a medical professional (such as the patient's
cardiologist) and the physiological condition of the patient (e.g., based on the
patient's normal resting heart rate, the patient's thoracic impedance, etc.)
Alternatively, the level of current, the pulse width, and the frequency of the pulses
may simply be set to an appropriate value based on typical impedance values for an
adult or child, and typical resting heart rates for an adult or child.
It should be appreciated that because pacing at a fixed rate may interfere with the
patient's own intrinsic heart rate, the device can be configured to perform such fixed
rate and energy pacing only in the event of a life-threatening Bradyarrythmia, a lack
of any detected cardiac activity following shock, or in response to pulseless electrical
activity following shock.
2. Demand (Adjustable Rate) Pacing
In accordance with an aspect of the present invention, a medical monitoring and
treatment device, such as the LifeVest® wearable cardioverter defibrillator, can also
be configured to pace the heart of a patient at a variable rate and a fixed energy in
response to various types of cardiac arrhythmias, including a bradyarrythmia (i.e., an
excessively slow heart rate), tachycardia (i.e., an excessively fast heart rate), an erratic
heart rate with no discernible regular sinus rhythm, a lack of sensed cardiac activity
(asystole), and pulseless electrical activity. Some of these cardiac arrhythmias may
occur following one or more defibrillation shocks.
As known to those skilled in the art, pacing at a fixed rate and energy may not be
appropriate to the particular type of cardiac arrhythmia of the patient, and even where
the rate and energy level is appropriate, pacing at a fixed rate can result in competition
between the rate at which the pacing pulses are being applied and the intrinsic rhythm
of the patient' s heart. For example, pacing at a fixed rate may result in the application
of a pacing pulse during the relative refractory period of the normal cardiac cycle (a
type of R wave on a T wave effect) that could promote ventricular tachycardia or
ventricular fibrillation. To overcome some of the disadvantages of fixed rate and
energy pacing, the medical monitoring and treatment device can be configured to
perform demand pacing, wherein the rate of the pacing pulses may be varied
dependent on the physiological state of the patient. For example, during demand
pacing, the device can deliver a pacing pulse only when needed by the patient. In
general, during the demand mode of pacing, the device searches for any intrinsic
cardiac activity of the patient, and if a heart beat is not detected within a designated
interval, a pacing pulse is delivered and a timer is set to the designated interval.
Where the designated interval expires without any detected intrinsic cardiac activity
of the patient, another pacing pulse is delivered and the timer reset. Alternatively,
where an intrinsic heart beat of the patient is detected within the designated interval,
the device resets the timer and continues to search for intrinsic cardiac activity.
Fig. 4 helps to illustrate some of the aspects of demand pacing and the manner in
which demand pacing can be performed by the medical monitoring and treatment
device. As illustrated in Fig. 4, the device may have a variable pacing interval 410
corresponding to the rate at which pacing pulses are delivered to the patient in the
absence of any detected intrinsic cardiac activity detected by the ECG sensing
electrodes 112 and ECG monitoring and detection circuitry. For example, the rate at
which pulsing paces are to be delivered to the patient (referred to as the "base pacing
rate" herein) may be set at 60 PPM and therefore, the corresponding base pacing
interval 410 would be set to 1 second.
The medical monitoring and treatment device may also have a hysteresis rate (not
shown in Fig. 4) corresponding to the detected intrinsic heart rate of the patient below
which the device performs pacing. According to some embodiments, the hysteresis
rate is a configurable parameter that is expressed as a percentage of the patient's
intrinsic heart rate. In the above example, the hysteresis rate may correspond to 50
beats per minute (BPM). In this example, if the intrinsic heart rate of the patient fell
to 50 BPM or below (e.g., more than approximately 1.2 seconds between detected
beats), the device would generate and apply a pacing impulse to the patient.
During application of a pacing pulse to the body of a patient and a short time
thereafter, the medical monitoring and treatment device may intentionally blank out a
portion of the ECG signals being received by the ECG monitoring and detection
circuitry to prevent this circuitry (e.g., amplifiers, A/D converters, etc.) from being
overwhelmed (e.g., saturated) by the pacing pulse. This may be performed in
hardware, software, or a combination of both. This period of time, referred to herein
as "the blanking interval" 420 may vary (e.g., between approximately 30ms to
200ms), but is typically between approximately 40ms to 80ms in duration.
In addition to the blanking interval 420, the medical monitoring and treatment
device can have a variable refractory period 430 that may vary dependent upon the
base pacing rate. The refractory period 430 corresponds to a period of time in which
signals sensed by the ECG sensing electrodes 112 and the ECG monitoring and
detection circuitry are ignored, and includes the blanking interval. The refractory
period 430 allows any generated QRS complexes or T waves induced in the patient by
virtue of the pacing pulse to be ignored, and not interpreted as intrinsic cardiac
activity of the patient. For example, where the base pacing rate is set to below 80
PPM, the refractory period might correspond to 340ms, and where the base pacing
rate is set above 90 PPM, the refractory period might correspond to 240ms. For
typical applications, the refractory period is generally between about 150ms and
500ms.
In accordance with an aspect of the present invention, the sensitivity of the ECG
monitoring and detection that is performed by the medical monitoring and treatment
device may also be varied to adjust the degree by which the ECG sensing electrodes
and associated ECG monitoring and detection circuitry can detect the patient's
intrinsic cardiac activity. For example, where the amplitude of certain discernable
portions (e.g., an R-wave) of a patient's intrinsic ECG signal is below that typically
encountered, the voltage threshold over which this discernable portion can be detected
as belonging to an ECG signal (and not attributed to noise or other factors) may be
lowered, for example from 2.5mV to 1.5 mV, to better detect the patient's intrinsic
cardiac activity. For instance, during an initial fitting of the medical monitoring and
treatment device, the sensitivity threshold of the device may be reduced to a minimal
value (e.g., 0.4mV) and the patient's intrinsic ECG signals may be monitored. The
sensitivity threshold may then be incrementally increased (thereby decreasing the
sensitivity of the device) and the patient' s intrinsic ECG signals monitored until these
ECG signals are no longer sensed. The sensitivity threshold may then be
incrementally decreased (thereby increasing the sensitivity of the device) until the
patient's intrinsic ECG signals are again sensed, and the sensitivity threshold of the
device may be set to approximately half this value.
As with fixed energy and rate pacing, the device may be configured to provide
pulses at a fixed energy level and a fixed pulse width in response to detection of any
of the above-noted events by the ECG sensing electrodes 112 and the ECG
monitoring and detection circuitry. The maximum current level of the current
waveform may be set to a value between approximately 10 mAmps to 200 mAmps,
the pulse width may be set to a fixed value between approximately 20ms to 40ms, and
the base rate of the pulses may be set to a fixed value between approximately 30
pulses per minute (PPM) to approximately 200 PPM, although the actual rate of the
pacing pulses can vary based upon the intrinsic cardiac activity of the patient. In
accordance with one embodiment, a 40ms constant current pulse is used, and the
current level is set to a fixed value based upon the input of a medical professional,
such as the patient' s cardiologist and the physiological condition of the patient. The
base pacing rate and the hysteresis rate may also be set based upon the input of the
patient's cardiologist (or other medical professional) and the physiological condition
of the patient, and the blanking interval and refractory period set to an appropriate
time interval based upon the base pacing rate and/or the hysteresis rate.
Although the base pacing rate may be set to a particular value based on the
physiological condition of the patient and input from a medical profession, the
medical monitoring and treatment device can include a number of different pacing
routines to respond to different cardiac arrhythmias, such as bradycardia, tachycardia,
an erratic heart rate with no discernable regular sinus rhythm, asystole, or pulseless
electrical activity. These pacing routines may be implemented using a variety of
hardware and software components and embodiments are not limited to a particular
configuration of hardware or software. For instance, the pacing routines may be
implemented using an application- specific integrated circuit (ASIC) tailored to
perform the functions described herein.
A. Bradycardia
As discussed above, where Bardycardia is detected and the intrinsic cardiac
rate of the patient is below that of the hysteresis rate, the medical monitoring and
treatment device will pace the patient at the pre-set base pacing rate. During this time,
the device will continue to monitor the patient' s intrinsic heart rate and will withhold
pacing pulses in the event that an intrinsic heart beat is detected within designated
interval corresponding to the hysteresis rate. This type of on demand pacing is
frequently termed "maintenance pacing."
B. Tachycardia
For responding to tachycardia, the medical monitoring and treatment device
may additionally include another pacing rate, termed an "anti-tachyarrhythmic pacing
rate" herein, above which the device will identify that the patient is suffering from
tachycardia, and will pace the patient in a manner to bring the patient' s intrinsic heart
back toward the base racing rate. For example, the device may employ a technique
known as overdrive pacing wherein a series of pacing pulses (e.g., between about 5
and 10 pacing pulses) are delivered to the patient at a frequency above the intrinsic
rate of the patient in an effort to gain control of the patient's heart rate. Once it is
determined that the device is in control of the patient's heart rate, the rate (i.e., the
frequency) of the pulses may be decremented, for example by about 10ms, and
another series of pacing pulses delivered. This delivery of pulses and the decrease in
frequency may continue until the detected intrinsic cardiac rate of the patient is below
the anti-tachyarrhythmic pacing rate, or at the base pacing rate. This type of pacing is
frequently termed "overdrive pacing" or "fast pacing."
C. Erratic Heart Rate
For responding to an erratic heart rate, the medical monitoring and treatment
device may perform a type of pacing that is similar to a combination of maintenance
pacing and overdrive pacing discussed above. For example, where the medical
monitoring and treatment device detects an erratic heart rate with no discernable sinus
rhythm, the device may deliver a series of pacing pulses (e.g., between about 5 and 10
pacing pulses) to the patient at a particular frequency. This frequency may be one that
is above a lower frequency of a series of detected intrinsic beats of the patient's heart
and below an upper frequency of the detected intrinsic beats of the patient's heart.
After delivering the series of pulses, the device may monitor the patient's heart to
determine if it has synchronized to the rate of the series of delivered pulses. Where
the intrinsic rate of the patient's heart is still erratic, the device may increase the
frequency of the series of pulses and deliver another series. This may continue until it
is established that the patient's heart is now in a more regular state. Upon
determining that the patient's heart is now in a more regular state, the device may
perform maintenance pacing if it is determined that the patient's intrinsic heart rate is
too low as discussed in section 2A above, or perform pacing at a decremented rate in
the manner discussed in section 2B above, if such is warranted.
D. Asystole or Pulseless Electrical Activity
For responding to asystole or a detected condition of pulseless electrical
activity, the medical monitoring and treatment device may perform maintenance
pacing similar to that described in section 2A above. This type of pacing would be
performed after a series of one or more defibrillating shocks that attempt to restore a
normal sinus rhythm to the heart of the patient.
In each of the above types of pacing, the medical monitoring and treatment
device may be configured to perform a particular type of pacing only after a
programmable delay after such cardiac arrhythmias are detected, or after a
programmable period of time after one or more defibrillating shocks are delivered.
3. Capture Management
In accordance with an aspect of the present invention, a medical monitoring and
treatment device, such as the LifeVest® wearable cardioverter defibrillator, can also
be configured to pace the heart of a patient using capture management with an
adjustable energy level and an adjustable rate in response to various types of cardiac
arrhythmias. The various types of cardiac arrhythmias can include a bradycardia,
tachycardia, an erratic heart rate with no discernable regular sinus rhythm, a lack of
sensed cardiac activity (asystole) following or independent of one or more
defibrillation shocks, a life-threatening Bradyarrythmia following one or more
defibrillation shocks, or pulseless electrical activity following one or more
defibrillation shocks.
As known to those skilled in the art, capture management refers to a type of
pacing in which the energy level of pacing pulses and the rate of delivery of those
pacing pulses may be varied based upon the detected intrinsic activity level of the
patient's heart and the detected response of the patient's heart to those pacing pulses.
In cardiac pacing, the term "capture" is used to refer to the response of a patient's
heart to a pulse of energy which results in ventricular depolarization. In cardiac
pacing, it is desirable to limit the amount of energy in each pulse to a minimal amount
required for capture; thereby minimizing the amount of discomfort associated with
external pacing.
In general, the manner in which the medical monitoring and treatment device can
perform capture management pacing is similar to that of demand pacing described
above, in that it may adjust the rate at which pacing pulses are delivered based upon
the detected intrinsic rate of cardiac activity of the patient. The sensitivity of the
device to the patient' s ECG may be adjusted in a similar manner to that described
above with respect to demand pacing. Further, capture management pacing may be
used to treat the same types of cardiac arrhythmias as the demand pacing described
above, such as bradycardia, tachycardia, an erratic heart rate with no discernable sinus
rhythm, asystole, or pulseless electrical activity.
However, in contrast to a device that performs demand pacing, a device that is
configured to perform capture management pacing will typically have a refractory
period 430 (see Fig. 4) that is significantly shorter than a device configured to perform
demand pacing. Indeed, when using capture management pacing, there may be no
refractory period 430 at all, but only a blanking interval 420. Alternatively, where
there is a refractory period 430, the refractory period 430 may be similar in duration
to the blanking interval 420. As would be appreciated by those skilled in the art, this
is because during capture management pacing, the response of the patient' s heart is
monitored by the ECG sensing electrodes 112 and ECG monitoring and detection
circuitry to detect whether the delivered pulse of energy resulted in capture. For this
reason, while the ECG monitoring and detection circuitry may be switched off or
effectively disabled during the delivery of energy pulses, it is important that it be
switched back on or otherwise enabled shortly thereafter to detect whether the
delivered pulse resulted in capture. In one embodiment in which a 40ms constant
current pulse is used, the blanking interval 420 may be set to approximately 45ms to
avoid saturation of the ECG monitoring and detection circuitry, but ensure that any
intrinsic electrical activity of the patient's heart that was induced by the pacing pulse
is detected.
During capture management pacing, the medical monitoring and treatment device
can deliver a pulse of energy at a determined energy level and monitor the patient's
response to determine if capture resulted. Where it is determined that the delivered
pulse did not result in capture, the energy level of the next pulse may be increased.
For example, where the device is a medical monitoring and treatment device that is
external to the patient, the initial setting may be configured to provide a 40ms
rectilinear and constant current pulse of energy at a current of 40 mAmps, and
increase the amount of current in increments of 2 mAmps until capture results. The
next pacing pulse may be delivered at increased current relative to the first pacing
pulse and at a desired rate relative to the first pacing pulse in the absence of any
detected intrinsic cardiac activity of the patient. Where the next pacing pulse does not
result in capture, the energy may be increased until capture is detected. The medical
monitoring and treatment device may then continue pacing at this energy level and at
a desired rate in the absence of any detected intrinsic cardiac activity of the patient.
During this period of time, the device monitors the patient' s cardiac response to the
pacing pulses, and may increment the energy level further, should it be determined
over one or more subsequent pulses that capture did not result.
In an alternative configuration, the medical monitoring and treatment device may
apply a series of pulses at an initial energy level and rate, and monitor the patient' s
response to determine if capture resulted. Where capture did not result, or where
capture resulted in response to some of the pulses, but not all, the device may increase
the energy of a next series of pulses until capture results for each pulse.
Alternatively, the device may be configured to identify a minimum amount of
energy that results in capture during capture management pacing. Where it is
determined that the delivered pulse did result in capture, the energy level of the next
pulse may be decreased. For example, where the device is a medical monitoring and
treatment device that is external to the patient, the initial setting may be configured to
provide a 40ms constant current pulse of energy at a current of 70mAmps. Where it is
determined that the delivered pulse resulted in capture, subsequent pacing pulse may
be delivered at decreased in increments of 5mAmps and at a desired rate relative to
the first pacing pulse in the absence of any detected intrinsic cardiac activity of the
patient until capture is no longer achieved. Where the next pacing pulse does not
result in capture, the energy setting may be increased to the last current known to
produce a pulse resulting in capture, and then delivering a pulse at the higher energy
setting, thus delivering the minimal amount of energy required for capture. The
medical monitoring and treatment device may then continue pacing at this energy
level and at a desired rate in the absence of any detected intrinsic cardiac activity of
the patient. During this period of time, a similar routine may be re-performed at
predetermined intervals to ensure that the minimum amount of energy is being
delivered for capture. In addition, during this period of time, the device monitors the
patient's cardiac response to the pacing pulses, and may increase the energy level
should it be determined over one or more subsequent pulses that capture did not
result.
It should be appreciated that in the various embodiments described above, an
external medical monitoring and treatment device has been described which may not
only provide life saving defibrillation or cardioversion therapy, but may also provide
a wide variety of different pacing regimens. Because the medical monitoring and
treatment device can monitor a patient's intrinsic cardiac activity, the patient's
thoracic impedance, and other physiological parameters of the patient, the device may
be configured to recommend various settings to a medical professional for review and
approval. The various settings that may be recommended may include a
recommended base pacing rate, a recommended hysteresis rate, a recommended antitachyarrhythmic
pacing rate, a recommended energy level (or initial energy level if
capture management is used), a recommended blanking interval, and/or refractory
period, and a recommended sensitivity threshold. In the case of a medical monitoring
and treatment device such as the LifeVest® cardioverter defibrillator, this initial
recommendation may be performed when the patient is being fitted for and trained on
the use of the device.
Although the ability to recommend such settings to a medical professional for
their review and approval is particularly well suited to a medical monitoring and
treatment device, such as the LifeVest® cardioverter defibrillator, such functionality
could also be implemented in an Automated External Defibrillator (AED) or an
Advanced Life Support (ALS) type of defibrillator, such as the M Series defibrillator,
R Series ALS defibrillator, R Series Plus defibrillator, or E Series defibrillator
manufactured by the Zoll Medical Corporation of Chelmsford MA. It should be
appreciated that monitoring the patient' s intrinsic cardiac activity and other
physiological parameters and making recommendations to a trained medical
professional for their review and approval (or possible modification) could reduce the
amount of time that is spent manually configuring such devices prior to use on the
patient.
Having thus described several aspects of at least one embodiment of this
invention, it is to be appreciated various alterations, modifications, and improvements
will readily occur to those skilled in the art. Such alterations, modifications, and
improvements are intended to be part of this disclosure, and are intended to be within
the scope of the invention. Accordingly, the foregoing description and drawings are
by way of example only.

What is claimed is:
CLAIMS
1. A non-invasive bodily-attached ambulatory medical monitoring and treatment
device comprising:
a battery;
at least one therapy electrode coupled to the battery;
a memory storing information indicative of a patient' s cardiac activity; and
at least one processor coupled to the memory and the at least one therapy
electrode and configured to:
identify a cardiac arrhythmia within the information; and
execute at least one pacing routine to treat the identified cardiac
arrhythmia.
2. The device according to claim 1, wherein the cardiac arrhythmia includes
bradycardia and the at least one pacing routine is configured to:
determine that a first interval has passed without detection of a heart beat; and
apply, responsive to determining that the first interval has passed, a pacing
pulse via the at least one therapy electrode.
3. The device according to claim 2, wherein the first interval is defined by a base
pacing rate and a hysteresis rate.
4. The device according to claim 3, wherein the at least one pacing routine is
further configured to:
detect an intrinsic heart beat prior to passage of a second interval;
determine a third interval based on the base pacing rate, the hysteresis rate,
and a point where the intrinsic heart beat was detected; and
determine whether another intrinsic heart beat occurs within the third interval.
5. The device according to claim 1, wherein the cardiac arrhythmia includes
tachycardia and the at least one pacing routine is configured to:
detect a plurality of intrinsic heart beats prior to passage of a first interval, the
plurality of intrinsic heart beats having an intrinsic frequency, the first interval being
defined by an anti-tachyarrhythmic pacing rate; and
apply, responsive to detecting the intrinsic frequency, a series of pacing pulses
via the at least one therapy electrode, the series of pacing pulses having a frequency
above the intrinsic frequency.
6. The device according to claim 1, wherein the cardiac arrhythmia includes an
erratic heart rate and the at least one pacing routine is configured to:
identify a first series of heart beats within the information, the first series
having a lower frequency;
identify a second series of heart beats within the information, the second series
a upper frequency; and
apply, responsive to identifying the erratic heart rate, a series of pacing pulses
via the at least one therapy electrode, the series of pacing pulses having a frequency
above the lower frequency and below the upper frequency.
7. The device according to claim 1, wherein the cardiac arrhythmia includes at
least one of asystole and pulseless electrical activity and the at least one pacing
routine is configured to:
determine that a first interval has passed without detection of a heart beat; and
apply, responsive to determining that the first interval has passed, a pacing
pulse via the at least one therapy electrode.
8. The device according to claim 1, wherein the at least one pacing routine is
further configured to:
determine whether the at least one pacing routine resulted in capture; and
adjust, responsive to determining that capture did not result, the characteristics
of pacing pulses applied during subsequent executions of the at least one pacing
routine.
9. The device according to claim 8, wherein the characteristics of the pacing
pulses subject to adjustment include a pulse energy level, a pulse rate, and a pulse
width.
10. The device according to claim 1, wherein the at least one pacing routine is
further configured to:
determine whether the at least one pacing routine resulted in capture; and
adjust, responsive to determining that capture did result, the characteristics of
pacing pulses applied during subsequent executions of the at least one pacing routine.
11. A non-invasive bodily-attached ambulatory defibrillator comprising:
a battery;
at least one therapy electrode coupled to the battery;
a memory storing information indicative of a patient' s cardiac activity; and
at least one processor coupled to the memory and the at least one therapy
electrode and configured to:
identify a cardiac arrhythmia within the information; and
execute at least one pacing routine to treat the identified cardiac
arrhythmia.
12. The defibrillator according to claim 11, wherein the cardiac arrhythmia
includes bradycardia and the at least one pacing routine is configured to:
determine that a first interval has passed without detection of a heart beat; and
apply, responsive to determining that the first interval has passed, a pacing
pulse via the at least one therapy electrode.
13. The defibrillator according to claim 12, wherein the first interval is defined by
a base pacing rate and a hysteresis rate.
14. The defibrillator according to claim 13, wherein the at least one pacing routine
is further configured to:
detect an intrinsic heart beat prior to passage of a second interval;
determine a third interval based on the base pacing rate, the hysteresis rate,
and a point where the intrinsic heart beat was detected; and
determine whether another intrinsic heart beat occurs within the third interval.
15. The defibrillator according to claim 11, wherein the cardiac arrhythmia
includes tachycardia and the at least one pacing routine is configured to:
detect a plurality of intrinsic heart beats prior to passage of a first interval, the
plurality of intrinsic heart beats having an intrinsic frequency, the first interval being
defined by an anti-tachyarrhythmic pacing rate; and
apply, responsive to detecting the intrinsic frequency, a series of pacing pulses
via the at least one therapy electrode, the series of pacing pulses having a frequency
above the intrinsic frequency.
16. The defibrillator according to claim 15, wherein the at least one pacing routine
is further configured to detect, after applying the series of pacing pulses, whether
another plurality of intrinsic heart beats occur within a second interval, the second
interval being defined by the anti-tachyarrhythmic pacing rate.
17. The defibrillator according to claim 11, wherein the cardiac arrhythmia
includes an erratic heart rate and the at least one pacing routine is configured to:
identify a first series of heart beats within the information, the first series
having a lower frequency;
identify a second series of heart beats within the information, the second series
a upper frequency; and
apply, responsive to identifying the erratic heart rate, a series of pacing pulses
via the at least one therapy electrode, the series of pacing pulses having a frequency
above the lower frequency and below the upper frequency.
18. The defibrillator according to claim 11, wherein the cardiac arrhythmia
includes at least one of asystole and pulseless electrical activity and the at least one
pacing routine is configured to:
determine that a first interval has passed without detection of a heart beat; and
apply, responsive to determining that the first interval has passed, a pacing
pulse via the at least one therapy electrode.
19. The defibrillator according to claim 18, wherein the at least one pacing routine
is further configured to apply a defibrillating shock prior to applying the pacing pulse.
20. The defibrillator according to claim 11, wherein the at least one pacing routine
is further configured to:
determine whether the at least one pacing routine resulted in capture; and
adjust, responsive to determining that capture did not result, the characteristics
of pacing pulses applied during subsequent executions of the at least one pacing
routine.
21. The defibrillator according to claim 20, wherein the characteristics of the
pacing pulses subject to adjustment include a pulse energy level, a pulse rate, and a
pulse width.
22. The defibrillator according to claim 11, wherein the at least one pacing routine
is further configured to:
determine whether the at least one pacing routine resulted in capture; and
adjust, responsive to determining that capture did result, the characteristics of
pacing pulses applied during subsequent executions of the at least one pacing routine.
23. A method of treating cardiac dysfunction using a non-invasive bodily-attached
ambulatory medical monitoring and treatment device, the method comprising:
identifying, by the non-invasive bodily-attached ambulatory medical
monitoring and treatment device, a cardiac arrhythmia within information indicative
of a patient' s cardiac activity; and
executing, by the non-invasive bodily-attached ambulatory medical
monitoring and treatment device, at least one pacing routine to treat the identified
cardiac arrhythmia.
24. The method according to claim 23, wherein the cardiac arrhythmia includes
bradycardia and executing the at least one pacing routine includes:
determining that a first interval has passed without detection of a heart beat;
and
applying, responsive to determining that the first interval has passed, a pacing
pulse via the at least one therapy electrode.
25. The method according to claim 24, wherein determining that the first interval
has passed includes defining the first interval using a base pacing rate and a hysteresis
rate.
26. The method according to claim 25, wherein executing the at least one pacing
routine includes:
detecting an intrinsic heart beat prior to passage of a second interval;
determining a third interval based on the base pacing rate, the hysteresis rate,
and a point where the intrinsic heart beat was detected; and
determining whether another intrinsic heart beat occurs within the third
interval.
27. The method according to claim 23, wherein the cardiac arrhythmia includes
tachycardia and executing the at least one pacing routine includes:
detecting a plurality of intrinsic heart beats prior to passage of a first interval,
the plurality of intrinsic heart beats having an intrinsic frequency, the first interval
being defined by an anti-tachyarrhythmic pacing rate; and
applying, responsive to detecting the intrinsic frequency, a series of pacing
pulses via the at least one therapy electrode, the series of pacing pulses having a
frequency above the intrinsic frequency.
28. The method according to claim 23, wherein the cardiac arrhythmia includes an
erratic heart rate and executing the at least one pacing routine includes:
identifying a first series of heart beats within the information, the first series
having a lower frequency;
identifying a second series of heart beats within the information, the second
series a upper frequency; and
applying, responsive to identifying the erratic heart rate, a series of pacing
pulses via the at least one therapy electrode, the series of pacing pulses having a
frequency above the lower frequency and below the upper frequency.
29. The method according to claim 23, wherein the cardiac arrhythmia includes at
least one of asystole and pulseless electrical activity and executing the at least one
pacing routine includes:
determining that a first interval has passed without detection of a heart beat;
and
applying, responsive to determining that the first interval has passed, a pacing
pulse via the at least one therapy electrode.
30. The method according to claim 29, wherein executing the at least one pacing
routine includes applying a defibrillating shock prior to applying the pacing pulse.
31. The method according to claim 23, wherein executing the at least one pacing
routine includes:
determining whether the at least one pacing routine resulted in successful
capture; and
adjusting, responsive to determining that capture did not result, the
characteristics of pacing pulses applied during subsequent executions of the at least
one pacing routine.
32. The method according to claim 31, wherein adjusting the characteristics
includes adjusting at least one of a pulse energy level, a pulse rate, and a pulse width.
33. The method according to claim 23, wherein the non-invasive bodily-attached
ambulatory medical monitoring and treatment device includes a non-invasive bodilyattached
ambulatory defibrillator and identifying the cardiac arrhythmia includes
identifying, by the non-invasive bodily-attached ambulatory defibrillator, the cardiac
arrhythmia.