Background of the Inyention
This disclosure relates generally to monitoring of electrocardiograms in
patient monitors. More particularly, the present invention relates to prediction of
ventricular tachyarrhythmias (VTAs) in patient monitors.
Patient monitors are electronic devices designed to display physiological
information about a subject. Electrocardiogram (ECG), electroencephalogram (EEG),
plethysmographic signals, and signals related to blood pressure, temperature, and
respiration represent typical physiological information contained in full-size patient
monitors. Patient monitors are typically also furnished with alarming functionality to
alert the nursing staff when a vital sign or physiological parameter of a patient exceeds
or drops below a preset limit. Alarms are normally both audible and visual effects
aiming to alert the staff to a life-threatening condition or to another event considered
vital. In most monitors, the alarm limits may be defined by the user, since the limits
typically depend on patient etiology, age, gender, medication, and various other
subjective factors. Each specific physiological parameter, such as heart rate or blood
pressure, may also be assigned more than one alarm limit. Furthermore, there is a lot
of data trended and available for caregivers to be reviewed in a patient monitor.
For recording an electrocardiogram, electrocardiographic leads are used at
specified locations of the subject for recording ECG waveforms. In typical clinical
practice, 12 leads are used to the record the ECG. However, the number of leads used
may vary. Each lead records a waveform representing the electrical activity generated
by the heart cardiac cycle by cycle and together the lead recordings provide spatial
information about the heart's electrical activity.
A normal cardiac cycle includes contractions of the atrial muscles, which are
activated by the autonomic sinoatrial node (SA node), also called the sinus node. An
electrophysiologic (EP) signal generated by the SA node spreads in the right and left
atrium leading to their contraction. The EP signal further reaches the atrioventricular
node (AV node) situated between the atria and the ventricles. The AV node delays the

We Claim :
1. A method for predicting ventricular tachyarrhythmia, the method comprising:
- determining (12) a set of repolarization parameters indicative of ventricular
repolarization in a subject's (401) heart, wherein the determining is performed in
successive time segments, thereby to obtain a time series of the set of repolarization
parameters;
- producing (13, 14; 21, 23), based on the time series, at least one change
indication variable indicative of changes in the ventricular repolarization of the heart;
and
^ - predicting (13-15) risk of potential ventricular tachyarrhythmia based on the
at least one change indication variable.
2. The method according to claim 1, wherein the producing comprises
producing (13,14) the at least one change indication variable, in which the at least one
change indication parameter comprises a trend variable indicative of slow changes in
the ventricular repolarization of the heart and at least one fast change variable indicative
of fast changes in the ventricular repolarization of the heart.
3. The method according to claim 2, wherein the producing comprises
- producing the trend variable, in which the trend variable represents a
weighted average of a plurality of repolarization parameters, wherein the plurality of
repolarization parameters belong to the set of repolarization parameters;
- estimating a relationship (31) between a repolarization parameter and heart
^ rate, wherein the repolarization parameter belongs to the set of repolarization
parameters and wherein the estimating is performed for at least one repolarization
parameter, thereby to obtain at least one relationship; and
- producing the at least one fast change variable, in which the at least one fast
change variable comprises a first variable indicative of similarity between successive
sets of repolarization parameters in the time series and a second variable indicative of
change in difference between a first and a second group of repolarization parameters,
wherein the first group is obtained through the at least one relationship and the second
group belongs to the time series.
4. The method according to claim 3, wherein the producing comprises
producing the first variable and a second variable, in which the first variable represents
Mahalanobis distance between selected repolarization parameters obtained in
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