Dynamic Tracking of ECG Heterogeneity to Estimate
Risk of Life-threatening Arrhythmias

There are over 350,000 cases of sudden cardiac death (SCD) in the United States each year, and over twenty percent of these cases involve people with no outward signs of serious heart disease.  For decades, researchers have been attempting to come up with methods of identifying electrocardiogram (ECG) patterns that reliably precede dangerous arrhythmias.  As these methods are found, devices are being created that monitor the heart in order to detect the onset of dangerous rhythms and to correct them before they cause death.

Recent research suggests that ECG heterogeneity, or waveforms that vary from one heartbeat to the next, often precedes arrhythmias.  This heterogeneity can be measured by placing multiple ECG electrodes on the chest and by then computing the variance in waveform morphology across the signals from these electrodes.  A crescendo in T-wave heterogeneity often signals the start of ventricular fibrillation, and R-wave heterogeneity has also been shown to precede ischemia-induced ventricular fibrillation.  In patients with coronary artery disease, exercise increases T-wave heterogeneity, but this effect is not seen in normal patients.  These results, when combined with other pieces of emerging evidence, suggest that R-wave and T-wave heterogeneity both have predictive value.   

In the future, researchers led by Richard L. Verrier, PhD, of Harvard Medical School hope to automate the process of heterogeneity detection and to augment the clinical evidence supporting the validity of ECG heterogeneity as a predictor of arrhythmia.  Someday soon, implantable devices may be programmed to measure and track heterogeneity.  These devices could help ward off arrhythmias by stimulating nerves such as the vagus nerve, by delivering drugs such as beta-blockers, and if necessary, by defibrillating the heart.   

   

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