Microvolt-Level T-Wave Alternans as a Marker of Vulnerability to Cardiac Arrhythmias: Principles and Detection Methods

Abstract

Sudden cardiac death (SCD) is defined as natural death from cardiac causes heralded by an abrupt loss of consciousness within one hour of the onset of acute symptoms (13). SCD claims more than 300,000 Americans each year and is the leading cause of cardiovascular death in Western societies. It is important to note that SCD is caused by rapid ventricular arrhythmias such as ventricular tachycardia (VT) or fibrillation (VF) that often occur without warning. The majority of patients who succumb to SCD do not have previously recognized arrhythmias and, therefore, are not known to be at high risk until after a catastrophic arrhythmic event has occurred when it is often too late. Consequently, it is of tantamount importance for physicians to identify, a priori, those patients at greatest risk for SCD so that appropriate clinical interventions can be made. Unfortunately, noninvasive techniques used previously to identify high-risk patients such as the signal average electrocardiograph (11,23), Holter monitoring (12), heart rate variability (9), and QT dispersion (2,26) have not demonstrated sufficient predictive accuracy to justify invasive electrophysiological testing or therapies in otherwise asymptomatic patients (i.e., before they experience a major clinical event) based on a positive result from one or more of these tests.