Analysis of complex T-wave oscillations for prediction of ventricular fibrillation

Increased attention has been focused on oscillatory behavior of the T wave as a manifestation of heightened electrical instability and risk for ventricular fibrillation (VF). This interest has stemmed from an increasing number of experimental and clinical studies indicating that the relatively simple ABAB oscillation of T-wave alternans (TWA) can be quantified to assess risk for arrhythmias. However, an important unanswered question is whether TWA represents the initial phase of a stepwise progression to higher-order oscillations that culminate in sudden arrhythmic death. Signals were analyzed from epicardial and endocardial ECGs from anesthetized dogs subjected to LAD coronary artery occlusion during fixed-rate atrial pacing. Our study was the first to demonstrate a stepwise increase in complexity of T-wave oscillations from TWA to T-wave tripling and quadrupling and to more complex forms just prior to onset of VF (Circ Res 2002;91:727-732). Discordant T-wave episodes, when T waves alternated out-of-phase, were found to be associated with increases in T-wave complexity and VF. None of the animals that failed to fibrillate exhibited discordant TWA. In these observations, complexity of T-wave oscillations points to a fundamental mechanistic link underlying the ability of TWA to predict lethal arrhythmias.