Phase Relation between Depolarization and Repolarization Alternans in ECG∗

T-Wave Alternans (TWA) in the electro cardiogram (ECG) has been widely investigated as a potential predictor of ventricular arrhythmia. However, large clinical trials show that TWA has a high negative predictive value (NPV) but poor positive predictive value (PPV). Therefore, there is need for exploration of approaches to improve PPV of TWA. More recent studies suggest that whether alternans is spatially concordant or discordant affects arrhythmic potential. Results of our previous animal and simulation studies show that the phase relation between depolarization and repolarization alternans has an effect on the transition of concordant to discordant alternans. Towards the eventual goal of developing indexes that complement TWA and improve prediction of arrhythmia, the objectives in this study were to verify the existence of R wave amplitude alternans (RWAA, a surrogate of depolarization alternans) and investigate the phase relationship between RWAA and TWA in clinical grade ECGs. Results show that RWAA does occur in ECGs and that the phase relationship between RWAA and TWA can be labile. These results support further investigation of the co-occurrence of these alternans for prediction of arrhythmic events.