Co-occurrence and phase relationship between alternans of the R wave amplitude (RWAA) and of the T wave (TWA) in ECGs.

Alternans of the T wave in ECG (TWA) has high negative but poor positive predictive value in the prediction of ventricular arrhythmia. Alternans of repolarization duration, i.e. of action potential duration (APD), causes TWA. Prior studies from our group showed that alternans of the maximum rate of depolarization also occurs when APD alternans occurs and the relationship between these two has the potential to affect formation of spatial discord, which may be more arrhythmogenic. Therefore, exploration of the co-occurrence of the alternans of depolarization and repolarization has the potential to improve the prediction. In the present study, we used a mathematical model to show that depolarization alternans appears as alternating amplitude of the R wave in the ECG. We also investigated the link between changes in R wave amplitude and TWA. Results from clinical grade ECGs available in the PhysioNet database show that amplitude of the R wave can change as predicted by our experimental results and the mathematical model. Using TWA as the marker of repolarization alternans and R wave amplitude alternans (RWAA) as the marker of depolarization alternans, we investigated the phase relation between them and observed that, similar to previous results from animals, the phase relation between the two can spontaneously change. That is, alternans of depolarization does co-occur with TWA and the phase relationship between the two is not invariant. These results support further investigation of the use of RWAA as a complementary method to TWA to improve positive predictive value for prediction of ventricular arrhythmia.

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.