Detection of repolarization alternans with an implantable cardioverter defibrillator lead

It has been suggested that repolarization alternans (RPA) may be mechanistically linked to the onset of ventricular tachycardia (VT) and/or ventricular fibrillation (VF). The detection and control of RPA may therefore be important in the development of a defense against sudden cardiac death. Here we investigate whether RPA could be detected using an implantable cardioverter defibrillator (ICD) lead prior to the onset of ischemia-induced VT or VF in pigs. In three animals, the RPA magnitude was computed from a signal acquired using an ICD lead placed in the right-ventricular apex. In each trial, the right main (n = 2) or the left anterior descending (n = 1) coronary artery was occluded for 10 min using a balloon catheter, followed by reperfusion for 30 min, and re-occlusion for 30 min. RPA magnitude was computed using the Modified Moving Average (MMA) method in a continuous manner over the entire duration of the experiment. RPA magnitude in each animal showed a sharp increase during the first occlusion phase. Two animals exhibited a prominent increase in RPA magnitude prior to the onset of VT or VF. In the one animal that did not show such an increase during re-occlusion, VF did not occur spontaneously. Our results thus indicate that it is indeed possible to detect and track the dynamics of RPA using an ICD lead in a consistent and robust manner. Furthermore, these results suggest that RPA occurs prior to VF during ischemia. In future ICDs, such an approach may be useful in formulating improved arrhythmia detection and control algorithms.