Miniaturized Radio Frequency Telemetric Pacemaker With Anti-Arrhythmic Pacing Protocol1

Abstract

Fatal arrhythmias and ventricular fibrillation (VF) which lead to sudden cardiac death are believed to be preceded by alternans, observed as a beat-to-beat variation of the T-wave amplitude on the ECG [1,2]. Previous studies to predict the onset of alternans involved the restitution curve, the functional relationship between the action potential duration (APD) and preceding diastolic interval (DI). It was hypothesized that alternans appears when the magnitude of the slope of the restitution curve exceeds one [3]. However, this hypothesis failed in various experimental studies [4]. One of the main reasons for failure of the restitution hypothesis was the fact that it was derived under assumption of constant or periodic pacing, where there is an inherent dependence of the DI on the immediate preceding APD. During periodic pacing, small changes in DI are translated into subsequent changes in the APD and thus, enhance instability of cardiac rhythms in the heart. However, under normal physiological conditions, intrinsic heart rate variability (HRV) ensures deviation of the heart from periodic pacing [4]. HRV is a variation in time interval between two consecutive heartbeats. Figure 1 shows a representative example of HRV as a change in RR interval for a normal sinus rhythm of a healthy adult male at rest. We can see that the RR interval, the time duration between two consecutive peaks of the ECG, varies over time.