Pacemaker system and method with ventricular rate smoothing during high rate atrial arrhythmia

A dual chamber pacemaker and method for ventricular rate smoothing during high rate episodes such as atrial fibrillation are provided. The pacemaker determines when there is a pathologically high atrial rate episode, such as by determining when atrial senses correspond to a spontaneous atrial rate above a predetermined upper rate limit. When such an episode is determined, the pacemaker determines a ventricular pacing escape interval, corresponding to a flywheel rate, the flywheel rate being set at the beginning of the episode to substantially equal the atrial rate just before the high rate episode. As long as the episode continues, the flywheel rate is incremented upward whenever a ventricular sense occurs, thereby following the average ventricular rate; whenever the flywheel escape interval times out and a ventricular pace is delivered, the flywheel rate is decremented. By allowing ventricular senses and pacing only after timeout of an escape interval which substantially equals average ventricular rate, the episode is treated by smoothing out ventricular rate variations while substantially maintaining the ventricular rate that would otherwise occur.