Atrial anti-arrhythmia pacemaker and method using high rate atrial and backup ventricular pacing

An atrial and ventricular pacemaker including an atrial pulse generator having the capability of delivering high rate atrial pacing pulses for electrophysiologic study and having the capability of delivering ventricular pacing pulses as a backup, during delivery of high rate atrial pacing pulses. Delivery of backup ventricular pacing pulses may be preconditioned upon the occurrence of a desired number, proportion or pattern of occurrences of paced ventricular beats preceding delivery of high rate atrial pacing pulses. Timing of ventricular backup pulses is synchronized to delivered atrial pacing pulses which occur closely timed to expiration of a defined ventricular escape interval for backup pacing. The defined escape interval for ventricular backup pacing may be set as a function of the average interval separating ventricular events preceding initiation of high rate atrial pacing.