Patent ID: 7133720

Claim:
A method including: detecting an episode of atrial fibrillation in an atrium; sensing ventricular depolarizations; measuring a duration of a present RR interval since a most recent ventricular depolarization; and delivering an atrial defibrillation shock synchronized to a ventricular depolarization, which concludes a present RR interval, if the present RR interval is shockable, in which the shockable present RR interval requires that the present RR interval includes at least a minimum time period after the expiration of a ventricular sensing refractory period of the present RR interval and before occurrence of the ventricular depolarization concluding the present RR interval, wherein the ventricular sensing refractory period inhibits restarting the RR interval in response to a ventricular depolarization detected during the ventricular refractory period.