Patent ID: 8886315

Claim:
A method comprising: (a) delivering biventricular cardiac resynchronization therapy (CRT) to a heart at an atrio-ventricular (AV) interval; (b) monitoring atrial contraction events; (c) monitoring intrinsic ventricular contraction events; (d) applying a biventricular CRT pacing stimulus on detection of an intrinsic ventricular contraction event to produce a ventricular-sense response (VSR); (e) recording electrical activity of the heart in a defined time window centered or off centered on a time of delivery of the biventricular CRT pacing stimulus to obtain an electrogram of the VSR; (f) comparing the electrogram of the VSR, or features thereof, to a template electrogram, or features thereof, of a pure biventricular paced beat to determine a similarity index between the electrogram of the VSR and the template electrogram; (g) determining whether the similarity index meets or exceeds a predetermined threshold, wherein if the similarity index meets or exceeds the threshold steps (a)-(f) are repeated; and (h) determining whether an atrial contraction event preceded the VSR if the threshold is not met or exceeded.