Abstract: Techniques for detecting atrial fibrillation via a ventricular lead are described. An implantable medical device according to the invention may monitor a ventricular depolarization rate via the ventricular lead in order to detect the effect of conducted atrial fibrillation of the ventricular rate. For example, the implantable medical device may detect an increase in the ventricular rate, or a decrease in the stability of the ventricular rate. The implantable medical device may also detect the effect of delivery of a pacing pulse on the length of an R-R interval subsequent to the delivery. A compensatory pause following delivery of a pacing pulse may indicate the presence of conducted atrial fibrillation. The implantable medical device may store information relating to detected episodes of atrial fibrillation for later review by a physician, so that atrial fibrillation may be diagnosed in situations where it might not otherwise be detected.

Abstract: A cardiac pacemaker and a method of its use. The pacemaker paces a patient's heart in a tachyarrhythmia prevention pacing mode for an extended time period, defines a metric of success of the tachyarrhythmia prevention pacing mode, monitors the metric over the extended time period and, responsive to the monitored metric, adjusts the tachyarrhythmia prevention pacing mode. Adjustment of the tachyarrhythmia prevention pacing mode may take the form of pacing the patient's heart with a different set of electrodes, pacing the patient's heart with a different tachyarrhythmia prevention pacing mode and/or terminating operation of the tachyarrhythmia prevention pacing mode.