Methods and apparatus for detecting ventricular depolarizations during atrial pacing

A method of declaring and responding to a premature ventricular contraction (PVC) using a pacing system comprising an implantable pulse generator adapted to be implanted in a patient's body, at least one active atrial electrode adapted to be disposed in operative relation to an atrial heart chamber, at least one indifferent atrial electrode adapted to be implanted in the patient's body, at least one active ventricular electrode adapted to be disposed in operative relation to a ventricular heart chamber, and an indifferent ventricular electrode adapted to be implanted in the patient's body, the pacing system further comprising:

• an atrial sense amplifier coupled to the active and indifferent atrial electrodes, responsive to natural atrial depolarizations and declaring an A-EVENT in response thereto;
• an atrial pace pulse generator coupled to the active and indifferent atrial electrodes and generating and delivering atrial pace (A-PACE) pulses;
• a ventricular sense amplifier coupled to the active and indifferent ventricular electrodes, responsive to natural ventricular depolarizations and declaring a V-EVENT in response thereto;
• a PVC sense electrode pair in the patient's body defining a PVC sense vector differing from a ventricular sense vector defined by the active and indifferent ventricular electrodes;
• V-A interval timer, timing out a V-A interval responsive to a V-EVENT declared by the ventricular sensing means;
• wherein the atrial pulse generator is responsive to the expiration of the V-A interval and generates an A-PACE pulse and at the expiration thereof;
• and
• a ventricular blanking circuit defining a predetermined ventricular blanking period following generation and delivery of an atrial pace pulse preventing said ventricular sense amplifier from declaring a V-EVENT during the ventricular blanking period;
• the method comprising:
• sensing a depolarization of the ventricles occurring during the ventricular blanking period across the PVC sense electrode pair and declaring a PVC;
• and
• triggering the V-A interval timer means to time out the V-A interval in response to the declared PVC.