Patent ID: 8600504

Claim:
An apparatus comprising: a first data input configured to receive an intrinsic electric cardiac signal produced by the heart and to measure a duration of an intrinsic electrical QRS complex using the electric cardiac signal; a second data input configured to receive a subject heart rate; ventricular pacing circuitry configured to provide ventricular pacing pulses in response to expiration of a specified atrioventricular (AV) delay; and control circuitry configured to use information about the duration of the QRS complex to: determine a first specified threshold value using information about the intrinsic electrical QRS complex; compare a subject's heart rate to the first specified threshold value; and when the subject's heart rate is less than the first specified threshold value, intermittently extend the specified AV delay by an amount that obtains respective intrinsic ventricular contractions; and when the subject's heart rate is greater than or equal to the first specified threshold value, shorten the specified AV delay to provide a shortened AV delay, wherein the shortened AV delay is less than the specified AV delay.