A review of the atrial upper rate algorithms of St. Jude Medical (Abbott) cardiac implantable electronic devices : Incidence of repetitive nonreentrant ventriculoatrial synchrony (RNRVAS).

This review focuses on the manifestations of the three triggered atrial upper rate functions of St Jude Medical cardiac implantable electronic devices. The occurrence of repetitive nonreentrant ventriculoatrial synchrony (RNRVAS) is also evaluated as a basis for the development of automatic mode switching (AMS) and as a trigger for atrial tachycardia/atrial fibrillation (AT/AF) event recordings. RNRVAS is a common trigger for AMS because all the atrial events or intervals are used to calculate the filtered atrial rate interval (FARI). Once AMS is initiated, it will also effectively stop RNRVAS because entry into AMS also shortens the postventricular atrial refractory period (PVARP). Recent design developments to eliminate or minimize unusual upper rare responses include the following: (1) P waves in the PVARP are no longer counted towards the FARI if they are followed by an atrial paced event. (2) In new devices the AT/AF detection algorithm substitutes the Moving Average Interval (a relatively complex calculation) with the new FARI average. (3) Improved design of the rate-responsive PVARP with a far more aggressive response than in the past (enhanced atrial protection interval).