Ventriculoatrial conduction in swine during cardiac pacing: animal model for retrograde conduction

Studies on cardiac conduction disorders and pacemaker tachycardias are usually conducted in patients because the phenomenon of ventriculoatrial (retrograde) conduction resulting from ectopic beats and pacing the ventricles has only been reported in humans. This study was conducted to characterize the ventriculoatrial (VA) conduction and retrograde P wave electrogram (EGM) amplitude and slew rate in 10 anesthetized pigs. Three transvenous pacemaker leads were positioned in the heart: one in the right atrial appendage, one in the sinoatrial (SA) node region, and another in the apex of the right ventricle. Ventriculoatrial conduction always occurred when the heart was paced from the right ventricle. There was a significant difference (p less than 0.05) between the amplitude and slew rate of the intrinsic P wave EGM (6.36 +/- 1.88 mV, 1.03 +/- 0.35 mV/msec) compared to the retrograde P wave EGM (3.12 +/- 1.37 mV, 0.57 +/- 0.18 mV/msec) detected at the SA node region. However, there was no significant difference between the intrinsic P wave EGM (4.81 +/- 2.01 mV, 0.40 +/- 0.26 mV/msec) and the retrograde P wave EGM (4.13 +/- 3.74 mV, 0.13 +/- 0.05 mV/msec) detected in the atrial appendage. The advantage of positioning an electrode in close proximity to the SA node for optimum atrial EGM detection and differentiation from retrograde P wave EGM is evident. The VA conduction time (178.5 +/- 8.5 msec) was significantly greater (p less than 0.01) than the antegrade conduction time (120.0 +/- 18.2 msec). The pig with its VA conduction is a useful model for pacemaker-induced tachycardias and for in vivo testing of drugs and/or pacemaker programs that can be utilized for controlling or preventing them.