Implantation of atrioventricular synchronous and atrioventricular universal pacemakers.

Implantation of pacemakers which sense in the atrium and the ventricle requires understanding of both antegrade conduction, from the atrium to the ventricle, and retrograde conduction, from the ventricle to the atrium. Of 53 patients undergoing pacemaker implantation, 25 (47%) had retained VA conduction and 25% of those with complete heart block had 1:1 retrograde (VA) conduction. Determination of both conduction intervals is made by recording the intrinsic deflections of the atrium and the ventricle and measuring the interval. Antegrade intervals (IDA leads to IDV) for those with intact conduction ranged from 189 to 325 msec (mean 212 msec). Retrograde intervals (StV leads to IDA) for those with intact VA conduction ranged from 110 to 346 msec (mean 235 msec). Of 16 patients having VDD and DDD pacemakers implanted without conduction studies, seven (44%) developed pacemaker-mediated tachycardia. The prevention of pacemaker-mediated reentry tachycardia requires knowledge of the VA conduction interval (if it exists) and programming of the atrial refractory period so that retrograde P waves fall within it and are unsensed.