Noninvasive measurement of retrograde conduction times in pacemaker patients.

Retrograde, or ventriculoatrial conduction (VAC) has been measured in 67% of pacemaker patients with SSS and 25% of patients with 3 degrees block. DDD pacers use the postventricular atrial refractory period (PVARP) to prevent sensing VAC. If the PVARP is too short, a pacer-mediated tachycardia (PMT) could occur. If too long, rapid atrial rates may not be sensed. To accurately set the PVARP, VAC must be measured. Five noninvasive methods are described: (1) Surface ECG during VVI pacing; (2) Atrial intracardiac electrograms during VVI pacing; (3) Initiating a PMT with long pacemaker AV interval; (4) Initiating a PMT at the maximum tracking rate; (5) DDI mode with electronic calipers. The description of these methods is intended to enable a physician to detect and measure VAC in patients with any manufacturer's DDD or VDD pacemaker.