For the past 10 years, VDD pacemakers have been substituted for DDD pacemakers, due to their ease of implantation and follow up. The degree of AV synchrony and associated factors were evaluated in the patients with VDDR pacemakers.

Twenty one patients, 10 males and 11 females, were enrolled. The mean age of the patient was 56 years. In the supine position, the atrial sensing threshold and cardiac cycle data were checked to evaluate the AV synchrony with a programmer. If the AV synchrony was less than 90%, it was considered improper synchronization.

The measured P wave amplitudes were 2.33 and 1.22mV at implant and follow up, respectively. From the follow up cardiac cycle data, the percentage of ventricular pacing only (Vp), atrial sensing and ventricular pacing (AsVp) and the total percentage of AV synchronization (PAS) were 21.38, 76.33 and 77.77%, respectively. Inadequate AV synchrony was observed in 11 patients. The causes were the absence of a minimal tracking limit, a faster pacing rate than the patient's resting rate, atrial fibrillation, sinus node dysfunction, atrial under sensing and functioning of the rate adaptive function in 4, 3 and 1 each, respectively. After rectifying the causes, the cardiac cycle data improved from 32.83 to 5.17% for the Vp, from 62.67 to 91.5% for the AsVp and from 65.52 to 94.38% in the PAS, all with statistical significance.

For proper AV synchrony, it is necessary to carefully manipulate, not only the P wave sensitivity, but also several other of the pacemaker parameters.