Haemodynamic benefit of a rate-adapted A-V delay in dual chamber pacing.

In dual chamber pacing, an improvement of exercise capacity is expected when the atrial refractory period is shortened, because the 2/1 point is increased. This objective can be achieved by greatly reducing atrioventricular delay (AVD) on exercise. Are such variations (up to 100-120 ms) detrimental from a haemodynamic standpoint? This study was performed to analyse this particular aspect of DDD pacing. Three DDD pacing modes, differing by their AVDs (fixed 200 ms AVD, fixed 150 ms AVD, and rate-adapted AVD) were tested in random order, with a haemodynamic protocol including ten patients with chronic atrio-ventricular (A-V) block. For the rate-adapted AVD pacing mode, AVD was reduced by 20 ms every 10 beats min-1 increment (from 220 ms at 90 beats min-1 to 100 ms at 150 beats min-1). Pacing rate was increased from 90 to 150 beats min-1 by increments of 10 beats min-1 every 5 min. Cardiac performance was significantly improved with the rate-adapted AVD above the two fixed AVDs, despite a large AVD variation. When AVD was rate adapted, cardiac index, stroke volume index and left ventricular systolic work index were generally higher and pulmonary capillary wedge pressure, pulmonary arterial pressure and systemic vascular resistances were generally lower, especially at 120, 130 and 140 beats min-1. Comparing the two fixed AVDs, 200 AVD improved cardiac function more at lower heart rates, whereas 150 AVD improved cardiac function more at higher heart rates. Despite its limitations, this study demonstrates that the potential benefits of reducing AVD with increasing heart rates should be twofold in dual chamber pacing: (a) haemodynamic, optimizing cardiac performance on exercise for all heart rates, especially in cases of organic heart disease; (b) electrophysiologic, permitting a sufficiently rapid maximal tracking rate in cases with long post-ventricular atrial refractory periods, allowing a satisfactory level of exercise.