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

In dual chamber pacing, an improvement of exercise capacityis expected when the atrial refractory period is shortened,because the 2/1 point is increased. This objective can be achievedby greatly reducing atrio-ventricular delay (AVD) on exercise.Are such variations (up to 100–120 ms) detrimental froma haemodynamic standpoint? This study was performed to analysethis 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 haemodynamicprotocol including ten patients with chronic atrio-ventricular(A-V) block. For the rate-adapted AVD pacing mode, AVD was reducedby 20 ms every 10beats min^–1 increment (from 220 ms at90 beats min^–1 to 100 ms at 150 beats min^–1). Pacingrate was increased from 90 to 150 beats min^–1 by incrementsof 10 beats min^–1 every 5 min. Cardiac performance was significantly improved with the rate-adaptedAVD above the two fixed AVDs, despite a large A VD variation.When A VD was rate adapted, cardiac index, stroke volume indexand left ventricular systolic work index were generally higherand pulmonary capillary wedge pressure, pulmonary arterial pressureand systemic vascular resistances were generally lower, especiallyat 120, 130 and 140 beats min^–1. Comparing the two fixedAVDs, 200 AVD improved cardiac function more at lower heartrates, whereas 150 AVD improved cardiac function more at higherheart rates. Despite its limitations, this study demonstratesthat the potential benefits of reducing AVD with increasingheart rates should be twofold in dual chamber pacing:

1. haemodynamic,optimizing cardiac performance on exercise forall heart rates,especially in cases of organic heart disease;
2. electrophysiologic,permitting a sufficiently rapid maximaltracking rate in caseswith long post-ventricular atrial refractoryperiods, allowinga satisfactory level of exercise.