EFFECTS OF ATRIAL, VENTRICULAR, AND ATRIOVENTRICULAR SEQUENTIAL PACING ON CORONARY FLOW RESERVE

Experimental animal data have indicated that altered left ventricular depolarization sequence as a result of right ventricular pacing may diminish coronary blood flow in the distribution of the left anterior descending coronary artery. To further investigate this, we compared the effects of atrial, ventricular, curd atrioventricular (AV) sequential pacing on coronary flow reserve. Twenty-seven patients (24 male, mean age 55 +/- 7 years) with normal left anterior descending coronary arteries were studied. Coronary flow reserve was calculated as the ratio of mean flow velocity at maximal coronary vasodilatation to mean flow velocity at baseline. The study consisted of two parts. In the first part, AV sequential pacing was compared to atrial pacing at the same rate; coronary flow reserve did not differ significantly between the two pacing modes (14 patients, 4.85 +/- 1.88 vs 5.47 +/- 1.55, respectively, P > 0.05). In the second part, all three pacing modalities were compared; coronary flow reserve was significantly higher during ventricular compared to AV sequential pacing, but not significantly different compared to atrial pacing (3.69 +/- 1.42 vs 2.90 +/- 0.86 vs 3.11 +/- 0.89, respectively, P < 0.05). This difference was secondary to a significant decrease in mean baseline velocity during ventricular pacing, while mean velocity during hyperemia was comparable between the three pacing modes. It is concluded that AV sequential pacing does not appear to exert a significant effect on coronary flow reserve. Ventricular pacing, however, may lower resting coronary blood velocity in some patients, without affecting maximal coronary blood velocity, resulting in a higher coronary flow reserve.