Low-grade exercise enhances platelet aggregability in patients with obstructive coronary disease independently of myocardial ischemia

Moderate and strenuous exercise is known to enhance platelet aggregability in patients with obstructive coronary artery disease (CAD), but the effect of low-grade exercise is not known. We assessed shear-induced platelet aggr egability before and after mild exercise (less than or equal to stage III o f the modified Bruce protocol) in 27 patients with documented CAD who were receiving aspirin and in 12 subjects without CAD (controls). Ex vivo platel et aggregability was assessed in flowing whole blood as the time to occlude a collagen and adenosine diphosphate-coated ring; shorter times indicated greater aggregability. Aggregability, plasma von Willebrand factor (vWF) an tigen, platelet and white cell counts, and hematocrit were measured at base line, immediately after exercise (peak), and at 30 and 180 minutes after ex ercise. Exercise of similar workloads induced myocardial ischemia in 14 pat ients (group 1), but not in the other 13 (group 2) nor in controls. Both pa tient groups showed a reduction in aggregation time at peak exercise compar ed with baseline (group 1: 84 +/- 17 seconds at peak vs 96 +/- 22 seconds a t baseline; group 2: 84 +/- 20 seconds at peak vs 99 +/- 20 seconds at base line; p <0.03 for both comparisons), with a return to baseline values withi n 180 minutes. No significant variation occurred in controls (89 +/- 18 sec onds at peak vs 85 +/- 21 second at baseline). Changes in vWF antigen did n ot differ significantly among groups. Aggregation times did not correlate w ith hematocrit or platelet and white cell counts. Thus, even low-grade exer cise transiently enhances whole blood platelet aggregability in patients wi th obstructive CAD, but not in controls. The effect is independent of myoca rdial ischemia, occurs despite aspirin, and is likely dependent on hemodyna mic factors interacting with coronary obstructions or dysfunctional endothe lium. (C) 2001 by Excerpta Medica, Inc.