Background--Platelet reactivity is increased by exercise in patients with obstructive coronary artery disease (CAD) but not in patients with syndrome X. In this study, we prospectively investigated whether the platelet response to exercise might help distinguish, among patients with angina, those with obstructive CAD from those with normal coronary arteries (NCAs).

Methods and Results--Venous blood samples were collected before and 5 minutes after exercise from 194 consecutive patients with stable angina. Platelet reactivity was measured by the platelet function analyzer (PFA)-100 system as the time for flowing whole blood to occlude a collagen-adenosine diphosphate ring (closure time). Coronary angiography showed CAD in 163 patients (84%) and NCA in 31 patients (16%). Baseline closure time was shorter in NCA patients (78.0±16 versus 95.5±23 seconds, P<0.0001). With exercise, closure time decreased in CAD patients (-15.5 seconds; 95% confidence limits [CL], -13.0 to -18.0 seconds; P<0.0001), but increased in NCA patients (12.5 seconds; 95% CL, 7.4 to 17.7 seconds; P=0.0004). An increase in closure time with exercise 10 seconds had 100% specificity and positive predictive value for NCAs. Similarly, a decrease 10 seconds had 100% specificity and positive predictive value for CAD. A closure time change (increase or decrease) 10 seconds allowed a correct classification of 55% of all patients.

Conclusions--Among patients with stable angina, the response of platelet reactivity to exercise was predictive of normal or stenosed coronary arteries at angiography. Specifically, an increase in closure time with exercise 10 seconds was invariably associated with the presence of NCA.