Platelet function and exercise-induced myocardial ischaemia in coronary heart disease patients.

Divergent reports of the effects of exercise-induced myocardial ischaemia on platelet function require clarification. This study examines the relationship between exercise, exertional myocardial ischaemia, and in vivo and ex vivo platelet function in 27 male patients, aged 35 to 69, with stable coronary heart disease (CHD). All medications were ceased at least 5 days prior to a maximal exercise test. Blood was sampled before and after exercise to measure plasma and serum thromboxane B2 (TXB2), plasma beta-thromboglobulin (BTG), platelet count ratio (PCR), platelet count (PC), haemoglobin (Hb), haematocrit (Hct) and white cell count (WCC). The exercise test and blood measurements were repeated 5 weeks later, under the same conditions to confirm the reproducibility of any changes. Thirteen patients had a positive test for ischaemia and 14 a negative test. The PC, Hb, Hct and WCC increased in all patients after exercise, confirming earlier reports. The BTG level increased (25 +/- 9 to 30 +/- 15 ng/ml, p less than 0.05; and 24 +/- 9 to 32 +/- 8 ng/ml, p less than 0.004 in the repeat test) and was unrelated to exertional ischaemia. A decrease in the PCR only occurred in the non-ischaemic group in the initial test (0.84 +/- 0.14 to 0.78 +/- 0.13, p less than 0.02) but was not reproducible (0.84 +/- 0.10 to 0.82 +/- 0.13). No change occurred in plasma TXB2 levels. Serum TXB2 increased after exercise in the ischaemic group (255 +/- 150 to 314 +/- 190 ng/ml, and 240 +/- 139 to 370 +/- 169 ng/ml, p less than 0.05) but not in the negative test group (467 +/- 255 to 441 +/- 174 ng/ml, and 421 +/- 299 to 464 +/- 297 ng/ml, p greater than 0.1). Serum TXB2 discriminated poorly between individuals with positive and negative exercise tests. Thus, stable exertional ischaemia does not activate circulating platelets nor is it associated a priori with activated platelets. It may be associated with an increase in maximum thromboxane A2 production capability. Brief strenuous exercise may activate platelets in CHD patients independent of exertional ischaemia.