Reversal of Abnormal Platelet Aggregability and Change in Exercise Tolerance in Patients with Angina

Nineteen patients with severe but stable angina pectoris who had positive ECG response to exercise on a bicycle ergometer and 11 normal subjects were studied. Patients received placebo for six weeks and were then randomized into placebo (n = 9) and propranolol (n = 10) treatment groups. Threshold for platelet aggregation in response to adenosine diphosphate (ADP) was measured in fresh platelet rich plasma. Mean concentration of ADP necessary for a biphasic threshold aggregation response was 1.56 AM (geometric mean) in patients and 3.85 ,uM in normals (P < 0.01). Serial studies with placebo showed no significant change in ADP threshold. With propranolol, 80 mg/day, platelet aggregation in response to ADP was entirely normalized; 3.79 ,uM ADP produced maximal aggregation compared to 1.32 gM before therapy (P < 0.01). No additional changes were noted with propranolol, 160 mg/day. In the propranolol-treated patients (80 mg/day) who demonstrated reduction in ADP-induced platelet aggregation, total work during exercise increased by 128%, from 765 ± 125 (standard error of mean) kpm during the control period to 1,792 ± 285 kpm (P < 0.01). Thus patients with angina and abnormal exercise tolerance demonstrate increased platelet aggregability in vitro which is restored toward normal with propranolol in dosage sufficient to improve exercise tolerance.