[Platelet function and coronary disease: demonstration of a so-called unstable platelet syndrome]

Radio-immunological assay of specific platelet substances in the serum allows assessment of in vivo platelet function at a given moment. Plasma levels of beta thromboglobulin (beta TG) platelet factor 4 (PF4) and thromboxane B2 (TXB2) were measured at rest and during exercise stress testing in 39 patients with known coronary artery disease with stable effort angina. The patients were divided into two groups according to the results of exercise ECG and thallium 201 myocardial scintigraphy: ischaemic (n = 28) and non-ischaemic (n = 11). Resting and exercise levels of the three platelet substances were compared with a group of normal controls (n = 14). The average control values at rest and on exercise were, respectively: PF4: 8.5 +/- 5 and 22 +/- 14 ng/ml; beta TG: 36 +/- 17 and 68 +/- 36 ng/ml and TXB2: 112 +/- 41 and 201 +/- 81 pg/ml. The average values of the non-ischaemic patients did not differ significantly, either at rest or during exercise. The variation of pathological values was higher in the ischaemic group. This seems to reflect the absence of univocal platelet behaviour and does not allow statistical comparison of mean values. Our results suggest the existence of an "unstable platelet syndrome", which seems to be associated with poor effort tolerance especially when present under resting conditions. There would seem to be a causal relationship between platelet instability and myocardial ischaemia, which would justify anti-platelet aggregation therapy in primary and secondary prophylaxis of myocardial infarction.