Aspirin, but not heparin, suppresses the transient increase in thromboxane biosynthesis associated with cardiac catheterization or coronary angioplasty

Objectives. We sought to study the dose dependence of in vivo suppression by aspirin of enhanced thromboxane biosynthesis in the setting of coronary angioplasty and to evaluate the effects of heparin and aspirin during cardiac catheterization. Background. Percutaneous transluminal coronary angioplasty induces a controlled injury of the intima of the diseased arterial segment, with rapid deposition of platelets at the site of dilation. Thus, it provides a clinical model of intracoronary platelet activation. Methods. The urinary excretion of a major enzymatic metabolite of thromboxane A₂, 11-dehydro-thromboxane B₂, was measured in 57 patients with stable coronary artery disease undergoing cardiac Catheterization (n = 28) or elective single-vessel percutaneous transluminal coronary angioplasty (n = 29). Three consecutive urine collections were obtained from all patients before during and after either procedure. Patients undergoing Catheterization were treated with the following regimens: a) no aspirin for ≥10 days and no heparin (n = 12); b) no aspirin for ≥10 days but heparin, 10,000 IU, at the time of Catheterization (n = 5); c) aspirin, 300 mg/day, for at least 5 days (n = 1). Patients undergoing coronary angioplasty were randomly assigned to short-term treatment with aspirin given as a) 75 mg/day for ≥5 days before angioplasty (n = 11); b) 300 mg/day for ≥3 days before angioptesty (n = 9); or c) 300 mg/day for ≥3 days before angiopiasty followed by 1,000 mg during angioplasty (n = 9). Results. In patients undergoing Catheterization, urinary 11-dehydro-thromboxane B₂ excretion (pg/mg creatinine) increased from 563 ± 481 (mean ± SD) to 1,684 ± 1,332 in the absence and from 620 ± 191 to 1,588 ± 597 in the presence of heparin. No increase was observed in the group receiving aspirin (from 240 ± 141 to 215 ± 115). In patients undergoing coronary angioplasty treated with aspirin, 75 mg/day, urinary 11-dehydro-thromboxane B₂ averaged 180 ± 112, 223 ± 178 and 294 ± 260, respectively, before, during and after the procedure. At 300 mg/day, the corresponding values were 185 ± 48, 217 ± 70 and 197 ± 93. In patients also receiving aspirin, 1,000 mg, during angioplasty, 11-dehydro-thromboxane B₂ averaged 151 ± 66, 138 ± 43 and 133 ± 77, respectively. Conclusions. Enhanced thromboxane biosynthesis associated with cardiac Catheterization or coronary angioplasty can be largely suppressed by low dose aspirin. This finding is consistent with the view that this alteration reflects platelet activation.