Thrombolysis in unstable angina: Randomized double-blind trial of t-PA and placebo

Background. Because coronary thrombosis is important in the pathogenesis of unstable angina and correlates with in-hospital cardiac events, we hypothesized that thrombolytic therapy would decrease cardiac events. Methods and Results. We randomized 70 patients with unstable angina to tissue-type plasminogen activator (t-PA) (0.49 MU/kg for 1 hour followed by 0.07 MU/kg per hour for 9 hours) or placebo. All patients received full doses of intravenous heparin for 96 hours and aspirin (325 mg beginning at 72 hours). The primary end points of the study were in-hospital death, myocardial infarction, and urgent revascularization. Three secondary end points were also evaluated. Myocardial perfusion was assessed with resting planar thallium scintigraphy 90 minutes after initiation of therapy. Silent ischemia was assessed with 48-hour Holter monitoring for ST shift beginning at time of initiation of drug therapy. Coronary angiography was performed at 18±6 hours and analyzed quantitatively to assess the stenosis responsible for unstable angina, the presence of intraluminal filling defects consistent with intracoronary thrombus, and stenosis morphology and severity. There was no difference in total in-hospital cardiac events between patients receiving t-PA (5% or 14%) and those receiving placebo (7% or 20%) (p=0.83). Resting thallium defects were larger in the patients receiving t-PA than in those receiving placebo (130±118 versus 76±84°, p<0.04), and this difference persisted when corrected for previous infarction. Although the numbers of patients with ST shift were similar, the duration of ST shift was significantly longer in the patients receiving t-PA than with placebo (20±46 versus 3±10 minutes, p<0.045). The frequency of intracoronary thrombi in patients with stenoses greater than 50% was significantly less in patients treated with t-PA (11 of 22, 52%) as compared with placebo (23 of 25, 92%) (p=0.002), but there was no significant difference in minimal lesion cross-sectional area (0.49±0.42 versus 0.57±1.08 cm², p=0.75) or ulceration index (0.79±0.16 versus 0.77±0.15, p=0.71) of the culprit artery. Conclusions. We conclude that a prolonged infusion of t-PA in unstable angina reduces intracoronary thrombi but does not significantly decrease in-hospital cardiac events. The sample size, however, does not provide sufficient power to rule out a treatment effect. Paradoxically, there appears to be an increase in ST shift and worsening of myocardial perfusion with t-PA compared with therapy with heparin alone.