This study sought to determine whether clinical variables can be used to identify patients at high risk of recurrent spontaneous myocardial ischemia or hemodynamic compromise during the 1st 4 days after intravenous thrombolysis for acute myocardial infarction. Of 288 patients randomly assigned to a conservative postthrombolysis strategy, 54 (19%) required urgent cardiac catheterization within 24 h; 75 (26%) underwent urgent cardiac catheterization within 4 days of admission. Of the clinical variables examined by multiple logistic regression analysis, only patient age and anterior wall myocardial infarction correlated with the need for urgent cardiac catheterization (p = 0.0016 and p = 0.017, respectively). Compared with recombinant tissue-type plasminogen activator or urokinase monotherapy, combination therapy with these agents was associated with a lower need for acute intervention during the 1st 24 h after admission, but the difference did not reach statistical significance (14% for combination therapy vs. 21% for each agent alone, p = 0.30). Of the 75 patients undergoing urgent coronary angiography, only 39% had an occluded infarct-related artery. Emergency coronary angioplasty was performed in 49% of the patients and coronary artery bypass graft surgery was performed urgently in 3%. Despite these interventions, the need for urgent cardiac catheterization was associated with an in-hospital mortality rate of 7% (vs. 3% in the group not requiring urgent angiography, p = 0.36); mean left ventricular ejection fraction was 50.5 +/- 11% (vs. 54.3 +/- 10.8%, p = 0.12) and regional infarct zone wall motion was -2.68 +/- 1.07 SD/chord (vs. -2.46 +/- 1.19 SD/chord; p = 0.44).(ABSTRACT TRUNCATED AT 250 WORDS)