Background Glycoprotein (GP) IIb/IIIa antagonists are potent inhibitors of thrombocyte aggregation and thrombus formation. Several large-scale randomized studies for prevention of thrombotic complications have shown their potential to reduce these complications in patients undergoing percutaneous transluminal coronary angioplasty (PTCA). It was the purpose of this observational trial to assess the frequency and efficacy of primary GP IIb/IIIa antagonist therapy as a bailout procedure for the prevention of threatened or abrupt vessel closure in patients after conventional balloon angioplasty. Methods And Results From January 1995 to December 1996, PTCA was performed in 1332 consecutive patients with coronary artery disease. Overall, threatened or abrupt vessel closure was observed in 63 (4.7%) patients of the patient population. In these patients, abciximab was administered (0.25 mg/kg body weight intravenous bolus, followed by a 12-hour infusion at 10 μg/min). Repeat PTCA was performed shortly after the administration of the abciximab bolus to achieve an optimal flow at the time of active GP IIb/IIIa therapy. One day after intervention, early follow-up angiography was performed. Follow-up after 1 year included the clinical status of all patients and, if possible, control angiography. Overall, the preintervention minimum lumen diameter (MLD) measured 0.74 ± 0.27 mm and the diameter stenosis was 75% ± 24%. The postintervention MLD increased to 2.60 ± 0.55 mm, and the diameter stenosis decreased to 24% ± 22%. At 24-hour angiographic follow-up, the MLD decreased to 2.47 ± 0.49 mm and the diameter stenosis increased to 28% ± 24%, correspondingly. The thrombus score decreased from 2.8 ± 1.5 before abciximab treatment to 0.88 ± 0.81 after abciximab treatment, and Thrombolysis In Myocardial Infarction flow grade increased from 2.1 ± 1.1 to 2.9 ± 0.3. In-hospital events occurred in 2 patients. Both patients had to undergo emergency coronary artery bypass grafting (1 of these patients died). During long-term follow-up, there were 10 clinical events (1 death, 3 repeat PTCA, and 6 coronary artery bypass graft operations for restenosis at the target lesion site). The cumulative event rate after 1 year (including acute and follow-up events) for both the total group and for the target vessel was 19%. Conclusions The results of this study demonstrate that GP IIb/IIIa antagonists are able to prevent vessel occlusion after PTCA complicated by subsequent threatened or abrupt vessel closure. In these situations, GP IIb/IIIa antagonists provide effective treatment for the reduction of thrombus at the target lesion site, which constitutes a second key element for threatened or abrupt vessel occlusion. (Am Heart J 1999;137:234-40.)