A trial fibrillation (AF) can adversely affect clinical outcomes after coronary artery bypass grafting (CABG),1,2 other major noncardiac surgery,3 and acute myocardial infarction (AMI).4 Although multiple predictors of an adverse outcome following percutaneous coronary intervention (PCI) have been identified,5 the prognostic significance of AF in the context of PCI is unknown. This study examined clinical outcomes after PCI in a large group of consecutive patients according to whether they were in AF or sinus rhythm at the time of the index PCI procedure. • • • The study population comprised 9,817 consecutive patients (17,862 lesions treated) from the Cardiovascular Research Foundation PCI Database who had not had an AMI in the preceding 72 hours and who underwent PCI of de novo lesions in native coronary arteries between January 1994 and January 1999. Baseline clinical demographics and in-hospital events were gathered prospectively by a dedicated data center and entered into the computerized database. Clinical outcomes were prospectively collected after hospital discharge through written questionnaire, telephone, and/or office interview. All adverse events were adjudicated after review of relevant source documents. Patients were divided into 2 groups according to the presence or absence of AF on the electrocardiogram taken at the time of PCI. There were 426 patients with AF, and 9,391 patients in sinus rhythm. Anginal symptoms were classified according to the Canadian Cardiovascular Society guidelines.6 Q-wave AMI was defined as the presence of new Q waves on the postprocedure electrocardiogram, and non–Q-wave AMI was defined as at least a fivefold increase above the upper limit of normal of the serum creatine kinase-MB fraction (without new Q waves). The choice of PCI rather than medical therapy or surgical revascularization was made by the attending cardiologist. Angiographic success was defined as a reduction of the stenosis by 20% and to 50% in all lesions. Procedural success was defined as angiographic success in the absence of major in-hospital complications (death, Q-wave MI, and emergency bypass surgery). All patients received 325 mg of aspirin orally 2 hours before the procedure and daily thereafter. Patients on warfarin had this terminated 2 to 3 days before the procedure to ensure an international normalized ratio 2 at the time of PCI. After stent placement, ticlopidine (250 mg twice daily) or clopidogrel (75 mg/day) was given routinely for 4 weeks. Warfarin was continued long-term in patients who were taking it before the PCI. Glycoprotein IIb/IIIa inhibitors were used in 7% of the patients in both treatment groups. The activated clotting time was maintained at 300 seconds for the duration of the procedure, unless glycoprotein IIb/IIIa inhibitors were used. Twelve-lead electrocardiograms were obtained at baseline, within 4 hours after the procedure, and on the following day (and more frequently if creatine kinase-MB was elevated or recurrent chest pain deFrom the Cardiovascular Research Foundation, Lenox Hill Heart and Vascular Institute, New York, New York. Dr. Dangas’ address is: Cardiovascular Research Foundation, Lenox Hill Heart and Vascular Institute, 55 East 59th Street, 6th Floor, New York, New York 10022. E-mail: gdangas@crf.org. Manuscript received April 15, 2002; revised manuscript received and accepted September 12, 2002. TABLE 1 Baseline Clinical Characteristics