Methods

The design, inclusion and exclusion criteria, and end point definition of the HORIZONS-AMI trial have previously been described in detail. In brief, the HORIZONS-AMI trial was a prospective, open-label, multicenter trial involving patients with STEMIs who underwent primary PCI as a management strategy. Patients with STEMIs presenting within 12 hours of symptom onset were randomized (1:1) to receive either unfractionated heparin plus glycoprotein IIb/IIIa inhibitor or bivalirudin monotherapy (plus bailout glycoprotein IIb/IIIa inhibitor) before primary PCI. Immediate coronary angiography was performed after randomization, followed by PCI, coronary artery bypass grafting, or medical management at the discretion of the physician. In a second randomization strategy, patients eligible for stenting were randomized (3:1) to receive TAXUS Express 2 paclitaxel-eluting stents (Boston Scientific Corporation, Natick, Massachusetts) or to an otherwise identical Express bare-metal stent (Boston Scientific Corporation). Clinical follow-up was performed at 30 days, 6 months, 1 year, 2 years, and 3 years. Use of warfarin or any long-term oral anticoagulation before randomization and major contraindication to long-term anticoagulation were major exclusion criteria to the HORIZONS-AMI study.

AF was defined as the absence of P waves and atrial activity represented by fibrillatory waves and irregular RR intervals. Patients were classified as having new-onset AF if they had no AF at presentation and no history of AF (including a history of paroxysmal AF) but had ≥1 episode of AF recorded on electrocardiography or telemetry during the index hospitalization after PCI (as reviewed by an independent electrocardiography core laboratory of the Cardiovascular Research Foundation, New York, New York). The primary end point of the present study was net adverse clinical events (NACEs), defined as the combination of major bleeding (unrelated to coronary artery bypass grafting) or a composite of major adverse cardiovascular events (MACEs), including death, reinfarction, target vessel revascularization for ischemia, and stroke. All events were adjudicated by an independent clinical events committee blinded to treatment assignment. Patients with and without new-onset AF after PCI were compared at 3 years with respect to MACEs, NACEs, and their individual components.

All analyses were performed by intention to treat. Chi-square tests were used to compare categorical variables, which are presented as proportions. Continuous variables were compared using Wilcoxon’s rank-sum tests and are presented as medians with interquartile ranges. Follow-up analysis was performed using time-to-event data, estimated using the Kaplan-Meier method, and were compared using the log-rank test. A stepwise logistic regression model with an entry and exit level of significance of 0.10 was used to identify independent predictors of new-onset AF. Potential covariates included in this regression model were age, male gender, body mass index, history of smoking, hypertension, hyperlipidemia, diabetes, previous myocardial infarction, congestive heart failure, New York Heart Association class III, peripheral vascular disease, chronic renal insufficiency, and ≥2-vessel coronary artery disease. Cox multivariate regression models were used to identify independent predictors of NACEs, MACEs, and death at 3 years. Variables included in the Cox regression models were age, hypertension, history of smoking, diabetes, previous myocardial infarction, previous PCI, left anterior descending coronary artery as the culprit vessel, symptom onset–to–balloon time, congestive heart failure, New York Heart Association class III, history of ventricular tachycardia or ventricular fibrillation, thienopyridine use, and chronic renal insufficiency. Variables included in the models were carefully selected to avoid overfitting. All statistical analyses were performed using SAS version 9.2 (SAS Institute Inc., Cary, North Carolina).

Results

Of the 3,343 patients with STEMIs who underwent primary PCI, 62 (1.9%) presented with AF at baseline and were excluded from the present analysis. Of the total studied population of 3,281 patients, post-PCI new-onset AF developed in 147 (4.5%) of patients.

Compared with patients without AF after PCI, patients with new-onset AF were older, were more often women, and had lower ejection fractions at baseline ( Table 1 ). There was no difference in the rate of postprocedural TIMI grade 3 flow achieved between the 2 groups at the end of the index PCI. Patients in the new-onset AF group were less likely to be discharged on thienopyridine (94% vs 98%, p = 0.002) but, as expected, were more likely to be discharged on warfarin (11% vs 3%) and amiodarone (20% vs 1%) (p <0.0001 for both).

Three-year clinical outcomes in patients with and without new-onset AF after PCI are listed in Table 2 and shown in Figure 1 . Patients with new-onset AF had significantly higher 3-year rates of NACEs (46.5% vs 25.7%, p <0.0001), MACEs (38.4% vs 21.2%, p <0.0001), death (11.9% vs 6.3%, p = 0.009), ischemic stroke (5.8% vs 1.5%, p <0.0001), definite or probable stent thrombosis (10.2% vs 4.8%, p = 0.005), and major bleeding unrelated to coronary artery bypass grafting (20.9% vs 8.2%, p <0.0001). Table 3 lists rates of stent thrombosis according to the types of stent received and according to the occurrence or not of new-onset AF. At 30 days and beyond, patient with new-onset AF after PCI had a higher rate of definite or probable stent thrombosis whether they received bare-metal stents or drug-eluting stents. Notably, patients with new-onset AF after PCI had lower rates of aspirin compliance at 1 year (91.7% vs 97.3%, p = 0.002), 2 years (89.3% vs 96.8%, p = 0.0002), and 3 years (86.2 vs 95.9%, p <0.0001) and lower rates of thienopyridine compliance at 30 days (91.4% vs 97.6%, p = 0.003) and 1 year (56.4% vs 70.5%, p = 0.0005).

Kaplan-Meier curves showing cumulative event rates of ischemic and bleeding outcomes through 3 years according to the presence or absence of new-onset AF: (A) NACEs, (B) MACEs, (C) all-cause death, (D) all strokes, (E) definite or probable stent thrombosis, and (F) major bleeding unrelated to coronary artery bypass grafting.

The only identifiable predictors of occurrence of new-onset AF after PCI were age (hazard ratio [HR] 1.75, 95% confidence interval [CI] 1.50 to 2.05, p <0.0001) and body mass index (HR 1.04, 95% CI 1.01 to 1.08, p = 0.02). New-onset AF was shown to be a strong independent predictor of NACEs (HR 1.74, 95% CI 1.30 to 2.34, p = 0.0002) and MACEs (HR 1.73, 95% CI 1.27 to 2.36, p = 0.0005), with a nonsignificant trend for all-cause death (HR 1.51, 95% CI 0.91 to 2.50, p = 0.11) at 3 years ( Table 4 ).

Table 4

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