Ablation of atrial fibrillation during coronary artery bypass grafting: Late outcomes in a Medicare population

Abstract

Background: This study compares outcomes of patients with preoperative atrial fibrillation undergoing coronary artery bypass grafting (CABG) with or without concomitant atrial fibrillation ablation in a nationally representative Medicare cohort.

Objectives: This study examined early and late outcomes in CABG patients with a preoperative history of atrial fibrillation to determine the correlation between surgical atrial fibrillation ablation to mortality and stroke or systemic embolization.

Methods: In the Medicare-linked Society of Thoracic Surgeons database, 361,138 patients underwent isolated CABG from 2006 to 2013; 34,600 (9.6%) had preoperative atrial fibrillation; 10,541 (30.5%) were treated with surgical ablation (ablation group), and 23,059 were not (no ablation group). Propensity score matching was performed using a hierarchical mixed model. Long-term survival was summarized using Kaplan-Meier curves and Cox regression models with robust variance estimation. The stroke or systemic embolization incidence was modeled using the Fine-Gray model. Median follow-up was 4 years.

Results: Long-term mortality in propensity score-matched CABG patients (mean age 74 years; Society of Thoracic Surgeons risk score, 2.25) receiving ablation versus no ablation was similar (log-rank P = .30). Stroke or systemic embolization occurred in 2.2% versus 2.1% at 30 days and 9.9% versus 12.0% at 5 years (Gray P = .0091). Landmark analysis from 2 to 5 years showed lower mortality (hazard ratio, 0.89; 95% confidence interval 0.82-0.97; P = .0358) and lower risk of stroke or systemic embolization (hazard ratio, 0.73; 95% confidence interval, 0.61-0.87; P = .0006) in the ablation group.

Conclusions: Concomitant ablation in CABG patients with preoperative atrial fibrillation is associated with lower stroke or systemic embolization and mortality in patients who survive more than 2 years.

Keywords: ablation; atrial fibrillation; coronary artery bypass grafting; maze.

Figure 1.

Flow diagram of study cohort. The STS database was queried for isolated CABG patients between 2006 and 2013. Exclusions and numbers of patients removed are shown on the left. This resulted in 34,600 patients with preoperative AF who were divided into those with or without surgical ablation during the CABG procedure. CMS=Centers for Medicare and Medicaid Services, CABG= coronary artery bypass grafting, CV= cardiovascular, PCI= percutaneous coronary intervention, STS=Society of Thoracic Surgeons.

Figure 2.

Propensity score match assessment of balance before and after matching. A one-to-one optimal matching algorithm was used to overcome differences in potential confounders between the two study groups. We compared the distribution of baseline characteristics before (black squares) and after matching (triangles). Before matching, the standardized differences ranged between −23 and 14, while in the matched sample, they ranged between −1.7 and 2.4, which indicates balance was achieved.

Figure 3.

Mortality outcomes of patients in 6 year follow up are shown for (A) unadjusted overall data and (B) adjusted matched data. Mortality risk was similar between groups in the adjusted group, p= 0.303. Landmark Analysis results for patients surviving past 2 years are shown for unmatched data in panel (C) and matched data in panel (D). Patients who had surgical ablation of atrial fibrillation had a lower risk of death, p=0.0358.

Figure 4.

Stroke or systemic embolization outcomes of patients in 6 year follow up are shown for (A) unadjusted overall data and (B) adjusted matched data. Landmark analysis results for patients surviving beyond 2 years are shown for unmatched data in panel (C) and matched data in panel (D). Patients who had surgical ablation of atrial fibrillation had a lower risk of stroke or systemic embolic event, p=0.0005.

Figure 5.

Patients undergoing isolated coronary artery bypass surgery with a history of preoperative atrial fibrillation (AF) may benefit from concomitant AF ablation. The Cox Maze IV maze lesion set is shown. However, detailed lesion set information was not available in our study. While early stroke and mortality were similar, stroke or systemic embolization and mortality for patients surviving more than 2 years was lower.