New-Onset Atrial Fibrillation After Alcohol Septal Ablation Versus Surgical Myectomy in Obstructive Hypertrophic Cardiomyopathy: A Propensity-Matched Analysis

BACKGROUND: Atrial fibrillation (AF) complicates 20-25% of hypertrophic obstructive cardiomyopathy (HOCM) cases and independently predicts heart failure progression, thromboembolism, and mortality. Both surgical myectomy (SM) and alcohol septal ablation (ASA) are associated with new-onset AF through opposing mechanisms; myectomy promoting left atrial reverse remodeling, ASA generating a chronic arrhythmogenic septal scar. Yet no propensity-matched study has directly compared AF incidence between these procedures. OBJECTIVES: To compare the incidence and temporal trajectory of new-onset AF following ASA versus SM at prespecified landmarks of Day 1, Day 7, and Day 30 in a propensity score-matched cohort with 3 years of follow-up. METHODS: Patients with obstructive HOCM who underwent ASA or SM without prior AF were identified in the TriNetX database between Jan. 2010 and Apr. 2023 and were followed for up to 3 years. After 1:1 propensity score matching on demographics, comorbidities, and atrial substrate risk factors, 223 patients remained in each cohort; new-onset AF was ascertained using clinical diagnosis codes applied symmetrically across both groups. RESULTS: Of 1,188 patients (539 ASA, 649 SM), 223 were matched per cohort (mean age 59.5 ± 15.5 years, 37.4% male, 80.3% White); all standardized mean differences were <0.20 after matching. At Day 1, AF occurred in 16.1% vs. 12.1% (ARD 4.0%; HR 1.22, 95% CI 0.74-2.01; p = 0.437). At Day 7, a significant divergence emerged (15.8% vs. 8.4%; ARD 7.4%; RR 1.87, 95% CI 1.10-3.21; p = 0.019). By Day 30, ASA carried a nearly three-fold higher AF risk (15.4% vs. 5.3%; ARD 10.1%; HR 2.75, 95% CI 1.39-5.42; p = 0.039), with AF-free survival of 82.59% vs. 93.83% (log-rank p = 0.002), with progressive Kaplan-Meier separation sustained through 3 years. CONCLUSIONS: In a propensity-matched cohort, ASA was associated with a progressively higher risk of new-onset AF compared with SM, with divergence emerging by Day 7 and widening through Day 30, consistent with substrate reversal after myectomy versus substrate maturation after ASA. These findings support incorporating differential AF risk into procedural selection discussions, extending postprocedural monitoring after ASA, and reassessing early anticoagulation thresholds in ASA patients.