Abstract 9755: Impact of Outflow Obstruction and Septal Myectomy on Long Term Risk of New Onset Atrial Fibrillation in Hypertrophic Cardiomyopathy

Abstract

Background: Atrial fibrillation (AF) is the most common sustained arrhythmia in hypertrophic cardiomyopathy (HCM), with patients having a 4 to 6 fold greater likelihood of developing AF as compared to the general population, and is an important cause of morbidity, impaired quality of life and embolic stroke in HCM. The impact of outflow obstruction and the influence of surgical septal myectomy on the development of new-onset AF has not been well described. Aim: To characterize the risk of new-onset AF in nonobstructive and obstructive HCM and compare to AF risk in patients after myectomy. Methods: 1767 consecutive HCM patients without prior AF history, seen at the Tufts HCM Institute between 2004 and 2019, including 712 with obstruction (outflow gradients ≥ 30mmHg at rest or following provocation) who did not undergo invasive septal reduction therapy (SRT), 552 with nonobstructive HCM (outflow gradients < 30mmHg), and 503 who underwent surgical myectomy were followed for an average of 4.3 ±4.2 years for new-onset symptomatic AF. Isolated post-operative episodes of AF, i.e., occurring within the first 3 months after myectomy, were excluded from analysis. Results: Patients with obstructive HCM who did not undergo SRT had a 1.5-fold increased risk for new-onset AF as compared to nonobstructive HCM (rate onset of 2.8%/year vs.1.7%/year, p=0.04), with freedom from AF at 10-years of 72% in obstructive patients. Patients undergoing myectomy were older (52 ± 15 vs. 50 ± 15 years; p<0.01), had larger LA dimension (42 ± 7 vs 40 ± 6mm; p<0.01), and higher HCM-AF risk scores (22 ± 3.5 vs. 19 ± 3.8; p<0.01) as compared to nonobstructive HCM. However, despite a higher predicted risk for new-onset AF at time of myectomy (2.7%/year vs. 1.5%/year), after myectomy the risk of new onset AF was no different from patients with nonobstructive HCM (hazard ratio 0.9; rate of onset of 1.8%/year vs. 1.7%/year; p=.73), with freedom from AF at 10-years of 83% post-myectomy. Conclusions: Patients with obstructive HCM have a higher risk of AF as compared to nonobstructive HCM. After myectomy risk of new-onset AF is substantially reduced, such that risk is no different from patients with nonobstructive HCM. These data demonstrate efficacy of myectomy in decreasing long term risk of AF in obstructive HCM.