Conduction Abnormalities and Long-Term Mortality Following Septal Myectomy in Patients With Obstructive Hypertrophic Cardiomyopathy

Background: Conduction abnormalities including bundle branch block are recognized sequelae following septal myectomy in patients with hypertrophic cardiomyopathy, but their incidence and effect on long-term mortality have not been well studied. Objectives: This study was conducted to determine the impact of conduction abnormalities on mortality in patients with obstructive hypertrophic cardiomyopathy following myectomy. Methods: The outcomes of 2,482 patients with obstructive hypertrophic cardiomyopathy who underwent transaortic septal myectomy from 1961 to 2016 were analyzed. Pre-operative and early post-operative electrocardiograms were reviewed to determine conduction status. The study endpoint was all-cause mortality. Results: Mean age at operation was 54.2 ± 14.6 years, and 1,370 patients (55.2%) were men. Pre-operatively, 2,159 patients (87.0%) had normal conduction, of whom 38.8% developed left bundle branch block, 1.1% developed right bundle branch block (RBBB), and 0.6% had complete heart block (CHB) after myectomy. Among 112 patients with baseline RBBB, 34.8% developed CHB post-operatively. Overall, only 2.3% of patients developed CHB. Over a median follow-up period of 8.6 years, overall mortality differed among post-operative conduction groups after adjustment for age, sex, and concomitant procedures (p = 0.015). Specifically, mortality in those with paced rhythm after myectomy was significantly increased relative to those with normal conduction (hazard ratio: 1.57; 95% confidence interval: 1.15 to 2.14; p = 0.005), although no significant difference was observed in left bundle branch block and RBBB (vs. normal) groups. Conclusions: Left bundle branch block is a common sequela after septal myectomy but does not influence post-operative mortality. Myectomy-related CHB is rare in patients with baseline normal conduction, while pre-existing RBBB greatly increases the risk for CHB. Persistent paced rhythm after operation is an independent predictor of mortality.