The effects of septal myectomy and alcohol septal ablation for hypertrophic cardiomyopathy on the cardiac conduction system.

AV conduction abnormalities are observed in 15-30% of patients with hypertrophic cardiomyopathy but are usually not severe enough to require permanent pacemaker implant. Both septal myectomy and alcohol septal ablation are effective options to relieve symptoms due to left ventricular outflow tract gradient in patients with hypertrophic cardiomyopathy but have procedure-specific effects on AV conduction and the His Purkinje system. Septal myectomy is associated with the development of LBBB in 50-100% of patients, while alcohol septal ablation is associated with RBBB in 37-70% of patients. Baseline abnormalities in the contralateral bundles and the presence of conduction disease have an important impact on the likelihood of the development of AV block for both of these therapies. AV block requiring permanent pacing occurs in approximately 2-3% of patients after septal myectomy and 10-15% of patients after alcohol septal ablation. Permanent pacemaker implant after alcohol septal ablation is more common in older patients (> 55 years old 13 vs. < 55 years old 5%; p = 0.06). Improved outcomes for septal myectomy and alcohol septal ablation are observed in experienced centers. Septal reduction therapies should be performed at medical centers with a dedicated hypertrophic cardiomyopathy program using a multidisciplinary approach.