Abstract 12214: Characterization of Iatrogenic Left Bundle Branch Block After Septal Myectomy for Hypertrophic Cardiomyopathy

Introduction: LBBB results in impaired transseptal conduction and delayed posterolateral LV activation. Criteria for left bundle branch block (LBBB) vary across scientific organizations. Septal myectomy for hypertrophic cardiomyopathy (HCM) could serve as an iatrogenic anatomic model to characterize LBBB. Objective: To describe ECG features of LBBB after septal myectomy for HCM. Methods: ECG data were analyzed for 377 HCM patients (204 male) who developed post-operative LBBB after extended septal myectomy between 2004-2018. Results: Average age of the cohort at myectomy was 53 ± 14 years. Baseline QRS duration (QRSd) was 94 ± 10ms. The post myectomy QRSd was 152 ± 15ms, consistent with an average ΔQRSd of 58 ± 13ms. There was positive correlation between pre and post myectomy QRSd (r = 0.485; p < 0.0001). The average LV end-diastolic diameter (LVEDd) pre and 2 months post myectomy was 40 ± 5.6mm and 46.2 ± 6.5mm, respectively. Positive correlation between post myectomy QRSd and post myectomy LVEDd was also observed (r = 0.340; p < 0.0001). Females and males had pre myectomy QRSd of 93 ± 10ms and 95 ± 10ms respectively (p = 0.007) and post myectomy QRSd of 147 ± 13ms (120-184ms) and 157 ± 14ms (126-209ms) respectively (p < 0.0001). ΔQRSd was less in females than males (54 ± 13ms vs. 62 ± 11ms; p<0.0001). Only 13 females and 3 males had post myectomy QRSd < 130ms. Only 23 males had QRSd < 140ms. Conclusions: Surgical myectomy serves as a model to characterize LBBB. Following myectomy, QRSd correlated with LVEDd as well as pre-myectomy QRSd, and was longer in males due to delayed depolarization of larger hearts in men. Notably only 3 males and a minority of females had QRSd < 130ms. These data provide important insights for the validation of electrocardiographic LBBB criteria.