Abstract 12234: Is Maintenance of a Subcutaneous Implantable Cardioverter-Defibrillator a Feasible Option in Hypertrophic Cardiomyopathy Patients With Left Bundle Branch Block After Septal Myectomy?

Introduction: Subcutaneous implantable cardioverter-defibrillators (SICD) are effective for sudden death (SCD) prevention in patients (pts) with hypertrophic cardiomyopathy (HCM). Pre-implant ECG screening to evaluate R and T wave sensing is done to decrease the risk of inappropriate shocks (IAS). Pts who undergo septal myectomy are at high risk of developing left bundle branch block (LBBB) that could potentially result in SICD T wave oversensing (TWOS). Objective: We describe 6 cases of pts with SICD and septal myectomy to understand the risks and benefits of maintaining SICD therapy in this cohort. Methods: We performed a retrospective cohort study of all pts with HCM who underwent SICD implantation and septal myectomy from 2013 to 2021. Results: Six pts with HCM underwent both SICD implantation and myectomy. Post myectomy ECGs for all pts show LBBB with QRS between 137 to 166 ms. Four of these pts were implanted prior to myectomy. The average time to myectomy after SICD was 1.3 years. Three out of the four pts have had no IAS or TWOS since myectomy. One patient experienced TWOS with 2 IAS 4 months after myectomy. The sensing vector was changed from primary to alternate with no further TWOS for the last 6 years. The remaining two pts underwent SICD implantation after myectomy, both of whom screened “OK” using the manual screening tool prior to implant. Neither patient has experienced IAS. One patient displayed episodes of TWOS and underwent vector change with no TWOS for the last 5 years. At the time of recent SICD generator replacement, he was screened using the automated programmer software and failed screening in all 3 vectors (Figure 1). Conclusions: This series demonstrates that maintenance of SICD is a viable option for SCD prevention in young pts who develop LBBB after septal myectomy. With close monitoring and vector adjustment, IAS and TWOS can be avoided. Further larger studies are necessary to assess the long-term risk of TWOS and IAS in this unique population.