Should We Screen for S-ICD Vectors in Hypertrophic Cardiomyopathy Post-Myectomy?

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Case Description: We describe a 40 year old Asian male with hypertrophic cardiomyopathy (HCM) who presented after an inappropriate shock from his subcutaneous ICD (S-ICD) but was otherwise asymptomatic. The device was placed 4 months ago for secondary prevention of sudden cardiac death (SCD). He underwent a septal myectomy 2 months prior to presentation for severe LVOT obstruction. EKG showed sinus rhythm with new post-myectomy LBBB. Troponins were normal. Device interrogation revealed a wide complex rhythm consistent with sinus tachycardia with LBBB and evidence of T-wave oversensing (TWOS). The S-ICD was turned off and no further arrythmias were seen on continuous telemetry. Subsequent vector rescreening reflected ineligibility for S-ICD, most likely due to altered QRS morphology post-myectomy. Accordingly, the S-ICD system was extracted and a dual chamber transvenous ICD was placed. Patient noted to be doing well at 3 months follow up.

Discussion:S-ICD is a safe and effective alternate to transvenous ICDs to prevent SCD in patients with HCM, especially those with a long life-expectancy. The pre-implant automated screening tool generates 3 sensing vectors. Screening is done to ensure at least 1 vector with suitable EKG morphology as low amplitude vectors and low R:T ratios increase risk of oversensing. However, post-surgical changes can alter the QRS morphology as seen above. This can significantly impact the screening process. Currently, there are no guidelines for rescreening. We propose rescreening in the setting of significant QRS changes (especially post-operatively) to reduce the risk of oversensing and undersensing in high risk populations.




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American Heart Association Scientific Sessions, November 11-13, 2023, Philadelphia, PA