Prevalence of subcutaneous implantable cardioverter-defibrillator candidacy based on template ECG screening in patients with hypertrophic cardiomyopathy

BACKGROUND: Subcutaneous implantable cardioverter-defibrillator (S-ICD) is a promising option for patients with hypertrophic cardiomyopathy (HCM). Patients with HCM can present markedly abnormal electrocardiograms (ECGs), and there are no data on what percentage of patients with HCM fail the prerequisite S-ICD vector screening. OBJECTIVE: The purpose of this study was to determine the failure rate of the prerequisite vector screening using 1 or 2 acceptable vectors stratified for risk profile for sudden cardiac death and predictors of failure. METHODS: ECG recordings from consecutive patients with HCM simulating the S-ICD sensing vectors were analyzed with the S-ICD screening tool. Eligibility was defined by 1 or 2 appropriate vectors. Medical history, ultrasound characteristics, and 12-lead ECG characteristics were analyzed and the individual arrhythmic risk at 5 year was determined to study potential predictors of failure. RESULTS: One hundred sixty-five (118 men; mean age 51 ± 16 years) patients were analyzed. Twenty-two patients (13%) had a high risk of sudden cardiac death, 33 (20%) had intermediate to high risk, and 110 (67%) had low risk. Twenty-six patients (16%) had no suitable vector, including 8 of 22 high-risk patients (36%). The primary cause of failure was high T-wave voltages in 25% of the vectors analyzed. T-wave inversions in >2 leads on the surface 12-lead ECG (odds ratio 15.6; 95% confidence interval 4.9-50.3; P < .001) and prior myectomy (odds ratio 8.4; 95% confidence interval 2.1-33.1; P = .002) were significantly associated with screening failure in a multivariable model. CONCLUSION: Currently available preimplant screening algorithms recommended by the manufacturer are associated with a significant failure rate in patients with HCM, particularly in the high-risk subgroup.