Disease Severity and Exercise Testing Reduce Subcutaneous Implantable Cardioverter-Defibrillator Left Sternal ECG Screening Success in Hypertrophic Cardiomyopathy

Background— The features of the hypertrophic cardiomyopathy (HCM) ECG make it a challenge for subcutaneous implantable cardioverter-defibrillator (S-ICD) screening. We aimed to investigate the causes of screening failure at rest and on exercise to inform optimal S-ICD ECG vector development. Methods and Results— One hundred and thirty-one HCM patients (age, 50±16 years; 92 males and 39 females) with ≥1 HCM risk factor for sudden death underwent S-ICD ECG screening at rest and on exercise. Fifty patients (38%) were ineligible for S-ICD because of screening failure in every lead vector: 33 (66%) failed in the supine position, 12 (24%) failed in the standing position, and 5 (10%) failed on exercise. In patients who could exercise and passed screening at rest, 31 (44%) had 1 vector safety, 16 (23%) had 2 vector safety, and 24 (33%) had 3 vector safety. Increased R:T wave ratio in the S-ICD screening ECG (odds ratio, 4.0; confidence interval, 3.0–5.3; P <0.001) was associated with screening failure, while R/T ratio <3 in aVF (odds ratio, 0.3; confidence interval, 0.12–0.69; P =0.006) and increasing age (odds ratio, 0.97; confidence interval, 0.95–0.99; P =0.03) was associated with reduced screening failure. European Society of Cardiology risk score was higher in those failing screening (risk score 5.5% [interquartile range, 3.2–8.7] in failed versus 4.5% [interquartile range, 2.9–7.4] in passed; P =0.04). Conclusions— HCM patients have a significant incidence of screening failure, which is determined primarily by the increased R:T ratio on the screening ECG and lead aVF. High-risk patients have an increased screening failure rate. Optimization of sensing algorithms is required to ensure that the highest risk HCM patients can benefit from S-ICD implantation.