Eligibility for the subcutaneous implantable cardioverter-defibrillator in patients with hypertrophic cardiomyopathy

BACKGROUND: High-risk hypertrophic cardiomyopathy (HCM) patients benefit from the implantable cardioverter defibrillator (ICD). The subcutaneous ICD (S-ICD) may provide comparable protection while avoiding the shortcomings of transvenous (TV) leads. We assessed S-ICD eligibility according to surface ECG screening test in a cohort of high-risk HCM patients. METHODS AND RESULTS: 47 HCM patients (3 S-ICD candidates; 41 TV-ICD patients without pacing indication; and 3 pacemaker-dependent TV-ICD patients) underwent 4 screening protocols: standard (n = 44); exercise (n = 33); continuous pacing (n = 44); alternating paced/spontaneous QRS (n = 41). Of the 44 patients in the standard screening group, 41 (93%) were eligible. Max LV thickness was inversely related to the number of qualifying leads (3 leads: 21 ± 4 mm; 2 leads: 22 ± 6 mm; 1 lead: 25 ± 6 mm; no leads: 28 ± 11 mm; P = 0.07). Of the 33 patients in the exercise group, 5 were ineligible (3 after exercise). Of these, 2 became eligible after moving sternal electrodes from the left to the right parasternal line (eligibility rate: 30/33; 91%). Of the 44 patients in the continuous pacing group, 28 (64%) were eligible, 8 of which with right parasternal electrodes. In the paced/spontaneous QRS group (n = 41), 21 patients (51%) had at least 1 eligible lead during pacing and retained compatibility on the same lead during spontaneous rhythm, 5 of which with right parasternal electrodes. CONCLUSIONS: S-ICD screening failure is low in HCM, provided that patients with severe hypertrophy are carefully evaluated. Exercise test should be performed and right parasternal leads tested. Pacemaker patients display lower eligibility rate.