Effect of diurnal variations in the QRS complex and T waves on the eligibility for subcutaneous implantable cardioverter-defibrillators

BACKGROUND Subcutaneous implantable cardioverter-defibrillators (S-ICDs) are an established therapy for preventing sudden cardiac death. However, a considerable number of patients still undergo inappropriate shocks even after conventional preim-plantation electrocardiographic (ECG) screening. OBJECTIVE This study aimed to elucidate the additional effect of diurnal variations in the QRS complex and T waves of 24-hour Hotter screening on S-ICD eligibility. METHODS Patients with transvenous ICDs who did not need pacing were selected for the study. The ECG was recorded by placing the electrodes to simulate the 3 sensing vectors of the S-ICD, with the patient in the standing and supine positions (conventional), during exercise, and during 24-hour Hotter screening. We investigated the additional discrimination of diurnal variations in patients ineligible for S-ICDs as well as characteristics of those patients. RESULTS Of the 86 patients (82% men; mean age 54 +/- 16 years) analyzed by all 3 screenings, 2 (2.3%) and 3 (3.4%) were considered ineligible by conventional and exercise screening, respectively. An additional 21 patients (24.4%) were found ineligible through Holler screening. A multivariate logistic regression analysis demonstrated that Brugada syndrome and an increased QRS duration per millisecond were associated with ineligibility (odds ratio 5.74; 95% confidence interval 1.74-20.2; P = .003 and odds ratio 1.04; 95% confidence interval 1.01-1.07; P = .007, respectively). T-wave oversensing was mostly observed during 0-6 AM, but no significant diurnal variations were observed in the incorrect QRS profiles. CONCLUSION The detection of diurnal variations through Holler monitoring in addition to conventional screening is expected to be useful for determining S-ICD eligibility.