Miwa N, et al. - In this study with patients with transvenous implantable cardioverter-defibrillators (ICDs) who did not need pacing, researchers investigated how subcutaneous (S)-ICD eligibility was additionally influenced by diurnal variations in the QRS complex and T waves of 24-hour Holter monitoring. In the standing and supine positions (conventional), during exercise, and during 24-hour Holter monitoring, they recorded electrocardiogram results in patients by placing the electrodes to simulate the three sensing vectors of the S-ICD. In patients ineligible for S-ICDs, the additional discrimination of diurnal variations, as well as patient features were investigated. By conventional and exercise screening ECGs, 2 (2.3%) and 3 (3.4%) patients, respectively, were considered ineligible, among a total 86 patients (82% men; mean age 54±16 years) who were analyzed by all three screenings. Holter screening revealed ineligibility of another 21 patients (24.4%). For determining S-ICD eligibility, Holter monitoring in addition to conventional screening for detecting diurnal variations is expected to have utility.