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The subcutaneous implantable cardioverter defibrillator (ICD) provides therapy for the prevention of sudden cardiac death while avoiding the numerous complications associated with transvenous leads. This relatively novel device employs an innovative approach to sensing and defibrillation from outside of the thoracic cage. Substantial data from cohort studies and registries have accrued and can be used to inform patient eligibility, implant technique, and efficacy compared with the standard transvenous ICD. This review serves to update the clinician as to current evidence and the nuances involved in the optimal utilization of this innovative technology.

Aims Published reports regarding inferolateral early repolarization (ER) syndrome (ERS) before 2013 possibly included patients with Brugada-pattern electrocardiogram (BrP-ECG) recorded only in the high intercostal spaces (HICS). We investigated the significance of HICS ECG recording in ERS patients. Methods and results Fifty-six patients showing inferolateral ER in the standard ECG and spontaneous ventricular fibrillation (VF) not linked to structural heart disease underwent drug provocation tests by sodium channel blockade with right precordial ECG (V1–V3) recording in the 2nd–4th intercostal spaces. The prevalence and long-term outcome of ERS patients with and without BrP-ECG in HICS were investigated. After 18 patients showing type 1 BrP-ECG in the standard ECG were excluded, 38 patients (34 males, mean age; 40.4 ± 13.6 years) were classified into four groups [group A ( n = 6;16%):patients with ER and type 1 BrP-ECG only in HICS, group B ( n = 5;13%):ERS with non-type 1 BrP-ECG only in HICS, group C ( n = 8;21%):ERS with non-type 1 BrP-ECG in the standard ECG, and group D ( n = 19;50%):ERS only, spontaneously or after drug provocation test]. During follow-up of 110.0 ± 55.4 months, the rate of VF recurrence including electrical storm was significantly higher in groups A (4/6:67%), B (4/5:80%), and C (4/8:50%) compared with D (2/19:11%) (A, B, and C vs. D, P < 0.05). Conclusions Approximately 30% of the patients with ERS who had been diagnosed with the previous criteria showed BrP-ECG only in HICS. Ventricular fibrillation mostly recurred in patients showing BrP-ECG in any precordial lead including HICS; these comprised 50% of the ERS cohort.

Backgrounds: Cardiac resynchronization therapy (CRT) is an established option for advanced heart failure (HF) with electro-mechanical dyssynchrony. However, it provides no benefit in an approximately one third of the patients, which is unpredictable by any clinical tool. We hypothesized that (1) magnetocardiography (MCG) capable of delineating ventricular conduction sequences with high spatio-temporal resolution identify heterogeneous (multi-directional) left ventricular (LV) intraventricular conduction (presumably indicative of local block) and that (2) it would hamper the CRT effect, thereby predicting poor prognosis after CRT implantation. Methods: We analyzed 64-Ch MCGs (1kHz) in 52 patients with advanced HF (LVEF 25±9%) and QRS prolongation (147±31ms) on ECG before CRT implantation. According to the QRS current arrow mapping, they were divided into Group-A with uni-directional homogeneous ventricular conduction (n=33) and Group-B with multi-directional heterogeneous ventricular conduction patterns (n=19). CRT responder was defined when LVESV decreased >15% or LVEF increased >15%. Results: Baseline LVEF, BNP, and NYHA class were comparable between the groups. After 6 months, responders were more frequently found in Group-A (27/33) than Group-B (4/19, p

Introduction: Anatomical and electrical separation of left ventricular (LV) and right ventricular (RV) electrodes is significant for successful cardiac resynchronization therapy (CRT). During bi-ventricular pacing, the electrical activation was composed by RV and LV pacing wavefronts. So the region with latest activation during intrinsic rhythm might not correspond to the optimal pacing site during CRT. Hypothesis: We assess the hypothesis that interlead electrical delay measurements during RV and LV pacing besides intrinsic rhythm could predict favorable response to CRT. Methods and results: We evaluated 51 heart failure patients (age 64±13 years, LV ejection fraction 28±12%, QRS duration 155±37ms) who had successfully implanted CRT. The LV-RV interlead electrical delay (IED) during intrinsic rhythm, RV pacing (RV pacing-LV sensing: RVp-LVs) and LV pacing (LV pacing-RV sensing: LVp-RVs) were measured intraoperatively by utilizing intracardiac electrograms. After CRT implantation, 33 (65%) patients responded to CRT. The responders showed a significantly higher value of RVp-LVs compared with non-responders (166±42 vs. 141±36ms, respectively, p=0.04) and the absolute value of the difference between RVp-LVs and LVp-RVs was lower in responders than in non-responders (16±19 vs. 28±22ms, respectively, p=0.04). The IED during intrinsic rhythm (71±53 vs. 40±44ms, p=0.07) and LVp-RVs (170±47 vs. 146±35, p=0.06) showed higher tendency in responders, however they couldn't predict responders. Moreover, among narrow QRS patients (n=21; median QRS duration 118ms, 95 to 140ms), RVp-LVs was significantly higher in responders than in non-responders (159±32 vs. 121±32ms, p=0.01). Same as the entire cohort, the IED during intrinsic rhythm couldn't predict responders (59±24 vs. 35±36ms, p=0.11). At multivariate analysis, RVp-LVs was the only independent predictor of reverse remodeling in narrow QRS subgroup (p=0.03). Conclusion: Interlead electrical delay during intrinsic rhythm couldn't predict LV reverse remodeling after CRT. However high value of RVp-LVs measured intraoperatively was associated with favorable response irrespective of QRS width, which implies an optimal LV lead position during CRT implantation.