Azygos Vein ICD Lead Implantation Lowers Defibrillation Threshold in a Patient with Hypertrophic Cardiomyopathy

A 14-year-old boy with hypertrophic cardiomyopathy (HCM) diagnosed at the age of 1 year and with massive left ventricular hypertrophy suffered an episode of ventricular fibrillation during mild effort. He underwent a dual-chamber implantable cardioverter defibrillator (ICD) implantation. The defibrillation threshold testing (DFT) was ineffective. Subcutaneous multi-coli arrays tunneled into the left postero-lateral position and connected to the superior vena cava (SVC) port of the dual-chamber ICD were added to increase the myocardial mass involved in the defibrillation shock pathway. A new DFT was unsuccessful. The patient was transferred to our hospital for myectomy. An epicardial defibrillation patch was placed on the left ventricular lateral wall, but again, DFT testing was ineffective using the right ventricular (RV) coil to lateral patch as shock pathway. Another epicardial defibrillation patch was then placed on the inferior wall. In this case, DFT testing was effective with a defibrillation pathway between the two patches and the can. In November 2015, a high shock impedance alarm was recorded through remote monitoring, thus compromising the safety of the ICD shock pathway. The patient underwent the implant of a new trans-venous defibrillation coil lead in the azygos vein. After few months, the patient developed symptomatic severe aortic regurgitation and underwent an aortic valve replacement. During the operation, DFT testing was performed and was successful. Our case illustrates that azygous vein ICD lead implantation is efficacious in HCM with massive hypertrophy and high DFT, and prompts further studies to systematically investigate its efficacy in this particular subgroup of the HCM population.

Defibrillation threshold of internal cardioversion prior to ablation predicts atrial fibrillation recurrence

Background: Many studies have reported the predictors of atrial fibrillation (AF) recurrence after persistent AF (peAF) ablation. However, the correlation between the atrial defibrillation threshold (DFT) for internal cardioversion (IC) and AF recurrence rate is little-studied. We investigated the relationship between DFT prior to catheter ablation for peAF and the AF recurrence. Method and Results: From June 2016 to May 2019, we enrolled 82 consecutive patients (mean age 65.0 ± 12.4 years), including 45 patients with peAF and 37 with long-standing peAF, at Hamamatsu medical center. In order to assess the DFT, we performed IC with gradually increasing energy prior to radiofrequency application. Forty-nine and 33 patients showed DFT values less than or equal to 10 J (group A) and greater than 10 J or unsuccessful defibrillation (group B), respectively. During the mean follow-up duration of 20.5 ± 13.1 months, patients in group B showed significantly higher AF recurrence rates than those in group A after the ablation procedure (P = 0.017). Multivariate analysis revealed that the DFT was the only predictive factor for AF recurrence (OR=1.07; 95% CI: 1.00-1.13, P = 0.047). Conclusions: The DFT for IC was one of the strongest prognostic factors in the peAF ablation procedure.

Defibrillation threshold modeling to refine implant recommendations for an extravascular ICD system

Background The extravascular ICD (EV ICD) is a novel defibrillator that couples a substernal lead to a device under the left axilla. The electrode locations for best defibrillation performance are unknown. In this study we use data from a 21 patient pilot study to address this question. Objective To create computational torso models to study the effect of device and lead position on defibrillation threshold (DFT). Methods Finite element models were developed from CT and intraoperative imaging of the 21 patients enrolled in the EV ICD Pilot Study. Between 150 and 200 combinations of electrode locations were created for each patient, including the actual implant locations as determined from post-implant CT. The shock amplitudes from DFT testing and multiple vector impedance measurements from a large subset of patients and their as-implanted models were used to calibrate global model parameters. In total, 3330 implant models were automatically meshed, simulated and analyzed to compute predicted DFT values. For each patient an acceptable implant zone was calculated in which it is predicted that they would pass implant DFT testing. The zones for all patients were aligned and combined using common anatomical landmarks so that a common zone for acceptable DFT performance could be calculated for the cohort. Results Two patients were omitted due to incomplete CT data and 16 models were used during the calibration phase. Final analysis was performed using 19 patient models. The model results recommend positioning the lead slightly left of the sternal midline with the most proximal electrode 10 mm above the xiphisternal junction. Similarly, the device should be positioned so that its upper margin is at the height of the leftmost projection of the heart as seen in the AP view, and its posterior margin aligned with the posterior margin of the ventricles. The figure illustrates these positions. The model predicts that using these locations will result in acceptable DFT performance for all 19 patients - including one who failed testing at implant. Conclusion Modeling showed that DFT is dependent on both lead and device location. Furthermore, the predicted DFT and impedance values are consistent with clinical measurements. Specific lead and device locations were determined that are both clinically identifiable and provide acceptable DFTs in all patients. Implant positioning Funding Acknowledgement Type of funding source: Private company. Main funding source(s): Medtronic PLC

P529Efficacy and safety of S-ICD implantation without use of defibrillation threshold testing: a retrospective multicentric observational study

Introduction The subcutaneous ICD (S-ICD) is a valid alternative to transvenous systems (TV-ICD) for the treatment of life-threatening arrhythmias, and the extravascular position of the lead allows a significant reduction of the risk of infection. Current guidelines recommend defibrillation threshold testing (DFT) at the time of S-ICD implantation (class I). Although randomised trials have proven the safety of TV-ICD implantation with no DFT, it is unclear whether such an approach could be adopted for S-ICD as well. The PRAETORIAN score, based on post-implantation chest X-ray, can accurately predict a high defibrillation threshold after S-ICD implantation. The aim of this retrospective multicentre study was to evaluate the efficacy and safety of S-ICD implantation with no DFT. Methods We enrolled 203 consecutive patients undergoing S-ICD implantation in six different centres between October 2012 and January 2019. It was left at discretion of the operator whether performing or not DFT at the time of the procedure. Baseline device settings were collected, and the PRAETORIAN score was retrospectively calculated whenever chest X-ray was available. Both remote or in-clinic device interrogation reports were systemically analysed, and all the shocks and arrhythmia episodes identified. All the patients provided consent form and ethical approval was obtained. Results The population (mean age 57.6 ± 14.2) was divided in two groups, based on whether DFT was performed at the time of the S-ICD implantation: 72 patients (35.4%) underwent DFT (DFT+ group), while 131 patients (64.5%) did not (DFT- group). In the DFT- group, mean LVEF was lower (32 ± 8% vs 42 ± 17%, p < 0.0001) and prevalence of diabetes mellitus and atrial fibrillation higher compared to the DFT+ group (27.5% vs 13.9%, p = 0.04 and 38.9% vs 19.44%, p = 0.007; respectively). In addition, the indication for S-ICD was more frequently primary prevention in the DFT- vs DFT+ group (70.8% vs 90.8%, p = 0.0004; respectively). No differences in terms of device programming were identified between the two cohorts. The PRAETORIAN score was significantly higher in the DFT- vs DFT+ patients (50 ± 26 vs 36 ± 18, p = 0.032; respectively). After a median follow-up of … months, we observed 5 appropriate shocks in 3 patients from the DFT+ group vs. 15 shocks in 8 patients from the DFT- group (p = 0.81). All the life-threatening arrhythmias were successfully recognised and treated by the device. DFT was complicated by pulseless electrical activity in one patient. One patient in the DFT- group suffered from an episode of ventricular tachycardia requiring a total of 4 shocks for being terminated. Six patients in the DFT- group died for non-arrhythmic causes. On the Kaplan-Meier analysis, cumulative survival was comparable between the two groups (log rank p value = 0.13). Conclusions This study suggests that implantation of S-ICD with no DFT might be reasonable. These results should be confirmed in prospective randomised trials.