Neves, R Almeida Lopes

Abstract Background Loss-of-function variants in TTN-encoded titin are the most common genetic cause of dilated cardiomyopathy (DCM). In addition, titin truncating variants (TTNtvs) are over-represented in early-onset atrial fibrillation (AF) and unexplained sudden cardiac arrest/death (SCA/SCD) suggesting that in rare circumstances TTNtvs may cause arrhythmias in a pre-cardiomyopathic electrical phase. Purpose To compare the prevalence of AF, sustained ventricular arrhythmias (VAs) and SCA/SCD between TTNtv-positive patients with genotype-positive but phenotype-negative (G+/P-) disease, non-dilated left ventricular cardiomyopathy (NDLVC) and DCM. Methods Retrospective review of 1,229 patients in our Arrhythmogenic/Dilated Cardiomyopathy Registry was used to identify those with TTNtvs in high proportion spliced-in (>90%) exons classified as pathogenic or likely pathogenic according to current American College of Medical Genetics and Genomics variant classification guidelines. Demographic, electrocardiographic, imaging and outcome data were extracted from the electronic record. After exclusion of those without satisfactory imaging data, each TTNtv-positive patient was classified as having G+/P- disease, NDLVC, or DCM according to the 2023 European Society of Cardiology Guidelines for the management of cardiomyopathies. The prevalence of AF, non-SCA major VA events (sustained VT and appropriate VT/VF-terminating ICD therapies), and SCA/SCD was then compared between the three left ventricular morphofunctional subgroups. Results Overall, 232 TTNtv-positive patients (mean age of 44 ± 17 years; 57% male) were included (average LVEF of 39 ± 17%; 32% with a history of AF; 23% with a history of non-SCA VA event and 6% with a history of SCA). Forty-nine (21%) were G+/P-, 45 (19%) had NDLVC, and 138 (59%) had DCM at the time of their most recent clinical evaluation. As expected, the prevalence of AF was higher in TTNtv-DCM patients when compared to both TTNtv-NDLVC [56/138 (41%) vs. 11/45 (24%); p=0.04] and G+/P- disease [56/138 (41%) vs. 5/49 (10%); p<0.001]. Similarly, the number of patients who experienced a non-SCA major VA event was higher in TTNtv-DCM than either TTNtv-NDLVC [44/138 (32%) vs. 6/45 (9%); p=0.01] or G+/P- disease [44/138 (31%) vs. 4/49 (8%); p<0.001]. Interestingly, no difference in the number of TTNtv-positive patients who experienced a SCA/SCD was observed across subgroups [2/49 (4%) for G+/P-; 2/45 (4%) for NDLVC; and 8/138 (6%) for DCM; p=ns for all comparisons]. Conclusion In patients with TTNtv substrates who were evaluated at a quaternary medical center, the prevalence of AF and major VA events correlates with left ventricular morphology/function with the greatest risk observed in those with DCM. However, the prevalence of AF and major VA events, including SCA, in TTNtv-positive patients with G+/P- and NDLVC disease is not trivial and highlights the ability of TTNtvs to present in a pre-cardiomyopathic electrical phase.

Abstract Background The extravascular implantable cardioverter defibrillator (EV-ICD) was designed to avoid lead-related complications associated with transvenous systems and deliver features such as anti-tachycardia pacing (ATP) and reduced generator size that provide an advantage over a subcutaneous ICD (S-ICD). As such, the EV-ICD is an attractive alternative for younger patients with genetic heart diseases (GHDs) who are not in need of permanent pacing. Objective To examine the indications, complications, and the clinical outcomes of patients with GHDs who received an EV-ICD. Methods A retrospective review of the electronic record was done for all GHD patients evaluated in genetic heart rhythm and/or cardiomyopathy clinics who had an EV-ICD implanted between 1/2021 and 2/2025. Basic demographic, ICD indications, complications, and therapy data were then extracted for all study patients. Results Overall, 23 patients (35% female; mean age 39 ± 16 years; 61% with a disease-causative genetic variant; mean LVEF 57%) with an underlying GHD (hypertrophic cardiomyopathy in 9, arrhythmogenic cardiomyopathy in 8, idiopathic ventricular fibrillation in 3, dilated cardiomyopathy in 2, and long QT syndrome in 1) had an EV-ICD implanted. For the majority, an EV-ICD was implanted for primary prevention (15/23; 65%) and represented their first ICD system (21/23; 91%). The success rate of the procedure was 96% with only one abandoned procedure because of poor R-wave sensing. Inadvertent intraprocedural lead placement in the pericardial space occurred in 1 patient with previous thoracotomy and surgically placed epicardial lead without sequelae or need for revision. Over a mean follow-up of 8±9 months, the rate of complications was low (1/23; 4%) with one electrode displacement and this patient underwent defibrillation threshold testing (DFT), the device properly detected VF and emitted a successful shock 30 J. Thus far, 2 patients have received appropriate VT/VF-terminating therapies (3 ICD shocks, 0 ATP) with successful conversion to sinus rhythm. One patient died following an electrical storm. One patient had 3 inappropriate ICD shock for sinus tachycardia while exercising followed by 1 successful shock for VF. Conclusion In this early experience, EV-ICDs appear to be safe and effective in younger patients with genetic arrhythmogenic and hypertrophic cardiomyopathies. Future studies are needed to better understand the utility of EV-ICDs in patients with cardiac channelopathies and advantages of EV-ICDs over transvenous and S-ICD systems in patients with an array of sudden death-predisposing GHDs.