A tertiary centre experience of routine exercise testing as part of subcutaneous ICD vector mapping

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Introduction The pre-implant patient screening process (vector mapping) for subcutaneous defibrillators (S-ICD) seeks to determine eligibility for implantation. It broadly requires at least one of three available vectors (primary, secondary or alternate) to pass under all conditions to mitigate risk of inappropriate device therapies. Vector mapping protocols currently require only supine and sitting/standing ECG. However, the standard operating procedure (SOP) in our centre also includes mapping at peak exercise, actioned after audit data highlighted an association between exercise and sensing complications (T and R wave changes, rate-related bundle branch block and noise/myopotential over-sensing). Aim To determine whether routine exercise testing during screening alters the outcome of vector mapping, and whether this correlates with inappropriate therapies post-implant. Method This was a single-centre retrospective study of 121 patients (79% male, mean BMI 29) who completed S-ICD vector mapping between October 2016 and August 2022. 10 patients were excluded as they were unable to tolerate exercise. Emblem automated screening tool (AST) and AST 2.0 was used to complete vector mapping and a revised SOP was devised in conjunction with their technical support team. Post- implant vector programming was based on device optimisation algorithms rather than exercise-inclusive screening recommendation, which provided additional observational data only. Results 75% were primary prevention devices and the 3 most prevalent aetiologies were dilated (22%), ischaemic (20%) and hypertrophic (18%) cardiomyopathies. In 29.7% (33/111) of participant’s, inclusion of exercise screening altered vector mapping success: The alternate vector saw the largest decrease (23.2%) in successful mapping once exercise was incorporated (69 participants passed supine and sitting/standing, 16 of those failed post-exercise), followed by secondary 13.1% (13/99) then primary 3.9% (4/103) – see Figure 1. Further retrospective analysis showed that in 16.2% (18/111) of patients, post-implant vector selection opposed screening recommendation. 6 of these patients experienced exercise-induced sensing complications with 4 leading to inappropriate shocks. After reprogramming in-line with screening, all but 1 patient have had no further issues. Conclusions Incorporation of exercise mapping into S-ICD screening protocols may improve vector selection to reduce inappropriate device therapies.