Evaluating the magnet response in deep subcutaneous implanted cardioverter defibrillator implants.

INTRODUCTION: The manufacturer of subcutaneous implantable cardioverter defibrillators (S-ICDs) acknowledges that 'deep implants' may fail to elicit a magnet response, however, does not define 'deep implant' or recommend a maximum implant depth. This study aims to systematically evaluate the effect of subcutaneous tissue depth and magnet types on evoked magnet response. METHODS: Sunshine Coast University Hospital's S-ICD cohort underwent magnet response evaluation; where bar and donut magnets were compared and the evoked magnet response was recorded in three separate zones, guided by a template. Ordinal regression (OR) models assessed the relationship between the evoked magnet response and tissue depth (TD), measured via post-implant X-Ray. The patient's ability to hear the magnet response audible tone was recorded. RESULTS: Patients (n = 39) with measurable TD (n = 30) were analyzed. The bar magnet evoked a magnet response in all zones in 53% of patients, compared with 73% of patients with the donut magnet (p = 0.18). The relationship between bar magnet response and TD showed the odds of an evoked magnet response decreased by 11% every 1 mm increase in TD (OR of 0.89, p < 0.01), whereas the donut magnet decreased by 16% per 1 mm (OR of 0.84, p < 0.01). Directly over the S-ICD was the most effective in evoking magnet response with the bar (85% of patients), and off-centre was most effective for the donut magnet (100%). BMI and Praetorian score were not significantly associated with magnet response. We found 23% of patients were unable to detect the audible tone. CONCLUSION: We observed a statistically significant association between TD and ability to evoke magnet response. The bar magnet was less reliable than the donut magnet for therapy inhibition in deep implants.

Electrogram analysis to detect cathodal and anodal capture in left ventricular cardiac resynchronization pacing leads.

AIMS: Our study analyzed cardiac electrograms (EGMs) to identify characteristics for detecting cathodal, anodal, or cathodal-anodal (simultaneous) capture in left ventricular (LV) quadripolar pacing leads of cardiac resynchronization therapy (CRT) patients. The relationship between these EGM characteristics and the electrocardiogram (ECG) was also examined. METHODS: We performed a retrospective analysis of 54 bipolar pacing configurations across nine patients with implanted CRT devices and quadripolar leads who had undergone a 12 lead ECG optimization. Three pacing tests (cathode unipolar, anode unipolar, and bipolar) per bipolar pair were performed, examining ECG and EGM morphology changes accompanying each test and any transitions of morphology or amplitude during voltage stepdown. RESULTS: During the cathode and anode unipolar pacing tests, the EGM was biphasic (negative/positive) or monophasic (positive) in 52/53 (98%), and biphasic (positive/negative) or monophasic (negative) in 50/51 (98%), respectively. During bipolar LV capture threshold testing, 30 bipolar pairs displayed a sudden increase in EGM amplitude (median 9.4 mV, interquartile range [7-14 mV]) when transitioning from cathodal-anodal capture to cathodal or anodal capture. Ninety percent of these EGM transitions had a corresponding simultaneous change in ECG, while 10% had no ECG changes. Two patients demonstrated "quad-site" capture on their quadripolar lead with multipoint pacing enabled and cathodal-anodal capture from each stimulus. CONCLUSION: EGM characteristics during LV pacing tests can reliably detect cathodal, anodal, or cathodal-anodal capture, with greater sensitivity than 12 lead ECG changes. Integration of EGM analysis into routine CRT device follow up can be performed easily and may have implications for CRT efficacy.

Atrioventricular block masked by posteroseptal bypass tract located in coronary sinus aneurysm.

Atrial fibrillation with concurrent ventricular preexcitation identifies a high-risk arrhythmic substrate and usually results in catheter ablation of the atrioventricular bypass tract. Electrocardiography can only approximate the anatomical location of an accessory pathway. Here we report a case where a bypass tract was localised to a coronary sinus aneurysm and antegrade atrioventricular conduction masked underlying atrioventricular nodal block.