PO-689-06 SUBCUTANEOUS IMPLANTABLE CARDIAC DEFIBRILLATOR (S-ICD) EVOKED MAGNET RESPONSE: EVALUATING THE EFFECTIVENESS OF USING A MAGNET TO INHIBIT THERAPY IN S-ICD DEEP IMPLANTS

Abstract

Subcutaneous implantable cardioverter defibrillators (S-ICDs) are relatively new ICD technology and currently the manufacturer acknowledges that in patients with ‘deep implants’, magnet application may fail to elicit a magnet response (MR). However, there is no definition of a ‘deep implant’ or maximum recommended implant depth.The use of a magnet to inhibit therapies in ICDs is critical to inhibit therapies to avoid over-sensing and inappropriate therapies, at end-of-life and palliation or in acute clinical situations. The aim of this study was to determine if ICD generators implanted at greater tissue depth were more difficult to inhibit with standard clinical magnets. As part of routine device follow up, Sunshine Coast University Hospital’s S-ICD cohort underwent MR evaluation; where bar and donut magnets were placed over the S-ICD and the evoked MR was recorded in three separate zones, guided by a template. Ordinal regression models and logistic regressions assessed the relationship between the evoked MR and the tissue depth (TD), measured via X-ray. The patient’s ability to hear the audible tone was also recorded. Patients (n=39) with measurable TD (n=30) were analysed. The relationship between bar MR and TD showed an OR of 0.89 (95% confidence interval: 0.82-0.97) p<0.01. Therefore, for every 1mm increase in TD the chance of inhibiting a higher number of zones decreased by approximately 11%. The relationship between donut MR and TD showed an OR of 0.84 (95% confidence interval: 0.73-0.96) p<0.01. Therefore, for every 1mm increase in TD the chance of inhibiting all 3 zones decreased by 16%. However, the donut magnet was able inhibit at least 2 zones for all TD values. BMI was not significant in predicting evoked MR. The patient’s ability to hear the audible alert was noted to be 77.0%. We observed a statistically significant association between tissue depth and ability to evoke magnet response. We also found a significant proportion of patients were unable to hear the evoked auditory alert.