This prospective blinded evaluation of the SP filter demonstrates that enabling the SP filter results in a significant reduction of inappropriate shocks by the S-ICD without a negative effect on appropriate shocks.

A new algorithm that uses correlation of the existing complex to previous complexes reduced TWOS episodes by approximately 40%. The algorithm has potential for a clinically meaningful decrease in inappropriate shocks.

A 25-year-old man with severe nonischemic dilated cardiomyopathy underwent subcutaneous implantable cardioverter defibrillator (S-ICD) implant and subsequently underwent HeartWare ventricular assist device (HVAD) placement. Postoperative interrogation revealed both primary and secondary S-ICD vectors inappropriately regarded sinus rhythm as "noise," and the alternate vector significantly undersensed sinus rhythm. The S-ICD was reinterrogated using high-resolution capture to visually confirm EMI with a dominant frequency in both the primary and secondary vectors of 46.67 Hz that fell within the S-ICD operational range of 9-60 Hz. The 46.67 Hz frequency correlated with the HVAD operational speed of 2,800 RPM. The HVAD pump speed was increased from 2,800 to 3,000 RPM, resulting in a dominant frequency of 50 Hz. The notch filter is nonprogrammable in S-ICDs. However, the built-in filter is 50 Hz for countries in European time zones as opposed to 60 Hz in US time zones due to differences in the anticipated noise from electrical sources within each continent. Thus, the S-ICD time zone was reprogrammed from EST to GMT, which reduced the notch filter from 60  to 50 Hz, resulting in S-ICD successfully eliminating EMI when the patient was in a supine position. The EMI interference was still intermittently present in the upright patient position. This case demonstrates the utility of high-resolution electrogram capture to identify the source and frequency of EMI in S-ICD and offers a potential avenue to troubleshoot dominant frequency oversensing by changing the device time zone.

Introduction Pre‐implant ECG screening is performed to ensure that S‐ICD recipients have at least one suitable sensing vector, yet cardiac over‐sensing remains the commonest cause of inappropriate shock therapy in the S‐ICD population. One explanation would be the presence of dynamic variations in ECG morphology that result in variations in vector eligibility. Methods Adult ICD patients had a 24‐h ambulatory ECG performed using a digital Holter positioned to record all three S‐ICD vectors. Using an S‐ICD simulator, automated screening was then performed at one‐minute intervals. In vectors with a mean vector score > 100 (the accepted value for a passing vector when screened on a single occasion), the percentage of all screening assessments that passed, eligible vector time (EVT), was calculated. EVT was compared statistically to QRS duration, corrected time to peak T (pTc) and mean vector score. Results Ambulatory monitoring was performed in 14 patients (mean age 63.7 ± 5.2 years, 71.4% male) with 42 vectors analysed. In 19 vectors the mean vector score was > 100. Within this “passing” cohort EVT varied between 42.7% and 100%. In 7/19 (37%) the EVT was <75%. A negative correlation was found between QRS duration and EVT (Pearson correlation ‐.60, p = .007). No correlation was found between EVT and mean vector score or pTc. Conclusion Vector eligibility is dynamic. When “passing” vectors are subjected to repeated screening, 37% are found to be ineligible, more than a quarter of the time. Further investigation is required to determine the clinical significance of these findings.

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