Introduction: Concern persists regarding inappropriate therapy (IT) burden from the subcutaneous implantable cardioverter defibrillator (S-ICD). The SMART Passä (SP) algorithm is a bandpass filter that aims to reduce IT. The algorithm’s ability to deactivate itself in community has implications for IT that require evaluation.
Objective: To investigate the effect of SP deactivation, its causes and how to manage this scenario, hypothesising that SP deactivation would increase the risk of IT and re-programming, or that lead/generator repositioning could reduce the risk.
Method: This study was a retrospective audit of Emblemä S-ICD devices (A209 and A219) implanted from 2016 to 2020 using data from health records and remote monitoring. Cox regression models were used to study the association between SP deactivation and IT.
Results: A total of 348 patients with 27 ± 16.6 months’ follow-up were studied. Overall, 73% of patients were implanted for primary prevention. A total of 38 patients (11.8%) patients received 83 shocks with 7.8% of patients receiving IT, totalling 44 IT, 43 of which were due to oversensing and 1 due to aberrantly conducted atrial fibrillation. SP deactivation was significantly associated with increased risk of IT (hazard ratio 7.76, 95% CI 3.30–18.28). Deactivation was commonly due to low amplitude R-waves (94%). Effective prevention of further IT included changing the programmed sensing vector, lead repositioning, and temporary deactivation for patients with air in the sensing circuit.
Conclusion: SP deactivation is a significant predictor of inappropriate shocks. If the SP filter is deactivated this is likely to suggest low amplitude R waves, either periodically or continuously. To reduce the risk of IT, the cause of the automatic SP deactivation should be investigated, and sensing vector changes should be strongly considered. If the SP algorithm is unable to sustain activation, lead repositioning should be considered, akin to a transvenous right ventricular ICD lead for poor sensing. By enabling an audible or electronic communication alert for SP deactivation, the S-ICD IT rate could be significantly reduced, warranting investigation in prospective patients.
