Predictors of Subcutaneous Implantable Cardioverter-Defibrillator Shocks and Prognostic Impact in Patients With Structural Heart Disease

Exploiting SMART pass filter deactivation detection to minimize inappropriate subcutaneous implantable cardioverter defibrillator therapies: a real-world single-centre experience and management guide

AIMS

The SMART Pass™ (SP) algorithm is a high-pass filter that aims to reduce inappropriate therapy (IT) in subcutaneous internal cardiac defibrillator (S-ICD), but SP can deactivate due to low amplitude sensed R waves or asystole. The association between IT and SP deactivation and management strategies were evaluated, hypothesizing SP deactivation increases the risk of IT and device re-programming, or lead/generator re-positioning could reduce this risk.

METHODS AND RESULTS

Retrospective single-centre audit of Emblem™ S-ICD devices implanted 2016 to 2020 utilizing health records and remote monitoring data. Cox regression models evaluated associations between SP deactivation and IT. A total of 348 patients (27 ± 16.6 months follow-up) were studied: 73% primary prevention. Thirty-eight patients (11.8%) received 83 shocks with 27 patients (7.8%) receiving a total of 44 IT. Causes of IT were oversensing (98%) and aberrantly conducted atrial fibrillation (2%). SP deactivation occurred in 32 of 348 patients (9%) and was significantly associated with increased risk of IT (hazard ratio 5.36, 95% CI 2.37-12.13). SP deactivation was due to low amplitude R waves (94%), associated with a higher defibrillation threshold at implant and presence of arrhythmogenic right ventricular cardiomyopathy. No further IT occurred 16 ± 15.5 months after corrective interventions, with changing the sensing vector being successful in 59% of cases.

CONCLUSION

To reduce the risk of IT, the cause of the SP deactivation should be investigated, and appropriate reprogramming, device, or lead modifications made. Utilizing the alert for SP deactivation and electrograms could pro-actively prevent IT.

Pre-implant predictors of inappropriate shocks with the third-generation subcutaneous implantable cardioverter defibrillator

AIMS

Despite recent improvements, inappropriate shocks emitted by implanted subcutaneous implantable cardioverter defibrillators (S-ICDs) remain a challenge in 'real-life' practice. We aimed to study the pre-implant factors associated with inappropriate shocks for the latest generation of S-ICDs.

METHODS AND RESULTS

Three-hundred patients implanted with the third-generation S-ICD system for primary or secondary prevention between January 2017 and March 2020 were included in this multicentre retrospective observational study. A follow-up of at least 6 months and pre-implant screening procedure data were mandatory for inclusion. During a mean follow-up of 22.8 (±11.4) months, 37 patients (12.3%) received appropriate S-ICD shock therapy, whereas 26 patients (8.7%) experienced inappropriate shocks (incidence 4.9 per 100 patient years). The total number of inappropriate shock episodes was 48, with nine patients experiencing multiple episodes. The causes of inappropriate shocks included supraventricular arrhythmias (34.6%) and cardiac (30.7%) or extra-cardiac noise (38.4%) oversensing. Using multivariate analysis, we explored the independent factors associated with inappropriate shocks. These were the availability of less than three sensing vectors during pre-implant screening [hazard ratio (HR), 0.33; 95% confidence interval (CI), 0.11-0.93; P = 0.035], low QRS/T wave ratio in Lead I (for a threshold <3; HR, 4.79; 95% CI, 2.00-11.49; P < 0.001), history of supraventricular tachycardia (HR, 8.67; 95% CI, 2.80-26.7; P < 0.001), and being overweight (body mass index > 25; HR, 2.66; 95% CI, 1.10-6.45; P = 0.03).

CONCLUSION

Automatic pre-implant screening data are a useful quantitative predictor of inappropriate shocks. Electrocardiogram features should be taken into consideration along with other clinical factors to identify patients at high risk of inappropriate shocks.