The Subcutaneous ICD: A Review of the UNTOUCHED and PRAETORIAN Trials

Subcutaneous Implantable Cardioverter-Defibrillator Lead Dislodgement Masquerading as Left Shoulder Pain

Implantable cardioverter-defibrillators (ICDs) have demonstrated efficacy in the prevention of sudden cardiac death secondary to cardiac arrhythmias in eligible patients. Complications with the subcutaneous ICD (S-ICD) are rarer than with the transvenous ICD but do still exist. Our patient presented four weeks after the insertion of S-ICD with complaints of left shoulder pain radiating to the chest wall and swelling over the S-ICD site. He was initially treated for rotator cuff injury and subacromial impingement syndrome but upon obtaining chest radiography was found to have a lead displacement traversing the splenic flexure of the colon. The patient was managed by a treatment team involving cardiology, surgery, and infectious disease and underwent S-ICD removal, exploratory laparotomy with splenic flexure mobilization, and completion of a four-week antibiotic course ultimately leading to reimplantation of S-ICD.

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.

Subcutaneous implantable cardioverter-defibrillator implantation position predicts successful defibrillation in obese and non-obese patients

BACKGROUND

Subcutaneous implantable cardioverter-defibrillators (S-ICD) are an alternative to transvenous ICDs for patients without a need for cardiac pacing. Obese patients have been proposed to be at higher risk for conversion failure with S-ICDs due to subcutaneous fat underneath the device. Optimal device positioning may promote equivalent outcomes between obese and non-obese patients by minimizing the effects of excess adipose tissue.

METHODS

A retrospective analysis of patients undergoing defibrillation testing at the time of S-ICD implantation was performed. The primary endpoint was the rate of successful conversion of ventricular fibrillation (VF) at the time of implant. The secondary endpoint was shock impedance.

RESULTS

A total of 184 patients were included in the study. The rate of successful conversion of VF was 90.3% for obese patients (n = 72) and 96.4% for non-obese patients (n = 112) (p = 0.086). Compared to non-obese patients, obese patients had a higher mean PRAETORIAN score (78.5 ± 58.1 vs. 48.8 ± 35.5, p < 0.001) and higher measured mean impedance (82.0 ohms ± 26.5 vs. 69.8 ohms ± 19.3, p < 0.001). Patients with a PRAETORIAN score < 90 all had successful defibrillation testing regardless of BMI.

CONCLUSIONS

In this study, a PRAETORIAN score < 90 was associated with a 100% success rate of defibrillation testing following S-ICD implantation regardless of patient body mass index (BMI). Thus, the impact of obesity on impedance and the risk of failed shocks may be minimized with close attention to implantation technique to achieve a low PRAETORIAN score.

Subcutaneous ICD for more and transvenous ICD for few?!

Implantable cardioverter defibrillators (ICDs) have been shown to reduce the risk of sudden cardiac death in primary or secondary prevention with thousands of ICDs implanted every year worldwide. Whilst ICD are more commonly implanted transvenously (TV), this approach carries high risk of peri- and post-procedural complications. Subcutaneous ICD (S-ICD) have been introduced to overcome the intravascular complications of TV system by placing all metalware outside the chest cavity for those with an indication for a defibrillator and no pacing requirements. In conclusion, a review of the current guidelines recommendations regarding S-ICD may be needed considering the emerging evidence which shows high efficacy and safety with contemporary devices and programming algorithms. A stronger recommendation may be developed for selective patients who have an indication for single-chamber ICD in the absence of negative screening, recurrent monomorphic ventricular tachycardia, cardiac resynchronization therapy, or pacemaker indication. These criteria encapsulate a large proportion (around 70%!) of all ICD eligible patients.