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

The ICD is an important part of the treatment and prevention of sudden cardiac death in many high-risk populations. Traditional transvenous ICDs (TV-ICDs) are associated with certain short- and long- term risks. The subcutaneous ICD (S-ICD) was developed in order to avoid these risks and complications. However, this system is associated with its own set of limitations and complications. First, patient selection is important, as S-ICDs do not provide pacing therapy currently. Second, pre-procedural screening is important to minimise T wave and myopotential oversensing. Finally, until recently, the S-ICD was primarily used in younger patients with fewer co-morbidities and less structural heart disease, limiting the general applicability of the device. S-ICDs achieve excellent rates of arrhythmia conversion and have demonstrated noninferiority to TV-ICDs in terms of complication rates in real-world studies. The objective of this review is to discuss the latest literature, including the UNTOUCHED and PRAETORIAN trials, and to address the risk of inappropriate shocks.

Abstract 15748: Failure of Subcutaneous Implantable Cardioverter Defibrillator in a Patient With Arrhythmogenic Right Ventricular Cardiomyopathy

Introduction: The subcutaneous ICD is an attractive option in ARVC patients as they rarely require pacing, it preserves vascular access, and it avoids the long-term morbidity related to intravascular lead placement. However, the limitations of the S ICD have not been fully demarcated by clinical trials. Case: After her father presented with a cardiac arrest, a 16-year-old female was diagnosed with ARVC on MRI after initially presenting with palpitations. This was corroborated via genetic testing, and an S ICD was placed after she passed pre-implant screening. Initially she did well, but she suffered inappropriate shocks approximately seven months after implant, in the setting of “hugging her boyfriend”. Interrogation revealed apparent noise, which was felt to be most likely due to lead fracture or possibly generator malfunction. At reoperation, first her lead was replaced, but continued noise was demonstrated intra-operatively, and thus her generator was also replaced. However, she was found again to have noise in each vector causing recurrent inappropriate shocks. Further testing ultimately determined that the noise was due to myopotentials, which were present in all vectors and unable to be programmed around. Ultimately, the S ICD was removed and replaced with a transvenous device. Discussion: While the S ICD is an attractive option in ARVC patients, the limitations of the technology must be acknowledged. The far-field nature of the sensing algorithm in the S ICD leads to a risk of myopotential oversensing. If this occurs, sometimes the system cannot be salvaged and the patient must be converted to a transvenous system. Recognizing this at the initial presentation with inappropriate shocks can avoid unsuccessful attempts at S ICD system modification and morbidity from future inappropriate shock events.

Pitfalls of the S-ICD therapy: experiences from a large tertiary centre

Aim The subcutaneous ICD (S-ICD) has evolved to a potential first option for many patients who have to be protected from sudden cardiac death. Many trials have underlined a similar performance regarding its effectiveness in relation to transvenous ICDs and have shown the expected benefits concerning infective endocarditis and lead failure. However, there have also been problems due to the peculiarities of the device, such as oversensing and myopotentials. In this study, we present patients from a large tertiary centre suffering from complications with an S-ICD and propose possible solutions. Methods and results All S-ICD patients who experienced complications related to the device (n = 40) of our large-scale single-centre S-ICD registry (n = 351 patients) were included in this study. Baseline characteristics, complications occurring and solutions to these problems were documented over a mean follow-up of 50 months. In most cases (n = 23), patients suffered from oversensing (18 cases with T wave or P wave oversensing, 5 due to myopotentials). Re-programming successfully prevented further oversensing episode in 13/23 patients. In 9 patients, generator or lead-related complications, mostly due to infectious reasons (5/9), occurred. Further problems consisted of ineffective shocks in one patient and need for antibradycardia stimulation in 2 patients and indication for CRT in 2 other patients. In total, the S-ICD had to be extracted in 10 patients. 7 of them received a tv-ICD subsequently, 3 patients refused re-implantation of any ICD. One other patient kept the ICD but had antitachycardic therapy deactivated due to inappropriate shocks for myopotential oversensing. Conclusion The S-ICD is a valuable option for many patients for the prevention of sudden cardiac death. Nonetheless, certain problems are immanent to the S-ICD (limited re-programming options, size of the generator) and should be addressed in future generations of the S-ICD. Graphic abstract