Real-World Subcutaneous ICD Use: A Hopeful Treatment Option?

Bruno Valdigem, MD, PhD

August 18, 2023

The Subcutaneous Implantable Cardioverter‑Defibrillator System Post Approval Study (S‑ICD PAS), which observed patients with subcutaneous implantable cardioverter-defibrillators (S‑ICDs) for 5 years, was recently published in the Journal of the American College of Cardiology.  The results are promising. But why has this treatment gotten such little traction in Brazil?

The transvenous implantable cardioverter-defibrillator (TV-ICD) is similar to the permanent pacemaker. It is often implanted through the subclavian or axillary vein (or dissection of the cephalic vein), with the leads positioned in the endocardium of the right ventricle through the vena cava. The generator is usually positioned in the left infraclavicular area.

The S‑ICD uses another strategy, however. The generator is positioned in the left flank under the latissimus dorsi or serratus muscles. The lead travels through the subcutaneous tissue to the sternum and rises parallel to this bone, usually along the left side. The idea is that the circuit transmitting the defibrillation current is composed of a lead located next to the sternum (like a defibrillation pad), and the generator stays adjacent to the free wall of the left ventricle (second defibrillation pad).

The greatest benefit of the S‑ICD is that it does not occupy the patient's vascular system. Infective endocarditis is a concern associated with systems inserted in the intravascular space. Positioning the leads in the right ventricle can also injure the tricuspid valve. In situations of infection, extracting the device is much more complicated. Another complication of implanting transvenous cardiac devices is the perforation of the right ventricular and atrial walls when the device is positioned. As the subcutaneous device is located far from the heart and outside the rib cage, the risk of endocarditis and injury to the heart is almost zero.

Since the S‑ICD was released in Brazil in 2016, a little more than 300 devices of this type have been implanted. Research, such as the ATLAS and PRAETORIAN studies, suggests the noninferiority of the S‑ICD, compared with the TV‑ICD. However, a critique of these studies is that the patient populations evaluated were selected based on certain criteria, and therefore the groups were significantly different from those found in the usual field of candidates for ICD implantation (ie, older patients with more comorbidities and cardiac conduction disease).

The S‑ICD PAS is a real-world, multicenter registry of US healthcare centers that was designed to assess long-term S‑ICD safety and efficacy in a diverse group of patients and implantation centers.

A total of 1643 patients with standard S‑ICD indications were enrolled in 86 US healthcare centers and observed for up to 5 years (median follow‑up of 4.2 years). Participants were implanted by operators with experience in a real‑world setting. The mean age of the patients was 53 years, 32% were women, and 29% were Black. According to the article, ischemic heart disease was present in 41% of patients, 74% had clinical heart failure, and the left ventricular ejection fraction was 32% ±15%.

The registry indicates little need for cardiac stimulation throughout the 5 years (1.6%), which, in some ways, assures us that, with adequate patient selection, there may be little need for antibradycardia therapy.

The fact that the S-ICD does not cause usual stimulation also reduces the need for antitachycardia therapy, as it is impossible to treat ventricular tachycardia with rapid stimulation (also known as overdrive or burst pacing).

The efficacy endpoint demonstrates that the S‑ICD functions in a typical ICD cohort. First shock efficacy for converting spontaneous arrhythmias was 92.2%, with an overall shock efficacy of 98.4%. The inappropriate shock rate was 15.8% at 5 years. Data on the TV‑ICD indicate a similar inappropriate shock rate: approximately 17% at 5 years (as in the SCD‑HeFT study). The most common cause of inappropriate shock in patients with S‑ICD was T‑wave oversensing or aberrant conduction.

We still need further information on the long‑term use of S‑ICD, but, for now, the new antitachycardia therapy seems a promising option. Moreover, both in Brazil and worldwide, strategies combining endocardial stimulation with fewer leads or smaller devices and S‑ICD antitachycardia support are being tested. For example, the implantation of permanent pacemakers in patients who had previously had an S‑ICD, or even the implantation of leadless pacemakers, may be exciting strategies for preserving the patency of vascular access and reducing the incidence of endocarditis.

This article was translated from Medscape's Portuguese edition.


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