ReviewSubcutaneous implantable cardioverter defibrillators in children, young adults and patients with congenital heart disease
Introduction
The number of implantable cardioverter defibrillators (ICD) implanted in children, adolescents and young adults is steadily increasing [1], [2], [3]. While the very first implantations were surgical, the progression toward transvenous devices has allowed to greatly reducing the morbidity associated with this type of intervention [4], [5]. Industrial research has enabled many technological developments with a gradual shift toward less invasive techniques, as well as a reduction in the size of the devices in the wake of global nanotechnology research. However, there are currently no devices specifically dedicated to the pediatric population, resulting in a rather startling situation in clinical practice: despite dramatic differences in terms of size and weight, the identical device (housing + lead) is implanted whether it be a child weighing less than 10 kg, a professional basketball player taller than 2 m or an overweight adult weighing more than 100 k. Although over one million adult patients worldwide have benefited from the implantation of a transvenous ICD, certain complications remain highly problematic in young patients who will face decades of monitoring and numerous changes in device housings and/or leads. The implantation procedure of an endocardial lead is fraught with an inherent morbidity (risk of pneumothorax, hemothorax, perforation, cardiac tamponade and displacement). Long-term complications mainly include device infection, with the endocardial lead favoring the occurrence of endocarditis, as well as lead dysfunctions, which are more common in younger patients because of an elevated physical activity and a greater cumulated physical stress [5], [6], [7], [8]. For these two types of complications, a device extraction procedure is most often proposed with its own set of complications and non-zero mortality [9], [10].
This alarming fact has led to the recent development of devices with subcutaneous leads (S-ICD System, Cameron Health/Boston Scientific) which appear particularly suitable for the young patient population or certain patients with complex congenital heart disease with no transvenous access to the heart or presenting a residual shunt. While the first studies have found satisfactory feasibility and safety thus initially positioning this approach as a very promising alternative route, there are also a number of limitations as well as a non-negligible risk of complications [11], [12], [13], [14].
In the present review, we aim to revisit the literature on subcutaneous ICDs, including the validation steps while emphasizing on the subgroup comprised of children, young adults and patients with congenital heart disease. We will describe the respective advantages and disadvantages of this approach in a first instance and attempt to define the preferential indications and future perspectives.
Section snippets
Basis of operation of a subcutaneous ICD
The subcutaneous defibrillation system includes: 1) a dedicated programmer, 2) a pulse generator positioned in a subcutaneous axillary pocket at the level of the fifth rib and 3) a single lead tunneling under the skin from the pulse generator toward the xiphoid process then, after a 90-degree turn, along the left sternal border toward the sternal manubrium; it is comprised of two sensing electrodes, the proximal sensing electrode positioned adjacent to the xiphoid and the distal sensing
Validation in the general population
Contrary to the validation of the transvenous ICD which was based on prospective, randomized studies involving very large population samples, the validation data of the subcutaneous ICD are modest, with limited follow-up times based primarily on isolated clinical cases, single-center studies, registries and a few comparison studies with the transvenous ICD [11], [12], [13], [14], [15]. The basic principle being that the treatment concept is the same and therefore the gain in terms of mortality
Absence of endocardial devices
The main advantage of the subcutaneous ICD lies in the fact that it allows eliminating all of the complications related to the presence of one or more endocardial leads, since the entire device is implanted in an extrathoracic position. The different studies have indeed failed, as expected, to find any intra- or peri-operative complications such as hemothorax, pneumothorax, hemopericardium, tamponade, arterial puncture or longer-term complications such as vein occlusion, endocarditis, cardiac
A certain number of patients are not able to benefit from this system
The primary limitation of this surgical route is that a certain number of patients cannot benefit from this approach, including: a negative screening test, young child, patient requiring anti-bradycardia or anti-tachycardia pacing.
In order to limit the risk of occurrence of inappropriate therapies due to T-wave oversensing, a screening is performed prior to implantation to confirm the existence of at least one vector allowing to obtain an acceptable R wave/T wave amplitude ratio, both at rest
A still-limited level of evidence
The subcutaneous ICD represents a significant innovation enabling to eliminate the complications observed in patients with an endocardial lead. This technique, as explained above, offers a number of theoretical advantages, but also a certain number of disadvantages. As with any innovation, the level of evidence as well as long-term data is much less abundant than for the so-called reference technique, i.e. the transvenous ICD [32], [33], [34]. It is more than likely that no large-scale studies
Conflict of interest
The authors report no relationships that could be construed as a conflict of interest.
References (36)
- et al.
Results of a multicenter retrospective implantable cardioverter–defibrillator registry of pediatric and congenital heart disease patients
J. Am. Coll. Cardiol.
(2008) Treatment of malignant ventricular tachyarrhythmias with the automatic implantable defibrillator
Int. J. Cardiol.
(1983)- et al.
System survival of nontransvenous implantable cardioverter–defibrillators compared to transvenous implantable cardioverterdefibrillators in pediatric and congenital heart disease patients
Heart Rhythm.
(2010) - et al.
Implantation-related complications of implantable cardioverter–defibrillators and cardiac resynchronization therapy devices: a systematic review of randomized clinical trials
J. Am. Coll. Cardiol.
(2011) A European perspective on lead extraction: part I
Heart Rhythm.
(2008)- et al.
The entirely subcutaneous implantable cardioverter–defibrillator: initial clinical experience in a large Dutch cohort
J. Am. Coll. Cardiol.
(2012) - et al.
Implantation and follow-up of totally subcutaneous versus conventional implantable cardioverter–defibrillators: a multicenter case–control study
Heart Rhythm.
(2013) - et al.
Sensitivity and specificity of the subcutaneous implantable cardioverter defibrillator pre-implant screening tool
Int. J. Cardiol.
(2015) - et al.
Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE Study and EFFORTLESS Registry
J. Am. Coll. Cardiol.
(2015) - et al.
Do clinically relevant transthoracic defibrillation energies cause myocardial damage and dysfunction?
Resuscitation
(2003)