ICD therapy in childhood and adolescence
Implantations of permanent internal cardioverter defibrillators (ICD) in children and adolescents continue to be the exception rather than the rule, as the more frequent probe problems and inadequately (incorrectly) delivered shock therapies are attempted to be avoided, particularly in children and adolescents. In most patients, an ICD device is therefore only implanted as a secondary preventive measure, i.e. after surviving a cardiac arrest.
Genetic arrhythmia syndromes, mostly ion channel diseases, represent the largest group of patients in this age group with an indication for ICD therapy.
The two best-known ion channel diseases with cardiac arrhythmias, some of which occur in childhood, are prolonged QT interval syndrome (long QT syndrome) and catecholamine-induced polymorphic ventricular tachycardia (catecholaminergic polymorphic ventricular tachycardia - CPVT). Other genetic diseases of the ion channels or the heart muscle and cardiac connective tissue cells include Brugada syndrome, which usually does not become symptomatic in childhood, and the various cardiomyopathies, such as arrhythmogenic right ventricular cardiomyopathy (ARVC), hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM).
In many of these diseases, either sufficiently protective drug therapy is not available (Brugada syndrome and ARVC), or the risk of a fatal initial manifestation of cardiac arrhythmia is particularly high due to the limited cardiac function in this disease (DCM), so that primary preventive implantation is often recommended.
Children and adolescents, as well as adults with congenital heart defects and the resulting cardiac dysfunction, should also be fitted with an ICD device as a primary preventive measure if there are frequent syncopes (fainting spells) that cannot be explained otherwise, or if ventricular tachycardias can be triggered in an electrophysiological examination. This also applies in particular to patients on the waiting list for transplantation.
ICD therapy in childhood and adolescence
Similar to conventional pacemakers (Fig. 1), various companies offer devices with an integrated pacemaker and ICD function (Fig. 2). In addition to programming the underlying pacemaker setting, which can treat both congenital and medication-induced bradycardic (too slow) cardiac arrhythmias, the possibility of dual-chamber pacing and dual-chamber sensing also provides better discrimination of tachycardic (too fast) atrial and ventricular arrhythmias through the horizontal atrial electrode: only the really critical ventricular tachycardias should be treated by shock delivery!
However, these systems can also be implanted using a ventricular electrode only (single-chamber ICD).
In addition to the stimulation poles at the end of the probe, the electrode suitable for shock delivery also has at least one "shock coil" (defibrillation electrode), which is located in the area of the right ventricle. Many electrodes also have a second defibrillation electrode unit in the area of the superior vena cava. However, as this may not be able to be positioned precisely due to the smaller body size of children, or may be displaced to another area of the vessel independently due to growth, or may also show adhesion tendencies with the superior vena cava wall, so-called "unicoil" electrodes with only one defibrillation electrode are often used in children and adolescents (Fig. 3).
In addition to the classic therapy of shock delivery (defibrillation), most devices also have other "antitachycardic" algorithms in which the increased heart rate is to be "brought down" again by stimulating the heart through the pacemaker electrodes above the patient's own pathological heart rate (antitachycardic pacing = overdrive stimulation). This involves either slowly lowering the stimulation frequency below the tachycardia frequency in a staircase-like manner (ramp) or delivering bursts of rapid stimulation (burst) in order to bring the heart back to its normal frequency.
More recently, however, a subcutaneously implanted defibrillator has become available that does not require any electrodes in the heart. This S-ICD requires only one additional electrode, which is implanted under the skin in the area of the sternum (subcutaneous). This avoids the dreaded probe problems. A disadvantage at present is the somewhat larger size of the unit (Fig. 4); the unit itself is implanted slightly deeper than the other devices, not in the area of the pectoral muscle but under the armpit on the left side. It should be noted, however, that this device cannot be used to stimulate the heart if a pacemaker is required, nor is antitachycardic pacing possible, so this device is not suitable for patients who require stimulation in the atrium or ventricle due to their medication. Translated with www.DeepL.com/Translator (free version)