Implantable cardioverter defibrillators (ICDs)
Implantable cardioverter-defibrillators, called ICDs for short, are tiny devices that continuously monitor the heart's rhythm and, if life-threatening ventricular tachycardia or ventricular fibrillation occurs, they restore the heart's natural rhythm with a rapid stimulation or discharge and can save lives. They are most commonly implanted in the subcutaneous tissue on the left side of the chest in the area below the collarbone. At least one electrode leading to the heart is attached, which the heart device monitors and applies therapy as needed.
Schematic representation of a single-cavity implantable cardioverter-defibrillator (ICD)
ICDs are implanted in patients at increased risk of life-threatening heart rhythm disorders (arrhythmias) such as ventricular tachycardia or ventricles fibrillation. Both arrhythmias can lead to sudden death of the patient. Patients at increased risk of these arrhythmias include, in particular, patients with reduced left ventricular function who have a left ventricular ejection fraction less than or equal to 35%. In addition, these are patients who have already experienced these life-threatening arrhythmias. The exception is patients who have had these arrhythmias during an acute myocardial infarction, if the infarction was well and timely treated and the left ventricular ejection fraction is greater than 35%, then an ICD is not recommended. In addition, your doctor may recommend ICD implantation for certain congenital conditions such as hypertrophic cardiomyopathy or arrhythmogenic cardiomyopathy, but only if there is an increased risk.
ECG curve of ventricles fibrillation, 12-lead recording - without defibrillation this arrhythmia quickly leads to death of the patient
The ICD is implanted under local anaesthesia through the apex of the site where the device will be placed, most commonly on the left side of the chest up into the area below the collarbone. In this area, the surgeon will make a short incision, about 4 cm long, in the subcutaneous tissue to create a site for the device and locate the vein running in this area either by puncture or preparation. Under X-ray control, 1-3 electrodes are inserted through the vein into the heart one at a time, depending on the type of device. A defibrillation electrode, which is slightly stronger than the others and has the ability to apply an electrical discharge in addition to stimulating the heart, must always be present - this electrode is inserted into the right ventricle. There may also be an atrial electrode, which is inserted into the right atrium, or a left ventricular electrode, which is inserted through the cardiac veins into the lateral wall of the left ventricle. Left ventricular electrodes are implanted for reasons of cardiac resynchronization and are only necessary in a minority of patients. The electrodes are attached to the device and the device is placed in a space in the subcutaneous tissue, also called the pocket. The wound is then stitched together. The procedure takes between 20 and 60 minutes, depending on the type.
Chest X-ray of a patient with a single-cavity ICD (only one electrode present, in the right ventricle)
After implantation, the patient usually stays in the hospital until the next day. After 10 days, the skin suture is pulled out and the device is checked at the implant centre. The patient is further monitored at approximately 6-12 monthly intervals. If the patient feels a discharge from the device or temporarily loses consciousness, it is necessary to come to one of the cardiac centres for a check-up within a few days. If the discharges or loss of consciousness are repeated in a short time, the emergency medical service should be called. The battery in the device allows the device to function for about 8-14 years, after the battery is exhausted the whole device must be replaced with a new one with a charged battery at short power, again under local anaesthesia. The electrodes are left original.
ICD device with defibrillation electrode, on the tip of the electrode there is a fixation spiral that holds the electrode in the heart
Life with the implanted device is without major limitations. However, strong electromagnetic fields can affect the function of the device. The use of normal appliances and passing through detection frames in shops is completely risk-free. However, complications may arise during an MRI scan, so the device must be specially adjusted before such an examination, otherwise the examination may not be performed.
All currently manufactured ICDs allow MRI scans to be performed after special setup.
Short-term complications of the procedure include bleeding into the subcutaneous pocket around the device, which usually resolves on its own and does not require surgery. In addition, the procedure may damage the lung during insertion of the electrode, this usually requires insertion of a drain to the lung and a prolonged hospital stay of 2-3 days before the lung heals and the drain can be removed. Furthermore, the electrode may become loose and dislodged in the heart and need to be reinserted back to the appropriate location with the next procedure.
Any foreign material in the body is prone to infectious complications, and so is an implanted ICD. The risk of infection increases with the number of device changes and also in otherwise debilitated patients, especially diabetics or patients with kidney failure. In case of infection, the entire system including the electrodes must be removed and a new one implanted after healing. Another complication that can occur is so-called inadequate discharge. This is a discharge of the device even though the patient has not had a severe ventricular arrhythmia. The discharge therefore occurs while the patient is fully conscious and is very painful. In recent years, the programming of the devices has been stabilised so that this complication rarely occurs.
A special type of ICD is the so-called subcutaneous ICD, or S-ICD. Here, the defibrillation electrode is not placed in the heart, but only in the subcutaneous tissue of the chest. The disadvantages are the slightly larger size of the device, lower durability and the inability to stimulate the heart. The big advantage is less invasiveness, where no foreign material is introduced into the heart and therefore the subcutaneous system is safer to remove in case of infection.
Subcutaneous ICD - schematic representation. The electrode is placed subcutaneously and does not interfere with the heart.
