An implantable cardioverter-defibrillator (ICD) is a small device that is placed under the skin, generally in the pectoral region. This device continuously monitors the patient’s heart rate and, if necessary, delivers an electric shock to restore the heart’s normal rhythm if an arrhythmia occurs.
There are two different models:
- Transvenous ICD
This is the most common model.
They have three main components:
- a pulse generator;
- electrodes (or leads) that are inserted into the veins and guided through them to the heart;
- a box implanted under the skin, usually below the collarbone.
The ICD’s pulse generator contains a battery and electronic circuits that control the device. The electrodes detect the heart’s electrical activity and transmit this information to the generator. If an abnormality occurs, such as ventricular tachycardia or ventricular fibrillation, the ICD delivers an electrical shock to restore a normal rhythm.
- Subcutaneous ICDs
These more recent devices differ from transvenous ICDs in that they do not have intracardiac leads. They are designed to be implanted under the skin in the armpit, with the main electrode placed along the breastbone, without entering the blood vessels or the heart.
This ICD monitors the heart rate with the subcutaneous electrode. When an arrhythmia is detected, it delivers an electrical shock through the skin and subcutaneous tissue to restore a normal heart rhythm.
- ICDs with cardiac resynchronization therapy
These devices combine the functions of an ICD with those of a cardiac resynchronization device. They are recommended for patients with heart failure and ventricular desynchronization, in which the heart’s ventricles do not contract in a coordinated way.
This ICD is equipped with three leads:
- one in the right atrium;
- one in the right ventricle;
- a third placed in a coronary vein to reach the left ventricle.
It delivers low electrical pulses to synchronize the contractions of both ventricles, improving the heart’s pumping efficiency. In the event of severe ventricular arrhythmia, it can also deliver an electric shock to restore a normal rhythm.
It is particularly beneficial for patients at risk of both ventricular arrhythmias and heart failure. It helps alleviate heart failure symptoms and improves patients’ quality of life.
- Single-chamber ICDs
In a single-chamber ICD, only one lead is implanted in the right ventricle. It is typically recommended for patients who do not require atrial pacing or cardiac resynchronization but are at risk for ventricular arrhythmias. This ICD only monitors the rhythm of the right ventricle. In the event of ventricular arrhythmia, it can deliver an electric shock to restore a normal rhythm. It can also provide pacing support for bradycardia, but only for the right ventricle.
- Dual-chamber ICDs
The dual chamber ICD is designed to monitor and pace both the right atrium and the right ventricle. It is often used for patients who require cardiac pacing to regulate their heart rhythm, in addition to protection against ventricular arrhythmias.
It uses two leads: one in the right atrium, the other in the right ventricle.
This device monitors the rhythm of both chambers. It can deliver electrical pulses to correct arrhythmia and provide cardiac pacing for bradycardia. In the event of ventricular arrhythmia, it can also deliver a shock to restore a normal rhythm.
- Multifunctional ICDs
These ICDs include additional features to meet specific needs.
For example, some models offer heart failure monitoring functions that measure specific parameters to identify early signs of a worsening condition.
Other ICDs feature technology that can reduce “inappropriate” shocks.
These multifunctional ICDs are designed to provide comprehensive management solutions for patients with complex heart conditions. They can, for instance, distinguish between benign arrhythmias and more serious ones.
Reviewed and approved by Lyric Institute’s cardiac pacing team
