An implantable cardioverter defibrillator (ICD) is a small electronic device surgically implanted inside the body, most commonly below the left collarbone, that continuously monitors heart rhythm and delivers targeted electrical therapy to correct life-threatening arrhythmias. It is the most effective treatment for preventing sudden cardiac death in people who are at high risk of, or who have survived, ventricular fibrillation or sustained ventricular tachycardia.
The ICD consists of a pulse generator (the device body, roughly the size of a matchbox) and one or more leads (thin insulated wires) that pass through a vein into the heart. The leads sense the heart’s electrical activity continuously. If a life-threatening rhythm is detected, the ICD responds with the appropriate therapy: anti-tachycardia pacing (ATP, a burst of rapid painless pacing pulses that can terminate certain forms of VT without a shock), cardioversion (a low-energy synchronised shock for certain arrhythmias), or defibrillation (a high-energy shock to terminate VF). Modern ICDs can also provide backup pacing if the heart rate falls too low, and in the CRT-D variant, coordinate left and right ventricular contractions in patients with heart failure.
After cardiac arrest caused by VF or VT, ICD implantation is the standard treatment for secondary prevention, assuming a reversible cause has been excluded. ICDs are also implanted for primary prevention in people with conditions carrying a high risk of sudden cardiac arrest, including dilated cardiomyopathy with severely reduced ejection fraction, hypertrophic cardiomyopathy with high-risk features, and inherited electrical conditions such as Long QT Syndrome and Brugada Syndrome.
Most people live normally with an ICD. Important considerations include driving restrictions (which must be notified to the DVLA), the management of electromagnetic interference from medical devices and certain environments, the psychological impact of living with the device and the possibility of shocks, and regular device clinic follow-up, which increasingly includes remote monitoring via a bedside transmitter. A Cardiac Nurse Specialist is the key point of contact for day-to-day questions about living with an ICD.
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