An implantable cardioverter-defibrillator (ICD) is a small electronic device placed inside the body to help control dangerous heart rhythms.

What it does

The heart normally beats in a steady rhythm, but some people develop life-threatening irregular rhythms (called arrhythmias), especially:

• Ventricular tachycardia
• Ventricular fibrillation

An ICD continuously monitors your heartbeat. If it detects a dangerous rhythm, it can:

• Deliver rapid pacing impulses to correct it, or
• Send a stronger shock to reset the heart back to normal rhythm

How it’s implanted

• Transvenous ICD
  • This is the most conventional type of ICD
  • The device is usually placed under the skin near the collarbone
  • Thin wires (leads) are threaded through veins into the heart
  • The procedure is typically done under local anaesthesia with sedation

• Subcutaneous ICD
  • A different type of implantable defibrillator is a ‘subcutaneous’ defibrillator. 
  • This doesn’t have any leads into the heart, but has a lead running under the skin of the left side of the chest and up alongside the breast bone (sternum). 
  • This is connected to the defibrillator which is positioned under the skin on the left side of the chest, under the armpit.
  • Only a small proportion of patients will benefit from a subcutaneous rather than transvenous ICD currently – your doctor will discuss the merits of each with you

Who needs one

Doctors may recommend an ICD for people who:

• Have survived a cardiac arrest
• Have certain heart conditions that increase the risk of sudden death
• Have severe heart failure or inherited rhythm disorders

What it feels like

• Most of the time, you won’t notice it working
• If it delivers a shock, it can feel like a sudden jolt or thump in the chest

Why it matters

ICDs are one of the most effective ways to prevent death from sudden cardiac arrest caused by dangerous arrhythmias.