Implantable cardioverter defibrillator

Implantable Cardioverter Defibrillator or ICD is a battery powered device used to correct abnormal fast heart rhythm. An ICD generator with battery and circuitry is usually implanted under the collarbone and is connected to the heart with wires.

ICD can pace the heart similarly to a pacemaker when the heart rate drop below a certain level but ICD can in addition also detect abnormally fast heart beat and correct it by sending a series of quick impulses to the heart (antitachycardic pacing) or by a small (cardioversion) or bigger (defibrillation) controlled electric shock.

ICD is implanted under local or general anesthesia in the same way as pacemaker implant.

ICD indications

The basic indications for ICD are as follows:

  • Primary prevention – severe heart failure due to previous heart attack or dilated cardiomyopathy with high risk of cardiac arrest.
  • Secondary prevention - previous successfully resuscitated cardiac arrest with a high risk of recurrence.

ICD vs pacemaker

As stated above, ICD has all the functionality of a normal pacemaker and can correct a slow heart beat by pacing. On top of that, ICD also detects abnormally fast heart rhythms that can lead to cardiac arrest and terminates them by fast pacing or electric shock. ICD box is somewhat bulkier but the implant technique is essentially identical to a normal pacemaker procedure.


ICD implant is a safe procedure but as every surgical procedure it is not entirely risk free. The complications involve bleeding, infection, pneumothorax (collapsed lung), tamponade (bleeding outside the heart), lead dislodgement and wound discomfort. In long term, an ICD may still be infected, the leads may get damaged and the device can give inappropriate and painful shocks. However, in most patients the implant is a straightforward and uncomplicated procedure and the ICD provides a valuable protection.