Cardiac resynchronization An ICD is a tiny, battery-operated device for monitoring the rhythm of your heart and detecting irregular heartbeats. It's attached to wires (called leads) which are introduced into the heart through a vein (transvenous). ICDs are very useful in preventing sudden death in patients with known, sustained ventricular tachycardia or fibrillation. 

An ICD is made of the following parts: 

  • The pulse generator is the size of a large pocket watch. It contains a battery and electrical circuits that read the electrical activity of your heart.
  • The electrodes are wires, called leads, which reach your heart through veins and connect your heart to the rest of the device. Your ICD may have 1 to 3 electrodes.
  • Most ICDs have a built-in pacemaker. Your heart may need pacing if it is beating too slowly or too fast, or if you have had a shock from the ICD.
  • There is a special kind of ICD called a subcutaneous ICD. This device has a lead that is placed in the tissue to the left of the breastbone rather than in the heart. This type of ICD cannot also be a pacemaker.