Implantable Cardioverter Defibrillator (ICD) Therapy


Definite high risk

Individuals considered at definite high risk for sudden cardiac arrest (SCA) who should be evaluated by an electrophysiologist (EP) to determine if implantable cardioverter defibrillator (ICD) therapy is warranted include:

  • SCA survivors
  • People who have sustained ventricular tachycardia (VT), a condition in which the heartbeat suddenly speeds up to dangerous levels
  • People who have a familial or genetic condition that puts them at high risk for sustained VT, such as long QT syndrome or hypertrophic cardiomyopathy.

Possible high risk

Individuals who may be at possible high risk for SCA who should be evaluated by a cardiologist to ascertain the need for further evaluation by an EP to determine if ICD therapy is warranted include:

  • People who have survived a heart attack (myocardial infarction) and who have impaired pumping function
  • People with congestive heart failure (CHF), due to either coronary artery disease or cardiomyopathy
  • People who have experienced palpitations, fainting spells, frequent episodes of dizziness, or known episodes of cardiac arrhythmia (abnormal heartbeat)
  • People with an immediate family member (blood relative) who has experienced SCA.

The Device and How it Works

An implantable cardioverter defibrillator (ICD) is a small, computerized device that is implanted in the upper chest of patients who are at risk for sudden cardiac arrest (SCA). Most ICDs can fit easily in the palm of the hand. The ICD detects abnormal heart rhythms, delivers electrical energy to the heart muscle, and restores a normal heartbeat.

While pacemakers are designed to speed up a slow heart rate, ICDs are designed to slow down a fast heart beat. Some ICDs also have built-in pacemakers and can address both problems. The ICD has two parts: the lead(s), which monitor the heart rhythm and deliver energy, and the generator which houses a battery and small computer. Energy is stored in the battery until it is needed. When it is not needed, the ICD simply monitors the heart rhythm.

ICDs are programmed to address the specific needs of each patient. They may be programmed to address or more of the following problems to restore a normal heartbeat:

  • Anti-tachycardia pacing (ATP): Delivery of small electrical impulses for when the heart is beating too fast
  • Cardioversion: Delivery of a low energy shock
  • Defibrillation: Delivery of a high energy shock for when the heart is beating dangerously fast
  • Bradycardia pacing: Delivery of small electrical impulses for when the heart is beating too slowly.