Cardiac Resynchronization Therapy

Cardiac resynchronization relies on electric leads to correct an arrhythmia commonly diagnosed in patients experiencing heart failure.

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The leads electrically stimulate heart muscle to synchronize the contractions of the heart’s two lower chambers, or ventricles. Only when the lower chambers beat in harmony can they contract with enough force to push blood carrying oxygen through the body.

More than 22 million people worldwide suffer from congestive heart failure (CHF), a potentially debilitating disease.

Until recently, lifestyle changes, medication and, sometimes, heart surgery were the only treatment options. Patients with severe symptoms, however, received little, if any, relief from such approaches. To make matters worse, up to 40 percent of patients with CHF also have an arrhythmia that further reduces the heart’s ability to beat properly.

Cardiac resynchronization therapy (CRT) is an innovative new therapy that can relieve CHF symptoms by improving the coordination of the heart’s contractions.CRT builds on the technology used in pacemakers and implantable cardioverter devices. CRT devices also can protect the patient from slow and fast heart rhythms.

The concept behind CRT is quite simple. Resynchronization restores the normal coordinated pumping action of the ventricles by overcoming the delay in electrical conduction caused by bundle branch block. This is accomplished by means of a special type of cardiac device.

These powerful, “built-in” devices have enormous potential to improve the quality of life and probably survival for patients with heart failure.


Risk Factors

The ideal candidate for a CRT device is someone with:

  • Moderate to severe CHF symptoms, despite lifestyle changes and medication
  • A weakened and enlarged heart muscle
  • A significant electrical delay in the lower pumping chambers (bundle branch block)

Some CRT candidates also have a high risk of Sudden Cardiac Death. For these patients, a special CRT device can stop potentially life-threatening rapid heartbeats by delivering an electrical shock known as defibrillation. This device incorporates a standard implantable cardioverter defibrillator (ICD) with a CRT pacemaker creating a “CRTD” device. (The “D” refers to defibrillation.)



Pacemakers are typically used to prevent symptoms due to an excessively slow heartbeat. The pacemaker continuously monitors the heartbeat and, when necessary, delivers tiny, imperceptible electrical signals to stimulate the heartbeat. Most pacemakers have two electrode wires, or cardiac leads, one in the right atrium and one in the right ventricle. This ensures the pacemaker will maintain the normal coordinated pumping relationship between the upper and lower chambers of the heart.

The wires that carry the electrical signals connect to an electrical pulse generator placed under the skin in the upper chest. In addition to the two cardiac leads (right atrium and right ventricle) used by a common pacemaker, the CRT device has a third cardiac lead that is positioned in a vein on the surface of the left ventricle.

This allows the CRT device to simultaneously stimulate the left and right ventricles and restore a coordinated, or “synchronous,” squeezing pattern. This is sometimes referred to as “bi-ventricular pacing” because both ventricles are electrically stimulated (paced) at the same time. This reduces the electrical delay and results in a more coordinated and effective heart beat.



The response to CRT can vary greatly among patients. Clinical studies involving more than 2000 patients worldwide demonstrate modest improvements in exercise tolerance, CHF severity, and quality of life in most patients. Improvement may happen quickly, but sometimes it can take several months.


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