Doctor's Perspective: ICDs Save Lives

March 19 -- It's tragic. A friend or loved one dies suddenly, unexpectedly. We might hear that he or she died of a "massive heart attack." But most commonly, this is not the case.

The common cause of sudden cardiac death, or SCD, is an abnormal heart rhythm called ventricular tachycardia or ventricular fibrillation. This rapid rhythm originates from areas of scarring in the lower chamber of the heart.

During an attack, the heart is unable to pump efficiently. The blood pressure falls. If a normal rhythm is not restored within four to six minutes, the patient may die.

Prompt initiation of CPR can save lives but, sadly, in most communities, only one in 10 victims of SCD ultimately survives.

A high-tech device called an implantable cardioverter-defibrillator, or ICD, has been proven to save lives in selected groups of patients.

This small, battery-powered device is implanted under the skin and connects to a wire threaded through the veins down into the heart. It waits silently, watching the heart rhythm every moment of every day.

If SCD strikes, the device leaps into action, delivering a lifesaving electrical shock directly to the heart. It restores a normal heart rhythm and saves the patient's life.

Evidence of Benefit

Studies have shown the benefit of ICD insertion in high risk patients. In particular, patients who have survived a cardiac arrest or have had short or long bursts of rapid ventricular tachycardia have an improved outcome if ICDs are implanted.

But these patients only account for a small percentage of the estimated 400,000 sudden deaths each year. There must be a better way to identify patients before their cardiac arrest so that this outcome can be avoided.

Investigators of the Multicenter Automatic Defibrillator Implantation Trial, or MADIT, considered that testing the amount of blood that the heart pumps, also known as the ejection fraction, could determine a future SCD.

A normal heart pumps out about 60 percent of its volume with each beat. But after one or more heart attacks, heart muscle is lost and the volume of blood the heart pumps out decreases.