Cardiac Resynchronization Therapy - CRT

This new heart failure treatment also reduces mortality

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Some patients with heart failure can experience a dramatic improvement in symptoms, fewer hospitalizations, and a reduced risk of death with a type of specialized pacemaker called cardiac resynchronization therapy (CRT). If you have been diagnosed with heart failure, you should talk to your doctor about the possibility of using CRT.

How Does CRT Work?

CRT uses uses cardiac pacing technology to re-coordinate the action of the right and left ventricles in selected patients with heart failure due to dilated cardiomyopathy.

Many patients with heart failure (approximately 30%) have an abnormality in the heart's electrical conducting system called left bundle branch block (or a variant of it known as "intraventricular conduction delay”). In these patients, the conduction abnormality causes the right and left ventricles to beat out of synch. In other words, instead of beating simultaneously the two ventricles beat slightly out of phase, one after the other. This asynchrony greatly reduces the efficiency of heart in patients with heart failure, and makes the heart failure worse.

CRT uses a specialized pacemaker that is capable of pacing both ventricles independently. This is different from typical pacemakers, which pace only the right ventricle.

By appropriately timing its pacing of the two ventricles, CRT is able to resynchronizes their beating so that the ventricles are contracting simultaneously instead of sequentially.

When the work of the two ventricles is coordinated in this way, the heart's efficiency increases, and the amount of work it takes for the heart to pump blood is reduced.

How Effective Is CRT?

Several randomized clinical trials have evaluated the effectiveness and safety of CRT in patients with heart failure and bundle branch block.

A meta-analysis looking at 14 of these trials that enrolled 4420 patients with heart failure concluded that, in appropriately selected patients, CRT reliably improves symptoms and functional capacity, reduces the rate of hospitalizations, and reduces the rate of mortality.

Studies have also shown that CRT can improve both the anatomy and function of the heart - tending to reduce the size of the dilated left ventricle, and therefore improving the left ventricular ejection fraction.

What Are the Complications of CRT?

CRT is a pacemaker, so it carries the same risk of complications you would see with any other pacemaker, including a small risk of infection, damage to the heart or blood vessels, and bleeding. In addition, additional risk is involved in placing a pacing lead capable of pacing the left ventricle. In about one in 20 patients, left ventricular pacing cannot be accomplished and CRT cannot be used.

Which Patients Should Be Considered For CRT?

Formal guidelines recommend that CRT be considered for patients with heart failure that is producing significant symptoms, who have a left ventricular ejection fraction of 0.35 or lower, and left bundle branch block.

Notably, most patients who meet these criteria for CRT will also meet criteria for an implantable defibrillator (ICD). So the most common type of CRT device used in clinical medicine is a combination ICD-CRT device.

Should Your Doctor Consider CRT?

If you have heart failure that is limiting your ability to function normally, and you are already receiving aggressive medical therapy for heart failure, you should discuss the possibility of CRT with your doctor. Your doctor will help you determine whether you are a good candidate for this form of therapy, and whether CRT is right for you.


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McAlister FA, Ezekowitz J, Hooton N, et al. Cardiac resynchronization therapy for patients with left ventricular systolic dysfunction: a systematic review. JAMA 2007; 297:2502.

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