Cardiac Resynchronization Therapy (CRT) for Heart Failure

Doctor explaining model to patient in examination room
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Certain people who have 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). While CRT is helpful only in some people who suffer from heart failure, if you have been diagnosed with heart failure you should talk to your doctor about the possibility of using CRT.

How CRT Works

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

Almost one in three people with this type of heart failure have an abnormality in the heart’s electrical conducting system called left bundle branch block (LBBB) (or a variant of LBBB known as "intraventricular conduction delay”). When LBBB is present in people with dilated cardiomyopathy, the right and left ventricles tend to beat out of synch. 

Normally, when the heart beats the right and left ventricles beat simultaneously, and blood is ejected from both ventricles at the same time. When LBBB is present, the two ventricle beat slightly out of phase. Because the left bundle branch (the electrical pathways that supply the left ventricle) is delayed, the right ventricle begins beating before the left ventricle does. This delay changes the geometry of the left ventricle, which in turn can substantially reduce the left ventricle’s ability to eject blood as efficiently as possible. As a result of this asynchrony between the two ventricles, overall cardiac function can become substantially reduced. Because these people are already dealing with significant heart failure, their symptoms of heart failure often become much worse.

The purpose of CRT is to re-coordinate the timing between the right and left ventricles, so they will begin beating simultaneously again. 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 resynchronize 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.

Effectiveness of CRT

Several randomized clinical trials have evaluated the effectiveness and the 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 can provide the following benefits:

  • improves symptoms and functional capacity
  • reduces the rate of hospitalizations
  • reduces 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, thereby improving the left ventricular ejection fraction.

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, there is a certain amount of added risk 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 People With Heart Failure Should Be Considered For CRT?

Formal guidelines for CRT are based on the results of clinical trials. In general, the benefits of CRT are related to the ejection fraction, and the presence and extent of LBBB. (The wider the QRS complex on the electrocardiogram, the worse the LBBB and the worse the asynchrony between the two ventricles.)

CRT therapy should be strongly considered for people who have heart failure from dilated cardiomyopathy and who also have:

  • ejection fractions < or = to 35%, AND
  • LBBB with a QRS duration of > or = 150 ms

Current guidelines also indicate that in people with ejection fractions < or = 35%, it is reasonable to consider CRT if the QRS is > or = 150ms with an intraventricular condition delay pattern -- that is who do not strictly have LBBB. Furthermore, it is also reasonable to consider using CRT in people who have ejection fractions < or = 35% along with LBBB whose QRS duration is > 130 ms. In these latter two groups pf patients, however, the clinical evidence for significant benefit with CRT is not as strong.

Finally, it is also reasonable to consider using CRT in people with heart failure whose ejection fractions are between 35-50% IF they also have some other indication for a permanent pacemaker, such as heart block. That is, if they’re going to need a pacemaker anyway, using a CRT pacemaker instead of a standard pacemaker does not add much risk, and may provide some benefit.

It should be pointed out that most people who meet these criteria for CRT will also meet criteria for an implantable defibrillator ( ICD ). Accordingly, the most common type of CRT device used in clinical medicine is a combination ICD-CRT device.

Studies have suggested that only a minority of people with heart failure who would be likely to benefit from CRT ever have the possibility brought up to them by their doctors. If you think you may be a candidate for this therapy and are interested in considering it, you may have to bring it up yourself.

A Word From Verywell

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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Article Sources
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