Cardiac Resynchronization Therapy

What Is Cardiac Resynchronization Therapy

In some people with heart failure, the electrical signal reaches the left ventricle late, for example because of left bundle branch block. As a result, the walls of the left ventricle do not contract in sync, and the already weak heart pump becomes even less efficient. Cardiac resynchronization therapy, or CRT, uses a special pacemaker to bring these contractions back into sync.

How It Works in Brief

A CRT device usually uses three leads (thin wires): in the right atrium, in the right ventricle, and in a vein on the surface of the left ventricle, reached through the coronary sinus, the opening of the heart's veins. The device paces both ventricles almost simultaneously on almost every heartbeat, so contractions are in sync again. In atrial fibrillation, the atrial lead may not be placed.

CRT-P and CRT-D

A CRT-P is a resynchronization device with a pacing function only, similar to a pacemaker. A CRT-D combines resynchronization with an ICD, so it can also stop dangerous ventricular rhythms with an electrical shock. These are covered on the Pacemaker Implantation and Implantable Cardioverter Defibrillator (ICD) pages. The doctor chooses the type based on the risk of sudden death, the cause of heart failure, your age, and your wishes.

Who Benefits

CRT is recommended for people with heart failure who still have symptoms despite taking guideline-based medicines, with an ejection fraction of 35 percent or less and a wide QRS wave on the ECG, a sign that the signal spreads slowly through the ventricles. The benefit is seen mainly with a QRS of 150 milliseconds or more with a left bundle branch block pattern; with a narrow QRS, CRT is not beneficial. CRT is also considered for people with a weak heart pump who need constant pacing because of heart block, and for pacemaker users whose pump has weakened. These tests are covered on the Electrocardiogram (ECG) and Echocardiography pages.

Results You Can Expect

In suitable patients, large studies show that CRT reduces symptoms, improves the ability to be active, reduces hospital stays for heart failure, and extends life expectancy. Some patients do not improve much even though the device works well. CRT complements, rather than replaces, heart failure medicines, which are covered on the Heart Failure Management page.

Patients usually stay 1 to 2 nights. Before you go home, the device is checked, a chest X-ray is taken, and you receive a device identification card.

Wound and arm. Keep the wound dry for about 1 week. Avoid raising the arm on the device side above your shoulder and avoid heavy lifting for about 4 to 6 weeks.

Heart failure medicines. Keep taking them. The doses may be adjusted once your condition improves.

Assessing the results. Symptoms often improve within a few weeks to months. Echocardiography is usually repeated about 3 to 6 months after implantation, and the device settings may be adjusted.

Device checks. Regular checks at the clinic and from home, which are covered on the Remote Heart Monitoring page. The device needs to pace almost every heartbeat to be beneficial, so arrhythmias that interfere with pacing are also treated.

Warning signs to watch for. Go to the emergency room right away if you experience:

• Worsening shortness of breath, especially when lying down
• Leg swelling or rapid weight gain over a few days
• Severe dizziness or fainting
• Repeated shocks from a CRT-D, or a shock with chest pain
• A wound that is red, swollen, or oozing pus, or accompanied by fever
• Persistent hiccups or twitching of the abdominal muscles