What is cardiac resynchronization therapy?
- Cardiac resynchronization therapy (CRT) is used to treat the delay in heart ventricle contractions that occur in some people with advanced heart failure
- Heart failure means the heart's pumping power is weaker than normal. With heart failure, blood moves through the heart and body at a slower rate, and pressure in the heart increases. A delay between the contraction of the right and left ventricles often occurs with heart failure, so the walls of the left ventricle are unable to contract at the same time.
- The CRT pacing device (also called a biventricular pacemaker) is an electronic, battery-powered device that is surgically implanted under the skin.
- The device has 2 or 3 leads (wires) that are positioned in the heart to help the heart beat in a more balanced way. The leads are implanted through a vein in the right atrium and right ventricle and into the coronary sinus vein to pace the left ventricle.
How it works:
When your heart rate drops below the set rate (programmed by your doctor), the device generates (fires) small electrical impulses that pass through the leads to the heart muscle. These impulses make the lower chambers (ventricles) of the heart muscle contract, causing the right and left ventricles to pump together. The end result is improved cardiac function.
The CRT device (biventricular pacemaker) has 2 or 3 leads that are positioned in the:
- Right atrium
- Right ventricle
- Left ventricle (via the coronary sinus vein)
Electrical system of the heart
The atria and ventricles work together, alternately contracting and relaxing to pump blood through the heart. The electrical system of the heart is the power source that makes this possible.
Normally, the electrical impulse begins at the sinoatrial (SA) node, located in the right atrium. The electrical activity spreads through the walls of the atria, causing them to contract.
Next, the electrical impulse travels through the AV node, located between the atria and ventricles. The AV node acts like a gate that slows the electrical signal before it enters the ventricles. This delay gives the atria time to contract before the ventricles do. From the AV node, the electrical impulse travels through the His-Purkinje network, a pathway of specialized electricity- conducting fibers. Then the impulse travels into the muscular walls of the ventricles, causing them to contract. This sequence occurs with every heartbeat (usually 60-100 times per minute).
Benefits of CRT
CRT improves symptoms of heart failure in about 50% of patients who have been treated maximally with medications but still have severe or moderately severe heart failure symptoms. CRT improves survival, quality of life, heart function, the ability to exercise, and helps decrease hospitalizations in select patients with severe or moderately severe heart failure.
CRT and ICD Therapy
Some patients with heart failure may benefit from a combination of CRT and an implantable cardiac defibrillator (ICD). These devices combine biventricular pacing with anti-tachycardia pacing and internal defibrillators to deliver treatment as needed.
Of the patients who receive a biventricular device at Cleveland Clinic, about 90 percent receive a device that also provides defibrillator therapy. However, only about 40 percent of the patients who receive defibrillators are also candidates for a device that includes biventricular stimulation (CRT/ICD combination device).
The CRT/ICD combination devices:
- Resynchronize the heartbeat
- Slow down an abnormal fast heart rhythm
- Prevent abnormally slow heart rhythms
- Record a history of the patient’s heart rate and rhythm
Some CRT and ICD combination therapies have an internal monitoring device inside so your doctor or nurse can track your heart rhythm and heart function, such as the pressure in areas of your heart.
You may be asked to use a telephone to transmit data electronically from your device to a computer server so your doctor or nurse can monitor your condition.
Is the Device Implant Procedure Safe?
A device implant is generally a very safe procedure. However, as with any invasive procedure, there are risks. Special precautions are taken to decrease your risks. Please discuss your specific concerns about the risks and benefits of the procedure with your doctor.
Will CRT Improve My Ejection Fraction?
Yes, CRT can help improve your ejection fraction. Ejection fraction (EF) is the measurement of how much blood is being pumped out of the left ventricle of the heart. A normal EF ranges from 50% to 70%. People with heart failure who have a poor ejection fraction (EF less than 35%) are at risk for fast, irregular and sometimes life-threatening heart rhythms. The CRT/ICD combination device can help protect you against these dangerous, fast heart rhythms.
Success of CRT
Cleveland Clinic experience has shown that CRT improves patients’ ejection fraction by 5% to 10%. In some cases, patients with a CRT device develop normal ventricular function. Based on our experience, it is not rare for a patient to increase his or her ejection fraction over 40%.
Who is Eligible to Receive a CRT Device?
People with heart failure who have a poor ejection fraction (<35%) are at risk for fast, irregular and sometimes life- threatening heart rhythms. Ejection fraction is the measurement of how much blood is being pumped out of the left ventricle of the heart. CRT may be appropriate for people who:
- have severe or moderately severe heart failure symptoms
- are taking medications to treat heart failure
- have delayed electrical activation of the heart (such as intraventricular conduction delay or bundle branch block)
- Have a history of cardiac arrest or are at risk for cardiac arrest
Together, you and your doctor will determine if this treatment is right for you.