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Cardiac Resynchronisation Therapy (CRT)

Cardiac resynchronization therapy (CRT) is a procedure to implant a device in your chest to make your heart’s chambers contract in a more organized and efficient way. CRT uses a device called a biventricular pacemaker that delivers electrical signals to both ventricles (lower chambers of heart). CRT devices are often used to treat conditions where electrical signals do not flow through the heart normally. Bundle branch block is a condition where electrical signal travel too slowly through the bundle branches in the heart. This causes the ventricles to contract weakly because they are not coordinated. Bundle branch block is common in patients with cardiomyopathy or heart failure. The CRT device goes under your skin, beneath your collarbone and is connected to your heart by wires called leads. A CRT device can detect when the heart is not beating in a coordinated manner. The CRT device then sends electrical signals to the heart to help the ventricles contract at the same time. This strengthens the heartbeat and increases the amount of blood pumped out of the heart.

Sometimes the device also contains an implantable cardioverter-defibrillator (ICD), which can deliver stronger electrical shocks if your heart rhythm becomes dangerously erratic.

Cardiac resynchronization therapy is a treatment for heart failure in people whose ventricles don’t contract at the same time. This treatment may reduce your symptoms of heart failure and reduce your risk of heart failure complications, including death.


Cardiac resynchronization therapy requires a minor surgical procedure to implant a device in your chest. The procedure typically takes a few hours and performed under local or general anesthesia. During surgery, insulated wires (leads, or electrodes) are inserted into a major vein under or near your collarbone and guided to your heart with the help of X-ray images. One end of each wire is secured to the appropriate position in your heart, while the other end is attached to a pulse generator, which is usually implanted under the skin beneath your collarbone.

Types of cardiac resynchronization therapy devices include:

  • Cardiac resynchronization therapy with a pacemaker (CRT-P). The device used for cardiac resynchronization therapy has three leads that connect the pacemaker to the right upper chamber of your heart (right atria) and both lower chambers (ventricles).
  • Cardiac resynchronization therapy with a pacemaker and an ICD (CRT-D). People with heart failure who also have a risk of sudden cardiac death may benefit from an ICD that can detect dangerous heart rhythms and deliver a stronger correcting shock of energy than a pacemaker can deliver. In these cases, a cardiac resynchronization therapy device that works as both a pacemaker and an ICD may be recommended.