What is Cardiac Resynchronization Therapy (CRT), benefits of CRT, types of CRT device, CRT-P, CRT-D(ICD), and Guidance and Control-2021

What is CRT(cardiac resynchronization therapy)?

CRT (Cardiac resynchronization therapy)  is a procedure to implant a device in your chest to make your heart’s chambers squeeze (contract) in a more organized and efficient way.

Cardiac resynchronization therapy (CRT) sends electrical signals to both of the heart’s lower chambers (ventricles) using a biventricular pacemaker (also known as a cardiac resynchronization device).

The ventricles contract in a more coordinated manner as a result of this signal, which improves blood pumping from the heart.

Cardiac resynchronization therapy (CRT) is a treatment for people with heart failure. 

A CRT device is implanted in the patient which causes the two heart chambers to contract simultaneously again.

In a healthy heart, the left and right ventricles contract at the same time. 

In patients with heart failure, the stimulus that causes the ventricles to contract often runs unevenly over both chambers. 

The ventricles contract unevenly, resulting in a less powerful heartbeat and a reduced ability of the heart to pump blood.

Each year, around 2,500 heart failure patients in the Netherlands receive a special pacemaker or ICD to keep the chambers of the heart pumping synchronously. 

This is called cardiac resynchronization therapy (CRT).

Video Credit:-Gebrüder Betz Medical Animation

[1] Who is CRT suitable for?

CRT is suitable for people whose ventricles do not contract synchronously. Often this is a combination of:

Decreased pumping function of the heart (heart failure).
A conduction disequilibrium (usually a left bundle branch block)

Patients with less severe symptoms of heart failure may also benefit from CRT. 

In such cases, it will ensure that the heart failure does not get any worse and that the pump function remains good.

Benefits of CRT in heart failure

[2] Benefits of CRT treatment include:

  • Improved quality of life
  • Fewer symptoms of heart failure
  • Improved exercise capacity
  • Fewer hospital admissions
  • Less chance of premature death

[3] Types of CRT devices:

Cardiac resynchronization therapy (CRT) uses a device called a biventricular pacemaker.

Usually, the doctor implants the CRT device just under the skin (subcutaneous) on the left side of the chest below the collarbone. It can be a:

  • Resynchronization Therapy with a pacemaker (CRT-P).

Pacemaker- Biventricular pacemaker: The pacemaker ensures that the heart rhythm does not become too slow.

The pacemaker is a device that makes the heartbeat in the right rhythm. A pacemaker is usually needed when the heart rhythm is too slow.

The pacemaker has a sensor that constantly monitors the heart rhythm. The pacemaker delivers electrical impulses to bring the heart back into the correct rhythm. 

The pacemaker takes exercise into account: the electrical impulses follow each other faster during exercise.

Who needs a pacemaker?

Usually, a pacemaker is needed when the heart rhythm is too slow. This occurs among others in:

Sick sinus syndrome.
AV block.
Long QT syndrome (LQTS)
After ablation of the bundle of His, 

In atrial fibrillation, a pacemaker can help the ventricles to contract in the correct rhythm.

There is a special pacemaker that makes the ventricles contract more synchronously (cardiac resynchronization therapy CRT).

The pacemaker has been in existence since 1932. At that time it was an external pacemaker on a moving cart. 

In 1958 people were given their first internal pacemakers. The technological development of pacemakers is rapid. 

Pacemakers are becoming smaller and have more adjustment options. In December 2012 the first wireless pacemaker was installed. 

At the moment it is only used experimentally.

There are different types of pacemakers. 

  • Single-chamber pacemaker
  • Dual-chamber pacemaker
  • Biventricular pacemaker

 Placement of a pacemaker

The placement of a pacemaker is a fairly simple procedure that takes 1.5 to 2 hours. With a special pacemaker (CRT), the procedure takes a little longer.

The pacemaker is often placed under the skin on the upper left. You will usually receive a local anesthetic and be conscious.

You will be given pain relief and medication.

Sometimes the electrode is placed on the outside of the heart, in which case heart surgery under general anesthesia is required.

The cardiologist makes an incision of 5 to 10 centimeters in the place where the pacemaker is to be placed.

There he makes a cavity under the skin in which he places the pacemaker.

Through a vein under the collarbone, the physician inserts lead into the heart. The ends of the wires hook onto the inside of the heart wall.

The other end of the wires is attached to the head of the pacemaker.

The pacemaker technician adjusts the pacemaker and checks that it is working properly.

Risks and Side Effects

  • Cardiac Resynchronization Therapy with a pacemaker and an ICD (CRT-D).

An ICD is an internal defibrillator that can intervene (2) in life-threatening arrhythmias in the ventricles, such as ventricular tachycardia or ventricular fibrillation.


The implantation of a biventricular ICD or pacemaker is similar to that of an ordinary ICD or pacemaker.

The difference is that the physician applies an electrode to both ventricles (biventricular).

With a standard ICD or pacemaker, the physician only places electrodes in the right atrium and/or the right ventricle.

With a biventricular device, the left ventricle also receives an electrode.

It is sometimes difficult to find the right place for the left ventricular electrode. Therefore, the implantation of a CRT sometimes takes some time. 

The tricky thing is that the heart is different in every patient and so is the best place for electrical stimulation.

CRT surgery:

If the procedure is successful, both electrodes simultaneously stimulate and the chambers contract synchronously. 

After the implantation of the pacemaker or ICD, it can take several months for the symptoms to subside. 

The heart has to get used to the new way of contracting the ventricles. 

After the implantation, the patient still needs medication and an adapted lifestyle as prescribed by the physician. 

Some patients benefit more from a CRT than others. Whether such a special pacemaker (CRT) improves the heart’s ability to contract depends, among other things, on

  • How the electrical impulses flow through the myocardial tissue
  • The damaged area of the heart

[4] Telemonitoring: Remote monitoring:

With the CRT device, the physician can remotely obtain important data about the functioning of the device, the functioning of the heart pump, and the patient’s heart rhythm. 

For example, the CRT device can detect an accumulation of fluid in the lungs. 

The doctor can then quickly inform the patient about the adjustment of medication or diet. This can prevent hospitalization.

(a) Guidance and monitoring:

Heart failure is a chronic disease. You will be treated by a cardiologist.

You will usually visit a heart failure outpatient clinic for monitoring and advice.

Here, you will be supported by a heart failure nurse. Other types of care are also available.

(2) Blood tests:

During treatment for heart failure, regular blood tests are needed.

For example, your doctor will check your kidney function and the salt (sodium and potassium) content of your blood.

These tests will help determine whether you are tolerating your medicines well and whether the dosage is correct.


Now, What should you do if you have serious symptoms?

Heart failure can suddenly get worse. Fluid can accumulate in the lungs in a short space of time. 

You suddenly become very short of breath. Sometimes you may hear wheezing. 

The symptoms do not disappear and often get worse when you lie down. Call 911 immediately if severe shortness of breath does not go away.

Emergency treatment in the hospital is then necessary.


I hope you will get some knowledge about CRT by reading this article. Comment down your thoughts on this article below. If you have any queries, then ask My Voice

Manu Saiyed

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