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

In this article, I will discuss what is Cardiac Resynchronization Therapy (CRT), the benefits of CRT in Heart Failure, types of CRT device, CRT-P, CRT-D(ICD) & Guidance and Control?

What is Cardiac Resynchronization Therapy (CRT)

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

The patient is implanted with a CRT device that allows the 2 heart chambers to contract again at the same time.

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

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

The chambers of the heart contract unevenly, making the heartbeat less powerful and the heart being able to pump out less blood.

Every year, approximately 2,500 heart failure patients in the Netherlands receive a special pacemaker or ICD to have the heart chambers pump synchronously. 

This is called cardiac resynchronization therapy (CRT).

Who is CRT suitable for?

CRT is suitable for people whose heart chambers do not contract synchronously. Often it is a combination of:

  • Reduced pumping function of the heart (heart failure).
  • A stimulus conduction disorder (usually a left bundle branch block)

Patients with less serious symptoms of heart failure can also benefit from CRT. 

It then ensures that the heart failure does not get worse and that the pump function remains good.

Benefits of CRT in heart failure condition:

Advantages of a CRT treatment are:

  • better quality of life
  • fewer complaints of heart failure
  • improvement of exercise capacity
  • fewer hospital admissions
  • less chance of premature death

Types of CRT device:

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

(1) CRT-P-(Pacemaker)

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

The pacemaker is a device that keeps the heart beating in the right rhythm. Usually, a pacemaker is needed if the heart rhythm is too slow.

The pacemaker has a sensor that continuously monitors the heart rhythm. The pacemaker gives off electric pulses to get the heart back into the correct rhythm. 

The pacemaker takes exertion into account: the electric pulses follow each other faster during exertion.

Who Needs a Pacemaker?

Usually, a pacemaker is needed if the heart rhythm is too slow. This occurs with, among other things:

  • Sick Sinus Syndrome.
  • AV block.
  • Long QT Syndrome (LQTS)
  • After ablation of the bundle of His, 

With atrial fibrillation, a pacemaker can keep the chambers contracting in the correct rhythm.

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

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

In 1958 people were first given an internal pacemaker. The technological development of pacemakers is fast. 

Pacemakers are getting smaller and have more and more settings. The first wireless pacemaker was installed in December 2012. 

This is currently only being used on an experimental basis.

There are different types of pacemakers

  • AAI pacemaker
  • VVI pacemaker
  • DDD pacemaker

Cardiac Resynchronization Therapy (CRT)

 Placing a pacemaker:

Placing 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 top left. You usually get a local anesthetic and are conscious.

You do, however, receive pain-relieving and soothing medicines.

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

The cardiologist makes a 5 to 10-centimeter cut where the pacemaker is to be placed. There he makes a hollow under the skin, in which he places the pacemaker.

The doctor inserts lead wires to the heart through a vein under the collarbone. The ends of the wires hook onto the inside of the heart wall.

The other end of the lead wires attaches to the head of the pacemaker.

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

Risks and Side Effects

(2) CRT-D-  Biventricular ICD :


An ICD  is an internal defibrillator that can (2) intervene in life-threatening rhythm disturbances in the heart chambers such as ventricular tachycardia or ventricular fibrillation


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

The difference is that the doctor provides both heart chambers (biventricular) with an electrode.

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

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

It is sometimes difficult to find the right place for the left chamber electrode. That is why the implantation of a CRT sometimes takes a little longer. 

The tricky part is that the heart is different for every patient and therefore the best place for electrical stimulation.

CRT operation:

If the procedure is successful, both electrodes give a stimulus at the same time and the chambers contract synchronously. 

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

The heart has to get used to the new way of contracting the heart chambers, as it were. 

After implantation, the patient still requires medication and an adjusted lifestyle as prescribed by the doctor. 

One patient benefits more from a CRT than another. Whether such a special pacemaker (CRT) makes the heart contract better depends, among other things, on:

  • how the electrical impulses run through the heart muscle tissue
  • the place of the heart that has been damaged

Telemonitoring: remote monitoring:

The CRT device allows the physician to remotely obtain important data about device function, heart pump function, and patient heart rhythm. 

For example, the CRT device can signal a fluid build-up in the lungs. 

The doctor can then quickly inform the patient about adjusting the medicines or the diet. This can prevent hospitalization.

Guidance and control:

Heart failure is a chronic disease. You are being treated by a cardiologist.

Usually, you go to a heart failure clinic for a check-up and advice.

Here you will be guided by a heart failure nurse. Other forms of guidance are also possible.

Prick blood:

Regular blood tests are required during treatment for heart failure.

For example, your doctor checks your kidney function and the level of salt (sodium and potassium) in your blood.

From this, it can be deduced whether you tolerate the medication well and whether the dosage is correct.

What to do in case of serious complaints?

Heart failure can suddenly get worse. Fluid accumulates in the lungs in a short time. 

You suddenly get very short of breath and short of breath. Sometimes you hear wheezing. 

The complaints do not disappear and often get worse when you lie down. Call 112 immediately if severe shortness of breath does not go away.

Urgent treatment is then required in the hospital.

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