Cardiac Resynchronisation Therapy (CRT)

What is CRT?

Most cases of heart failure occur because the main pumping chamber of the heart (the left ventricle) is not contracting well enough. Normally all parts of the ventricle contract simultaneously. In some patients with heart failure contraction of part of the ventricle is delayed relative to the rest. This is referred to as dys-synchronous contraction. Dys-synchronous contraction makes the heart less effective as a pump. The aim of CRT (Cardiac Resynchronisation Therapy) is to stimulate the ventricle to contract simultaneously, thereby improving its function.

What are the benefits of CRT?

In appropriately-selected patients CRT has been proven to improve symptoms of heart failure and quality of life, to reduce the chance of being admitted to hospital with worsening heart failure, and to make people live longer.

What does CRT involve?

CRT is performed by implanting a special CRT (‘biventricular’) pacemaker or ICD (Links to those sections). Most pacemakers and all ICDs include a lead positioned in the right ventricle of the heart. CRT devices have an extra lead that is positioned overlying the left ventricle (picture). These leads are used to stimulate (‘pace’) both ventricles simultaneously. In addition most devices incorporate another lead positioned in the right atrium of the heart so that contraction of the atria and ventricles can be coordinated.

How are CRT devices implanted?

In general the implant procedure is similar to that of a pacemaker or ICD (links). The only difference is that an extra lead must be implanted to pace the left ventricle. This lead is passed into a cardiac vein overlying the left ventricle. Implantation of a left ventricular lead can be time consuming and is not possible in every case, for a variety of reasons.

Are there any risks to CRT device implantation?

The risks include all of those relevant to pacemaker and ICD implantation (links). The following risks are also recognised with CRT device implantation:
  1. Kidney Function Problems: X-ray contrast (‘dye’) must be used to outline the cardiac veins. This can cause deterioration in kidney function, which is usually temporary and reversible.
  2. Coronary sinus dissection: It is possible to cause a tear in the wall of the cardiac veins while attempting to position the left ventricular lead. This is rarely serious, but occasionally means that the implant procedure has to be abandoned on that occasion.
  3. Phrenic nerve capture: The phrenic nerve, which supplies the diaphragm, runs very close to the cardiac veins over the left ventricle. Although great care is taken during the implant to ensure that the CRT device does not stimulate the phrenic nerve, a ‘twitch’ from the diaphragm is rarely seen during follow-up. If this cannot be prevented by reprogramming the device, reoperation may be necessary.


Follow-up of CRT devices is as described for pacemakers and ICDs. They do however need some special programming to be able to resynchronise your heart; everybody’s heart is different after all. This is done at the first check usually and uses an echo scan to define what programming helps your heart pump best.


London bridge hospital