Cardiac Resynchronisation Therapy (CRT)
Cardiac Resynchronisation Therapy (CRT) uses a special kind of pacemaker to improve the function of the heart.
Indication
Some people with heart failure (reduced heart function) also have an abnormality of the normal electrical activation of the heart called ‘left bundle branch block’.
In normal electrical conduction, the electrical wavefront of activation passes from the sinus node at the back of the heart, through the AV node in the middle of the heart, and then to the ventricles via the left and right bundles. This enables rapid, synchronous activation of the heart.
When the ‘left bundle’ is blocked, contraction of the heart is dyssynchronous.
CRT restores normal synchronous contraction helping to improve heart function and reduce symptoms.
The Two Types of Cardiac Resynchronisation Therapy (CRT)
There are two forms of CRT:
- CRT pacemaker
- CRT defibrillator - with the same functions as the pacemaker, but with the additional function of being able to shock the heart in the event of a dangerous rhythm
If you are not deemed at high risk of a dangerous heart rhythm, then a CRT pacemaker is better - with thinner leads, smaller device, and longer battery life, and overall a lower risk of complication.
Upgrade of an Existing Pacemaker or Defibrillator
If you already have a pacemaker or defibrillator and the function of your heart is reduced, then you may benefit from upgrade of your existing device to a cardiac resynchronisation pacemaker/defibrillator.
Most often, 1-2 extra pacemaker or defibrillator leads will be inserted into the heart. The leads - a combination of old and the new - are then inserted into a new cardiac resynchronisation device.
The procedure is performed in a similar way to that described below.
Procedure of CRT Implantation
The CRT device is made up of a generator (about 4-5cm long, and 7-13mm thick), and 2-3 pacemaker/defibrillator leads. Each lead is a thin insulated wire that runs from the generator to the heart.
The procedure is performed in hospital under sedation or general anaesthetic. After antibiotic medication is given to help prevent infection, a small incision is made below the collar bone. A ‘pocket’ is then made under the skin to house the generator. 2-3 leads are passed into the nearby vein - called the subclavian vein - and then into the heart where they are attached to the inner lining of the heart by small screws. Finally, the wound is closed with absorbable sutures and a dressing placed over the incision.
If 3 leads are used, then one is place in the atrium, one in the right ventricle, and one on the outside wall of the left ventricle. The ventricular leads work together to resynchronise the heart.
Typically, the procedure takes between 1.5 and 2 hours to perform.
Risks
Of implantation:
- bleeding, infection, pericardial effusion (fluid around heart), lead dislodgement requiring reposition, and pneumothorax (air around lungs) occur in 1-2% of cases
- the risk of more serious complication including stroke, heart attack, emergency surgery to correct a complication, occurs in 0.1%
Long-term:
- over time there is a small ongoing risk of device malfunction, tricuspid valve dysfunction (leakiness of a valve on the right side of the heart), or infection
Summary
Trials have clearly shown that patients with heart failure and left bundle branch block, live longer and better with a cardiac resynchronisation device. While there are small risks with implantation, overall the risk of not placing a device is higher if the heart function has not improved with medication or other measures.