Cardiac resynchronisation therapy (CRT) is a specialised form of pacemaker treatment used in people with heart failure whose ventricles beat in an uncoordinated way. By pacing both ventricles simultaneously, CRT resynchronises the heart’s pumping action, improves cardiac output, and reduces heart failure symptoms.
Why the ventricles can fall out of sync
In a healthy heart, the left and right ventricles contract at almost exactly the same time, producing an efficient, coordinated beat. In some people with heart failure and electrical conduction abnormalities (particularly left bundle branch block, LBBB), the left ventricle contracts noticeably later than the right. This dyssynchrony reduces pumping efficiency and worsens heart failure symptoms.
How CRT works
A CRT device looks similar to a conventional pacemaker but has three leads: one in the right atrium, one in the right ventricle, and one on the outer (lateral) wall of the left ventricle, positioned through a branch of the coronary sinus. The device coordinates the timing of both ventricular leads to ensure the heart contracts as a unit.
CRT-P and CRT-D
CRT devices come in two forms:
- CRT-P (pacemaker): provides resynchronisation and pacing without a defibrillation function
- CRT-D (defibrillator): combines resynchronisation with the ability to detect and treat ventricular fibrillation or dangerous VT, as with a standard ICD
CRT-D is typically chosen for patients who also meet ICD criteria, including many cardiac arrest survivors with reduced heart function.
Benefits
In eligible patients, CRT can significantly improve exercise capacity, reduce breathlessness, decrease hospitalisation rates, and improve quality of life. In some patients, particularly those with severe dyssynchrony, CRT can lead to partial or even significant recovery of cardiac function (reverse remodelling).
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