Cardiac resynchronisation therapy

New therapies for heart failure are needed. Professor Martin Cowie examines the case for CRT

Heart failure (HF) affects 900,000 people in the UK and impacts on both length and quality of life.

HF is more common in the elderly. Its prevalence is increasing due to people living longer and because survival from MI has improved, leaving people with damaged hearts that are at high risk of failing subsequently.

Despite increased use of evidence-based drug therapies, such as ACE inhibitors and beta-blockers, many patients with HF still have symptoms and repeated hospitalisations for symptom control are common.

The prognosis of HF remains poor, with death most commonly caused by either progressive heart failure or sudden cardiac death due to ventricular arrhythmia.

New treatments are therefore still needed.

What is CRT?

Cardiac resynchronisation therapy (CRT), also known as biventricular pacing, is a new approach to managing chronic HF in selected patients. This treatment is not yet used widely in the UK but it is likely to have a major impact on clinical practice in the future.

CRT is designed to correct uncoordinated (dysynchronous) ventricular contraction. This occurs in an estimated 30 per cent of patients with moderate-to-severe HF, and is very likely in patients with left bundle branch block on the ECG. Conventional ‘single chamber’ pacemakers pace only the right ventricle, and ‘dual chamber’ pacemakers pace the right ventricle and right atrium.

CRT involves insertion of pacing leads into the right atrium and right ventricle with a third lead inserted to pace the left ventricle via the coronary sinus. This helps restore co-ordinated cardiac contraction and in many patients will help improve their heart failure symptoms.

The procedure

Implantation of a CRT device is very similar to that of a conventional pacemaker. The patient will be sedated for the procedure, and local anaesthetic is used around the pacemaker implantation site.

The placement of the left ventricular lead can be technically demanding and may take several hours.

After implantation, the device needs to be fine-tuned to ensure that the optimal settings are in use. This is usually done at the time of the pacing check several weeks after implantation. 

CRT implantation is a very safe procedure. The complication rate in experienced centres will be less than 1–2 per cent. The procedure carries a small risk of lead displacement, coronary sinus dissection and device-related infection.

The evidence

Recent clinical trials have shown that CRT can improve cardiac function and reduce morbidity and mortality in selected patients with moderate to severe heart failure.

CARE-HF (Cardiac Resynchronisation — Heart Failure) was a major European multicentre trial reported last year that compared CRT plus standard medical therapy with standard medical therapy alone in 813 patients.

The CRT was associated with statistically and clinically significant reductions in unplanned hospitalisations, improved symptoms and improved quality of life.

There was also a significant 36 per cent reduction in mortality in the CRT group over a 29-month follow up.

A key point to note is that these benefits of CRT are on top of those achieved with the best drug therapy, such as ACE inhibitors, beta-blockers and aldosterone antagonists.

CARE-HF, therefore, provides strong evidence in favour of increasing the uptake of this new treatment. It makes sense to select, for the CRT procedure, the same type of patients as included in CARE-HF.

These were patients with low ejection fractions (systolic HF) and evidence of ventricular dysynchrony, who were still symptomatic at rest or on mild exertion (NYHA class III or IV) despite receiving optimum drug therapy.

Recent analyses have also shown that CRT is cost-effective, with the cost per quality adjusted life year being well below the notional £30,000 set by NICE.

Success rate

CRT does not always work — up to 20 per cent of patients do not respond to the biventricular pacing.

Developments in patient selection for treatment, perhaps using echocardiographic techniques to measure dysynchrony more accurately, are expected to improve the response rate.

There is currently no evidence that CRT is effective in patients with mild symptoms, and it should not be used if drug therapy has not yet been optimised.

CRT can be given on its own, or it can be combined with an implantable defibrillator to reduce further the risk of sudden cardiac death.

Further studies are needed to determine how best to choose between CRT and CRT-D for individual patients.

After implantation of the CRT device, patients will be advised to check for signs of infection at the incision site or for excessive bruising (a sign of possible bleeding in the pacemaker pocket) and to contact the pacing clinic if they have any problems.

GP follow-up

GPs will not need to be directly involved in follow-up of CRT patients. If you have any concerns about your patient, you should refer them back to the pacing or HF clinic as soon as possible. It is worth making sure that a hospital appointment has been organised for shortly after implantation.

At follow-up, pacemaker function will be checked and the patient’s drug therapy will be adjusted as necessary.

Many patients do not require as many diuretics after CRT; if the dose is not reduced, they may develop postural hypotension or renal impairment.

The patient’s other HF drug therapy might also be modified in response to post-implantation change in cardiac function — some patients can tolerate higher doses of ACE inhibitors and beta-blockers after the implantation.

You might wish to check BP (standing and sitting) and U&Es/creatinine, but patients should be followed-up in hospital until their drug therapy is restabilised.

Professor Cowie is professor of cardiology, National Heart and Lung Institute, Imperial College London

What the CRT involves

  • Cardiac resynchronisation therapy (CRT) is a new approach to managing chronic HF.
  • CRT can improve cardiac function and reduce morbidity and mortality in selected patients.
  • CRT is designed to correct unco-ordinated (dysynchronous) ventricular contraction.
  • Implantation of a CRT device is similar to that of a pacemaker. It is very safe.
  • Up to 20 per cent of patients do not respond to the biventricular pacing.
  • There is no evidence that CRT is effective in patients with mild symptoms, and it should not be used if drug therapy has not yet been optimised.


  • Chow A W, Lane R E, Cowie MR. New pacing technologies for heart failure. BMJ 2003; 326: 1,073–7.
  • Cleland J G F, Daubert J-C, Erdmann E, et al. for the Cardiac Resynchronization — Heart Failure (CARE-HF) study investigators. The effect of cardiac resynchronization on morbidity and mortality in heart failure. N Engl J Med 2005;352:1,539–49.
  • Calvert MJ, Freemantle N, Yao G, et al. for the CARE-HF investigators. Cost-effectiveness of cardiac resynchronization therapy: results from the CARE-HF trial. Eur Heart J 2005; 26: 2,681–8.

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