Ongoing trials of cardiac resynchronisation

Abstract

Heart failure is an increasingly common and debilitating condition for which pharmacological therapy has, so far, provided only partial relief. Despite medical therapy the overall prognosis remains poor with high rates of sudden death and death from progressive heart failure. Device based therapies offer considerable promise both for the relief of symptoms and for improving prognosis. Cardiac resynchronisation therapy (CRT) has already been shown to improve the symptoms of heart failure when optimal pharmacological therapy (including aggressive diuretic therapy, ACE inhibitors, b-blockers and spironolactone) has failed. Two large trials (CARE-HF and COMPANION) are currently investigating the effects of CRT on morbidity and mortality in patients with heart failure and sinus rhythm who have left ventricular systolic dysfunction and ventricular dyssynchrony. A series of small and medium sized studies are assessing the effects of CRT in patients similar to the above but who also have atrial fibrillation. Other potential indications for CRT that are being explored include heart failure due to left ventricular diastolic function and for the prevention of iatrogenic dyssynchrony caused by conventional pacing. The MADIT-II study suggests a small benefit from routine implantation of defibrillators in patients with heart failure who have a markedly depressed (<30%) ejection fraction due to prior myocardial infarction even in the absence of specific marker of risk for sudden arrhythmic death. Much greater benefit was observed in patients with QRS >150 msec, an ECG marker for cardiac dyssynchrony. The COMPANION trial will not only assess the effects of CRT alone but also the effects of a combined CRT and defibrillator device. Premature over-interpretation of the limited amount of existing data threatens to undermine the evidence that will form the basis of future guidelines and funding decisions. Those involved in trials have an ethical duty to minimise device implantation into patients who have been randomised to the control group (cross-overs). Doctors may have difficulty explaining to patients why they implanted a CRT device should the current trials not show benefit. Patients should be warned that CRT is still an experimental therapy that has not yet been proven to alter outcome substantially.