Chronic heart failure is common, affecting about 900 000 people in the United Kingdom and with a prevalence of about 6-10% in people aged over 65 years1; despite modern drug treatment, it carries a high morbidity and a 10% annual mortality. About a third of patients with chronic heart failure have a left ventricular ejection fraction ≤35%,2 up to 40% of whom are at risk of worse outcomes and more severe heart failure identified by conduction delay (QRS duration on a surface electrocardiogram of >120 ms).3

A recent addition to therapeutic algorithms for chronic heart failure is cardiac resynchronisation therapy (also known as biventricular pacing). Cardiac resynchronisation therapy is a well proved treatment for patients with heart failure who have left ventricular systolic dysfunction and conduction delay, and it can reduce symptoms and admission to hospital and improve quality of life and prognosis. Clear mortality benefits have moved it from a treatment for intractable symptoms to one that, alongside β blockers, angiotensin converting enzyme inhibitors, and aldosterone antagonists, is now a routine therapy for patients …