The prevalence of atrial fibrillation (AF) in patients with moderate to advanced heart failure has been estimated as around 15–30% and rises with increased severity of heart failure.1 In such patients, there is clinical evidence of complex neurohormonal activation, cellular and extracellular alterations and electrophysiological changes. Arrhythmia is associated with adverse outcomes in patients with impaired or preserved left ventricular systolic function.1 2 However, it is not clear whether AF directly increases cardiac mortality or is simply a marker of severe disease.1 An interesting temporal relation between AF and heart failure was reported in Framingham study, and subjects with AF or heart failure subsequently developing the other condition had a poor prognosis.3 Factors including loss of atrioventricular (AV) synchrony, reduced diastolic filling, loss of atrial systole and irregular ventricular response related to AF have all contributed to higher morbidity and mortality in patients with low left ventricular ejection fraction.1

Cardiac resynchronisation therapy (CRT) is an established treatment for selected patients with advanced heart failure and cardiac dyssynchrony.4 Although AF and heart failure often coexist and are associated with worse clinical outcomes, current guidelines do not recommend CRT for these patients because of the scarcity of supporting clinical data.4 The benefit of CRT is believed to be achieved by a mechanism which corrects underlying electromechanical abnormalities, commonly manifested as a wide QRS complex, in patients with advanced heart failure.5 6 However, …