Conduction disturbances are commonly observed in patients with heart failure with left ventricular systolic dysfunction (LVSD).^1–3 Conduction disturbances increase in prevalence and severity as disease progresses. Several controlled studies have shown that correcting for conduction disturbance related electromechanical asynchrony by atrio-biventricular pacing may significantly improve symptoms and exercise tolerance in patients with drug refractory heart failure and a wide QRS complex or prolonged PR interval.^4,5 This suggests that conduction disturbances and electromechanical correlates contribute to increased symptoms and exercise intolerance regardless of baseline LVSD severity.

In such a context, between September 1999 and January 2001 we conducted a prospective, observational study of 103 consecutive patients with heart failure (mean age 60 (13) years) with chronic LVSD to determine whether conduction time intervals as simply measured on surface ECG may independently influence symptoms and exercise tolerance. Patients with an echocardiographically determined left ventricular ejection fraction (LVEF) of < 40% and left ventricular end diastolic diameter (LVEDD) > 60 mm and who were in stable sinus rhythm were considered for participation in the study. Eighteen patients were in New York Heart Association (NYHA) functional class I, 47 in class II, 27 in class III, …