Congestive heart failure (CHF) is a progressive syndrome marked by structural and electrical changes (remodelling). In approximately 30% of patients with CHF, ventricular dilatation is accompanied by intraventricular conduction delays, most commonly left bundle branch block (LBBB) [1]. Intraventricular conduction defects produce asynchronous ventricular activation characterized by delay in left ventricular (LV) lateral wall contraction [2], and places the failing heart at a further mechanical disadvantage. Ventricular dyssynchrony has been associated with suboptimal filling, paradoxical septal motion, reduced LV contractility and increased mitral regurgitation [3] and has been signified as an independent predictor for cardiac mortality [2]. The clinical and mechanical manifestations of ventricular dyssynchrony can be treated by simultaneously pacing both the right and left ventricles usually in association with right atrial sensing, resulting in atrial-synchronized biventricular pacing or cardiac resynchronization therapy (CRT) [3]. This resynchronization of segmental LV mechanics as well as re-coordination of both atrio-ventricular and inter-ventricular contraction reduces the conduction delay between the two ventricles and restores a normal mechanical relationship between left and right ventricular contraction. Subsequently, there is an increase in cardiac output, decrement in mitral regurgitation [4] and reverse LV remodelling [5].
Patient selection criteria
At present, the subset of patients with moderate to severe drug-refractory CHF with ventricular dyssynchrony, manifested as prolonged QRS duration on the electrocardiogram, are considered candidates for CRT. Subsequently, indications for CRT are New York Heart Association (NYHA) class III or IV despite optimal medical therapy, LV ejection fraction (LVEF) of 35% or less and QRS duration of 120-130 ms or more [6]. Echocardiography, including tissue synchronization imaging (TSI) and myocardial velocities extracted from multiple views, has been advocated to better define mechanical dyssynchrony instead of electrocardiographic measurements [7]. Its role, however, in the decision making and optimization of CRT remains a matter of debate and is currently under investigation [8, 9]. The weight of evidence supporting the clinical benefit of CRT has been corroborated in randomised controlled trials enrolling more than 4000 patients. In comparison to standard pharmacological therapy CRT has...


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