Cardiac resynchronisation therapy (CRT) was first introduced for clinical use in 1996 and has been approved for treatment of heart failure (HF) and incorporated into guidelines for almost a decade. However, the question of deciding who will benefit most from this treatment remains open and numerous studies have described a spectrum from ‘super-responders’ to an apparent total lack of improvement or even deterioration of symptoms.1 Other issues are the relative lack of hard evidence for benefit from CRT in patients with QRS between 120 and 150 ms,2 the impact of residual myocardial contractile function on the improvement of left ventricular (LV) function after CRT,3 and the role of systolic dyssynchrony-guided placement of LV lead.4 The latest European Society of Cardiology (ESC) guideline for chronic HF patients recommended that for patients with LV ejection fraction (EF) ≤35% and in New York Heart Association (NYHA) Class III and IV, CRT is indicated for those with a prolonged QRS duration of ≥120 ms with left branch bundle block (LBBB) QRS morphology (Class I, Level of Evidence: A) or a QRS duration of ≥150 ms irrespective of QRS morphology (Class IIa, Level of Evidence: A). For patients with NYHA Class II, CRT is recommended for patients with EF ≤30% and a QRS duration of ≥130 ms with LBBB QRS morphology (Class I, Level of Evidence: A) or a QRS duration of ≥150 ms irrespective of QRS morphology (Class IIa, Level of Evidence: A).5 Of note, these patients should be expected to survive for >1 year. In spite of the general acceptance of the use of CRT for these specific HF subpopulations, it is possible that this therapy could be used in a wider range of patients as well as fine tuning the selection criteria to improve overall outcome.

Narrow QRS and coexisting systolic dyssynchrony

HF patients with narrow QRS complexes (commonly …