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QRS morphology as a predictor of the response to cardiac resynchronisation therapy: fact or fashion?
  1. John G F Cleland1,
  2. Nick Freemantle2
  1. 1National Heart & Lung Institute, Royal Brompton & Harefield Hospitals, Imperial College, London, UK
  2. 2Institute of Epidemiology & Health, University College, London, UK
  1. Correspondence to Professor John G F Cleland, National Heart & Lung Institute,, Royal Brompton & Harefield Hospitals, Imperial College, London UB9 6JH, UK; j.cleland{at}

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It has become fashionable to suggest that cardiac resynchronisation therapy (CRT) is only effective in patients with electrocardiographic evidence of left bundle branch block (LBBB).1 ,2 In their Heart publication, Cunnington et al3 publish a meta-analysis using aggregate data on morbidity and mortality from several large trials, suggesting that patients who do not have LBBB do not benefit from CRT. However, their analysis does not exclude a 39% reduction in mortality with CRT in such patients and does not provide statistical evidence of heterogeneity of the effect of CRT amongst patients with different QRS morphologies. This analysis should not be used to deny patients a potentially highly beneficial treatment.

Do we need to demonstrate the effect of an intervention in every subgroup of patients or, having demonstrated benefit in a broad population of patients, should we assume that any apparent heterogeneity of effect is due to the play of chance? Ultimately, the individual clinician has to make the best decision for the individual patient based on the best interpretation of the data in their possession; it is easy to get lost in the minutiae and miss the larger picture. There are many examples of erroneous conclusions being drawn from subgroup analyses. There is never sufficient time, energy or resources to provide robust evidence for every subgroup of patients.4 ,5 Accordingly, guidelines on treatment have generally avoided making recommendations based on subgroup analyses of clinical trials; at least that was the case before the advent of CRT. For some reason, possibly related to the psychology of those who implant, regulate or ration CRT devices, many confident assertions have been made about subgroup effects, few of which stand up to scrutiny.

When addressing the issue of QRS morphology, it is important to distinguish three groups of patients …

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  • Contributors Both authors contributed equally to this editorial.

  • Competing interests JGFC has received honoraria and research support from Medtronic, Biotronik, Sorin and St Jude.

  • Provenance and peer review Commissioned; internally peer reviewed.

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