Background Varied rates of individual symptomatic response are cited for cardiac resynchronisation therapy (CRT) but have never been systematically evaluated together. Nor has spontaneous recovery rate been routinely subtracted, to clearly identify rate of symptomatic response genuinely attributable to CRT.

Method and Results First, we systematically reviewed the last 92 papers on PubMed about CRT. 74% referred to responder rates but only 18% recognised the existence of “response to doing nothing”. Second, we examined symptomatic response rates in the randomised CRT trials CARE-HF, COMPANION, CONTAK-CD, MIRACLE, MIRACLE-ICD, MIRACLE-ICD II, MUSTIC, and REVERSE, totalling 3904 patients. The weighted average symptomatic response rate, assessed using the clinical composite score was 54% for those randomised to CRT vs 40% for those randomised to no CRT. Using NYHA score, these values were 51% and 35% respectively. When symptomatic response rate was measured using 6-min walk distance and Minnesota Living with Heart Failure Quality of Life Score, a much larger spontaneous improvement was seen in the control arm of the blinded studies (device implanted but turned off in the control arm) compared to the open studies (no device implanted in the control arm). Spontaneous improvement was almost twice as high in the control arms of the blinded studies vs the open studies. With 6-min walk distances, 55% of the improvement in distance walked in the CRT arm was seen in the control arm for the blinded studies, vs 25% in the open. These values were 56% and 23% respectively with the Minnesota Living with Heart Failure Quality of Life Score.

Conclusions Quoting CRT responder rates in isolation, without recognising spontaneous responders, is common but invalid. Response rate with CRT, at 54%, is not the response rate attributable to CRT, which is only 14% of implanted patients. Three-quarters of those who “responded” with CRT would have done so even without CRT. Subjective quantitative markers seem to show an additional placebo effect and the placebo effect is more pronounced in the blinded studies than open studies. CRT definitely prevents death and reduces symptoms, but commonly-quoted “responder rates” are exaggerated, and are dependent on the measure used, and the blinding methodology used in the trial referenced.

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Abstract 001 Figure 1

Weighted average improvement in 6-min walk distance and Minnesota living with heart failure score in control and therapeutic arms of CRT trails.