Reviews/Heart Failure Management/Cardiac resynchronisation therapy reduces mortality in heart failure with reduced ejection fraction and left bundle branch block
CRT · HFM-CRT-01 · v2
Borderline: within 4 points of the Established/Likely boundary, so a re-grade could land either side.
A pacemaker-based treatment that re-coordinates the heart's two pumping chambers was tested in several large trials of patients with weak hearts and electrical conduction delay. In one trial of more symptomatic patients, fewer people died over about two and a half years with the treatment than without it [1]. In a long follow-up of a second trial, the survival gain was clear specifically in patients with the left bundle-branch block wiring pattern [6]. Where the electrical delay is very narrow, a separate trial found no benefit and a possible increase in deaths [11], which marks out where the therapy stops working. The limitation the panel kept returning to is that no single trial enrolled exactly the combination in the claim and measured death as its main, successful result; the picture is built by stitching trials together. For that reason, and because one trial found no overall survival difference [8], the panel stopped short of its highest tier.
The corpus contains two independent randomised hard-outcome findings of reduced all-cause death with cardiac resynchronisation: CARE-HF in symptomatic systolic heart failure with dyssynchrony, 20% vs 30%, hazard ratio 0.64 [1], and the MADIT-CRT long-term left bundle-branch block subgroup, 18% vs 29%, hazard ratio 0.59 [6]. MADIT-CRT's original report concentrated its heart-failure-event benefit in the QRS 150 ms or more subgroup, locating the width cut the claim names [8]. EchoCRT, enrolling QRS under 130 ms, found no event reduction and more deaths, hazard ratio 1.81 [11], bounding the therapy below the QRS threshold. A national registry of 64,698 patients reports falling two-year mortality after implantation but is observational and not restricted to the triad [5]. The contested point: The division is whether the exact triad of HFrEF, left bundle-branch block and QRS over 150 ms is itself tested for mortality, or only assembled across differently enrolled trials. The specific QRS over 150 ms clause is where it strains: MADIT-CRT original was null for overall death [8], and the long-term LBBB survival benefit did not differ by QRS duration [6].
All 24 papers behind this claim with their DOIs and what each does to it, the panel’s arbitration, the evidence gap map and the open research questions. Free, and sent to your inbox.
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One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
MADIT-CRT original [8] found no significant difference in overall risk of death (3% annual rate in each arm); its QRS>=150 benefit was in heart-failure events, not mortality, so the QRS>150 mortality clause is not carried by that trial.
No corpus trial prospectively enrolled the exact triad (HFrEF + LBBB + QRS>150) with all-cause mortality as a significant primary endpoint; CARE-HF's mortality reduction [1] came from a dyssynchrony population not restricted to LBBB or QRS>150, so applying it to the precise triad is indirect.
Where it remains uncertain. No single corpus trial enrolled the precise triad with all-cause mortality as a significant primary endpoint, and MADIT-CRT original found no overall mortality difference with a 3% annual rate in each arm [8], while the LBBB survival benefit did not differ by QRS duration [6].
Aleatory
Mortality verdicts turn on modest numbers of deaths within subgroups (e.g. EchoCRT 45 vs 26 deaths [11]), leaving play in the estimates.
Epistemic
No corpus trial prospectively enrolled HFrEF + LBBB + QRS>150 with all-cause mortality as a significant primary endpoint; the triad is reconstructed from [1], [6], [8] and [11].
Inferential
CARE-HF enrolled a dyssynchrony, NYHA III/IV population not restricted to LBBB or QRS>150 [1], so its mortality reduction is applied to the claim's narrower cohort by indirect inference.
The load-bearing papers from a corpus of 24, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Randomized all-cause mortality reduction with CRT in symptomatic HFrEF, the anchor mortality finding.
“There were 82 deaths in the cardiac-resynchronization group, as compared with 120 in the medical-therapy group (20 percent vs. 30 percent; hazard ratio 0.64; 95 percent confidence interval, 0.48 to 0.85; P<0.002).”
Panel auditInternal validity: high · scope of inference: NYHA III/IV HFrEF with cardiac dyssynchrony on standard therapy; QRS and LBBB status not specified in abstract.Key limitations: entry by dyssynchrony not LBBB or QRS>150 · mortality is secondary endpoint
LBBB-specific all-cause mortality benefit, directly matching the morphology clause of the claim.
“the cumulative rate of death from any cause among patients with left bundle-branch block was 18% among patients randomly assigned to CRT-D, as compared with 29% among those randomly assigned to defibrillator therapy alone (adjusted hazard ratio in the CRT-D group, 0.59; 95% confidence interval [CI], 0.43 to 0.80; P<0.001).”
Panel auditInternal validity: medium · scope of inference: Mild (NYHA I/II) HFrEF with LBBB; benefit stated not to differ by QRS duration within LBBB.Key limitations: mild HF population · post-trial registry follow-up · QRS>150 not isolated within LBBB
Locates the greatest CRT benefit in the QRS>=150 ms subgroup, supporting the QRS clause; benefit here was HF events, not mortality.
“The superiority of CRT was driven by a 41% reduction in the risk of heart-failure events, a finding that was evident primarily in a prespecified subgroup of patients with a QRS duration of 150 msec or more.”
Panel auditInternal validity: high · scope of inference: Mild (NYHA I/II) HFrEF, EF 30% or less, QRS 130 ms or more; HF-event benefit concentrated at QRS 150 ms or more.Key limitations: mild HF population · mortality benefit absent despite HF-event benefit · QRS>=150 subgroup benefit was for HF events not death
Real-world registry corroboration of improved survival after CRT, though observational and not triad-restricted.
“At 2 years, total mortality [hazard ratio (HR): 0.72; 95% confidence interval (CI) 0.69-0.76] and total mortality or HF hospitalization (HR: 0.59; 95% CI 0.57-0.62) decreased”
Panel auditInternal validity: medium · scope of inference: Real-world CRT recipients in England; temporal trend in outcomes.Key limitations: no CRT vs no-CRT contrast · era comparison only · LBBB and QRS not stratified
4 of 24 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
Independent randomized mortality evidence supports the direction and the LBBB/wide-QRS scope, but the absence of an exact-triad mortality-primary trial and one null overall-mortality result hold the verdict one band below Established.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
No mortality-primary trial of the exact triad. Every all-cause mortality reduction in the corpus comes from a population broader or narrower than HFrEF + LBBB + QRS>150 [1][6][8], so the claim rests on cross-trial assembly rather than direct test. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: A randomised trial enrolling only HFrEF patients with LBBB and QRS>150 ms, CRT versus control, powered for all-cause mortality as the primary endpoint.
Open question: Does CRT reduce all-cause mortality specifically in patients with HFrEF, LBBB and QRS greater than 150 ms? Why it is still open: No corpus trial enrolled this triad with all-cause mortality as a significant primary endpoint; the signal is assembled from [1], [6] and [8].
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 21 Oct 2026 · protocol v0.19