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Cardiovascular Magnetic Resonance to Guide Defibrillator Implantation for LVEF of 36% to 50%
Key result
Primary prevention ICD fails to reduce sudden cardiac death or significant ventricular arrhythmias versus ILR.
- HR 0.76
- 95% CI 0.37-1.58
- n=353
Why the trial?
Primary-prevention ICDs are restricted to ejection fractions of 35% or below, yet most sudden cardiac deaths occur in patients with higher ejection fractions. CMR GUIDE asked whether CMR-detected myocardial scar identifies patients with mild-moderate systolic dysfunction (LVEF 36-50%) who benefit from a defibrillator.
Does a primary prevention implantable cardioverter-defibrillator (ICD) reduce the composite of sudden cardiac death or hemodynamically significant ventricular arrhythmia in adults with cardiomyopathy, LVEF 36-50%, and CMR-defined myocardial scar?
Population
353 patients LVEF 36-50% + CMR myocardial scar
Comparison
Primary prevention ICD vs implantable loop recorder
Design
Open-label multicenter randomized trial (18 sites; Australia, Germany, UK)
Follow-up
Median 6.3 years (IQR 4.8-7.6)
Authors
Discussion
2 takesMember takes
Where experts stand
Experts broadly read CMR GUIDE as a negative trial that does not support scar-guided ICD implantation in mid-range LVEF, though several highlight provocative signals in sudden cardiac death and younger patients that deserve further study.
Most commentators agree the trial missed its primary endpoint and that myocardial scar alone does not justify expanding ICD indications beyond current ejection-fraction thresholds. The community splits on how much weight to give the secondary signals, with some electrophysiologists calling them clinically meaningful and others warning against over-interpreting an underpowered, overall null result. The live question is whether age, scar pattern, or other refinements can identify a subgroup that truly benefits.
Agreement
Multiple clinicians emphasize that CMR GUIDE was a negative trial and that LGE-defined scar in the LVEF 36-50% range does not, on its own, justify routine ICD implantation.
4 clinicians say this directly
Main debate
Is CMR GUIDE simply null, or does it carry practice-relevant signals?
Decidedly null, do not over-interpret1
The primary endpoint was clearly negative, and the scar hypothesis lacks randomized support.vs
Important signals despite a negative primary endpoint2
Reductions in sudden cardiac death and benefit in younger patients are nuanced findings worth integrating into clinical discussions.+1Not placed6 reporting, watching, or context only
What they’re arguing about
supportiveneutralcautiouscritical
Counts are expert takes we classified by axis. Tap a row to see the takes behind its count.
Still unclear
Whether age cutoffs, scar burden or pattern, genetics, or arrhythmic phenotype can refine selection enough to identify a subgroup with clear ICD benefit in this LVEF range. The SCD reduction signal needs confirmation in a larger, adequately powered trial. The finding that ICDs may convert fatal arrhythmias into survived documented events, raising the numerator for recorded ventricular arrhythmias, complicates interpretation of the composite endpoint.
Key expert perspectives
This is a decidedly null trial and should not be over-interpreted
Argues there is neither evidence for ICD benefit in patients with LVEF 36-50% and scar nor support for the scar theory of patient selection. Cautions against reading too much into an underpowered trial despite acknowledging that trials are hard and costly.
Distilled from their postX post
The trial carries nuanced signals about SCD and younger patients that matter for clinical practice
As an electrophysiologist associated with the trial, sees the positive signal in younger patients and the reduction in SCD rates as important and relevant to real-world discussions with patients about ICD therapy. Acknowledges the primary endpoint was not positive but urges careful, nuanced analysis.
Clinically relevant question but likely underpowered to answer it
Praises the trial's clear objectives and clinical relevance but reads the negative result as likely reflecting insufficient power rather than absence of effect.
Distilled from their postX post
Implication
Does not support primary prevention ICD in LVEF 36-50% with scar; challenges CMR late gadolinium enhancement alone for defibrillator selection.
Key Points
- To determine whether primary prevention implantable cardioverter-defibrillators reduce sudden cardiac death or hemodynamically significant ventricular arrhythmias in patients with moderately reduced left ventricular ejection fraction and cardiovascular magnetic resonance-detected myocardial scar.
- Open-label randomized clinical trial (NCT01918215) conducted at 18 sites across Australia, Germany, and the UK enrolling 353 adults with ischemic or nonischemic cardiomyopathy, an LVEF of 36% to 50%, and CMR-defined myocardial scar receiving guideline-directed medical therapy.
- Participants were randomly assigned to receive either a primary prevention implantable cardioverter-defibrillator (ICD; n = 180) or an implantable loop recorder (ILR; n = 173) and followed for a median of 6.3 years.
- The primary composite outcome of sudden cardiac death or hemodynamically significant ventricular arrhythmia occurred in 7.8% (14/180) of the ICD group vs 9.2% (16/173) of the ILR group (HR, 0.76; 95% CI, 0.37–1.58).
- Sudden cardiac death alone occurred in 1.7% of the ICD group vs 5.8% of the ILR group (HR, 0.26; 95% CI, 0.07–0.95), whereas hemodynamically significant ventricular arrhythmia occurred in 6.7% vs 3.5%, respectively (HR, 1.77; 95% CI, 0.65–4.81).
- All-cause mortality, cardiovascular mortality, and heart failure hospitalizations were similar between groups, though a prespecified subgroup analysis showed fewer primary events in patients younger than 70 years receiving ICDs (3.3% vs 10.0%; HR, 0.28; 95% CI, 0.09–0.89; P = .01 for interaction).
Evidence details
What drove the result?
| Outcome | ICD | ILR |
|---|---|---|
| Sudden cardiac death or HSVA | 14 (7.8%) | 16 (9.2%) |
| HR 0.76 (95% CI 0.37-1.58) - not significant | ||
| Sudden cardiac death | 3 (1.7%) | 10 (5.8%) |
| Also a secondary outcome - lower with ICD (HR 0.26, 0.07-0.95) | ||
| Significant ventricular arrhythmia (HSVA) | 12 (6.7%) | 6 (3.5%) |
| Numerically higher with ICD (HR 1.77, 0.65-4.81); components moved in opposite directions | ||
| Primary outcome, age <70 years | 3.3% | 10.0% |
| Prespecified subgroup - HR 0.28 (0.09-0.89); reversed at >=70 (HR 2.33); P=.01 for interaction | ||
Limitations & tradeoffs
Statistical certainty
only 30 primary events occurred; the wide CI (0.37-1.58) allows meaningful benefit or harm.
Representation
participants were 82% men and 72% had an ischemic etiology.
Design limitations
the trial was open-label.
Structured PICO
Does a primary prevention implantable cardioverter-defibrillator (ICD) reduce the composite of sudden cardiac death or hemodynamically significant ventricular arrhythmia in adults with cardiomyopathy, LVEF 36-50%, and CMR-defined myocardial scar?
P
Population
353 adults with ischemic or nonischemic cardiomyopathy, LVEF 36% to 50%, and CMR-defined myocardial scar, followed for a median of 6.3 years.
I
Intervention
Primary prevention implantable cardioverter-defibrillator (ICD) (n=180)
C
Comparator
Implantable loop recorder (ILR) (n=173)
O
Outcome
Composite of sudden cardiac death (SCD) or hemodynamically significant ventricular arrhythmia (HSVA)composite
Main Result
Hazard Ratio: 0.76 (95% CI 0.37–1.58)
Absolute Event Rate: 7.8% vs 9.2%
In patients with an LVEF of 36% to 50% and CMR-defined myocardial scar, prophylactic ICD implantation did not significantly reduce the composite of sudden cardiac death or hemodynamically significant ventricular arrhythmia compared to an implantable loop recorder.
Coverage & sources
Journal, society, and media accounts. Useful signal, not independent expert judgment.
Cite This Study
Selvanayagam et al. (2026) conducted an RCT in Ischemic or nonischemic cardiomyopathy with LVEF 36% to 50% and myocardial scar (n=353). Primary prevention implantable cardioverter-defibrillator (ICD) vs. Implantable loop recorder (ILR) was evaluated on Composite of sudden cardiac death (SCD) or hemodynamically significant ventricular arrhythmia (HSVA) (HR 0.76, 95% CI 0.37-1.58). Primary prevention ICD implantation did not reduce sudden cardiac death or hemodynamically significant ventricular arrhythmia compared to an implantable loop recorder (HR 0.76; 95% CI 0.37-1.58).