Scar on CMR did not justify an ICD when LVEF was 36–50%

Design

Open-label randomised trial, 18 sites

Population

353 adults with cardiomyopathy, LVEF 36–50% and CMR myocardial scar

Primary outcome

Sudden cardiac death or haemodynamically significant ventricular arrhythmia

Effect

7.8% vs 9.2%, HR 0.76 (95% CI 0.37–1.58); median follow-up 6.3 years

CMR GUIDE randomised 353 patients with ischaemic or non-ischaemic cardiomyopathy, LVEF 36–50% and late gadolinium enhancement on cardiac MRI to a primary prevention ICD or an implantable loop recorder. All were on guideline-directed therapy, at 18 sites in Australia, Germany and the UK. Median follow-up was 6.3 years.

The primary composite of sudden cardiac death or haemodynamically significant ventricular arrhythmia occurred in 7.8% with an ICD and 9.2% with a loop recorder (HR 0.76), not a significant difference. Sudden death alone was lower with an ICD (1.7% vs 5.8%), but that was a secondary outcome. All-cause mortality, cardiovascular mortality and heart failure admissions were similar.

The idea that scar identifies who needs a device above the 35% threshold remains unproven. A prespecified age subgroup suggested benefit under 70 and none over 70, but the trial was small and this should shape future trials rather than today's implants.

• Keep to the LVEF 35% threshold for primary prevention ICDs
• Do not refer for an ICD on the basis of scar alone when LVEF is 36–50%
• Continue to optimise medical therapy and reassess LVEF
• Use scar as a marker for closer arrhythmia follow-up rather than device implantation

Why it matters

It removes the strongest argument for extending ICDs beyond the 35% LVEF threshold using scar imaging.

Don't overread it

With 353 patients and 30 primary events, the trial was too small to rule out a modest benefit.

The statistics, in plain English

The primary HR 0.76 (95% CI 0.37–1.58) is very wide: compatible with a 63% reduction or a 58% increase. The trial could not exclude a meaningful benefit, but it did not show one. The fall in sudden death (HR 0.26, 0.07–0.95) rests on 13 events and is a secondary outcome, so it is hypothesis-generating.

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