Vutrisiran's benefit in a heart amyloidosis trial held through four years

Transthyretin amyloid cardiomyopathy is a disease in which a blood protein called transthyretin misfolds and deposits in the heart muscle, stiffening it until the heart fails. The main HELIOS-B trial showed that vutrisiran, a drug that switches off production of that protein, reduced deaths and cardiovascular events over about three years. A follow-up analysis published in Circulation on 3 November asked what happens when treatment continues for longer [s1].

What the drug is

Vutrisiran is a small interfering RNA therapy — a molecule that silences the gene for transthyretin in the liver, cutting the supply of the protein that goes on to misfold [s1]. It is given as an injection of 25 mg once every three months [s1]. By reducing how much transthyretin circulates, the aim is to slow or halt the deposits that accumulate in the heart. Unlike drugs that try to clear existing deposits, this approach works upstream, at the source of the protein, which is why the question of how early treatment starts is central to the disease.

HELIOS-B compared vutrisiran against placebo [s1]. After the main trial reported — showing a reduction in all-cause mortality and recurrent cardiovascular events after 33 to 36 months — participants were offered entry into an open-label extension, in which everyone receives the active drug [s1]. The new report covers that extension [s2].

How the extension was built

Of 654 participants in HELIOS-B (326 assigned to vutrisiran, 328 to placebo), 478 completed the double-blind phase and 466 entered the open-label extension — 243 who had been on vutrisiran all along and 223 who had been on placebo [s1]. In the extension, the first group continued vutrisiran ("continuous vutrisiran") while the second switched from placebo to the drug ("placebo/vutrisiran") [s1].

That design sets up the key comparison. Both groups now receive vutrisiran, but one started roughly three years earlier than the other. Comparing them asks whether the head start of early treatment leaves a lasting mark. Prespecified endpoints assessed through month 48 included a composite of all-cause mortality and cardiovascular events, death alone, a quality-of-life score, heart-failure class, and the cardiac blood markers NT-proBNP and troponin I [s1].

What it found

Through month 48, the group that had been on vutrisiran continuously fared better than the group that started on placebo [s1]. The risk of a first cardiovascular event or death was 37% lower in the continuous group (hazard ratio 0.63; 95% confidence interval 0.51–0.79; p=0.0001), and the risk of death from any cause was also 37% lower (hazard ratio 0.63; 95% CI 0.46–0.84; p=0.0023) [s1].

The functional and biological measures moved the same way. On the Kansas City Cardiomyopathy Questionnaire, a standard quality-of-life scale, the continuous group scored higher by a least-squares mean difference of 9.0 points (95% CI 5.3–12.6; p<0.0001) [s1]. More patients in that group had improved or stable New York Heart Association heart-failure class (odds ratio 1.6; 95% CI 1.1–2.2; p=0.0084) [s1]. The cardiac markers held lower too, with adjusted fold-change ratios of 0.66 for NT-proBNP (95% CI 0.58–0.74) and 0.71 for troponin I (95% CI 0.64–0.79), both p<0.0001 [s1]. NT-proBNP and troponin I are blood markers of cardiac strain and injury, so lower values point to a heart under less stress [s1]. The authors report that these benefits were echoed in the subgroup of patients taking vutrisiran as their only amyloidosis treatment, and that no new safety signals emerged [s1].

What is, and is not, established

The extension supports a specific message: long-term vutrisiran delivered sustained benefits across mortality, cardiovascular events, cardiac biomarkers, functional status, and quality of life through four years, and patients who started the drug earlier did better than those who started later — which the authors read as underscoring the value of early diagnosis and treatment [s1].

The qualifications matter. Once the extension began, everyone was on the active drug, so this is no longer a randomised comparison of drug against placebo; it compares earlier starters with later starters, and the two groups differ in ways beyond timing [s1]. The people who reached the extension are, by definition, those who survived and stayed well enough to continue, which can flatter long-term results [s1]. The analysis is of a single trial in a specific, relatively rare disease [s1]. And an open-label extension, in which patients and doctors know the treatment, carries more room for expectation to colour the softer measures than the original blinded trial did [s1].

Red flags: anyone with amyloid cardiomyopathy who notices worsening breathlessness, swelling in the legs, sudden weight gain, or fainting should contact their cardiology team, as these can signal worsening heart failure. This article describes a clinical trial and is not medical advice. Treatment decisions in transthyretin amyloidosis are for patients and their specialists.