Vutrisiran on top of tafamidis: consistent direction, smaller numbers

Design

prespecified subgroup analysis of a randomised, placebo-controlled trial (HELIOS-B)

Population

654 patients with ATTR cardiomyopathy; 259 (40%) on tafamidis at baseline

Primary outcome

all-cause mortality and recurrent cardiovascular events

Effect

rate ratio 0.79 (95% CI 0.51-1.21) with tafamidis vs 0.67 (0.49-0.93) without; interaction P = 0.55

HELIOS-B randomised patients with transthyretin amyloid cardiomyopathy to vutrisiran 25 mg or placebo three-monthly for up to 36 months, with tafamidis permitted and stratified at randomisation. This analysis of 654 participants compared the 259 (40%) already taking tafamidis with those who were not. For the primary outcome of all-cause mortality and recurrent cardiovascular events, the rate ratio was 0.79 (95% CI 0.51-1.21) on background tafamidis and 0.67 (95% CI 0.49-0.93) without, with no significant interaction (P = 0.55). The pattern held across mortality, cardiovascular events and outpatient worsening heart failure (all interaction P > 0.20). Six-minute walk distance was preserved in both strata; the improvement in Kansas City Cardiomyopathy Questionnaire score looked attenuated on tafamidis.

The question this is being asked to answer is whether to add an RNA interference agent to a stabiliser, and it does not answer it. What it shows is that the trial found no statistical evidence that background tafamidis abolished vutrisiran's effect — which is a different and weaker claim. The confidence interval on tafamidis crosses 1.0, so within that stratum the trial cannot demonstrate benefit at all.

In a disease where both drugs are expensive and, in India, largely out of reach outside a small number of centres and patients, the honest position is that combination therapy is mechanistically attractive and clinically unproven. The authors say the same: prospective study of combination therapy is needed.

• Do not read a non-significant interaction as evidence that adding vutrisiran to tafamidis works.
• Where a patient is already established on tafamidis, discuss combination as unproven rather than recommended.
• Cost and access make this a specialist-centre conversation in India; confirm availability before raising it.
• Track functional capacity and symptom scores separately — they diverged here.
• Stratification was prespecified, which makes this a better subgroup analysis than most, but still a subgroup analysis.

Why it matters

The combination is already being asked for in clinic, and the evidence behind it is thinner than the headline suggests.

Don't overread it

This is a prespecified subgroup analysis, not a randomised comparison of combination against tafamidis alone.

The statistics, in plain English

A P value of 0.55 for interaction means the trial could not show the effect differs between strata — with 259 patients on tafamidis, only a very large difference would have been detected. Meanwhile the rate ratio of 0.79 with a 95% CI of 0.51-1.21 crosses 1.0, so in that stratum the trial is compatible with anything from a substantial benefit to a modest harm. Both statements are true at once, and only the second tells you what is known about combination therapy.

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