A closely watched drug for a serious and underdiagnosed heart condition did not meet its main goal in a large international trial, and researchers say the most instructive part may be why. Eplontersen did not significantly reduce cardiovascular deaths and repeat cardiovascular events compared with placebo in the overall study population, according to late breaking results presented at ESC Congress 2026 in Munich and published simultaneously in the New England Journal of Medicine.
The condition is transthyretin amyloid cardiomyopathy, or ATTR-CM, in which a liver protein misfolds and deposits in heart muscle, progressively stiffening it. Long considered rare, it is now recognized through better imaging as a meaningful cause of heart failure in older adults, particularly men, and is often mistaken for other cardiac conditions for years. Presenting investigator Mathew Maurer of Columbia University Irving Medical Center estimated that 300,000 to 500,000 people are living with it worldwide.
For patients and families tracking this field, the outcome is not a simple failure. It reflects a growing problem in testing new drugs for conditions that already have an effective treatment.
Inside the Numbers from CARDIO-TTRansform
CARDIO-TTRansform enrolled 1,432 patients with either the inherited or age related form of ATTR-CM across 130 centers in 20 countries. Participants were randomly assigned to eplontersen at 45 milligrams or placebo, injected under the skin every four weeks alongside standard care. As trial eligibility required a thickened interventricular septum of at least 12 millimeters, a history of heart failure at New York Heart Association class III or below, and a raised NT-proBNP level, the population skewed toward established but not end stage disease.
Eplontersen is an RNA targeted therapy designed to reduce how much transthyretin the liver produces. The drug did lower circulating levels of that protein as expected. That biological effect did not translate into a statistically significant reduction in the main combined measure of cardiovascular death and recurrent cardiovascular events over 140 weeks.
The primary endpoint event counts were 381 events among 210 patients taking eplontersen, against 392 events among 231 on placebo. The rate ratio was 0.89, with a confidence interval from 0.73 to 1.09 and a p value of 0.277. That interval crosses the line of no difference, meaning the study could not rule out either a modest benefit or none. The drug was generally well tolerated, with a safety profile consistent with earlier experience.
Background Stabilizer Use Complicated the Comparison
The complication is that most participants ended up taking another effective drug during the study. Tafamidis, a transthyretin stabilizer that works by a different mechanism, was already available and became more widely used during the trial's long follow up.
Stabilizer use stood at 57 percent at enrollment, and an additional 24 percent of patients in each arm started one during follow up, pushing total use to roughly 80 percent by the end. The European Society of Cardiology summarized the trial results with Maurer's assessment that baseline stabilizer use "appeared to influence the primary results."
No additional benefit was observed in patients already receiving background stabilizer therapy. In a prespecified subgroup analysis, patients who were not on a stabilizer at the start experienced fewer primary endpoint events on eplontersen, reaching nominal statistical significance. Investigators also reported a signal among patients with earlier stage disease. Subgroup results are hypothesis generating rather than proof, and they are not a basis for prescribing decisions.
Implications for Patients Living with ATTR-CM
Nothing about this result changes current treatment. Eplontersen is approved for hereditary transthyretin amyloid polyneuropathy under the brand name Wainua, not for ATTR-CM, and patients taking tafamidis or another prescribed therapy should continue as directed by their cardiologist. Tafamidis, acoramidis and vutrisiran are the disease modifying options currently available for the cardiac form in the United States.
The practical significance is about what comes next. As effective therapies become standard, trials testing an additional drug on top of them face a harder statistical task, because the comparison group is no longer untreated. That challenge is not unique to amyloidosis, and it increasingly shapes how cardiology trials are designed, enrolled and interpreted.
Patients with unexplained heart failure, especially older adults with thickened heart walls, carpal tunnel syndrome in both hands or spinal stenosis, may reasonably ask a cardiologist whether ATTR-CM has been considered. Diagnosis typically involves imaging and blood or urine testing.
The trial is registered as NCT04136171. with the full paper now available, the debate will center on whether the stabilizer explanation holds and whether a trial in untreated patients is still feasible.
Key Questions Answered
What is ATTR-CM? A condition in which the transthyretin protein misfolds and builds up in heart muscle, stiffening it and causing heart failure. It occurs in inherited and age related forms, most often diagnosed in older adults.
What did the trial find? Eplontersen did not significantly reduce cardiovascular death and recurrent cardiovascular events compared with placebo across the whole study population over 140 weeks.
Why did most participants take another drug? Tafamidis was already available and became more widely used during the trial. Stabilizer use rose from 57 percent at the start to roughly 80 percent by the end, in both study groups.
Does the subgroup result mean the drug works for some patients? It suggests a possibility worth testing further. Subgroup analyses cannot establish benefit on their own, and the investigator presenting the data urged caution.
Should anyone change their treatment? No. This trial does not alter current care. Do not start or stop any prescribed therapy without speaking to the clinician managing your treatment.
How would someone know to ask about this condition? Unexplained heart failure in an older adult, thickened heart walls on imaging, carpal tunnel syndrome affecting both hands, or spinal stenosis can prompt a cardiologist to evaluate for it.
What happens next? The full results are now published, and further analyses by stabilizer use and disease stage are expected to shape how the field designs the next generation of trials.
