High-Dose Tafamidis Boosts Survival in Cardiomyopathy

Treatment with oral tafamidis at 80 mg/day provided a significantly greater survival benefit than dosing at 20 mg/day in patients with transthyretin amyloid cardiomyopathy in the long-term extension of the landmark ATTR-ACT trial, Thibaud Damy, MD, PhD, reported at the European Society of Cardiology Heart Failure Discoveries virtual meeting.

Moreover, the superior survival benefit achieved by taking four 20-mg capsules of tafamidis (Vyndaqel) once daily – or its more convenient once-daily, single-capsule, 61-mg bioequivalent formulation marketed as Vyndamax – came at no cost in terms of side effects and toxicity, compared with low-dose therapy for this progressive multisystem disease, according to Dr. Damy, professor of cardiology at the University of Paris and head of the French National Referral Center for Cardiac Amyloidosis at Henri Mondor University Hospital, Créteil, France.

"There are no side effects with tafamidis," he said. "It doesn't act on any receptors, it just acts on the formation of amyloid fibrils, so there are no side effects at whatever dosage is used. And in ATTR-ACT there was actually a trend towards increased side effects in the placebo group because the amyloidosis is everywhere, so by decreasing the amyloidosis process you improve not only the heart but all the organs, and the patient has a better quality of life."

ATTR-ACT (Transthyretin Amyloidosis Cardiomyopathy Clinical Trial) was a phase 3, double-blind study in which 441 patients with transthyretin amyloidosis cardiomyopathy (TAC) in 13 countries were randomized to tafamidis at either 80 mg or 20 mg per day or placebo and followed prospectively for 30 months. At 30 months, all-cause mortality was 29.5% in patients who received tafamidis, compared with 42.9% in controls, for a statistically significant and clinically important 30% relative risk reduction, establishing tafamidis as the first disease-modifying therapy for this disease (N Engl J Med. 2018 Sep 13;379[11]:1007-16).

Patients in the 80-mg group had a 20% reduction in the risk of death, compared with the 20-mg group, at 30 months in an analysis adjusted for baseline age, 6-minute walk distance, and N-terminal pro-B-type natriuretic peptide, all of which are known to impact survival in TAC. This between-group survival difference wasn't statistically significant, providing one impetus for the subsequent long-term extension study, in which patients remained on their original dose of tafamidis, and the controls who'd been on placebo for 30 months were randomized 2:1 to tafamidis at 80 mg or 20 mg per day.

The primary endpoint in the long-term extension was a composite of all-cause mortality, heart transplantation, or implantation of a ventricular assist device. At a median follow-up of 39 months since ATTR-ACT began, the high-dose tafamidis group had an adjusted 33% reduction in the risk of this endpoint, compared with patients on 20 mg per day, a difference that barely missed statistical significance. At that point, everyone in the long-term extension was switched to the once-daily 61-mg formulation of tafamidis free acid, which is bioequivalent to four 20-mg capsules of tafamidis.

Dr. Damy's key message: At a median of 51 months of follow-up, the group originally on 80 mg of tafamidis displayed a highly significant adjusted 43% reduction in risk of the composite endpoint, compared with those who had been on 20 mg per day.

Session chair Petar M. Seferovic, MD, PhD, pronounced the ATTR-ACT trial and its long-term extension "a breakthrough advancement."

"This is the first time in human medical history that we have a drug which improves the long-term outcome, including survival, in patients with this form of hypertrophic cardiomyopathy. So this is extremely important. It's one of the major steps forward in the treatment of patients with myocardial disease," said Dr. Seferovic, president of the European Society of Cardiology Heart Failure Association and professor of internal medicine at the University of Belgrade, Serbia.

Discussant Loreena Hill, PhD, of Queen's University in Belfast, Northern Ireland, observed that TAC is a devastating disease with a formidable symptom burden and an average survival of just 2-5 years after diagnosis.

"It is often underdiagnosed, and yet it is estimated to account for up to 13% of patients with heart failure and preserved ejection fraction," she said, adding that she considers the long-term extension results "extremely positive."

Nailing Down the Prevalence of Hereditary TAC: The Discovery Study

TAC occurs when transthyretin, a transport protein, becomes destabilized and misfolds, promoting deposition of amyloid fibrils in the myocardium and elsewhere. In the heart, the result is progressive ventricular wall thickening and stiffness, manifest as restrictive cardiomyopathy and progressive nonischemic heart failure. The cause of transthyretin destabilization can be either autosomal dominant inheritance of any of more than 100 pathogenic mutations in the transthyretin gene identified to date or a spontaneous wild-type protein.

Dr. Damy was a coinvestigator in the recently published multicenter DISCOVERY study, in which 1,001 patients with clinically suspected cardiac amyloidosis, the great majority of them from the United States, were screened for pathogenic transthyretin genetic mutations. The overall prevalence of such mutations was 8% in the American patients, with the Val122Ile mutation being identified in 11% of African Americans (Amyloid. 2020 May 26;1-8).

The prevalence of wild-type amyloidosis causing TAC hasn't yet been studied with anything approaching the rigor of DISCOVERY, but the available evidence suggests the wild-type version is roughly as common as the hereditary forms.

Although DISCOVERY and other studies indicate that TAC is far more common than generally realized, Pfizer has priced Vyndaqel and Vyndamax as though TAC is a rare disease, with a U.S. list price of around $225,000 per year.

"Obviously, the cost will go down over time," Dr. Seferovic predicted.

Diagnosing TAC

Audience members mostly wanted to know how to identify individuals with TAC who are buried within the huge population of patients with heart failure with preserved ejection fraction. Dr. Damy said it's actually a simple matter using a screening framework developed by an 11-member TAC expert panel on which he served. A definitive diagnosis can usually be achieved noninvasively at a low cost using bone scintigraphy, he added.

The panel recommended screening via bone scintigraphy in patients with an increased left ventricular wall thickness of 14 mm or more in men over age 65 and women older than 70 who either have heart failure or red flag symptoms.

These red flags for TAC include an echocardiographic finding of reduced longitudinal strain with relative apical sparing, a discrepancy between left ventricular wall thickness on imaging and normal or low-normal voltages on a standard 12-lead ECG, diffuse gadolinium enhancement or marked extracellular volume expansion on cardiac magnetic resonance imaging, a history of bilateral carpal tunnel syndrome, symptoms of polyneuropathy, and mildly increased serum troponin levels on multiple occasions (JACC Heart Fail. 2019 Aug;7[8]:709-16).

Dr. Damy reported receiving institutional research grant support from Pfizer, the study sponsor, and serving on a scientific advisory board for the company.

This story originally appeared on MDedge.com.

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