Long-term all-cause and cardiovascular-related mortality in patients with ATTR-CM treated with continuous tafamidis vs placebo to tafamidis by NAC stage at baseline
Authors: Damy T , Angeli F S , Wang R , Maurer M S , Fontana M 
Published: October 2024

Abstract

Background
The National Amyloidosis Centre (NAC) staging system is used to stratify patients with transthyretin amyloid cardiomyopathy (ATTR-CM) into prognostic categories.[1]

Purpose
This post hoc analysis evaluated all-cause and cardiovascular (CV)-related mortality in patients receiving tafamidis 80 mg or placebo by NAC stage at baseline in the phase 3 Tafamidis in Transthyretin Cardiomyopathy Clinical Trial (ATTR-ACT) and its long-term extension (LTE) study.[2,3]

Methods
Patients in ATTR-ACT were randomised to tafamidis meglumine 80 mg, 20 mg, or placebo for 30 months, stratified by transthyretin (TTR) genotype (wild-type or variant) and NYHA class (I or II/III). Patients with an NT-proBNP &lt;600 ng/l or eGFR &lt;25 ml/min/1.73m² were excluded. After completing ATTR-ACT, patients could receive tafamidis 61 mg up to 60 months in the open-label LTE study. Heart transplant and cardiac mechanical assist device implantation were treated as death in the mortality assessments. Secondary analyses were change from baseline in Kansas City Cardiomyopathy Questionnaire (KCCQ) clinical and overall summary (CS, OS) scores and frequency of all-cause and CV-related hospitalisations.

Results
Of 350 patients, 42%, 38% and 20% had NAC stage I, II and III at baseline, respectively. Patients at stage III tended to be older, more likely female, and with a variant TTR genotype vs those at a lower stage (Table). At the end of follow-up, all-cause mortality was consistently lower in patients continuously treated with tafamidis vs those who initially received placebo across NAC stages (I: 36% vs 61%; : 55% vs 74%; III: 69% vs 88%). The hazard ratio (HR [95% CI]) for all-cause mortality with continuous tafamidis treatment vs placebo to tafamidis was 0.43 (0.26-0.70; P&lt;0.001), 0.51 (0.33-0.80; P=0.003) and 0.75 (0.44-1.29; P=0.298), for patients at stage I, II and III, respectively. Similar trends were observed in CV-related mortality at the end of follow-up, where HR (95% CI) for continuous tafamidis-treated patients at stage I, II and III was 0.39 (0.22-0.70; P=0.001), 0.51 (0.31-0.85; P=0.009) and 0.75 (0.42-1.33; P=0.320). The separation of survival curves was seen in the first few months of tafamidis treatment in patients at NAC stage I (Figure A). Such early separation was not seen in those at stage II or III. Starting from Month 18, statistically smaller declines in KCCQ-OS and CS scores were frequently observed in the continuous tafamidis vs placebo to tafamidis groups at stages I and II. Across NAC stages, all-cause and CV-related hospitalisations were lower in the continuous tafamidis vs placebo to tafamidis group (Figure B).

Conclusions
Continuous tafamidis treatment reduced mortality and hospitalisations (both all-cause and CV-related) across all NAC stages. These reductions were larger and occurred earlier in patients with NAC stage I, emphasising the importance of early disease-modifying treatment in patients with ATTR-CM.[3] NCT01994889, NCT02791230.