Abstract Body (Do not enter title and authors here): Introduction: Patients with transthyretin amyloid cardiomyopathy (ATTR-CM) typically have low serum transthyretin (sTTR) levels, worsening heart failure, and increased mortality. A recent study has shown the association of sTTR levels ≥20mg/dL with reduced risk of all-cause mortality and cardiovascular mortality (CVM). It has also been shown that regardless of baseline sTTR level, greater increases in sTTR levels are associated with greater improvements in cardiovascular outcomes. Acoramidis, a near-complete (≥90%) TTR stabilizer, demonstrated a rapid and sustained increase from baseline in sTTR by Day 28 and reduced risk of cardiovascular outcomes in patients with ATTR-CM.

Hypothesis: Acoramidis-mediated early increase in sTTR levels ≥20 mg/dL (lower limit of normal) at Day 28 reduces risks of CVM and cardiovascular-related hospitalizations (CVH) in patients with ATTR-CM.

Methods: Analyses were conducted in the ATTRibute-CM modified intention-to-treat (mITT) population (acoramidis: 409; placebo: 202). The sTTR concentrations (normal range is 20-40 mg/dL) were assessed using an immunoturbidimetric method (Abbott ARCHITECT system) in a central laboratory. The proportion of participants with sTTR levels below normal at baseline and Day 28 were determined. The relationship between sTTR levels <20 or ≥20 mg/dL, at Day 28 across the pooled acoramidis and placebo treatment groups, and subsequent risk of CVM and of CVH over 30 months were analyzed using a stratified log-rank test.

Results: At baseline about 25% of study participants had sTTR levels below normal in both treatment groups. At Day 28, less than 2% of participants had sTTR levels <20 mg/dL in the acoramidis arm compared with 26% in the placebo arm (Table 1). When acoramidis and placebo treatment groups were pooled based on sTTR levels <20 or ≥20 mg/dL at Day 28, participants with sTTR ≥20 mg/dL were associated with a lower risk of the composite endpoint of CVM or first CVH at Month 30 in comparison with <20 mg/dL (p<0.0001) (Figure 1A). Comparable findings were observed for the individual components (CVM, first CVH) (Figure 1B and C).

Conclusion: Across treatment groups, sTTR levels above normal range (≥20 mg/dL) at Day 28 were associated with a lower risk of cardiovascular outcomes at Month 30, when compared with sTTR levels below normal range (<20 mg/dL). Thus, these observations demonstrate that higher sTTR levels over time may have the potential for clinical benefits in both CVM and CVH.