The association of cardiac biomarkers, the intensity of Tc99 pyrophosphate uptake, and survival in patients evaluated for transthyretin cardiac amyloidosis in the early therapeutics era

BACKGROUND: Transthyretin amyloid cardiomyopathy (ATTR-CM) is an increasingly recognized cause of heart failure. Given the expansion of noninvasive diagnosis with 99mTc-pyrophosphate (99mTc-PYP) scanning, and clinical use of the transthyretin stabilizer, tafamidis, we sought to examine the interplay of planar imaging heart-to-contralateral lung (H/CL) ratio, cardiac biomarkers, and survival probability in a contemporary cohort of patients referred for noninvasive evaluation of ATTR-CM.

METHODS: This single-center retrospective cohort study included 351 consecutive patients who underwent a standardized imaging protocol with 99mTc-PYP scanning for the evaluation of ATTR-CM from January 1, 2018, to January 1, 2020. After the exclusion of light chain amyloidosis, patients were characterized as scan consistent with ATTR (+ATTR-CM) or scan not consistent with ATTR (-ATTR-CM) using current guidelines. Linear regression was used to examine the relationship between biomarkers and H/CL and univariate Cox proportional hazards models were used to assess the probability of transplant-free survival.

RESULTS: We included 318 patients in the analysis (n = 86 patients +ATTR-CM; n = 232 patients -ATTR-CM). The median follow-up time was 20.1 months. During the study period, 67% of +ATTR-CM patients received tafamidis (median treatment duration, 17 months). The median H/CL ratio was 1.58 (interquartile range, 1.40-1.75). An H/CL ratio of more than 1.6 or less than 1.6 did not seem to have an impact on survival probability in +ATTR-CM patients (P = .30; hazard ratio, 0.65; 95% confidence interval, 0.31-1.41). Cardiac biomarkers were poorly correlated with H/CL (troponin T, R2 = 0.024; N-terminal pro-B-type natriuretic peptide, R2 =0.023). The Gillmore staging system predicted survival probability in +ATTR-CM as well as in the entire cohort referred for scanning. There was a trend toward longer survival among those who were -ATTR-CM compared with +ATTR-CM (P = .051; hazard ratio, 0.64; 95% confidence interval, 0.40-1.00).

CONCLUSIONS: At a large referral center, the intensity of 99mTc-PYP uptake (H/CL ratio) has neither correlation with cardiac biomarker concentrations nor prognostic usefulness in an analysis of intermediate term outcomes in the early therapeutics era. The H/CL ratio has diagnostic value, but offers little prognostic value in patients with ATTR-CM. Established staging schema were predictive of survival in this contemporary cohort, re-emphasizing the importance of cardiac biomarkers and renal function in assessing disease severity and prognosis.