Relationship and prognostic importance of thyroid hormone and N-terminal pro-B-Type natriuretic peptide for patients after acute coronary syndromes: a longitudinal observational study

Background: Altered thyroid function and increased rates of N-terminal pro-B-Type natriuretic peptide (NT-pro-BNP) are highly prevalent in coronary artery disease (CAD) patients with heart failure, and are associated with unfavorable prognosis. This study was undertaken to examine the relationship and prognostic impact of thyroid hormones, inflammatory biomarkers, and NT-pro-BNP on long-term outcomes in patients after acute coronary syndrome (ACS). Methods: The study comprised of 642 patients (age 58 +/- 10 years, 77 % male) attending an in-patient cardiac rehabilitation program after experiencing ACS. Patients were evaluated for demographic, clinical and CAD risk factors as well as thyroid hormones (e.g., fT3, fT4 level, fT3/fT4 ratio), inflammatory biomarkers (hs-CRP, IL-6) and NT-pro-BNP levels. Data on fT3/fT4 ratio and NT-pro-BNP levels were not normally distributed and were natural-log transformed (ln). Both all-cause (cumulative) and cardiac-related mortality were considered the primary outcomes of interest. Results: According to the Cox model, age, NYHA class, (ln) NT-pro-BNP levels (HR 1.53, 95 % CI 1.13-2.07), fT4 level (HR 1.15, 95 % CI 1.04-1.27), and (ln) fT3/fT4 ratio (HR 0.08, 95 % CI 0.02-0.32) were the most important predictors of all-cause mortality among CAD patients after ACS. Similarly, age, NYHA class, (ln) NT-pro-BNP levels (HR 1.62, 95 % CI 1.11-2.36), fT4 (HR 1.15, 95 % CI 1.02-1.29) and (ln) fT3/fT4 ratio (HR 0.10, 95 % CI 0.02-0.55) independently predicted cardiac-related mortality. Kaplan-Meier analyses provided significant prognostic information with the highest risk for all-cause mortality in the low cut off measures of fT3/fT4 ratio <0.206 and NT-pro-BNP >= 290.4 ng/L (HR 2.03, 95 % CI 1.39-2.96) and fT4 level >12.54 pg/ml (HR = 2.34, 95 % CI 1.05-5.18). There was no association between hs-CRP, IL-6 and mortality in CAD patients after ACS. Conclusions: Thyroid hormones (i.e., fT4 level and fT3/fT4 ratio) together with NT-pro-BNP level may be valuable and simple predictors of long-term outcomes of CAD patients after experiencing ACS.