Prognostic Value of Free Triiodothyronine in Patients with Dilated Cardiomyopathy
Dilated cardiomyopathy (DCM) is a significant cause of heart failure, affecting approximately 1 in 2500 to 1 in 250 individuals in the general population. It primarily impacts younger adults and is characterized by left ventricular dilation and systolic dysfunction, independent of hypertension, valvular heart disease, congenital abnormalities, or coronary artery disease. The disease arises from the myocardium’s response to genetic and environmental insults. Traditional risk-prediction models for DCM rely on parameters related to cardiac function, but their clinical application remains limited. Therefore, accurate risk classification in DCM patients is crucial for guiding interventions.
The cardiovascular system, particularly the heart, is a major target of thyroid hormone (TH) action. Thyroid hormones, including thyroxin (T4) and triiodothyronine (T3), have significant biological effects on the heart. T3, the more potent hormone, influences cardiac output, systemic vascular resistance, angiogenesis, and endothelial function. Free triiodothyronine (FT3), the active form of T3, plays a critical role in these processes. Reduced FT3 levels are associated with poor hemodynamics and low serum sodium levels, which are independent predictors of poor survival. Additionally, heart diseases can lead to changes in TH concentrations, which are linked to higher morbidity and mortality even in the absence of pre-existing thyroid disease.
This study aimed to evaluate the prognostic value of FT3 levels in patients with DCM. The research was conducted at the First Affiliated Hospital of Nanjing Medical University from October 2009 to December 2014. A total of 176 consecutive patients diagnosed with DCM were included. After excluding patients with missing FT3 values and those lost to follow-up, data from 146 patients were analyzed. The median follow-up time was 79.9 months, during which 61 patients died (non-survival group) and 85 patients survived (survival group).
The study measured FT3 levels using fluoroimmunoassay and assessed other biochemical markers, including free thyroxin (FT4), thyroid-stimulating hormone (TSH), red blood cell count, hemoglobin, blood urea nitrogen (BUN), and serum creatinine. The primary endpoint was all-cause mortality. The results showed that FT3 levels were significantly lower in the non-survival group compared to the survival group (3.65 ± 0.83 pmol/L vs. 4.36 ± 1.91 pmol/L; P = 0.003). FT3 also exhibited a positive correlation with red blood cell count and hemoglobin, and a negative correlation with age, BUN, and serum creatinine.
Patients with lower FT3 levels (≤3.49 pmol/L) had a higher risk of all-cause mortality (P for log-rank = 0.001). Multivariate Cox regression analysis confirmed that FT3 levels were significantly associated with all-cause mortality (hazard ratio: 0.70, 95% confidence interval 0.52–0.95, P for trend = 0.021). These findings suggest that low FT3 levels are an independent predictor of poor long-term outcomes in DCM patients.
The study also explored the relationship between FT3 levels and other clinical parameters. Patients in the non-survival group were older and had lower diastolic blood pressure (DBP) compared to the survival group. No significant differences were observed in sex, smoking status, drinking habits, comorbidities, left ventricular diastolic dimension (LVDd), or left ventricular ejection fraction (LVEF) between the two groups. However, the non-survival group had lower red blood cell counts and hemoglobin levels, and higher serum creatinine, BUN, and high-density lipoprotein cholesterol (HDL-C) levels.
The correlation analysis revealed that FT3 levels were positively correlated with red blood cell count and hemoglobin, and negatively correlated with age, BUN, and serum creatinine. These findings highlight the complex interplay between thyroid function and cardiovascular health in DCM patients.
The study’s results align with previous research indicating that thyroid dysfunction is a predictor of poor prognosis in DCM. Low FT3 levels may contribute to adverse cardiac events by reducing cardiac contractility, increasing systemic vascular resistance, and impairing diastolic function. The renin-angiotensin-aldosterone system’s dysregulation in hypothyroidism may also play a role in these adverse outcomes.
The study’s findings have important clinical implications. Early detection and intervention in patients with low FT3 levels could improve outcomes in DCM. Thyroid hormone supplementation, particularly with T3, may offer therapeutic benefits, although further research is needed to confirm its efficacy. The study also underscores the importance of monitoring thyroid function in DCM patients as part of a comprehensive risk assessment strategy.
In conclusion, this study demonstrates that low FT3 levels are associated with increased all-cause mortality in patients with DCM. The findings provide valuable insights into the prognostic significance of thyroid function in DCM and highlight the need for further research to explore the potential benefits of thyroid hormone therapy in this patient population.
doi.org/10.1097/CM9.0000000000000896
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