Long-Term Outcome in Patients With Heart Failure Treated With Levothyroxine: An Observational Nationwide Cohort Study

Area of Science:

• Cardiology
• Endocrinology
• Public Health

Background:

• Hypothyroidism negatively impacts cardiovascular health.
• The role of levothyroxine (L-T4) substitution in heart failure (HF) patients remains debated.
• Understanding L-T4's cardiovascular effects in HF is crucial for patient management.

Purpose of the Study:

• To investigate the effects of levothyroxine (L-T4) treatment on cardiovascular outcomes in patients with heart failure (HF).
• To assess the association between L-T4 therapy and mortality, myocardial infarction (MI), cardiovascular death, and major adverse cardiovascular events (MACE) in HF patients.

Main Methods:

• A retrospective cohort study utilizing nationwide Danish registers.
• Inclusion criteria: Danish citizens aged ≥18 years diagnosed with HF between 1997 and 2012.
• Analysis involved Poisson regression to calculate incidence rate ratios (IRRs) for outcomes including all-cause mortality, cardiovascular death, MI, and MACE.

Main Results:

• The study included 224,670 HF patients; 147,253 died during follow-up.
• Ongoing and incident L-T4 treatment was associated with increased risks of all-cause mortality (IRR 1.25; 1.13), cardiovascular death (IRR 1.23; 1.11), and MACE (IRR 1.26; 1.05).
• Ongoing L-T4 treatment increased MI risk (IRR 1.32), while incident L-T4 treatment showed a reduced risk (IRR 0.87).

Conclusions:

• Levothyroxine (L-T4) treatment in heart failure (HF) patients is linked to higher risks of mortality, cardiovascular death, and MACE.
• The findings suggest a complex relationship, with ongoing L-T4 therapy posing risks, while initiating treatment may offer some benefit regarding MI.
• Further research is warranted to elucidate the specific mechanisms and optimal management strategies for L-T4 in HF populations.