From the Guidelines
Thyroid function is checked in heart failure because thyroid hormones significantly impact cardiac function, and identifying and treating thyroid dysfunction can improve cardiac function and heart failure symptoms, as recommended by the 2016 ESC guidelines for the diagnosis and treatment of acute and chronic heart failure 1. Thyroid hormones have a profound effect on the cardiovascular system, and both hypothyroidism and hyperthyroidism can either cause or worsen heart failure.
- Hypothyroidism decreases cardiac output and can lead to diastolic dysfunction,
- while hyperthyroidism increases heart rate and cardiac workload, potentially precipitating or worsening heart failure. Standard testing includes measuring thyroid-stimulating hormone (TSH) and free T4 levels. If thyroid dysfunction is identified, treatment is essential - hypothyroidism typically requires levothyroxine replacement (starting at 25-50 mcg daily in heart failure patients, with gradual titration based on TSH levels), while hyperthyroidism may require medications like methimazole or propylthiourol. Treating underlying thyroid disorders can dramatically improve cardiac function and heart failure symptoms, sometimes even resolving heart failure completely if thyroid dysfunction was the primary cause. Additionally, amiodarone, a medication commonly used in heart failure patients with arrhythmias, can cause thyroid dysfunction, making monitoring particularly important in these patients, as noted in the 2016 scientific statement from the American Heart Association 1. The importance of checking thyroid function in heart failure patients is also emphasized in the 2009 ACCF/AHA guidelines for the diagnosis and management of heart failure in adults 1. Overall, checking thyroid function is a crucial part of the initial evaluation of patients with heart failure, as it can help identify underlying thyroid disorders that may be contributing to the development or worsening of heart failure, and treating these disorders can significantly improve patient outcomes.
From the Research
Thyroid Dysfunction and Heart Failure
The relationship between thyroid dysfunction and heart failure is complex, with thyroid hormones playing a crucial role in maintaining cardiac homeostasis 2, 3, 4. Thyroid dysfunction, including hypothyroidism, hyperthyroidism, and low triiodothyronine syndrome (LT3S), can have direct effects on myocardial contractility, systolic and diastolic blood pressure, heart mass, heart rate, ejection fraction, and heart output, ultimately leading to heart failure.
Mechanisms and Associations
The mechanisms by which thyroid dysfunction contributes to heart failure are not fully understood, but it is thought that thyroid hormones regulate key processes related to the maintenance of cardiac function 2. Abnormal thyroid hormone levels can lead to neurohormonal activation, which negatively impacts cardiac function 3. Additionally, thyroid hormone replacement therapy for hypothyroid patients may reduce cardiovascular events 4.
Prevalence of Thyroid Dysfunction in Heart Failure
Studies have shown that thyroid dysfunction is common in patients with heart failure, with a significant prevalence of hypothyroidism, hyperthyroidism, and low T3 syndrome 5, 6. The prevalence of abnormal thyroid function correlates with disease severity, and thyroid hormone levels can vary at a local level independently of serum levels, leading to local cardiac hypothyroidism in heart failure 6.
Clinical Implications
The association between thyroid dysfunction and heart failure has important clinical implications, and physicians should consider thyroid function when managing patients with heart failure 3. Thyroid hormone modulation may be a promising therapeutic approach to heart failure, with several clinical and experimental studies showing beneficial effects of thyroid hormone supplementation 6. However, further studies are needed to evaluate the safety and efficacy of thyroid hormone therapy in this context.
- Key points to consider:
- Thyroid dysfunction is common in patients with heart failure
- Thyroid hormones play a crucial role in maintaining cardiac homeostasis
- Abnormal thyroid hormone levels can lead to neurohormonal activation, negatively impacting cardiac function
- Thyroid hormone replacement therapy may reduce cardiovascular events
- Thyroid hormone modulation may be a promising therapeutic approach to heart failure 2, 3, 4, 5, 6