Can thyroid disorders cause heart disease?

Can Thyroid Disorders Cause Heart Disease?

Yes, both hyperthyroidism and hypothyroidism directly cause significant cardiovascular disease through multiple mechanisms affecting cardiac structure, function, and hemodynamics, with effects ranging from arrhythmias and heart failure to increased cardiovascular mortality.

Hyperthyroidism and Cardiovascular Disease

Direct Cardiac Effects

Hyperthyroidism causes profound cardiovascular changes that can lead to serious heart disease:

• Tachycardia and arrhythmias are among the most common manifestations, with atrial fibrillation occurring frequently in hyperthyroid patients 1
• Decreased systemic vascular resistance and increased cardiac output result from thyroid hormone's direct effects on the heart and blood vessels 1, 2
• Pulmonary artery hypertension can develop, leading to right ventricular dilatation 1
• Heart failure may occur in severe, long-standing hyperthyroidism, particularly with persistent tachycardia or rapid atrial fibrillation 1, 2

Mortality Risk

Cardiovascular complications are the chief cause of death after treatment of hyperthyroidism, especially in patients over 50 years of age 1, 2. This underscores the serious nature of thyroid-induced heart disease.

Clinical Urgency

• Patients with cardiac symptoms, arrhythmias, or TSH <0.1 mIU/L require urgent evaluation and treatment 1
• Beta-blockers (atenolol or propranolol) should be initiated promptly to control heart rate and mitigate cardiovascular complications, with the goal of lowering heart rate to nearly normal 1, 2

Hypothyroidism and Cardiovascular Disease

Hemodynamic Alterations

Hypothyroidism causes distinct cardiovascular pathology:

• Bradycardia is one of the most common cardiovascular manifestations 3
• Systemic vascular resistance increases by as much as 50%, leading to mild hypertension, particularly diastolic hypertension 3
• Low cardiac output results from the combination of bradycardia, decreased ventricular filling, and decreased cardiac contractility 3
• Diastolic relaxation and filling are significantly slowed 3

Structural Heart Disease

• Myocardial fibrosis develops as hypothyroidism stimulates fibroblasts 3
• Chronic hypothyroidism leads to loss of coronary arterioles, impaired blood flow, and maladaptive changes in myocyte shape 3
• Pericardial effusions can occur in severe, long-standing hypothyroidism 3

Heart Failure Considerations

Despite significant hemodynamic changes, clinical heart failure is relatively rare in hypothyroidism because cardiac output is usually sufficient to meet the lowered systemic metabolic demands 3. However, dilated cardiomyopathy has been reported in case reports, with improvement following thyroid hormone replacement 3.

Subclinical Thyroid Disease and Cardiovascular Risk

Even subclinical thyroid dysfunction significantly impacts cardiovascular health:

• Subclinical hypothyroidism increases the risk of cardiovascular heart disease mortality and CHD events 4
• Subclinical hyperthyroidism carries higher risk of CHD mortality and atrial fibrillation, particularly when TSH is very low 4
• Middle changes in thyroid hormone levels increase cardiovascular mortality from 20% to 80% 4

Screening Recommendations

Thyroid function tests are recommended in all patients presenting with heart failure due to the potential contribution of thyroid dysfunction 3. High-risk populations requiring vigilant screening include elderly patients, those with atrial fibrillation or cardiac disease, post-partum women, and patients with Down syndrome 1.

Mechanisms of Thyroid-Induced Heart Disease

The cardiovascular effects occur through multiple pathways:

• Direct effects on myocardial contractility and heart rate through thyroid hormone receptors located in myocardium and vessels 4
• Dyslipidemia, hypertension, and endothelial dysfunction contribute to progressive cardiovascular disease 4
• Systolic and diastolic myocardial dysfunction develop through altered calcium handling and gene expression 4

Treatment Implications

Levothyroxine Considerations

When treating hypothyroidism, cardiac monitoring is essential:

• Monitor for cardiac arrhythmias during treatment in patients with coronary artery disease 5
• If cardiac symptoms develop or worsen, reduce the levothyroxine dose or withhold for one week and restart at a lower dose 5
• Cardiovascular adverse reactions from levothyroxine include palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, and cardiac arrest 5

Restoration of Euthyroid State

Restoration of normal thyroid function most often reverses the abnormal cardiovascular hemodynamics 6, making prompt diagnosis and treatment essential for preventing permanent cardiac damage.