Cardiovascular Effects of Hashimoto's Thyroiditis

Primary Heart Rate Changes

• Bradycardia is the hallmark cardiac finding in hypothyroidism resulting from Hashimoto's thyroiditis, with the American Heart Association implying a need for careful management of this condition 1, 2, 3
• The low cardiac output in hypothyroidism is caused by three mechanisms: bradycardia, decreased ventricular filling, and decreased cardiac contractility, as noted by the American College of Cardiology 1, 2, 3
• Systemic vascular resistance can increase by as much as 50%, and diastolic relaxation and filling are slowed, according to the American Heart Association 1, 2, 3

Additional Cardiovascular Manifestations

• Mild hypertension and narrowed pulse pressure commonly occur in patients with Hashimoto's thyroiditis, as reported by the American College of Cardiology 1, 2, 3
• Pericardial effusions and nonpitting edema can develop in severe, long-standing hypothyroidism, as noted by the American Heart Association 1, 2, 3
• Clinical heart failure is rare because cardiac output is usually sufficient to meet the lowered systemic demands in hypothyroidism, according to the American College of Cardiology 1, 2, 3

Management Recommendations

Thyroid Function Testing

• Thyroid function tests are recommended in all patients presenting with heart failure due to the relative ease of diagnosis and availability of definitive treatments, as suggested by the American Heart Association 1, 2, 3

Levothyroxine Treatment Strategy

• Initial dosages of levothyroxine should be tailored, with lower starting doses used for elderly patients with known cardiovascular disease, as recommended by the Endocrine Society 4
• TSH monitoring should be performed 6-8 weeks after initiating levothyroxine or changing the dose, then annually once TSH is at goal, according to the American Association of Clinical Endocrinologists 5

Critical Dosing Considerations

• Minimal TSH elevations may not require dosage adjustment in patients who feel well, particularly those with arrhythmias or other cardiac disorders, as noted by the American Heart Association 5, 6, 7
• The rapidity of dosage adjustment depends on the patient's age and medical comorbidities, according to the American College of Cardiology 5, 6, 7

Common Pitfalls to Avoid

• Overtreatment with levothyroxine can increase cardiovascular risk, with about 1 in 4 patients receiving levothyroxine being maintained unintentionally on doses sufficient to fully suppress TSH, as reported by the American Academy of Family Physicians 8