Hypothyroidism may have more impact on cardiac health than hyperthyroidism

ORLANDO – Thyroid disorders can have significant effects on the heart and the cardiovascular system, Christine Kessler, MN, ANP-C, CNS, BC-ADM, FAANP, said at the Cardiovascular & Respiratory Summit by Global Academy for Medical Education.

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Christine Kessler

Even subclinical hypothyroidism “can be really impactful,” said Ms. Kessler, the founder of Metabolic Medicine Associates in King George, Va.

Thyroid function should be evaluated in patients with a fast resting heart fate, new-onset atrial fibrillation (AFib), idiopathic heart failure, bradycardia, using amiodarone, resistant hypertension, pericardial effusion, and statin-resistant hyperlipidemia, said Ms. Kessler, who also is a nurse practitioner and researcher. Other patients who should be evaluated: those older than 60 years, with a family history of autoimmune disease, fertility issues, new-onset anxiety/depression, and patients with high-risk pregnancy. Hypothyroidism may have more impact on cardiac health than does hyperthyroidism.

Levels of thyroid-stimulating hormone (TSH), triiodothyronine (T₃), and free thyroxine (FT₄) are typically used to evaluate thyroid function. High TSH levels are usually indicative of hypothyroidism if FT₄ and T₃ are low; hyperthyroidism is likely the diagnosis if TSH is low while FT₄ and T₃ are high. Subclinical hypothyroidism is characterized by high TSH and normal FT₄ and T₃ levels; subclinical hyperthyroidism is associated with low TSH with normal FT₄ and T₃ levels.*

Hypothyroidism can cause increased diastolic hypertension and systemic vascular resistance, elevated levels of C-reactive protein (CRP) and homocysteine, decreased myocardial contractility, decreased cardiac output, reduced heart rate, and liver function abnormalities. Most commonly, it is caused by the autoimmune disease Hashimoto’s hypothyroidism but also can result from radiation, thyroidectomy, nontoxic multinodular goiter, and drugs with antithyroid activity such as birth control medications that contain estrogen. Hypothyroidism also raises the risk of coronary artery disease through lipid aberrations such as increased LDL level and decreased number of LDL cholesterol receptors. Myocardial contractility from hypothyroidism also increases the risk of mortality in patients with heart disease and heart failure. Clinicians also should take special precautions with narcotics and anesthesia when caring for patients with hypothyroidism because of the risk of bradycardia, Ms. Kessler said.

In subclinical hypothyroidism, clinicians should treat with half the recommended dose of levothyroxine in patients aged 45-65 years and who have high levels of lipids and CRP. “At the age of 70, I don’t worry if you’re subclinical unless [the patient is] profoundly, profoundly symptomatic,” she said. In overt hypotension, the main concern is an increased risk of ischemic heart disease that can result from overtreatment, and these patients usually are started on a low dose of levothyroxine with escalated doses until the patient achieves a euthyroid state.

Hyperthyroidism is most commonly caused by Grave’s disease, with 85% of those affected younger than age 40 years. Other causes include toxic multinodular goiter, toxic adenoma, TSH-producing pituitary adenomas, resistance to thyroid hormone, thyroiditis, excessive ingestion of iodine, shrinking of the thyroid gland, and a human chorionic gonadotropin–producing tumor such as struma ovarii. Common cardiac complications of hyperthyroidism are increased heart rate and blood pressure, reduced systemic vascular resistance, and increased cardiovascular disease and mortality in addition to increased cardiac hypertrophy, pulmonary hypertension, and heart failure. Heart rhythm, atrial fibrillation, atrial flutter, increased sinus tachycardia, and increased angina are all possible complications of hyperthyroidism.

Treatment priorities for hyperthyroidism are the immediately relieving any symptoms, reducing thyroid hormone production, and blocking the conversion of T₄ to T₃. For symptomatic patients, beta-blockers will help relieve symptoms and block the T4/T₃ conversion. Follow-up treatment should include antithyroid drugs such as methimazole or propylthiouracil.

Patients who have subclinical hyperthyroidism are usually asymptomatic and may not always require treatment.

“In subclinical hypothyroidism, keep your mitts off the older patients. They’re usually going to do better, and you don’t want to throw them into hyperthyroidism,” she said. “If they’re [experiencing] subclinical hyperthyroidism, you’re going to treat them, because if not, they’re going to go into AFib, cardiovascular death, [and] they’re going to have osteoporosis. It’s not a good thing.”

Ms. Kessler reports being on the speakers bureau and an adviser for Novo Nordisk on obesity, and an adviser for them on type 2 diabetes, as well. She also reports being the study chairperson for the Florajen Patient Trial Program. The Cardiovascular & Respiratory Summit is part of Global Academy for Medical Education. Global Academy for Medical Education and this news organization are owned by the same parent company.

Correction, 7/31/19: An earlier version of this article misstated the definition of subclinical hypothyroidism.