Thyrotoxic dilated cardiomyopathy: personal experience and case collection from the literature

Thyrotoxic Cardiomyopathy: State of the Art

Thyroid hormones, mainly triiodothyronine, have genomic and non-genomic effects on cardiomyocytes related to the contractile function of the heart. Thyrotoxicosis, which is the set of signs and symptoms derived from the excess of circulating thyroid hormones, leads to increased cardiac output and decreased systemic vascular resistance, increasing the volume of circulating blood and causing systolic hypertension. In addition, the shortening of the refractory period of cardiomyocytes produces sinus tachycardia and atrial fibrillation. This leads to heart failure. Approximately 1% of patients with thyrotoxicosis develop thyrotoxic cardiomyopathy, a rare but potentially fatal form of dilated cardiomyopathy. Thyrotoxic cardiomyopathy represents a diagnosis of exclusion, and prompt identification is crucial as it is a reversible cause of heart failure, and heart function can be recovered after achieving a euthyroid state using antithyroid drugs. Radioactive iodine therapy and surgery are not the best initial therapeutic approach. Moreover, it is important to manage cardiovascular symptoms, for which beta blockers are the first-line therapeutic option.

A Case of Severe Dilated Cardiomyopathy and Hyperthyroidism

Hyperthyroidism often leads to heart failure when left untreated, specifically high output heart failure and left ventricular (LV) hypertrophy. A very minimal portion of those develop severe LV dysfunction. We report a case of a 65-year-old male who presented with signs and symptoms of heart failure and was found to have hyperthyroidism, severe systolic dysfunction, and severe dilated cardiomyopathy.

The patient is a 65-year-old African American male with a history of hypertension (HTN) who presented with complaints of dyspnea on exertion and bilateral lower limb edema of one-week duration. A review of systems revealed paroxysmal nocturnal dyspnea, orthopnea, palpitations, fatigue, and weight loss. Physical exam showed tachycardia but otherwise no exophthalmos, no thyromegaly, no thyroid nodules, clear lungs, normal heart sounds, regular heart rhythm, normal reflexes, and 2+ edema of bilateral lower extremities up to the knees. Labs showed elevated B-natriuretic peptide, severely suppressed thyroid-stimulating hormone, elevated free triiodothyronine (FT3), and free thyroxine (FT4). Electrocardiogram (EKG) revealed sinus tachycardia, incomplete left bundle branch block, and non-specific T wave abnormality. Echocardiography revealed abnormal (LV) structure and function, with moderate to severe dilatation without LV hypertrophy, severe LV systolic dysfunction with ejection fraction (EF) 30-35%, and an abnormal LV diastolic function.

The patient was managed with diuresis for acute onset heart failure and with beta-blocker and methimazole for symptomatic hyperthyroidism.

Thyroid assessment is an important step in evaluating any patient with suspected heart failure. This case highlights the balance that should exist between treating hyperthyroidism symptoms and managing disease states such as acute heart failure.