Abstract and Introduction
Context: Thyroid hormone plays a critical role in cardiovascular function. Severe hypothyroidism can be associated with "myxedema heart" characterized by relative bradycardia and pericardial effusion. Effusions associated with severe hypothyroidism can be large. Despite the large volume of effusions, tamponade is not a common consequence. However, with the incorporation of echocardiography into routine practice for evaluation of effusion, echocardiographic findings suggestive of clinical tamponade occur frequently.
Case Description: We report a series of 3 patients with large pericardial effusions secondary to severe hypothyroidism. These cases serve to demonstrate the discordance between echocardiographic signs consistent with tamponade with a patient's stable clinical hemodynamics. We also report the development of bronchial obstruction, a rare complication of a large effusion due to severe hypothyroidism.
Conclusions: While pericardial effusion associated with severe hypothyroidism has been described for decades, the echocardiographic findings may be less well known and may lead to unnecessary downstream testing or invasive management. We use our case series to facilitate a summary of what is known about the epidemiology, mechanism and physiology, and expected outcomes of myxedema associated pericardial effusion. Finally, in the setting of current paucity of clinical guidelines, we aim to familiarize clinicians with the phenomenon of pseudotamponade and suggest management strategies for myxedema associated pericardial effusion to guide clinicians to use conservative medical management in majority of cases.
The relationship between thyroid hormone and cardiovascular function has been well described.[1,2] Thyroid hormone, in the form of triiodothyronine (T3), exerts its action on the myocardium via the nuclear thyroid hormone receptor α. T3 directs inotropic and chronotropic effects on the heart by modulating the expression of sarcoplasmic reticulum calcium channels, β 1 adrenergic receptors, and nuclear thyroid hormone receptor α. Thyroid hormone also indirectly affects cardiac function due to its actions on the vasculature. T3 promotes smooth muscle relaxation and normal arteriolar remodelling. Given the critical role of thyroid hormone in cardiac homeostasis, it is not surprising for the hypothyroid state to cause cardiac dysfunction. Hypothyroidism has been associated with heart failure, cardiomyopathy, arrhythmias, systemic diastolic hypertension, dyslipidemia, and atherosclerotic disease. Hypothyroidism has also been implicated as a primary etiology of pericarditis, pericardial effusion, and, even more rarely, cardiac tamponade.[4,5]
The "myxedema heart" was first described by Zondek in 1918 as a syndrome of cardiac alterations, including large cardiac silhouette, electrocardiogram (ECG) changes indicative of a large pericardial effusion including bradycardia, low voltage, nonspecific T-wave abnormalities, and electrical alternans, which reversed with thyroid hormone extract. Enlarged cardiac silhouette is a common finding in severe hypothyroidism secondary to moderate to large pericardial effusions. The incidence of pericardial effusion in hypothyroidism is 3% in the early mild stage and up to 80% in patients with myxedema.[7,8] Some series report 2% to 10% of moderate to large pericardial effusions are due to hypothyroidism.[9–11] The pathophysiology of pericardial effusions in hypothyroidism is not completely understood. In 1979, Parving et al demonstrated abnormal albumin metabolism in myxedematous patients with a high rate of transcapillary escape and prolonged transit in extravascular space compared to the euthyroid patient, leading to generalized edema. Others have suggested that the serous pericardial effusion in myxedema is due to accumulation of albumin and other plasma proteins due to extravascular escape and impairment of the lymphatic drainage. These processes increase osmotic pressure in the setting of relatively low oncotic pressure gradient between the pericardium and myocardium.[7,12] Pathophysiologic changes seen with albumin metabolism, protein leak, and impaired lymphatic drainage are all corrected with thyroxine replacement.
Despite the fact that myxedema-associated effusion can be large, defined as >500 mL or echo-free space greater than 20mm at its greatest width, the distensibility of the pericardium and slow rate of fluid accumulation protects against hemodynamic compromise due to cardiac tamponade.[13,14]
Clinical manifestations of cardiac tamponade include impaired cardiac filling due to increased pressure within the pericardial space, impairing venous return, and systemic perfusion, eventually leading to systemic hypotension and cardiogenic shock. The diagnosis of cardiac tamponade is a clinical diagnosis made in the setting of pericardial effusion associated with tachycardia, hypotension, jugular venous distention, and frequently pulsus paradoxus, defined as inspiratory systolic fall in arterial pressure of ≥10 mmHg. Collateral data supporting the diagnosis of large pericardial effusion include a large cardiac silhouette on chest radiograph and electrical alternans on ECG. However, the latter clinical findings may lack both sensitivity and specificity, especially early in the disease course.
Traditionally, cardiac tamponade due to myxedema associated pericardial effusion was considered to be a rare complication due to the slow accumulation of fluid in the pericardial space.[4,5] The first case of cardiac tamponade due to myxedema was described by Martin and Spathis in 1965. However, in more recent patient series the frequency of echocardiographic signs of tamponade was reported to be as high as 50% in patients with severe hypothyroidism. We will present a series of 3 patients with large pericardial effusions associated with severe hypothyroidism who demonstrated echocardiographic findings consistent with tamponade, but without hemodynamic compromise (Table 1). We will use these cases to explore the echocardiographic findings in severe hypothyroidism. We then review the literature on myxedema pericardial effusions to give guidance to clinicians on the management of this condition.
J Endo Soc. 2021;5(1) © 2021 Endocrine Society