Hypothyroidism and certain cardiac abnormalities

From Lewis S. Blevins Jr, MD  –  Hypothyroidism may be associated with certain cardiac abnormalities. One of the more common manifestations is bradycardia which is a slow heart rate. First-degree atrioventricular block and other electrical disturbances of the heart may also result. The peripheral blood vessels clamp down to try to shunt blood to the central parts of the body to maintain body temperature in patients with hypothyroidism and this can result in diastolic hypertension …… that means the lower number of your blood pressure is too high. Some people have impaired cardiac responses to exercise. In severe cases of hypothyroidism, the heart may become feeble and may not pump very well leading to congestive heart failure or what I used to refer to as “myxedema heart.” Pericardial effusions, or an abnormal collection of fluid in the pericardial sac that surrounds the heart, are uncommon and mostly seen in patients with severe hypothyroidism. Most of these manifestations are seen in patients with primary hypothyroidism, due to actual thyroid disease, rather than in patients with pituitary diseases and resultant hypothyroidism.

The reason for this observation is that patients with primary thyroid disease have the potential to develop full-blown complete deficiency of thyroid hormone. Interestingly, in patients with loss of pituitary function, and even total loss of pituitary function, the T4 and T3 levels are either low normal or slightly low. They are almost never zero unless someone also has primary thyroid disease. This is because the thyroid gland has a constitutive ability to secrete some thyroid hormone even when TSH is absent. So, until today, and after a quarter of a century of caring for patients with pituitary disorders, I have never seen a patient with cardiac manifestations of hypothyroidism in the setting of pituitary disease. Today’s patient had a heart rate that was low normal but he had 1st degree heart block on a recent EKG…..meaning the PR interval was too long for those of you who want to understand these things. His T4 level was frankly low while his T3 level was low normal. Thyroid hormone should fix this problem!

I suppose that I should go ahead and mention that heart block can also be seen in patients with acromegaly treated with somatostatin analogues.

Patients with acromegaly may develop an acromegalic cardiomyopathy, valvular heart disease, and hypertension with hypertensive heart disease. Obstructive sleep apnea may complicate cardiac matters in patients with acromegaly.

Patients with TSH-producing pituitary tumors may develop hyperthyroidism with systolic hypertension, atrial arrhythmias and impaired cardiac responses to exercise.

Patients with Parkinson’s disease who take very high doses of cabergoline may develop endomyocardial thickening and valvular heart disease. These abnormalities have not been conclusively proven in patients taking cabergoline for pituitary adenomas.

I have seen one patient with Cushing’s disease who appeared to have cortisol toxicity leading to cardiac failure. Importantly, however, patients with Cushing’s disease are more likely, or prone, to develop coronary artery disease due to the associated hyperlipidemia, hypertension, and hyperglycemia.

Then, there’s growth hormone deficiency that leads to a number of important changes that are believed to increase cardiovascular risk including increased levels of CRP, hyperlipidemia, abnormal PAI-1 levels, intima media (the middle layer of blood vessels) thickening, and more. Further, growth hormone replacement has been shown to have beneficial effects on cardiac function which would lead me to believe that some patients with growth hormone deficiency probably have mild cardiac dysfunction.

Clearly, the heart is more than a pump for circulation of hormones. It obviously responds to them as well. Further, the heart even makes hormones! Atrial naturetic peptide. Aldosterone. Probably others, too. This stuff is just too complex!

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