Hypothyroidism is often associated with adverse cardiovascular risk factors such as high
cholesterol together with
hypertension, endothelial dysfunction, and other atherosclerotic cardiovascular risk factors. The changed hemodynamic characteristics result in reduced cardiac index, and the renal perfusion is impaired with
hyponatremia, and low
renin and
aldosterone production. The ischemic abnormalities are probably related to long-term consequences of a slow development of
hypothyroidism, while the hemodynamic changes can develop in very short-term
hypothyroidism. Replacement of
hypothyroidism with
levothyroxine is associated with a normalization of basal metabolic rate. Most patients with preexisting angina experience a gradual amelioration of symptoms, but in some cases the initial
therapy may precipitate an unrecognized ischemic state, worsen a preexisting angina, or even result in
myocardial infarction. It is therefore advisable to start replacement slowly and if needed perform a stress test and/or coronary angiography before. It may also in some cases be necessary to monitor the patients closely in a hospital setting during initiation of
levothyroxine. Elderly hypothyroid patients with
unstable angina pose a particular challenging problem, especially if coronary
vascular surgery is indicated. No increased risk of peri- or postoperative death has been noted in small studies, although more complications have been described. It may be relevant to treat the cardiac vascular occlusion before starting replacement with
levothyroxine in some cases, after careful weighting of pros and cons in each individual case.