Serum levels of 3,5,3'-triiodothyronine, 3,3',5'-triiodothyronine and thyroxine in acute myocardial infarction.

The serum levels of thyroxine (T4), 3,5,3′-triiodothyronine (T3) and 3,3′,5′-triiodothyronine (rT3) were monitored by a radioimmunoassay (RIA) method over the first 9 days of disease in 27 patients with acute myocardial infarction (AMI) admitted to a coronary care unit. The data were subjected to statistical analysis by computer and compared with normal values previously obtained in a group of 60 healthy adult volunteers by the same RIA method. In terms of the mean % difference between the normal subjects and the patients with AMI, we observed, on day 1, a decrease of 33% in T3(p<0.01), an increase of 78% in rT3 (p<0.01), and a decrease of 13% (p<0.05) in T4. Over the 9 days studied the serum values of T3 decreased and tended to become stabilized, at about day 9, at levels lower than the initial values; the rT3 had returned to normal by day 9, and it was not possible to demonstrate any statistical significance. in the peak value of day 1. T4 showed no statistically significant variation with time. The patients that died within 30 days of the initial symptoms differed from the survivors in that their rT3 levels were significantly higher. The patients receiving corticosteroid and digitalis therapy bad higher rT3 levels than those not receiving such therapy. The results confirm that in the initial phase of AMI there may be a shift in the peripheral conversion of T4 from T3 to rT3. This behaviour seems to be influenced by the severity of the diseae, the diet and therapy with corticosteroids and digitalis.