"Low T3-syndrome" in acute myocardial infarction--relationship to beta-adrenergic blockade and clinical course.

Serum levels of T4, T3 rT3 and resin T3 uptake were followed for 5 days in 40 patients with acute myocardial infarction (AMI) allocated to early treatment either with alprenolol or placebo. There was a significant fall in T3 (P less than 0.05) and an increase in rT3 (P less than 0.05) without any significant difference between the alprenolol - (n = 19) and placebo - (n = 21) treated groups. The risk of missing a further 20% change in se-T3 and se-rT3 after alprenolol compared to placebo treatment (beta) was less than 0.10 and less than 0.50, respectively. In patients with a severe clinical course, the fall in T3 and increase in rT3 was significantly greater than in patients without complications. No change in T4 was observed either with respect to the clinical course nor following alprenolol. The data suggest that alprenolol can be given in the acute phase of myocardial infarction without causing any additional disturbance in the serum levels of T3 and T4.