REDUCTION IN TRIIODOTHYRONINE LEVELS FOLLOWING MODIFIED FONTAN PROCEDURE

Diminished cardiac function is a common manifestation following the mo dified Fontan procedure. Since thyroid hormone has important effects o n cardiovascular function, the present study was undertaken to evaluat e changes in thyroid hormone levels following this operation. A contro l group consisting of children undergoing open heart procedures other than a Fontan procedure was also evaluated. Serum total and free triio dothyronine (T3), total and free thyroxine (T4), thyroid stimulating h ormone (TSH), and thyroglobulin were measured by immunoassays. The Fon tan group demonstrated an initial increase in free T4, while free T3, total T3, total T4, TSH, and thyroglobulin were reduced. Over the subs equent days, free T4 decreased to below the preoperative value. By the fifth and eighth postoperative days, free T3, total T3, free T4, and total T4 remained reduced, while TSH and thyroglobulin began increasin g toward the preoperative levels. The control group also demonstrated decreases in free T3 and TSH. However, these values had returned to ba seline by the fifth post-operative day. The results indicate that chil dren undergoing open heart surgery have suppression of the pituitary-t hyroid axis, and that this is prolonged in patients undergoing Fontan procedure. The decreased levels of T3 following Fontan procedure may h ave adverse effects on the recovery of patients undergoing this operat ion.