THYROTOXICOSIS INCREASES RIGHT-TO-LEFT SHUNT IN CONGENITAL CYANOTIC HEART-DISEASE

We wish to report two cases of congenital cyanotic heart disease in wh om coexisting thyrotoxicosis increased the right to left shunt. We rev iew the literature on the cardiac and respiratory effects of thyroid h ormone to try to explain this phenomenon. Two patients, one with Fallo t's tetralogy (diagnosed at 68 yars of age), the other with a ventricu lar septal defect, developed thyrotoxicosis which resulted in a dramat ic but reversible deterioration in their cardiac condition. We conclud e that thyrotoxicosis increases right to left shunt in congenital cyan otic heart disease. This effect is profound but reversible. We suggest that when an unexplained rapid deterioration occurs in patients with congenital cyanotic heart disease, thyrotoxicosis should be excluded.