Exercise ability after Mustard's operation.

Twenty children who were well six to 12 years after undergoing Mustard's operation for transposition of the great arteries were studied. Each child performed a graded maximal treadmill test with measurements of gas exchange and oxygen saturation, and had electrocardiography carried out. Nineteen were also catheterised, and oxygen consumption was measured so that pulmonary and systemic flow could be calculated. Compared with 20 age and size matched controls, seven of the patients had normal exercise tolerance (as judged by a maximal oxygen consumption of greater than 40 ml/kg/min), 10 showed a moderate reduction (30-39 ml/kg/min), and three were more seriously limited. None of the patients with normal exercise tolerance had obstruction of venous return but six of those with mild impairment of exercise ability had partial or complete obstruction of one or both of the vena cavas. More severe limitation was associated with pulmonary vascular disease and fixed ventricular outflow tract obstruction. Formal exercise testing of apparently well children who have undergone Mustard's operation identifies those with haemodynamic abnormalities that may require intervention.