Morphologic changes induced by dilation of the pulmonary valve anulus with overlarge balloons in normal newborn lambs.

The optimal method for balloon dilation valvuloplasty of congenital pulmonary valve stenosis has not been established. The cardiac damage produced by using a balloon the same size as the pulmonary anulus has not been described. The use of balloons that are larger than the anulus or of a dynamic dilation technique may enhance gradient reduction, but their added risks are not known. The pulmonary valve anuli of 14 normal newborn lambs were dilated with angioplasty balloons 20% smaller to 90% larger than the anulus; in 3 dilations, a dynamic technique was used, consisting of withdrawal of the fully inflated balloon from the anulus into the body of the right ventricle. Twelve lambs were killed immediately after the procedure and 2 were killed later, and detailed gross anatomic and microscopic observations of the heart were made. These observations support the following conclusions: (1) Dilation of the pulmonary valve anulus with overlarge balloons is "clinically" well tolerated in normal newborn lambs. (2) The major damage to the heart from any balloon is not the pulmonary anulus, but to the right ventricular outflow tract and free wall, with mural hemorrhages of varying size. (3) Trauma is minor if the balloon is 30% larger than the anulus, but is considerable when the balloon is 50% larger; (4) Trauma is worst subjacent to the proximal end of the balloon, so that longer balloons may cause greater damage; and (5) Resolution of acute right ventricular hemorrhage occurs with small, patchy areas of fibrosis.