Arteriovenous fistula in the neonate.

Arteriovenous fistulas have long intrigued cardiologists, in part because they are uncommon but also because of their physiologic effects, both local and general. For instance, a fistula in an extremity in children enhances growth of that extremity, whereas a fistula located in the kidney can cause systemic hypertension. Besides local effects, systemic arteriovenous fistulas, if large, have major systemic effects. They decrease systemic vascular resistance, increase cardiac output and are associated with an expanded blood volume. The magnitude of these physiologic changes depends directly on the size of the fistulous communication or communications and results in the clinical findings of sharp arterial pulses, widened pulse pressure, tachycardia and cardiomegaly. Arteriovenous fistula in neonates. In this issue of the Journal, Musewe and associates (1) describe 10 neonates with either an intracranial arteriovenous fistula or one involving a subclavian artery and vein. Their article emphasizes some of the unique aspects of arteriovenous fistulas in the neonate and the contribution of echocardiography to an understanding of the hemodynamics of this condition in this age group. Because of the fetal and transitional circulations, arteriovenous fistulas have particular features in neonates that are not present in infants, children or adults. In an arteriovenous fistula, the decreased systemic arterial resistance is coupled with an increased cardiac output. Therefore, an increased volume of systemic venous blood returns to the chambers of the right side of the heart. In the neonate, the increased venous return has major consequences that lead to a right to left shunt at both the atrial and the ductal levels. In the neonate, the pulmonary vascular resistance is elevated and, with the fistula reducing systemic resistance, a right to left shunt occurs through the ductus arteriosus. Indeed, catheterization studies (2-6) of these neonates have shown pulmonary hypertension and right to