Morphological Studies of Pulmonary Arteriovenous Shunting in a Lamb Model of Superior Cavopulmonary Anastomosis

Excerpt

The formation of pulmonary arteriovenous malformations (PAVMs) is now well described following surgical connection of the superior vena cava to the pulmonary arteries. The behavior of PAVMs is as fascinating as their cause is elusive. These abnormal vascular connections produce intrapulmonary shunting. The resulting systemic hypoxemia can be both progressive and clinically significant. The incidence and clinical impact of PAVMs are increased in patients operated on at a young age and in those with heterotaxy syndrome (left isomerism/polysplenia). Although the exact causes of PAVMs are not known, they are clearly associated with anatomic configurations in which there is no direct passage of hepatic venous blood to the pulmonary arterial system. They develop whenever hepatic venous blood must first pass through the systemic circulation before reaching the pulmonary vascular bed. One of the most intriguing clinical characteristics of PAVMs is their regression following surgical redirection of hepatic venous blood to the pulmonary arterial system. Regression can occur after either a completion Fontan procedure or heart transplantation. The clinical importance of PAVMs has been limited by the widespread practice of limiting the length of time between a superior cavopulmonary anastomosis and a completion Fontan procedure. Progression to a Fontan procedure improves systemic oxygenation both by eliminating intracardiac right-to-left shunting and by causing regression of the PAVMs. …