The pulmonary artery (PA) functions as a low resistance conduit for blood to travel from the right heart to the systemic circulation. However, to view the PA as a passive conduit is to underestimate the complex physiologic interactions between the neurohormonal control of vascular tone, environmental factors (including infectious agents, toxins, and prolonged hypoxia), and congenital abnormalities that may occur within the PA. An understanding of the normal PA physiology is of paramount importance in understanding the clinical course of pathologic disease states. Although the acute PA response to a congenital abnormality or an environmental insult may be beneficial in the short term, prolonged response may lead to a severely debilitating and life-shortening pathologic condition. Recognition of pathologic conditions within the PA and the role of altered PA physiology is the focus of this chapter.
The following sections attempt to provide a detailed discussion of the common and rare congenital and acquired abnormalities affecting the PA. The presentation, etiology, and clinical course of pathologic PA conditions are outlined. In order to provide guidance on the delivery and timing of optimal and appropriate therapy, the diagnostic work-up and data on medical, surgical, and percutaneous treatments are presented. Also discussed are "clinical pearls" that should lead the clinician to consider a rare PA abnormality over a more common disease process.
ANATOMY, EMBRYOLOGY, AND PHYSIOLOGY OF THE PULMONARY ARTERY
The precursors to the adult pulmonary arterial system become recognizable by day 27 of fetal development. The main PA forms from the division of the truncus arteriosus by the aorticopulmonary septum (Figure 46-1).1 The right and left sixth aortic arches, known as the pulmonary arches, form the proximal right and left pulmonary arteries, respectively. By day 29 of embryologic development, the sixth aortic arches are continuous with the pulmonary trunk. The distal portion of the left sixth arch forms the ductus arteriosus, and the distal part of the right sixth arch involutes.2 Buds from the sixth arch arteries grow into primitive lungs and anastomose with the primitive pulmonary circulation.3
Embryologic transformation of aortic arches into the adult arterial system. (A) Aortic arches at 6 weeks of development demonstrating disappearance of the first and second arches. (B) Aortic arches at 7 weeks of development demonstrating further transformation with the disappearance of parts of the dorsal aorta and the fifth aortic arch. (C) Aortic arches at 8 weeks of development demonstrating patency of the ductus arteriosus. (D) Arterial system at 6 months after birth.
Reproduced, with permission, from The cardiovascular system. In: Moore KL, Persaud TVN, eds. The Developing Human: Clinically Oriented Embryology. 3rd ed. Philadelphia, PA: WB Saunders; 1993:304-353.
The absence of a PA (PA interruption) and anomalous left PA (pulmonary sling) are two rare conditions resulting from abnormal embryologic development of ...