Normally the aortic valve is posterior, inferior and to the right compared with the pulmonary valve (Fig. l). It is thought that differential growth of the two sides of the conus, that is, resorption of the subaortic conus with expansile growth of the subpulmonary conus, allows the aortic valve to develop fibrous continuity with the atrioventricular canal and the pulmonary valve to be lifted anteriorly and superiorly above the infundibulum.' Each valve has three cusps of approximately equal size (Fig. 2). The right coronary artery arises from the most anterior of the aortic sinuses of Valsalva and the left coronary from the left posterior sinus of Valsalva (Fig. 3). The aorta ascends to the right of the main pulmonary artery and arches leftward and posteriorly to the left of the trachea and over the left main stem bronchus (Fig. 4). In the normal left arch the first branch of the aorta is the right brachiocephalic artery which divides to form the right subclavian and right common carotid arteries. The second branch is the left common carotid artery and the last branch is the left subclavian artery. The ductus arteriosus joins the lesser curvature of the aorta just beyond the left subclavian artery. The ductus usually closes in the neonatal period leaving the ligamentum arteriosum. Occasionally a ductus diverticulum, protruding from the under surface of the arch, may persist from months to years. The descending aorta proceeds inferiorly to the left of the spine and An audio-visual tape based on this article is available as Tape #7 of the Videotextbook of 2-D and Doppler Echocardiography-a Futura Publication.passes through the aortic hiatus in the diaphragm.The main pulmonary artery turns posteriorly a short distance above the valve, courses to the left of the ascending aorta, and bifurcates into right and left branches (Fig. 1). The right pulmonary artery passes posterior to the ascending aorta and superior vena cava to reach the hilum of the right lung. The left pulmonary artery runs anterior to the descending aorta towards the left lung. The ductus arteriosus arises at or just distal to the bifurcation of the pulmonary artery and courses superior to the left pulmonary artery to reach the aorta. The ligamentum arteriosum attaches to the distal aspect of the main pulmonary artery or to the proximal left pulmonary artery.
Anomalies of the Conotruncus
Tetralogy of Fallot (TOF)The "tetralogy" of Fallot consists of a ventricular septal defect (VSD), infundibular pulmonary stenosis, dextroposition of the aorta and right ventricular (RV) hypertrophy.2 Actually, this complex anomaly appears to be due solely to deficient growth of the subpulmonary infund i b~l u m .~ Normally, the infundibular septum fills the space between the two limbs of the septal band. In TOF, however, the infundibular septum is displaced anteriorly and superiorly making contact only with the superior ramus of the septal band (that is, malaligned with respect to the interventricular ~e p t u m ) .~The resulting VSD is simply the unoccupied space bet...
