interrogation using continuous wave Doppler identifies both systolic and diastolic flow immediately distal to the site of stenosis Suprasternal sections can also be used to identify the origin of the pulmonary arteries from the common trunk (Video 40.11) These cuts, in addition, will demonstrate any interruption of the aortic arch, the side of the aortic arch, and additional anomalies such as presence of an arterial duct or aortic coarctation Retrograde diastolic flow is observed quite frequently in the aortic arch, reflecting the low diastolic pressure in the pulmonary arteries FIG 40.14 Oblique image of the heart taken from a subcostal window demonstrating the truncal valve overriding a ventricular septal defect (asterisk) and the origin of the left pulmonary artery (LPA) FIG 40.15 Oblique image of the heart taken from a subcostal window demonstrating the truncal valve and the origin of the common pulmonary artery (PA), in a patient with common arterial trunk (Tr) of the type I variety FIG 40.16 Oblique image of the heart taken from a subcostal window demonstrating the right (RPA) and left (LPA) pulmonary arteries It was considered that this patient may have had a short segment of common pulmonary artery FIG 40.17 Oblique image of the heart taken from a subcostal window demonstrating the arterial trunk, the origin of the pulmonary artery from it, and the integrity of the aortic arch FIG 40.18 Image of the heart taken from a subcostal window with anterior angulation of the transducer The origins of the right (RPA) and left (LPA) pulmonary arteries are widely separated, and the origin of the left pulmonary artery is hypoplastic Color mapping demonstrates mild regurgitation of the truncal valve (asterisk) It is not unusual for interruption of the aortic arch to be associated with common arterial trunk, often in combination with significant dysplasia of the truncal valvar leaflets producing insufficiency and/or stenosis Almost always the ascending aorta is relatively hypoplastic, being smaller than the proximal pulmonary arteries, with the common trunk itself showing pulmonary dominance The interruption can occur at any of the classical sites At the time of