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asynchronous closure of the valvar leaflets or production of a duplicate sound by vibrations within the arterial trunk In most infants, there will also be a loud ejection click, heard best at the apex, which coincides with the opening of the truncal valve There is often an ejection systolic murmur heard maximally at the mid-to-upper left sternal border, or a harsh pansystolic murmur maximally at the lower left sternal border Less common murmurs include the apical mid-diastolic murmur, which results from flow, and an early diastolic murmur heard maximally along the left sternal edge, indicating truncal valvar insufficiency Surprisingly, in perhaps one-tenth of patients, no murmur is heard at all at the time of presentation This indicates an absence of turbulence within the ventricles or their outflow tracts Electrocardiography Sinus rhythm is usual, and conduction through the heart is similarly normal The QRS axis is extremely variable and nonspecific but is almost always directed inferiorly The distribution of ventricular forces is also variable, reflecting the variability encountered in ventricular hypertrophy The majority of patients show evidence of combined ventricular hypertrophy, with isolated right ventricular hypertrophy also a frequent finding It is unusual to find evidence of isolated left ventricular hypertrophy or a normal pattern Inversion of the T waves is sometimes seen in the left precordial leads, probably reflecting the impaired coronary arterial diastolic flow Radiologic Features The chest radiograph shows significant cardiomegaly, with an increase in pulmonary vascular markings (Fig 40.9) The aortic arch is right sided in approximately one-third of patients This finding, in association with increased pulmonary vascularity, is strongly suggestive of common trunk It may be possible to see an unusually high origin of the left pulmonary artery with no intervening confluent pulmonary arterial segment Although the truncal root itself is dilated, the arterial pedicle tends to appear narrow simply because of its commonality When flow of blood to the lungs is decreased, the heart is less enlarged and the pulmonary vascular markings are closer to normal Pronounced discrepancy between the vascular markings on the two sides suggests unilateral atresia, or absence, of one pulmonary artery FIG 40.9 Chest radiograph obtained from a 4-week-old infant with common arterial trunk, demonstrating increased pulmonary vascular markings Echocardiography It is possible in most instances to evaluate patients with such precision that only cross-sectional echocardiography is required prior to corrective surgery.27 The goals of echocardiography are to define the ventricular origin and pattern of branching of the common arterial trunk, to determine the morphology and any functional abnormalities of the truncal valve, to exclude any stenosis at the origins of the pulmonary arteries, to distinguish a perimembranous ventricular septal defect from one with a muscular posteroinferior rim, to exclude any abnormalities of the aorta, and to define all other associated lesions The parasternal long-axis cut of the left ventricle will usually show the common arterial trunk overriding the ventricular septum, with its valve forming the superior border of the ventricular septal defect (Fig 40.10) This feature, of course, is lacking when the trunk has a univentricular origin If the pulmonary arteries have a confluent segment, it will be seen arising posteriorly from the common trunk in this view The leaflets of the truncal valve are frequently dysplastic and occasionally prolapse, causing the ventricular septal defect to be restrictive Indeed, the leaflets may occasionally coapt directly on the crest of the ventricular septum Color flow Doppler interrogation will demonstrate flow to the aorta from both the right and left ventricle and will document any truncal insufficiency FIG 40.10 Echocardiographic image from a parasternal window demonstrating the long axis of the heart There is a common arterial trunk (Tr), which overrides the crest of the muscular ventricular septum LV, Left ventricle, RV, right ventricle
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