Investigations Electrocardiography The electrocardiographic features are not specific for ventricular septal defects Instead, they reflect the hemodynamic state In patients with large unrestrictive defects presenting with a high pulmonary blood flow in infancy, there will be a normal sinus rhythm, probably with tachycardia, a frontal QRS axis within the normal range for age, and biventricular hypertrophy Finding a superior axis suggests multiple defects,37 that the lesion is the ventricular component of an atrioventricular septal defect, or that an isolated perimembranous defect with separate atrioventricular junctions excavates extensively to open to the right ventricular inlet Tall upright T waves over the right precordial leads that persist past the first week of infancy strongly suggest that the right ventricular pressure is at systemic levels Cardiac rhythm, and the QRS axis, is usually normal in those with large restrictive defects after the first few months of life The QRS pattern is that of left ventricular dominance, with deep Q waves over the left chest leads indicating left ventricular volume overload The electrocardiogram may be normal in patients with small restrictive defects Serial electrocardiograms provide more prognostic information in the early months of life than does a single tracing Large and unrestrictive defects maintain the biventricular QRS morphology, while the smaller defects show the normal diminution of right ventricular forces with age At any age, the presence of pulmonary vascular disease or severe obstruction to the right ventricular outflow tract is reflected by right without left ventricular hypertrophy and by right axis deviation Should significant aortic regurgitation complicate a small defect or, alternatively, occur in a patient with established obstruction of the right ventricular outflow tract, the changes of left ventricular volume overload will come to dominate the picture Radiology Once more, radiologic findings reflect the hemodynamic state The chest radiograph is usually normal in the first days of life With the development of left-to-right shunting, the lung vascularity become plethoric When flow to the lungs is large, as in unrestrictive defects, cardiomegaly is noted and pulmonary plethora is marked (Fig 32.19) The cardiac contour in such infants has no specific features The lungs tend to be hyperinflated, with flattened diaphragmatic contours Subsegmental or segmental collapse of the lower lobes, particularly the left lower lobe, is often seen A markedly enlarged heart may compress the left main bronchus, causing collapse of the left lower lobe When defects are restrictive, with only mild elevation of the pulmonary flow, the chest radiograph may appear normal FIG 32.19 Frontal (A) and lateral (B) chest radiographs of a 13-week-old infant with a large ventricular defect Note the increased pulmonary vascularity and nonspecific enlargement of the cardiac silhouette The lungs are hyperinflated The development and progression of pulmonary vascular disease is reflected in diminution of the peripheral pulmonary vascular shadows, leading to the classic “pruning” of the peripheral pulmonary arteries, which is seen best in older children and adults This is accompanied by a progressive overall reduction in cardiac size as the flow of blood to the lungs falls, but with characteristic enlargement of the pulmonary knob When obstruction develops in the right ventricular outflow tract, there is a reduction in both central and peripheral pulmonary arterial shadowing, but enlargement of the pulmonary trunk is rare When this is complicated by aortic regurgitation, there will be progressive enlargement of the heart, with the cardiac contour suggesting left ventricular dominance As the prolapsed leaflet or leaflets of the aortic valve reduce the size of the defect or close the defect, there will be a progressive reduction in the prominence of pulmonary vascular markings Echocardiography Cross-sectional echocardiographic examination38–41 is now recognized as the technique of choice for diagnosis,42 demonstrating the precise location and size of the defects, the degree and direction of flow, and the presence of any associated defects Perimembranous defects are recognized in long-axis, fourchamber, and short-axis views, with fibrous continuity between the leaflets of the tricuspid and aortic valves being the pathognomic feature In parasternal short-axis sections, with the aortic valve seen face on, the perimembranous or central component of the ventricular base extends from approximately 9 to 11 o'clock relative to the perimeter of the left ventricular outflow tract In subcostal short-axis sections, when the orifice of the tricuspid valve is seen face on, the perimembranous region is located at the commissure between its anterosuperior and septal leaflets In both of these views as well as the apical three-chamber plane, the fibrous continuity between the leaflets of the tricuspid and aortic valves is easily appreciated (Fig 32.20; Videos 32.1 and 32.2) FIG 32.20 Echocardiographic images demonstrating characteristic features of a perimembranous central ventricular septal defect (VSD) (A) The parasternal short-axis plane demonstrates the defect extending from approximately the 9 to 11 o'clock position relative to the left ventricular outflow tract There is fibrous continuity between the septal leaflet of the tricuspid valve (S) and the aortic valve (AoV) (B) The apical plane angled toward the left ventricular outflow tract again demonstrates the ventricular septal defect with fibrous continuity between the tricuspid and aortic valves This view is often mistaken to represent outlet extension of the ventricular septal defect; however, when it is recognized that the outlet septum is in a