in patients with an interatrial communication have been suggested The most widely accepted explanation postulates a reciprocal relationship of changes in pulmonary and systemic venous return with respiration.46 The murmurs associated with an atrial septal defect are typically soft They may be absent in infancy and early childhood, explaining the relative lateness of diagnosis in most individuals It is extremely uncommon for a murmur to arise at the site of the interatrial communication itself, since there is usually little or no gradient across it Instead, the murmurs are generated by rapid blood flow through the right heart and the pulmonary arterial bed Almost all individuals with a clinically recognizable atrial septal defect have a systolic ejection murmur at the high left sternal border, which is related to rapid flow across the pulmonary valve The murmur is usually soft, and a murmur of greater than grade 3 to 6 should suggest the possibility of accompanying pulmonary valve or artery stenosis Most individuals with a large left-to-right shunt through an interatrial communication also have a soft mid-diastolic murmur at the lower left sternal border This murmur is always subtle and is almost never recognized unless specifically listened for The murmur is that of relative tricuspid stenosis and is generated by rapid flow across a normal tricuspid valve Unlike the murmur of organic or relative mitral stenosis, this murmur is not low-pitched and rumbling Rather, it is of medium pitch and is often scratchy The physical findings associated with an interatrial communication are completely different when there is pulmonary vascular disease With an increase in right ventricular pressure, the left parasternal lift may become more pronounced The width of splitting of the second heart sound decreases47 and the intensity of the pulmonary component increases in intensity in proportion to the degree of elevation of pulmonary artery diastolic pressure If pulmonary hypertension is severe, new murmurs of pulmonary and tricuspid regurgitation may occur The murmur of hypertensive pulmonary regurgitation is typically high-pitched and decrescendo, being maximal at the high and middle left sternal border This murmur is usually clinically indistinguishable from the murmur of aortic regurgitation unless the second heart sound is widely split, and it can be appreciated that the diastolic murmur begins with the second pulmonary component The murmur of tricuspid regurgitation is high-pitched and systolic; it is usually maximal at the lower left sternal border It may be either early or pansystolic, and it may increase in intensity with inspiration, a feature known as the Carvallo sign.48 Investigations and Diagnosis Electrocardiography Normal sinus rhythm is the rule in childhood, but atrial flutter or fibrillation is seen with increasing frequency after 40 years of age The morphology of the P wave is usually normal in oval fossa defects, but one review demonstrated that the frontal plane axis of the P wave was less than 15 degrees in nearly half of sinus venosus defects, suggesting a low atrial focus.49 In children with deficient atrial septation, the frontal plane QRS axis is almost always in the range from 90 to 170 degrees, but in the adult the axis may shift leftward to the range of 70 to 90 degrees Although left-axis deviation occurring in the setting of an atrial shunt strongly suggests the presence of an ostium primum defect, approximately 5% of those with oval fossa and sinus venosus defects have this axis.26,49 Mild to moderate right ventricular hypertrophy is present in more than five-sixths of patients and is usually manifested by an RSR′ pattern, or “crochetage,” in the right precordial and inferior leads, respectively (see Fig 29.1) The R or R′ wave rarely exceeds 15 mm unless there is significant elevation of pulmonary vascular resistance and pulmonary arterial pressure.14,33 The QRS duration is either normal or mildly prolonged, rarely exceeding 0.11 second Complete right bundle branch block is very rare in childhood but occurs in nearly half of these patients older than 60 years.32 Radiology The chest radiograph shows mild to moderate cardiomegaly in most patients, but up to 17% have a heart of normal size even in the presence of a large left-to-right shunt.33,50 Irrespective of whether or not the heart is enlarged, there is almost always an abnormal contour as well as a large right atrium, right ventricle, and pulmonary trunk and a diminutive aorta (see Fig 29.2) Pulmonary vascular markings are usually increased when the ratio of pulmonary-to-systemic flow is 2 to 1 or greater, but the vascularity correlates poorly with the magnitude of the shunt.51 Once pulmonary vascular disease develops, the typical findings of Eisenmenger syndrome may be present, with aneurysmal dilation of the proximal pulmonary arteries and distal tapering of the vessels In patients with a sinus venosus defect, there may be localized dilation of the proximal superior caval vein at the entrance of the anomalous pulmonary veins, giving the appearance of a higher-than-normal vascular pedicle in the right hilum In most patients with this type of defect, the radiologic findings are identical to those of a typical defect within the oval fossa Echocardiography Echocardiography, particularly when combined with Doppler studies, has proved to be diagnostic in the majority of patients with interatrial communications These techniques allow accurate assessment of the size and location of the defect, as well as the degree of right ventricular volume overload Both the Mmode and cross-sectional echocardiogram are useful in detecting the most significant hemodynamic effect of an important atrial shunt, namely right ventricular enlargement (Fig 29.14) The classic M-mode echocardiographic findings are nearly always present when there is a large left-to-right shunt Right ventricular dimensions are increased, and there is frequently flattened or paradoxic septal motion (Fig 29.15).52–55 Several parameters have been used to judge the magnitude of left-to-right shunting,56,57 but given the decreasing reliance on an exact shunt calculation in clinical decision-making, these are rarely used in day-to-day practice FIG 29.14 Parasternal short-axis section at the level of the left ventricular (LV) papillary muscles The cavity of the right ventricle (RV) is significantly enlarged in the setting of a moderate-sized oval fossa defect