The majority of young infants presenting with coarctation will have normal right ventricular dominance with extreme right-axis deviation Later, left ventricular hypertrophy supervenes There are early electrocardiographic signs of left ventricular dominance and strain in some infants This has been linked to subendocardial ischemia47 or coexisting aortic stenosis No specific features indicate interruption, although, a prolonged QT interval may be seen secondary to the hypocalcemia of DiGeorge syndrome Echocardiography Echocardiography is the initial diagnostic method of choice in infancy for the evaluation of aortic arch anomalies The aortic arch is best visualized from the suprasternal notch in the superior paracoronal view, revealing details of the entire arch (Fig 45.14) In patients with coarctation, there is most commonly a short, narrowed segment just distal to the left subclavian artery caused by the obstructive shelf projecting into the aorta posteriorly There may be also a longer segment of narrowing involving the isthmus It must be remembered that the apparent anterior shelf often seen on the anterior wall of the aorta is not part of the coarctation but the overlapping point of entry of the duct.48 It is important, especially in infants, to assess the size of the transverse and proximal aortic arch, as it can often be hypoplastic (Fig 45.15) or stenotic This is an important factor in helping to decide on the approach that should be taken for repair In the absence of an arterial duct, the hemodynamic severity of coarctation can readily be assessed by Doppler echocardiography FIG 45.14 Suprasternal echocardiogram showing severe discrete coarctation at the arrow in a neonate (Video 45.2) AAo, Ascending aorta; DAo, descending aorta FIG 45.15 Suprasternal echocardiogram showing hypoplasia of the transverse arch (black arrow) with coarctation seen distally (Video 45.3) AAo, Ascending aorta; BA, brachiocephalic artery; DAo, descending aorta; LPA, left pulmonary artery The spectral recording shows an extension of antegrade flow and a persisting gradient into diastole, the so-called diastolic tail or runoff The spectral recording can be analyzed further49 according to the peak velocity and the half-time of diastolic velocity decay to determine the severity of the coarctation (Fig 45.16) Another useful finding is the carotid-subclavian arterial index, which is the ratio of the diameter of the aortic arch at the left subclavian artery to the distance between the left carotid artery and the left subclavian artery, with a ratio of less than 1.5 being both sensitive and specific for coarctation in infants and neonates.50 In neonates with a patent arterial duct, measurements of ratio of diameters of the isthmus and descending aorta along with the delineation of the posterior shelf and a discrepancy in blood pressure between the limbs has been shown to identify those with coarctation satisfactorily.51 In isolated coarctation, the peak instantaneous pressure drop across the obstruction can be calculated from the peak velocity of the jet by using the simplified Bernoulli equation In the presence of a significant associated obstructive lesion in the left heart, it is necessary to quantify the peak velocity of the jet proximal to the site of coarctation This can often be significantly raised and, if not taken into account by using the expanded Bernoulli equation, the gradient can be significantly overestimated.52 The remaining examination must focus on the possibility of associated malformations, with care taken to assess the mitral and aortic valves accurately Left ventricular mass should be measured and an M-mode assessment of left ventricular shortening fraction should be made It must always be remembered that in the presence of coarctation severe enough to cause low cardiac output, the severity of associated obstructive lesions in the left heart can be underestimated All of these observations must be modified in the presence of an arterial duct When this is large, any gradient across the site of coarctation will be obviated and the pattern of flow altered Under these circumstances, much more reliance is placed on adequate imaging of the stenotic area In experienced hands, the diagnosis of coarctation using Doppler echocardiography can be made with 95% sensitivity and 99% specificity.53