FIG 15.6 Schematic of morbidity attributed to the hemodynamically significant ductus arteriosus (HSDA) as a consequence of pulmonary overcirculation and systemic hypoperfusion IVH, Intraventricular hemorrhage; LCOS, low cardiac output syndrome; NEC, necrotizing enterocolitis; PVL, periventricular leukomalacia (Modified from Teixeira LS, McNamara PJ Enhanced intensive care for the neonatal ductus arteriosus Acta Paediatr 2006;95[4]:394–403.) Diagnosis of a Hemodynamically Significant Arterial Duct Clinical Presentation The classical clinical features include a continuous murmur, hyperactive precordium, bounding pulses, and wide pulse pressure More commonly, a systolic murmur is audible that radiates widely across the precordium and back However, in many of those born prior to term, cardiac auscultation is unremarkable.111 In the first week of life, despite the presence of a large duct, typical clinical signs are often absent Such a situation is widely recognized as the silent duct, most likely due to continued elevation of pulmonary vascular resistance Surfactant, by assisting the natural postnatal fall in pulmonary arterial resistance, has been shown to alter the timing of clinical presentation, specifically, by increasing the volume of the systemic-to-pulmonary shunt, which leads to an earlier clinical presentation.112,113 The existence of a hemodynamically significant but silent duct has been confirmed by cardiac catheterization114,115 and detailed echocardiographic evaluation.116 Such a situation should be suspected in a setting of delayed hypotension during the second and third days, failure of oxygenation, increasing requirements for ventilator support, or metabolic acidosis The infant is more likely to present with both systolic and diastolic hypotension due to the inability of the immature myocardium to compensate for shunting at high volume throughout the cardiac cycle.117,118 Ancillary Tests Although not very sensitive, chest radiography may show cardiomegaly and/or signs of pulmonary congestion, whereas the electrocardiogram may show signs of left atrial or ventricular enlargement.119,120 The latter may be more useful for the identification of subendocardial ischemia secondary to low coronary arterial perfusion pressures in neonates with a large duct,121 although this association has not been formally evaluated Echocardiographic Confirmation of the Hemodynamically Significant Arterial Duct Echocardiography is the primary tool for assessment of the ductus arteriosus Echocardiography confirmation of ductal significance prior to treatment is standard of care in many institutions due to the unreliability of clinical assessment,122 a desire to avoid the side effects of unnecessary medication, and the potential complications of indomethacin administration to neonates with duct dependent circulation (left-sided congenital heart disease [CHD]) The determination of ductal significance using echocardiography involves assessment of size, patterns of transductal flow, systemic and/or end-organ perfusion, and characterization of the degree of volume loading of the heart ▪ The size of the duct is obtained from a suprasternal short-axis view (Fig 15.7A) using two-dimensional or color Doppler A transductal diameter less than 1.5 mm is associated with retrograde or absent postductal aortic diastolic flow.19 A diameter of more than 1.5 mm resulted in a positive likelihood ratio of 5.5 and a negative likelihood ratio of 0.22 for prediction of the need for therapeutic intervention In a prospective study of 116 neonates, transductal diameter was the most accurate echocardiographic marker in predicting clinical and hemodynamic significance.123 However, reliance on a single measurement may lead to error for several reasons First, the measurement of internal ductal diameter may be difficult, even with clear twodimensional images and the measurement using color Doppler may be influenced by gain settings Second, the transductal diameter is not consistent throughout, often with tapering at the pulmonary end, and shunt volume is determined by the smallest diameter which may not be accurately identified depending on the imaging plane and both patient and operator factors Third, the studies investigating the predictive value of ductal diameter were limited by small sample sizes Finally, using an absolute cutoff does not consider the relationship between ductal size and infant size Some studies have proposed indexing ductal and left pulmonary artery (LPA) diameter,124 although this approach may also be questionable, particularly in established shunts A large ductus with high-volume left-to-right shunt may significantly increase flow in the branch pulmonary arteries, and this may result in LPA dilation and reduce the value of indexing