Andersons pediatric cardiology 1084

Cardiac Catheterization and Angiography Most cardiologists would not consider catheterization a necessary diagnostic procedure for children with typical clinical findings If it is undertaken, it is usually possible to probe the duct from the pulmonary trunk and to pass a catheter through the vessel and down the aorta When the catheter apparently crosses a duct, but turns in a headward direction, the alert investigator should consider the presence of an aortopulmonary window The size of the shunt may be difficult to quantify by oximetry because it is difficult to obtain a truly representative sample distal to the site of shunting Pulmonary arterial pressure is usually normal or slightly elevated The duct can be visualized by selective aortography with injection of contrast media in the last part of the aortic arch (Fig 41.13) FIG 41.13 Lateral arteriograms showing various ductal anatomies However, therapeutic catheterization is currently the treatment of choice for most children and adults with a patent duct In this regard, complete hemodynamic assessment is important prior to attempting closure, particularly in the adult In patients with an elevated pulmonary arterial pressure, assessment of pulmonary vascular resistance and its response to vasodilating agents may be helpful in determining suitability of closure Assessment of hemodynamics during temporary test occlusion with a balloon catheter may also be a helpful maneuver in assessing advisability of closure in marginal cases.69 Angiography defines the anatomy Such detailed assessment is essential before attempting closure so that the proper device and size can be chosen Important features include the minimal diameter (usually at the pulmonary arterial end), the largest diameter (usually at the aortic ampulla), the length of the duct, and its relationship to the anterior border of the tracheal shadow, the latter helping to guide positioning of the device.40 Other imaging modalities are available to confirm the presence of ductal patency Radionuclide scanning can be used to detect the presence of shunting, but anatomic localization is lacking Magnetic resonance imaging provides anatomic detail70 and is particularly useful in the setting of unusual ductal geometry and in those with associated abnormalities of the aortic arch (Fig 41.14).71,72 Examples include the patient with a ductal aneurysm presenting as a mass in the chest, the duct associated with a vascular ring, a right aortic arch, or cervical arch With velocity encoding of cine magnetic resonance signals, patterns of shunting can be detected.73,74 In the adult, computed tomography can assess the degree of calcification, an important feature if surgical closure is considered However, in general, the simpler technique of cross-sectional echocardiography with color flow Doppler provides sufficient anatomic and hemodynamic detail to define the anatomy and its variations and points the way to proper management FIG 41.14 Volume-rendered magnetic resonance image showing the anatomy of the aortic arch in an infant with hypoplastic left heart syndrome Ductal anatomy (DA) and its relationship to the ascending aorta (AAO, arrow) and left subclavian artery (LSCA) are clearly understood LPA, Left pulmonary artery Diagnostic Problems Other causes of a continuous murmur may create confusion The venous hum often causes difficulty to the inexperienced auscultator This noise, which can be loud, is usually best heard in the supraclavicular fossa, and although audible bilaterally, it is usually louder on the right A venous hum, when loud, may be transmitted below the clavicle and may be misdiagnosed as being from a patent duct This error can be avoided by exerting pressure over the root of the neck, turning the head to the side, or lying the child down These maneuvers readily obliterate the venous hum, while having no effect on the murmur generated by ductal flow An aortopulmonary window rarely causes a continuous murmur similar to that of persistent ductal patency However, more typically the