Laboratory Studies
Cyanotic conditions may be associated with elevations in red cell volume reflected in the hemoglobin and hematocrit. This elevation is a reactive process to the body's demand for oxygen and is not a primary polycythemia. CBC count, clotting profile, renal function, and ferritin and uric acid levels should be measured.
Imaging Studies
Echocardiography either in utero or by transthoracic or transesophageal imaging generally confirms the diagnosis (see following images).
Subcostal view of a 1-year-old child with L-transposition of the great arteries, valvular and subvalvular pulmonic stenosis, and a moderate outlet ventriculoseptal defect (VSD). Note the ventriculoarterial discordance. Note the posterior, rightward position of the pulmonary artery. [PA = pulmonary artery, LV = left ventricle, RV = right ventricle].
Apical image revealing atrioventricular discordance. Note the pulmonary venous return into the left atrium, with sequential flow through the tricuspid valve to the right ventricle. The right ventricle is systemic. [LA = left atrium, RA = right atrium, LV = left ventricle, RV = right ventricle].
Chest radiography reveals parallel great vessels. The upper left heart border is formed by the aorta and appears straight, and the pulmonary artery knob is absent because of the rightward, posterior displacement of the artery.
Transesophageal echocardiography (TEE) may be needed to assess ventricular function, AV valve regurgitation, and pulmonary outflow tract if this information is not provided by transthoracic imaging, particularly in the patient who has undergone an operation.
Nuclear cardiology assessment of ventricular function may be indicated. Radionuclide angiography usually better reports right ventricular function compared with echocardiography.
Cardiac magnetic resonance imaging (MRI) evaluates ventricular volumes, ventricular function, and valvular or conduit function. It is reasonable (class IIa recommendation) in adults with CCTGA to determine systemic RV dimensions and systolic function. [12]
Other Tests
Electrocardiography is affected by the associated cardiac anomalies but commonly shows AV block, atrial arrhythmias, and abnormal initial ventricular activation due to disordered anatomy of the conduction system. With ventricular inversion, the ventricular bundle branches are inverted and the initial activation is oriented from right-to-left. This results in reversal of the normal Q-wave pattern in the precordial leads such that Q waves are present in the right precordial leads but absent in the left precordial leads. The ECG in patients with congenitally corrected transposition may therefore be misinterpreted as inferior myocardial infarction.
A Holter monitor is used for assessment of AV block and atrial arrhythmias.
Procedures
Cardiac catheterization carries a significant risk of inducing transient or complete heart block. Note the following:
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Use caution. Transient or permanent complete heart block may be induced in this condition because the conduction system lies just below the pulmonic valve.
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Always use a balloon-tipped catheter to approach the pulmonic valve. Always have transvenous pacing capability available during this procedure.
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Limit catheterization to assessment of pulmonic stenosis, shunt volume, pulmonary vascular resistance before and in response to therapy, and angiography in preparation for reparative surgery.
Histologic Findings
Anderson et al identified both a normal-appearing AV node in the usual position without connections to a penetrating bundle and an accessory AV node located in the right atrium at the junction of the mitral valve and the left border of the right atrial appendage. [13, 14] This second AV node connects directly to an aberrantly located penetrating bundle. The bundle passes laterally onto the pulmonary outflow tract just below the pulmonic valve, then descends to the interventricular septum, remaining on the right side of the septum rather than the left side (ie, normal system). The course varies depending on the integrity of the ventricular septum.
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Subcostal view of a 1-year-old child with L-transposition of the great arteries, valvular and subvalvular pulmonic stenosis, and a moderate outlet ventriculoseptal defect (VSD). Note the ventriculoarterial discordance. Note the posterior, rightward position of the pulmonary artery. [PA = pulmonary artery, LV = left ventricle, RV = right ventricle].
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Apical image revealing atrioventricular discordance. Note the pulmonary venous return into the left atrium, with sequential flow through the tricuspid valve to the right ventricle. The right ventricle is systemic. [LA = left atrium, RA = right atrium, LV = left ventricle, RV = right ventricle].
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Post-Rastelli repair with left ventricle to aortic baffle through a ventriculoseptal defect (VSD) complicated by subaortic stenosis.
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This image demonstrates a calcified pulmonary homograft anterior and adjacent to the chest wall (right ventricle to pulmonary artery bifurcation) with significant homograft stenosis and prior pulmonary valvular endocarditis (same patient as in Image 3).
