Cardiac catheterization is not necessary in our patient, because our patient's diagnosis has been well defined by the bedside findings and the laboratory assessment, particularly the echocardiographic evaluation.
Echocardiography, however, must identify all of the essential anatomic and hemodynamic information. Cardiac catheterization may be advisable if critical information remains unidentified or unclear. The cardiologist and the surgeon jointly should make this determination. Magnetic resonance angiography can provide valuable information regarding pulmonary artery anatomy. This may be indicated in the infant with more severe tetralogy.
Chronic hypoxemia
These are the measurements obtained at cardiac catheterization in another patient with tetralogy of Fallot, demonstrating findings similar to those expected in our patient. This patient was breathing room air. There are two levels of pressure change between the right ventricle and the pulmonary artery, as indicated by the drop in systolic pressure from 90 to 40 to 15 mmHg. This is characteristic of tetralogy of Fallot in which there are usually obstruction at both the right ventricular infundibulum and pulmonary valve. Systolic pressures in the right and left ventricles are identical, consistent with a large, unrestricted ventricular septal defect. Oxygen saturation data indicates bidirectional shunting. Decrease in saturation of 15% from left atrium to aorta clearly indicates the right-to-left shunt. In addition, however, there is an increase from 65% at the superior vena cava to 70% at the pulmonary artery. With reliable equipment and proper sampling technique, an increase in oxygen saturation of 3% or more is consistent with a left-to-right shunt. The left ventricle normally starts to contract before the right ventricle, thus patients with tetralogy of Fallot often demonstrate a small left-to-right shunt.