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Cyanotic congenital heart disease results from any lesion that limits pulmonary blood flow or allows mixing of arterial and venous blood, thereby producing lower systemic saturation. Multiple anatomic conditions can lead to cyanosis (Table 135-1).
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SHUNT LESIONS WITH RIGHT VENTRICULAR OUTFLOW TRACT OBSTRUCTION
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Tetralogy of Fallot (TOF) has four classic findings:
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Ventricular septal defect (VSD),
Right ventricular outflow tract (RVOT) obstruction,
Right ventricular hypertrophy,
Overriding aorta.
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Because of the position of the VSD, the RVOT becomes narrowed. This constriction will limit the amount of blood flow into the pulmonary circulation from the right ventricle (RV). Instead, desaturated blood is shunted from right to left across the VSD, resulting in systemic cyanosis (Figure 135-1).
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Typically, there are two types of RVOT obstruction: a fixed stenosis at or above the pulmonary valve and a dynamic component in the infundibulum below the valve. The infundibular tissue can spasm, causing acute worsening of the obstruction. The overall amount of obstruction will determine the degree of cyanosis. Some patients’ RVOT obstruction will be minimal, with a valve that is mildly hypoplastic, resulting in little to no cyanosis (a “pink tet”). Others will have near fusion of the valve leaflets with severely decreased pulmonary blood flow and severe cyanosis (a “blue tet”). In this case, another shunting lesion such as a patent ductus arteriosus (PDA) is necessary for adequate oxygenation and survival. Most patients fall somewhere between these two extremes of disease.
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TOF is typically diagnosed by echocardiogram (ECG) either prenatally or shortly after birth. On auscultation, there is an ejection murmur along the left sternal border. On chest radiography, the heart is described as boot-shaped, with the right ventricular apex upturned and a concave main pulmonary artery (PA) segment. There are also reduced pulmonary vascular markings.
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Importantly, these patients are subject to hypercyanotic spells, known as “tet spells.” While more likely to occur in patients with more significant cyanosis, all patients can ...