Review Question - QID 105490

Squatting in an attempt to relieve distress is most commonly seen with Tetralogy of Fallot.

The primary features of Tetralogy of Fallot follow the mnemonic PROV: P) Pulmonary stenosis, R) Right ventricular hypertrophy, O) Overriding aorta, and V) Ventricular septal defect. The pulmonary stenosis can be thought of as a right ventricular outflow obstruction, and thus in the presence of a VSD, blood is preferentially shunted from the right to the left heart. In bypassing the lungs, this deoxygenated blood causes cyanosis. During "Tet spells", shunting is exaggerated and causes distress, which the child learns to remedy by squatting. Squatting increases the peripheral vascular resistance, mitigating the pressure differential between the left and right outflow tracts, thereby increasing the blood flow through the pulmonary artery. While this decreases the shunting and improves the oxygen saturation of the systemic blood, the increased volume of blood through the stenotic pulmonary artery increases the intensity of the murmur.

Saenz et al. describe the signs and symptoms that should raise suspicion for congenital heart disease: difficulty feeding, feeding lasting longer than 30 minutes, tachypnea, sweating, subcostral retractions, and cyanosis. They further specifically describe the clinical presentation of a "Tet spell" as characterized by hyperpnea, irritability, cyanosis, and decreased murmur intensity. During the spell itself, there is increased shunting hence the cyanosis and diminished murmur. While squatting is effective at immediately diminishing the cyanosis, most children with Tetralogy will eventually undergo a multi-stage surgical repair by the age of four.

Bailliard et al. describe the diagnostic tests most helpful in determining a diagnosis of Tetralogy: chest radiograph, electrocardiogram, and echocardiogram. Echocardiogram is the preferred method as it is not only definitively diagnostic but provides useful information towards which surgical approach is most appropriate. The refinement of fetal screening and echocardiography has led approximately half of all Tetralogy to be diagnosed antenatally.

Illustration A depicts a heart with Tetralogy of Fallot. A) Pulmonary stenosis (i.e. right ventricular outflow obstruction), B) Overriding aorta, C) Ventral septal defect, D) Right ventricular hypertrophy.

Incorrect Answers:
Answers 1 and 2: The murmur of either an ASD or a VSD could be expected to increase with increased PVR, but neither would be expected to cause cyanosis in the absence of pulmonary hypertension. Moreover, squatting would be expected to exacerbate instead of mitigate symptoms.
Answers 4 and 5: A child with TGA would not be expected to survive to 30 months without intervention. Moreover, children with TGA are ductus dependent, which would cause a constant instead of isolated systolic murmur.