When hypoxic (Tet) spells occur, they are usually progressive. During a spell, the child typically becomes restless and agitated and may cry inconsolably. An ambulatory toddler may
ASD, Atrial septal defect; AV, atrioventricular; AVM, arteriovenous malformation; PDA, patent ductus arteriosus; VSD, ventricular septal defect.
Figure 144-1 Tetralogy of Fallot. AO, Aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.
squat. Hyperpnea occurs with gradually increasing cyanosis and loss of the murmur. In severe spells, prolonged unconsciousness and convulsions, hemiparesis, or death may occur. Independent of hypoxic spells, patients with unrepaired tetralogy of Fallot are at increased risk for cerebral thromboembolism and cerebral abscesses resulting, in part, from their right-to-left intracardiac shunt.
The electrocardiogram (ECG) usually has right axis deviation and right ventricular hypertrophy. The classic chest x-ray finding is a bootshaped heart created by the small main pulmonaryartery and upturned apex secondary to right ventricular hypertrophy. Echocardiography shows the anatomic features, including the anatomic level and quantification of pulmonary stenosis.Coronary anomalies, most commonly a left anterior descendingcoronary artery arising from the right coronary artery and crossing the anterior surface of the right ventricular outflow tract, arepresent in 5% of patients with tetralogy of Fallot.
The natural history of tetralogy of Fallot is progression of pulmonary stenosis and cyanosis. Treatment of hypoxic spells consists of oxygen administration and placing the child in the knee-chest position (to increase venous return). Traditionally, morphine sulfate is given (to relax the pulmonary infundibulum and for sedation). If necessary, the systemic vascular resistance can be increased acutely through the administration of an α-adrenergic agonist (phenylephrine). The occurrence of a cyanotic spell is an indication to proceed with surgical repair.
Complete surgical repair with VSD closure and removal or patching of the pulmonary stenosis can be performed in infancy. Occasionally, palliative shunt surgery between the subclavian artery and pulmonary artery is performed for complex forms of tetralogy of Fallot and more complete repair is done at a later time. Subacute bacterial endocarditis prophylaxis is indicated until 6 months after complete repair unless there is a residual VSD. Prophylaxis is then continued as long as there is a residual VSD.
Figure 144-2 Transposition of the great vessels. AO, Aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.
Although dextroposed transposition of the great arteries represents only about 5% of congenital heart defects, it is the mostcommon cyanotic lesion to present in the newborn period(Fig. 144-2). Transposition of the great arteries is ventriculoarterial discordance secondary to abnormalities of septationof the truncus arteriosus. In dextroposed transposition, theaorta arises from the right ventricle, anterior and to the rightof the pulmonary artery, which arises from the left ventricle.This results in desaturated blood returning to the right sideof the heart and being pumped back out to the body, whilewell-oxygenated blood returning from the lungs enters the leftside of the heart and is pumped back to the lungs. Withoutmixing of the two circulations, death occurs quickly. Mixing can occur at the atrial (patent foramen ovale/atrial septal defect [ASD]), ventricular [VSD], or great vessel (patentductus arteriosus [PDA]) level.