A cause of cyanotic congenital heart disease. The
tetralogy is composed of a ventricular septal defect, right ventricular
outflow tract (RVOT) obstruction, overriding aorta, and right ventricular
Five to 7% of all congenital heart disease.
Autosomal dominant. Risk for tetralogy of
Fallot in a sibling of the proband is 1%; risk for any congenital heart
disease in a sibling is approximately 3%.
Etiology remains to be defined. The physiological
impact of tetralogy is variable, and dependent primarily on the degree of
obstruction to right ventricular outflow and the size of the ventricular
septal defect (VSD) (usually large). Right ventricular outflow obstruction
may occur below the pulmonary valve, at the valve annulus, or distally as
far as the pulmonary arteries. This obstruction, together with a
nonrestrictive VSD, results in right-to-left shunting of blood and arterial
hypoxemia. Hypoxia, hypercarbia, and acidosis increase pulmonary vascular
resistance and increase right-to-left shunting; similarly, decreases in
systemic vascular resistance increase right-to-left shunting. These factors
are important in the development of “TET” spells (episodes of paroxysmal
hypercyanosis) as is infundibular spasm of the RVOT. However, the precise
etiology of these episodes is unclear.
Clinical history and presentation in neonatal period or
early infancy. Radiographic and echocardiographic findings.
Cyanosis is the predominant sign and tends to be
most severe in the neonatal period, improving up to 2 years of age. Symptoms
include exertional dyspnea; “TET” spells precipitated by crying or feeding
and characterized by shortness of breath, restlessness, occasionally
syncope, and cyanosis. Examination may reveal cyanosis, clubbing, signs of
ventricular failure, a right ventricular heave, a systolic ejection murmur
caused by flow across the obstructed right ventricular outflow and a single
second valve sound (S2). The chest radiography reveals a boot-shaped cardiac shadow and the ECG
shows right axis deviation and right ventricular hypertrophy.
Echocardiography is required to define the cardiac anatomy; a right aortic
arch is present in 20% of cases. Polycythemia is commonly present and
hyperviscosity is a potential problem. Treatment may involve palliative
surgery by a Blalock-Taussig (B-T) shunt or by definitive correction in
early life (now the most common method). Following repair of the tetralogy,
ventricular ectopic beats become more common with time, ventricular
dysrhythmia and supraventricular tachycardia are common (up to 70% of
patients). Right bundle branch block is common and occurs with left anterior
hemiblock in 10% of patients. Right ventricular dysfunction/ failure and
pulmonary hypertension are common following repair, and may be reflected by
decreased exercise tolerance. Patients palliated with a B-T shunt will have
an absent or weak right radial pulse, are polycythemic, and are at increased
risk of intracerebral abscess, cerebrovascular infarction, and bacterial
endocarditis. A 30-year survival rate of 86% following repair was
suggested by one series.
Full history and examination to
elicit frequency and duration of cyanotic episodes; examine for evidence of
ventricular failure. If repaired, note type and date of repair and assess