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At a glance

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 hypertrophy.

History

Named after the French physician Dr Etienne-Louis Arthur Fallot, who described a panel of three cyanotic patients with the above features in 1888.

Incidence

From 5 to 7% of all congenital heart disease.

Genetic inheritance

Autosomal dominant with variable penetrance. Disruption of the balanced interaction of transcription factors important to cardiogenesis plays a significant role in non-syndromic tetralogy of Fallot. 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%.

Pathophysiology

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.

Diagnosis

Clinical history and presentation in neonatal period or early infancy. Radiographic and echocardiographic findings.

Clinical aspects

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 ...

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