Teratology of Fallot (TOF)

Abstract

TOF is one of the most common congenital heart diseases. It is characterized by the presence of four structural defects including (a) RVO obstruction, (b) large VSD, (c) overriding of aorta on VSD, and (d) right ventricular hypertrophy. The etiology of TOF is not fully understood but there are many aspects suspected to contribute in the developing of TOF. These aspects include genetic aspect, embryological aspect, anatomical aspect, and hemodynamic aspect. The severity of clinical features of TOF mainly depends on the severity of RVO obstruction. The clinical features vary with age. In newborn, the patient may be normal or have cyanosis according to the severity of RVO obstruction and patency of ductus arteriosus. In infants, the commonest features are poor feeding and failure to thrive. In older children, the patient may develop severe cyanosis in presence of exacerbating factors including exercise, stress, metabolic (acidosis and dehydration), drugs (beta receptor against), and ductus arteriosus closure. This condition is called “hypercyanotic spell” which is characterized by squatting posture to compensate for the cyanosis. This condition is treated by simple procedure (such as knee-chest posture), beta-agonist, and alpha-adrenergic agonist (phenylephrine). The TOF is diagnosed by (a) clinical features including history and physical examination, (b) laboratory tests including full blood count, coagulation profile, arterial blood gases, and blood culture, (c) ECG, and (d) imaging including CXR, echocardiography, and MRI. There are many differential diagnoses for TOF which may have cyanosis and should be distinguished from TOF. These differential diagnoses include cardiac, respiratory, chest wall, vascular, hematological, and neurological diseases. TOF management depends on many factors including age of the patient, severity of RVO obstruction and clinical features, and presence of complications. The medical treatment for a patient with TOF is unclear to be beneficial and some patients may benefit from afterload—reducing drugs like sildenafil and nitric oxide specifically in those with severe pulmonary insufficiency and pulmonary hypertension. The option of choice for a patient with TOF is surgical treatment but also its not curative. The surgical treatment includes the correction of surgical defects and either replacement or repair of the pulmonary valve. The bioprosthetic valve is preferable to the mechanical valve. The surgery does not eliminate the risk of arrhythmia so some patients may need AICD or radiofrequency ablation. The surgery has many complications which are divided into (a) short-term complications including cardiac tamponade, rebleeding, continuous raising of RV pressure, right ventricular failure, atrial arrhythmia, wound infection, heart block, and residual VSD and (b) long-term complications including continuous RVO obstruction, pulmonary valve sufficiency, both ventricular and atrial arrhythmia, right ventricular failure, and endocarditis. Patient with TOF needs primary and secondary prevention from endocarditis by using prophylactic antibiotics in some invasive procedures. In the long term, the patient may need reoperation or re-replacement of pulmonary valve. The TOF has many complications which are divided into (a) short-term complications including paradoxical emboli and hypercyanotic spell (b) long-term complications including arrhythmias, pulmonary valve regurgitation, CHF, and sudden death.