Patients with cyanotic congenital heart disease have arterial oxygen desaturation resulting from the shunting of systemic venous blood to the arterial circulation. The magnitude of shunting determines the severity of desaturation. Most children with cyanotic heart disease do not survive to adulthood without surgical intervention. In adults, the most common causes of cyanotic congenital heart disease are tetralogy of Fallot61 and Eisenmenger’s syndrome.
Tetralogy of Fallot
Tetralogy of Fallot, the most common cyanotic congenital heart defect after infancy, is characterized by a large ventricular septal defect, an aorta that overrides the left and right ventricles, obstruction of the right ventricular outflow tract (obstruction may be subvalvular, valvular, supravalvular, or in the pulmonary arterial branches), and right ventricular hypertrophy (Figure 5). Several abnormalities may occur in association with tetralogy of Fallot, including right aortic arch in 25 percent of patients,62,63 atrial septal defect in 10 percent (so-called pentalogy of Fallot),62 and coronary arterial anomalies in 10 percent.64
Most patients with tetralogy of Fallot have substantial right-to-left shunting and therefore have cyanosis. Because of the large ventricular septal defect, the right and left ventricular pressures are equal. Right-to-left shunting of venous blood occurs because of increased resistance to flow in the right ventricular outflow tract, the severity of which determines the magnitude of shunting. Since the resistance to flow across the right ventricular outflow tract is relatively fixed, changes in systemic vascular resistance affect the magnitude of right-to-left shunting. A decrease in systemic vascular resistance increases right-to-left shunting, whereas an increase in systemic resistance decreases right-to-left shunting.
Most patients with tetralogy of Fallot have cyanosis from birth or beginning in the first year of life. In childhood, such patients may have sudden hypoxic "spells," characterized by tachypnea and hyperpnea, followed by worsening cyanosis and, in some cases, loss of consciousness, seizures, cerebrovascular accidents, and even death.65 Such spells do not occur in adolescents or adults. Adults with tetralogy of Fallot have dyspnea and limited tolerance of exercise. They may have complications of chronic cyanosis, including erythrocytosis, hyperviscosity, abnormalities of hemostasis, cerebral abscesses or stroke, and endocarditis.66,67 Without surgical intervention, most patients die in childhood: the rate of survival is 66 percent at 1 year of age, 40 percent at 3 years, 11 percent at 20 years, 6 percent at 30 years, and 3 percent at 40 years.68
Patients with tetralogy of Fallot have cyanosis and digital clubbing, the severity of which is determined by the degree of obstruction of the right ventricular outflow tract. The peripheral pulses are normal. A right ventricular lift or tap is palpable. In some patients, a systolic thrill (caused by turbulent flow across the right ventricular outflow tract) is palpable. The first heart sound is normal, but the second heart sound is single, since its pulmonary component is inaudible. An aortic ejection click (due to a dilated, overriding aorta) may be heard. A systolic ejection murmur, audible along the left sternal border, is caused by the obstruction of right ventricular outflow. The intensity and duration of the murmur are inversely related to the severity of the obstruction of right ventricular outflow; a soft, short murmur suggests that severe obstruction is present.
The electrocardiogram shows right-axis deviation and right ventricular hypertrophy. On radiography, the size of the heart is normal or small, and lung markings are diminished. The heart is classically "boot-shaped," with an upturned right ventricular apex and a concave main pulmonary arterial segment. A right-sided aortic arch may be present. Arterial oxygen desaturation is evident, as is compensatory erythrocytosis, the magnitude of which is proportional to the severity of the desaturation.
Echocardiography can be used to establish the diagnosis,69 as well as to assess the presence of associated abnormalities, the level and severity of the obstruction of the right ventricular outflow tract, the size of the main pulmonary artery and its branches, and the number and location of ventricular septal defects.70 Right-to-left shunting through the ventricular septal defect can be visualized by color Doppler imaging, and the severity of right ventricular outflow tract obstruction can be determined by spectral Doppler measurement. With catheterization, it is possible to confirm the diagnosis and obtain additional anatomical and hemodynamic data, including the location and magnitude of right-to-left shunting, the level and severity of right ventricular outflow obstruction, the anatomical features of the right ventricular outflow tract and the main pulmonary artery and its branches, and the origin and course of the coronary arteries.71 Magnetic resonance imaging can also provide much of this information.72,73,74
Surgical repair is recommended to relieve symptoms and to improve survival. Previously, infants underwent one of three palliative procedures to increase pulmonary blood flow (all three involve anastomosis of a systemic artery to a pulmonary artery), thereby reducing the severity of cyanosis and improving exercise tolerance. These procedures are the Waterston operation (a side-to-side anastomosis of the ascending aorta and the right pulmonary artery), the Potts operation (a side-to-side anastomosis of the descending aorta to the left pulmonary artery), and the Blalock–Taussig operation (end-to-side anastomosis of the subclavian artery to the pulmonary artery). Often, however, these procedures were associated with long-term complications, such as pulmonary hypertension, left ventricular volume overload, and distortion of the pulmonary arterial branches.75
Currently, complete surgical correction (closure of the ventricular septal defect and relief of right ventricular outflow obstruction) is performed when patients are very young.76,77 The mortality associated with surgery is less than 3.0 percent in children76,78 and 2.5 to 8.5 percent in adults.79,80 At present, palliative shunting or balloon pulmonary valvuloplasty is performed only in severely ill infants for whom complete repair is unsuitable (e.g., those with underdeveloped pulmonary arteries).81 These procedures increase pulmonary blood flow and allow the pulmonary arteries to enlarge so that corrective surgery may be undertaken at a later time. Patients with tetralogy of Fallot (either repaired or unrepaired) are at risk for endocarditis and should therefore receive prophylaxis with antibiotics before dental or elective surgical procedures.
Although patients with repaired tetralogy of Fallot are usually asymptomatic, their survival is somewhat poorer than that of an age-matched control population, because of an increased risk of sudden death (presumably from cardiac causes).82,83 In one series,82 the rate of survival 32 years after surgery was 86 percent among patients with repaired tetralogy and 96 percent in an age-matched control population. Ventricular arrhythmias can be detected with Holter monitoring in 40 to 50 percent of patients with repaired tetralogy of Fallot84 and are most likely to occur in patients who are older at the time of surgical repair85 and those with moderate or severe pulmonary regurgitation,86 systolic and diastolic ventricular dysfunction,87 prolonged cardiopulmonary bypass,84 or prolongation of the QRS interval (to >180 msec).88 Patients with repaired tetralogy of Fallot often have atrial fibrillation or flutter, which may cause considerable morbidity.89
Patients with repaired tetralogy of Fallot are at risk for other chronic complications. Pulmonary regurgitation may develop as a consequence of surgical repair of the right ventricular outflow tract.86,90 Although even substantial regurgitation can be tolerated for long periods, enlargement of the right ventricle eventually occurs, with resultant right ventricular dysfunction, and repair or replacement of the pulmonary valve may be required.91 An aneurysm may form at the site where the right ventricular outflow tract was repaired. Although such aneurysms are usually identified incidentally, rupture has been reported in rare cases.92
Alternatively, patients may have residual or recurrent obstruction of the right ventricular outflow tract, requiring repeated surgery. Approximately 10 to 20 percent of patients with repaired tetralogy of Fallot have residual ventricular septal defects, and such patients may require repeated surgery if the defects are of sufficient size. Right bundle-branch block is common after repair of tetralogy of Fallot, but complete heart block is rare. Finally, aortic regurgitation may occur but is usually mild.
Source: The New England Journal of Medicine, vol 342 no.5, pp 334-342, February 2000
