Tetralogy of Fallot

Definition and Initial ManagementTop

Tetralogy of Fallot is the most common form of cyanotic congenital heart defect, accounting roughly for ~10% of all congenital heart diseases. The defect is due to the antero-cephalad deviation of the outlet septum, leading to the four features of a nonrestrictive ventricular septal defect (VSD), an overriding aorta, right ventricular outflow tract obstruction (usually infundibular and valvular), and right ventricular hypertrophy. There is a slight male predominance.

Initial Palliative Shunts

Most of the patients who had the initial systemic-to-pulmonary palliative procedures performed had these reversed or closed at the time of definitive repair later in childhood.

Types of palliative shunts:

1) Blalock-Taussig shunt (classic or modified): Anastomosis between the subclavian artery and the pulmonary artery.

2) Waterston shunt: The ascending aorta and the right pulmonary artery are anastomosed.

3) Potts shunt: This is an anastomosis of the descending aorta and the left pulmonary artery.

Surgical Repair in Infancy

Surgical repair is performed in infancy and involves patch closure of the VSD, relief of the right ventricular outflow tract obstruction involving resection of the infundibular muscle, insertion of a transannular patch to augment the outflow, and closure or ligation of the previous palliative shunt.

In individuals who have had transannular patch repair there is usually severe pulmonary regurgitation present in patients with transannular patch repair. Although well tolerated for many years, it can lead to significant right ventricular dilation and dysfunction. There might also be residual obstruction to the right ventricular outflow tract at multiple levels. Many patients will also develop supraventricular arrhythmias (atrial flutter and fibrillation) as a result of the increased right atrial pressures. Of more concern is the development of sustained ventricular tachycardia, the electrical focus of which is usually at the site of infundibulectomy or the VSD patch. Some patients have aortic root and/or ascending aortic dilation with associated significant aortic regurgitation.

Contemporary surgical techniques do not use transannular patch augmentation and try to maintain some integrity of the pulmonary valve to avoid the sequelae of long-term severe pulmonary regurgitation. In patients whose anatomy is not suitable for direct repair (eg, due to an anomalous coronary artery course across the right ventricular outflow tract) an alternative surgical repair such as Rastelli repair (VSD closure and right ventricle to pulmonary artery valved conduit placement) is undertaken. The main issue with these patients in long-term follow-up is conduit stenosis/regurgitation and requirements for periodic interventions in the conduit.

Clinical Features Top

Symptoms: In adulthood many patients are relatively asymptomatic; however, many of these patients have limited their daily activities (subconsciously) and hence may not have significant symptoms. Most adult patients will demonstrate significant abnormalities in objective tests of functional capacity. When patients have symptoms, these will be of dyspnea on exertion and decrease in exercise tolerance. Particular attention should be paid to symptoms of palpitations, presyncope, and syncope, as these might be related to ventricular tachycardia.

Signs: Patients after repair have a previous midline sternotomy scar; those with initial palliation have additional left or right lateral thoracotomy scars. Individuals with previous Blalock-Taussig shunts have an absent (or very faint) radial and/or brachial pulse on the side of the shunt. Blood pressure should be measured in the arm with the normal pulse. Palpation of the precordium usually reveals a right parasternal lift associated with right ventricular enlargement. If a thrill is felt, it may indicate the presence of a VSD patch leak. Auscultation usually reveals a normal first heart sound and often a widely split second heart sound (presence of right bundle branch block [RBBB]). In cases where a transannular patch has been used to augment the right ventricular outflow tract, there usually is very little pulmonary valve tissue present, which is reflected by a single second heart sound (the aortic valve component of the second heart sound only). A right-sided fourth heart sound and third heart sound may be present depending on the function of the right ventricle. A systolic ejection murmur is heard in almost all patients and reflects the flow across the right ventricular outflow tract even in the absence of obstruction. There is also a low-pitched diastolic murmur from pulmonary regurgitation heard along the sternal border. A subgroup of patients develops aortic root/ascending aorta dilatation leading to progressive aortic insufficiency, which can be detected on physical examination.

DiagnosisTop

Diagnostic Tests

1. Electrocardiography (ECG): In the majority of patients, the rhythm is sinus; however, atrial flutter and fibrillation may be seen. RBBB is present in virtually all patients. Particular attention should be paid to the QRS complex duration, as there is a strong correlation between a QRS complex duration >180 milliseconds and the risk of sudden death from arrhythmia. Signs of right ventricular hypertrophy are present, and there may be evidence of right atrium enlargement.

2. Chest radiography reveals evidence of previous sternotomy. The right ventricle is usually enlarged.

3. Echocardiography can assess the size and function of the right ventricle as well as the presence and degree of pulmonary regurgitation and right ventricular outflow tract obstruction. The VSD patch can also be assessed for the presence of patch leaks. In patients after Rastelli repair, evaluation for conduit stenosis and regurgitation can be challenging on echocardiography due to the location of the conduit; often alternative imaging modalities are used for to evaluate the severity of conduit dysfunction. The evaluation of the aortic root and ascending aorta should be part of echocardiographic surveillance in these patients.

4. Cardiac magnetic resonance imaging (MRI): Serial assessment (quantitative) of right ventricular volumes, ejection fraction, and pulmonary regurgitation fraction is performed with cardiac MRI, which is considered the gold standard for evaluating the right ventricle. In individuals with intracardiac devices that are not MRI compatible, gated computed tomography (CT) imaging can provide right ventricular volumetric evaluations. Both MRI and CT should be performed in centers with expertise in congenital heart disease imaging.

Treatment Top

Current recommendations for surgical reintervention (after the initial repair) are aortic valve replacement for severe aortic regurgitation with signs or symptoms of left ventricular dysfunction, pulmonary valve replacement in severe symptomatic pulmonary regurgitation, and severe or symptomatic right ventricular outflow tract obstruction. Pulmonary valve replacement can be considered in patients with asymptomatic but severe pulmonary regurgitation associated with decreased exercise capacity on objective testing; progressive right ventricular dilation, dysfunction, or both; and sustained ventricular tachycardia.

Follow-Up and PrognosisTop

Annual follow-up (clinical evaluation and imaging) in specialized centers is recommended for all patients with tetralogy of Fallot.

The prognosis in patients with repaired tetralogy of Fallot depends on several factors including type of corrective surgery (eg, using transannular patch), associated defects, and age at initial surgery, to name a few. For most adult patients with repaired tetralogy of Fallot, the most important factor that influences prognosis is the degree of pulmonary regurgitation and resultant right ventricular dilatation. Tachyarrhythmias (both atrial and ventricular) have a significant impact on morbidity and mortality. In many patients the development of arrhythmias is directly linked to worsening hemodynamics. For this reason, early evaluation and management of these patients is key.