Tetralogy of Fallot
Tetralogy of Fallot is the most common form of cyanotic congenital heart disease. The defect consists of a hole between the right and left ventricle (VSD) in conjunction with an obstruction between the right ventricle and the pulmonary artery (pulmonary stenosis). As a result of these two abnormalities, unoxygenated blood can bypass the lungs, enter the aorta and produce cyanosis.
Most patients with tetralogy of Fallot require cardiac surgery early in childhood. In some instances, the initial operation is a shunt which improves oxygenation and allows the surgeon to delay correction until the pulmonary arteries are larger. Repair of tetralogy of Fallot involves closure of the VSD and relief of obstruction between the right ventricle and the pulmonary artery. Successful surgery eliminates cyanosis, relieves the obstruction between the right ventricle and the pulmonary artery, and improves exercise capacity. Relief of pulmonary valve stenosis produces a leak in the pulmonary valve, referred to as pulmonary regurgitation.
Most adults who were successfully repaired during childhood continue to do well although ongoing follow up with an adult congenital heart disease specialist is important to address potential long term issues such as arrhythmias, right ventricular function, and abnormalities of the pulmonary valve and pulmonary arteries. Pregnancy is generally well tolerated in patients with a satisfactory repair.
Adults with tetralogy of Fallot may experience atrial or ventricular arrhythmias. Atrial arrhythmias arise from the upper chamber of the heart. The most common form seen in patients with tetralogy of Fallot is atrial flutter although atrial fibrillation and other forms of atrial arrhythmias also occur. These arrhythmias can result in heart racing, diminished stamina, dizziness and fluid retention. Restoration of a normal rhythm is generally advised. Treatment modalities may include electrical cardioversion, medications, or catheter ablation.
Ventricular arrhythmias originate from the bottom chamber of the heart. They can be self limited or sustained and in some instances can result in a dangerously rapid heart rate. Treatment depends on the type of arrhythmia but may include medications, radiofrequency ablation and/or an implantable cardioverter defibrillator (ICD). Patients who experience these arrhythmias should be evaluated by cardiologists with expertise in adults with congenital heart disease and arrhythmias.
Assessment of Repair
Periodic assessment of tetralogy of Fallot repair is an important part of the follow up during adulthood. The rationale for follow up is to ensure that any residual abnormalities resulting from childhood repair are appropriately addressed in the adult.
The most common issue in adults following childhood repair concerns the status of the pulmonary valve and the right ventricle. Following repair of tetralogy of Fallot, most patients are left with a leak in their pulmonary valve, known as pulmonary insufficiency. Although this leak is generally well tolerated throughout childhood and adolescence, it can result in progressive enlargement of the right ventricle over time. In many patients, a pulmonary valve replacement may be recommended to eliminate the leak and reduce the size of the right ventricle.
Criteria for pulmonary valve replacement is related to size and function of the right ventricle, exercise capacity, presence of arrhythmias, and other factors. Cardiac MRI is an important tool in the evaluation of the right ventricle, allowing us to quantify the volume and function of the right ventricle and degree of pulmonary regurgitation more accurately than with echocardiography. Cardiac MRI also provides excellent visualization of the pulmonary arteries, and can detect pulmonary artery narrowing which may require treatment with a stent.
When pulmonary valve replacement is required, it is performed with a bioprosthetic valve which avoids the need for anticoagulation and enables the insertion of a catheter valve in the future when the surgical valve needs to be replaced. In some patients, the surgeon may also choose to reduce the size of the right ventricle by revising the RV outflow patch that was created at the time of the initial repair. In addition to the surgical approach for pulmonary valve replacement, catheter replacement of the pulmonary valve can also be performed if the anatomy is suitable. Following a pulmonary valve replacement, there is usually a decrease in the right ventricle size of approximately 30%.
Though less common, other indications for reoperation during adulthood include the presence of significant obstruction between the right ventricle and pulmonary artery, a significant residual VSD, or an important leak in the tricuspid valve (tricuspid regurgitation). In rare instances, surgical replacement of the aortic valve and aortic root may be indicated because of a leak in the aortic valve and marked enlargement of the aorta.
In rare instances, a patient with Tetralogy of Fallot may reach adulthood without repair or by means of a systemic to pulmonary artery shunt. Careful evaluation of these patients will determine whether they may still be candidates for corrective surgery.