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Treatment

Tet spells

Tet spells may be treated with beta-blockers such as propranolol, but acute episodes require rapid intervention with morphine or intranasal fentanyl to reduce ventilatory drive, a vasopressor such as phenylephrine, or norepinephrine to increase systemic vascular resistance, and IV fluids for volume expansion.

Oxygen (100%) may be effective in treating spells because it is a potent pulmonary vasodilator and systemic vasoconstrictor. This allows more blood flow to the lungs by decreasing shunting of deoxygenated blood from the right to left ventricle through the VSD. There are also simple procedures such as squatting and the knee chest position which increase systemic vascular resistance and decrease right-to-left shunting of deoxygenated blood into the systemic circulation.

If the spells are refractory to the above treatments, people are usually intubated and sedated. The treatment of last resort for tet spells is extracorporeal membrane oxygenation (ECMO) along with consideration of Blalock Taussig shunt (BT shunt).

Total surgical repair

Total surgical repair of TOF is a curative surgery. Different techniques can be used in performing TOF repair. However, a transatrial, transpulmonary artery approach is used for most cases. The repair consists of two main steps: closure of the VSD with a patch and reconstruction of the right ventricular outflow tract.

This open-heart surgery is designed to relieve the right ventricular outflow tract stenosis by careful resection of muscle and to repair the VSD. Additional reparative or reconstructive surgery may be done on patients as required by their particular cardiac anatomy.

Timing of surgery in asymptomatic patients is usually between the ages of 2 months to one year. However, in symptomatic patients showing worsening blood oxygen levels, severe tet-spells (cyanotic spells), or dependence on prostaglandins from early neonatal period (to keep the ductus arteriosus open) need to be planned fairly urgently

Potential surgical repair complications include residual ventricular septal defect, residual outflow tract obstruction, complete atrioventricular block, arrhythmias, aneurysm of right ventricular outflow patch, and pulmonary valve insufficiency. Long-term complications most commonly include pulmonary valve regurgitation, and arrhythmias.

Total repair of tetralogy of Fallot initially carried a high mortality risk, but this risk has gone down steadily over the years. Surgery is now often carried out in infants one year of age or younger with less than 5% perioperative mortality. Post surgery, most patients enjoy an active life free of symptoms. Currently, long-term survival is close to 90%. Today the adult TOF population continues to grow and is one of the most common congenital heart defects seen in adult outpatient clinics.

Palliative surgery

Initially surgery involved forming a side to end anastomosis between the subclavian artery and the pulmonary artery -i.e a systemic to pulmonary arterial shunt. This redirected a large portion of the partially oxygenated blood leaving the heart for the body into the lungs, increasing flow through the pulmonary circuit, and relieving symptoms. The first Blalock-Thomas-Taussig shunt surgery was performed on 15-month-old Eileen Saxon on November 29, 1944 with dramatic results.

The Potts shunt and the Waterston-Cooley shunt are other shunt procedures which were developed for the same purpose. These are no longer used.

Currently, palliative surgery is not normally performed on infants with TOF except for extreme cases. For example, in symptomatic infants, a two-stage repair (initial systemic to arterial shunt placement followed by total surgical repair) may be done. Potential complications include inadequate pulmonary blood flow, pulmonary artery distortion, inadequate growth of the pulmonary arteries, and acquired pulmonary atresia.

Complications

Short Term Complications

Residual ventricular septal defects and persistent right ventricular outflow blockage are common problems in the immediate postoperative period. Arrhythmias such as ventricular tachycardia, atrial fibrillation/flutter, and intra-atrial re-entrant tachycardia can occur after tetralogy repair. With broad complex tachycardia, the ECG will likely show a right bundle branch block or left bundle branch block patterns. Patients who have had their hearts repaired may experience sudden cardiac death. Risk factors for tachyarrhythmias and sudden cardiac death include:

• Age (at repair)
• Male gender
• Transient complete heart block beyond post operative day three
• QRS duration greater than 180 milliseconds

Long-Term Complications

Adult patients with congenital cardiac disease are on the rise at a rate of about 5% per year, outpacing the pediatric population.  Right ventricular volume overload form pulmonary insufficiency, right ventricular aneurysm from outflow patch or ventriculotomy, distal pulmonary artery obstruction, ventricular hypertrophy, chamber enlargement, biventricular dysfunction, and aortic root dilation and insufficient are all long-term complications seen in these patients. Arrhythmia, heart failure, and complications from reoperations are the three primary causes of death in individuals with corrected tetralogy of Fallot. QRS duration greater than 180 milliseconds, older age at repair (greater than 3 years), significant pulmonary valve or tricuspid valve regurgitation, history of syncope, multifocal premature ventricular contractions, and ventricular tachycardia are some of the factors associated with sudden death after 30 years of procedure. Pulmonary insufficiency is the most common reason for reoperation, and pulmonary valve replacement criteria have traditionally been based on the severity of the regurgitant fraction on a magnetic resonance or CT scan. Right and left ventricular end-systolic and end-diastolic volume indices, ejection fractions, and the existence of aneurysm generating obstructive outflow are all parameters seen in this research. Exercise intolerance, heart failure signs and symptoms, syncope, and prolonged ventricular tachycardia are all possible symptoms. A transcatheter pulmonary valve method can also be used to replace a pulmonary valve.

Pregnancy Complications

In comparison to the general obstetric population, women who had their tetralogy of Fallot repaired completely have similar outcomes. The degree of pulmonary regurgitation with right or left ventricular dysfunction, as well as the level of pulmonary hypertension, are linked to an increased risk of pregnancy complications. Fetal death is more likely in women who have moderate right ventricular hypertension or who have undergone a palliative shunt. In comparison to 0.8 percent of the general population, offspring of women with tetralogy have a 3 percent to 5 percent chance of developing congenital cardiac disease. If the 22q11 deletion is present, there is a 50% chance of transferring the damaged chromosome, with a high risk of a congenital cardiac abnormality.

Diagnosis

A CXR (Chest X-Ray) of a child with tetralogy of Fallot

There are three different useful diagnostic tests used for the diagnosis of Tetralogy of Fallot. These include a chest radiograph, electrocardiogram, and echocardiogram. The echocardiography determines the final diagnosis and typically offers enough information for surgical treatment planning. About half of all patients are now diagnosed before they are born.

Chest Radiograph

Before more sophisticated techniques became available, chest x-ray was the definitive method of diagnosis. The abnormal "coeur-en-sabot" (boot-like) appearance of a heart with tetralogy of Fallot is classically visible via chest x-ray, although most infants with tetralogy may not show this finding. The boot like shape is due to the right ventricular hypertrophy present in TOF. Lung fields are often dark (absence of interstitial lung markings) due to decreased pulmonary blood flow.

Electrocardiogram

Electrocardiography shows right ventricular hypertrophy (RVH), along with right axis deviation. RVH is noted on EKG as tall R-waves in lead V1 and deep S-waves in lead V5-V6.

Echocardiogram

Congenital heart defects are now diagnosed with echocardiography, which is quick, involves no radiation, is very specific, and can be done prenatally.

Echocardiography establishes the presence of TOF by demonstrating a VSD, RVH, and aortic override. Many patients are diagnosed prenatally. Color Doppler (type of echocardiography) measures the degree of pulmonary stenosis. Additionally, close monitoring of the ductus arteriosus is done in the neonatal period to ensure that there is adequate blood flow through the pulmonary valve.

In certain cases, coronary artery anatomy cannot be clearly viewed using echocardiogram. In this case, cardiac catheterization can be done.

Genetics

From a genetics perspective, it is important to screen for DiGeorge in all babies with TOF.

Related Disorders

The following illnesses have symptoms that are comparable to tetralogy of Fallot. For a differential diagnosis, comparisons between these disorders provides valuable knowledge.

Atrial Septal Defects

Atrial septal defects (ASDs) are a kind of congenital heart abnormality in which a tiny opening exists between the two atria of the heart. The burden on the right side of the heart is increased as a result of these abnormalities, as is the blood flow to the lungs. This leads to excessive blood flow to the lungs and an increased workload on the right side of the heart.

Ventricular Septal Defects

Ventricular septal defects (VSDs) are a kind of congenital heart abnormality in which one of the ventricles is missing. Two atria and one big ventricle are common in infants with congenital abnormalities. Symptoms of these diseases include an unusually high rate of breathing (tachypnea), a blue hue to the skin (cyanosis), wheezing, a rapid heartbeat (tachycardia), and/or an abnormally enlarged liver, which are similar to those of other congenital heart problems (hepatomegaly). VSDs can also lead to a build-up of fluid around the heart, which can lead to congestive heart failure.

Atrioventricular Septal Defect

Atrioventricular septal defect (AVSD) is an uncommon congenital heart condition characterized by faulty development of the heart's septa and valves. Congestive heart failure is common in infants with the entire version of the condition. Fluid builds up in other parts of the body, particularly the lungs. Breathing difficulties may result from pulmonary congestion (dyspnea).

Mitral Valve Stenosis

Mitral valve stenosis is an uncommon cardiac abnormality that can occur at birth (congenital) or develop later in life (acquired). The aberrant narrowing of the mitral valve's opening characterizes this condition.