Tetralogy of Fallot

Cyanotic Heart Defect

Cyanotic disorder with decreased pulmonary blood flow

1. Tetralogy of Fallot (TOF)

Most complex congenital heart defect with decrease pulmonary blood flow, include combination of 4 defect.

a. Ventricular septal defect; opening between left and right ventricle.

b. Overriding of aorta; displacement of aorta over ventricular septal defect.

c. Pulmonary stenosis; narrowing of pulmonary valve.

d. Right ventricular hypertrophy; thickening wall of right ventricle.

Pathophysiology 

Systemic circulation into right atrium and then reaches the right ventricle.

The outflow of blood from right ventricle to lung is restricted due to pulmonary stenosis.

Leading right ventricular hypertrophy

Pressure in right ventricle increases due to severe pulmonary stenosis - blood starts shunting right to left through ventricular septal defect.

Unoxygenated blood mixes with oxygenated blood because of pulmonary stenosis, blood flow to lung reducing.

Unoxygenated blood reaching in systemic circulation ( through overriding aorta) increases.

Leading to cyanosis.

Body attempts to compensate for unoxygenated blood by developing polycythemia, resulting increase viscosity of blood causes slowing of circulation and may causes - 

Thrombophlebitis; inflammation of wall of vein associated with thrombosis.

Emboli

Cerebrovascular disease

Clinical features

1. Symptoms seen in Tetralogy of Fallot is cyanosis.

Degree of cyanosis depends on severity of pulmonary stenosis.

2. Infant with mild pulmonary stenosis; pink at rest

Cyanosed on crying or during a activity.

3. In severe obstruction, cyanosis occur even at rest.

Infant skin become dusky or bluish

4. Clubbing of finger and toe nails occur by 1-2 years of age.

5. Excercise causes dyspnea

Squatting position; relieve dyspnea

6. Tett spells 

Paroxysmal dyspenic attacks 

Infant become dyspenic, restless, cyanotic and gasp for breath.

Prolonged episodes lead to - unconsciousness, convulsions

Dyspenic and cyanotic spells, result in hypoxia and acidosis

5. Failure to thrive

Diagnostic evaluation

1. Cardiac examination

Harsh systolic murmur

2. Electrocardiogram

Right ventricular hypertrophy; present in ECG

3. Chest radiograph

Boot- shaped heart seen due to right ventricular hypertrophy.

Pulmonary artery small and aorta is larger than normal. Right aortic arch seen ( arch of aorta turns into right instead of left).

Due to reduced or diminished pulmonary blood flow hilar areas of lung appear clear.

4. Echocardiography

With color flow 2D echo and continuous wave Doppler; VSD, overriding aorta and pulmonary stenosis visualized.

5. Cardiac catheterization

Shows systolic hypertension in right ventricle with rapid fall in pressure as catheter goes into pulmonary artery.

Therapeutic Management

1. Place infant/ child; knee chest position

Enhance systemic venous return which helps to dilate right ventricles, decreasing right ventricular pressure leading to right to left shunting.

2. Propanol

Administer dose of 1mg/kg body weight; 4 times in a day

(Reduce pulmonary artery and valve spasm)

3. Intravenous prostaglandin E1 Therapy

Given to neonated with TOF.

Helps in keeping ductus arteriosus patient.

Increasing pulmonary blood flow 

Improving systemic arterial blood oxygenation.

Surgical Management

1. Palliative surgery

a. Blalock- taussing shunt

Create pathway for blood to reach lung.

In older infants and children- artificial ductus created by connecting right or left subclavian artery to pulmonary artery of same side.

Allows increased blood flow to lungs

Performed through lateral thoracotomy incision.

b. Pott's procedure

Upper descending aorta is anastomosed with left pulmonary artery.

c. Waterston shunt

Involve side to side anastomosis of ascending aorta with right pulmonary artery.

d. Brock's procedure

Pulmonary valvotomy done to correct pulmonary stenosis.

Surgery increases pulmonary blood flow but not correct ventricular septal defect.

2. Corrective surgery

Total correction of TOF is done using circulatory arrest under deep hypothermia for young infants and heart-lung machine for older children.

a. Patch closure of ventricular septal defect (VSD).

b. Pulmonary valvotomy for pulmonary stenosis.

c. If pulmonary stenosis is severe;

Hemograft conduit is placed from right ventricle to pulmonary artery to bypass the obstruction.

Post operative complications

Complication of total repair include- 

1. Conduction abnormalities

2. Residual ventricular septal defect

3. Residual pulmonary stenosis

4. Pulmonary valve regurgitation