Tetrology of Fallot (TOF)

Tetralogy of Fallot (TOF) is a congenital heart defect which is classically understood to involve four anatomical abnormalities of the heart (although only three of them are always present). It is the most common cyanotic heart defect, and the most common cause of blue baby syndrome.It was described in 1672 by Niels Stensen, in 1773 by Edward Sandifort, and in  1888 by the French physician Etienne-Louis Arthur Fallot, after whom it is named.

Components of Tetrology of Fallot (TOF)

Pulmonary Stenosis                                     Over riding aorta

Right Ventricular Hypertrophy             Ventricular Septal Defect

Quiet cardiac impulse

Systolic thrill, murmur (due to PS-Pulmonary Stenosis)

S₂ loud and Single

Large ventricular septal defect

Pulmonary Stenosis; usually infundibular

Overriding aorta

Right Ventricular Hypertrophy.

History of Tetrology of Fallot (TOF)

Commonest cause of cyanotic heart disease after first year of life.

Cyanotic spells at height of activity often leading to syncope or convulsion

Squatting relieves dyspnoea and cyanosis by increasing systemic vascular resistance there by promoting pulmonary flow and venous return.

Physical Examination of Tetrology of Fallot (TOF)

Stunted growth

Clubbing and cyanosis (central)

Single S2

Harsh systolic ejection murmur of PS in second left intercostal space radiating to left shoulder; VSD is usually silent.

Tetralogy of Fallot results from low oxygenation of blood due to the mixing of oxygenated and deoxygenated blood in the left ventricle via the ventricular septal defect (VSD) and preferential flow of the mixed blood from both ventricles through the aorta because of the obstruction to flow through the pulmonary valve. This is known as a right-to-left shunt. The primary symptom is low blood oxygen saturation with or without cyanosis from birth or developing in the first year of life. If the baby is not cyanotic then it is sometimes referred to as a “pink tet.”Other symptoms include a heart murmur which may range from almost imperceptible to very loud, difficulty in feeding, failure to gain weight, retarded growth and physical development, dyspnea on exertion, clubbing of the fingers and toes, and polycythemia.
Children with tetralogy of Fallot may develop “tet spells.” The precise mechanism of these episodes is in doubt, but presumably results from a transient increase in resistance to blood flow to the lungs with increased preferential flow of desaturated blood to the body. Tet spells are characterized by a sudden, marked increase in cyanosis followed by syncope, and may result in hypoxic brain injury and death. Older children will often squat during a tet spell, which increases systemic vascular resistance and allows for a temporary reversal of the shunt.

Diagnosis of Tetrology of Fallot (TOF)

Normal cardiac size

Small pulmonary artery

Concave upper left heart border

Boot shaped heart

Pulmonary oligemia

Right sided aortic arch in 25 percent cases (also seen in truncus arteriousus, pulmonary atresia with Ventricular Septal Defect (VSD), Transposition of great arteries (TGA)

ECG findings in Tetrology of Fallot (TOF)

RVH (Right Ventricular Hypertrophy)

Laboratory findings in Tetrology of Fallot (TOF)

Reduced arterial oxygen saturation

Polycythemia

Trilogy of Fallot – Pulmonary Stenosis with reversed inter-artrail shunt

Pentalogy of Fallot -Tetralogy + Atrial Septal Defect (ASD)

X- ray findings in Tetrology of Fallot (TOF)

Boot shaped(Couer en sabot),prominent rigft ventricle with decreased pulmonary vascularity

Echo findings in Tetrology of Fallot (TOF)

Helps in defining

Size and location of main pulmonary artery

Level of right ventricular outflow obstruction

Extent of overriding of aorta

Ventricular Septal Defect (VSD)

Right sided aortic arch (important for operating surgeon while repair)

Treatment  for Tetrology of Fallot (TOF)

Improvement of pulmonary flow by Blalock’s operation (Subclavian – pulmonary artery anastomosis)

Complete repair at a later date

Associated Defects          :         1. Absent pulmonary valve

2. Absence of left pulmonary artery.

3. Pulmonary atresia

Complications of  Tetrology of Fallot (TOF)

Cyanotic spell, often thereaten life

Cerebral embolism and abscess

Clinical Differentiation between valvular and infundibular stenosis

The infundibular stenosis has the following characteristics :

1. Systolic thrill and murmur are maximal in third or fourth left parasternal area.

2. Systolic murmur is long, and is not preceded by any ejection click.

3. Pulmonary valve closure is delayed but P2 is normal.