Tetralogy of Fallot (TOF): Treatment and Complications by Nurses Note

Tetralogy of Fallot (TOF)

It is the most common cyanotic congenital heart disease in patients who survive infancy.

 It is composed of 4 distinct anatomic abnormalities:

1. Large non-restrictive VSD.
2. Right ventricular outflow tract obstruction (infundibular pulmonary stenosis ).
3. Overriding of the aorta.
4. Right ventricular hypertrophy.

Embryology

TOF occurs as the result of anterocephalad malalignment of the infundibular septum, resulting in a ventricular septal defect, right ventricular outflow tract obstruction (subpulmonic obstruction ) and overriding of the aorta.

Cyanotic Fallot

When the resistance to pulmonary outflow is greater than the systemic resistance, right to left shunting of blood across the VSD occurs, resulting in central cyanosis.

Acyanotic Fallot

When the resistance to the pulmonary outflow is lower than the systemic resistance, then a predominant left to right shunt occurs across the VSD and cyanosis is absent.

  Initially, in TOF, cyanosis is episodic, occurring during feeding, crying, fever, exercise, etc, when systemic vasodilation occurs causing an increased right to left shunting across the VSD.

A baby born cyanotic is unlikely to have TOF.

Cyanosis becomes more prominent after about 5-6 months of life due to the following reasons:

1. HbF is the predominant Hb present in the first few years of life. It binds less avidly to O2 and releases it easily at times of need. Hence, when an infant with TOF, in the first 5 to 6 months of life develops cyanotic spells, O2 is easily released from HbF and hence cyanosis is minimal. After 5-6 months of age, HbF is replaced by HbA2. HbA2 binds O2 more avidly and releases it less readily at times of need and so the child becomes cyanotic.
2. With the growth of the child, the O2 demand for growth increases and cyanosis becomes more prominent.

TOF may be associated with other cardiac anomalies like:

1. Patent foramen ovale.
2. ASD.
3. AR.
4. Right-sided aortic arch ( It is the most common anomaly, seen in 25 to 30% of cases, its likelihood increasing with increasing severity of RVOT obstruction and particularly in pulmonary atresia).
5. PDA.
6. Anomalous origin of the coronary arteries.
7. Absence of left pulmonary artery.

Pentology of Fallot

The presence of ASD along with TOF is called pentology of Fallot.

Triology of Fallot

Right ventricular outflow tract obstruction with RV hypertrophy and right to left shunt across interatrial septum in the absence of VSD  is called triology of fallot (PH, RVH, and ASD)

TOF Associated Syndrome 

1. TAR (thrombocytopenia and absent radius.
2. Down Syndrome (hypotonia, mental retardation, mongoloid facies, hyperextensible joints).
3. Di-George syndrome (Thymic hypoplasia, parathyroid hypoplasia, ear anomalies).
4. CHARGE association ( coloboma, choanal atresia, mental and growth retardation, genital and ear anomalies).
5. Velocardiofacial.

Clinical Features Tetralogy of Fallot (TOF)

A silent precordium is often characteristic.

 On auscultation, a loud, single S2 (representing aortic valve closure) and an ESM is best heard over the 3rd and 4th left intercostal spaces.

 The intensity and duration of the murmur is inversely proportional to the severity of RVOT obstruction.

 Because of a large ventricular septal defect, VSD murmur is inconspicuous.

ECG

ECG shows right axis deviation. A large monophasic R wave is present in V1, with abrupt transition to an rS complex in V2, V3 and Rs complexes in v5, V6.

Chest X-ray

This shows a normal shaped heart with characteristic appearance termed as 'Coeur en Sabot' or 'boot-shaped heart' (tilted apex). There is pulmonary oligaemia. Boot shaped heart is due to the prominence of RV and concavity in the region is due to underdeveloped RVOT and main pulmonary artery.

Complications Tetralogy of Fallot (TOF)

1. Marked secondary polycythemia may result in intravascular thrombosis leading to cerebrovascular accidents and paradoxical emboli.
2. Cerebral abscess (common causative organism being streptococcus)
3. Incidence of Pulmonary tuberculosis and tuberculoma is high.
4. Infective endocarditis (common causative organism being streptococcus ).
5. CCF is a rare Complication and if present may be secondary to
1. Infective endocarditis
2. Pregnancy
3. Anaemia
4. Systemic hypertension
5. Aortic regurgitation
6. Acquired calcific stenosis of the bicuspid aortic valve
7. Pulmonary atresia with large systemic arterial collaterals-RV failure
8. Accessory tricuspid leaflet occluding the VSD-RV failure.

Treatment of Tetralogy of Fallot (TOF)

Medical

Treatment of cyanotic spells by

1. Squatting or knee-chest position
2. Nasal O2
3. Morphine
4. B-blockers (propranolol)
• Morphine and b-blockers (propranolol ) help to relieve infundibular spasm.
• Propranolol initially at the dose of 0.01 mg/kg IV followed by oral dose of 3-5 mg/kg/day is advocated. Morphine sulphate is given at the dose of 0.1 mg/kg IV.
5. Correct metabolic acidosis with sodium bicarbonate -1 mEq/kg IV.

Surgical

Total correction is advocated and is the definitive treatment.

If pulmonary arteries are excessively small, then early definitive correction of TOF is not possible. A palliative procedure (Blalock-Taussig shunt) is done until the pulmonary arteries have enlarged sufficiently.

Blalock-Taussig Procedure: In left-sided aortic arch-Left subclavian to left pulmonary artery. In right-sided aortic arch-Right subclavian to right pulmonary artery.

This procedure results in absent radial pulse on the side of anastomosis and continuous murmur at the site of anastomosis.

Waterston Procedure: Ascending aorta to right pulmonary artery.

Pott's Procedure: Descending aorta to left pulmonary artery.

Reference: Alagappan medicine