TETRALOGY OF FALLOT

In an article called ''Dissection of a Monstrous Fetus in Paris", in 1671 was where the description of this congenital anomaly was first done. I picked up thus topic as I personally found it very interesting and hope to keep it as interesting to you too. Etteine Louis Arthur Fallot was the first person who elegantly described four cardinal features of this malformation to differentiate it from other cyanotic heart diseases; hence the name, Tetralogy of Fallot. Fallot used terminologies like 'the blue disease' or 'cardiac cyanosis'.

ETIOLOGY

The cause of this anomaly has been attributed to:

• Untreated maternal diabetes
• Maternal intake of retinoic acid
• Phenylketonuria
• Trisomy 13, 18, 21
• Micro-deletions of chromosome 22q11.2
• JAG1/NOTCH2 mutations

PATHOPHYSIOLOGY

The development of heart starts at around 20-23rd day of gestation. 

The primary defect in Tetralogy of Fallot is the mis-alignment of the conal septum thus resulting in a ventricular septal defect (VSD). In most cases the conal septum is protruded anteriorly and obstructs the pulmonary outflow tract resulting in hypoplasia of distal structures.In a mild obstruction there is left-to-right shunt through the septum; whereas in a severe obstruction, there is right-to-left shunt, resulting in low systemic perfusion and cyanosis. The VSD is notably large and hence the pressures in both right and left ventricles is the same.  

A characteristic of untreated Tetralogy of Fallot is Hypercyanotic Spells or Tet spells; that is, the child develops sudden and severe cyanosis and hypoxia when he does some assertive activities like defecation, crying, kicking etc. 

The exact cause of this phenomenon is still being searched for, but a previously known hypothesis works good: When there is an outflow tract obstruction exaggerated by above mentioned activities, increase in pulmonary vascular resistance, decrease in systemic resistance, it causes a fall in pO2 resulting in hyperapnea and cholinergic stimulation. The released catecholamines further constrict the outflow tract. 

SIGNS AND SYMPTOMS

Children with severe outflow obstruction will have severe pain and hypercyanotic spells during feeding which will lead to poor weight gain and slow development. Hypercyanotic spells occur most commonly in children between 2-4 months. If very severe, the spell can lead to limp, dyspnoea and sometimes death.

Auscultation gives a loud harsh grade 3 - 5/6 systolic ejection murmur at the left mid and upper sternal border. S2 is single because it is large and has no pressure gradient.

DIAGNOSIS

A chest X- ray 

Shows boot shaped heart with a concave main pulmonary artery segment and diminished pulmonary vascular markings.

ECG findings: 

Increased right ventricular forces will result in high peak R waves in V1;

Also atrial enlargement will give prominent P waves in V1. Right ventricular hypertrophy is demonstrated by rightward deviation of axis. 

 

Electrocardiogram; 

This is the mainstay in diagnosis of TOF. One can see the aorta over-riding the VSD by Color- Doppler imaging. VSD and ventricular outflow obstruction can also be seen.

Oxygen level measurements by pulse oximetry can be used.

Cardiac catheterisation: This is used to understand heart structures and plan for surgery. The catheter is inserted in an artery or vein of the arm, groin or neck. A dye is then injected to make the heart structures visible.

TREATMENT FOR TOF

• For symptomatic neonates, Prostaglandin E1 infusion is preferred.

• Management of hypercyanotic spells: These require immediate actions;

1. Place infants in knee-chest position.
2. Take to a calm environment.
3. Give supplemental oxygen and IV fluids for volume expansion.

If the spells persist, standard medical therapy is recommended including- 

(Taken from MSD manual)

Additional therapies (if required) include -

• Ketamine for increasing systemic BP
• Intranasal midazolam and intranasal fentanyl are other substitutes for morphine.

If positioning and drugs do not relieve the symptoms, immediate tracheal intubation, general anesthesia and surgical intervention are to be initiated.

Surgery is the most effective treatment available for tetralogy of Fallot. The treatment options include:

• Intracardiac repair
• Temporary procedure using a shunt

INTRACARDIAC REPAIR

This surgery is done during the first year after birth and includes precise repairing. 

1. The surgeon places a patch between the ventricular septal defect to close it.
2. The narrowed pulmonary valve is widened to increase pulmonary flow of blood.

After the repair, right ventricle will not have to work as hard and hence the thickness will regress on its own and blood oxygen levels will improve; thus lessening the symptoms.

TEMPORARY SURGERY

Occasionally, before intracardiac repair, the babies need to have a temporary surgery to improve oxygen supply to lungs. In this procedure, the surgeon creates a shunt (bypass)  between a large artery of the aorta and the pulmonary artery. A modified BLALOCK- TAUSSIG SHUNT is used to connect subclavian artery to the ipsilateral pulmonary artery.

This shunt is removed when the baby is undergoing intracardiac repair. 

AFTER SURGERY:

Most patients do well; long term complications are common though, which include:

• Chronic pulmonary regurgitation where blood pumps back into the right ventricle (pumping chamber).
• Tricuspid valve incompetence
• Inefficient ventricular septal defect repair
• Arrhythmias
• Coronary artery disease (CAD)
• Aortic root dilation (of the ascending aorta)
• Sudden cardiac death

The patient needs to have lifelong regular visits to the cardiologist for follow up to prevent any greater complications. Prophylaxis for endocarditis is to be taken in consideration.

Hope i stood successful in keeping this topic worth reading; shower your thoughts in the comment section!!