This is the commonest cyanotic congenital heart disease.

Pathology

The four components are a large VSD, RVOT obstruction, RVH and overriding of the aorta. Actually, only the first two are needed.

The VSD is perimembranous, with subpulmonary extension.

The RVOT obstruction is most commonly infundibular only (45%). 30% cases have infundibular + valve stenosis. 10% have valve stenosis alone.

Pulmonary atresia is seen in 15%.

Right aortic arch occurs in 25%.

Pulmonary arteries are small. Branch PA ostial stenosis can occur, especially on the left.

5% have abnormal coronaries- commonest being LAD originating from RCA and passing in front of the RVOT, disallowing an incision here.

AVSD occurs in 2%, especially in Downs.

Clinical features

Cyanosis at birth. Murmur at birth.

Cyanotic spells in infancy.

Dyspnoea on exertion and squatting later in life.

Left parasternal tap.

Pulmonary ejection systolic murmur, usually with a thrill. If RVOT obstruction is very severe, the murmur will be soft.

Single S2 because P2 is soft.

Aortic ejection click.

ECG

Right axis deviation.

RVH without strain. No strain because RV pressure is not suprasystemic.

CXR

Decresed pulmonary vasculature.

Concave pulmonary bay.

Upturned apex with no cardiomegaly- called boot-shaped heart or coeur en sabot. Coeur en sabot means wooden shoe in French.

Natural history

Cyanosis worsens with age due to increasing RVOT obstruction and polycythemia.

Hypoxic spell

The incidence peaks between 2 and 4 months of age. It usually occurs in the morning. It is characterised by crying, hyperpnea and cyanosis. Murmur becomes less intense during the spell. There is no relation with the degree of cyanosis at rest.

Hold the child in knee-chest position. Give morphine 0.2 mg/kg SC or IM. This works by suppressing the respiratory center.  Oxygen is usually given. Soda bicarbonate is useful if there is acidosis.

In refractory cases, phenylephrine, ketamine or propranolol are useful. Phenylephrine is a systemic vasoconstrictor. Ketamine is a sedative and a systemic vasoconstrictor.

For prevention, propranolol 1 mg/kg qid orally is given if there is a delay to surgery.

Palliative procedures

Indications are low weight babies (<2.5kg), very young babies (<3M), unfavourable coronary anatomy, pulmonary atresia in neonate, hypoplastic pulmonary annulus in infant and hypoplastic pulmonary arteries in children.

Classic Blalock-Taussig shunt is an end to side anastomosis of the right subclavian artery to the right pulmonary artery (left for right aortic arch). This can be done only if age is more than 3 months.

Modified Blalock-Taussig shunt – a Gore-Tex interposition shunt is placed between the left subclavian artery and the left pulmonary artery (right for right aortic arch). This can be done even if age is less than 3 months.

Waterston shunt, between ascending aorta and right pulmonary artery, and Potts shunt, between descending aorta and left pulmonary artery, are not done now due to many complications like a very large shunt.

Repair

Indications for repair are hypoxic spell and oxygen saturation less than 80%.

Elective repair is done at 1 to 2 years. Earlier repair is done if symptoms are present.

The repair is preferably done via atrial and pulmonary artery approaches rather than via a right ventriculotomy. The VSD is closed with a patch, the infundibular stenosis is resected and the valvular stenosis is relieved by a pulmonary valvotomy. Placement of a fabric patch in the RVOT is avoided if possible.

If LAD courses in front of the RVOT, primary repair may not be adequate, in which case, a conduit is also placed between the RV and the PA so that there are two outlets now for the RV.