Obligatory right to left shunt at the atrial level

Obligatory right to left shunt at the atrial level

Abstract: Obligatory right to left shunt at the atrial level occurs in tricuspid atresia, pulmonary atresia with intact interventricular septum and total anomalous pulmonary venous connection.

Obligatory R→L shunt at the atrial level means that the right to left shunt is mandated by the physiology in such a way that postnatal survival is not possible without that shunt. In some cases with an insufficient shunting across the interatrial septum, procedures to enhance the shunting may be undertaken in the immediate newborn period to sustain life.

Tricuspid atresia

The obligatory R→L shunt at atrial level is needed in tricuspid atresia because there is no other outlet for the right atrium. Blood returning to the right atrium from the vena cavae and coronary sinus reach the left atrium through an atrial septal defect. This blood passes through the left ventricle and can reach the right ventricle if there is an associated ventricular septal defect. In the absence of ventricular septal defect, the pulmonary blood flow is provided by a patent ductus arteriosus.

Pulmonary atresia with intact interventricular septum

In pulmonary atresia with intact ventricular septum, there is an obligatory R→L shunt at atrial level because right ventricle has no outflow. Right ventricular cavity can either be diminutive or sizable with significant tricuspid regurgitation. Pulmonary blood flow is through a patent ductus arteriosus and major aortopulmonary collateral (MAPCAs). Vigorous flap like movement of the primum portion of the interatrial septum has been described in a case of hypoplastic right heart with intact interventricular septum, pulmonary atresia, secundum atrial septal defect and patent ductus arteriosus [1]. Authors mention that vigorous motion of secundum atrial septum which acts an interatrial baffle in the developing human fetus is well documented.

Total anomalous pulmonary venous connection

When all the pulmonary veins drain to the right side of the heart – either through a supra cardiac, intracardiac or infracardiac channel, blood is transferred to the left side of the heart usually through an obligatory R→L shunt at the atrial level.

Reference

1. Sethuraman KR, Balachandar J, Chandrasekar S. Atrial septal motion in obligatory right to left shunt. Int J Cardiol. 1984 Jul;6(1):87-8.