Atrial septal defect (ASD) with bidirectional shunt

Atrial septal defect (ASD) with bidirectional shunt


Atrial septal defect (ASD) with bidirectional shuntAtrial septal defect (ASD) with bidirectional shunt: Subcostal four chamber view shows a large defect in the interatrial septum (ASD). Right atrium (RA) and right ventricle (RV) are dilated, while left atrium (LA) and left ventricle (LV) are not. Blue color on colour flow mapping indicates right to left shunt across the atrial septal defect (R>L Shunt) in the subcostal view as the flow is away from the transducer.

This view shows red coloured flow across the ASD indicating a left to right shunt (L>R shunt). In addition there is a mosaic (multi colored) jet spreading from the closed tricuspid valve into the right atrium, due to tricuspid regurgitation (TR jet).

Bidirectional shunt can occur in ASD even without pulmonary hypertension. This is because transient right to left shunt can occur in certain phases of respiration and Valsalva maneuver. The volume of that right to left shunt is so small that there won’t be any clinical cyanosis. Still there is a small risk of paradoxical embolism. But here there is severe pulmonary hypertension which has caused reversal of shunt, though some left to right shunting is also persisting. As the pulmonary hypertension progresses, the shunt may become fully right to left.

Bidirectional shunts in uncomplicated ASD has been described by Galve E et al [1]. They noted this in older patients, unrelated to pulmonary hypertension and considered it to be a sequel of chronic right ventricular volume overload. Shunts were determined by measuring the pulmonary vein to systemic artery oxygen stepdown.

Bidirectional shunting across the ASD on Doppler echocardiogram along with right ventricular hypertrophy and systolic flattening of the interventricular septum are generally considered as features of pulmonary hypertension [2]. When the shunt is bidirectional, effective pulmonary blood flow can be equal to systemic blood flow (Qp/Qs = 1). Qp/Qs will be <1 when the shunt becomes purely right to left [3]. Both are suggestive of Eisenmenger physiology in the presence of pulmonary hypertension.

References

  1. Galve E, Angel J, Evangelista A, Anivarro I, Permanyer-Miralda G, Soler-Soler J. Bidirectional shunt in uncomplicated atrial septal defect. Br Heart J. 1984 May;51(5):480-4.
  2. Torres AJ. Hemodynamic assessment of atrial septal defects. J Thorac Dis. 2018 Sep;10(Suppl 24):S2882-S2889.
  3. Forlemu AN, Ajmal M, Saririan M. Atrial Septal Defect with Eisenmenger Syndrome: A Rare Presentation. Case Rep Cardiol. 2020 Mar 9;2020:8681761.