ASD with right to left shunt on colour Doppler echocardiography

ASD with right to left shunt on colour Doppler echocardiographyASD with right to left shunt on colour Doppler echocardiography

Classically atrial septal defect is best imaged from the subcostal view on echocardiography as the septum is perpendicular to the ultrasound beam in this view. The ASD is marked with stars in the left image panel. Right image panel shows the colour Doppler flow pattern across the ASD. Blue colour indicates that the flow is away from the transducer. In this case a downward flow across the ASD in this view is from right atrium to left atrium (right to left shunt).

When right to left shunt across the atrial septum is noted in an infant during echocardiography, the first thing to look for is total anomalous pulmonary venous connection. When all the pulmonary veins are connected to the right atrium instead of the left, there is an obligatory right to left shunt across the ASD in order to sustain life. In an adult, right to left shunt across the ASD would mean severe pulmonary hypertension and reversal of the shunt. But transient right to left shunt across the ASD can occur even without severe pulmonary hypertension due to phasic fluctuation of atrial pressures with respiration and Valsalva maneuver.

Right to left shunt across ASD can occur with and without pulmonary hypertension. An echocardiographic study has detailed the exact timings of right to left shunt in various situations. While some occurred at the time of tricuspid valve closure, others occurred due to tricuspid regurgitation jet while still others occurred during atrial contraction [1].

Reference

  1. Oki T, Iuchi A, Fukuda N, Tabata T, Hayashi M, Tanimoto M, Manabe K, Kageji Y, Sasaki M, Hama M, Ito S. Assessment of Right-to-Left Shunt Flow in Atrial Septal Defect by Transesophageal Color and Pulsed Doppler Echocardiography. J Am Soc Echocardiogr. 1994 Sep-Oct;7(5):506-15.