Webster et al used Doppler echocardiography to grade the severity of a right-to-left shunt within the heart. The authors are from Auckland Hospital in New Zealand.


Causes of right-to-left shunt that were evaluated:

(1) patent foramen ovale

(2) atrial septal defect (ASD)


Technique: contrast echocardiography with an apical 4 chamber view following injection of microbubbles into the right atrium


The examination is considered abnormal if microbubbles appear in the left atrium or left ventricle in 1 to 3 cardiac cycles after injection of microbubbles in the right atrium.


The number of bubbles in the left side of the heart (atrium and ventricle) is counted in each frame. The maximum number is used as a semiquantitative measure shunt severity.

Maximum Number of Bubbles


1 to 5


6 to 20


21 or more



Microbubbles are injected:

(1) at rest

(2) during a Valsalva maneuver


The Valsalva maneuver tends to increase the grade of the shunt.


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