Agitated saline microbubbes can be used for right to left shunt detection. They create enough reflection to cause opacification of the right chambers of the heart and get dissolved while passing through pulmonary circulation (thus creating no contrast in the left heart).

Method:

Agitate 1 cc of air in 9 cc of air (using two 10 cc syringes and 3 way stop-cock) and inject rapidly into the venous circulation. In case of intra or extra cardiac shunts the bubbles will be noted in the left side of the heart. In case of intracardiac shunt the bubbles usually appear in the left heart in 3–5 cardiac cycles after the opacification of the right heart. In case of intrapulmonary shunts the bubbles are more likely to appear more than 6 cardiac cycles after opacification of the right heart. In case of negative study repeat the study with Valsalva maneuver (bubbles are expected to be seen after the Valsalva release in patients who have the shunt which becomes more obvious with increased right sided pressures).

Note: in cases of significantly elevated left atrial pressure the detection of PFO/ASD by bubble study may be limited and color Doppler technique may be more diagnostic.