From the Guidelines
Intrapulmonary shunting on an agitated saline echocardiogram is diagnosed when microbubbles appear in the left heart chambers after 3 to 8 cardiac cycles following their appearance in the right heart, with a semiquantitative grading system used to assess the severity of the shunt 1. The diagnostic criteria for intrapulmonary shunting on an agitated saline echocardiogram involve the appearance of microbubbles in the left heart chambers after a delay, which distinguishes intrapulmonary shunts from intracardiac shunts.
- The test involves injecting agitated saline into a peripheral vein while performing echocardiography.
- The presence of microbubbles in the left heart after the appropriate delay confirms intrapulmonary shunting, with the severity of the shunt assessed using a semiquantitative grading system, which includes grades 0 to 3 based on the number of bubbles and the degree of opacification of the left atrium 1.
- This finding is significant in diagnosing conditions like hepatopulmonary syndrome, pulmonary arteriovenous malformations, and hereditary hemorrhagic telangiectasia. The physiological basis for this diagnostic approach is that microbubbles (>10 μm) normally get filtered by pulmonary capillaries (7-10 μm), so their appearance in the left heart indicates abnormal vascular communications allowing blood to bypass normal pulmonary filtration.
- The use of agitated saline contrast echocardiography is a valuable tool in the investigation of congenital heart disease, including the detection of intrapulmonary shunts 1.
- The technique has a high sensitivity and specificity for detecting pulmonary arteriovenous malformations, with a semiquantitative grading system used to assess the severity of the shunt 1.
From the Research
Diagnostic Criteria for Agitated Saline Echocardiogram Finding of Intrapulmonary Shunting
- The diagnosis of intrapulmonary shunting using agitated saline echocardiogram is based on the appearance of contrast bubbles in the left atrium, which indicates the presence of a right-to-left shunt 2, 3.
- The timing and pattern of contrast bubble appearance can help differentiate between intracardiac and extracardiac shunts, with intrapulmonary shunts typically showing a delayed appearance of contrast bubbles in the left atrium 4.
- The use of acoustic intensity mapping can improve the diagnosis of intrapulmonary shunting by analyzing the temporal changes in contrast density over time 4.
- Pulmonary shunting can be graded based on the number of contrast bubbles appearing in the left atrium, with higher grades indicating more significant shunting 5.
- Small pulmonary shunts (grade 1) may not have significant clinical implications, but larger shunts can increase the risk of paradoxical embolization and other complications 5.
- Agitated saline contrast echocardiography is a useful tool for detecting intrapulmonary shunts, particularly in patients with hepatopulmonary syndrome or other conditions associated with pulmonary shunting 3, 6.
- The technique involves injecting agitated saline contrast into a peripheral vein and observing the appearance of contrast bubbles in the left atrium using echocardiography 2, 6.
- Provocative maneuvers, such as the Valsalva maneuver, can increase the sensitivity of the test by increasing the pressure gradient between the right and left atria 6.