What is the significance of echocardiographic intrapulmonary shunting diagnosed by agitated saline (contrast)?

From the Guidelines

Echocardiographic intrapulmonary shunting diagnosed by agitated saline is a significant finding that identifies abnormal blood flow pathways between the pulmonary and systemic circulations, which can guide management decisions and impact patient outcomes in terms of morbidity, mortality, and quality of life. This technique involves injecting agitated saline solution containing microbubbles into a peripheral vein while performing an echocardiogram. In normal circulation, these bubbles are filtered by the lungs. However, when intrapulmonary shunting is present, bubbles appear in the left heart chambers after 3-6 cardiac cycles (distinguishing it from intracardiac shunts, where bubbles appear immediately) 1.

The clinical importance of this finding lies in its ability to indicate conditions like hepatopulmonary syndrome in liver disease patients, pulmonary arteriovenous malformations in hereditary hemorrhagic telangiectasia, or other causes of hypoxemia that don't respond to supplemental oxygen 1. The degree of shunting correlates with hypoxemia severity and can guide management decisions including oxygen therapy, consideration for liver transplantation in appropriate cases, or embolization of arteriovenous malformations.

According to the 2019 ACC/AHA/ASE advanced training statement on echocardiography, the use of agitated saline contrast in the evaluation of patients with suspected right-to-left shunts is considered a standard requirement for Level II training in echocardiography 1. Additionally, the 2018 AHA/ACC guideline for the management of adults with congenital heart disease emphasizes the importance of diagnosing and managing pulmonary hypertension, which can be associated with intrapulmonary shunting 1.

Key points to consider when interpreting the results of an echocardiographic intrapulmonary shunting study include:

• The presence and degree of shunting, which can guide management decisions
• The underlying cause of the shunting, such as hepatopulmonary syndrome or pulmonary arteriovenous malformations
• The correlation between the degree of shunting and hypoxemia severity
• The potential need for further testing, such as cardiac catheterization, to confirm the diagnosis and guide management decisions 1.

Overall, echocardiographic intrapulmonary shunting diagnosed by agitated saline is a valuable diagnostic tool that can provide important information about abnormal blood flow pathways between the pulmonary and systemic circulations, and can guide management decisions to improve patient outcomes.

From the Research

Significance of Echocardiographic Intrapulmonary Shunting

• Echocardiographic intrapulmonary shunting diagnosed by agitated saline is significant in detecting right-to-left cardiopulmonary shunts, which can cause refractory hypoxia in critically ill patients 2.
• The use of agitated saline contrast in combination with transthoracic echocardiography can confirm the diagnosis of significant intrapulmonary shunting, as seen in a case of a 54-year-old man with end-stage cirrhosis of the liver 3.
• Pulmonary shunting can be associated with diseases such as hereditary hemorrhagic telangiectasia, hepatopulmonary syndrome, and some congenital heart defects, and carries the risk of severe neurologic complications due to paradoxical embolization 4.

Clinical Implications

• The detection of intrapulmonary shunting using saline contrast echocardiography can have important clinical implications, including the need for antibiotic prophylaxis to prevent brain abscesses after procedures with risk for bacteremia 4.
• Small pulmonary shunts on saline contrast echocardiography may lack clinical implication, but further research is needed to fully understand the significance of different pulmonary shunt grades 4.
• Echocardiography can be a useful tool in diagnosing intrapulmonary shunts and understanding the pathophysiology of hypoxemia in patients with hepatopulmonary syndrome 5.

Diagnostic Techniques

• Agitated saline bubble study can be used for the early diagnosis of right-to-left cardiopulmonary shunts, and point-of-care ultrasound (POCUS) can be used to detect the most common types of shunts seen in the intensive care unit 2.
• Acoustic intensity mapping of saline contrast studies can improve the differential diagnosis of intracardiac and extracardiac shunts, and can be used to define the unique patterns of saline contrast entry into and exit from the left heart 6.