How is a bubble study on echocardiogram (echo) interpreted based on the number of cardiac beats?

From the Guidelines

Interpreting a bubble study on echocardiography is based on the timing and number of bubbles appearing in the left heart chambers, with a semiquantitative grading system developed to correlate with the diagnosis of pulmonary arteriovenous malformation (PAVM) 1. The grading system is defined as follows:

• Grade 0: no opacification
• Grade 1: <30 bubbles
• Grade 2: moderate filling
• Grade 3: complete opacification of the left atrium The timing of bubble appearance is also crucial, with bubbles typically appearing after 3 to 8 cardiac cycles in the left atrium in patients with an intrapulmonary shunt 1. Key factors to consider when interpreting bubble study results include:
• The number of bubbles, with higher grades associated with larger shunts and cerebral complications 1
• The timing of bubble appearance, with delays suggesting an intrapulmonary shunt 1
• The clinical significance of the findings, which depends on the patient's symptoms and other clinical factors It is essential to note that the grading system correlates well with the diagnosis of PAVM, with higher grades associated with larger shunts and cerebral complications, and that adverse events, including air embolism, are rare with transthoracic contrast echocardiography (TTCE) occurring in <1% 1.

From the Research

Interpretation of Bubble Study on Echo

The interpretation of a bubble study on echo is based on the appearance of microbubbles in the left side of the heart after injection of agitated saline, which indicates a right-to-left shunt.

• The number of beats it takes for the microbubbles to appear can vary, but a time window of 20 to 25 seconds has been suggested as a reliable indicator of a shunt 2.
• The Valsalva maneuver can increase the sensitivity of the test by causing an atrial septal swing, which can help to detect right-to-left shunts 3.
• The appearance of microbubbles in the right middle cerebral artery during transcranial Doppler sonography can also indicate a right-to-left shunt, with a higher sensitivity when performed with the Valsalva maneuver 4.

Factors Affecting Interpretation

Several factors can affect the interpretation of a bubble study, including:

• The type of contrast agent used, with Echovist being more sensitive than agitated saline 2.
• The presence of other cardiac abnormalities, such as atrial septal defects or pulmonary arterio-venous malformations 5.
• The patient's respiratory and cardiac status, with false negatives potentially occurring due to respiratory-phasic variation or elevated left atrial pressure 5.

Clinical Implications

The detection of a right-to-left shunt using a bubble study can have significant clinical implications, including:

• The identification of a potential cause of paradoxical embolism in patients with cryptogenic stroke or transient ischemic attack 6.
• The need for further evaluation and potential treatment, such as antiplatelet or anticoagulant therapy, or referral for shunt closure 6.