Pulmonary AVM & Bubble Test

Summary

This video explains pulmonary arteriovenous malformations (AVMs), their diagnosis, and the bubble test procedure. Pulmonary AVMs disrupt normal blood flow in the lungs, leading to potential embolic events like stroke or myocardial infarction. The bubble test, which involves agitating saline with air and injecting it into the bloodstream, is a key diagnostic tool. Proper technique and timing, including the Valsalva maneuver, are crucial for accurate results. The video also discusses the grading system for AVMs based on bubble counts, with higher grades indicating increased risk. This lecture provides essential insights for diagnosing and managing pulmonary AVMs.

Takeaways

• 😀 Pulmonary arteriovenous (AV) malformations occur when blood flows directly from the pulmonary artery to the pulmonary vein, bypassing capillary filtration, which can cause embolic events like strokes and myocardial infarctions.
• 😀 These malformations can be congenital or sporadic, with hereditary cases often showing symptoms in childhood, such as mucosal bleeding (e.g., nosebleeds) and shortness of breath.
• 😀 Most pulmonary AV malformations are asymptomatic and may only present symptoms in individuals around the age of 40-60, but severe hereditary forms can appear earlier.
• 😀 The first diagnostic step for suspected pulmonary AV malformation is an echocardiogram with a bubble test to detect abnormal blood flow between the arteries and veins.
• 😀 The bubble test is highly sensitive (over 95-100%) when performed correctly, but errors in technique can reduce its effectiveness.
• 😀 To perform the bubble test, mix 1 cc of air with 9 cc of normal saline, ensuring rapid mixing and injection to ensure clear detection of bubbles.
• 😀 The Valsalva maneuver (bearing down) should be performed immediately before injecting the agitated saline to enhance the visibility of bubbles in the heart.
• 😀 A positive result in the bubble test shows bubbles entering the left atrium after passing through the right atrium, indicating a pulmonary AV malformation.
• 😀 When analyzing the bubble test, the number of bubbles seen in the left atrium is counted to determine the severity of the malformation: Grade 1 (<30 bubbles), Grade 2 (30-100 bubbles), and Grade 3 (>100 bubbles).
• 😀 Grade 2 and 3 malformations carry an increased risk of neurological events like strokes due to the higher number of microbubbles passing into the systemic circulation.
• 😀 In cases where the initial window for detecting bubbles is unclear, adding a drop of the patient's blood to the saline mix can improve the quality of the test and increase its sensitivity.

Q & A

What is the primary function of the capillary system in the lungs?

The primary function of the capillary system in the lungs is to facilitate blood gas exchange and filter out materials, such as thrombotic, fat, or septic materials, from entering the venous system.

What can happen if the capillary system in the lungs is disturbed?

If the capillary system is disturbed, blood may directly contact the pulmonary artery and pulmonary vein, which can result in embolic events, including ischemic strokes, myocardial infarction, or cerebral abscesses.

What are the potential causes of pulmonary arteriovenous malformation (AVM)?

Pulmonary AVMs can be congenital (often associated with hereditary hemorrhagic telangiectasia, or HHT) or sporadic (occurring without an associated syndrome).

What are the common symptoms of pulmonary AVM in hereditary cases?

In hereditary cases, particularly in those with HHT, symptoms may include mucosal bleeding (such as nosebleeds) and exertional shortness of breath, which may present early in childhood.

At what age do symptoms of pulmonary AVM typically become apparent?

Symptoms of pulmonary AVM typically become apparent between the ages of 40 to 60, although severe hereditary cases may present symptoms in childhood.

What is the first diagnostic step in evaluating pulmonary AVM in patients with unexplained shortness of breath?

The first diagnostic step in these patients is echocardiography with a bubble test, which helps detect the presence of a pulmonary AVM.

What is the sensitivity of the bubble test for detecting pulmonary AVM?

The sensitivity of the bubble test, if performed correctly, is over 95% to 100%. However, technical errors can reduce its accuracy.

What are some common mistakes that can reduce the sensitivity of the bubble test?

Common mistakes include not mixing the saline solution with the correct amount of air, performing the test too slowly, or improper timing during the Valsalva maneuver.

How should the Valsalva maneuver be performed during a bubble test?

The Valsalva maneuver should be performed immediately before injecting the agitated saline solution. The patient should bear down and hold the breath, creating a steady, tight belly. The assistant then injects the solution while the patient holds the Valsalva, and the bubbles should be observed after a few seconds.

How do you interpret the results of a bubble test for pulmonary AVM?

If the bubbles appear in the left atrium within five heartbeats of showing up in the right atrium, it suggests a pulmonary AVM. The number of bubbles in each frame helps to grade the shunt as mild (Grade 1), moderate (Grade 2), or severe (Grade 3). Grade 2 and 3 shunts indicate a higher risk for neurological events such as stroke.

What is the purpose of adding a few drops of blood to the saline mixture during a bubble test?

Adding a few drops of the patient's blood to the saline mixture helps improve the sensitivity and quality of the bubble test, especially in cases where the imaging window is less than ideal.

What is the significance of observing the timing of bubble appearance in the right and left atrium during a bubble test?

The timing of bubble appearance in the right and left atrium helps differentiate between pulmonary AVM and other conditions. In pulmonary AVM, the bubbles appear in the left atrium after approximately five heartbeats of showing up in the right atrium.