Bubble Study

A bubble study, also called a bubble echocardiogram or agitated saline contrast study, is a type of ultrasound test that checks blood flow through your heart and lungs. It can show if blood is flowing through an abnormal passage called a shunt. The shunt might connect the right and left sides of your heart. Or it might link your pulmonary arteries and veins, which carry blood between your heart and lungs.

A bubble study can be done along with any of these imaging tests:

• Transthoracic echo (TTE): This is the typical type of echo you get to diagnose heart issues. The ultrasound probe stays on the outside of your chest to take pictures.
• Transesophageal echo (TEE): For this test, your provider guides a tiny ultrasound probe down your throat to take pictures while you’re sedated.
• Transcranial Doppler (TCD) ultrasound: This test creates images of the blood vessels leading to your brain. Certain heart and lung shunts can affect blood flow to your brain in ways that raise your risk for a stroke. 

Why do I need a bubble echocardiogram?

You may need a bubble study if you have signs or symptoms of a shunt, like low blood oxygen levels and shortness of breath, or you’ve had a stroke without a clear cause.

Blood should normally pass through your lungs to pick up oxygen and get rid of waste. In addition, capillaries in your lungs filter out tiny blood clots so they don’t flow back through your body and cause problems. A bubble study can show if any blood skips this step. The results guide treatment.

This test most commonly diagnoses:

• Patent foramen ovale (PFO): This is a hole that lets blood pass from your right atrium to left atrium (top chambers of the heart). Normally, blood should go to your lungs first.
• Atrial septal defect (ASD): This is another type of hole between your top heart chambers. A standard echo, without saline contrast, can diagnose many ASDs. But certain types only show up with a bubble study.
• Pulmonary arteriovenous malformation: Also called a pulmonary AVM, this type of shunt connects your pulmonary arteries and pulmonary veins. It lets blood that’s leaving your heart go right back to your body, rather than going to your lungs.

How does a bubble study work?

A bubble study is similar to an echocardiogram without contrast. You lie on your side, and a healthcare provider takes ultrasound images of your heart. But there’s a key difference. During a bubble study, your provider injects a substance called agitated saline into a vein in your arm. It acts as a contrast agent. That means it enhances the ultrasound images to better show blood flow.

Saline is salt water. Your provider “agitates” it by quickly mixing it with a small amount of air. This makes tiny bubbles, called microbubbles. Your provider may also add a bit of your own blood to help make more bubbles.

The bubbles flow through your veins and into your heart. Your provider looks at exactly where they appear on the ultrasound images. This shows them if blood is flowing in normal or abnormal ways.

You usually don’t need any special prep for a transthoracic echo or transcranial Doppler ultrasound. For a transesophageal echo, you’ll need to fast (typically for at least six hours) beforehand. Your provider may also give you other instructions.

What happens during the test?

The exact steps can vary based on the type of imaging test you’re getting. To perform a bubble study with a transthoracic echo, your healthcare provider will:

• Help you get comfortable: You’ll lie on your left side, if you’re able.
• Apply gel to your chest: The gel helps transmit sound between your heart and the ultrasound device.
• Start an IV: Your provider will insert an IV into a vein in your inner elbow or forearm. They’ll inject the agitated saline and wait for it to travel to your heart. It enters at the right atrium.
• Ask you to breathe or cough in certain ways: Your provider may ask you to do a Valsalva maneuver or cough forcefully. These actions help raise the pressure in your right atrium to force bubbles to go through a shunt, if there is one.
• Watch the ultrasound: If bubbles appear on the left side of your heart, it means you may have a shunt. If bubbles don’t appear there, it means blood is flowing as it should from your right atrium to your lungs.
• End the test: Once your provider gets enough information, they’ll stop taking pictures and remove your IV. They’ll wipe the gel from your chest and help you prepare to leave.

You can usually go back to your usual activities right after the test and drive yourself home. But if you have a transesophageal echo, the process is a little different. Because you’re sedated, you’ll have to stay for a bit after the test so your provider can monitor you. And you can’t drive for 24 hours. So, you’ll need someone to drive you home.

Your healthcare provider will schedule a time with you to go over the test results.

What are the risks of this test?

A bubble study is a safe and low-risk test. A very rare complication during the test is a stroke, which is typically mild and treatable.

It’s possible for a bubble study to produce false negatives. That means it shows there’s no shunt, but there actually is one. This is more likely to happen if you have raised pressure in the right side of your heart, due to a condition like mitral valve disease. Your healthcare provider will consider your medical history when interpreting the test results.

What type of results do you get and what do they mean?

The results of a bubble study can be either positive or negative. Here’s what those mean:

• Positive: Bubbles appeared on the left side of your heart. You likely have a shunt.
• Negative: Bubbles didn’t appear on the left side of your heart. You likely don’t have a shunt.

Providers look closely at the echo images to learn more about the exact type of shunt you have. For example:

• Bubbles that enter the right side and quickly appear on the left side suggest a shunt in the heart, like a PFO or ASD.
• Bubbles that enter the right side and then, after a delay, appear on the left side suggest a pulmonary AVM. Another sign is if bubbles directly come from the pulmonary veins.
• The number of beats it takes for the bubbles to appear on the left side of the heart determines whether the shunt is cardiac or pulmonary.

The larger the shunt, the more bubbles will be visible in the images.

If the results are abnormal, what are the next steps?

You may need treatment for a shunt. Your healthcare provider may recommend:

• Medications (blood thinners) to prevent blood clots that could cause a stroke
• A procedure or surgery to close the shunt

Your provider will explain any next steps and what you can expect.