Bubble Study for Patent Foramen Ovale (PFO)

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Swedish Vascular Ultrasound

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PFO Testing: Right to left cardiac shunt (RLS) detection

A patent foramen ovale (PFO) is a defect in the wall between the two upper chambers of the heart, and is sometimes referred to as a “hole in the heart.” It is present in everyone prior to birth, and closes in 80% of the population. This defect is an incomplete closure of the atrial septum, that can allow blood to pass directly from the right atrium to the left atrium (referred to as right-to-left cardiac shunt (RLS), bypassing the filtering system of the lungs. If blood clots are present, they can move unfiltered into the left atrium and then into the brain, causing a stroke.

The Bubble Study, using transcranial doppler ultrasound, has proven to be a sensitive and specific method to diagnose right-to-left cardiac shunt (RLS).

Test Indications

Younger patients who have had stroke or TIA without recognized common vascular risk factors.

What to Expect

Prior to test

It is important to be well hydrated, so drink water prior to your appointment.

At the testing center

You will be asked about your medical and surgical history
You may have your blood pressure taken
You may be allowed to have a family member or friend with you in the exam room during the test

During the exam

You will lie comfortably on a stretcher in the testing room while the technologist positions a band like frame to your head to hold the ultrasound transducers in place. An intravenous line will be started in the arm to allow for injections of agitated saline. The technologist will also place an ultrasound transducer near your sternum to obtain an ultrasound signal from your pulmonary artery.
While the middle cerebral arteries that supply blood flow to the brain are monitored, agitated saline that contains micro air-bubbles is injected into the intravenous line in the arm. These tiny micro air bubbles can be easily detected and counted during the TCD exam, which verifies the absence or presence of a right-to-left cardiac shunt.
When the exam is completed, the technologist will remove the ultrasound device and the ultrasound gel will be taken off with a soft cloth

When the exam is done

You will be ready to leave depending on the results. If the technologist has critical findings you will be asked to wait at the facility for further instructions from your doctor after the results are conveyed. The technologist may need to take more images if requested by your physician.

How long will it take?

40 – 60 minutes

Will it hurt?

The TCD ultrasound exam is non-invasive and painless. You will feel a needle stick when the IV is placed in your arm.


A specialized physician will analyze the images and send a report to your doctor. Your doctor will talk to you about the results and any further tests or treatments. After the test, call your doctor if you have worsening symptoms.