An echocardiogram is a common, non-invasive imaging test that uses high-frequency sound waves to create moving pictures of the heart’s structure and function. A bubble echocardiogram, also known as an agitated saline contrast study, is a specialized version of this ultrasound technique. It involves injecting a temporary contrast agent into the bloodstream to enhance the visualization of blood flow pathways within the heart. This method is particularly effective for detecting abnormal connections or holes that might not be visible on a standard ultrasound, providing a clearer picture of the heart’s internal circulation.
What is the Saline Contrast Agent?
The “bubble” in the study’s name refers to microscopic bubbles created from sterile saline solution and a small amount of air. This saline solution is mechanically agitated, often between two syringes connected by a three-way stopcock, to generate a suspension of tiny microbubbles. Sometimes, a small amount of the patient’s own blood is mixed in, as the blood’s protein content helps stabilize the microbubbles and improve the contrast quality.
These microbubbles are not the same as commercial contrast dyes used in other medical imaging and are safe for the body. Once injected into a vein, they reflect ultrasound waves, causing the blood in the right side of the heart to appear bright white. The bubbles are quickly filtered out and absorbed by the lungs as they pass through the pulmonary circulation, meaning they normally do not travel beyond the right side of the heart.
The Steps of the Procedure
The patient usually begins by lying on an examination couch, often on their left side, which helps obtain the best images of the heart. Electrocardiogram (ECG) stickers are placed on the chest to monitor the heart’s rhythm throughout the test. An intravenous (IV) cannula is inserted into a vein, typically in the arm, to allow for the injection of the contrast agent.
A standard echocardiogram is performed first, where a transducer is placed on the chest with a lubricating gel to capture initial images. Once imaging is underway, the prepared agitated saline solution is rapidly injected through the IV line. The microbubbles travel quickly through the vein and into the heart’s right-sided chambers.
To improve the chances of visualizing a small defect, the patient may be asked to perform a Valsalva maneuver, which involves bearing down. This temporary straining increases the pressure inside the chest and the right side of the heart. The agitated saline is typically injected just before or during the release of this maneuver, which momentarily causes pressure changes that can force the microbubbles across any existing abnormal connection.
Conditions Diagnosed with a Bubble Study
The primary purpose of the bubble study is to identify a shunt, which is an abnormal connection allowing blood to pass from the right side of the heart to the left side. Normally, the microbubbles should only be seen on the right side of the heart before being filtered by the lungs. If the bubbles appear in the left-sided chambers, it signifies a right-to-left shunt, confirming a structural defect.
The most common findings confirmed by this test are a Patent Foramen Ovale (PFO) and an Atrial Septal Defect (ASD). A PFO is a flap-like opening between the upper chambers (atria) that failed to close completely after birth, a condition present in about 25% of the general population. An ASD is a true hole in the wall separating the atria. The bubble study is invaluable because these small defects often do not show up on a standard echocardiogram.
Patient Preparation and Safety Considerations
Little specific preparation is required for a bubble echocardiogram. Patients are typically advised to take all their usual medications and can eat and drink normally beforehand. Staying well-hydrated may help ensure easier insertion of the IV cannula. The test is considered safe and non-invasive, generally taking about 30 to 45 minutes to complete.
The risks associated with the procedure are minimal, as the contrast agent is sterile saline and air, which is naturally and rapidly absorbed by the body. Some patients may experience minor discomfort or bruising at the IV insertion site. The Valsalva maneuver can occasionally cause mild, temporary side effects like a slight headache or dizziness due to the pressure changes.