A “bubble study” is a specialized, non-invasive diagnostic procedure that helps physicians visualize the movement of blood within the heart. The purpose of this test is to identify abnormal passages or openings between the chambers of the heart, which are not visible during a standard ultrasound. The procedure is a routine, low-risk method performed in conjunction with an echocardiogram, using sound waves to create moving images of the heart’s structure and function. This enhanced imaging technique provides specific details about blood flow, helping to detect subtle anomalies.
Defining the Bubble Study
The bubble study is formally known as Contrast Echocardiography with Agitated Saline. This test uses a prepared solution as a contrast agent to trace blood flow, providing detail a conventional echocardiogram cannot achieve alone. Standard ultrasound imaging effectively views the heart’s muscle and valves but struggles to track subtle, abnormal blood movements across structures.
The contrast agent is sterile saline solution forcefully mixed, or agitated, with a small amount of air or the patient’s blood immediately before injection. This agitation creates microscopic gas bubbles, or microbubbles, that are highly reflective on the ultrasound screen and allow blood flow to be traced.
When injected into a vein, the microbubbles travel through the bloodstream and enter the right side of the heart. In a normal circulatory system, these bubbles are filtered out by the capillaries in the lungs and should never appear on the left side of the heart.
The appearance of microbubbles in the left heart chambers indicates a “shunt,” which is an abnormal connection allowing blood to flow from the right side to the left side (a right-to-left shunt). The contrast agent acts as a temporary, visible tracer to pinpoint exactly where this abnormal crossing occurs.
How the Procedure is Performed
The bubble study is typically performed in an outpatient setting and takes approximately 30 to 45 minutes. The patient lies down on a cushioned table, often on their left side, to optimize the ultrasound view of the heart. Electrodes are placed on the chest to monitor the heart’s rhythm throughout the examination.
A healthcare professional inserts an intravenous (IV) cannula into a vein in the arm to provide access for injecting the contrast agent. Once the IV is secured, the sonographer or nurse prepares the agitated saline solution by rapidly moving the mixture between two connected syringes. This creates the frothy mixture of microbubbles, which is then injected through the IV line while the sonographer captures images with the ultrasound transducer.
The injection is quick, and the microbubbles travel rapidly toward the heart’s right side, allowing the sonographer to watch their path on the echocardiogram screen.
To increase the test’s sensitivity and reveal shunts that may only open intermittently, the patient is often asked to perform the Valsalva maneuver. This involves straining or bearing down, which temporarily increases pressure within the chest. Releasing this strain maximizes the pressure gradient between the right and left sides of the heart, potentially forcing an otherwise closed opening to let bubbles pass through.
Conditions Diagnosed by the Bubble Study
The primary utility of the bubble study is detecting structural abnormalities that create a right-to-left shunt. The two most common conditions identified are the Patent Foramen Ovale (PFO) and the Atrial Septal Defect (ASD). Both involve an opening in the wall separating the heart’s two upper chambers, the atria.
A PFO is a flap-like opening, a remnant of fetal circulation, that fails to fully seal after birth. An ASD, by contrast, is a true structural hole in the atrial wall that developed abnormally. The bubble study is highly effective at visualizing the crossing of microbubbles through either of these defects.
Physicians frequently order this test for patients who have experienced an unexplained stroke or transient ischemic attack (TIA), often referred to as cryptogenic stroke. In these cases, a PFO is suspected of allowing a small clot (embolus) to pass from the venous system directly into the arterial system, bypassing the lungs and traveling to the brain.
The bubble study can also help diagnose pulmonary arteriovenous malformations (PAVMs), which are abnormal connections between arteries and veins in the lungs. Like intracardiac shunts, PAVMs allow venous blood to enter the systemic circulation without being properly filtered.
Interpreting the Results and Next Steps
The interpretation of the bubble study focuses on the location and timing of the microbubbles after they enter the heart. A negative result means the microbubbles appear only in the right side of the heart, where they are absorbed and dispersed in the pulmonary circulation without crossing to the left. This confirms the absence of a right-to-left shunt.
A positive result is confirmed when microbubbles are observed in the left atrium or left ventricle. The timing helps determine the shunt source: an immediate appearance (within three to five heartbeats) suggests an intracardiac shunt (PFO or ASD), while a delayed appearance (after five heartbeats) can indicate a pulmonary shunt (PAVM).
The severity of the shunt is graded semi-quantitatively based on the maximum number of microbubbles counted in the left heart chambers in a single image. A small shunt might show just a few bubbles, while a large shunt can show a dense cloud of contrast opacifying the left chambers.
Shunt Grading System
A widely accepted grading system classifies shunts as:
- Small shunt: Between three and nine bubbles.
- Moderate shunt: Ten to thirty bubbles.
- Large shunt: More than thirty bubbles crossing.
Following a positive result, the physician or cardiologist determines the appropriate next steps based on the shunt size, the patient’s symptoms, and medical history. Management options range from observation to prescribing antiplatelet medications or blood thinners. In high-risk situations, a catheter-based procedure, such as a PFO closure, may be recommended to close the defect.