A positive bubble study means some blood is slipping from the right side of your circulation to the left without first passing through the lungs. In most people the route is a small flap-like opening between the heart’s upper chambers that never sealed after birth, something about 1 in 4 adults carry.1PubMed. Cryptogenic stroke and patent foramen ovale: clinical clues to paradoxical embolism Finding it is not the same as finding a problem, and what the result means for you depends mostly on why the test was ordered.
What the Bubbles Are Showing
The bubbles come from about 8 mL of salt water mixed with 1 mL of air, sometimes plus a little of your own blood.2PubMed Central. Agitated Saline Contrast Echocardiography in the diagnosis of right to left shunts: Guidance and recommendations from the British Society of Echocardiography The mix is pushed rapidly back and forth between two syringes until it turns into a white froth.3PubMed Central. The role of agitated saline contrast echocardiography in the evaluation of pulmonary hypertension It is then injected into an arm vein, at about 1 mL per second, while the ultrasound watches your heart.4PubMed Central. The role of agitated saline contrast echocardiography in the evaluation of pulmonary hypertension
The test happens during a standard ultrasound of the heart, with a probe on your chest. The injection may feel cool. You may be asked to cough or bear down as the bubbles go in. Several injections are often given, and the whole thing takes only minutes.
Ultrasound bounces off the boundary between liquid and air, so each bubble shows up as a bright speck against the dark, blood-filled chambers. Within a beat or two of the injection, the right chambers fill with a cloud of white specks, which tells the team the test has worked. The right side always fills, so the only question is whether specks later appear in the left chambers, which normally stay clear.
The bubbles are larger than the lungs’ tiniest blood vessels, so normally the lungs filter them all out.5PubMed. Exercise-induced intrapulmonary arteriovenous shunting in healthy humans Bubbles appearing in the left side of the heart mean blood bypassed that filter, which your report may call a right-to-left shunt. The bubbles themselves are harmless and dissolve on their own.
Heart Hole or Lung Vessels, What the Timing Tells Doctors
Doctors count the heartbeats between bubbles appearing on the right and on the left.6Alberta Sono. Shunts & Bubble Studies Bubbles crossing within about 3 heartbeats usually suggest an opening inside the heart.7PubMed Central. Intrapulmonary Shunt Confirmed by Intracardiac Echocardiography in the Diagnosis of Hepatopulmonary Syndrome Arrival after roughly 3 to 8 beats points to abnormal vessels in the lungs.8PubMed Central. Delayed bubble, coil and trouble: young stroke as a presentation of paradoxical embolism from previously unrecognised pulmonary arterio-venous malformation (PAVN) Timing cutoffs vary slightly between centres, with some using 1 to 2 beats for the heart.9Alberta Sono. Shunts & Bubble Studies
Your report may use the words “early” or “immediate” for crossing that usually means a heart-level shunt, and “late” or “delayed” for crossing that suggests the lungs. It may also grade the shunt by bubble count. It is reasonable to ask which pattern yours showed.
Timing is a strong clue but not a final answer. A borderline result is often settled with a different test, such as a throat ultrasound, which can show the actual opening.
Before birth, everyone has an opening between the upper heart chambers, and it usually seals after the first breaths.10PubMed Central. Patent Foramen Ovale Closure in 2019 In some people the two layers never fully fuse, leaving a slit-like flap called a patent foramen ovale.11PubMed Central. Patent Foramen Ovale Closure in 201912Cleveland Clinic Journal of Medicine. Approach to ASD and PFO: When and how to fix a ‘hole in the heart’
The flap is held shut by higher pressure in the left upper chamber. When pressure on the right rises during coughing, lifting or straining, it can briefly open and let blood and bubbles through. That is why the opening often only turns up with a provoking maneuver.
An atrial septal defect (ASD) is a true hole in the wall between the upper chambers. Blood through an ASD usually flows mostly left to right, unlike a PFO, which opens only when right-side pressure rises.13Cleveland Clinic Journal of Medicine. Approach to ASD and PFO: When and how to fix a ‘hole in the heart’ A scope-style ultrasound down the throat usually tells the two apart.14Cleveland Clinic Journal of Medicine. Approach to ASD and PFO: When and how to fix a ‘hole in the heart’
Late bubbles can come from abnormal artery-vein links in the lungs, which can occasionally let a clot reach the brain.15PubMed Central. Delayed bubble, coil and trouble: young stroke as a presentation of paradoxical embolism from previously unrecognised pulmonary arterio-venous malformation (PAVN) In advanced liver disease, late bubbles can signal widened lung vessels called hepatopulmonary syndrome.16PubMed. Role of Quantitation of Saline Bubble Studies in Patients with Liver Cirrhosis This affects about 5 to 32% of people with cirrhosis and causes low oxygen that extra oxygen barely fixes.17Journal of Acute Care. The Bubble Test for Diagnosis of Hepatopulmonary Syndrome
Does It Explain a Stroke
A clot from a leg vein can pass through a PFO and travel to the brain instead of being caught in the lungs.18PubMed. Cryptogenic stroke and patent foramen ovale: clinical clues to paradoxical embolism
Still, since about 25% of people have a PFO, finding one after a stroke doesn’t prove it was the cause.19PubMed. Cryptogenic stroke and patent foramen ovale: clinical clues to paradoxical embolism Doctors first rule out other causes, and a stroke with no found cause may be called cryptogenic stroke.20PubMed. Cryptogenic stroke and patent foramen ovale: clinical clues to paradoxical embolism They typically look for narrowed neck or brain arteries, an irregular rhythm such as atrial fibrillation, and clot sources in the heart before suspecting the PFO.
A PFO is more likely the cause if you had a prior leg clot or lung clot, or recent long travel.21PubMed. Cryptogenic stroke and patent foramen ovale: clinical clues to paradoxical embolism Migraine, sleep apnea, waking up with the stroke, or straining just before symptoms are also clues.22PubMed. Cryptogenic stroke and patent foramen ovale: clinical clues to paradoxical embolism
Doctors also use a risk score called RoPE, and a score of 6 or more makes it more likely the PFO caused the stroke.23PubMed Central. Association between RoPE score and PFO grading on bubble echocardiography in cryptogenic stroke patients: a retrospective cohort study A score of 5 or less makes another cause more likely.24PubMed Central. Association between RoPE score and PFO grading on bubble echocardiography in cryptogenic stroke patients: a retrospective cohort study The score is a points tally using factors such as age and the absence of stroke risk factors like high blood pressure, diabetes and smoking. Younger people without those risk factors score higher.
Age shifts the picture too. The PFO link is strongest in people under 60, while in older people other causes such as artery disease are more common, so the same result weighs differently at different ages.
How Big Is the Shunt and Why It Matters
Doctors count bubbles in the left heart to grade the shunt from small to large.25PubMed. Quantification of patent foramen ovale shunt severity by transesophageal echocardiogram and transcranial doppler in routine clinical practice More than 20 bubbles within 3 heartbeats on a throat ultrasound counts as a large shunt, a recognised reason to consider closure after an unexplained stroke.26PubMed. Quantification of patent foramen ovale shunt severity by transesophageal echocardiogram and transcranial doppler in routine clinical practice
Reports often sort results into small, moderate and large. A handful of bubbles suggests a small shunt, while a dense cloud filling the left chambers suggests a large one. Systems vary a little between labs.
A tiny shunt in someone whose stroke had another cause is rarely the target of treatment. Size is read together with your age, history and the look of the PFO itself, such as a long tunnel or a floppy wall.
Many PFOs only show when you bear down as if straining.27PubMed. Different Valsalva Manoeuvre Procedures for the Diagnosis of Right-to-Left Shunt by Contrast-Transcranial Doppler In one comparison, about 11% tested positive at rest but about 26% while bearing down.28PubMed. Different Valsalva Manoeuvre Procedures for the Diagnosis of Right-to-Left Shunt by Contrast-Transcranial Doppler A negative test without proper bearing down may therefore miss a PFO.
To do it well, take a breath and push as if straining on the toilet. Hold until you’re told to stop, then release. The release is when bubbles are most likely to cross.
Migraine, Diving and Exercise
About half of people with migraine with aura have a PFO, while migraine without aura shows no link.29PubMed Central. Efficacy of transcatheter patent foramen ovale closure for drug-resistant migraine: initial experience in Japan and long-term outcome Aura is a set of temporary symptoms, usually visual, such as zigzag lines or blind spots, that appear before or with the headache. Having aura does not mean you have a PFO, since about half of people with it do not. More bubbles has been tied to more disabling headaches,30PubMed Central. Right Heart Contrast Echocardiography Microbubble Count and Migraine Severity: A Dose–Effect Relationship Study but a clear benefit of this link for patients hasn’t been shown.31PubMed. Migraine with aura and TCD bubble-test: The significance of positive result
A PFO raises decompression sickness risk about fivefold.32Divernet. Diving With a PFO: Risks, Testing, and Safe Diving Strategies The absolute risk stays small, about 1 episode per 1,000 dives versus 2 per 10,000.33Divernet. Diving With a PFO: Risks, Testing, and Safe Diving Strategies34PubMed. Patent foramen ovale influences the presentation of decompression illness in SCUBA divers
Decompression sickness happens when nitrogen dissolved in the blood forms bubbles on ascent, and a PFO may let those bubbles cross to the arteries. It matters most for divers who push limits, such as deep or repeated dives. If you dive, a dive doctor can discuss conservative dive profiles, and avoiding heavy straining after dives is often advised. Some divers choose closure, others adjust their diving.
About 9 in 10 healthy people show late bubbles during hard exercise.35PubMed. Exercise-induced intrapulmonary arteriovenous shunting in healthy humans36PubMed. Intrapulmonary shunting and pulmonary gas exchange during normoxic and hypoxic exercise in healthy humans These lung shortcuts close within 3 minutes of stopping.37PubMed. Exercise-induced intrapulmonary arteriovenous shunting in healthy humans A late positive during exercise testing can therefore be normal.
What Tests Come Next
A standard chest ultrasound catches about 83% of shunts.38PubMed Central. Comparative Accuracy of TCD, TTE, TEE, and Cardiac CT in Detecting Right-to-Left Shunt in Embolic Stroke of Undetermined Source A throat ultrasound catches about 95% and shows the wall’s anatomy best.39PubMed Central. Comparative Accuracy of TCD, TTE, TEE, and Cardiac CT in Detecting Right-to-Left Shunt in Embolic Stroke of Undetermined Source A head Doppler that listens for bubbles in brain arteries caught every shunt in one comparison, but has more false alarms.40PubMed Central. Comparative Accuracy of TCD, TTE, TEE, and Cardiac CT in Detecting Right-to-Left Shunt in Embolic Stroke of Undetermined Source Misses do happen: in one group, 4 of 7 confirmed shunts were missed on chest ultrasound.41Journal of Asian Pacific Society of Cardiology. Comparison of Simultaneously Performed Transcranial Doppler and Transthoracic Echocardiogram in Patients with Suspected Patent Foramen Ovale
Follow-up is most likely when the result will affect a decision, such as after an unexplained stroke in a younger person. If the study was done for another reason and nothing about your health points to a problem, doctors often stop at the first result.
For a throat ultrasound you are sedated and a thin probe goes down your throat. You shouldn’t eat beforehand, and you need a ride home. The probe sits just behind the heart, so it sees the wall between the upper chambers without ribs and lungs in the way. It can show a PFO’s shape, whether the wall is floppy, and whether an ASD or other cause is present.
Does a PFO Need to Be Closed
For people under 60 with an unexplained stroke and a high-risk PFO, closure within 6 months lowers repeat stroke risk.42Escardio. Patent foramen ovale in patients with cryptogenic stroke: to close or not to close? In one long trial, repeat stroke ran about 0.6 per 100 people per year after closure versus 1.1 with medicine alone.43PubMed. Long-Term Outcomes of Patent Foramen Ovale Closure or Medical Therapy after Stroke Closure did not change survival.44Escardio. Patent foramen ovale in patients with cryptogenic stroke: to close or not to close?
If you had no stroke, an incidental PFO usually needs no treatment, and closure for migraine alone is not standard. It helps to ask whether yours was found by chance or as part of a workup.
Closure is done through a vein in the groin. A catheter is guided up into the heart and a small device is placed across the PFO, usually with sedation or light anaesthesia. Many people go home the same day or the next. Over the following months the heart’s own tissue grows over the device, and a bubble study at about 6 months checks for leftover leaks.45PubMed Central. Long-term Echocardiographic Features After Percutaneous Closure of Patent Foramen Ovale
Most people are given blood-thinning medicine such as aspirin for a period afterward, with the exact plan set by the doctor. Strenuous activity is usually limited for a short time while the device settles. Some people develop an irregular heart rhythm after closure, which usually settles but is a reason to report palpitations.