Last Updated on June 3, 2026 by Don Gerig, RDCS
A Patent Foramen Ovale (PFO) is a slit-like defect resulting from an incomplete fusion of the foramen ovale within the atrial septum. Studies show that 20-25% of the population have a PFO and echocardiography is often used to diagnosis it. This week we will review the 4 things needed to rule out a PFO during an echo bubble study.
Patent Foramen Ovale (PFO)
- Incomplete fusion of the foramen ovale
- Not a true deficiency (separation) of the atrial septal tissue
- Slit-like defect
PFO: Risks & Symptoms
- Migraine headaches
- TIA, CVA
Echo Bubble Study
We have written extensively on the correct techniques to perform an echo bubble study. Please review our past blogs here:
- 7 Indications for an Echo Bubble Study
- 9 Steps to Perform an Echo Bubble Study
- 6 Tips to Improve an Echo Bubble Study!
Patent Foramen Ovale and Echo Bubble Studies
- Echo bubble studies are the principal means of diagnosis
- Potential for misinterpretation (false positive and/false negative)
Positive PFO Shunt
- Appearance of micro-bubbles in the left atrium shortly after right atrial opacification suggests an intracardiac right-to-left shunt
- First, inject saline without Valsalva to look for a resting shunt
Resting PFO Shunt
- Resting study: Bubble study without Valsalva
- Resting shunt: Agitated saline crosses from right-left without Valsalva
- A resting shunt has:
- Worse outcomes
- Predictor for stroke recurrence
Valsalva PFO Shunt
- If the first injection of agitated saline produces a positive result then there is no need for further imaging
- If the first injection is negative: Repeat with Valsalva
Valsalva Timing
- Injection: Performed while the patient is bearing down
- Valsalva Release: As contrast enters the RA
- Complete opacification of the RA occurs at the end of Valsalva
Valsalva Mechanism
- Valsalva momentarily alters the pressure gradient between the left and right atria
- This causes the septum primum, on the left side of the atrial septum, to transiently lift up and open the septum – like a door jamb
Acceptable Valsalva
- The interatrial septum shifts to the left
- An incorrect technique results in a lower detection rate of PFOs in echo
Valsalva Tips
- The patient bears down for 5–10 seconds
- Press on the patients’ abdomen and ask the patient to use their abdominal muscles to push back against your hand
- The patient may need several practice attempts
- Valsalva TEE
- Valsalva during TEE is dependent on the level of sedation
- Ask the patient to cough forcefully several times
- Perform the agitated bubble study toward the end of the TEE (patient less sedated)
Standard Timing
- Intracardiac shunt (PFO/ASD): bubbles typically appear in the LA within 3 cardiac cycles of RA opacification.
- Intrapulmonary shunt: bubbles usually appear after 4–6 cardiac cycles.
Important Exceptions
- Large pulmonary AV shunts may occasionally allow bubbles to appear earlier than expected, including within 3–5 cycles. Delayed appearance of bubbles can also occur with PFO in patients with enlarged atria, atrial fibrillation, or suboptimal Valsalva maneuver.
False Negative PFO: Echo Bubble Study
The main reason for a false negative study is because of inadequate technique. In order to feel confident in your diagnosis to rule out a PFO with an Echo Bubble Study there are 4 things to keep in mind:
4 Things Needed To Rule Out a PFO
1. Dense opacification. It is important to make sure the agitated saline was prepared correctly and administered in such a way as to densely opacify the right heart.
2. IAS Shift. The interatrial septum should visibly shift from right to left ensuring the Valsalva was correctly performed.
3. No bubbles in the LA.
If there is dense opacification of the right heart and an IAS shift (R-L) and no bubbles in the left atrium within 3 cardiac cycles a clinically significant PFO is unlikely.
4. Late Bubbles.
If bubbles appear in the LA after more than 3–5 cardiac cycles (commonly 4–8 cycles), this suggests transpulmonary shunting such as PAVM.
Echo Bubble Study vs Color Doppler
In a study by Marriott (2013):
- 1162 patients who underwent TTE agitated saline bubble studies
- Agitated bubble and Valsalva maneuver was compared with color flow
- 403 studies had shunting but 48% were only positive with Valsalva
- Strong agreement with TEE findings
- TTE color was insensitive (22% accurate) for detection of PFO compared with agitated saline bubble study
Transthoracic color flow imaging is too insensitive for PFO screening. An agitated saline bubble study is simple and highly accurate for the detection of right-to-left atrial communication with correctly performed Valsalva
Conclusion
It is recommended to use an echo-bubble study with Valsalva as the primary diagnostic tool for the detection of PFO in clinical practice.
Learn Echo Bubble Studies With More Confidence
Improve how you perform and interpret agitated saline bubble studies with practical, case-based instruction from CardioServ.
This self-paced course covers:
- Bubble study preparation and injection technique
- Image optimization tips
- PFO detection and common pitfalls
- Persistent left superior vena cava
- Pulmonary arteriovenous malformations
- Bubble studies for guided procedures
References
- Gupta, S. K., Shetkar, S. S., & Ramakrishnan, S. (2015). Saline Contrast Echocardiography in the Era of Multimodality Imaging — Importance of “ Bubbling It Right .” Echocardiography, 1707–1719. https://doi.org/10.1111/echo.13035
- Marriott, K., Ultrasound, M. C., Manins, V., Forshaw, A., Ultrasound, M. C., Wright, J., & Pascoe, R. (2013). Detection of Right-to-Left Atrial Communication Using Agitated Saline Contrast Imaging : Experience with 1162 Patients and Recommendations for Echocardiography. Journal of the American Society of Echocardiography, 26(1), 96–102. https://doi.org/10.1016/j.echo.2012.09.007
- Porter, T. R., Abdelmoneim, S., Belcik, J. T., Mcculloch, M. L., Mulvagh, S. L., Olson, J. J., … Wei, K. (2014). Guidelines for the Cardiac Sonographer in the Performance of Contrast Echocardiography : A Focused Update from the American Society of Echocardiography. Journal of the American Society of Echocardiography, 27(8), 797–810. https://doi.org/10.1016/j.echo.2014.05.011
- Puledda, F., Toscano, M., Pieroni, A., Veneroso, G., Piero, V. Di, & Vicenzini, E. (2016). Right-to-left shunt detection sensitivity with air – saline and air – succinil gelatin transcranial Doppler. International Journal of Stroke, 11(2), 229–238. https://doi.org/10.1177/1747493015609938
- Superiority of the Combination of Blood and Agitated Saline for Routine Contrast Enhancement
Fan, Sandra et al. Journal of the American Society of Echocardiography, Volume 12, Issue 2, 94 – 98 - Romero, R., Frey, J. L., Schwamm, L. H., Demaerschalk, B. M., Chaliki, H. P., Parikh, G., … Babikian, V. L. (2009). Cerebral Ischemic Events Associated With ‘ Bubble Study ’ for Identification of Right to Left Shunts. Stroke, 2342–2348. https://doi.org/10.1161/STROKEAHA.109.549683
