Thread by @SamuelB316

If you're in clinical practice, you've probably coming across an agitated saline contrast (ASC) study today in some way, shape or form - unclear etiology of hypoxemia, cryptogenic CVA, RV dilation, etc. In light of our review 👇, a 🧵 1/ onlinejase.com/article/S0894-…

The principle is simple - agitated saline microbubbles should never be seen in left-sided cardiac structures (i.e. LA, LV, aorta) and if they are, shunting is happening at some level. Classic teaching here is that the lungs act as a sieve for the microbubbles. 2/

This is partially true. The average pulmonary capillary diameter is ~7-8um (👇) so anything larger will be "filtered" out. What about smaller microbubbles (and there are certainly smaller microbubbles made during the agitation process)? 3/

Turns out these smaller bubbles will dissolve between 190 and 550ms, which is less than the typical RBC transit time through the pulmonary capillary system (👇median ~1.2s). 4/

From here on out, it is worth noting that the person performing the echo is *way* more important than the person reading it. How the study is interpreted and the presence of L-sided bubbles will depend on the image quality and the dedication to provocative maneuvers. @mghecho 5/

To maximize the utility of a bubble study, we need:
- Complete opacification of the RA adjacent to the interatrial septum (IAS)
- *Well-performed* provocative maneuvers so RA pressure > LA pressure (with bowing of the IAS towards the LA). 6/

Direct visualization of bubbles crossing the IAS or exiting a pulmonary vein is the most accurate way of diagnosing an intracardiac or intrapulmonary shunt *regardless* of the timing of their appearance (more succinctly noted in the @ASE360 guidelines 👇). ::1...2...3..:: 7/

3-6? Initially established from case studies and subsequently expanded. An attempt to utilize a simple concept (bubbles will take longer to traverse the pulmonary circulation), but fails to account for variation in patient hemodynamics and pulmonary AVM sizes. 8/

The counting method should be used only if we can't get a good view of the IAS or the origin of L-sided microbubbles.
Similarly, if we see IAS bowing towards the LA with complete opacification and *no L-sided bubbles* we can feel confident there is no intracardiac shunt. 9/

While a lot of us use the 👀 test to quantify the degree of intracardiac shunting, only #HHT has developed a standardized rubric for the degree of shunting.

In the major PFO closure trials, grading was similar 👇 and based on the maximum number of bubbles *in the LA*. 10/

Bubbles in the LA *before or simultaneously* with the RA? Think anomalous venous connection / sinus venosus defect. We need our amazing sonographers to:
- Image non-traditional sites (CS, L-sided SVC, IVC, pulmonary veins)
- Repeat injections in the other arm (or leg). 11/

Safety?
- *If needed*, ASC studies are safe in a variety of populations, including pregnancy, pregnancy, MCS (careful with ECMO alarms!) onlinejase.com/article/S0894-… 12/

Take a look through the entire review if interested in a more in-depth analysis. Thanks for reading! #EchoFirst @ASE360 @JournalASEcho @TimChurchillMD @MayoNamasivayam @Ph_Bertrand