Thread by @TJHeartFellows

Following yesterday's #echofirst images of SAM, it’s time for another #tweetorial!

By senior fellow @NoahHaroian

#ACCFIT #Meded #FOAMed #cardiology #cardiotwitter

In this tweetorial, you will learn:
🟢The “ingredients” for SAM
🟢Who is at-risk for SAM
🟢How to treat SAM

Why are humans a set up for SAM?

Simple - because we have a cardiac loop.

Wait, what is the “cardiac loop”?

Answer: blood’s “U-turn” through the left ventricle.

Why do we have a loop in the first place?

Because evolution.

Learn more in this fascinating comparative biology article by Sherrid et al.

ahajournals.org/doi/10.1161/JA…

In short, as vertebrates emerged from the sea to live on land, gravity waged war on venous return

Nature had two options
🅰️Make the same pump work harder (energetically costly)
🅱️Figure out something new

Nature picked 🅱️

So what was nature’s big plan?

Move the atria ABOVE the ventricles – aka the “atrial ascent”

Now vertebrates can live on land, adequately preloaded, without expending extra energy.

#winning

But all that glitters is not gold.

An unintended consequence of the atrial ascent is that we now have a cardiac loop – a design flaw leaving us prone to LVOT obstruction from SAM

🔑It all starts when blood is re-directed from the “U-turn”, accumulating in a “dead end” behind the mitral valve and PUSHING the anterior MV leaflet into the LVOT.

🔑Smaller "gates" into the LVOT (coaptation-septum distance) re-direct more flow into the dead end

But more importantly, misdirected flow creates

🔥LEAFLET SLACK 🔥

“Without leaflet slack, the mitral leaflets will remain in their more or less central position in the LV, regardless of the hemodynamic force compelling them forward.” – Sherrid, et al.

Once a slack leaflet is in the LVOT, it's like a sail waiting for a breeze

In keeping with our analogy, the severity now depends on two things:
-How big is the ⛵️ (aka amount of leaflet slack)?
-How strong is the 💨 (aka velocity of ejection flow)?

What about the Venturi effect?

The “pulling” force generated by high velocity LVOT flow that “sucks” the leaflet into the LVOT.

Bottom line – mechanistic studies show SAM is driven by pushing, not pulling, the anterior leaflet into LVOT.

sciencedirect.com/science/articl…

🟢The “ingredients” for SAM

⭐️Small gate (Re-directs flow into the “dead end”, pushing leaflet into LVOT)
⭐️Big sail (leaflet slack)
⭐️Lots of wind (High ejection velocity)

Modified diagram from a fantastic review article by Manabe, et al.

link.springer.com/article/10.100…

🟢Who is at-risk for SAM

Using a substrate-based approach….

🟢How to treat SAM

Also using a substrate-based approach…

Before we end, an important pearl:

🔑 🔑 🔑ALWAYS consider SAM in an unstable patient 🔑 🔑 🔑

Why? fixing hypotension often requires LESS pressors

link.springer.com/article/10.100…

To concluded, you should now understand

🟢The “ingredients” for SAM
🟢Who is at-risk for SAM
🟢How to treat SAM