Thread by @adnanalkhouli

🧵What does the left atrial appendage do? Is it just a nidus for thrombus?

A brief review of proposed & proven functions of the LAA👇

#CardioTwitter #EPeeps #MedEd
@drpaulfriedman @ChetRihal

#1 LAA plays a very important capacitance role.

Animal studies in 1990s showed:

- LAA is more compliant than LA
- LAA acts like a decompression chamber during systole
- The capacitance/reservoir role is key when LAP is elevated
- Eliminating LAA acutely ⬆️ LA pressure in dogs

- Effect of LAAO on hemodynamics in humans is debatable

- OBS data ➡️ that LAAO ⬆️ LAP, ⬇️ LA transport function, ⬆️ HF

- However, in LAAOS III RCT there was no ⬆️ in HF admissions w LAAO

- Caveat: epicardial closure vs ednocadail plugging of LAA don’t produce similar effects

#2 LAA has a hemostatic function

Data from hemostasis I & II studies & PRAGUE-17 showed that

- Epicardial LAAO has considerable impact on neurohormonal parameters & BP. This effect was persistent during mid term f/u

- Endocardial LAAO has minimal or no hormonal or BP impact

#3 Arrhythmia roles of the LAA

- LAA is suggested to be an underrecognized source of AF initiation

- THE BELIEF trial showed that empirical isolation of the LAA ⬆️ freedom from AF without increasing complications

- A meta analysis by Friedman et al confirmed this concept

- BUT: stroke risk w electrical isolation of LAA was a major concern

- However, Di Biase et al showed that this risk can be mitigated with appropriate OAC or LAAO

- LAA may not always be pro-AF. Melduni showed that routine LAAO during surgery was associated w ⬆️ post-op AF👇

#4 LAA as a source of stem cells

- In 2000-2010s. several groups showed that the LAA contains a large number of cardiac progenitor cells (CPCs) - reported to present up to 20% of LAA tissue in some studies!

- This fueled an interest in the role for LAA in regenerative medicine

- First in human feasibility studies (Patching the myocardium w LAA CPCs during CABG) has been published

- A limited number of ‘efficacy’ studies in animals showed a potential role for LAA CPC in myocardial salvage after myocardial infarction

#5 Coronary protection

It has been suggested that the left and right atrial appendages overlay & protect the origin of the coronary arteries from the friction associated with the dynamic motion of the heart. However, this proposed function hasn’t been studied.

In Summary,

📌 The LAA has important roles hemodynamic, hemostatic & electrical functions. Our knowledge of those functions is limited.

📌 While we continue to learn about this unique structure, we should not discard it as a mere nidus for thrombus.