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Left Atrial Appendage Important for Heart Health & Repair?

by Steve S. Ryan

Left Atrial Appendage; Source: Boston Scientific Inc. educational brochure

In a remarkable experimental study using mice hearts, Israeli scientists discovered that the Left Atrial Appendage is a reservoir of different types of stem cells which can stimulate the heart to repair itself.

This study confirms the revolutionary view that the heart contains stem cells which help heal diseased tissue. These stem cells function as progenitor cells, that is, they can regenerate and turn into not only cardiac muscle cells, but also other kinds of cells such as blood vessels, connective tissue, and, “most importantly, a certain kind of cardiac tissue that is important for the body’s immune system.”

In other words, cells from the Left Atrial Appendage have the ability to stimulate an injured heart to heal itself.”

Though groundbreaking, this research is preliminary. Further experimental studies are necessary to determine how exactly and under what conditions these LAA stem cells work. Are they vestigial or a remnant reservoir of stem cell building blocks left over from fetal and early childhood development and which now serve no or little active function? The study did not imply there was an actual ongoing repair mechanism in the heart from these progenitor cells in the LAA. And is the LAA the only source of cardiac repair? Many people over the years have had their LAAs removed or closed off without seemingly dire consequences to their heart health. (Thanks to Pete for calling our attention to this article and its importance.)

The Left Atrial Appendage (LAA) Defined

The Left Atrial Appendage (LAA) is a pocket or sleeve-like structure on the outside top of the left atrium which opens into the left atrium. It’s a complicated structure with often more than one lobe. From an embryonic perspective, the LAA is more related to the ventricles than to the smooth-walled atrium. It has a distinct anatomy which contains numerous trabeculae (muscle fibers) which resemble the ventricles.

Left Atrial Appendage with clot - dissected autopsy photo; Stamford Sch of Med with permission at

Clot in Left Atrial Appendage (LAA)

In the first trimester or two of our time in the womb, the Left Atrial Appendage (LAA) was originally our left atrium (LA). When the final real Left Atrium (LA) formed gradually from the conjunction and evolutionary development of the four pulmonary veins, the actual LA chamber grew and ballooned out, pushing the smaller remnant LA up to the left top of the Left Atrium where it became known as the Left Atrial Appendage (LAA) with its own functions and behaviors.

But as we age and as heart disease/A-Fib, etc. start to set in, the LAA can turn into “the most lethal, no longer essential appendage in the human anatomy.” (Thanks to Shannon Dickson for these insights about the LAA.)

Most A-Fib blood clots which cause stroke come from the Left Atrial Appendage. By closing off the Left Atrial Appendage, most but not all risk of stroke is eliminated even if you are still in A-Fib.

Functions of the Left Atrial Appendage

  1. The Left Atrial Appendage functions like a reservoir or decompression chamber or a surge tank on a hot water heater to prevent surges of blood in the left atrium when the mitral valve is closed.Without it, there is increased pressure on the pulmonary veins and left atrium which might possibly lead to heart problems later.
  2. Cutting out, stapling shut or closing off the LAA reduces the amount of blood pumped by the heart and may result in exercise intolerance for people with an active life style. (In dogs the LAA provides 17.2% volume of blood pumped by the Left Atrium.)
  3. The LAA also has a high concentration of Atrial Natriuretic Factor (ANF) granules which help to reduce blood pressure. The LAA functions as a storage device for ANF. But recent preliminary research indicates that the Right Atrial Appendage compensates for the loss of the LAA by producing more ANF.
  4. The Left Atrial Appendage may also function as a reservoir of different types of stem cells which can stimulate the heart to repair itself (thanks to the research of the above Israeli scientists).

Should the Left Atrial Appendage be Routinely Cut Out or Closed Off?

Almost all surgical treatments for A-Fib cut out or close off the Left Atrial Appendage (LAA). In A-Fib, blood stagnates in the LAA and clots tend to form. The rationale for closing off the LAA is that, in case the surgery fails which happens occasionally, the patient is still protected from having an A-Fib stroke. 90%-95% of A-Fib strokes come from clots which originate in the LAA. By closing off the Left Atrial Appendage, most but not all risk of stroke is eliminated even if you are still in A-Fib.

VIDEO: See our library of videos about Atrial FibrillationWatch an endoscopic view of stapling and removal of the Left Atrial Appendage. (1:34 min.) Go to video->

And even if a person is no longer in A-Fib, closing off the LAA may still prevent a stroke. The LAA is where most clots originate. If a surgeon is already working on the heart, why not close off the LAA and reduce the patient’s chance of having a future stroke? (If a surgeon doesn’t close off the LAA, they could be sued if a patient later had a stroke, even if the patient was no longer in A-Fib.) Living with a greatly reduced risk of stroke is more important for most people even at the loss of the functions of the LAA.

In the future even people without A-Fib may have their Left Atrial Appendage closed off if it prevents or reduces the risk of a stroke. This may be more important for older people, particularly women, who are at a greater risk of stroke as we age. There are currently a variety of devices, surgical and non-surgical, which can do this. (LAA closure may be an important new way to reduce strokes, particularly in the elderly.)

Why are we more at risk of a stroke as we age? Abnormal platelet aggregation (clumping, platelets sticking together) tends to increase as we age. Any blood particle larger than 5-10 micrometers can clog capillaries. Capillaries are tiny and very narrow—with a diameter of only 8-10 micrometers on average, while platelets are usually 2-4 micrometers. If they clump together, it doesn’t take much to block a capillary. If enough capillaries become blocked in the brain, an ischemic stroke can occur. Older people tend to be less active and have weaker hearts which can result in less blood flow or perfusion (hypoperfusion) and more platelet clumping. (This lower perfusion in the brain also produces cognitive decline over time.)

No Option if You Want to have Surgery for A-Fib?

For patients undergoing A-Fib surgery in the US, surgeons automatically remove/close off your LAA. Patients aren’t offered the option of not having the LAA removed. It’s not the same in other countries where removing the LAA isn’t automatic. What triggers the removal? The LAA isn’t removed unless a patient has “a CHADS2 score ≥1, in the presence of rapid firing coming from the left atrial appendage (LAA), and when the procedure is deemed safe.”

But some question the need or benefit of removing the LAA if one is no longer in A-Fib after surgery. For a patient made A-Fib free, would their heart function better or more normally if they still had their LAA? Few clinical studies have been done on this subject. The author isn’t aware of any Surgeons (or EPs) who do pre- and post-LAA closure measurements of exercise ability, heart pumping function, etc. of the heart with and without the Left Atrial Appendage.


Close off the Left Atrial Appendage? Though this is a hard call, I’d recommend holding on to your Left Atrial Appendage (LAA) as long as possible. In addition to the first three functions of the LAA described above, this new Israeli study demonstrates that the LAA functions as a reservoir of different types of stem cells which can stimulate the heart to repair itself. This may turn out to be an invaluable, irreplaceable function of the LAA more important for heart health than all the others.

But as we age and/or develop A-Fib, we may have to have our LAA removed or closed off to prevent a stroke which can be a fate worse than death. This is a decision to be made with your doctor and may change as you age and change.

References for this article
Kaneko, T. et al. Hybrid Surgical and Catheter Treatment for Atrial Fibrillation. ISRN Cardiology, Volume 2013, Article ID 920635.

Even, Dan. “Israeli scientists discover the heart’s hidden healing cells.” HAERETZ, May 7, 2013

Leinonen, Jussi V. et al. “Left Atrial Appendages from Adult Hearts Contain a Reservoir of Diverse Cardiac Progenitor Cells.” PLOS ONE, 8(3): e59288. doi: 10.1371/journal.pone.0059228.

Al-Saady, N M, et al. Left atrial appendage: structure, function, and role in thromboembolism. Heart 1999;82:547-554 doi:10.1136/hrt.82.5.547

Hondo T. et al. “The Role of the left atrial appendage. A volume loading study in open-chest dogs.” Jpn Heart J 1995 Mar;36(2):225-34.

Widmaier, Eric P.; Hershel Raff, Kevin T. Strang (2008). Vander’s Human Physiology, 11th Ed. McGraw-Hill. pp. 291, 509–10. ISBN 978-0-07-304962-5.

Posted June 2013

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Last updated: Friday, April 13, 2018

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