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Left Atrial Appendage

2016 AF: Thickening of Left Atrium and Fibrosis Amount Predicts Outcome of A-Fib Ablation

AF Symposium 2016

Thickening of Left Atrium and Amount of Fibrosis Predicts Outcome of A-Fib Ablation

by Steve S. Ryan, PhD

Dr. Nassir F. Marrouche

Dr. Nassir F. Marrouche

Dr. Nassir F. Marrouche, University of Utah (CARMA), is known for ground-breaking, thought-provoking research using MRI. His presentation was entitled “Atrial and Ventricular Myopathy: A Novel risk predictor for stroke and cardiovascular events.”

Amount of Fibrosis Better Predictor of Stroke Risk (and Heart Attack)

Dr. Marrouche began by showing how today’s stroke guidelines (CHADS2 or CHA2DS2-VASc) are mediocre predictive tools overall, according to most studies. Whereas atrial fibrosis detected by Delayed Enhancement-MRI (DE-MRI) is a better predictor of stroke risk.

DE-MRI stands for Delayed Enhancement Magnetic Resonant Imaging.

In Dr. Marrouche’s study, patients with more than 21% fibrosis had a 19.6% risk of stroke while those with under 8.5% fibrosis had only a 1% risk. The more fibrosis, the greater risk of clots forming in the Left Atrial Appendage (LAA).

In a study by King, higher levels of fibrosis were associated with ‘Major Adverse Cardiac Events’ (MACE), not only stroke but heart attack and deep vein thrombosis (a blood clot within a vein).

Cardiomyopathy and Fibrosis

Dr. Marrouche showed slides of normal atrial myocytes (muscle cells) vs. examples with extensive fibrosis where collagen replaced most of the red myocytes (which store oxygen until needed for muscular activity).

This is an important finding which may change the way we look at fibrosis.

This fibrosis correlated with abnormality of the atria (atrial myopathy) and deterioration of the ability of heart muscles to contract (cardiomyopathy). This is an important finding which may change the way we look at fibrosis.

(For further information on Dr. Marrouche’s work, see Higher Fibrosis at Greater Risk of Stroke and Precludes Catheter Ablation.)

Fibrosis/Myopathy Correlates with Atrial Strain

Dr. Marrouche showed slides of how the left atrium of an A-Fib patient with extensive fibrosis worked much harder to pump and had nearly three times more strain than a patient with mild fibrosis. (This may be why the left atrium often stretches and expands in remodeling.)

A-Fib Thickens Left Atrial Shape

In another ground-breaking observation, Dr. Marrouche showed slides of how the shape of the left atrium (LA) gets thicker as one progresses from no-A-Fib to paroxysmal to persistent A-Fib. In fact, in a study by Bieging, LA shape (thickness) is a strong independent predictor of outcome after AF ablation.

Left Atrial Appendage and Stroke Risk

Dr. Marrouche found that the Left Atrial Appendage (LAA) length, thickness and orientation correlate with stroke risk. These findings open up new avenues of research in A-Fib. Just looking at the LAA might produce an indication of stroke risk, which can be combined with other predictive measures.

Left Ventricular Disease Predicts Recurrence after Ablation Therapy

Some A-Fib patients also have a diseased Left Ventricle (LV) which shows up using ‘Late Gadolinium Enhancement- MRI’ (LGE-MRI). In a study by Suksaranjit, the recurrence rate after an ablation was 69% in patients with Left Ventricular LGE-MRI revealed disease, compared to 38% in patients without LV LGE-MRI. These patients also have more major adverse cardiac and cerebrovascular events.


Dr. Marrouche is now using both the amount of fibrosis and left atrial shape to stage and treat A-Fib patients. The main points we can learn from Dr. Marrouche’s research are:

Fibrosis makes the heart stiff, less flexible and weak, overworks the heart, reduces pumping efficiency and leads to other heart problems.

• Fibrosis puts you are greater risk of a stroke and other vascular problems.
• More fibrosis leads to thickened heart tissue, strains the heart and reduces the ability of the heart muscles to contract.
• A-Fib changes the thickness/shape of the left atrium.
• A-Fib can also change the length, thickness and orientation of the Left Atrial Appendage (LAA).
• Left Ventricular disease may accompany or be caused by A-Fib, be measured by MRI, and predict recurrence after catheter ablation..

What Patients Need To Know

Don’t delay! Your A-Fib leads to fibrosis! A-Fib produces fibrosis which is considered permanent and irreversible. Any treatment plan for A-Fib must try to prevent or stop remodeling and fibrosis.

Caveat: After reading Dr. Marrouche’s research and new insights that atrial fibrosis detected by DE-MRI is a better predictor of stroke risk (than CHADS2 or CHA2DS2-VASc), don’t rush into your EPs office asking about using MRI to diagnose your amount of fibrosis. Not every MRI technician and doctor has the special training and experience necessary to perform Dr. Marrouche’s testing. (And insurance companies may not want to pay for this testing. However, that may soon change.)

References for this article

Return to 2016 AF Symposium Reports by Steve Ryan, PhD

If you find any errors on this page, email us. Y Last updated: Monday, February 22, 2016

FAQs Understanding Atrial Fibrillation: The Left Atrial Appendage, What’s its role?

 FAQs Understanding A-Fib: LAA

FAQs Understanding Your A-Fib A-Fib.com9. “My surgeon wants to close off my LAA during my Mini-Maze surgery. Should I agree? What’s the role of the Left Atrial Appendage?”

The Left Atrial Appendage (LAA) is a pocket or sleeve-like structure on the outside left 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.

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,” according to Shannon Dickson of Afibbers.org.

Sometimes during a difficult A-Fib catheter ablation case (persistent or long-standing persistent), the LAA has to be partially or completely electrically isolated from the rest of the heart. When the LAA is ablated, there is a 70% chance of significantly reducing its emptying volume. If the LAA emptying volume is reduced to less than 40 millileters/sec, the patient would have to be put on blood thinners for life or their LAA would have to be removed or closed off. Otherwise clots would form in the LAA because of low blood flow.

Left Atrial Appendage; Source: Boston Scientific Inc. educational brochureFunctions 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 or stapling shut 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.)
  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 (See
    Left Atrial Appendage May be Important for Heart Repair http://a-fib.com/laa-important-for-heart-health-repair/

The LAA, Blood Clots and Stroke Risk: In A-Fib, blood stagnates in the LAA and clots tend to form. By closing off the Left Atrial Appendage, most but not all risk of stroke is eliminated even if you are still in A-Fib.

On the other hand, cutting out or stapling shut the LAA also reduces the amount of blood pumped by the heart and may result in exercise intolerance for people with an active life style.

One considered advantage of the Mini-Maze operations is that the Left Atrial Appendage (LAA) is routinely closed off.

The Controversy: Some question the need or benefit of removing the Left Atrial Appendage (LAA) if someone is no longer in A-Fib. For a patient made A-Fib free, would their heart function better or more normally if they still had their LAA?

Editor’s comment: If you are thinking of having a Cox Maze or Mini-Maze, discuss removing the LAA with the surgeon. Ask if they close off the Left Atrial Appendage and with what: sutures, stapler or the AtriClip, and their success rate of complete closure.

Go back to FAQ Understanding A-Fib

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