Does Everyone Have a Left Atrial Appendage?

Virtually every human being is born with a left atrial appendage, a small, finger-like pouch extending from the upper-left chamber of the heart. Congenital absence of this structure is so rare that, as of late 2024, only 23 cases had been documented in the entire medical literature.¹ So for all practical purposes, yes, you have one. But the appendage you have may look quite different from someone else’s, and that variation turns out to matter more than most people realize.

What the Left Atrial Appendage Actually Is

The left atrial appendage, often shortened to LAA, is a small sac that protrudes from the left atrium, which is the chamber that receives oxygen-rich blood returning from the lungs. It forms early in embryonic development as the original embryonic left atrium; the smooth-walled chamber that later becomes the main left atrium develops separately and eventually dwarfs the appendage in size.² The result is a small, irregular pouch with a trabeculated interior, meaning it has ridges and muscular bundles inside rather than smooth walls. Think of it as the original left atrium that never went away.

For most of cardiac history, the LAA was treated as a vestigial structure, something that existed but didn’t seem to do much. That view has changed substantially over the past few decades, as research revealed that the appendage plays roles in hormone production, blood pressure regulation, and acting as a decompression chamber when pressure in the left atrium rises.

Not All Left Atrial Appendages Look the Same

If you could look at a hundred people’s LAAs side by side, you’d be struck by how different they are. Researchers have classified them into four broad shapes, each named for its visual resemblance. A “chicken wing” shape bends sharply at some point along its length, folding back on itself. A “windsock” is a single elongated lobe that may taper. A “cactus” has a main lobe with smaller secondary lobes branching off. And a “cauliflower” is short, complex, and has multiple lobes without a clear dominant trunk.

How common each type is depends on the population being studied. In a large multicenter study of patients with atrial fibrillation, nearly half had the chicken wing type, about 30 percent had the cactus shape, roughly one in five had a windsock, and only about 3 percent had the cauliflower type.³ Studies that include people without atrial fibrillation sometimes find different proportions, with the windsock shape being more common in some control groups.⁴ The point is that these shapes represent a spectrum, and many people’s appendages don’t fall neatly into a single category.

The number of lobes also varies. Some people have a single-lobe LAA while others have three, four, or more. This variability isn’t random decoration. The complexity of the structure, particularly how many lobes it has, influences how blood flows through it and whether blood is prone to pooling inside.

Why Shape Matters for Stroke Risk

The reason cardiologists care about LAA shape at all is clot formation. In people with atrial fibrillation, an irregular heart rhythm that causes the atria to quiver rather than contract forcefully, blood can stagnate in the appendage. That stagnation, combined with the rough interior texture of the LAA’s walls, creates ideal conditions for clots to form.⁵ If a clot breaks free and travels to the brain, the result is a stroke.

Not all shapes carry equal risk. A meta-analysis found that people with the chicken wing morphology had about 41 percent lower stroke risk compared to those with other shapes.⁶ The likely explanation is geometric: the sharp bend in a chicken wing makes it harder for blood to sit undisturbed. Shapes that allow blood to stagnate in deep recesses, like the cauliflower, are associated with higher risk. One study found that the cauliflower shape was the most dangerous comparator, with other morphologies measured against it.⁷

The number of lobes also independently predicts clot formation. In one study, the overwhelming majority of patients who had clots in their LAA, about 94 percent, had three or more lobes, while clots were found in fewer than 1 percent of those with one or two lobes.⁸ That finding held even after accounting for other known risk factors. It suggests that some people may carry a congenital, shape-based predisposition to clotting if they ever develop atrial fibrillation.

The Appendage Does More Than Sit There

The LAA is not just a passive pouch. It serves as a reservoir when pressure in the left atrium rises, stretching to absorb extra volume and preventing the main chamber from becoming dangerously overloaded. Research during cardiac surgery, where the LAA can be temporarily clamped, has shown that the appendage is more compliant (stretchier) than the rest of the left atrium and makes a real contribution to this buffering role, particularly when the heart is under stress from pressure or volume overload.⁹

The appendage is also an endocrine organ. It produces atrial natriuretic peptide, a hormone that helps regulate blood pressure and fluid balance by telling the kidneys to excrete more sodium and water. When the LAA is closed off or removed, levels of this hormone shift. One study found that after LAA closure, a precursor to atrial natriuretic peptide dropped significantly in patients who had elevated baseline levels.¹⁰ However, the clinical significance of this hormonal shift is debated. A randomized trial that followed patients for up to two years after LAA amputation found no meaningful worsening of heart failure symptoms despite the hormone change, suggesting the body compensates.¹¹

The distinction between epicardial and endocardial closure devices may matter here. A study comparing the two approaches found that epicardial devices, which seal the LAA from the outside, caused more pronounced short-term hormonal changes, including drops in adrenaline, noradrenaline, and aldosterone, along with lower blood pressure at follow-up. Endocardial devices, which plug the opening from the inside, had a milder hormonal footprint.¹² The body’s response to losing the LAA’s hormonal output may depend in part on how the appendage is dealt with.

The LAA as a Trigger for Atrial Fibrillation

Beyond clot formation, the LAA has an electrical role that only became clear relatively recently. Cardiologists performing ablation procedures for atrial fibrillation, where abnormal electrical signals are targeted and destroyed, have found that the appendage itself can be the source of the arrhythmia. In patients undergoing repeat ablation procedures because a first attempt failed, the LAA was responsible for triggering the arrhythmia in roughly a quarter of cases.¹³ This finding reframed the appendage from a passive bystander to an active participant in the electrical misfiring that causes the atrium to fibrillate.

For people with persistent or recurrent atrial fibrillation, this means the LAA is sometimes not just the place where dangerous clots form but also part of the reason the arrhythmia keeps returning. Electrical isolation of the appendage during ablation procedures is becoming a more common strategy in those repeat cases.

What Happens When the LAA Is Closed Off or Removed

Because the LAA is the source of most clots in people with atrial fibrillation who go on to have strokes, a logical intervention is to seal it shut. Two main approaches exist: implanting a plug-like device inside the opening (endocardial occlusion) or placing a clip or staple around it from the outside during surgery (epicardial exclusion). The Watchman device is the best-known endocardial option, and it was shown in a landmark trial to be noninferior to the blood thinner warfarin for preventing stroke, though the procedure itself carried a higher risk of complications like pericardial effusion and procedural stroke compared to simply staying on medication.¹⁴

A meta-analysis comparing the Watchman to the Amplatzer device, another endocardial plug, found no statistically significant differences between the two in major safety or efficacy outcomes, including stroke prevention, bleeding, and death.¹⁵ The choice between devices tends to come down to anatomical fit rather than one being clearly superior.

After LAA closure, the heart does adjust. One study found improvements in left ventricular pumping efficiency and left atrial strain after the procedure, suggesting the heart may actually function better once the hemodynamic dead-end of the appendage is sealed off.¹⁶ That said, about a quarter of patients in that study were hospitalized for heart failure during follow-up, a reminder that the people receiving these devices tend to have significant underlying heart disease to begin with.

How the LAA Changes with Age

Your LAA at age 20 is not the same structure as your LAA at age 70. A large autopsy study of 500 hearts found that the appendage’s length, width, and opening all grow until about age 20, after which further changes are small in absolute terms but still detectable statistically.¹⁷ Dynamic CT imaging has shown that both the minimum and maximum volumes of the LAA tick upward over the decades, while its emptying efficiency decreases by roughly 2 percent per decade in both men and women. Men tend to have longer and wider appendages than women at any given age.¹⁸

The opening of the LAA also becomes more oval-shaped with age, and this remodeling correlates with heavier hearts. A study of donor hearts found that people with oval-shaped openings were on average several years older and had significantly heavier hearts than those with round openings.¹⁹ This progressive enlargement and loss of contractile efficiency may partly explain why stroke risk from atrial fibrillation rises so sharply with age: the older the LAA, the more sluggishly blood moves through it.

How Doctors See Inside It

If you have atrial fibrillation and your doctor needs to know whether a clot is sitting in your LAA, the traditional test is transesophageal echocardiography, an ultrasound probe passed down the throat to get a close-up view of the heart from behind. It’s uncomfortable but provides excellent images. Cardiac CT has emerged as a less invasive alternative. A meta-analysis of 27 studies involving nearly 7,000 patients found that CT with a delayed imaging protocol (waiting a few extra seconds for contrast dye to fill the appendage) achieved sensitivity of about 98 percent and specificity of essentially 100 percent for detecting clots.²⁰ A separate prospective study confirmed that dual-phase CT picked up clots with 96 percent sensitivity and 100 percent specificity when measured against the echocardiographic standard.²¹

The practical upshot is that for many patients, especially those who can’t tolerate having a probe in their throat, a well-done CT scan can answer the clot question reliably. This matters for people about to undergo a procedure like cardioversion (resetting the heart’s rhythm), where an undetected LAA clot could become a stroke the moment normal rhythm resumes.

How the Left Compares to the Right

Both atria have appendages, but they are not anatomical twins. The right atrial appendage tends to have a wider neck relative to its size, a smaller internal volume, and a more interconnected “dendritic” pattern of muscular ridges compared to the left.²² These structural differences may explain why clots form overwhelmingly in the left appendage rather than the right during atrial fibrillation. The right appendage’s wider opening allows blood to flow in and out more freely, while the left’s narrower neck and more complex interior create the stagnation that favors clotting.

In atrial fibrillation, blood velocity inside both appendages drops by about half compared to normal rhythm, but the left appendage also enlarges in response to the arrhythmia, while the right does not remodel in the same way.²³ This asymmetric remodeling further concentrates risk on the left side.

Rare Congenital Variants

While congenital absence of the LAA is the rarest anomaly, it’s not the only way the appendages can develop abnormally. In some congenital heart defects, both atrial appendages end up on the same side of the heart, lying next to each other rather than flanking the great arteries as they normally do. This is called juxtaposition of the atrial appendages, and it’s primarily associated with other complex congenital heart malformations rather than occurring in isolation.²⁴ Left juxtaposition, where both appendages sit to the left, is more common than right juxtaposition, though both are rare.

For the handful of people discovered to have no LAA at all, the finding is typically incidental, caught on imaging done for some other reason. In at least one documented case, the absence was viewed as a happy accident for the patient, who had atrial fibrillation but lacked the structure where dangerous clots would otherwise form.¹ It’s the kind of anatomical absence that creates no deficit and, in the right clinical context, turns out to be protective.

Genetics and the Appendage

The genetic architecture behind LAA shape and size remains poorly mapped, but there are hints that it overlaps with the genetics of atrial fibrillation itself. A study that combined gene expression data from left atrial tissue with genome-wide genetic data found that about two-thirds of expressed genes were regulated by common genetic variants, and roughly half of the known genetic risk regions for atrial fibrillation showed evidence of altering gene expression in left atrial tissue.²⁵ Among the implicated genes were those involved in cardiac transcription and ion channel function, suggesting that the same genetic variation that shapes the appendage’s physical form could also influence its electrical behavior.

This line of research is still in its early stages. Nobody can yet tell you, based on a genetic test, what shape your LAA is or how many lobes it has. But the finding that LAA morphology predicts clot risk independently of other known factors, combined with early evidence of genetic regulation of left atrial tissue, raises the prospect that LAA anatomy could eventually become part of personalized stroke risk assessment for people who develop atrial fibrillation.