Variability of the Left Atrial Appendage in Human Hearts
Variability of the Left Atrial Appendage in Human Hearts
Rafał Kamiński 0 1
Adam Kosiński 0 1
Mariola Brala 0 1
Grzegorz Piwko 0 1
Ewa Lewicka 0 1
Alicja Dąbrowska-Kugacka 0 1
Grzegorz Raczak 0 1
Dariusz Kozłowski 0 1
Marek Grzybiak 0 1
0 1 Department of Clinical Anatomy, Medical University of Gdańsk, Gdańsk, Poland, 2 Department of Cardiology and Electrotherapy, Hospital of Medical University of Gdańsk , Gdańsk , Poland
1 Editor: Ingo Ahrens, University Hospital Medical Centre , GERMANY
Atrial fibrillation increases the risk of thrombus formation. It is commonly responsible for cerebral stroke whereas less frequently for pulmonary embolism. The aim of the study was to describe the morphology of the left atrial appendage in the human heart with respect to sex, age and weight. Macroscopic examination was carried out on 100 left appendages taken from the hearts of the patients aged 18-77, both sexes. All hearts preserved in 4% water solution of formaldehyde carried neither marks of coronary artery disease nor congenital abnormalities. Three axes of appendage orientation were performed. After the appendage had been cut off, morphological examination was performed in long and perpendicular axes. Measurements of the appendages were taken from anatomical specimens and their silicone casts. We classified the left atrial appendage into 4 morphological groups according to the number of lobes. Most left atrial appendages in female population were composed of 2 lobes. In the male group typically 2 or 3-lobed appendages were observed. The mean left atrial appendage orifice ranged from 12.0 to 16.0 mm and the most significant difference in the orifices between males and females was observed in LAA type 2 (about 3.3 mm). A smaller orifice and narrower, tubular shape of the LAA lobes could explain a higher risk of thrombus formation during nonvalvular atrial fibrillation in women. Knowledge of anatomical variability of the LAA helps diagnose some undefined echoes in the appendage during transesophageal echocardiographic examination.
Competing Interests: The authors have declared
that no competing interests exist.
Atrial fibrillation (AF) is the most common arrhythmia in the world, characterized by the
mechanical dysfunction of both atria and their appendages. It affects about 1–2% of the general
population [1,2] with estimated prevalence of 3 million people in the United States . AF
significantly increases the risk of thrombus formation in both appendages and is frequently
responsible for cerebral stroke while rarely for pulmonary embolism . The risk of embolic
stroke incident is five-fold higher in people with AF . The presence of thrombus in both
appendages can be examined by transesophageal echocardiography (TEE) . In literature, we
can find some cases demonstrating difficulties with evaluation of the contents in the left atrial
appendage (LAA) by TEE imaging . LAA anatomy with different shapes and lobes has been
regarded as a primary source of blood stasis and thrombus formation  and can correlate
with the risk of stroke in patients with AF . Currently, oral anticoagulation therapy is the
most effective prophylactic approach in patients with AF and increased risk of
thromboembolic events . Unfortunately, only 50–60% of patients taking Coumadin (warfarin) fall into
the therapeutic range, thus effective, long-term anticoagulation is very difficult . New oral
anticoagulant drugs like: dabigatran, rivaroxaban, apixaban–are the alternative to warfarin, but
they are still associated with potential bleeding complications and there is no antagonist agent
in case of bleeding events .
The aim of our study was evaluation of the left atrial appendage morphology in human
hearts. Morphometric measurements of both heart appendages and their silicone casts were
analysed by sex, heart’s weight and age in two groups: below 60 years of age (Y), and above
60 years of age (O).
Material and Methods
Our research project was approved by Independent Research Bioethics Committee of Medical
University of Gdańsk (IRBC) and achieved permit number: NKEBN/40-119/2010.
Investigation has been conducted according to the principles expressed in the Declaration of Helsinki.
The decision of IRBC repeals the need for the consent of donors and their next of kin for the
implementation of the research presented in the article. IRBC specifically waived the need for
written informed consent from the donors/next of kin. Macroscopic examination was carried
out on 100 left appendages (Y-62, O-38) taken from the hearts of both sexes aged 18–77. In all
cases, clinical data invariably indicated a negative history of cardiovascular disease and death
due to noncardiac causes. The hearts evaluated via gross examination showed no evidence of
pathologies. Subsequently, the hearts were preserved in 4% water solution of formaldehyde.
The hearts weighted from 210–490 grams. Classical anatomical studies were applied. After
removing the pericardium we evaluated the shape of the left atrial appendage (LAA). Because
of the LAA shape variability, we proposed to distinguish 4 types of the appendage (Table 1).
Type 1 was composed of the proximal and lower-distal lobe (Fig 1), type 2 had three lobes–
proximal, middle and distal (Fig 2), type 3 –proximal and upper-distal lobe (Fig 3) and type 4 –
central lobe and superior and inferior lobe/lobes (Fig 4). For the purpose of macroscopic
examination we assigned 3 axes of LAA. The long axis was a dimension from the base to the apex of
the appendage, the short axis was a distance between upper and lower edge of the appendage
and the perpendicular axis was between both walls of the appendage. After the appendage had
LAA t.1 The dominant lobe extended from the left atrium towards the anterio-lateral direction. The distal
part characterized itself as a narrow tube with its apex facing down
LAA t.2 The dominant lobe (proximal) extended from the lateral wall of the left atrium and descended
towards anterio-lateral direction. The middle lobe folded up towards the base of the heart and
bent down again to form a distal lobe
LAA t.3 The proximal lobe extended from the anterio-lateral part of the left atrium wall and ran slightly
down, next it continued into the distal lobe with its apex facing up and bent towards the
beginning of the aorta and the pulmonary trunk
LAA t.4 The main trunk of appendage (central lobe) started from anterio-lateral part of the left atrium wall
and run in horizontal plane towards the anterior surface of the heart. On the upper and lower
edge of the main lobe most commonly two small lobes were found:superior and inferior
Fig 1. LAA type 1: A diagram, an anatomical sample and a silicone cast. A-proximal lobe, B-distal lobe.
Fig 2. LAA type 2: A diagram, an anatomical sample and a silicone cast. A-proximal lobe, B-middle lobe, C-distal lobe.
Fig 3. LAA type 3: A diagram, an anatomical sample and a silicone cast. A-proximal lobe, B-distal lobe.
been cut off, morphological examination was performed and external measurements were
taken in the long and short axes. To evaluate the internal measurements of the LAA we
prepared their silicone casts by means of silicone mass (MM 922, catalyser B-5). All data were
analysed by the R statistical program.
Atrial appendage occurred in 56% examined hearts and was composed of two parts. The
dominant lobe extended from the left atrium towards the anterio-lateral direction. The distal part
characterized itself as a narrow tube with its apex facing down (Fig 1). The ostium of the
Fig 4. LAA type 4: A diagram, an anatomical sample and a silicone cast. A-central lobe, B-superior lobe, C- inferior lobe.
proximal lobe to the left atrium was smaller in females than in males and measured: 18.8 and
19.7 mm, respectively. In both groups, the size of the proximal lobe was similar. The distal lobe
was longer in females by about 3 mm and narrower by about 1 mm. Moreover, in people over
60 years of age the distal lobe was longer by about 2.8 mm compared to younger group. The
ostium size in the older group was bigger compared to the younger one and measured 17.7 and
22.9 mm, respectively (Table 2).
Left atrial appendage type 2
Atrial appendage type 2 was present in 23% examined hearts and was composed of 3 lobes.
The dominant lobe (proximal) extended from the lateral wall of the left atrium and descended
towards anterio-lateral direction. The middle lobe folded up towards the base of the heart and
bent down again to form a distal lobe. In the female group the ostium was smaller than in the
male one by about 3.6 mm and measured 12.0 and 15.6 mm, respectively. In the female group
all lobes of the LAA t.2 were smaller. Moreover both the connections between proximal and
middle lobes and between middle and distal lobes were narrower by over 7 and 3.6 mm,
respectively. In the older group the distal lobe was longer and wider by 4.7 and 3.4 mm, respectively.
The proximal lobe did not differ between the younger and the older group (Table 3).
Left atrial appendage type 3
Left atrial appendage type 3 occurred in 13% of the examined hearts and was composed of 2
lobes. The proximal lobe extended from the anterio-lateral part of the left atrium wall and
ran slightly down, next it continued into the distal lobe with its apex facing up and bent
towards the beginning of the aorta and the pulmonary trunk. Generally, the female
appendage was bigger compared to the male one. The connection between the appendage and the
left atrium (orifice) in females was smaller by about 1.3 mm compared to males. The
proximal lobe was significantly bigger in females by about 2.2 mm in the short axis and 6.4 mm in
the long axis, contrary to the distal part which was shorter in that group. Because of few LAA
t.3 in the examined material of the hearts, we were unable to make a comparison between the
hearts above and over 60 years of age (Table 4).
Left atrial appendage type 4
Left atrial appendage type 4 was the rarest one and was observed only in 8% of the hearts. It
was composed mainly of 3 parts. The main trunk of the appendage (central lobe) started from
the anterio-lateral part of the left atrium wall and descended (ran) in horizontal plane towards
the anterior surface of the heart. On the upper and lower edge of the main lobe most commonly
two small lobes were found: superior and inferior. In the female population the central lobe
was bigger contrary to the male group: both in the long and short axes but the ostium of the
appendage was 1.5 mm smaller in that group. The superior lobe was 3 mm bigger in the short
axis in the female group compared to male one, with the similar dimension in the long axis.
The inferior lobe was bigger in females in all dimensions (Table 5).
The most frequent type of LAA in males was type 1, which occurred in 54% of the hearts.
LAA type 2 was observed in 31%, LAA type 3 –in 9% and the rarest LAA type 4 was noticed
only in 6% of the hearts. In the female group the most common appendage was type 1, it
occurred in 61%, next one was LAA type 3–24%, LAA type 4–9% and the most infrequently
occurring one—LAA type 2 observed only in 6% (Table 6).
On the basis of our study we noticed that in the female group, the connection between the
left atrium and the appendage was smaller in all types of LAA. The smallest difference between
the sizes of the orifices in both groups was observed in LAA type 1, whereas the biggest one
was in LAA type 2 (Table 7).
In medical journals there are few publications describing gross morphology of the left atrial
appendage. Studies presenting LAA taken from a CT image reconstruction are most common.
Generally, LAA is described as a tubular, narrow, hooked and finger-like structure [12,13] or a
pouch–like extension of the body of the atrium . On the basis of 220 LAA casts
examinations Ernst et al. observed variability of LAA . They described the course and ramifications
of the principal axis of the LAA and the orifice diameters. The course of the principal axis was
straight (7%), slightly bent and slightly spiral (23%), slightly bent and extremely spiral (5%),
extremely bent and slightly spiral (24%) and extremely bent and extremely spiral (42%). The
mean orifice diameters for LAA with >5 branches and >40 twigs were 15.0 and 21.0 mm,
respectively. The first, “lobe classification” of LAA morphology was published in 1997 in
Circulation by Veinot et al.. They determined the orifice diameter, width, length and the number
of lobes, unfortunately they did not describe the relation of the lobes in all types of LAA. They
distinguished 4 types of LAA. The dominant type was the appendage composed of two lobes
which occurred in 54% of the hearts, three-lobed LAA existed in 23%, one-lobed appendage was
observed in 20% and the rarest one, composed of 4 lobes was found only in 3% of the examined
hearts. Moreover they found the orifice size to be age- and sex-related. In men and women over
20 years old, the mean orifice diameters of 11.6 and 10.7 mm were found, respectively. On the
basis of our research we also found LAA orifice diameters to be sex-related. In women we
observed a smaller orifice size in all types of LAA. Comparing female and male groups we
noticed that the biggest difference in the orifice size was in LAA type 2 and accounted for 9.0
and 12.3 mm, respectively. This feature can be useful for determination of a proper size of the
occluder device placed in the LAA as a prevention of stroke in patients with nonvalvular AF
(nvAF),[17,18,19]. In other types of LAA there were no so significant differences in the orifice
size: LAA t.1–0.5 mm; LAA t.3–1.6 mm; LAA t.4 -1.9 mm. Su et al. determined LAA orifice
to be mostly oval in shape, not round. The longer dimension was 17.4±4 mm and the shorter
one– 10.9 ± 4.2 mm. In our work we studied only the longer dimension of the LAA orifice and
it measured from 12 to 16 mm, depending on the LAA type. In the studies which were carried
out in living patients (Transesophageal Echocardiography or Computed Tomography), the
orifice size was bigger. Nucifora et al.  presented LAA in 3-dimential TEE and they showed
that the longer dimension of LAA orifice measured 22.3 ± 4.5 mm, and shorter one– 16.5 ± 4.3
mm. Moreover they pointed out that in patients with paroxysmal or persistent AF the orifice of
the LAA was bigger and it changed its shape from oval to more roundish. The differences in the
LAA orifice sizes observed in post-mortem and alive examination were the caused by
with an obvious bend in the proximal or middle part of the dominant lobe,or folding back of
the LAA anatomy on itself at some distance from the perceived LAA ostium. this type of
the LAA may have the secondary lobes or twigs
with one dominant lobe of sufficient length as the primary structure. variations of this LAA
type arise with the location and number of secondary or even tertiary lobes arising from
the dominant lobe
with limited overall length with more complex internal characteristics. Variations of this LAA
type have a more irregular shape of the LAA ostium and a variable number of lobes with
lack of a dominant lobe
with dominant central lobe with secondary lobes extending from the central lobe in both
superior and inferior directions
formaldehyde, affecting the heart tissue and time of preservation. According to our study LAA
type 1 was very often observed in male and female hearts. The main difference in the appendage
between both groups was the distal lobe which was narrower and longer in women. That tubular
shape of the distal lobe, which gets longer, especially in women over 60 years old may determine
a different course of the coagulation process during nvAF. The analysis of the LAA type 2
occurring more commonly in the male population showed that it was definitely larger than in
women. Moreover, the orifice and proximal-middle lobe connections were significantly smaller
in females, which can be conducive to thrombus formation, too. LAA type 3 was more
commonly observed in females than in males. Also, the appendage was longer in women with the
smaller orifice to the left atrium. Such morphological features of the left atrial appendage may
increase the risk of ischaemic stroke in women. Available clinical data suggest a higher
thromboembolism (TE) rate in women. CHA2DS2-VASc score predicting TE events reflects this
finding by providing risk stratification scheme which takes into account the sex of patients with
atrial fibrillation,[22,23,24]. New advanced visualization techniques of the heart allow us to
perform evaluation of the LAA. Using a computed tomography and reconstruction of the images,
Wang et.al formed a new classification of LAA (Table 8),. In our study, we generally focused
on the main, invariable lobes which compose LAA not on the twigs or small ramifications.
Comparing our results to the Veinot’s classification we observed similar incidence of LAA
types. The most frequent type of LAA was the two-lobed appendage (type 1 and type 3): 69%,
the three-lobed LAA was found in 23% examined hearts. WindSock and ChickenWing LAA in
Wang’s classification existed in 66% and fulfilled the criteria of our LAA type 1and type 3 which
were observed in 69%. Our research showed that the most common types of LAA in the female
group were type 1 and type 3 (85% of all female hearts), but in themale group the dominant
types of LAA were type 1 and type 2 (85% of all male hearts). This showed that in women we
can mostly find 2-lobed LAA but in men mostly 2- and 3-lobed LAA. Moreover, the Ucerler’s
et al. study showed that the most common type of LAA was the 2-lobed appendage .
Summing up, in our population we can mostly find 2-lobed left atrial appendage. This knowledge
could be useful in some unclear cases during TEE examination when thrombus or
“normal”anatomy of the LAA have to be differentiated .
The study results confirmed considerable morphological differences in the LAA. A significant
variability was found in the appendage shape and the dimensions of the structures observed–
with the tendency to reach lower values in the hearts in women. In the majority of cases, both
in males and females, the appendages had 2 lobes, while 3-lobed appendages were less common
and mainly found in men. This anatomical variability seems to be clinically significant and
may affect the course of the coagulation process inside the appendage, and thus may be the
cause of the diagnostic errors when TEE is performed.
Conceived and designed the experiments: RK. Performed the experiments: RK AK MG MB
GP. Analyzed the data: RK AK EL DK GR. Contributed reagents/materials/analysis tools: RK
MB ADK. Wrote the paper: RK AK MB.
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