(Circulation. 1997;96:3112-3115.)
© 1997 American Heart Association, Inc.
Articles |
Anatomy of the Normal Left Atrial Appendage
A Quantitative Study of Age-Related Changes in 500 Autopsy Hearts: Implications for Echocardiographic Examination
From the Division of Anatomic Pathology (J.P.V., P.J.H., W.D.E.), the Division of Cardiovascular Diseases and Internal Medicine (F.G., B.K.K., J.B.S., A.J.T.), and the Section of Biostatistics (K.R.B., J.T.E.), Mayo Clinic and Mayo Foundation, Rochester, Minn.
Correspondence to Bijoy K. Khandheria, MBBS, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Background Transesophageal echocardiography (TEE) is the diagnostic modality of choice for visualizing the left atrial appendage (LAA). This study defined the morphology of the LAA in normal autopsy specimen hearts and considered the implications of these findings for TEE studies.
Methods and Results Five hundred normal autopsy hearts were
reviewed (25 male and 25 female subjects from each decade for 10
decades). LAA length, width, orifice size, and number of lobes were
recorded. Number of lobes was compared between sexes with the rank
sum test and regressed against age. Mean length, width, and orifice
size increased with age, up to age 20 years, in both sexes. Rates were
significantly different between sexes for LAA size (P=.011)
and width (P=.006). After age 20, statistically significant
but clinically insignificant age-related changes were observed.
Fifty-four percent of LAAs had two lobes (range, 1 to 4), with no age
or sex differences. Lobes exist in different planes of the heart. Most
pectinate muscles were 
1 mm in width. Pectinate muscles <1
mm (2.6% of cases) were seen in only the first and last decades.
Conclusions Age- and sex-related differences in LAA dimensions exist. These differences and the existence of multilobed appendages are important in the accurate TEE evaluation of LAA. Because lobes exist in different planes, imaging must be done in multiple planes to visualize the entire LAA.
Key Words: aging • echocardiography • imaging • structure
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Transesophageal echocardiography (TEE) is an integral part of any comprehensive ultrasonographic examination of the heart and great vessels because the proximity of the esophagus to the heart and great vessels permits high-quality imaging in nearly all patients undergoing TEE.1 This technique is safe to perform, and the list of indications continues to increase.1 Emboli from an intracardiac source are an important and frequent cause of transient ischemic attacks and cerebrovascular accidents. The left atrial appendage (LAA) is often suspected of harboring the source of embolic material. Recent investigations1 2 3 4 5 6 7 8 have focused on the clinical usefulness of TEE and its superiority over transthoracic echocardiography in the evaluation of the LAA as a source of thromboembolism; in fact, this is one of the most common indications for performing TEE.1 Recent studies have proposed the use of TEE before cardioversion for detection of left atrial and LAA thrombus in patients with atrial fibrillation.9 10 This recommendation is based on a commonly entertained but unproved theory that the absence of thrombus in the left atrium and LAA, as determined with TEE, may safely allow early cardioversion without prior prolonged anticoagulation.
With the increasing use of TEE for morphological and functional evaluation of the LAA, it has become important to obtain information about normal LAA anatomy. Because we could not find a detailed study of the normal LAA, this study was initiated.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Study Patients
Specimens of 500 normal human hearts from autopsies performed between 1960 and 1982 were procured from the Mayo Clinic tissue registry.11 12 13 14 Specimens were excluded if a clinical history of cardiac disease or pulmonary or systemic hypertension was present or if any evidence of heart disease was noted at autopsy. All specimens were reexamined grossly to ensure exclusion of abnormal specimens. Specimens with nonintact or nonreconstructable LAA were excluded from the study.
We obtained specimens from 25 male and 25 female subjects from each decade of life, ages 1 to 100 years.
Anatomic Measurements
For each heart, measurements of LAA length, width, orifice size,
and number of lobes were recorded (Figs 1
and 2).
The LAA shape and presence or absence of pectinate muscles and their
size were also recorded.
|
|
The left atrium was opened and the orifice size was measured, with a
ruler calibrated in centimeters, from a point just inferior
to the left superior pulmonary vein to the opposite side of the
orifice opening (Fig 1
). The shape was elliptical rather than round.
The orifice width was taken as the maximum dimension of the ellipse.
Length was measured as the distance perpendicular from the opening of
the orifice to the apex of the LAA tip. The widest external width was
noted.
The number of lobes was counted by external examination and confirmed
by probe exploration after the LAA was opened. Pectinate muscle size
(<1 mm or 1 mm) was recorded.
A lobe was defined by the following criteria: (1) it was a visible outpouching from the main tubular body of the LAA, usually demarcated by an external crease; (2) it was internally capable of admitting a 2-mm probe (ie, it was not simply a tag of external adipose tissue); (3) it was occasionally but not necessarily associated with a change in direction of the main tubular body of the LAA; (4) it could lie in a different anatomic plane than the main tubular body; and (5) by definition, the LAA must have at least one lobe (ie, a tubular body with a blind-ending sac).
Statistical Methods
The distribution of each measurement was examined overall and by
age category (<20 or 20 years). Means and standard deviations were
calculated separately for the two age strata overall and by sex.
To analyze age- and sex-specific distribution of each measurement, two-segment linear logistic regression models were estimated. These models assumed that the logarithm of the odds of having a measurement greater (versus less) than any constant c is linear from age 0 to 20 years and from age 20 onward. The probability of sex-specific intercepts and slopes was also considered. The models were fit using SAS PROC LOGISTIC, and model choice was based on Akaike's information criterion.15 The advantage of these semiparametric models is that they generate age- and sex-specific prediction intervals directly, without having to make distribution assumptions. To corroborate these results qualitatively and to provide intuitively understandable growth rates, segmented linear regression was also performed, again with allowance for possible sex differences.
Body Size
For subjects <20 years, the separate effects of age and body
size on the LAA dimensions were assessed with multiple linear
regression models, including various combinations of age, height,
weight, and body surface area. The choice among models was guided by
Mallows' Cp statistics.16
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Means and standard deviations of each measurement by sex and age (
20 or <20 years) are shown in the
Table. Prediction intervals
based on logistic models are shown in Figs 3, 4, and 5.
Age and sex accounted for only 27%, 28%, and 13% of the variation of
LAA orifice size, length, and width in subjects younger than 20 years.
In subjects 20 years, age and sex accounted for only 3%, 1%, and
2% of the variation of these three parameters.
|
|
|
|
Mean orifice size, length, and width increased at average rates of
0.024, 0.041, and 0.030 cm/yr, respectively, during the first 20 years
of life (P<.01). Length and width increased at a slower
rate in female subjects. In adults 20 years old, orifice size
increased, length decreased, and width increased at average rates of
0.0016, -0.0040, and 0.0019 cm/yr, respectively. However, these
average rates of change were due almost exclusively to the changes
observed in male subjects, in whom the estimated rates were 0.0026,
-0.0072, and 0.0037 cm/yr, respectively (based on selected
models).
Effects of Body Size
When age, sex, and body size factors of height and weight or
body surface area were considered simultaneously in the
<20-year age group, the best model (based on Mallows' Cp) for LAA
diameter and length was based on age and sex. LAA width was associated
slightly more strongly with height than with age, but this difference
was not enough to warrant substituting height for age in the model.
None of the body size measurements had an independent association with
LAA dimensions. In the 20-year age group, body size did not make a
significant contribution to prediction except that height tended to
replace sex as a predictor of LAA width (P=.02). Overall, in
both groups, body size made little additional contribution over age and
sex in predicting LAA dimensions.
Fifty-four percent of LAAs had two lobes, and the number ranged between
one and four lobes (Fig 6).
There were no age or sex differences.
|
Most LAAs (97%) had pectinate muscles 1 mm in width. Pectinate
muscles <1 mm (3.0%) were noted only in the first and last
decades. No sex-related differences were noted.
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The LAA is a small, muscular extension of the left atrium arising near the left pulmonary veins. It arises anterolaterally and lies in the left atrioventricular sulcus atop the proximal portion of the left circumflex artery.
It has been described as a long, narrow, tubular, wavy, hooked appendage with a narrow junction and crenelated lumen.13 14 17 Differences between the LAA and the right atrial appendage have also been noted,13 14 17 18 and their importance in the assessment of situs and congenital heart malformations has been stressed. No previous study has defined the range of normal dimensions in a large number of normal hearts.
Unlike the right atrial appendage, in which the normal anatomy has been studied in 23 randomly selected patients,18 the LAA has been relatively ignored except for general observations. This study demonstrated age- and sex-related differences in LAA dimensions and firmly established that the LAA is multilobed (80% have two or more lobes). These lobes often lie in different planes.
Improved imaging techniques and the use of biplane19 and multiplane20 TEE have allowed visualization of the LAA, which previously was difficult to visualize by other imaging methods. Because accuracy of LAA thrombus detection with TEE is important in the precardioversion evaluation of patients with atrial fibrillation,9 10 21 it is vital to know what variations, especially in location and size of the pectinate muscle, exist in the normal anatomy of the LAA.
Mistaking a normal lobe for a thrombus or missing an LAA thrombus in a secondary lobe is possible if one is not aware of the variable anatomy of the LAA. This study demonstrated variability in the anatomy of the LAA and substantiated the existence of the multilobed LAA and thus the importance of searching for more than one lobe with TEE.
Larger pectinate muscles (1 mm) occur in 97% of LAAs and
constitute another potential pitfall in TEE imaging of the LAA. Small
(<1 mm) pectinate muscles were seen only in the first and last
decades of life.
Conclusions
The accurate detection of thrombus and intra-atrial masses with
TEE is important in the evaluation of patients with atrial fibrillation
or stroke (or both). One must be aware of the complexity and
variability of the shape, size, and number of lobes of the LAA and the
size of the pectinate muscle to avoid misinterpretation. This study
established the complexity of the LAA and age- and sex-related changes
associated with it.
Received April 9, 1997; revision received May 27, 1997; accepted June 6, 1997.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. Khandheria BK, Seward JB, Tajik AJ. Transesophageal echocardiography. Mayo Clin Proc. 1994;69:856-863.[Medline] [Order article via Infotrieve]
2.
Pollick C, Taylor D. Assessment of left atrial
appendage function by transesophageal
echocardiography: implications for the development
of thrombus. Circulation. 1991;84:223-231.
3.
Pop G, Sutherland GR, Koudstaal PJ, Sit TW, de Jong G,
Roelandt JR. Transesophageal
echocardiography in the detection of intracardiac
embolic sources in patients with transient ischemic
attacks. Stroke. 1990;21:560-565.
4. Aschenberg W, Schluter M, Kremer P, Schroder E, Siglow V, Bleifeld W. Transesophageal two-dimensional echocardiography for the detection of left atrial appendage thrombus. J Am Coll Cardiol. 1986;7:163-166.[Abstract]
5. Arora R, Jolly N, Singh B, Mohan JC, Kalra GS, Sethi KK, Khalilullah M. Clinical utility of transoesophageal echocardiography: preliminary experience of 100 cases. Indian Heart J. 1991;43:357-360.[Medline] [Order article via Infotrieve]
6. Verhorst PM, Kamp O, Visser CA, Verheugt FW. Left atrial appendage flow velocity assessment using transesophageal echocardiography in nonrheumatic atrial fibrillation and systemic embolism. Am J Cardiol. 1993;71:192-196.[Medline] [Order article via Infotrieve]
7. Black IW, Hopkins AP, Lee LC, Walsh WF. Left atrial spontaneous echo contrast: a clinical and echocardiographic analysis. J Am Coll Cardiol. 1991;18:398-404.[Abstract]
8. Pozzoli M, Febo O, Torbicki A, Tramarin R, Calsamiglia G, Cobelli F, Specchia G, Roelandt JR. Left atrial appendage dysfunction: a cause of thrombosis? Evidence by transesophageal echocardiography-Doppler studies. J Am Soc Echocardiogr. 1991;4:435-441.[Medline] [Order article via Infotrieve]
9.
Manning WJ, Silverman DI, Gordon SP, Krumholz HM,
Douglas PS. Cardioversion from atrial fibrillation without
prolonged anticoagulation with use of transesophageal
echocardiography to exclude the presence of atrial
thrombi. N Engl J Med. 1993;328:750-755.
10. Manning WJ, Silverman DI, Keighley CS, Oettgen P, Douglas PS. Transesophageal echocardiographically facilitated early cardioversion from atrial fibrillation using short-term anticoagulation: final results of a prospective 4.5-year study. J Am Coll Cardiol. 1995;25:1354-1361.[Abstract]
11. Hagen PT, Scholz DG, Edwards WD. Incidence and size of patent foramen ovale during the first 10 decades of life: an autopsy study of 965 normal hearts. Mayo Clin Proc. 1984;59:17-20.[Medline] [Order article via Infotrieve]
12. Scholz DG, Kitzman DW, Hagen PT, Ilstrup DM, Edwards WD. Age-related changes in normal human hearts during the first 10 decades of life, I: a quantitative anatomic study of 200 specimens from subjects from birth to 19 years old. Mayo Clin Proc. 1988;63:126-136.[Medline] [Order article via Infotrieve]
13. Kitzman DW, Scholz DG, Hagen PT, Ilstrup DM, Edwards WD. Age-related changes in normal human hearts during the first 10 decades of life, II: a quantitative anatomic study of 765 specimens from subjects 20 to 99 years old. Mayo Clin Proc. 1988;63:137-146.[Medline] [Order article via Infotrieve]
14.
Sharma S, Devine W, Anderson RH, Zuberbuhler JR.
The determination of atrial arrangement by examination of appendage
morphology in 1842 heart specimens. Br Heart J. 1988;60:227-231.
15. Akaike H. Fitting autoregressive models for prediction. Ann Inst Stat Math. 1969;21:243-247.
16. Gorman JW, Toman RJ. Selection of variables for fitting equations to data. Technometrics. 1966;8:27-51.
17.
Tuccillo B, Stümper O, Hess J, van Suijlen RJ,
Bos E, Roelandt JR, Sutherland GR.
Transoesophageal echocardiographic
evaluation of atrial morphology in children with congenital heart
disease. Eur Heart J. 1992;13:223-231.
18. Manolis AS, Varriale P, Baptist SJ. Necropsy study of right atrial appendage: morphology and quantitative measurements. Clin Cardiol. 1988;11:788-792.[Medline] [Order article via Infotrieve]
19. Seward JB, Khandheria BK, Edwards WD, Oh JK, Freeman WK, Tajik AJ. Biplanar transesophageal echocardiography: anatomic correlations, image orientation, and clinical applications. Mayo Clin Proc. 1990;65:1193-1213.[Medline] [Order article via Infotrieve]
20. Seward JB, Khandheria BK, Freeman WK, Oh JK, Enriquez-Sarano M, Miller FA, Edwards WD, Tajik AJ. Multiplane transesophageal echocardiography: image orientation, examination technique, anatomic correlations, and clinical applications. Mayo Clin Proc. 1993;68:523-551.[Medline] [Order article via Infotrieve]
21. Orsinelli DA, Pearson AC. Usefulness of multiplane transesophageal echocardiography in differentiating left atrial appendage thrombus from pectinate muscles. Am Heart J. 1996;131:622-623.[Medline] [Order article via Infotrieve]
This article has been cited by other articles:
 |
|
 |
|
  K. A. Mizuguchi, T. M. Burch, B. E. Bulwer, A. A. Fox, R. J. Rizzo, and S. K. Shernan Thrombus or Bilobar Left Atrial Appendage? Diagnosis by Real-Time Three-Dimensional Transesophageal Echocardiography Anesth. Analg., January 1, 2009; 108(1): 70 - 72. [Full Text] [PDF]
|
|
|
|
 |
|
 J. A. Cabrera, S. Y. Ho, V. Climent, and D. Sanchez-Quintana The architecture of the left lateral atrial wall: a particular anatomic region with implications for ablation of atrial fibrillation Eur. Heart J., February 1, 2008; 29(3): 356 - 362. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. M. Lacomis, O. Goitein, C. Deible, P. L. Moran, G. Mamone, S. Madan, and D. Schwartzman Dynamic multidimensional imaging of the human left atrial appendage Europace, December 1, 2007; 9(12): 1134 - 1140. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. P. O'Brien, M. B. Srichai, E. M. Hecht, D. C. Kim, and J. E. Jacobs Anatomy of the Heart at Multidetector CT: What the Radiologist Needs to Know RadioGraphics, November 1, 2007; 27(6): 1569 - 1582. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. Donal, H. Yamada, C. Leclercq, and D. Herpin The Left Atrial Appendage, a Small, Blind-Ended Structure: A Review of Its Echocardiographic Evaluation and Its Clinical Role Chest, September 1, 2005; 128(3): 1853 - 1862. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Erdogan, M. T. Goren, R. Diz-Kucukkaya, and M. Inanc Assessment of Cardiac Structure and Left Atrial Appendage Functions in Primary Antiphospholipid Syndrome: A Transesophageal Echocardiographic Study Stroke, March 1, 2005; 36(3): 592 - 596. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Stollberger, B. Schneider, and J. Finsterer Elimination of the Left Atrial Appendage To Prevent Stroke or Embolism?: Anatomic, Physiologic, and Pathophysiologic Considerations Chest, December 1, 2003; 124(6): 2356 - 2362. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Y. Ho, R. H. Anderson, and D. Sanchez-Quintana Atrial structure and fibres: morphologic bases of atrial conduction Cardiovasc Res, May 1, 2002; 54(2): 325 - 336. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Shimizu, Y. Murakami, S.-i. Inoue, Y. Ohta, K. Nakamura, H. Katoh, T. Sakne, N. Takahashi, S. Ohata, T. Sugamori, et al. High Plasma Brain Natriuretic Polypeptide Level as a Marker of Risk for Thromboembolism in Patients With Nonvalvular Atrial Fibrillation Stroke, April 1, 2002; 33(4): 1005 - 1010. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. L. Klein, R. D. Murray, and R. A. Grimm Role of transesophageal echocardiography-guided cardioversion of patients with atrial fibrillation J. Am. Coll. Cardiol., March 1, 2001; 37(3): 691 - 704. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Agmon, B. K. Khandheria, F. Gentile, and J. B. Seward Echocardiographic assessment of the left atrial appendage J. Am. Coll. Cardiol., December 1, 1999; 34(7): 1867 - 1877. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Ernst, C. Stollberger, J. Finsterer, B. K. Khandheria, F. Gentile, J. B. Seward, A. J. Tajik, J. P. Veinot, P. J. Harrity, W. D. Edwards, et al. Determination of Left Atrial Appendage Morphology • Response Circulation, November 24, 1998; 98(21): 2355 - 2355. [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||