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An investigation of the anatomical variations of left atrial appendage by multidetector computed tomographic coronary angiography
European Journal of Radiology 81 (2012) 1575–1580
Contents lists available at ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
An investigation of the anatomical variations of left atrial appendage by multidetector computed tomographic coronary angiography Mustafa Koplay ∗ , Cengiz Erol, Yahya Paksoy, Ali Sami Kivrak, Seda Özbek Department of Radiology, Selcuklu Medical Faculty, Selcuk University, The Central Campus, 42075 Konya, Turkey
a r t i c l e
i n f o
Article history: Received 12 February 2011 Accepted 21 April 2011 Keywords: Left atrial appendage Variations MDCT
a b s t r a c t Purpose: The left atrial appendage (LAA) is usually known as a long, tubular, hooked structure derived from the left atrium. However, it varies widely in terms of anatomical shape. In this study, anatomical shape variations of the LAA were investigated and classified in vivo in a large group of patients by multidetector computed tomography (MDCT) coronary angiography. Materials and Methods: The study included 320 consecutive patients (223 men and 97 women, with a mean age of 58 years) who underwent MDCT coronary angiography. MDCT was performed with a 64-detectorrow computed tomographic scanner. LAA anatomical variations were classified as five main types and further divided into subtypes. In addition, we gave the classifications descriptive names according to the anatomical external appearance of the LAA: horseshoe (type 1), hand-finger (type 2a), fan (type 2b), wing (type 2c), hook (type 3), wedge (type 4) and swan (type 5) shapes. The types and subtypes of the LAA variations and the presence of thrombus were recorded. Results: In our study, the LAA tip orientation was used and the LAA was divided into type 1, type 2a, 2b, 2c, type 3, type 4 and type 5 in 44 (13.8%), 65 (20.3%), 155 (48.4%), 8 (2.5%), 27 (8.4%), 6 (1.9%) and 15 (4.7%) patients, respectively. LAA thrombus was detected in four patients (1.25%), who had classified LAA shapes of type 2a and type 2b. Conclusions: The LAA has multiple anatomical shape variations. We demonstrated previously undefined new shape types of LAA. Knowledge of LAA variations is important in order to avoid procedure-related complications when ablative treatment is to be performed or if surgical procedures are indicated in this region. MDCT coronary angiography provides important and detailed information about determining and evaluating these variations before undertaking a planned procedure in this region. © 2011 Elsevier Ireland Ltd. All rights reserved.
The left atrial appendage (LAA) is usually known as a long, tubular, hooked structure derived from the left atrium [1,2]. However, it varies widely in terms of anatomical shape [1,3]. It lies within the borders of the pericardium, superior to the left ventricular free wall and adjacent to the superior lateral aspect of the main pulmonary artery [2]. Clinically, the LAA is an important region because of its association with atrial tachyarrhythmias and thrombi [3,4]. Recently, developing technologies have produced new interventional methods in the treatment of this region [2,4–7]. It is important to be aware of the anatomy of the LAA during surgical procedures and for interventional and diagnostic purposes. To obtain the correct diagnosis and treatment during interventional procedures and to perform complication-free surgery, knowledge of the anatomy and possible variations of this area is important [2–4].
In the evaluation of the LAA, imaging methods such as echocardiography, computed tomography (CT), magnetic resonance (MR) angiography and conventional angiography have been used [8]. Recent advances in CT techniques, such as multidetector scanners, make it possible to visualize the cardiac anatomy and vascular structures in detail. Multidetector computed tomography (MDCT) is a reliable and noninvasive tool for diagnosing vascular anomalies and in the determination of cardiac anatomy [9]. For this reason, MDCT can also detect the real incidence of LAA variations in vivo. In this study, we classified LAA by means of anatomical shape and investigated the frequency and its relationship with trombus formation using MDCT coronary angiography. 1. Materials and methods 1.1. Patients
∗ Corresponding author. Tel.: +90 332 2415000x41134. E-mail address: [email protected] (M. Koplay). 0720-048X/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrad.2011.04.060
We conducted a retrospective analysis of 320 patients (223 men, 69.7%, and 97 women, 30.3%; age range, 32–78 years; mean, 58 years) who underwent MDCT coronary angiography between
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Fig. 1. Left lateral (a) and anteroposterior view (b) of 3D volume-rendering images show the type 1 LAA. Ao, Aorta; Cx: left circumflex coronary artery; LAA, left atrial appendage; LAD, left anterior descending coronary artery; LPA, left pulmonary artery; LV, left ventricle; MPA, main pulmonary artery; PV, pulmonary vein; RAA, right atrial appendage; RPA, right pulmonary artery; T, appendage tip. See manuscript for details.
January 2008 and April 2009. The indications for MDCT coronary angiography were angina pectoris, symptoms suggesting coronary artery disease, atypical chest pain, difficulty in diagnosis based on conventional angiography, and screening for coronary artery disease. MDCT coronary angiography was not performed on patients with sustained arrhythmia, a heart rate greater than 80 beats/min despite -blocker use, known allergic reaction to contrast media, poor renal function (serum creatinine >1.5 mg/dL), pregnancy, respiratory insufficiency, poor clinical condition. The procedures used were in accordance with the recommendations found in the Helsinki declaration and institutional review board approval. 1.2. MDCT scan protocol and image analysis The study was retrospective and MDCT angiography was used to detect anatomical shape variations of the LAA. MDCT angiography was performed with a 64-slice CT scanner (Somatom Sensation 64, Siemens Medical Solutions, Forchheim, Germany). The scan was performed during a 10-second breath hold, with a 0.6 mm collimation, and 0.6 mm slice thickness reconstruction. During the image acquisition, 80 ml of non-ionic iodinated contrast agent was injected intravenously at a rate 5 ml/s followed by 40 ml of saline at 5 ml/s. Imaging was obtained by retrospective ECG-gating. Reconstructed images were then transferred to a processing workstation for further analysis with specialized software (Vitrea 2; Vital Images, Inc., Minneapolis, MN). In addition to traditional axial images, multiplanar reconstructions (MPR) and three-dimensional volume-rendering (3D VR) images were used to assess the LAA anatomical shape variations. LAA shapes were categorized similar to the previous studies of Lacomis et al. [3]. This previous study used only three types of classification based on the orientation and location of the LAA ‘tip;’ we have defined five types of classification, with subtypes, defined as follows: Type 1: Appendage tip is oriented superiorly parallel to the pulmonary artery (Fig. 1). Type 2a: Appendage tip is long like a finger and oriented inferiorly parallel to the pulmonary artery (Fig. 2a). Type 2b: Appendage tip is short and not prominent; it is oriented inferiorly parallel to the pulmonary artery (Fig. 2b). Type 2c: Appendage tip is prominent and oriented inferiorly parallel to the pulmonary artery, giving the appendage the shape of wing (Fig. 2c). Type 3: Appendage tip is oriented superiorly but then turns medially; it is located between the pulmonary artery and the left atrial body (Fig. 3).
Type 4: Appendage tip is oriented superiorly but then turns posteriorly parallel to the pulmonary artery (Fig. 4). Type 5: Appendage tip is first oriented superiorly but then turns anteriorly parallel to the pulmonary artery (Fig. 5). Moreover, to make the types easier to remember, we gave the classifications descriptive names according to the anatomical external appearance of the LAA: horseshoe (type 1), hand-finger (type 2a), fan (type 2b), wing (type 2c), hook (type 3), wedge (type 4) and swan (type 5) shapes. The types and subtypes of the LAA variations and the presence of thrombus were recorded. 1.3. Statistical analysis Data were analyzed using SPSS for Windows 11.0 software. Pearson’s chi-square test was used for the analysis of LAA types in gender distribution and the presence of thrombus. A probability test less than 0.05 was considered to be statistically significant. 2. Results In our study, the distribution of the types of LAA classifications was found to be the following: type 1 13.8% (n = 44), type 2a 20.3% (n = 65), type 2b 48.4% (n = 155), type 2c 2.5% (n = 8), type 3 8.4% (n = 27), type 4 1.9% (n = 6), type 5 4.7% (n = 15). The gender distribution of the types is summarized in Table 1. In addition, LAA thrombus was detected in four patients (1.25%), who had classified LAA shapes of type 2a (n = 3) and type 2b (n = 1) (Fig. 6). There is no statistical significance relation between LAA types and thrombus (P = 0.26, X2 = 7.69, SD = 6). We found type 3 more frequently in women. This difference was statistically significant (P = 0.015, X2 = 15.8, SD = 6).
Table 1 The distribution of left atrial appendage types according to gender. Type
Male (n = 223)
Female (n = 97)
Total (n = 320)
Type 1 Type 2a Type 2b Type 2c Type 3 Type 4 Type 5
32 (10%) 47 (14.7%) 115 (35.9%) 5 (1.6%) 10 (3.1%) 4 (1.3%) 10 (3.1%)
12 (3.8%) 18 (5.6%) 40 (12.5%) 3 (0.9%) 17 (5.3%) 2 (0.6%) 5 (1.6%)
44 (13.8%) 65 (20.3%) 155 (48.4%) 8 (2.5%) 27 (8.4%) 6 (1.9%) 15 (4.7%)
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Fig. 2. 3D volume-rendering images show the type 2a, type 2b and type 2c LAA. Ao, Aorta; Cx: left circumflex coronary artery; LAA, left atrial appendage; LAD, left anterior descending coronary artery; MPA, main pulmonary artery; PV, pulmonary vein; T, appendage tip. See manuscript for details.
3. Discussion The shape of the left atrial appendage is highly variable. It embryologically originates from the body of the left atrium and is occasionally regarded as a minor extension of the atrium [10]. The LAA has a complex anatomical structure divided into trabecular and smooth regions. The trabecular LAA is the remnant of the original embryonic left atrium that occurs during the third week of gestation [11]. The main smooth walled left atrial cavity occurs later and develops from the overhang of the pulmonary veins [2]. Studies related to the detailed description of the different anatomic shapes of the LAA are rare in vivo. The LAA structure was
initially described from the results of autopsied hearts [12,13]. Ernst et al. revealed varying anatomic shapes of the LAA in 220 cases at autopsy [14]. They were classified as slightly spiraled, extremely spiraled, slightly bent, extremely bent and straight. Another study of 500 hearts at autopsy was performed with classifications according to the number of lobes as external features of the LAA [15]. Most of the LAA specimens (54%) had 2 lobes. Others had 3 lobes (23%), 1 lobe (20%) and 4 lobes (3%). In another study using transesophageal echocardiography (TEE), the authors found 1 lobe (29.1%), 2 lobes (49%) and multiple lobes (22%) [16]. Lacomis et al. [3] defined LAA anatomical shapes according to 3 types based on the orientation and location of the LAA ‘tip’. In patients without atrial fibrillation
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Fig. 3. Left lateral (a) and superior view (b) of 3D volume-rendering images show the type 3 LAA. Ao, Aorta; LAA, left atrial appendage; MPA, main pulmonary artery; PV, pulmonary vein; T, appendage tip. See manuscript for details.
Fig. 4. Left lateral (a) and superior view (b) of 3D volume-rendering images show the type 4 LAA. Ao, Aorta; LAA, left atrial appendage; LPA, left pulmonary artery; MPA, main pulmonary artery; PV, pulmonary vein; T, appendage tip. See manuscript for details.
Fig. 5. Left lateral (a) and superior view (b) of 3D volume-rendering images show the type 5 LAA. Ao, Aorta; LAA, left atrial appendage; MPA, main pulmonary artery; PV, pulmonary vein; T, appendage tip. See manuscript for details.
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Fig. 6. Axial CT scan (a) and 3D volume-rendering (b) images show the thrombosed LAA. Arrow, left atrial appendage; star, thrombus; T, appendage tip.
(AF), the frequency of the type was found to be 30% (type I), 60% (type II) and 10% (type III). In patients with paroxysmal AF, the distribution was found to be 20% (type I), 68% (type II) and 12% (type III). In patients with persistent AF, the distribution was found to be 10%, 70% and 20% for types I, II and III, respectively. In our study, we also used tip orientation for classification of LAA shape similar to Lacomis et al. We divided type 2 into subtypes, and in addition, we found two new types (type 4 and type 5). However, we named the types according to the anatomical external appearance of the LAA: horseshoe, hand-finger, fan, wing, hook, wedge and swan shapes for type 1, 2a, 2b, 2c, 3, 4 and 5 respectively. We found the following distributions across patients: type 1 13.8%; type 2a 20.3%; type 2b 48.4%; type 2c 2.5%; type 3 8.4%; type 4 1.9% and type 5 4.7%. The rates of type 2 were similar to a study in patients with persistent AF from Lacomis et al. The frequency of type 3 was lower than reported in this earlier study. In addition, we detected type 3 more frequently in women. Finally, we described a new view in the LAA anatomical shapes and anatomical relationships. The LAA is an important cardiac structure, and it is most commonly associated with thrombus formation, which causes stroke, infarction, and emboli, particularly in patients with atrial fibrillation. Although the exact pathogenesis of this thrombus formation is not fully known, it is likely related to the stasis of blood flow within the LAA [2]. The most effective prophylaxis of stroke in atrial fibrillation is warfarin; however, it may cause bleeding in many patients, especially in the elderly [2,17]. Because of this complication, it is used in only about 50% of patients who could medically benefit from it [18]. Therefore, with the development of new technology, alternative treatment methods such as obliteration or amputation of the LAA, surgical LAA exclusion and percutaneous LAA transcatheter occlusion for the prophylaxis of thromboembolism have been used [2,6,7,12,19]. In addition, focal atrial tachyarrhythmias originated from the LAA can be seen [4]. Recently, left atrium radio frequency ablation for certain areas, including the LAA, has been suggested to increase the success rate of treating patients with atrial fibrillation [20]. In our study, LAA thrombus was detected in four patients (1.25%), and they were medically treated. We found thrombus only in type 2a (n = 3) and type 2b (n = 1). This is probably due to slow flow in the LAA blind-ends within the finger shapes. The limitation of the study is minority of the thrombus cases. Hence, further studies including large series of appendage thrombus investigating the relationship between the shape of appendage and thrombus formation should be done. The diagnostic methods used for the detection of thrombus and the evaluation of anatomical shape variations in the LAA are conventional angiography, transthoracic echocardiography, TEE, CT
and MR angiography. Although conventional angiography has been used extensively for the investigation of thrombus in the LAA [21], it is now rarely used because it is an invasive method [2]. Therefore, noninvasive techniques, such as echocardiography, CT and MR angiography, have become more widely used. Transthoracic echocardiography does not usually afford imaging of the LAA. [2]. However, TEE does allow imaging of the LAA, and it has recently become an efficacious tool for the detection of thrombus within the LAA [12,22]. However, TEE is semi-invasive, and it depends on an operator. In recent years, MDCT and MR angiography have been reported as diagnostically valuable tools for detecting LAA anatomy and thrombus [12,23]. MR angiography is often of limited value when the patient is uncooperative, and it is not a preferred method due to its cost and prolonged scan time. In addition, because of movement artifacts, MR cannot provide optimal imaging of the heart. With recent advances in CT technology, MDCT has replaced conventional angiography in most clinical conditions. We showed that VR images acquired from 3D CT provide an excellent overview of the LAA anatomy. In conclusion, multiple anatomical shape variations in the LAA were demonstrated in this study. We demonstrated previously undefined new shape types of LAA. These variations should be considered when interpreting images of the LAA. It is important to be aware of the presence of LAA variations in order to avoid procedure-related complications when ablative treatments are to be performed or if surgical procedures are indicated in this region. MDCT seems to be the best imaging method to detect LAA anatomy. We conclude that MPR and the 3D VR imaging features of MDCT provide important and detailed information in determining these variations and allowing more complete evaluations before a planned procedure in this region.
References [1] Kerut EK. Anatomy of the left atrial appendage. Echocardiography 2008;25:669–73. [2] Al-Saady NM, Obel OA, Camm AJ. Left atrial appendage: structure, function, and role in thromboembolism. Heart 1999;82:547–54. [3] Lacomis JM, Goitein O, Deible C, et al. Dynamic multidimensional imaging of the human left atrial appendage. Europace 2007;9:1134–40. [4] Yun-Long W, Xue-Bin L, Xin W, et al. Focal atrial tachycardia from the left atrial appendage: electrocardiographic and electrophysiologic characterization and long-term outcomes of radiofrequency ablation. J Cardiovasc Electrophysiol 2007;18:459–64. [5] Blackshear J, Johnson W, Odell J, et al. Thoracoscopic extracardiac obliteration of the left atrial appendage for stroke risk reduction in atrial fibrillation. J Am Coll Cardiol 2003;42:1249–52. [6] Onalan O, Lashevsky I, Hamad A, Crystal E. Nonpharmacologic stroke prevention in atrial fibrillation. Expert Rev Cardiovasc Ther 2005;3:619–33.
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[7] Fountain R, Holmes D, Hodgson P, Chandrasekaran K, Van Tassel R, Sick P. Potential applicability and utilization of left atrial appendage occlusion devices in patients with atrial fibrillation. Am Heart J 2006;152:720–3. [8] Qamruddin S, Shinbane J, Shriki J, Naqvi TZ. Left atrial appendage: structure, function, imaging modalities and therapeutic options. Expert Rev Cardiovasc Ther 2010;8:65–75. [9] Van Ooijen PMA, Dorgelo J, Zijlstra F, Oudkerk M. Detection, visualization and evaluation of anomalous coronary anatomy on 16-slice multidetectorrow CT. Eur Radiol 2004;14:2163–71. [10] Donal E, Yamada H, Leclercq C, Herpin D. The left atrial appendage, a small, blind-ended structure: a review of its echocardiographic evaluation and its clinical role. Chest 2005;128:1853–62. [11] Sadler TW. Cardiovascular system. In: Langman J, editor. Langman’s Medical Embryology. 6th ed. Baltimore: Williams and Wilkins; 1990. p. 179–227. [12] Hara H, Virmani R, Holmes Jr DR, et al. Is the left atrial appendage more than a simple appendage? Catheter Cardiovasc Interv 2009;1(74):234–42. [13] 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;60:227–31. [14] Ernst G, Stöllberger C, Abzieher F, et al. Morphology of the left atrial appendage. Anat Rec 1995;242:553–61. [15] Veinot JP, Harrity PJ, Gentile F, et al. Anatomy of the normal left atrial appendage: a quantitative study of agerelated changes in 500 autopsy hearts: implications for echocardiographic examination. Circulation 1997;96:3112–5.
[16] Meissner I, Whisnant JP, Khandheria BK, et al. Prevalence of potential risk factors for stroke assessed by transesophageal echocardiography and carotid ultrasonography: the SPARC Study. Mayo Clin Proc 1999;74: 862–9. [17] Hylek EM, Evans-Molina C, Shea C, Henault LE, Regan S. Major hemorrhage and tolerability of warfarin in the first year of therapy among elderly patients with atrial fibrillation. Circulation 2007;115:2689–96. [18] Bungard TJ, Ghali WA, Teo KK, McAlister FA, Tsuyuki RT. Why do patients with atrial fibrillation not receive warfarin? Arch Intern Med 2000;160: 41–6. [19] Mohrs O, Schraeder R, Petersen S, et al. Percutaneous left atrial appendage transcatheter occlusion (PLAATO): planning follow-up using contrast-enhanced MRI. Am J Radiol 2006;186:361–4. [20] Wongcharoen W, Tsao HM, Wu MH, et al. Morphologic characteristics of the left atrial appendage, roof, and septum: implications for the ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:951–6. [21] Sakomoto I, Hayashi K, Matsunaga N, et al. Coronary angiographic finding of thrombus in the left atrial appendage. Acta Radiol 1996;37:749–53. [22] Manning WJ, Weintraub RM, Waksmonski CA, et al. Accuracy of transesophageal echocardiography for identifying left atrial thrombi. A prospective, intraoperative study. Ann Intern Med 1995;123:817–22. [23] Ohyama H, Hosomi N, Takahashi T, et al. Comparison of magnetic resonance imaging and transesophageal echocardiography in detection of thrombus in the left atrial appendage. Stroke 2003;34:2436–9.
Contents lists available at ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
An investigation of the anatomical variations of left atrial appendage by multidetector computed tomographic coronary angiography Mustafa Koplay ∗ , Cengiz Erol, Yahya Paksoy, Ali Sami Kivrak, Seda Özbek Department of Radiology, Selcuklu Medical Faculty, Selcuk University, The Central Campus, 42075 Konya, Turkey
a r t i c l e
i n f o
Article history: Received 12 February 2011 Accepted 21 April 2011 Keywords: Left atrial appendage Variations MDCT
a b s t r a c t Purpose: The left atrial appendage (LAA) is usually known as a long, tubular, hooked structure derived from the left atrium. However, it varies widely in terms of anatomical shape. In this study, anatomical shape variations of the LAA were investigated and classified in vivo in a large group of patients by multidetector computed tomography (MDCT) coronary angiography. Materials and Methods: The study included 320 consecutive patients (223 men and 97 women, with a mean age of 58 years) who underwent MDCT coronary angiography. MDCT was performed with a 64-detectorrow computed tomographic scanner. LAA anatomical variations were classified as five main types and further divided into subtypes. In addition, we gave the classifications descriptive names according to the anatomical external appearance of the LAA: horseshoe (type 1), hand-finger (type 2a), fan (type 2b), wing (type 2c), hook (type 3), wedge (type 4) and swan (type 5) shapes. The types and subtypes of the LAA variations and the presence of thrombus were recorded. Results: In our study, the LAA tip orientation was used and the LAA was divided into type 1, type 2a, 2b, 2c, type 3, type 4 and type 5 in 44 (13.8%), 65 (20.3%), 155 (48.4%), 8 (2.5%), 27 (8.4%), 6 (1.9%) and 15 (4.7%) patients, respectively. LAA thrombus was detected in four patients (1.25%), who had classified LAA shapes of type 2a and type 2b. Conclusions: The LAA has multiple anatomical shape variations. We demonstrated previously undefined new shape types of LAA. Knowledge of LAA variations is important in order to avoid procedure-related complications when ablative treatment is to be performed or if surgical procedures are indicated in this region. MDCT coronary angiography provides important and detailed information about determining and evaluating these variations before undertaking a planned procedure in this region. © 2011 Elsevier Ireland Ltd. All rights reserved.
The left atrial appendage (LAA) is usually known as a long, tubular, hooked structure derived from the left atrium [1,2]. However, it varies widely in terms of anatomical shape [1,3]. It lies within the borders of the pericardium, superior to the left ventricular free wall and adjacent to the superior lateral aspect of the main pulmonary artery [2]. Clinically, the LAA is an important region because of its association with atrial tachyarrhythmias and thrombi [3,4]. Recently, developing technologies have produced new interventional methods in the treatment of this region [2,4–7]. It is important to be aware of the anatomy of the LAA during surgical procedures and for interventional and diagnostic purposes. To obtain the correct diagnosis and treatment during interventional procedures and to perform complication-free surgery, knowledge of the anatomy and possible variations of this area is important [2–4].
In the evaluation of the LAA, imaging methods such as echocardiography, computed tomography (CT), magnetic resonance (MR) angiography and conventional angiography have been used [8]. Recent advances in CT techniques, such as multidetector scanners, make it possible to visualize the cardiac anatomy and vascular structures in detail. Multidetector computed tomography (MDCT) is a reliable and noninvasive tool for diagnosing vascular anomalies and in the determination of cardiac anatomy [9]. For this reason, MDCT can also detect the real incidence of LAA variations in vivo. In this study, we classified LAA by means of anatomical shape and investigated the frequency and its relationship with trombus formation using MDCT coronary angiography. 1. Materials and methods 1.1. Patients
∗ Corresponding author. Tel.: +90 332 2415000x41134. E-mail address: [email protected] (M. Koplay). 0720-048X/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrad.2011.04.060
We conducted a retrospective analysis of 320 patients (223 men, 69.7%, and 97 women, 30.3%; age range, 32–78 years; mean, 58 years) who underwent MDCT coronary angiography between
1576
M. Koplay et al. / European Journal of Radiology 81 (2012) 1575–1580
Fig. 1. Left lateral (a) and anteroposterior view (b) of 3D volume-rendering images show the type 1 LAA. Ao, Aorta; Cx: left circumflex coronary artery; LAA, left atrial appendage; LAD, left anterior descending coronary artery; LPA, left pulmonary artery; LV, left ventricle; MPA, main pulmonary artery; PV, pulmonary vein; RAA, right atrial appendage; RPA, right pulmonary artery; T, appendage tip. See manuscript for details.
January 2008 and April 2009. The indications for MDCT coronary angiography were angina pectoris, symptoms suggesting coronary artery disease, atypical chest pain, difficulty in diagnosis based on conventional angiography, and screening for coronary artery disease. MDCT coronary angiography was not performed on patients with sustained arrhythmia, a heart rate greater than 80 beats/min despite -blocker use, known allergic reaction to contrast media, poor renal function (serum creatinine >1.5 mg/dL), pregnancy, respiratory insufficiency, poor clinical condition. The procedures used were in accordance with the recommendations found in the Helsinki declaration and institutional review board approval. 1.2. MDCT scan protocol and image analysis The study was retrospective and MDCT angiography was used to detect anatomical shape variations of the LAA. MDCT angiography was performed with a 64-slice CT scanner (Somatom Sensation 64, Siemens Medical Solutions, Forchheim, Germany). The scan was performed during a 10-second breath hold, with a 0.6 mm collimation, and 0.6 mm slice thickness reconstruction. During the image acquisition, 80 ml of non-ionic iodinated contrast agent was injected intravenously at a rate 5 ml/s followed by 40 ml of saline at 5 ml/s. Imaging was obtained by retrospective ECG-gating. Reconstructed images were then transferred to a processing workstation for further analysis with specialized software (Vitrea 2; Vital Images, Inc., Minneapolis, MN). In addition to traditional axial images, multiplanar reconstructions (MPR) and three-dimensional volume-rendering (3D VR) images were used to assess the LAA anatomical shape variations. LAA shapes were categorized similar to the previous studies of Lacomis et al. [3]. This previous study used only three types of classification based on the orientation and location of the LAA ‘tip;’ we have defined five types of classification, with subtypes, defined as follows: Type 1: Appendage tip is oriented superiorly parallel to the pulmonary artery (Fig. 1). Type 2a: Appendage tip is long like a finger and oriented inferiorly parallel to the pulmonary artery (Fig. 2a). Type 2b: Appendage tip is short and not prominent; it is oriented inferiorly parallel to the pulmonary artery (Fig. 2b). Type 2c: Appendage tip is prominent and oriented inferiorly parallel to the pulmonary artery, giving the appendage the shape of wing (Fig. 2c). Type 3: Appendage tip is oriented superiorly but then turns medially; it is located between the pulmonary artery and the left atrial body (Fig. 3).
Type 4: Appendage tip is oriented superiorly but then turns posteriorly parallel to the pulmonary artery (Fig. 4). Type 5: Appendage tip is first oriented superiorly but then turns anteriorly parallel to the pulmonary artery (Fig. 5). Moreover, to make the types easier to remember, we gave the classifications descriptive names according to the anatomical external appearance of the LAA: horseshoe (type 1), hand-finger (type 2a), fan (type 2b), wing (type 2c), hook (type 3), wedge (type 4) and swan (type 5) shapes. The types and subtypes of the LAA variations and the presence of thrombus were recorded. 1.3. Statistical analysis Data were analyzed using SPSS for Windows 11.0 software. Pearson’s chi-square test was used for the analysis of LAA types in gender distribution and the presence of thrombus. A probability test less than 0.05 was considered to be statistically significant. 2. Results In our study, the distribution of the types of LAA classifications was found to be the following: type 1 13.8% (n = 44), type 2a 20.3% (n = 65), type 2b 48.4% (n = 155), type 2c 2.5% (n = 8), type 3 8.4% (n = 27), type 4 1.9% (n = 6), type 5 4.7% (n = 15). The gender distribution of the types is summarized in Table 1. In addition, LAA thrombus was detected in four patients (1.25%), who had classified LAA shapes of type 2a (n = 3) and type 2b (n = 1) (Fig. 6). There is no statistical significance relation between LAA types and thrombus (P = 0.26, X2 = 7.69, SD = 6). We found type 3 more frequently in women. This difference was statistically significant (P = 0.015, X2 = 15.8, SD = 6).
Table 1 The distribution of left atrial appendage types according to gender. Type
Male (n = 223)
Female (n = 97)
Total (n = 320)
Type 1 Type 2a Type 2b Type 2c Type 3 Type 4 Type 5
32 (10%) 47 (14.7%) 115 (35.9%) 5 (1.6%) 10 (3.1%) 4 (1.3%) 10 (3.1%)
12 (3.8%) 18 (5.6%) 40 (12.5%) 3 (0.9%) 17 (5.3%) 2 (0.6%) 5 (1.6%)
44 (13.8%) 65 (20.3%) 155 (48.4%) 8 (2.5%) 27 (8.4%) 6 (1.9%) 15 (4.7%)
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Fig. 2. 3D volume-rendering images show the type 2a, type 2b and type 2c LAA. Ao, Aorta; Cx: left circumflex coronary artery; LAA, left atrial appendage; LAD, left anterior descending coronary artery; MPA, main pulmonary artery; PV, pulmonary vein; T, appendage tip. See manuscript for details.
3. Discussion The shape of the left atrial appendage is highly variable. It embryologically originates from the body of the left atrium and is occasionally regarded as a minor extension of the atrium [10]. The LAA has a complex anatomical structure divided into trabecular and smooth regions. The trabecular LAA is the remnant of the original embryonic left atrium that occurs during the third week of gestation [11]. The main smooth walled left atrial cavity occurs later and develops from the overhang of the pulmonary veins [2]. Studies related to the detailed description of the different anatomic shapes of the LAA are rare in vivo. The LAA structure was
initially described from the results of autopsied hearts [12,13]. Ernst et al. revealed varying anatomic shapes of the LAA in 220 cases at autopsy [14]. They were classified as slightly spiraled, extremely spiraled, slightly bent, extremely bent and straight. Another study of 500 hearts at autopsy was performed with classifications according to the number of lobes as external features of the LAA [15]. Most of the LAA specimens (54%) had 2 lobes. Others had 3 lobes (23%), 1 lobe (20%) and 4 lobes (3%). In another study using transesophageal echocardiography (TEE), the authors found 1 lobe (29.1%), 2 lobes (49%) and multiple lobes (22%) [16]. Lacomis et al. [3] defined LAA anatomical shapes according to 3 types based on the orientation and location of the LAA ‘tip’. In patients without atrial fibrillation
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Fig. 3. Left lateral (a) and superior view (b) of 3D volume-rendering images show the type 3 LAA. Ao, Aorta; LAA, left atrial appendage; MPA, main pulmonary artery; PV, pulmonary vein; T, appendage tip. See manuscript for details.
Fig. 4. Left lateral (a) and superior view (b) of 3D volume-rendering images show the type 4 LAA. Ao, Aorta; LAA, left atrial appendage; LPA, left pulmonary artery; MPA, main pulmonary artery; PV, pulmonary vein; T, appendage tip. See manuscript for details.
Fig. 5. Left lateral (a) and superior view (b) of 3D volume-rendering images show the type 5 LAA. Ao, Aorta; LAA, left atrial appendage; MPA, main pulmonary artery; PV, pulmonary vein; T, appendage tip. See manuscript for details.
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Fig. 6. Axial CT scan (a) and 3D volume-rendering (b) images show the thrombosed LAA. Arrow, left atrial appendage; star, thrombus; T, appendage tip.
(AF), the frequency of the type was found to be 30% (type I), 60% (type II) and 10% (type III). In patients with paroxysmal AF, the distribution was found to be 20% (type I), 68% (type II) and 12% (type III). In patients with persistent AF, the distribution was found to be 10%, 70% and 20% for types I, II and III, respectively. In our study, we also used tip orientation for classification of LAA shape similar to Lacomis et al. We divided type 2 into subtypes, and in addition, we found two new types (type 4 and type 5). However, we named the types according to the anatomical external appearance of the LAA: horseshoe, hand-finger, fan, wing, hook, wedge and swan shapes for type 1, 2a, 2b, 2c, 3, 4 and 5 respectively. We found the following distributions across patients: type 1 13.8%; type 2a 20.3%; type 2b 48.4%; type 2c 2.5%; type 3 8.4%; type 4 1.9% and type 5 4.7%. The rates of type 2 were similar to a study in patients with persistent AF from Lacomis et al. The frequency of type 3 was lower than reported in this earlier study. In addition, we detected type 3 more frequently in women. Finally, we described a new view in the LAA anatomical shapes and anatomical relationships. The LAA is an important cardiac structure, and it is most commonly associated with thrombus formation, which causes stroke, infarction, and emboli, particularly in patients with atrial fibrillation. Although the exact pathogenesis of this thrombus formation is not fully known, it is likely related to the stasis of blood flow within the LAA [2]. The most effective prophylaxis of stroke in atrial fibrillation is warfarin; however, it may cause bleeding in many patients, especially in the elderly [2,17]. Because of this complication, it is used in only about 50% of patients who could medically benefit from it [18]. Therefore, with the development of new technology, alternative treatment methods such as obliteration or amputation of the LAA, surgical LAA exclusion and percutaneous LAA transcatheter occlusion for the prophylaxis of thromboembolism have been used [2,6,7,12,19]. In addition, focal atrial tachyarrhythmias originated from the LAA can be seen [4]. Recently, left atrium radio frequency ablation for certain areas, including the LAA, has been suggested to increase the success rate of treating patients with atrial fibrillation [20]. In our study, LAA thrombus was detected in four patients (1.25%), and they were medically treated. We found thrombus only in type 2a (n = 3) and type 2b (n = 1). This is probably due to slow flow in the LAA blind-ends within the finger shapes. The limitation of the study is minority of the thrombus cases. Hence, further studies including large series of appendage thrombus investigating the relationship between the shape of appendage and thrombus formation should be done. The diagnostic methods used for the detection of thrombus and the evaluation of anatomical shape variations in the LAA are conventional angiography, transthoracic echocardiography, TEE, CT
and MR angiography. Although conventional angiography has been used extensively for the investigation of thrombus in the LAA [21], it is now rarely used because it is an invasive method [2]. Therefore, noninvasive techniques, such as echocardiography, CT and MR angiography, have become more widely used. Transthoracic echocardiography does not usually afford imaging of the LAA. [2]. However, TEE does allow imaging of the LAA, and it has recently become an efficacious tool for the detection of thrombus within the LAA [12,22]. However, TEE is semi-invasive, and it depends on an operator. In recent years, MDCT and MR angiography have been reported as diagnostically valuable tools for detecting LAA anatomy and thrombus [12,23]. MR angiography is often of limited value when the patient is uncooperative, and it is not a preferred method due to its cost and prolonged scan time. In addition, because of movement artifacts, MR cannot provide optimal imaging of the heart. With recent advances in CT technology, MDCT has replaced conventional angiography in most clinical conditions. We showed that VR images acquired from 3D CT provide an excellent overview of the LAA anatomy. In conclusion, multiple anatomical shape variations in the LAA were demonstrated in this study. We demonstrated previously undefined new shape types of LAA. These variations should be considered when interpreting images of the LAA. It is important to be aware of the presence of LAA variations in order to avoid procedure-related complications when ablative treatments are to be performed or if surgical procedures are indicated in this region. MDCT seems to be the best imaging method to detect LAA anatomy. We conclude that MPR and the 3D VR imaging features of MDCT provide important and detailed information in determining these variations and allowing more complete evaluations before a planned procedure in this region.
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