REVIEW URRENT C OPINION
Left atrial volumes: two-dimensional, threedimensional, cardiac magnetic resonance and computed tomography measurements Anita C. Boyd a,c and Liza Thomas a,b,c
Purpose of review Evaluation of left atrial volume is important, as it is a biomarker of cardiovascular disease and outcomes and correlates with diastolic dysfunction severity. Left atrial volume measurements by different imaging modalities, including 2D and 3D echocardiography (2DE and 3DE), cardiac magnetic resonance (CMR) and computed tomography (CT), are reviewed in regard to recent advances, methodology, prognostic value and limitations. Recent findings Left atrial volume assessments correlate well between the different imaging modalities; however, 2DE significantly underestimates left atrial measurements. Assessment of the left atrial minimum volume and left atrial phasic function derived volumetrically have reported superior predictive value for major adverse cardiovascular events and elevated left ventricular diastolic pressure compared with the left atrial maximum volume. Summary The different imaging modalities used to assess left atrial volumes are not interchangeable, particularly for serial measurements. Although 2DE underestimates left atrial volumes, most normative as well as predictive data have been obtained using this modality. Standardization, with established normative data and classification criteria, needs to be established for other imaging modalities, additionally incorporating assessment of left atrial minimum and phasic volumes. Despite the limitations of the more simplistic 2DE, its measurements are well defined with significant prognostic value. The incremental prognostic value of the more complex imaging techniques needs to be further validated. Keywords cardiac magnetic resonance, computed tomography, echocardiography, left atrial volume
INTRODUCTION The primary role of the left atrium is to maintain optimal left ventricular filling and cardiac output, in response to changing left ventricular hemodynamics [1]. This is achieved through alterations in the phasic components (conduit, contractile and reservoir) of atrial function. The left atrium is affected by left ventricular pressure and diastolic dysfunction [2], body size (i.e. body surface area) [3], advanced age [4], atrial fibrillation [5], volume and pressure overload (valvular disease) [6] and exercise [7]. The thin-walled left atrium thereby maintains adequate left ventricular filling by size and phasic function adaptation. Left atrial size is a particularly important biomarker of the severity and chronicity of left ventricular diastolic dysfunction [2]. Left atrial size has www.co-cardiology.com
also been shown to be an independent predictor of exercise capacity [7] and of adverse cardiovascular outcomes and mortality in a variety of conditions, including coronary artery disease, hypertension, congestive heart failure and stroke [8–10]. Additionally, left atrial size is associated with an incremental risk of developing atrial fibrillation [11]. a Westmead Private Cardiology, bSouth Western Sydney Clinical School, University of New South Wales, Liverpool Hospital and cWestern Clinical School, University of Sydney, New South Wales, Australia
Correspondence to Professor Liza Thomas, Department of Cardiology, Liverpool Hospital, Elizabeth Drive, Sydney, New South Wales 2070, Australia. Tel: +61 02 87383797; fax: +61 02 87383054; e-mail: [email protected] Curr Opin Cardiol 2014, 29:408–416 DOI:10.1097/HCO.0000000000000087 Volume 29 Number 5 September 2014
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Left atrial volume imaging and measurements Boyd and Thomas
2D ECHOCARDIOGRAPHY
KEY POINTS Good correlations of left atrial volumes between imaging modalities. Imaging modalities are not interchangeable. 2DE is the most accessible, but consistently underestimates left atrial volumes compared with the other imaging modalities. The choice of imaging modality used to assess left atrial volumes should be tailored for specific indication and clinical need.
Measurement of left atrial size is performed using certain predetermined caveats: exclusion of the left atrial appendage laterally, the confluence of the pulmonary veins superiorly and the funnel of the mitral valve inferiorly, with a line drawn along the mitral annular plane. ‘Normal’ values defined by similar methodology and selection criteria have demonstrated similar values both in population based studies [12] and in studies of healthy subjects [4]. Indexing left atrial size to body surface area is essential, as body surface area has been shown to be an independent predictor of left atrial size [3]; indexation negates sex-based differences as well. Phasic atrial function can also be assessed reliably through volumetric assessment [13]. The left atrial maximum volume at ventricular end systole (just before the mitral valve opening) is the most commonly used left atrial volume and is the basis of current American Society of Echocardiography (ASE) guidelines [14]. However, left atrial minimum volume at end ventricular diastole (mitral valve closure) and phasic function has also demonstrated predictive value [15–17]. Thus, reference values and categorical classifications of phasic left atrial volumes need to be developed for each imaging modality, as they are not interchangeable across the various modalities. To define an ‘optimal imaging modality’ [2D echocardiography (2DE), 3D echocardiography (3DE), cardiac magnetic resonance (CMR) or computed tomography (CT)], one needs to consider ease of use, availability of reference ranges, reproducibility, limited geometric assumptions, phasic assessment and widespread availability. Below we discuss in greater detail specific strengths and weaknesses of these imaging modalities with particular reference to recent findings on methodology (Table 1 [18 ,19,20,21 ,22,23, 24 ,25 ,26–29,30 ]) and prognostic value (Table 2 [31,32,33 ,34 ,35–37,38 ,39 ,40,41 ,42 ,43 ,44, 45 ,46 ]). &
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Left atrial dimension has been extensively referred to in the literature; however, left atrial enlargement is ‘asymmetric’ and thus single plane diameter assessment often results in underestimation of left atrial size [47]. Furthermore, indexed left atrial volumes were more strongly associated with cardiovascular disease than left atrial diameter or area [11]. There are several methods to measure the left atrial volume using 2DE, including Simpson’s biplane method of discs (Fig. 1), biplane area length and the prolate ellipse [14]. Differences in measurements have been reported between these methods; the prolate ellipse consistently underestimates left atrial volumes, whereas the two biplane methods compare closely [21 ,48] and are recommended as the standard for left atrial volumes in ASE guidelines [14]. The biplane area length method has the most accurate estimation of volumes compared with CT, providing the closest approximation to the true left atrial volume [18 ]. Recently, a simplified singleplane assessment of left atrial volume (particularly in instances with suboptimal two chamber views) was shown to be reliable, with good correlations to biplane and 3DE left atrial volumes, and with excellent agreement for grading of left atrial enlargement [19]. A novel 2D tissue-tracking assessment of left atrial volume has also been demonstrated to reduce variability and acquisition time compared with 2D biplane area length and 3D methods [20], although further validation in larger groups is necessary to endorse this technique. Left atrial volume by 2DE is relatively independent of loading conditions [49], performed with relative ease [14], reproducible [4], and widely available, and its clinical utility is evidenced by its incorporation into the algorithm to grade left ventricular diastolic function [50]. Biplane 2DE left atrial volume correlates closely with CT [51], CMR [21 ] and 3DE [47]. Additionally, 2DE enables assessment of the complex physiology of the left atrium by measuring blood flow and tissue deformation. There is a significant body of literature on normal values, and it is 2DE-derived ‘normal’ values that are provided in the ASE guidelines. Recently, 2DE left atrial volumes have been used to predict adverse outcomes in patients with significant mitral regurgitation [31], congestive heart failure recurrence in patients with left atrial remodeling [32], cardiac events and death in diabetic patients with increased left atrial volumes [33 ]. New research studies have demonstrated left atrial volume as a predictor of silent ischemia in end-stage renal disease [34 ] and as a predictor for antitachycardia pacing and/or shock for ventricular arrhythmias in high-risk hypertrophic cardiomyopathy [35]. Left
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Imaging and echocardiography Table 1. Recent findings of left atrial volume methodology using 2DE, 3DE, CMR and CT 2DE
3DE
CMR
CT
Biplane area length had greatest left atrial volume compared with prolate ellipse and Simpson’s disc & methods [18 ]
Higher correlations than 2DE & measurements to CMR [21 ,22] and CT imaging [23]
Good agreement with CT [27]
More accurate than 2DE [27]
Simplified single plane shows good agreement for grading of left atrial enlargement [19]
Semiautomated technique with & good correlation to CMR [24 ]
Simplified single-plane area length method has good correlation with the full-volume method [28]
Excellent correlation to CMR even in atrial fibrillation & [30 ]
Novel 2D tissue tracking technique to estimate left atrial volume [20]
Excellent agreement for classification of left atrial enlargement with CMR in patients referred for a wide range of cardiovascular conditions [22]
Biplane area length method had the best correlation to the reference Simpson’s biplane method. All methods showed excellent reproducibility [29]
Specific left atrial quantification & software analysis tools [21 ] Simpson’s biplane demonstrates good correlation to full volume left atrial analysis [23] 3DE speckle tracking volumetric && assessment [25 ,26] 2DE, two-dimensional echocardiography; 3DE, three-dimensional echocardiography; CMR, cardiac magnetic resonance; CT, computed tomography.
Table 2. Recent findings of the prognostic value of left atrial volume using 2DE, 3DE, CMR and CT 2DE
3DE
CMR
CT
Adverse outcomes in significant mitral regurgitation [31]
Left atrial minimum volume best independent predictor of major adverse cardiovascular && events [39 ]
Mortality, cardiac transplant and heart failure admissions in nonischemic dilated & cardiomyopathy [41 ]
Arrhythmia recurrence in patients with persistent & atrial fibrillation [45 ]
Congestive heart failure recurrence in patients with left atrial remodeling [32]
Left atrial expansion index predicts arrhythmia elimination [40]
Left atrial minimum volume and left atrial ejection fraction associated with elevated left ventricular end && diastolic pressure [42 ]
Larger left atrial volumes in persistent compared with paroxysmal atrial & fibrillation [46 ].
Cardiac events and death in diabetics with increased left && atrial volumes [33 ]
Left atrial emptying volume associated with major cardiovascular events following ST-elevation && myocardial infarction [43 ]
Silent ischemia in end stage & renal disease [34 ]
Late gadolinium enhancement predicts recurrent arrhythmias [44]
Effects of cardiomyopathies, including hypertrophic cardiomyopathy [35], hypertension [36] and Fabry disease [37] Left atrial minimum volume predictive of atrial fibrillation && recurrence [38 ] 2DE, two-dimensional echocardiography; 3DE, three-dimensional echocardiography; CMR, cardiac magnetic resonance; CT, computed tomography.
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Left atrial volume imaging and measurements Boyd and Thomas
ablation in patients with persistent atrial fibrillation [38 ]. 2DE, however, consistently underestimates left atrial volumes with a systematic bias compared with 3DE and the other imaging modalities [22,28,30 ]. The limitations of 2DE are because of geometric assumptions, foreshortening of the left atrium that is in the far field by nonfocused imaging and suboptimal left atrial border visualization (particularly the apical two chamber view) leading to tracing errors [47]. The reported normal range for 2D left atrial volumes is narrow, and thus even slight errors in obtaining the measurements could result in abnormal classification of left atrial enlargement. Furthermore, 2D left atrial volumes have limited reproducibility [30 ]. &&
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FIGURE 1. Biplane Simpson’s measurement of left atrial volume using 2D echocardiography. Reproduced with permission from [14].
atrial volumes have also been used to assess the effects of hypertension [36] and may be increased in Fabry cardiomyopathy prior to the development of left ventricular hypertrophy [37]. Recently, left atrial minimum volume has been shown to be predictive of atrial fibrillation recurrence following
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3D ECHOCARDIOGRAPHY Real-time 3DE assessment of left atrial volumes eliminates the limitations of geometric assumptions of 2DE and thereby increases the reproducibility of measurements (Fig. 2). 3DE left atrial volumes have higher correlations than 2DE measurements to CMR [21 ,22] and CT imaging [23]. However, one study reports that 3D and 2D measurements have similar
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FIGURE 2. Left atrial volume using 3D echocardiography. 0268-4705 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
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Imaging and echocardiography
variability [22], whereas a previous study reported less test–retest variation for 3DE, critical for serial investigation [52]. Initially, 3D left atrial volume measurement involved slice analysis with improved measurements versus 2DE, at the expense of significantly increased analysis times [52]. More recently, semiautomated contour detection has shown good correlation with manual tracing techniques and CMR, with reduced analysis times [24 ] using a simple fivepoint marking system [39 ]. Mor-Avi et al. [22] demonstrated in a multicenter study that overall agreement in classification of left atrial enlargement, using a cutoff of 34 ml/m2, was excellent between 3DE and CMR (four false-negatives and seven false-positives, kappa 0.88). In contrast, 2DE showed good correlation with CMR, but was inferior at classifying left atrial enlargement (25 false-negatives and two false-positives; kappa 0.71) [22]. Realtime 3D assessment has been shown to increase accuracy and reproducibility with a variability of 7% compared with 2D techniques with variability of 12% [22,53], particularly when using the specific left atrial software analysis tools [21 ]. Simpson’s biplane technique has also been applied to 3DE evaluation of left atrial volumes with good correlation to full-volume left atrial analysis and with reduced bias and analysis time [23]. 3DE speckletracking volumetric assessment to measure left atrial volumes has also been recently developed [25 ,26], although these techniques require further validation. The use of contrast with 3DE has been demonstrated to improve accuracy for left ventricular volumes [54], but similar data are currently lacking for the left atrium. 3DE left atrial volume has been demonstrated to improve prognostic value over 2DE left atrial volume, although such data are limited [55,56]. Recently, Wu et al. [39 ] demonstrated that 3D left atrial minimum volume was the best predictor of major adverse cardiovascular events at 2.5-year follow-up, with incremental value over 3D left atrial maximum and 2D volumes in nonselected patients with cardiovascular disease (excluding subjects with atrial fibrillation, mitral valve disease and age or¼65 years of age. Am J Cardiol 2008; 101:1626–1629. 16. Fatema K, Barnes ME, Bailey KR, et al. Minimum vs. maximum left atrial volume for prediction of first atrial fibrillation or flutter in an elderly cohort: a prospective study. Eur J Echocardiogr 2009; 10:282–286.
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Left atrial volume imaging and measurements Boyd and Thomas 17. Russo C, Jin Z, Homma S, et al. Left atrial minimum volume and reservoir function as correlates of left ventricular diastolic function: impact of left ventricular systolic function. Heart 2012; 98:813–820. 18. Al-Mohaissen MA, Kazmi MH, Chan KL, Chow BJ. Validation of two-dimen& sional methods for left atrial volume measurement: a comparison of echocardiography with cardiac computed tomography. Echocardiography 2013; 30:1135–1142. Comparison of 2DE left atrial volume methods and CT using biplane area length, biplane Simpson’s and prolate ellipse methods. 19. Vieira-Filho NG, Mancuso FJ, Oliveira WA, et al. Simplified single plane echocardiography is comparable to conventional biplane two-dimensional echocardiography in the evaluation of left atrial volume: a study validated by threedimensional echocardiography in 143 individuals. Echocardiography 2014; 31:265–272. 20. Li SY, Zhang L, Zhao BW, et al. Two-dimensional tissue tracking: a novel echocardiographic technique to measure left atrial volume: comparison with biplane area length method and real time three-dimensional echocardiography. Echocardiography 2014. [Epub ahead of print] 21. Buechel RR, Stephan FP, Sommer G, et al. Head-to-head comparison of two& dimensional and three-dimensional echocardiographic methods for left atrial chamber quantification with magnetic resonance imaging. J Am Soc Echocardiogr 2013; 26:428–435. Direct comparison between left atrial volume methods from 2DE (Simpson’s modified biplane, biplane are a length and prolate ellipse) and 3DE (4D left atrial analysis and volumetric analysis using QLAB quantification software) in 60 consecutive patients. 22. Mor-Avi V, Yodwut C, Jenkins C, et al. Real-time 3D echocardiographic quantification of left atrial volume: multicenter study for validation with CMR. JACC Cardiovasc Imaging 2012; 5:769–777. 23. Iwataki M, Takeuchi M, Otani K, et al. Measurement of left atrial volume from transthoracic three-dimensional echocardiographic datasets using the biplane Simpson’s technique. J Am Soc Echocardiogr 2012; 25:1319–1326. 24. Muller H, Reverdin S, Burri H, et al. Measurement of left and right atrial volume & in patients undergoing ablation for atrial arrhythmias: comparison of a manual versus semiautomatic algorithm of real time 3D echocardiography. Echocardiography 2014; 31:499–507. Semiautomated border detection method of left atrial volumes shows excellent correlation with multiplane analysis in patients with paroxysmal or persistent atrial fibrillation. 25. Nemes A, Domsik P, Kalapos A, et al. Comparison of three-dimensional && speckle tracking echocardiography and two-dimensional echocardiography for evaluation of left atrial size and function in healthy volunteers (results from the MAGYAR-Healthy Study). Echocardiography 2013. [Epub ahead of print] Description of a new technique, which combines left atrial function analysis using 2D speckle tracking and automated left atrial volume analysis. 26. Perez de Isla L, Feltes G, Moreno J, et al. Quantification of left atrial volumes using three-dimensional wall motion tracking echocardiographic technology: comparison with cardiac magnetic resonance. Eur Heart J Cardiovasc Imaging 2014. [Epub ahead of print] 27. Kuhl JT, Lonborg J, Fuchs A, et al. Assessment of left atrial volume and function: a comparative study between echocardiography, magnetic resonance imaging and multi slice computed tomography. Int J Cardiovasc Imaging 2012; 28:1061–1071. 28. Madueme PC, Mazur W, Hor KN, et al. Comparison of area-length method by echocardiography versus full-volume quantification by cardiac magnetic resonance imaging for the assessment of left atrial volumes in children, adolescents, and young adults. Pediatr Cardiol 2014; 35:645–651. 29. Nacif MS, Barranhas AD, Turkbey E, et al. Left atrial volume quantification using cardiac MRI in atrial fibrillation: comparison of the Simpson’s method with biplane area-length, ellipse, and three-dimensional methods. Diagn Interv Radiol 2013; 19:213–220. 30. Agner BF, Kuhl JT, Linde JJ, et al. Assessment of left atrial volume and function & in patients with permanent atrial fibrillation: comparison of cardiac magnetic resonance imaging, 320-slice multidetector computed tomography, and transthoracic echocardiography. Eur Heart J Cardiovasc Imaging 2014; 15:532–540. CMR and multidetector CT measurements of left atrial volumes are improved compared with 2DE and correlate closely even in patients with permanent atrial fibrillation. 31. Arias A, Pizarro R, Oberti P, et al. Prognostic value of left atrial volume in asymptomatic organic mitral regurgitation. J Am Soc Echocardiogr 2013; 26:699–705. 32. Yamaguchi K, Yoshitomi H, Ito S, et al. Left atrial remodeling and recurrence of congestive heart failure in patients initially diagnosed with heart failure. Echocardiography 2013. [Epub ahead of print] 33. Poulsen MK, Dahl JS, Henriksen JE, et al. Left atrial volume index: relation to long&& term clinical outcome in type 2 diabetes. J Am Coll Cardiol 2013; 62:2416– 2421. Left atrial enlargement (32 ml/m2) was the only independent predictor of higher cardiac event rate and death rate in type 2 diabetes patients with no history of cardiovascular disease. 34. Choi MJ, Kim JK, Kim SG, et al. Left atrial volume index is a predictor of silent & myocardial ischemia in high-risk patients with end-stage renal disease. Int J Cardiovasc Imaging 2013; 29:1433–1439. Severe left atrial enlargement independently predicts the presence of silent myocardial ischemia in asymptomatic patients with end-stage renal disease.
35. Debonnaire P, Thijssen J, Leong DP, et al. Global longitudinal strain and left atrial volume index improve prediction of appropriate implantable cardioverter defibrillator therapy in hypertrophic cardiomyopathy patients. Int J Cardiovasc Imaging 2014; 30:549–558. 36. Boyd AC, Eshoo S, Richards DA, Thomas L. Hypertension accelerates the ‘normal’ aging process with a premature increase in left atrial volume. J Am Soc Hypertens 2013; 7:149–156. 37. Boyd AC, Lo Q, Devine K, et al. Left atrial enlargement and reduced atrial compliance occurs early in Fabry cardiomyopathy. J Am Soc Echocardiogr 2013; 26:1415–1423. 38. Kohari M, Zado E, Marchlinski FE, et al. Left atrial volume best predicts && recurrence after catheter ablation in patients with persistent and longstanding persistent atrial fibrillation. Pacing Clin Electrophysiol 2014; 37:422– 429. Left atrial minimum volume was the only independent imaging parameter predicting atrial fibrillation recurrence post pulmonary vein isolation by multiple logistic regression analysis. 39. Wu VC, Takeuchi M, Kuwaki H, et al. Prognostic value of LA volumes && assessed by transthoracic 3D echocardiography: comparison with 2D echocardiography. JACC Cardiovasc Imaging 2013; 6:1025–1035. One of the few studies that demonstrate the superior prognostic value of 3DE left atrial volumes compared with 2DE left atrial volumes. 40. Montserrat S, Gabrielli L, Borras R, et al. Left atrial size and function by threedimensional echocardiography to predict arrhythmia recurrence after first and repeated ablation of atrial fibrillation. Eur Heart J Cardiovasc Imaging 2014; 15:515–522. 41. Gulati A, Ismail TF, Jabbour A, et al. Clinical utility and prognostic value of & left atrial volume assessment by cardiovascular magnetic resonance in nonischaemic dilated cardiomyopathy. Eur J Heart Fail 2013; 15:660– 670. Left atrial volume (>72 ml/m2) by CMR predicted death or cardiac transplantation in patients with nonischemic dilated cardiomyopathy after 5-year follow-up. 42. Posina K, McLaughlin J, Rhee P, et al. Relationship of phasic left atrial volume && and emptying function to left ventricular filling pressure: a cardiovascular magnetic resonance study. J Cardiovasc Magn Reson 2013; 15:99. CMR left atrial minimum volume and emptying fraction were best correlated with left ventricular end-diastolic pressure by catheterization. 43. Lonborg JT, Engstrom T, Moller JE, et al. Left atrial volume and function in && patients following ST elevation myocardial infarction and the association with clinical outcome: a cardiovascular magnetic resonance study. Eur Heart J Cardiovasc Imaging 2013; 14:118–127. Left atrial total emptying (fractional change) was independently associated with major adverse cardiac events in patients following ST-elevation myocardial infarction. 44. McGann C, Akoum N, Patel A, et al. Atrial fibrillation ablation outcome is predicted by left atrial remodeling on MRI. Circ Arrhythm Electrophysiol 2014; 7:23–30. 45. Moon J, Lee HJ, Shim J, et al. Distinct prognostic impacts of both atrial & volumes on outcomes after radiofrequency ablation of nonvalvular atrial fibrillation: three-dimensional imaging study using multidetector computed tomography. Int J Cardiol 2013; 168:5430–5436. 3D left atrial volume by CT was independently associated with failure to maintain sinus rhythm 3 months following ablation for persistent atrial fibrillation. 46. Amin V, Finkel J, Halpern E, Frisch DR. Impact of left atrial volume on outcomes & of pulmonary vein isolation in patients with nonparoxysmal (persistent) and paroxysmal atrial fibrillation. Am J Cardiol 2013; 112:966–970. Left atrial volumes using CT were enlarged in patients with nonparoxysmal atrial fibrillation compared with paroxysmal atrial fibrillation. 47. Russo C, Hahn RT, Jin Z, et al. Comparison of echocardiographic single-plane versus biplane method in the assessment of left atrial volume and validation by real time three-dimensional echocardiography. J Am Soc Echocardiogr 2010; 23:954–960. 48. Jiamsripong P, Honda T, Reuss CS, et al. Three methods for evaluation of left atrial volume. Eur J Echocardiogr 2008; 9:351–355. 49. Tsang TS, Barnes ME, Gersh BJ, et al. Left atrial volume as a morphophysiologic expression of left ventricular diastolic dysfunction and relation to cardiovascular risk burden. Am J Cardiol 2002; 90:1284–1289. 50. Nagueh SF, Appleton CP, Gillebert TC, et al. Recommendations for the evaluation of left ventricular diastolic function by echocardiography. J Am Soc Echocardiogr 2009; 22:107–133. 51. Kircher B, Abbott JA, Pau S, et al. Left atrial volume determination by biplane two-dimensional echocardiography: validation by cine computed tomography. Am Heart J 1991; 121 (3 Pt 1):864–871. 52. Jenkins C, Bricknell K, Marwick TH. Use of real-time three-dimensional echocardiography to measure left atrial volume: comparison with other echocardiographic techniques. J Am Soc Echocardiogr 2005; 18:991– 997. 53. Aune E, Baekkevar M, Roislien J, et al. Normal reference ranges for left and right atrial volume indexes and ejection fractions obtained with real-time threedimensional echocardiography. Eur J Echocardiogr 2009; 10:738–744. 54. Jenkins C, Moir S, Chan J, et al. Left ventricular volume measurement with echocardiography: a comparison of left ventricular opacification, three-dimensional echocardiography, or both with magnetic resonance imaging. Eur Heart J 2009; 30:98–106.
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62. Hudsmith LE, Cheng AS, Tyler DJ, et al. Assessment of left atrial volumes at 1.5 Tesla and 3 Tesla using FLASH and SSFP cine imaging. J Cardiovasc Magn Reson 2007; 9:673–679. 63. Kataoka A, Funabashi N, Takahashi A, et al. Quantitative evaluation of left atrial volumes and ejection fraction by 320-slice computed-tomography in comparison with three- and two-dimensional echocardiography: a single-center retrospective-study in 22 subjects. Int J Cardiol 2011; 153:47–54. 64. Shin SY, Yong HS, Na JO, et al. A simplified method to determine left atrial volume and transport function using multislice computed tomography in patients with atrial fibrillation: comparison with transthoracic echocardiography. Int J Cardiovasc Imaging 2012; 28:1205–1216. 65. Wen Z, Zhang Z, Yu W, et al. Assessing the left atrial phasic volume and function with dual-source CT: comparison with 3T MRI. Int J Cardiovasc Imaging 2010; 26 (Suppl 1):83–92. 66. To AC, Flamm SD, Marwick TH, Klein AL. Clinical utility of multimodality LA imaging: assessment of size, function, and structure. JACC Cardiovasc Imaging 2011; 4:788–798. 67. Takagi Y, Ehara S, Okuyama T, et al. Comparison of determinations of left atrial volume by the biplane area-length and Simpson’s methods using 64slice computed tomography. J Cardiol 2009; 53:257–264. 68. Gweon HM, Kim SJ, Kim TH, et al. Evaluation of left atrial volumes using multidetector computed tomography: comparison with echocardiography. Korean J Radiol 2010; 11:286–294.
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Left atrial volumes: two-dimensional, threedimensional, cardiac magnetic resonance and computed tomography measurements Anita C. Boyd a,c and Liza Thomas a,b,c
Purpose of review Evaluation of left atrial volume is important, as it is a biomarker of cardiovascular disease and outcomes and correlates with diastolic dysfunction severity. Left atrial volume measurements by different imaging modalities, including 2D and 3D echocardiography (2DE and 3DE), cardiac magnetic resonance (CMR) and computed tomography (CT), are reviewed in regard to recent advances, methodology, prognostic value and limitations. Recent findings Left atrial volume assessments correlate well between the different imaging modalities; however, 2DE significantly underestimates left atrial measurements. Assessment of the left atrial minimum volume and left atrial phasic function derived volumetrically have reported superior predictive value for major adverse cardiovascular events and elevated left ventricular diastolic pressure compared with the left atrial maximum volume. Summary The different imaging modalities used to assess left atrial volumes are not interchangeable, particularly for serial measurements. Although 2DE underestimates left atrial volumes, most normative as well as predictive data have been obtained using this modality. Standardization, with established normative data and classification criteria, needs to be established for other imaging modalities, additionally incorporating assessment of left atrial minimum and phasic volumes. Despite the limitations of the more simplistic 2DE, its measurements are well defined with significant prognostic value. The incremental prognostic value of the more complex imaging techniques needs to be further validated. Keywords cardiac magnetic resonance, computed tomography, echocardiography, left atrial volume
INTRODUCTION The primary role of the left atrium is to maintain optimal left ventricular filling and cardiac output, in response to changing left ventricular hemodynamics [1]. This is achieved through alterations in the phasic components (conduit, contractile and reservoir) of atrial function. The left atrium is affected by left ventricular pressure and diastolic dysfunction [2], body size (i.e. body surface area) [3], advanced age [4], atrial fibrillation [5], volume and pressure overload (valvular disease) [6] and exercise [7]. The thin-walled left atrium thereby maintains adequate left ventricular filling by size and phasic function adaptation. Left atrial size is a particularly important biomarker of the severity and chronicity of left ventricular diastolic dysfunction [2]. Left atrial size has www.co-cardiology.com
also been shown to be an independent predictor of exercise capacity [7] and of adverse cardiovascular outcomes and mortality in a variety of conditions, including coronary artery disease, hypertension, congestive heart failure and stroke [8–10]. Additionally, left atrial size is associated with an incremental risk of developing atrial fibrillation [11]. a Westmead Private Cardiology, bSouth Western Sydney Clinical School, University of New South Wales, Liverpool Hospital and cWestern Clinical School, University of Sydney, New South Wales, Australia
Correspondence to Professor Liza Thomas, Department of Cardiology, Liverpool Hospital, Elizabeth Drive, Sydney, New South Wales 2070, Australia. Tel: +61 02 87383797; fax: +61 02 87383054; e-mail: [email protected] Curr Opin Cardiol 2014, 29:408–416 DOI:10.1097/HCO.0000000000000087 Volume 29 Number 5 September 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Left atrial volume imaging and measurements Boyd and Thomas
2D ECHOCARDIOGRAPHY
KEY POINTS Good correlations of left atrial volumes between imaging modalities. Imaging modalities are not interchangeable. 2DE is the most accessible, but consistently underestimates left atrial volumes compared with the other imaging modalities. The choice of imaging modality used to assess left atrial volumes should be tailored for specific indication and clinical need.
Measurement of left atrial size is performed using certain predetermined caveats: exclusion of the left atrial appendage laterally, the confluence of the pulmonary veins superiorly and the funnel of the mitral valve inferiorly, with a line drawn along the mitral annular plane. ‘Normal’ values defined by similar methodology and selection criteria have demonstrated similar values both in population based studies [12] and in studies of healthy subjects [4]. Indexing left atrial size to body surface area is essential, as body surface area has been shown to be an independent predictor of left atrial size [3]; indexation negates sex-based differences as well. Phasic atrial function can also be assessed reliably through volumetric assessment [13]. The left atrial maximum volume at ventricular end systole (just before the mitral valve opening) is the most commonly used left atrial volume and is the basis of current American Society of Echocardiography (ASE) guidelines [14]. However, left atrial minimum volume at end ventricular diastole (mitral valve closure) and phasic function has also demonstrated predictive value [15–17]. Thus, reference values and categorical classifications of phasic left atrial volumes need to be developed for each imaging modality, as they are not interchangeable across the various modalities. To define an ‘optimal imaging modality’ [2D echocardiography (2DE), 3D echocardiography (3DE), cardiac magnetic resonance (CMR) or computed tomography (CT)], one needs to consider ease of use, availability of reference ranges, reproducibility, limited geometric assumptions, phasic assessment and widespread availability. Below we discuss in greater detail specific strengths and weaknesses of these imaging modalities with particular reference to recent findings on methodology (Table 1 [18 ,19,20,21 ,22,23, 24 ,25 ,26–29,30 ]) and prognostic value (Table 2 [31,32,33 ,34 ,35–37,38 ,39 ,40,41 ,42 ,43 ,44, 45 ,46 ]). &
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Left atrial dimension has been extensively referred to in the literature; however, left atrial enlargement is ‘asymmetric’ and thus single plane diameter assessment often results in underestimation of left atrial size [47]. Furthermore, indexed left atrial volumes were more strongly associated with cardiovascular disease than left atrial diameter or area [11]. There are several methods to measure the left atrial volume using 2DE, including Simpson’s biplane method of discs (Fig. 1), biplane area length and the prolate ellipse [14]. Differences in measurements have been reported between these methods; the prolate ellipse consistently underestimates left atrial volumes, whereas the two biplane methods compare closely [21 ,48] and are recommended as the standard for left atrial volumes in ASE guidelines [14]. The biplane area length method has the most accurate estimation of volumes compared with CT, providing the closest approximation to the true left atrial volume [18 ]. Recently, a simplified singleplane assessment of left atrial volume (particularly in instances with suboptimal two chamber views) was shown to be reliable, with good correlations to biplane and 3DE left atrial volumes, and with excellent agreement for grading of left atrial enlargement [19]. A novel 2D tissue-tracking assessment of left atrial volume has also been demonstrated to reduce variability and acquisition time compared with 2D biplane area length and 3D methods [20], although further validation in larger groups is necessary to endorse this technique. Left atrial volume by 2DE is relatively independent of loading conditions [49], performed with relative ease [14], reproducible [4], and widely available, and its clinical utility is evidenced by its incorporation into the algorithm to grade left ventricular diastolic function [50]. Biplane 2DE left atrial volume correlates closely with CT [51], CMR [21 ] and 3DE [47]. Additionally, 2DE enables assessment of the complex physiology of the left atrium by measuring blood flow and tissue deformation. There is a significant body of literature on normal values, and it is 2DE-derived ‘normal’ values that are provided in the ASE guidelines. Recently, 2DE left atrial volumes have been used to predict adverse outcomes in patients with significant mitral regurgitation [31], congestive heart failure recurrence in patients with left atrial remodeling [32], cardiac events and death in diabetic patients with increased left atrial volumes [33 ]. New research studies have demonstrated left atrial volume as a predictor of silent ischemia in end-stage renal disease [34 ] and as a predictor for antitachycardia pacing and/or shock for ventricular arrhythmias in high-risk hypertrophic cardiomyopathy [35]. Left
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Imaging and echocardiography Table 1. Recent findings of left atrial volume methodology using 2DE, 3DE, CMR and CT 2DE
3DE
CMR
CT
Biplane area length had greatest left atrial volume compared with prolate ellipse and Simpson’s disc & methods [18 ]
Higher correlations than 2DE & measurements to CMR [21 ,22] and CT imaging [23]
Good agreement with CT [27]
More accurate than 2DE [27]
Simplified single plane shows good agreement for grading of left atrial enlargement [19]
Semiautomated technique with & good correlation to CMR [24 ]
Simplified single-plane area length method has good correlation with the full-volume method [28]
Excellent correlation to CMR even in atrial fibrillation & [30 ]
Novel 2D tissue tracking technique to estimate left atrial volume [20]
Excellent agreement for classification of left atrial enlargement with CMR in patients referred for a wide range of cardiovascular conditions [22]
Biplane area length method had the best correlation to the reference Simpson’s biplane method. All methods showed excellent reproducibility [29]
Specific left atrial quantification & software analysis tools [21 ] Simpson’s biplane demonstrates good correlation to full volume left atrial analysis [23] 3DE speckle tracking volumetric && assessment [25 ,26] 2DE, two-dimensional echocardiography; 3DE, three-dimensional echocardiography; CMR, cardiac magnetic resonance; CT, computed tomography.
Table 2. Recent findings of the prognostic value of left atrial volume using 2DE, 3DE, CMR and CT 2DE
3DE
CMR
CT
Adverse outcomes in significant mitral regurgitation [31]
Left atrial minimum volume best independent predictor of major adverse cardiovascular && events [39 ]
Mortality, cardiac transplant and heart failure admissions in nonischemic dilated & cardiomyopathy [41 ]
Arrhythmia recurrence in patients with persistent & atrial fibrillation [45 ]
Congestive heart failure recurrence in patients with left atrial remodeling [32]
Left atrial expansion index predicts arrhythmia elimination [40]
Left atrial minimum volume and left atrial ejection fraction associated with elevated left ventricular end && diastolic pressure [42 ]
Larger left atrial volumes in persistent compared with paroxysmal atrial & fibrillation [46 ].
Cardiac events and death in diabetics with increased left && atrial volumes [33 ]
Left atrial emptying volume associated with major cardiovascular events following ST-elevation && myocardial infarction [43 ]
Silent ischemia in end stage & renal disease [34 ]
Late gadolinium enhancement predicts recurrent arrhythmias [44]
Effects of cardiomyopathies, including hypertrophic cardiomyopathy [35], hypertension [36] and Fabry disease [37] Left atrial minimum volume predictive of atrial fibrillation && recurrence [38 ] 2DE, two-dimensional echocardiography; 3DE, three-dimensional echocardiography; CMR, cardiac magnetic resonance; CT, computed tomography.
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Left atrial volume imaging and measurements Boyd and Thomas
ablation in patients with persistent atrial fibrillation [38 ]. 2DE, however, consistently underestimates left atrial volumes with a systematic bias compared with 3DE and the other imaging modalities [22,28,30 ]. The limitations of 2DE are because of geometric assumptions, foreshortening of the left atrium that is in the far field by nonfocused imaging and suboptimal left atrial border visualization (particularly the apical two chamber view) leading to tracing errors [47]. The reported normal range for 2D left atrial volumes is narrow, and thus even slight errors in obtaining the measurements could result in abnormal classification of left atrial enlargement. Furthermore, 2D left atrial volumes have limited reproducibility [30 ]. &&
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FIGURE 1. Biplane Simpson’s measurement of left atrial volume using 2D echocardiography. Reproduced with permission from [14].
atrial volumes have also been used to assess the effects of hypertension [36] and may be increased in Fabry cardiomyopathy prior to the development of left ventricular hypertrophy [37]. Recently, left atrial minimum volume has been shown to be predictive of atrial fibrillation recurrence following
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3D ECHOCARDIOGRAPHY Real-time 3DE assessment of left atrial volumes eliminates the limitations of geometric assumptions of 2DE and thereby increases the reproducibility of measurements (Fig. 2). 3DE left atrial volumes have higher correlations than 2DE measurements to CMR [21 ,22] and CT imaging [23]. However, one study reports that 3D and 2D measurements have similar
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FIGURE 2. Left atrial volume using 3D echocardiography. 0268-4705 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
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Imaging and echocardiography
variability [22], whereas a previous study reported less test–retest variation for 3DE, critical for serial investigation [52]. Initially, 3D left atrial volume measurement involved slice analysis with improved measurements versus 2DE, at the expense of significantly increased analysis times [52]. More recently, semiautomated contour detection has shown good correlation with manual tracing techniques and CMR, with reduced analysis times [24 ] using a simple fivepoint marking system [39 ]. Mor-Avi et al. [22] demonstrated in a multicenter study that overall agreement in classification of left atrial enlargement, using a cutoff of 34 ml/m2, was excellent between 3DE and CMR (four false-negatives and seven false-positives, kappa 0.88). In contrast, 2DE showed good correlation with CMR, but was inferior at classifying left atrial enlargement (25 false-negatives and two false-positives; kappa 0.71) [22]. Realtime 3D assessment has been shown to increase accuracy and reproducibility with a variability of 7% compared with 2D techniques with variability of 12% [22,53], particularly when using the specific left atrial software analysis tools [21 ]. Simpson’s biplane technique has also been applied to 3DE evaluation of left atrial volumes with good correlation to full-volume left atrial analysis and with reduced bias and analysis time [23]. 3DE speckletracking volumetric assessment to measure left atrial volumes has also been recently developed [25 ,26], although these techniques require further validation. The use of contrast with 3DE has been demonstrated to improve accuracy for left ventricular volumes [54], but similar data are currently lacking for the left atrium. 3DE left atrial volume has been demonstrated to improve prognostic value over 2DE left atrial volume, although such data are limited [55,56]. Recently, Wu et al. [39 ] demonstrated that 3D left atrial minimum volume was the best predictor of major adverse cardiovascular events at 2.5-year follow-up, with incremental value over 3D left atrial maximum and 2D volumes in nonselected patients with cardiovascular disease (excluding subjects with atrial fibrillation, mitral valve disease and age or¼65 years of age. Am J Cardiol 2008; 101:1626–1629. 16. Fatema K, Barnes ME, Bailey KR, et al. Minimum vs. maximum left atrial volume for prediction of first atrial fibrillation or flutter in an elderly cohort: a prospective study. Eur J Echocardiogr 2009; 10:282–286.
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Left atrial volume imaging and measurements Boyd and Thomas 17. Russo C, Jin Z, Homma S, et al. Left atrial minimum volume and reservoir function as correlates of left ventricular diastolic function: impact of left ventricular systolic function. Heart 2012; 98:813–820. 18. Al-Mohaissen MA, Kazmi MH, Chan KL, Chow BJ. Validation of two-dimen& sional methods for left atrial volume measurement: a comparison of echocardiography with cardiac computed tomography. Echocardiography 2013; 30:1135–1142. Comparison of 2DE left atrial volume methods and CT using biplane area length, biplane Simpson’s and prolate ellipse methods. 19. Vieira-Filho NG, Mancuso FJ, Oliveira WA, et al. Simplified single plane echocardiography is comparable to conventional biplane two-dimensional echocardiography in the evaluation of left atrial volume: a study validated by threedimensional echocardiography in 143 individuals. Echocardiography 2014; 31:265–272. 20. Li SY, Zhang L, Zhao BW, et al. Two-dimensional tissue tracking: a novel echocardiographic technique to measure left atrial volume: comparison with biplane area length method and real time three-dimensional echocardiography. Echocardiography 2014. [Epub ahead of print] 21. Buechel RR, Stephan FP, Sommer G, et al. Head-to-head comparison of two& dimensional and three-dimensional echocardiographic methods for left atrial chamber quantification with magnetic resonance imaging. J Am Soc Echocardiogr 2013; 26:428–435. Direct comparison between left atrial volume methods from 2DE (Simpson’s modified biplane, biplane are a length and prolate ellipse) and 3DE (4D left atrial analysis and volumetric analysis using QLAB quantification software) in 60 consecutive patients. 22. Mor-Avi V, Yodwut C, Jenkins C, et al. Real-time 3D echocardiographic quantification of left atrial volume: multicenter study for validation with CMR. JACC Cardiovasc Imaging 2012; 5:769–777. 23. Iwataki M, Takeuchi M, Otani K, et al. Measurement of left atrial volume from transthoracic three-dimensional echocardiographic datasets using the biplane Simpson’s technique. J Am Soc Echocardiogr 2012; 25:1319–1326. 24. Muller H, Reverdin S, Burri H, et al. Measurement of left and right atrial volume & in patients undergoing ablation for atrial arrhythmias: comparison of a manual versus semiautomatic algorithm of real time 3D echocardiography. Echocardiography 2014; 31:499–507. Semiautomated border detection method of left atrial volumes shows excellent correlation with multiplane analysis in patients with paroxysmal or persistent atrial fibrillation. 25. Nemes A, Domsik P, Kalapos A, et al. Comparison of three-dimensional && speckle tracking echocardiography and two-dimensional echocardiography for evaluation of left atrial size and function in healthy volunteers (results from the MAGYAR-Healthy Study). Echocardiography 2013. [Epub ahead of print] Description of a new technique, which combines left atrial function analysis using 2D speckle tracking and automated left atrial volume analysis. 26. Perez de Isla L, Feltes G, Moreno J, et al. Quantification of left atrial volumes using three-dimensional wall motion tracking echocardiographic technology: comparison with cardiac magnetic resonance. Eur Heart J Cardiovasc Imaging 2014. [Epub ahead of print] 27. Kuhl JT, Lonborg J, Fuchs A, et al. Assessment of left atrial volume and function: a comparative study between echocardiography, magnetic resonance imaging and multi slice computed tomography. Int J Cardiovasc Imaging 2012; 28:1061–1071. 28. Madueme PC, Mazur W, Hor KN, et al. Comparison of area-length method by echocardiography versus full-volume quantification by cardiac magnetic resonance imaging for the assessment of left atrial volumes in children, adolescents, and young adults. Pediatr Cardiol 2014; 35:645–651. 29. Nacif MS, Barranhas AD, Turkbey E, et al. Left atrial volume quantification using cardiac MRI in atrial fibrillation: comparison of the Simpson’s method with biplane area-length, ellipse, and three-dimensional methods. Diagn Interv Radiol 2013; 19:213–220. 30. Agner BF, Kuhl JT, Linde JJ, et al. Assessment of left atrial volume and function & in patients with permanent atrial fibrillation: comparison of cardiac magnetic resonance imaging, 320-slice multidetector computed tomography, and transthoracic echocardiography. Eur Heart J Cardiovasc Imaging 2014; 15:532–540. CMR and multidetector CT measurements of left atrial volumes are improved compared with 2DE and correlate closely even in patients with permanent atrial fibrillation. 31. Arias A, Pizarro R, Oberti P, et al. Prognostic value of left atrial volume in asymptomatic organic mitral regurgitation. J Am Soc Echocardiogr 2013; 26:699–705. 32. Yamaguchi K, Yoshitomi H, Ito S, et al. Left atrial remodeling and recurrence of congestive heart failure in patients initially diagnosed with heart failure. Echocardiography 2013. [Epub ahead of print] 33. Poulsen MK, Dahl JS, Henriksen JE, et al. Left atrial volume index: relation to long&& term clinical outcome in type 2 diabetes. J Am Coll Cardiol 2013; 62:2416– 2421. Left atrial enlargement (32 ml/m2) was the only independent predictor of higher cardiac event rate and death rate in type 2 diabetes patients with no history of cardiovascular disease. 34. Choi MJ, Kim JK, Kim SG, et al. Left atrial volume index is a predictor of silent & myocardial ischemia in high-risk patients with end-stage renal disease. Int J Cardiovasc Imaging 2013; 29:1433–1439. Severe left atrial enlargement independently predicts the presence of silent myocardial ischemia in asymptomatic patients with end-stage renal disease.
35. Debonnaire P, Thijssen J, Leong DP, et al. Global longitudinal strain and left atrial volume index improve prediction of appropriate implantable cardioverter defibrillator therapy in hypertrophic cardiomyopathy patients. Int J Cardiovasc Imaging 2014; 30:549–558. 36. Boyd AC, Eshoo S, Richards DA, Thomas L. Hypertension accelerates the ‘normal’ aging process with a premature increase in left atrial volume. J Am Soc Hypertens 2013; 7:149–156. 37. Boyd AC, Lo Q, Devine K, et al. Left atrial enlargement and reduced atrial compliance occurs early in Fabry cardiomyopathy. J Am Soc Echocardiogr 2013; 26:1415–1423. 38. Kohari M, Zado E, Marchlinski FE, et al. Left atrial volume best predicts && recurrence after catheter ablation in patients with persistent and longstanding persistent atrial fibrillation. Pacing Clin Electrophysiol 2014; 37:422– 429. Left atrial minimum volume was the only independent imaging parameter predicting atrial fibrillation recurrence post pulmonary vein isolation by multiple logistic regression analysis. 39. Wu VC, Takeuchi M, Kuwaki H, et al. Prognostic value of LA volumes && assessed by transthoracic 3D echocardiography: comparison with 2D echocardiography. JACC Cardiovasc Imaging 2013; 6:1025–1035. One of the few studies that demonstrate the superior prognostic value of 3DE left atrial volumes compared with 2DE left atrial volumes. 40. Montserrat S, Gabrielli L, Borras R, et al. Left atrial size and function by threedimensional echocardiography to predict arrhythmia recurrence after first and repeated ablation of atrial fibrillation. Eur Heart J Cardiovasc Imaging 2014; 15:515–522. 41. Gulati A, Ismail TF, Jabbour A, et al. Clinical utility and prognostic value of & left atrial volume assessment by cardiovascular magnetic resonance in nonischaemic dilated cardiomyopathy. Eur J Heart Fail 2013; 15:660– 670. Left atrial volume (>72 ml/m2) by CMR predicted death or cardiac transplantation in patients with nonischemic dilated cardiomyopathy after 5-year follow-up. 42. Posina K, McLaughlin J, Rhee P, et al. Relationship of phasic left atrial volume && and emptying function to left ventricular filling pressure: a cardiovascular magnetic resonance study. J Cardiovasc Magn Reson 2013; 15:99. CMR left atrial minimum volume and emptying fraction were best correlated with left ventricular end-diastolic pressure by catheterization. 43. Lonborg JT, Engstrom T, Moller JE, et al. Left atrial volume and function in && patients following ST elevation myocardial infarction and the association with clinical outcome: a cardiovascular magnetic resonance study. Eur Heart J Cardiovasc Imaging 2013; 14:118–127. Left atrial total emptying (fractional change) was independently associated with major adverse cardiac events in patients following ST-elevation myocardial infarction. 44. McGann C, Akoum N, Patel A, et al. Atrial fibrillation ablation outcome is predicted by left atrial remodeling on MRI. Circ Arrhythm Electrophysiol 2014; 7:23–30. 45. Moon J, Lee HJ, Shim J, et al. Distinct prognostic impacts of both atrial & volumes on outcomes after radiofrequency ablation of nonvalvular atrial fibrillation: three-dimensional imaging study using multidetector computed tomography. Int J Cardiol 2013; 168:5430–5436. 3D left atrial volume by CT was independently associated with failure to maintain sinus rhythm 3 months following ablation for persistent atrial fibrillation. 46. Amin V, Finkel J, Halpern E, Frisch DR. Impact of left atrial volume on outcomes & of pulmonary vein isolation in patients with nonparoxysmal (persistent) and paroxysmal atrial fibrillation. Am J Cardiol 2013; 112:966–970. Left atrial volumes using CT were enlarged in patients with nonparoxysmal atrial fibrillation compared with paroxysmal atrial fibrillation. 47. Russo C, Hahn RT, Jin Z, et al. Comparison of echocardiographic single-plane versus biplane method in the assessment of left atrial volume and validation by real time three-dimensional echocardiography. J Am Soc Echocardiogr 2010; 23:954–960. 48. Jiamsripong P, Honda T, Reuss CS, et al. Three methods for evaluation of left atrial volume. Eur J Echocardiogr 2008; 9:351–355. 49. Tsang TS, Barnes ME, Gersh BJ, et al. Left atrial volume as a morphophysiologic expression of left ventricular diastolic dysfunction and relation to cardiovascular risk burden. Am J Cardiol 2002; 90:1284–1289. 50. Nagueh SF, Appleton CP, Gillebert TC, et al. Recommendations for the evaluation of left ventricular diastolic function by echocardiography. J Am Soc Echocardiogr 2009; 22:107–133. 51. Kircher B, Abbott JA, Pau S, et al. 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62. Hudsmith LE, Cheng AS, Tyler DJ, et al. Assessment of left atrial volumes at 1.5 Tesla and 3 Tesla using FLASH and SSFP cine imaging. J Cardiovasc Magn Reson 2007; 9:673–679. 63. Kataoka A, Funabashi N, Takahashi A, et al. Quantitative evaluation of left atrial volumes and ejection fraction by 320-slice computed-tomography in comparison with three- and two-dimensional echocardiography: a single-center retrospective-study in 22 subjects. Int J Cardiol 2011; 153:47–54. 64. Shin SY, Yong HS, Na JO, et al. A simplified method to determine left atrial volume and transport function using multislice computed tomography in patients with atrial fibrillation: comparison with transthoracic echocardiography. Int J Cardiovasc Imaging 2012; 28:1205–1216. 65. Wen Z, Zhang Z, Yu W, et al. Assessing the left atrial phasic volume and function with dual-source CT: comparison with 3T MRI. Int J Cardiovasc Imaging 2010; 26 (Suppl 1):83–92. 66. To AC, Flamm SD, Marwick TH, Klein AL. Clinical utility of multimodality LA imaging: assessment of size, function, and structure. JACC Cardiovasc Imaging 2011; 4:788–798. 67. Takagi Y, Ehara S, Okuyama T, et al. Comparison of determinations of left atrial volume by the biplane area-length and Simpson’s methods using 64slice computed tomography. J Cardiol 2009; 53:257–264. 68. Gweon HM, Kim SJ, Kim TH, et al. Evaluation of left atrial volumes using multidetector computed tomography: comparison with echocardiography. Korean J Radiol 2010; 11:286–294.
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