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      Left atrial volume, a simple measure but strong predictor of cardiovascular events in non-contrast computed tomography

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          Abstract

          Left atrial volume (LAV) emerged as a marker of cardiovascular disease many years ago with a large body of supporting scientific evidence. Since then, it has found clinical utility in the cardiovascular field, especially in cardiology and neurology. It remains of great interest as to why so simple a measure carries such a strong prognostic impact for a wide variety of cardiovascular diseases [1,2]. Among these disorders are ischemic heart disease, heart failure (HF) [[3], [4], [5], [6]], hypertrophic cardiomyopathy (HCM) [7], atrial fibrillation (AFib) and even for predicting stroke in the absence of AFib. To understand why LAV is so sensitive [8], we look to the mechanisms of left atrial remodeling with a common endpoint of increased LAV, left atrium (LA) dilatation and hypocontractility, and eventually resulting in AFib [1] (Table 1). Identifying increased LAV will allow early detection of LA dysfunction [1] and alert clinicians to treat the patient in a timely manner to reduce the negative consequences of long-standing incompletely treated diseases or pathologic states (Table 1). Table 1 Underlying pathophysiologic mechanisms that affect LA size and function. Table 1 Pathophysiologic mechanism Effect on LA Examples of diseases and pathologic states Pressure and/or volume overload Hypertrophy, necrosis, apoptosis and fibrosis at cellular and extracellular matrix levels [1] Neurohumoral activation such as atrial natriuretic peptide (ANP) [1,18] • LV systolic dysfunction (HFrEF) [3,4] • LV diastolic dysfunction (HEpEF) [5,6] • Ischemic heart disease [3,4] • Post-myocardial infarction [3,4] • Hypertension • Aortic stenosis • Aortic insufficiency • HCM [7] • Mitral stenosis • Mitral regurgitation • LV dilatation [3,4] • LV myocardial scar [3,4] • Iron deposition on the myocardium • Sarcoidosis • Amyloidosis • Obesity • LV hypertrophy on athletes • Aging • Dilated cardiomyopathies • Obstructive Sleep Apnea Tachycardia • AFib • Hyperthyroidism • Drug induced tachycardia • Energetic beverages • Caffeine in excess Abbreviations: HFrEF: Heart failure with reduced ejection fraction, HEpEF: Heart failure with preserve ejection fraction, HCM: Hypertrophic cardiomyopathy, LV: Left ventricle, AFib: Atrial fibrillation. The power of LAV has been tested in long-term follow up of patients, underscoring its predictive nature [9]. This predictive capability has been largely validated with echocardiography (Echo), where its value was originally confirmed, and with other newer and more accurate methods such as cardiovascular magnetic resonance (CMR) and contrast-enhanced cardiac computed tomography (CT). The latter has traditionally been performed using retrospective acquisition of coronary computed tomography angiography (CCTA) images in different pathologic states (such as those described in Table 1). The accuracy of the different imaging modalities has been largely documented, however two-dimensional echocardiographic (2D-echo) methods are somewhat limited, [10] three-dimensional (3D) echocardiography (3D-echo) has better accuracy and reproducibility but is not widely used in routine clinical practice (despite newer rapid imaging and analysis strategies that improve its utilization) [10], atrial strain imaging can detect LA dysfunction before the manifestation of LA structural changes since its parameters are influenced by loading conditions, rhythm irregularity and fibrosis [11], but, as it is for 3D-echo, is not widely used in routine clinical practice. CMR is the gold standard method for the assessment of cardiac structure and function [12] due to its strong accuracy and reproducibility, and LAV reference ranges are published and validated for different gender and ages [13]. CCTA, based on its retrospective acquisition, allows 3D visualization of the LA and is readily available for analysis without additional testing with high spatial resolution across the cardiac cycle [14]. In the real world, obtaining this strong predictor in asymptomatic population is limited, since it is not feasible to perform 3D-echo, CMR and CCTA just to obtain the LAV in this group. 3D-echo and CMR are not ubiquitous, and CCTA requires somewhat greater radiation doses, even with dose-limiting protocols [15], since it necessitates retrospective acquisition and the use of contrast media. Thus, given the clinical relevance of LAV assessment, it would be preferable to have a highly accurate and reproducible method such as those described, but also one that is widely used and that overcomes the real-world limitations described. Toward this end, Cardona et al. developed a method to test whether a highly reproducible and accurate LAV could be obtained on more commonly-performed non-contrast coronary artery calcium (CAC) scans. Their study is particularly clinically relevant since CAC scans are widely available, have a well-established operator-independent protocol, do not require contrast media, and are acquired with radiation doses significantly lower than CCTA. Cardona et al. in their recent publication [16] provide a valuable contribution by measuring LAV using the standard CAC protocol, and proving that it is feasible and highly accurate compared with the reference standard of CCTA. They overcame certain technical limitations that are attributed to non-contrast CT studies, including not having to modify the standard acquisition protocol, and developing a method to use the mitral valve plane as a landmark in a multiplanar reformatting approach. This new method reduced an important source of variability and low reproducibility, and provided excellent interobserver and intra-observer reproducibility. The authors identified several additional technical characteristics of the non-contrast gated CT scan and of the LA anatomy that allows this approach to be feasible. These included the fact that both CAC scan and CCTA are ECG-gated, that the LA is surrounded by easily identifiable structures on non-contrast CT images, the lower density of the interatrial septum, and that the mitral annulus has specific and easily identifiable landmarks (fat in the auriculo-ventricular groove, the circumflex artery and the coronary sinus). There is a difference between LAV from CAC scan and from the reference standard on CCTA, due to technical reasons such the potential inclusion of part of the esophageal wall, the overestimation related to the thicker slices of the CAC scans, and the decreased endocardial border definition of the non-contrast enhanced study. Even though these differences were statistically significant, they had little clinical relevance since they only represent 4% of the average measured LA volume. Normal reference values will need to be established for this approach in an asymptomatic population since the reported values are measured at end-systole and not in mid-diastole as for CAC scans. Likewise, the technique will require validation in symptomatic individuals with pathologic states (Table 1), and in long-term follow-up cohorts to validate its predictive strength. Cardona et al. have advanced the field by proving that standard CAC scans can be used to quantify LAV. This tool allows the benefit of LAV measurements to be applied to routine CAC scans, and should help to improve cardiovascular risk prediction in asymptomatic populations mainly for those subjects with new-onset AFib [17]. It is likely that using this method will reclassify the cardiovascular risk of an individual, above and beyond the metric of the CAC score and in addition to conventional risk stratification scales. Conflict of interest The author declare that there is no conflict of interest.

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          Natriuretic peptides.

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            Left atrial volume as a morphophysiologic expression of left ventricular diastolic dysfunction and relation to cardiovascular risk burden.

            Left ventricular (LV) diastolic dysfunction is prevalent in the community. Current assessment of diastolic function can be complex, involving Doppler evaluation of an array of hemodynamic data. The relation between left atrial (LA) volume and diastolic function, and between LA volume and cardiovascular risk and disease burden are not well known. In the present prospective study of 140 adults, mean age 58 +/- 19 years, referred for a clinically-indicated echocardiogram and in sinus rhythm, with no history of atrial arrhythmias or valvular heart disease, we determined the LA volume, LV diastolic function status, cardiovascular risk score (based on age, gender, history of systemic hypertension, diabetes mellitus, hyperlipidemia, and smoking), and cardiovascular disease burden (based on confirmed vascular disease, congestive heart failure, and transient ischemic attack or stroke). LA volume was found to correlate positively with age, body surface area, cardiovascular risk score, LV end-diastolic and end-systolic dimensions, LV mass, diastolic function grade, tissue Doppler E/E', tricuspid regurgitation velocity, and negatively with LV ejection fraction (all p <0.006). In a multivariate clinical model, LA volume indexed to body surface area (indexed LA volume) was independently associated with cardiovascular risk score (p <0.001), congestive heart failure (p = 0.014), vascular disease (p = 0.012), transient ischemic attack or stroke (p = 0.021), and history of smoking (p = 0.008). In a clinical and echocardiographic model, indexed LA volume was strongly associated with diastolic function grade (p <0.001), independent of LV ejection fraction, age, gender, and cardiovascular risk score. In patients without a history of atrial arrhythmias or valvular heart disease, LA volume expressed the severity of diastolic dysfunction and provided an index of cardiovascular risk and disease burden.
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              Left atrial deformation: Useful index for early detection of cardiac damage in chronic mitral regurgitation

              In chronic mitral regurgitation (MR) left atrium is one of the first cardiac structures that is involved in remodeling and ultrastructural changes for a progressive volume overload. Severe left atrial (LA) dilation on echocardiography and new onset of atrial fibrillation in asymptomatic patients with preserved Left Ventricular (LV) function, appeared as a Class IIb recommendation for consideration for surgical mitral valve repair in the actual guidelines. However, before atrial dilatation and dysfunction, several ultrastructural changes appear in the atrial muscle tissue that are difficult to identify with the standard echocardiography. Speckle tracking echocardiography (STE) can analyze LA function: it has been showed that it can indirectly identify structural tissue modifications from excessive atrial effort in the early stages of MR up to the full depression of atrial function in the late stages where there are advanced ultrastructural alterations. This review aims to summarize current knowledge on the role of atrial strain identifying early structural alterations of the atrial tissue in the rising stages of MR considering that Left Atrial Peak Longitudinal Strain (PALS) considered useful parameter for a more extensive evaluation of MR patients.
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                Author and article information

                Contributors
                Journal
                Int J Cardiol Heart Vasc
                Int J Cardiol Heart Vasc
                International Journal of Cardiology. Heart & Vasculature
                Elsevier
                2352-9067
                03 May 2019
                June 2019
                03 May 2019
                : 23
                : 100368
                Affiliations
                American British Cowdray Medical Center, Mexico City, Mexico
                Author notes
                [* ]154 Carlos Graef Fernandez Ave. Room 207. Tlaxala, Cuajimalpa, 05300 Mexico City, Mexico. lilisierra@ 123456wdevel.net
                Article
                S2352-9067(19)30071-5 100368
                10.1016/j.ijcha.2019.100368
                6503131
                0d00863c-3bee-4787-ab40-2838a26f7f03
                © 2019 The Author

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

                History
                : 19 April 2019
                : 22 April 2019
                : 23 April 2019
                Categories
                Editorial

                lav, left atrial volume,hf, heart failure,hcm, hypertrophic cardiomyopathy,afib, atrial fibrillation,la, left atrium,echo, echocardiography,cmr, cardiovascular magnetic resonance,ct, computed tomography,ccta, coronary computed tomography angiography,2d-echo, two-dimensional echocardiographic,3d, three-dimensional,3d-echo, three-dimensional echocardiography,cac, coronary artery calcium,left atrial volume,coronary artery calcium scan,coronary artery computed tomography angiography,non-contrast

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