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Introduction |
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The left ventricle is normally shaped as a prolate ellipsoid or ellipse, where the long axis (LAX) is twice as long as the short axis (SAX). The average wall thickness is 10.9  2.0 mm and an average mass of 92 16 gm/m2. Disease states may cause the heart to remodel where the cavity size, wall thickness, or both are altered. Geometric changes in the heart alter its functionality and can be predictive of mortality, morbidity, and severity of the disease state. |
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Short Axis to Long Axis Ratios |
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| Measurements of SAX to LAX ratios can describe the geometric shape of the left ventricle. A normal SAX to LAX ratio is 0.45 to 0.62. |
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| In concentric remodeling, the LV mass remains constant but the ventricular volume decreases. Concentric remodeling is not to be confused with concentric hypertrophy which will be discussed later. The decrease in SAX and LAX is contributed equally by both diameters. Consequently the SAX/LAX ration remains in the normal range, 0.52 ± 0.04. |
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| In eccentric hypertrophy, the mass and the volume of the heart markedly increase. The increase in LAX and SAX diameters also occurs equally, so the SAX/LAX ratio is near the upper end of normal, 0.63 ± 0.03. As the SAX/LAX ratio approaches unity the heart will have remodeled itself to a spherical shape. As the heart becomes more spherical, the meridional stress is shifted to circumferential stress. The circumferential fibers then take on a more important role in the genesis of a stroke volume. |
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| The left ventricle dilates when it decompensates and becomes more spherical. The spherical shape allows it to form a more even distribution of regional stress and improves ventricular efficiency. The spherical changes can occur either globally or regionally. As the left ventricle becomes spherical the SAX/LAX ratio approaches unity.
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| SAX and LAX of Left Ventricle |
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| LV Status |
SAX/LAX |
| Normal |
0.45-0.62 |
| Concentric Remodeling |
0.52 ± 0.04 |
| Eccentric Hypertrophy |
0.63 ± 0.03 |
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| Table of LV Geometry |
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Volume to Mass Ratios |
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| Besides SAX/LAX ratios, the volume to mass ratios can give a clue to the geometric shape of the heart. The normal volume to mass (V/M) ratio is 0.8 at end-diastole and 0.26 at end-systole . Slices from apex to base of the heart show that the V/M ratio is not uniform for each slice. The volume to mass ratio decreases from the base where the V/M ratio is 0.8 to the apex where the V/M ratio is 0.25. Note that the LV mass exceeds the LV volume at each slice. |
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| Volume/Mass Ratios of LV |
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While the SAX/LAX ratio is commonly used, other measurements of sphericity have been developed. Area-to-perimeter ratios and volume-to-surface-area ratios have been developed. In test models, the volume-to-surface-area ratios appear to be more sensitive. |
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Symmetrical vs Asymmetrical Hypertrophy |
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| The left ventricular wall has similar thickness in the different walls, being slightly thicker in the interventricular septal area which is a shared wall with the right ventricle. All of the walls thicknesses are measured from endocardial to epicardial border, except the septum, which is measured from right ventricular endocardial border to the left ventricular endocardial border. |
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| If the ventricle becomes hypertrophied, the wall thickness will increase. The heart can hypertrophy symmetrically or asymmetrically. Symmetrical hypertrophy occurs when all of the wall proportionally thicken. Asymmetrical hypertrophy occurs when some wall(s) proportionally thicken more than other walls. |
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Relative Wall Thickness |
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The inferolateral (formerly posterior) wall is used as a relative measurement against the other wall thickness to determine if the hypertrophy is symmetrical or asymmetrical. In symmetrical hypertrophy, all of the wall's thickness will increase in the same relative ratio to the inferolateral (posterior) wall thickness (PWT). In asymmetrical hypertrophy, the inferolateral wall is relatively less affected, while other walls may increase in thickness . Therefore, in asymmetrical hypertrophy, the relative wall thickness is markedly increased. |
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LVSAX - Normal
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LVSAX - Concentric Hypertrophy
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LVSAX - Asymmetrical Hypertrophy (ASH)
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Ventricular Modeling |
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The left ventricle, when exposed to stress, damage or disease, can respond with remodeling. In the images below, the different models of mass, volume, and posterior wall thickness are presented for each model. |
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Ventricular Modeling |
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Concentric Remodeling |
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Concentric Hypertrophy |
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Hypertrophic Cardiomyopathy |
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| Hypertrophic cardiomyopathy is a condition that is characterized by increased left ventricular mass with decreased ventricular volumes. Consequently, the relative wall thickness is markedly increased, much more than concentric hypertrophy. The volume to mass ratio is markedly decreased. Systolic stress is decreased. Endocardial shortening is increased. |
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| Hypertrophic Cardiomyopathy |
Hypertrophic Cardiomyopathy |
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Eccentric Hypertrophy |
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| Eccentric hypertrophy, usually due to conditions of volume overload (aortic or mitral regurgitation) results in a markedly increased left ventricular mass and markedly increased left ventricular volumes. The regional wall thickness is near normal or slightly decreased. The volume-to-mass ratio is near normal or slightly increased also. Systolic stress is markedly increased. Interestingly, the systolic shortening of the endocardial and midwall fibers are normal. |
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| Eccentric Cardiomyopathy |
Eccentric Cardiomyopathy |
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Dilated Cardiomyopathy |
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| Dilated cardiomyopathy has a markedly increased mass, similar to eccentric hypertrophy. However, the volume of the left ventricle is maximally increased, even more than eccentric hypertrophy. Consequently, the relative wall thickness is decreased and the volume-to-mass ratio is increased. Systolic stress is severely increased. Endocardial and midwall shortening is decreased. |
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| Dilated Cardiomyopathy |
Dilated Cardiomyopathy |
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Left Ventricular Shape |
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The shape of the ventricle along in the long axis and the short axis can be measured by 2D mode via the midesophageal two and/or four chamber views and the mid-transgastric short axis view, respectively.
 To quickly gauge the shape of the ventricle, set your scan depth to 10 or 12 cm. In the midesophageal 2CV, midesophageal 4CV and the transgastric mid short axis views, the size of the left atrium, left ventricle, and wall thickness can be qualitatively and semi-quantitatively evaluated to indicate the shape of the ventricle. All measurements should be done at end-diastole. The shape and size of the left ventricle, right ventricle, right atrium and left atrium can be quickly determined. |
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Regional Shape |
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Regional dysfunction may lead to regional changes in shape. The left ventricular endocardial contour exhibits changes in curvature. Curvature is a major determinant of wall tension and changes in ventricular shape occur because of acute elevation of wall stress at the time of infarction. The heart then remodels to evenly distribute the wall stress to improve efficiency. The areas of infarction may expand, and if so, the myocardium typically thins. Echocardiographic analysis of regional shape can be difficult if the tomographic plane is tangential or if the image is poor quality. |
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Limitations |
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2D echocardiography has many limitations that prevent its routine use to calculate left ventricular mass, volumes and diameters. Endocardial detection may be difficult with 2D echocardiography. The slower frame rate (30-60 fps) when compared to M mode (1000 fps) cause image degradation. Also, poor lateral resolution may result in dropout of an endocardial wall. Near field artifact causes blurring of the endocardial wall. Some views may yield poor quality or foreshortened views that can cause errors in calculations. Besides the technical limitations, the manual calculations are time consuming. Since the calculations are time consuming, clinical diagnosis of the type of remodeling is usually qualitative, rather than quantitative.
Automated border detection (ABD) functions on echocardiographic machines can automate the process of describing geometry and global function of the left ventricle. Automated border detection detects the endocardial boarder using integrated backscatter. Once the border is detected, beat-to-beat calculations of area changes are possible. Since the calculations are time related, cardiac function can be compared to time. dV/dt and times to peak and negative dV/dt plus beat-to-beat volume, ejection fraction, fractional shortening changes can be calculated. Automated border detection can exhibit the same difficulties and inaccuracies that 2D echocardiographic measurements contain.
Since the echocardiographic measurements are in two dimensions, three dimensional changes in geometry of the left ventricle may be missed because of assumptions made during 2D echocardiographic calculations. 3D echocardiography would obviate the need for assumptions and should provide the most accurate measurements of cardiac mass, volume, and function.
The American Society of Echocardiography has published recommendations for the quantitative analysis of the endocardial contour. The endocardial border detection is the most important factor in the quality of the scan. Harmonics, manipulating the gain and depth and view of the scan, or utilization of contrast echocardiography all help to improve the quality of the scan.
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