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ADVANCED SYSTOLIC FUNCTION Albert T. Cheung, M.D. Department of Anesthesiology and Critical Care University of Pennsylvania, Philadelphia, PA Multiplane 2-dimensional TEE permits the entire left ventricle to be imaged throughout the cardiac cycle. Direct imaging of the left ventricle throughout the cardiac cycle can be used to provide information about left ventricular wall thickness, chamber size, and contractile performance. TEE measurements of global systolic function are useful for clinical decision making because they provide information pertaining to prognosis, the risk of cardiac operations, the severity of valvular heart disease, the extent of coronary artery disease, and the responses to vasoactive or other cardiovascular drug therapy. For example, in the American Heart Association guidelines for the management of patients with valvular heart disease, the decision for aortic valve replacement in patients with chronic aortic regurgitation without symptoms of heart failure is contingent on measures of left ventricular ejection fraction and left ventricular diameters (Figure 4, ACC/AHA 2006 Guidelines for the Management of Patients with Valvular Heart Disease). GLOBAL LEFT VENTRICULAR SIZE AND SYSTOLIC FUNCTION The normal left ventricle is a muscular organ of nearly uniform wall thickness surrounding a cavity with a circular cross section. The cross sectional area of the left ventricular cavity is greatest at the base and decreases toward the apex. Contraction of myocardial fibers during systole causes an increase in left ventricular wall thickness and a decrease in both the diameter and the length of the left ventricular chamber. The mitral valve leaflets, chordae tendineae, papillary muscles, and left ventricular apex provide anatomical landmarks for establishing the level of the cross-sectional imaging planes during the 2-dimensional echocardiographic examination. The entire left ventricle can be examined by TEE using the transgastric short-axis imaging planes at the level of the left ventricular apex, mid-papillary muscles, and left ventricular base. Alternatively, the entire left ventricle can also be examined using the TEE mid-esophageal long-axis imaging planes at multiplane angles of 0-20° (4-chamber), 80-100° (2-chamber), and 120-160° (long-axis). Chronic systolic pressure overload caused by hypertension or aortic stenosis produces concentric left ventricular hypertrophy. In patients with compensated left ventricular hypertrophy, left ventricular mass increases relative to the cavity volume. This change can be most readily detected by TEE as an increase in left ventricular wall thickness. A left ventricular end-diastolic posterior wall thickness greater than 1.1 cm suggests left ventricular hypertrophy. Chronic volume overload caused by congestive heart failure, aortic regurgitation, or mitral regurgitation also causes left ventricular hypertrophy. In contrast to chronic pressure overload, volume overload causes an increase in left ventricular cavity size without an increase in ventricular wall thickness. An end-diastolic short-axis left ventricular cavity diameter greater than 5.5 cm or cross-sectional area greater than 22 cm2 at the mid-papillary level suggests left ventricular dilation or eccentric hypertophy. Left ventricular end diastolic and end systolic cavity volume can be measured from the mid-esophageal left ventricular 4 chamber and 2 chamber views using Simpson’s rule. This measurement is accomplished by tracing the left ventricular endocardial border up to the mitral valve annulus and then using the calipers to measure the length of the left ventricular cavity from the mitral valve annulus to the apex. The accuracy of TEE for quantifying left ventricular volume is not as well established as with TTE. Foreshortening of the left ventricular cavity occurs if the long-axis cross sectional imaging plane is not directed through the true left ventricular apex and will cause underestimation of the actual left ventricular cavity volume. Representative normal echocardiographic values measured using Simpson’s rule are: LV end-diastolic volume of 56-155 ml, LV end-systolic volume of 19-58 ml, and LV ejection fraction of > 55%. Reference values for left ventricular dimensions measured by echocardiography have recently been published in a consensus report from the American Society of Echocardiography. In that report, dimensions are indexed by gender, height, and body surface area. It is also important to note that the published reference dimensions were obtained from transthoracic echocardiographic studies measuring left ventricular dimensions at the mitral valve chordal level rather. TEE measurements often obtained at the transgastric left ventricular mid-papillary muscle level may yield slightly smaller dimensions. From: J Am Soc Echocardiogr 2005;18:1440-1463. From: J Am Soc Echocardiogr 2005;18:1440-1463. Global indexes of left ventricular systolic function can be measured from the TEE images based on the relative speed and change in end-diastolic and end-systolic left ventricular cavity size. The transgastric left ventricular short axis end diastolic area (EDA) and end systolic area (ESA) are often used for this purpose and are measured by manual planimetry of the area bounded by the endocardium. The end systolic diameter (ESD) is approximately 2.8 cm and the ESA is approximately 6.2 cm2 in normal adults. 1. Fractional shortening (FS) is the percent decrease in left ventricular cavity short axis diameter from end diastole (LVIDed) to end systole (LVIDes) and can be measured from the endocardial border or the midwall of the left ventricle. FS = (LVIDed – LVIDes)/LVIDed x100 (Normal range = 14-45%) 2. Fractional area change (FAC) is the percent decrease in the left ventricular cavity cross-sectional area from end-diastole to end-systole. FAC (%) = (EDA − ESA) × 100 EDA (Normal = 57%). 3. Mean velocity of circumferential fiber shortening (Vcf ) Vcf (circumference/second) = EDD − ESD × 100 EDD × LVET where EDD = end-diastolic LV cavity diameter, ESD = end-systolic LV cavity diameter, and LVET = left ventricular ejection time (seconds). 4. Heart rate corrected mean velocity of circumferential fiber shortening (Vcfc) Vcfc (circ/s) = Vcf R − R interval (Normal ≥ 1.1 circ/s) All of these indexes of global ventricular function are based on a single cross-section of the left ventricle. The presence of ventricular asymmetry or dysynergy, especially when abnormal regions are not within the plane of the image used to calculate the index may render the index a poor indicator of global left ventricular function. Corrections to the global left ventricular ejection fraction can be estimated based on the presence of akinetic or dyskinetic regions outside of the imaging plane. For example, global left ventricular ejection fraction estimated from the transgastric mid-ventricular short axis image should be decreased by approximately 10% in the presence of an akinetic left ventricular apex. Alternatively, a qualitative estimation of global ventricular function can be made based on visual inspection. Global ventricular function is graded as being normal, mildly, moderately, or severely impaired based on estimation of the left ventricular ejection fraction. The advantages of visual assessment are that it is based on multiple views, incorporates multiple parameters of left ventricular function, and can be performed immediately without the need for off-line image analysis. Studies have demonstrated that visual assessment of left ventricular function, despite its limitations, correlate well with quantitative measurements and is a useful parameter for predicting cardiac risk and morbidity. An echocardiographic left ventricular ejection fraction less than 30% is consistent with severe left ventricular dysfunction based on clinical trials involving patients with heart failure. Subjective estimation of global ventricular function or left ventricular ejection fraction is dependent on the experience of the echocardiographer and inter-observer variability may exist depending upon the parameters used to grade ventricular function. The accuracy and consistency of subjective estimation of global ventricular function can be improved by calibrating the estimation with established methods of quantification. One difficulty encountered with the assessment of left ventricular function is that measures of systolic performance are dependent on the ventricular loading conditions at the time of the study. An abnormally high systolic blood pressure increases left ventricular afterload and decreases the FAC or Vcfc. A reduction in preload decreases both left ventricular end diastolic and end systolic cavity size. For these reasons, it is necessary to plot indexes such as the FAC or Vcfc against the systolic blood pressure or left ventricular wall stress to obtain an afterload-independent assessment of ventricular contractility. Left ventricular meridional wall stress (ESWS), an estimate of afterload that incorporates measures of peak systolic blood pressure (SBP), left ventricular wall thickness (H), and left ventricular end-systolic cavity diameter (ESD) can be estimated with the following formula : ESWS (x103 dynes/cm2) = (0.334)(SBP)(ESD) (H )(1+ H / ESD) Estimating load-independent indexes of left ventricular contractile performance is tedious to perform clinically, but has been used in clinical studies to demonstrate the increase in left ventricular contractility in response to inotropic agents or the decrease in ventricular contractility in response to volatile anesthetic agents. Despite the recognition that performance measures such as ejection fraction are load-depend, echocardiographic measures of global left ventricular function has proven prognostic value in the clinical setting. LEFT VENTRICULAR FUNCTION AND THE ECHO REPORT The American Society of Echocardiography, European Society of Echocardiography, American College of Cardiology, and the American Heart Association have published guidelines with recommendations for definitions used in the reporting of cardiac imaging studies (15-16). Attached is an example of a format that can be used for the reporting of left ventricular size and function as assessed by the echocardiographic examination. CONCLUSION Echocardiographic measurements of left ventricular wall thickness, cavity size, and segmental wall motion obtained by TEE can be used to assess global and regional left ventricular function. The information provided by TEE is an important supplement to hemodynamic and electrocardiographic measurements for the diagnosis of left ventricular hypertrophy, cardiomyopathy, and the consequences of myocardial ischemia and infarction. It is important to recognize that left ventricular volumes cannot be directly measured from a single cross-sectional image. It is also important to recognize that left ventricular systolic function is dynamic and changes in response to anesthetic agents, vasoactive drug therapy, intravascular volume status, and arterial blood pressure. REFERENCES 1. American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Society of Cardiovascular Anesthesiologists. Society for Cardiovascular Angiography and Interventions. Society of Thoracic Surgeons. Bonow RO, et l. ACC/AHA 2006 guidelines for the management of patients with valvular heart disease. Circulation 2006;114:e84-231 2. 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Hauser AM, Gangadharan V, Ramos RG, et al: Sequence of mechanical, electrical and clinical effects of repeated coronary artery occlusion in human beings. J Am Coll Cardiol 1985;5:193-7. 13. Lang RM, Vignon P, Weinert L, et al: Echocardiographic qunatification of regional ventricular wall motion with color kinesis. Circulation 1996;93:1877-85. 14. Cahalan MK, Ionescu P, Melton, et al: Automated real-time analyisis of intraoperative transesophageal echocardiograms. Anesthesiol 1993;78:477-85. 15. Lang RM, Bierig M, Devereux RB, et al: Recommendations for chamber quantification: A report from the ASE Guidelines and Standards Committee and the Chamber Quantification Writing Group, developed in conjunction with the European Association of Echocardiography, a branch of the European Society of Cardiology. J Am Soc Echocardiogr 2005;18:1440-1463. 16. Hendel RC, Budoff MJ, Cardella JF, et al. ACC/AHA/ACR/ASE/ASNC/HRS/NASCI/RSNA/SAIP/SCAI/ SCCT/SCMR/SIR 2008 Key Data Elements and Definitions for Cardiac Imaging: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Data Standards. Circulation 2009;119:154-86