Left Ventricle Systolic Function

Objectives

At the completion of this chapter, the student will be able to:

Obtain the TEE acoustic views Evaluate Left Ventricular Systolic Function with 2D Mode Evaluate Left Ventricular Systolic Function with Doppler Mode

Introduction

Global systolic function is predictive of outcome for ischemic heart disease, cardiomyopathies, and valvular heart disease.  Echocardiography is an excellent method to measure the global and regional systolic function of the heart.  Systolic function has been the focus of left ventricular echocardiography, until it was realized that diastolic function of the left ventricle is also important.  The size and shape of the left ventricle can be quantified with echocardiography.  The size and shape of the left ventricle can indicate the different types of pathology associated with systolic and/or diastolic dysfunction.  The parameters describing systolic function of the left ventricle commonly include ejection fraction, cardiac output, fractional area change, and preload indices.  Recently, more sophisticated indices of systolic function have become available.  Diastolic function and measurement has been the recent focus as we begin to understand more about the diastology of the left ventricle and it's importance to left ventricular physiology.

The assessment and evaluation of global systolic function of the left ventricle can be performed by M Mode, 2D, and Doppler echocardiography. The various modes of echocardiography can give an indication of the geometry, global function, and its performance.  Regional function of the left ventricle may affect the left ventricle's global performance.  Right ventricular function and pericardial factors can also affect global left ventricular function.  Normal systolic function does not imply a normal heart, as diastolic dysfunction may also be present.  The various modes of echocardiography can indicate the global function, and, if impaired, the etiology or mechanism of the impairment.

Factors Affecting Global Function

LV systolic function is affected by five factors:

Preload Afterload Contractility Heart Rate/Rhythm Synchronous Contraction

Contractility is the most difficult to measure because it requires that the other four factors remain constant.  A change in preload often affects other factors in the intact heart, which can obscure the effect of changing the preload.  An acute reduction in preload, via a drug effect or by decreasing the intravascular volume, can cause a change in heart rate, afterload, and, contractility.  While the Frank-Starling mechanism of changing ventricular performance in response to preload or afterload changes does occur, an intrinsic change in contractility can also occur. Frank-Starling Mechanism

Asynchronous contraction of the heart, via bundle branch block or a right ventricular pacemaker, may cause a marked decrease in cardiac function, or even, tricuspid regurgitation after tricuspid valve repair. Biventricular pacing has been shown to improve ventricular performance and induce remodeling.

Left Ventricular Global Indices

Clinical evaluation of the global systolic function of the heart can include the evaluation of preload, afterload, cardiac output, ejection fraction, end-systolic volume, end-diastolic volume, and dimensions of the heart.  The left ventricle is not mechanically isolated from the right ventricle, so right ventricular function can affect the left ventricular function.  Left atrial function can affect the left ventricular performance via its contribution to the cardiac output. Advanced systolic function assessments include Tei Index, pressure-area curves, fractional area shortening, fractional area change, and end-systolic adn end-diastolic volume calculations. These are discussed in detail in the Advanced Section of E-echocardiography.com Some indices are "load" dependent and other are "load" independent. Ejection fraction is load dependent such that preload and afterload can effect the ejection fraction.   LV Systolic Evaluation  Afterload  Cardiac Output  End-Systolic Volume  End-Diastolic Volume  Ejection Fraction  Fractional Area Change  Fractional Shortening  Left Ventricular Internal Diameter  Wall Thickness  Pressure-Area Curve  Tei Index (Myocardial Performance Index)  Right Ventricular Function  Left Atrial Function

In the past, the pulmonary artery catheter was used to correlate cardiac output with the preload indices derived from a PAC, but, the correlation was poor.  Echocardiography provides a left ventricular area measurement, from which left ventricular volume can be calculated.  The volume calculation has a much better correlation with cardiac output than the PAC indices.  By utilizing Doppler and 2D, cardiac output can be calculated.  Afterload can be determined by the measurement of wall stress.  Wall stress is a cumbersome calculation that is usually not performed in clinical situations.  Contractility, as evident by the load-dependent ejection fraction is easily qualitatively or quantitatively measured.  Poor ejection fraction correlates with decreased postoperative survival or successful outcomes.

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