Final Feigenbaum’s Echocardiography DIGITAL

Feigenbaum’s Echocardiography

Chapter 5 Evaluation of Systolic Function of the Left Ventricle

improved. Initial ultrasound equipment had relatively poor gray- scale registration. As such, the precise boundary between the blood pool and tissue was o en di cult to determine. One early approach to linear measurements involved a “leading-edge to leading-edge” technique. Using this technique, septal thickness was dened as the leading edge of the septum on its right ventricular side to the leading edge of bright endocardial echoes on the le ventricular side of the ventricular septum. Depending on gray scale, image intensity, and resolution, the leading edge itself could be as much as 1 or 2 mm in thickness. Renements in image processing have allowed greater levels of gray-scale registration with a substantially rened visual- ization of the actual tissue–blood pool boundary. It is now com- mon practice to measure chamber dimensions, as dened by the actual tissue–blood interface, rather than the distance between the leading-edge echoes. Table 5.1 outlines many of the linear measure- ments that can be made for assessment of le ventricular function. e location of these measurements is schematized in Figure 5.1 and further demonstrated in Figure 5.2. Although the temporal resolution of a dedicated M-mode beam is superior to that of two-dimensional echocardiography, the ability to visualize the entire le ventricle, and to ensure a true minor-axis dimension, mitigates this potential advantage for most purposes. ere are multiple limitations of linear measurements for deter- mining ventricular performance. One of the most obvious is that many forms of acquired heart disease, especially coronary artery disease, result in regional variation in ventricular shape and func- tion. By denition, a linear measurement provides information regarding dimension and contractility only along a single line. is may either underestimate the severity of global dysfunction if only a normal region is interrogated, or overestimate the abnormality if the M-mode beam exclusively transits the wall motion abnormal- ity. An additional limitation of an M-mode measurement of the le ventricle is that it o en does not re‘ect the true minor-axis

GENERAL PRINCIPLES Most forms of acquired heart diseases may be associated with abnor- malities of le ventricular systolic function at some point in their nat- ural history. An assessment of le ventricular systolic function should be part of virtually all echocardiographic examinations. Assessment of systolic function provides valuable prognostic information, plays a crucial role in selection of medical therapy, and is instrumental in determining the timing of surgery for valvular heart disease. is chapter will deal with echocardiographic techniques for evaluation of both global and regional le ventricular systolic function. Since its inception echocardiography has played a role for assessment of le ventricular systolic function, initially begin- ning with M-mode echocardiography and progressing to modern platforms providing comprehensive three-dimensional imaging of the le ventricle with the ability to extract detailed parameters of ventricular function. is chapter will concentrate on the currently utilized and commercially available methods for evaluation of le ventricular systolic function. Older techniques and techniques which have been utilized for investigational purposes only are men- tioned for historical purposes, or for their relevance with respect to limitations which may still be present in modern analysis systems. LINEAR MEASUREMENTS e rst attempts to quantify le ventricular function involved lin- ear measurements of the minor-axis dimension from a dedicated M-mode echocardiogram. Linear measurements have the disadvan- tage of determining ventricular function only along a single interro- gation line. e precise location at which linear measurements are made has varied as the resolution of ultrasound instrumentation has

Table 5.1

LINEAR MEASUREMENTS OF LEFT VENTRICULAR SIZE AND FUNCTION

Parameter

Formula

Abbreviation

Units

LV internal dimension in diastole

LVID d LVID S

mm (or cm)

mm (or cm)

LV internal dimension in systole

Fractional shortening

(LVID d

– LVID s

)/LVID d

FS

% or 0.XX

σ m

mm Hg or dyne-cm 2

Meridional wall stress in systole

PR/h

) 3

cm 3 or mL

Cubed LV volume in diastole

(LVID d

+ PW) 3

Cubed LV + myocardial volume

(IVS + LVID d

cm 3 or mL

× ET)

Velocity of circumferential shortening

(LVID d

– LVID s

)/(LVID d

VCf

Circumference/s

ET, ejection time; h, wall thickness; PR, pressure × radius; PW, posterior wall.

6 100

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