Global ventricular systolic function in ACS is assessed through either wall motion scoring and global ventricular ejection fraction.
WALL MOTION SCORING
Wall motion scoring analysis assigns a numeric value to the degree of contractile dysfunction in each segment. Most common scoring criteria are seen in Table 5.1
Once all segments are assigned individual scores, total score is calculated as a sum of individual scores. A wall motion score index (WMSI) in then calculated as a ratio between the total score over the number of evaluated segments. The WMSI is a dimensionless index.
For a fully visualized normal ventricle the total score is 17 (all segments have normal contractility). Because all 17 segments are evaluated, the WMSI of a normal heart is 17/17 = 1. For abnormal ventricles, the higher the WMSI, the more significant is the abnormal wall motion.
TABLE 5.1 Left Ventricular Wall Motion Scoring
Wall motion score index =
Sum of individual segment scores
Number of evaluated segments
ASSESSMENT OF VENTRICULAR EJECTION FRACTION
Numerous studies have consistently shown left ventricular ejection fraction (LVEF) as one of the most powerful predictors of future mortality and morbidity in patients with heart disease.3
LVEF is the single most powerful predictor of mortality and the risk for developing life-threatening ventricular arrhythmias after myocardial infarction.4
Furthermore, once the ACS resolves, the residual LVEF is important for treatment options as LVEF cutoff values are built into recommendations for both medical and electrical device therapies. Even with treatment and clinical stabilization of heart failure, there is an inverse, almost linear, relationship between LVEF and survival in the patient whose LVEF is <45% (Figure 5.1
By definition, LVEF is the percentage of the end-diastolic volume that is ejected with each systole as the stroke volume. Thus, to calculate the LVEF one needs to estimate the end-systolic and end-diastolic volume of the left ventricle.
For two-dimensional echocardiography, biplane Simpson’s rule is routinely used for estimation of LVEF.6
Most modern ultrasound systems provide a semiautomated software package for the Simpson’s rule analysis. Operators are usually required to trace only the left ventricular endocardial border at end-diastolic and end-systolic in the apical four-chamber and two-chamber views; the software package then automatically calculates the left ventricular end-diastolic volume, end-systolic volume, and LVEF (Figure 5.2
With the advent of real-time three-dimensional (RT3D) transthoracic techniques, left ventricular volumes and LVEF can now be calculated with greater accuracy than is possible with the biplane Simpson’s rule (Figure 5.3
). RT3D-derived left ventricular volume data are now comparable to those obtained by cardiac magnetic resonance imaging, the prior gold standard for such calculations.7
Thus, whenever available, left ventricular volumes and LVEF in ACS should be calculated from an RT3D system. The biplane Simpson’s rule should be the next best method for such calculations when only a two-dimensional ultrasound system is available.