Accuracy of Ejection Fraction Measurements
abstract & commentary
Synopsis: Volumetric MRI and echo techniques give virtually identical results for left ventricular volumes and ejection fraction, and are highly reproducible.
Source: Chuang ML, et al. J Am Coll Cardiol 2000; 35:477-484.
Left ventricular ejection fraction (ef) remains the most powerful predictor of mortality in heart disease and is important for selecting a variety of therapies from drugs to surgery. Echocardiography has largely replaced radionuclide angiography as the preferred technique for estimating left ventricular volumes and EF, but recently magnetic resonance imaging (MRI) techniques have been shown to be highly accurate. Thus, Chuang and colleagues evaluated 35 adults (10 normals and 25 dilated cardiomyopathy patients) with biplane and volumetric (short axis stack technique) cine MRI, and biplane and volumetric echocardiography (multiplane 3D reconstruction). Biplane echocardiography underestimated left ventricular volumes by a consistent amount throughout the cardiac cycle (~10%) such that EF was no different by the four methods (50-53%). When EF was grouped into ³ 55%, > 35% to < 55%, and < 35%, volumetric MRI and echo only differed by one category in two cardiomyopathy patients (8%), but biplane methods misclassified EF in six to 11 patients (22-44%) vs. volumetric methods. Also, intra- and interobserver variability was better with volumetric methods by a factor of two- to threefold. Chuang et al conclude that volumetric MRI and echo techniques give virtually identical results for left ventricular volumes and EF, and are highly reproducible. By contrast, biplane methods by both imaging techniques give more divergent EF values with worse reproducibility. Thus, the choice of a left ventricular volume measurement method is more important than the imaging technique for measuring left ventricular size and systolic function.
Comment by Michael H. Crawford, MD
Ejection fraction, despite its drawbacks, continues to be a popular measurement of left ventricular systolic performance, which has considerable data to support its use. Echocardiographic estimates of EF are frequently used because of their perceived accuracy and ease of application. However, other imaging techniques can also provide EF measurements. Radionuclide multiple gated acquisition (MUGA) techniques used to be popular but have been replaced by SPECT sestamibi studies with 3D reconstruction of the ventricle. This study evaluates biplane and volumetric MRI techniques and shows that volumetric measurements are more accurate and reproducible than biplane MRI. Also, biplane echo is less accurate than volumetric echo, probably because of the variability in obtaining the correct imaging planes with echo. Unfortunately, volumetric echo techniques are not in widespread use yet, so volumetric MRI looks attractive because it gives equivalent results to volumetric echo and is more readily available. Also, echo studies are not always suitable for EF quantitation. Thus, if 3D echo is not available and EF needs to be accurately measured, MRI seems cost effective.
The disadvantages of MRI are that it takes more time to acquire and process volumetric images, it is not readily applicable to critically ill patients or the claustrophobic, and patients with implanted metal devices may not be suitable. Also, for most clinical purposes, a high degree of accuracy may not be critical, since much of the literature on the clinical usefulness of EF is based upon inferior older technology. Hopefully, 3D technology will be standard on echocardiographic machines in the near future and refinements in harmonic imaging or use of contrast will eliminate poor quality echoes.
Accurate ejection fraction measurements are best obtained with:
a. MRI.
b. echo.
c. SPECT thallium.
d. volumetric techniques.
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