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Single Cutoff for Normal Ranges of Left Ventricular Ejection Fraction Is Not Appropriate

November 4, 2009
Written by: , Filed in: Cardiac Imaging
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Background
Left ventricular ejection fraction (LVEF) is a widely relied upon measure of cardiac function.

The objective of a recent study was to assess variability of normal LVEF across a range of processing workstations and operators.

This retrospective study has concluded that errors in calculation of ejection fraction is due to both systematic and random factors.

Participants
64 patients were identified who were studied on a single camera at Royal United Hospital, Bath, England and who had normal wall motion on gated wall motion study and normal echocardiogram.

Methodology
Study data were transferred to 11 regional hospitals where they were processed using up to 18 regional protocols according to standard methods and filters. Various statistical analyses of results were performed, including the overall mean and variance of LVEFs.

In a subset of cases where studies were processed twice each by two independent operators or twice by one operator, the intra-operator and inter-operator variability was assessed. The effect of the ratio of counts in the LV region of interest to the background and the effect of the total number of counts in the LV were compared to reproducibility of the calculation of the EF.

Cardiac CTA: What You Need to Know
 
 University of California San Francisco, Department of Radiology
 Course Director: Gautham P. Reddy, MD, MPH

 
  Coronary artery disease is the leading cause of morbidity and mortality in industrialized countries. With the advent of 64-detector CT scanners, CT has become an essential tool for evaluation of the heart and great vessels, and is a promising technique for assessment of the coronary arteries.
 
  Click here to read more or order:
  Cardiac CTA: What You Need to Know

Results of the Study
All 64 studies were processed on 13 of 18 systems. Mean EF of these normal studies was 61.9%, while average standard deviation of the EF on each system measured 7.6%. The lower limit of normal for each system (mean, 2 SD) ranged from 40% to 51%. The overall variance of the EF was 27.2 and was estimated to consist of a systematic variance of 6.3 and a random variance of 21.0, corresponding to SDs of 2.5% and 4.6%, respectively.

No significant differences in intra-operator variability were noted. Standard deviation of the intra-operator variability in EF ranged from 1.80% to 3.61% on various systems. SD of inter-operator variability in EF ranged from 2.16% to 6.40% and was significant in three of eight systems where two operators analyzed data.

Conclusions
Based on the large random variation, it is not appropriate to use a single cutoff for normal value, but to instead have an equivocal range where other factors would be used to determine options. Where possible, patients should be studied on the same system. Furthermore, all studies should be processed twice, preferably by independent operators, and the two values averaged. If they greatly differ, the study should be processed a third time.

Reviewer’s Comments
It is important to realize that even though a system may report a numeric value to several decimal places, the accuracy and even reproducibility of these values is not assured. My experience is that vendors will not always do the necessary validation prior to marketing a new system and, as this paper shows, there can be both systematic and random variation. Studies like these are necessary to establish ranges of normal.

Author: Lionel S. Zuckier, MD

Reference:
Hiscock SC, Evans MJ, et al. Investigation of Normal Ranges for Left Ventricular Ejection Fraction in Cardiac Gated Blood Pool Imaging Studies Using Different Processing Workstations. Nucl Med Commun; 2008; 29 (February): 103-109:

Cardiac CTA: What You Need to Know
 
 University of California San Francisco, Department of Radiology
 Course Director: Gautham P. Reddy, MD, MPH

 
  Coronary artery disease is the leading cause of morbidity and mortality in industrialized countries. With the advent of 64-detector CT scanners, CT has become an essential tool for evaluation of the heart and great vessels, and is a promising technique for assessment of the coronary arteries.
 
  Click here to read more or order:
  Cardiac CTA: What You Need to Know
.

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