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Variability between Observers in the Semiautomatic Angiographical Calculation of Ejection Fraction

Calvo, Isabel; Galache, José G; Alonso, Carmen;
Diarte, José A; Sanchez-Rubio, Juan;
Molinero, Edmundo; Placer, Luis J

Hospital Universitario Miguel Servet, Zaragoza, Spain

SUMMARY
Introduction: Correct identification of ventricular contours in systole and diastole is the base of reliable ejection fraction (EF) calculations. Quantification software supplemented to angiographer simplifies calculations and should improve reproducibility.
Aims: Determine the utility fundamentally in observers with distinct experience.
Methods: Prospective study, analytical and randomised, performed by two observers with distinct experience. 200 EF calculations were made in 100 consecutive patients, using the software package for left ventricular function calculation, by the automatic procedure with fine manual adjustment integrated in the monoplanar INTEGRIS H3000 cardiovascular system, Philips Medical System.
Results: Mean EF for the most experienced observer, 0.61 ± 0.33 (range: 0.18-0.90) and 0.62 ± 0.34 (range: 0.16-0.92) for the second one. Pearson correlation coefficient was 0.85 and non-significant "p". 78% of cases the difference in EF obtained by each observer was <0.09, and in 38% of cases < 0.02. Correlation between telediastolic volumes (TDV) of both samples was 0.83 and 0.88 between telesystolic volumes (TSV).
In aquinetic ventricular segment patients the interobserver variability was similar (correlation coefficient 0.84). Neither extrasystolia, nor basal rhythm modified it significantly.
Conclusions
1.- Variability in EF calculation with this semiautomated method is low, independently to the observer experience degree.
2.- Correlation between mean ventricular volumes obtained with this system by distinct observers is good.
3.- Alterations in segment contractibility, rhythm and extrasystolia have little influence on the method reliability.

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INTRODUCTION
   Determination of ventricular volumes in systole and diastole from the perimeter of the ventricular cavity is perhaps the most widespread method for the calculation of angiographical ejection fraction (EF).

   Ventricular contours are determined on the plane in both phases of the cardiac cycle. A mathematical equation transforms perimeters into volume measurements of the cavity (expressed as cubic centimeters or milliliters).

   Perimeter is commonly obtained through the 30º right anterior oblique projections so that cardiac cavity is shown surrounded by anterior and diaphragmatic walls. The disadvantage of this method is that the measurements taken are not 3-dimensional and, therefore, they could be affected by segmentary alterations of the contractility of the named territories surrounding perimeter.

   Nowadays, computer software enables automatic registration of the perimeter; the system also allows the user to redefine manually the ventricular cavity contours in case the result is not satisfactory. The new perimeter can be partially or completely marked.

AIMS
   Check the utility of the determination of ventricular volumes in systole and diastole from the perimeter of the ventricular cavity for the calculation of the angiographic ejection fraction (EF).

   Prove that this system is very useful even for non experienced observers, making possible a good approach to reality.

METHODS
   The study was carried out by two observers: one with more than 25-years experience in hemodynamic studies and the other with less than 8-months experience.

   Hemodynamic studies on 100 consecutive patients who underwent coronariography for different causes were collected.

   Each observer made two EF calculations from every ventriculography: first with the automatic procedure and secondly with the manual adjustment of the ventricular cavities perimeter in both phases of the cardiac cycle. Ventricular volume in systole and diastole and EF were obtained as a result.

   Automatic procedure and posterior fine manual adjustment integrated in the monoplanar INTEGRIS H3000 cardiovascular system, Philips Medical System were used.

   The system was calibrated for every patient in order to determine the factor which enables to correct the amplification and distortion of the image. Measurements obtained this way are real size.

   The calibration technique was that internationally accepted: metal ball (Ø26 mm) filmed with the same incidence angle and distance to the tube and X-ray intensifier as the left ventricle.

   The data were analyzed with SPSS for medicine. A p-value < 0.01 was considered statistically significant.

RESULTS
   The mean age of the patients was 62. Motives for coronariographic study were ischemic cardiomyopathy, valvulopathy, dilated cardiomyopathy or transplanted patients undergoing a protocolary hemodynamic study.

   Regarding the general statistic analysis, no statistically significant differences were found between the values stated by each observer for diastolic and systolic volumes and EF. The Pearson correlation coefficient was excellent for all these measurements (see Table 1). Notice that correlation coefficient for EF calculations was 0.85 (a=0.01).

   In 78% of cases the difference in EF obtained by each observer was <0.09 and in 38% <0.02. These percentages show the excellent correlation between both observers when calculating EF.

   Subsequently, the existence of some factor which could influence the excellent correlation between observers was investigated. In this sense, the variables considered were: rhythm alterations, corporal mass of the subjects and alterations in the segmentary contractility which could make more difficult the tracing of the ventricular perimeter. The results are stated below:

· 41 patients showed rhythm alterations during the ventriculography. These alterations consisted of frequent ventricular or supraventricular extrasystolia, atrial arrhythmias and some short series of ventricular tachycardia due to irritation of the endocardium of the ventricular cavity. No significant differences were found between any of these parameters. The correlation coefficient for EF was 0.87. (see Table 1)
· The correlation was also very good (0.89) for the 26 patients with the highest corporal mass indexes, as shown in Table 2.

· Finally, the correlation in the group of 29 patients which showed alterations in the segmentary contractility in order to check if these alterations influence the EF calculation was studied. No statistically significant differences neither between the volumes (p<0.05) nor between the ejection fraction were found. The correlation coefficient was 0.84 (see Table 2).

DISCUSSION
   It is well known there are several methods for the calculation of the angiographical EF. In the authors' opinion, the method based on the perimeter of the ventricular cavity to calculate the ventricular volume is one of the best as the results provided are very close to the exact EF values. Thanks to its easy implementation and reproducibility, this technique can be applied by people with little hemodynamic experience. This fact has no significant effect on EF calculation.

   Although the study included enough subjects, it involved an important limitation: ventricular volumes are determined starting form a 2-dimensional measurement: the perimeter of the cardiac cavity in systole and diastole, which is transformed mathematically into a volume measurement. This process implies that the ejection fraction could get miscalculated in patients with alterations in segmentary contractility.

   In any case, correlation between observers with different experience degree is always good and the method supplies great reproducibility for the EF calculation -although it could get minimally diminished in those patients with alterations in regional contractility.

CONCLUSIONS
   Variability in the semiautomatic angiographical calculation of ejection fraction is low and independent of the observers experience degree.

   The correlation between ventricular volumes obtained with this method by different observers is good. This fact confirms the easy implementation of this technique

   Alterations in segmentary contractility, rhythm and a high corporal mass index have little influence on the method realibility. In all these cases, excellent correlations were obtained

 

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2nd Virtual Congress of Cardiology

Dr. Florencio Garófalo
Steering Committee
President
Dr. Raúl Bretal
Scientific Committee
President
Dr. Armando Pacher
Technical Committee - CETIFAC
President
fgaro@fac.org.ar
fgaro@satlink.com
rbretal@fac.org.ar
rbretal@netverk.com.ar
apacher@fac.org.ar
apacher@satlink.com

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