Correlation Of Left Ventricular Ejection Fraction Calculation Biology Essay

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Introduction: Left ventricular ejection fraction (LVEF) represents the most significant evaluation for prognosis of patients with cardiac disease. Echocardiography provides a non-invasive means of evaluating the parameters of systolic and diastolic function of LV. While the conventional method of visual assessment of echocardiographic images is rapid and adaptable, it shows high inter- and intra-observer variability.

Subject and methods: Hundred consecutive patients visiting the echocardiography lab of National Institute of Cardiovascular Diseases (NICVD) with a history of ischemic heart disease and scheduled for coronary catherization were enrolled in the study by convenience sampling. Their EF was estimated using the "eyeballing" method of visual assessment and by the application of Teichholz M-mode formula. Values of EF above 50% were considered normal while that below 35% was categorized as severe.

Results: Results were obtained using the chi-square test and regression analysis. No statistically significant co-relation was found between EF calculated by Teichholz M-mode formula and through visual assessment.

Conclusion: Unlike previous studies, our study does not correlate the values of ejection fraction derived from the geometrical and non-geometrical assumptions. However, due to instantaneous results and easy performance, the conventional method of visual estimation maybe regarded as an efficient means for evaluation of left ventricular ejection fraction.

Keywords: Echocardiography, Ejection fraction, Visual assessment, M-mode formula.

OBJECTIVE: This study was undertaken to correlate the variability between left ventricular ejection fraction (LVEEF) data obtained from the conventional "eyeballing method" of visual assessment and by the application of Teichholz M-mode formula.

INTRODUCTION: The most established assessment of global left ventricular (LV) function is the left ventricular ejection fraction (LVEF). Although a simple measure of LV contractility, it has been acknowledged as an effective predictor of major clinical outcomes amongst cardiac patients [1]. Moreover, it helps in selection of optimal management strategies accordingly, such as implantation of an intra-cardiac defibrillator (ICD) [2]. It is particularly reliable in therapeutic decision making in adjuvant chemotherapy for cancer and for patients with heart failure, and in determining the optimal time of surgery [1-3]. Non-invasive imaging modalities of ejection fraction assessment commonly include cardiac magnetic resonance imaging (MRI) [4], radionuclide ventriculography [5], two- and three-dimensional echocardiography [6] and as of late, cardiac computed tomography. Being cost effective, versatile and least time consuming, echocardiography has evolved as the most widely used technique to provide substantial information on LV systolic function [7]. Various quantitative measures are used for calculating echocardiographic results including Teichholz M-mode formula, cubed M-mode formula, biplane Simpson's formula, wall motion scoring, length-area method from the four-chamber view and eyeballing visual assessment. However, diverse correlations have been found with different modalities employed and therefore, single modality must be used for each follow-up assessment [8]. In our clinical setup, visual assessment of 2D electrocardiographic images of left ventricle is most frequently used to determine LVEF [9]. This rapid assessment through the experience of a sonographer, without the aid of an analytical apparatus has reported high accuracy when compared to formulas for quantifications dependant on geometrical assumptions and correlated closely with all the formal methods [10]. However, a recent meta-analysis suggested high variability in this subjective evaluation [11]. Our study aims to compare the two basic measures of estimating LVEF in clinical practice and to find any positive correlation between the geometrical and non-geometrical methods.

SUBJECT AND METHODS: A prospective, case controlled, observational study was carried out in the echo cardiography lab of National Institute of Cardiovascular Diseases (NICVD), Karachi from the month of August till November 2010.

A sample size of 100 consecutive patients was collected by convenience sampling comprising of 73 males and 27 females between the ages of 40 and 70 years who had a history of ischemic heart disease and were admitted to the South Ward of National Institute of Cardiovascular Diseases and were scheduled for the procedure of coronary catherization were enrolled in the study prospectively.

Inclusion criterion: All male and female candidiates between the set age limits, who were in sinus rhythm, without significant valvulopathy presenting with symptoms of ischemic heart disease and with ECG features of anterior and inferior wall myocardial infarction or st or non-st elevation Myocardial Infarction, were taken into account. Care was taken to include patients with hypertension, diabetes mellitus, dyslipidemia, cardiac failure, stable angina, unstable angina

Exclusion criterion: Patients with valvular heart diseases, ventricular hypertrophy, congenital heart diseases, atrial fibrillation, atrial flutter, heart block, pre-excitation syndrome and bundle branch block were excluded.

All patients underwent Wide-angle 2-D echocardiography using a commercially available mechanical sector scan (Advanced Technology LaboratoriesMark V). The frame rate of the system varies from 45.5 frames/sec at a scan depth of 5 cm to 18.5 frames/sec at a depth of 21cm. The images are converted to digital format by a digital scan converter and presented in video format to the observer, allowing greater resolution and an enhanced gray scale. All patients were studied in the left lateral recumbent position, using multiple views through the left parasternal and apical windows. M-mode examination and estimation of LVEF was done with the ultrasonic beam directed at the chamber between the mitral valve echoes and the papillary muscle echoes. The view selected for measurement was the parasternal long-axis view.

Each echo was subjected to both calculative method and visual assessment for the calculation of the Ejection Fraction. The values obtained were divided into normal, mild, moderate and severe on the basis of reduction of the ejection fraction as a consequence of heart disease. Values of ejection fraction above 50% were considered normal, and those below 35% were considered severe. Values of EF in the range of 35-39% were categorized into moderate values and from 40-50% were considered as mild values for EF. The echo findings were then co-related with the diagnosis of septal abnormalities (if any).

Analysis for Teichholz M-mode formula: For the calculative method, the M-mode cursor was placed through the septal and posterior LV walls just beyond the tip of the mitral leaflets. In the resultant M-mode image, measurements of the RV internal dimension, interventricular septum thickness, LV internal dimension (LVED) and LV posterior wall thickness at end-diastole (timed on ECG or point of largest LV internal dimension) and LV internal dimension (LVES) and LV posterior wall thickness at end-systole (ECG timed or point of smallest LV internal dimension) were taken. Moreover two measurements were made, one just below the tips of the mitral valve leaflets (D1) and the second one (D2) halfway between Dl and the most distal portion of the visualized left ventricle. With this information, the fractional shortening and the ejection fraction were calculated. 

Fractional shortening was expressed as a percentage:

Ejection fraction was calculated using the formula:

LVEF= (%ΔD²) + ([1- ΔD²] [% ΔL²])

Where %ΔD was the percentage fractional shortening of the minor axis and % ΔL was the percentage fractional shortening of the long axis.

All dimensions were measured from the endocardial markings of opposing walls perpendicular to an imaginary long axis bisecting the LV cavity from mitral valve to apex. End-diastole was determined as the largest cavity Silhouette.

M-mode examination and estimation of LVEF. This was

done with the ultrasonic beam directed at the chamber

between the mitral valve echoes and the papillary muscle

echoes. Measurements of LV dimension (D) were made

from leading edge to leading edge at end-diastole indicated

by the Q wave of a simultaneously recorded ECG8 and

at end-systole corresponding to the peak downward motion

of the intraventricular septum. End-systolic and end-diastolic

ventricular volumes were calculated with the with the Teichholz formula:

V mt=[(7.0/2.4)+D] (D3)

where:

V mt = volume (cm3) from M-mode Teichholz calculation [19].

Analysis for visual assessment: For the visual two dimensional EF evaluations, the four-and two-chambered view was displayed simultaneously and the eye-balling methodology was used to estimate the EF. The visual assessment was performed by four experienced echocardiographers and by two novices who were kept unaware of all clinical data and previous readings. Ejection fraction was assessed by visual estimation of the routine 2D data-set, taking into account various factors such as left ventricular wall motion, wall thickening and change in cavity area. A numerical value was assigned and rounded up/down to the nearest 5%.

Statistical Analysis: The data collected was sorted and analyzed on MS Excel and Statistical Package for the Social Sciences (SPSS) version 17. Results were compared using the chi square test. P value < 0.05 was considered as statistically significant.

STATISTICS AND RESULTS: When evaluated in a total of 100 patients at echocardiography, ejection fraction was determined by both visual assessment and calculation method. The results of Ejection Fraction were divided into Normal, Mild, Moderate, Severe depending on the decrease in percentage from normal.

Table-1 shows the distribution of EF when performed by Visual Assessment.

Table1: EF VISUALIZED

Frequency

Percent

normal

38

38.0

mild

23

23.0

moderate

24

24.0

severe

15

15.0

Total

100

100.0

Table-2 shows the distribution of EF when performed by Calculation Method.

Table2: EF CALCULATED

Frequency

Percent

normal

34

34.0

mild

34

34.0

moderate

17

17.0

severe

15

15.0

Total

100

100.0

From the 100 patients, the diagnosis at echocardiography was divided into the ones with segmental wall abnormality present and the ones without. Table-3and Figure-2 shows the distribution of this Diagnosis.

Table3: Diagnosis at ECHO

Frequency

Percent

segmental wall abnormality present

51

51.0

no segmental wall abnormality present

49

49.0

Total

100

100.0

Figure 1

Crosstabs Evaluation

The EF by visual method when analyzed along with the diagnosis; results showed that of the 38 patients with Normal EF, 16 (42.1%) had segmental wall abnormality which formed a 31.4% of this diagnosis and 22 (57.9%) were without segmental wall normality which formed 44.9% of the diagnosis.

Of the 23 patients with Mild EF, 11(47.8%) had segmental wall abnormality which formed a 21.6% of this diagnosis and 12(52.2%) were without segmental wall normality which formed 24.5% of the diagnosis.

Of the 24 patients with Moderate EF, 14(58.3%) had segmental wall abnormality which formed a 27.5% of this diagnosis and 10(41.6%) were without segmental wall normality which formed 20.4% of the diagnosis.

Of the 15 patients with Severe EF, 10(66.7%) had segmental wall abnormality which formed a 19.6% of this diagnosis and 5(33.3%) were without segmental wall normality which formed 10.2% of the diagnosis.Table-4 and Figure 3

Table-4: EF VISUALIZED * diagnosis Cross tabulation

diagnosis

P-value

segmental wall abnormality present

no segmental wall abnormality present

EF VISUALIZED

normal

n

16

22

.162

n%

31.4%

44.9%

mild

n

11

12

.739

n%

21.6%

24.5%

moderate

n

14

10

.399

n%

27.5%

20.4%

severe

n

10

5

.189

n%

19.6%

10.2%

Total

n

51

49

n%

100.0%

100.0%

Figure 2: EF VISUALISED

The EF by calculation method when analyzed along with the diagnosis; results showed that of the 34 patients with Normal EF, 16 (47%) had segmental wall abnormality which formed a 31.4% of this diagnosis and 18 (53%) were without segmental wall normality which formed 36.7% of the diagnosis.

Of the 34 patients with Mild EF, 17(50%) had segmental wall abnormality which formed a 33.3% of this diagnosis and 17(50%) were without segmental wall normality which formed 34.7% of the diagnosis.

Of the 17 patients with Moderate EF, 8(47%) had segmental wall abnormality which formed a 15.7% of this diagnosis and 9(53%) were without segmental wall normality which formed 18.4% of the diagnosis.

Of the 15 patients with Severe EF, 10(66.7%) had segmental wall abnormality which formed a 19.6% of this diagnosis and 5(33.3%) were without segmental wall normality which formed 10.2% of the diagnosis.Table-5 and Figure 4

Table-5: EF CALCULATED * diagnosis Cross tabulation

diagnosis

P-value

segmental wall abnormality present

no segmental wall abnormality present

EF CALCULATED

normal

n

16

18

.583

n%

31.4%

36.7%

mild

n

17

17

.785

n%

33.3%

34.7%

moderate

n

8

9

.709

n%

15.7%

18.4%

severe

n

10

5

.189

n%

19.6%

10.2%

Total

n

51

49

n%

100.0%

100.0%

Figure 3: EF CALCULATED

Comparison of the results

Comparison of the results obtained from both visual and calculative methods showed 11.7% higher results for normal patients by visual method then by calculative. . Upon diagnosis the results with positive segmental wall abnormality were the same by both methods and the increase (22.2% higher) was in the negative findings

47.8% higher results for mild patients by calculative method were obtained over visual method. Upon diagnosis the results with segmental wall abnormality were 54.5% higher for positive findings and the 41.6% higher for the negative findings.

41.1% higher results for moderate patients by visual method over calculative method were observed .Upon diagnosis the results with segmental wall abnormality were 75% higher for positive findings and the 11.1% higher for the negative findings.

Meanwhile the results for severe patients were same by both methods. Figure-4 shows these comparisons.

Figure 4: EF Comparisons

Regression analysis: There were not significant correlations between ef calculated using eyeballing method and Teichholz m-method. (R=0.479)

DISCUSSION:

Both the visual analysis and the formula-based methods described in this study have their respective advantages and limitations, which may affect agreement between them. Although known to show interobserver variation, the "eyeballing" method of visual evaluation is most frequently used for calculating LVEF from two-dimensional echocardiographic images [9]. Assessment of LV function using the M-mode measurements is limited as it uses one dimensional left ventricular short-axis [12] and lacks the ability to account for regional wall abnormalities [13]. However, the Framingham Heart Study has used M-mode measurements for valuable insight into the ECG criteria for hypertrophy and adverse prognosis of ventricular hypertrophy [14-15]. Visual assessment by 2D echocardiography assesses LV function tomographically and is less restricted by segmental abnormalities [13].

When ejection fraction was analyzed by means of visual estimation, normal range (≥50%) was obtained in 38% of the patients, whereas 34% showed normal values when subjected to Teichholz M-mode measurement. However, in assessment of severe values of EF (<35%), both calculative and visual methods showed these values in 38% of the patients, hence demonstrating the same results.

Visual assessment can principally provide all information regarding wall motion and provides analysis on atrio-ventricular plane displacement, as stated in a study by Shahgaldi and colleagues [7]. In another study, Sievers et al. affirmed that the interobserver variability was smaller for the quantitative assessment than for the visual estimation but the visual approach for EF assessment may be used for rapid assessment of left ventricular function in clinical practice where accuracy is of less concern. For most precise analysis, however, the quantitative standard short axis approach is required [16]. Another study showed that eyeballing ejection fraction correlated closely with all formal methods such as Simpson ejection fraction, atrioventricular (AV) plane displacement, wall motion score index, and fractional shortening, indicating that eyeballing ejection fraction may be the most accurate echocardiographic method for the assessment of left ventricular systolic function. Since it is readily and quickly performed, eyeballing ejection fraction could be used for routine echocardiography instead of formal methods [17]. Rich and colleagues assessed the reliability of using two-dimensional echocardiography (2DE) to visually estimate the EF during real-time viewing, without the need of digitizers, planimetry, or calculations and showed that VE correlated closely to the values determined in all patients with gated nuclear angiography, enable echocardiographers to easily use 2 DE for a reliable and instantaneous assessment of ventricular function, without the need of sophisticated analytical equipment [18].

CONCLUSION: Using chi-square test and regression analysis in our study, no statistically significant correlation was illustrated between visually assessed LVEF and LVEF calculated from Teichholz M-mode method, unlike some previous clinical studies. However, it needs further corroboration in future. Nonetheless, evaluation of global LVEF using the conventional method of visual assessment may represent an efficient and rapid alternative to methods based on geometrical assumptions.

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