Visually estimated ejection fraction by two dimensional and triplane echocardiography is closely correlated with quantitative ejection fraction by real-time three dimensional echocardiography

Echocardiography is a noninvasive imaging technique that provides immediate assessment of global and regional LV function. LVEF is the most commonly used parameter of LV systolic function. The assessment of LV function is an important clinical tool and is of great clinical importance in the evaluation and prognosis of patients with coronary artery disease, hypertension, diabetes, valvular disease, and congestive heart failure [1]. The reliable assessment of LV systolic function is important for therapeutic decision making in heart failure [2].

EF can be assessed using a variety of modalities including contrast ventriculography [3], magnetic resonance imaging (MRI) [4] and echocardiography [5]. By far echocardiography is the least expensive, most widely available technique and it is noninvasive, can be performed bedside, is rapid and very safe. LVEF is a measure of LV systolic function that has been shown to predict mortality in a number of conditions [6–8].

However, 2DE has a number of well-known limitations, the two most important perhaps being LV foreshortening and that different projection are not possible to acquire during the same cardiac cycle. The latter is particularly important in patients with variable heart rhythm (i.e. atrial fibrillation). Both these limitations can be overcome using a 3D-array transducer for acquiring the apical four-two-and three chamber views simultaneously in the TP mode.

RT3DE has shown excellent agreement to MRI in measuring both LV volumes and EF and has also proven to be superior to quantitative 2DE regarding EF [9–11]. These data are suggesting that RT3DE is interchangeable with MRI in measuring LVEF.

Quantitative 2D-EF using BPS rule can be somewhat time consuming, and the endocardial border tracing is sometimes difficult to perform, especially in patients with poor image quality, since it is performed on still frames. In clinical practice eyeballing for the evaluation of LVEF can be done faster and is often easier to perform, especially in patients with poor image quality.

Previous studies have demonstrated the value of eyeballing EF [12–16] and one study revealed good correlation with quantitative 2DE measurements [12]. However, the studies comparing to radionuclide methods were performed before the introduction of second harmonics and although eyeballing EF measurement have proven to be robust when performed careful, it is still considered highly subjective and questioned in both clinical and research settings.

The aim of this study was to investigate the correlation and variability of visually assess EF by 2DE and TPE in comparison to quantitative 3DE-EF measurements.

All EF measurements, both 2D and 3D were feasible in all patients. EF was 54.7 ± 8.9% by 3DE, 55 ± 8% by 2D eyeballing and 55 ± 9% by TP eyeballing. Statistical analysis showed no significant differences in EF between the 2DE methods and 3DE.

Regression analysis

There were excellent correlations between EF measured by 3D and eyeballing 2DE and TP (r = 0.91 and r = 0.95 respectively). Linear regression between 3D vs eyeballing 2DE and between 3D and eyeballing TP is shown in figure 3.

An optimal method for determining LVEF by echocardiography should be rapid, reliable, and widely applicable in order to utilized routinely in a clinical laboratory. Off-line echocardiographic analysis techniques using software's and operator-performed border tracing meet these criteria poorly, explaining their lack of widespread use despite validation in different laboratories [14, 15]. The major advantage of visual estimation of LVEF is that the reader can integrate all information regarding wall motion, atrioventricular plane displacement (AV-plane), etc. Its principal limitations are dependency on the skill of the reader and the inter – and intraobserver variability.

In the present study, eyeballing EF both using 2D and TP mode showed excellent correlation with quantitatively measured EF using RT3DE (r = 0.91 and r = 0.95 respectively) and without any significant bias (-0.5 ± 3.7% and -0.2 ± 2.9% respectively). Intraobserver variability was 3.8% for eyeballing 2D, 3.2% for eyeballing TP and 2.3% for quantitative 3D-EF. Interobserver variability was 7.5% for eyeballing 2D and 8.4% for eyeballing TP.

Lavine et al. showed in concordance to our study excellent correlation (r = 0.90) between 2D eyeballing in comparison to radioventriculography (RVG) [18]. In their study they compared eyeballing EF and wall motion scoring (WMS), showing that WMS had better correlation (r = 0.97) in comparison to RVG. This r-value is almost identical to our TP eyeballing determination, where eyeballing has the advantages of being less time-consuming than WMS analysis.

Two advantages of using TPE are that when EF is determined it is based from same cardiac cycle, and that TP can overcome the problem of LV foreshortening. Another advantage is that the acquisition time is reduced because the transducer is not moved to obtain data from multiple views. Although, this advantages didn't transfer into significant differences between 2D and TP-EF determination in our study. There is an apparent trend towards a smaller variability using TP in comparison to 2D. The variability in this study is very small and is likely to be more pronounced in clinical routine. Thus there might be significant advantage in using TP over 2D for EF assessment in everyday clinical routine.

It might be suggested that the accuracy of eyeballing EF is dependent of the skill of the reader and that visual assessment of EF is accurate only in very experienced hands. However, our results are in concordance with those shown by the other groups, indicating that eyeballing EF commonly can be used with a high level of accuracy [12–16]. Indeed Jensen-Urstad et al. showed in their study that Simpson's rule correlated worst (r = 0.45–0.51) when comparing EF by different methods (eyeballing, WMS and AV-plane) in comparison to radionuclide imaging during acute myocardial infarction [13]. Furthermore, it has been shown in a study by Akinboboye et al [19] that eyeballing EF is a method easy to learn. If a person with no previous experience of echocardiography, after each evaluation is given instant feedback from a experienced reader, about 60 cases in joint reading is required to achieve the same accuracy as an experienced echocardiographer.

Even though quantitative measurement of LVEF is generally recommended [20], visual assessments of EF is commonly used in everyday clinical practice due to both suboptimal image quality and lack of time.

The results of the present and prior studies suggest that eyeballing EF could be accepted for clinical use provided that the variability of the eyeballing EF in the echocardiography laboratory is low. Therefore, the variability of using visual estimation of LVEF should be regularly tested in any echocardiography laboratory using this as the recommended method.

Visual estimation of LVEF both using 2D and TP by an experienced reader correlates well with quantitative EF determined by RT3DE. There is an apparent trend towards a smaller variability using TP in comparison to 2D, this was however not statistically significant.