The functional parameters of the heart are routinely calculated by echocardiography as it is available, rapid, and noninvasive procedure. Since it is a real-time imaging technique, it is not limited by arrhythmias. But, poor acoustic windows may be produced by patient factors, like, obesity, previous operations (especially those of the cardiothoracic nature) and advanced pulmonary disease. This will prevent good delineation of cardiovascular structures. In addition, it is operator dependent [6, 7].
Now cardiac magnetic resonance imaging (CMRI) is considered the gold standard for noninvasive assessment of LV functional parameters, as it provides high-quality images of cardiac chambers. On the other hand, it is an expensive imaging technique with limited availability and needs proper training. In addition, accidentally motion artifacts that occur during imaging may affect the image quality. CMRI also cannot deal with patients with metallic implants [6, 7].
The assessment of coronary artery disease by cardiac CT angiography using multi-detector CT has improved a lot recently. In addition, MDCT is capable 0f measuring LV volumes and function with the same dose of contrast, the same amount of radiation exposure, and the same data set used for evaluation of coronary artery disease [8].
In this study, we found that mean EF obtained with MDCT was 61.22 ± 9.50% slightly higher than that obtained by echocardiography which was 61.14 ± 10.90%. Evaluation of LVEF by linear regression analysis showed moderate correlation as r = 0.345 and p value < 0.05, also Bland-Altman plot showed good inter-technique agreement analysis as it showed a mean value of difference (± SD) of 0.08 ± 11.6% (p < 0.05). The 95% limits of agreement ranged from −3.3 to 3.2%.
We observed that results made by MDCT are slightly higher values for LVEF when compared with 2D echocardiography, although mild reduction is expected in beta blocked patients. Although it was not statistically significant, may be the cause is limitation of evaluation technique leading to underestimation or overestimation. Mean difference in EF measurements between MDCT and 2D echocardiography is small; however, standard deviation of the mean difference is quietly high, causing wide limits of agreement. May be due to calculation of the EF by 2D echocardiography was done using Simpson’s method based on geometrical assumption.
The results of the current study are in-line with the results of previous studies that found a good correlation between MDCT and 2D echocardiography in the assessment of EF. Darpan Bansal et al. found a moderate correlation between MDCT and 2D echocardiography in 52 patients (r = 0.32, p < 0.001) [9]. Salm et al. performed on 25 patients revealed good agreement between 16-row MDCT and echocardiography (r = 0.96; p < 0.0001) [10]. Henneman et al. [11] found excellent correlation between 64-row MDCT and echocardiography in 40 patients (r = 0.91, p < 0.0001) [10]. Kim et al. studied 19 patient with suspected CAD using 16-row MDCT and detected good correlation in the calculation of LVEF between the two modalities (r = 0.846; p < 0.05) [12], and this was consistent with the current results.
The results we obtained correlate with the previous studies and confirms that assessment of LVEF is reliable with the MDCT is feasible and may be considered as a useful clinical index, compared to results made by 2D echocardiography. In addition, fully automated software made by CT proved to be faster, accurate, and user friendly.
In this study, we found mean LVESV measured by MDCT was 70.23 ± 38.35 slightly lower than that obtained by 2D echocardiography which was 72.13 ± 32.69 Evaluation of LVESV by linear regression analysis revealed good correlation r = 0.8, p value < 0.05. Bland-Altman plot showed good inter-technique agreement as it showed a mean value of difference (± SD) of 2.4 ± 47.4 mL (p < 0.05). The 95% limits of agreement ranged from −11.2 to 16.2. Mean LVEDV measured by MDCT was 172.22 ± 53.57 slightly lower than that obtained by 2D echocardiography which was 173.76 ± 62.45. Evaluation of LVEDV by linear regression analysis revealed good correlation r = 0.84, p value < 0.05. Bland-Altman plot showed good inter-technique agreement as it showed a mean value of difference (± SD) of 2.28 ± 80.4 mL (p < 0.05). The 95% limits of agreement ranged from −20.2 to 25.2; mean LV mass by MDCT was 164.63 ± 52.57, lower than that obtained by 2D echocardiography which was 198.32 ± 72.54.
In this study, we found that EDV and ESV obtained by MDCT are slightly lower than those calculated by 2D echocardiography. The LV volume overestimation or underestimation may be due to inclusion or exclusion of the papillary muscle [13].
In this study, the slight underestimation of LV volumes by MDCT was observed compared with 2D echocardiography; this is explained by the fact that calculation of the LV volumes measured by 2D echocardiography include papillary muscles but in CT papillary muscles were automatically excluded from the blood pool, which allows for precise determination of blood volume in the LV. This also explains why the mean LV mass by MDCT is lower than 2D echocardiography.
The results of this study are in-line with results of previous studies found good correlation between 2D echocardiography and MDCT in estimation of global LV volumes. In a study by Mohamed I, Amin et al. correlation between MDCT and 2D echocardiography was excellent regarding LVESV (r2 = 0.94, p < 0.001∗∗), LVEDV (r2 = 0.99, p < 0.001∗∗) [8]. In the study by Graaf et al. [14] excellent correlations were observed between MDCT and 2D echocardiography for LVEDV (r2 = 0.91; p < 0.001) and LVESV (r2 = 0.94; p < 0.001) [13] in Lim SJ et al. [7], correlation coefficients between the two modalities for the assessment of LVESV was good (r2 = 0.97, p < 0.001) and LVEDV was good (r2 = 0.82, p < 0.001). This in-line agreement with the current study results
We also found a negative correlation between EF and ESV; EDV measured by MDCT (p value < 0.05) value but no correlation between those measured by 2D echocardiography. This proves that MDCT is more reliable than 2D echocardiography in assessment of LV parameters. This is explained as 2D echocardiography is operator dependent.
Study limitations
Although assessment of cardiac function is feasible with 128-row MDCT, several limitations were found. The main limitation of the current study was the absence of a true gold standard such as cardiac MRI. The gold standard in the noninvasive analysis of LV function is cardiac MRI. It provides a high degree of accuracy as well as excellent temporal and spatial resolution. Concerning quantitative measurements, cardiac MRI is considered as a clinically accepted standard. In addition, MRI technique is the most relevant cardiac imaging modality available due to good contrast found between blood-filled ventricles and the surrounding myocardium; many previous studies have demonstrated excellent correlations between MDCT and MRI in the measurement of LV volumes and function. So, in order to validate the performance of 128-row MDCT for the assessment of LV function and volumes, a direct comparison must be done between 128-row MDCT and MRI [14, 15].
Also, in patients with a heart rate > 65 bpm, additional beta-blocking medication was administered before MDCT had been done, but not before 2D echocardiography. So potential bias may have been found by the administration of beta-blockade immediately before the MDCT examination. But new developments in MDCT technology is allowing examination of patients with higher heart rates and reducing the dose of beta-blockers [16, 17].
As well as the use of contrast agents in MDCT may affect LV volumes and LVEF. Another disadvantage of MDCT in general is the radiation exposure to the patient. But, assessment of LV functional parameters could be calculated retrospectively from the data acquired from the CT angiography [14, 18].