## 4 Discussion  
The present study sought to investigate the variation in size of the mitral annulus during dilation of the left atrium. The following are the most important findings of the current paper: (1) the longitudinal diameter of the mitral annulus correlates with the latero-lateral LA diameter; (2) the transverse diameter of the mitral annulus correlates with the antero-posterior LA diameter; (3) the MA area correlates with the LA volume; (4) the LA volume can be estimated from the MA area using the following formula: \(\text{LAV}=12\times\text{MA area}+50\text{mL}\). This is, to the best of our knowledge, the first study using MDCT that demonstrates an association between mitral annulus dimensions and left atrial dimensions. Our hereby proposed formula can be used to predict LA volume (LAV) based on MA area. The Bland-Altman difference plot [5] was used to test the agreement between the measured LAV and predicted LAV based on the formula. Plotting the differences against means showed that there was good agreement between the predicted and the measured LA volumes. Furthermore, we have calculated the 95 percent limits of agreement for each comparison, showing the difference between the measured and estimated LAV for the majority of patients. We have also calculated the confidence intervals for the 95% limits of agreement. Because the discrepancies within the means are not clinically significant, the two techniques for estimating the LAV can be employed interchangeably, and a simple mitral valve area measurement can thus predict the dilation of the left atrium. This applies exclusively to patients without LV dysfunction, organic valvular disease, or replacement of the mitral valve. This study used MDCT to estimate the size of the left atrium and the mitral annulus, since it offers a better soft-tissue resolution due to the use of intravenous contrast and better delineation of cardiac structures, compared to transthoracic and transesophageal ultrasonography. Several computed tomography studies within the literature attempted to find the normal reference values for the left atrial volume. In the study conducted by [PERSON] et al. [6], which included 74 subjects, values of the left atrial volume were determined and normalized by age, sex, and body surface area. A statistically significant difference was noted for different ages; the mean left atrial volume varied from 63 mL (30-39 patient age interval) to 68 mL (40-49 years), 83 mL (50-59 years), and 80 mL (60-70 years) [6]. We defined a normal mitral annulus and normal left atrium based on the work of [PERSON] et al. [7], [PERSON] et al. [8], and [PERSON] et al. [9]. [PERSON]'s study measured the normal left atrium in MDCT for both men and women, and obtained the following results: 74 mL for women, 86 mL for men, and 80 mL for all subjects. According to [PERSON] et al. and [PERSON] et al., normal mitral valve dimensions differ between male and female subjects in the following way: area = 8.4 \(\pm\) 1.2 for female, 9.3 \(\pm\) 1.6 for male, and 8.9 \(\pm\) 1.5 cm\({}^{2}\) overall; perimeter = 107.0 \(\pm\) 7.0 mm for female, 113 \(\pm\) 10 mm for male, and 110 \(\pm\) 9.0 mm overall; longitudinal diameter = 36.1 \(\pm\) 2.9 for female, 38.8 \(\pm\) 3.9 for male, and 37.6 \(\pm\) 3.7 mm overall; transversal diameter = 27.1 \(\pm\) 2.3 for female, 27.8 \(\pm\) 3.0 for male, and 27.5 \(\pm\) 2.7 mm overall. The volumes of the left atrium found in our study (139 \(\pm\) 56.3 mL) are higher than those found in the ROMICAT study (97.4 \(\pm\) 27.3 mL) [10]. All our patients displayed atrial fibrillation, 42.9% of which presented persistent AF. This can explain the increased volume of the left atrium, in contrast to patients from the ROMICAT trial, which comprised individuals with risk factors for coronary artery disease. Our data complete the results of [PERSON] et al. [8], who measured the MA area with MDCT and found values in the range of 9.9 \(\pm\) 3.0 cm\({}^{2}\); [PERSON] et al.