The use of dedicated long-axis views focused on the left atrium improves the accuracy of left atrial volumes and emptying fraction measured by cardiovascular magnetic resonance

Abstract

Background: The use of apical views focused on the left atrium (LA) has improved the accuracy of LA volume evaluation by two-dimensional (2D) echocardiography. However, routine cardiovascular magnetic resonance (CMR) evaluation of LA volumes still uses standard 2- and 4-chamber cine images focused on the left ventricle (LV). To investigate the potential of LA-focused CMR cine images, we compared LA maximuml (LAVmax) and minimum (LAVmin) volumes, and emptying fraction (LAEF), calculated on both standard and LA-focused long-axis cine images, with LA volumes and LAEF obtained by short-axis cine stacks covering the LA. LA strain was also calculated and compared between standard and LA-focused images.

Methods: LA volumes and LAEF were obtained from 108 consecutive patients by applying the biplane area-length algorithm to both standard and LA-focused 2- and 4-chamber cine images. Manual segmentation of a short-axis cine stack covering the LA was used as the reference method. In addition, LA strain reservoir (εs), conduit (εe) and booster pump (εa) were calculated using CMR feature-tracking.

Results: Compared to the reference method, the standard approach significantly underestimated LA volumes (LAVmax: bias - 13 ml; LOA = + 11, - 37 ml; LAVmax i: bias - 7 ml/m²; LOA = + 7, - 21 ml/m²; LAVmin; bias - 10 ml, LOA: + 9, - 28 ml; LAVmin i: bias - 5 ml/m², LOA: + 5, - 16 ml/m²), and overestimated LA-EF (bias 5%, LOA: + 23, - 14%). Conversely, LA volumes (LAVmax: bias 0 ml; LOA: + 10, - 10 ml; LAVmax i: bias 0 ml/m²; LOA: + 5, - 6 ml/m²; LAVmin: bias - 2 ml; LOA: + 7, - 10 ml; LAVmin i: bias - 1 ml/m²; LOA: + 3, - 5 ml/m²) and LAEF (bias 2%, LOA: + 11, - 7%) by LA-focused cine images were similar to those measured using the reference method. LA volumes by LA-focused images were obtained faster than using the reference method (1.2 vs 4.5 min, p < 0.001). LA strain (εs: bias 7%, LOA = 25, - 11%; εe: bias 4%, LOA = 15, - 8%; εa: bias 3%, LOA = 14, - 8%) was significantly higher in standard vs. LA-focused images (p < 0.001).

Conclusion: LA volumes and LAEF measured using dedicated LA-focused long-axis cine images are more accurate than using standard LV-focused cine images. Moreover, LA strain is significantly lower in LA-focused vs. standard images.

Keywords: Accuracy; Cardiac magnetic resonance; Left atrial emptying fraction; Left atrial strain; Left atrial volume.

Fig. 1

Method used to obtain the left-atrial focused long-axis cine images. Left atrial (LA)-focused 4- and 2-chamber long-axis cine images were planned from the standard long-axis cine images. Starting from the end-systolic standard 4-chamber cine image (A1), the LA-focused 2-chamber image (B) was obtained, oriented parallel to the interatrial septum, by selecting a perpendicular plane passing through the roof of the LA and the center of the mitral annulus. From the cine image in panel B, a perpendicular plane was selected, again intercepting the roof of the LA and the center of the mitral annulus, to obtain the LA-focused 4-chamber cine image (C). Before acquisition, the plane orientation to obtain LA-focused cine images was cross-checked in the standard 3-chamber cine image (A2), to avoid the inclusion of the adjacent aortic root in the final images

Fig. 2

LA volumes and left atrial emptying fraction (LAEF) quantification on standard (A), left-atrial focused (B) and reference short-axis images (C). The biplane area-length method was applied to A and B while C was analyzed using the Simpson’s disc summation algorithm. All images represent end-systolic frames. In the standard images (A) the LA is clearly foreshortened compared to the LA focused cine images (B).  LAVmin: Minimum left atrial volume; LAVMax: Maximimum left atrial volume

Fig. 3

Left atrial maximum volume (LAVmax): comparison between methods. Comparison of LAVmax obtained using the biplane area-length method applied to both the standard (top panels) and the LA-focused (bottom panels) cine images, with LAVmax derived by the short-axis segmentation used as reference

Fig. 4

Distribution of the patients in LA size categories according to the method used for LAVmax quantification. The method using a short-axis stack of cine images covering the entire LA, from the atrio-ventricular ring to the base, was considered as reference. Arrows with superimposed numbers show the patients who change category by using either the standard or the LA-focused 4- and 2-chamber cine images

Fig. 5

Left atrial minimum volume (LAVmin): comparison between methods. Comparison of LAVmin obtained using the biplane area-length method applied to both the standard (top panels) and the LA-focused (bottom panels) cine images, with LAVmin derived by the short-axis segmentation used as reference

Fig. 6

Left atrial emptying fraction: comparison between methods. Comparison of left atrial emptying fraction (LAEF) obtained using the biplane area-length method applied to both the standard (top panels) and the LA-focused (bottom panels) cine images, with LAEF derived by the short-axis segmentation that were taken as reference

Fig. 7

Left atrial maximum volume index (LAVmax-i): comparison between methods. Comparison of LAVmax-i obtained using the biplane area-length method applied to both the standard (top panels) and the LA-focused (bottom panels) cine images, with LAVmax-i derived by the short-axis segmentation used as reference

Fig. 8

Left atrial minimum volume index (LAVmin-i): comparison between methods. Comparison of LAVmin-I obtained using the biplane area-length method applied to both the standard (top panels) and the LA-focused (bottom panels) cine images, with LAVmin-i derived by the short-axis segmentation used as reference