Cardiac cycle-dependent left atrial dynamics: implications for catheter ablation of atrial fibrillation

Abstract

Background: Left atrial (LA) volume determines prognosis and response to therapy for atrial fibrillation. Integration of electroanatomic maps with three-dimensional images rendered from computed tomography and magnetic resonance imaging (MRI) is used to facilitate atrial fibrillation ablation.

Objective: The purpose of this study was to measure LA volume changes and regional motion during the cardiac cycle that might affect the accuracy of image integration and to determine their relationship to standard LA volume measurements.

Methods: MRI was performed in 30 patients with paroxysmal atrial fibrillation. LA time-volume curves were generated and used to divide LA ejection fraction into pumping ejection fraction and conduit ejection fraction and to determine maximum LA volume (LA(max)) and preatrial contraction volume. LA volume was measured using an MRI angiogram and traditional geometric models from echocardiography (area-length model and ellipsoid model). In-plane displacement of the pulmonary veins, anterior left atrium, mitral annulus, and LA appendage was measured.

Results: LA(max) was 107 +/- 36 mL and occurred at 42% +/- 5% of the R-R interval. Preatrial contraction volume was 86 +/- 34 mL and occurred at 81% +/- 4% of the R-R interval. LA ejection fraction was 45% +/- 10%, and pumping ejection fraction was 31% +/- 10%. LA volume measurements made from MRI angiogram, area-length model, and ellipsoid model underestimated LA(max) by 21 +/- 25 mL, 16 +/- 26 mL, and 35 +/- 22 mL, respectively. Anterior LA, mitral annulus, and LA appendage were significantly displaced during the cardiac cycle (8.8 +/- 2.0 mm, 13.2 +/- 3.8 mm, and 10.2 +/- 3.4 mm, respectively); the pulmonary veins were not displaced.

Conclusion: LA volume changes significantly during the cardiac cycle, and substantial regional variation in LA motion exists. Standard measurements of LA volume significantly underestimate LA(max) compared to the gold standard measure of three-dimensional volumetrics.

Figure 1

Each line represents the unique time volume curve (TVC) for each of the 30 patients. The dark-bold line represents the “average” TVC. α represents LAMAX which is 107±36ml and ranged from 51ml to 188ml. β represents the PACV which is 86±34ml and ranged from 34ml to 170ml. Measurements for the conduit ejection fraction (CEF) and pump ejection fraction (PEF) are noted and were 25±9% and 31±10%, respectively. The reduction in LAV following α represents mitral valve opening. In addition to the variation in volume present in the cohort, a variety of ‘patterns’ in left atrial filling and emptying are present. These patterns are reflected by the different filling and emptying slopes and by the relative contribution of mitral valve opening and atrial systole.

Figure 2

Several views of the left atrium during its maximum and minimum volume are shown. A horizontal white line is drawn through the center of each image as a point of reference and the identically sized yellow vertical line on the left border of the image confirms that the horizontal reference line is equally positioned on the LAMAX and LAMIN images. The red lines on the LAMIN images represent the in-plane displacement of various points of interest. The red dots represent the lack of significant motion. The top row represents LAMAX and the bottom row represents LAMIN. Panels A, B, and D respectively show the ridge separating the left upper pulmonary vein and the left atrial appendage (LAA), the postero-lateral mitral valve annulus (MITRAL), and the anterior left atrium at the level of the sino-tubular junction which is represented by the white dot (AntLA). The posterior aspects of the right lower pulmonary vein (RLPV) and the left lower pulmonary vein (LLPV) are shown in panels C and D.

Figure 3

On the left, linear regression analysis shows that global left atrial ejection fraction (LAEF) and its conduit (CEF) and pumping (PEF) components are inversely related to LAV (maximum volume). The graph on the right shows that no significant relationship exists between the LAV and the timing of the LA ejection cycle.

Figure 4

Bland-Altman plots reveal the relationship of the left atrial volume (LAV) as measured from a magnetic resonance angiogram (MRA), the area-length model (AL), and the ellipsoid model (EL) with the maximum left atrial volume (LAMAX) and pre-atrial contraction volume (PACV) as determined by the gold-standard time volume curves. LAMAX is underestimated by MRA, AL, and EL. The bias and limits of agreement are reduced when MRA, AL, and EL are compared to PACV.

Figure 5

The posterior aspects of the pulmonary vein ostia are minimally displaced; where as, the anterior left atrium at the level of the sino-tubular junction (AntLA), the postero-lateral mitral valve annulus (MITRAL), and the ridge separating the left superior pulmonary vein and the left atrial appendage (LAA) exhibit substantially more motion.