Topographic mapping of left ventricular regional contractile injury in ischemic mitral regurgitation

Abstract

Objective: Restrictive leaflet tethering resulting from regional left ventricular (LV) contractile injury causes ischemic mitral regurgitation (MR). We hypothesized that 3-dimensional LV topographic mapping by MRI-based multiparametric strain analysis could characterize the regional contractile injury patterns that differentiate ischemic coronary artery disease patients who have ischemic MR from those who do not.

Methods: Magnetic resonance imaging-based multiparametric strain data were calculated for 15,300 LV grid points in 100 normal volunteers. Strain parameters from ischemic MR (n = 10) and ischemic no-MR (n = 36) patients were then normalized to this normal human strain database with z score quantification of standard deviation from the normal mean. Mean multiparametric strain z scores were calculated for 18 LV subregions (basilar/mid/apical levels; 6 LV regions). Mean strain z scores for papillary muscle-related (basilar/mid levels of anterolateral, posterolateral, and posterior) and nonpapillary muscle-related (all other) subregions were compared between ischemic MR and ischemic no-MR groups.

Results: Across all patients, contractile injury was greater in the papillary muscle-related regions compared with the nonpapillary regions (P = .007). In the papillary regions, contractile injury was greater in the ischemic MR group compared with the no-MR group (z scores, 1.91 ± 1.13 vs 1.20 ± 1.01, respectively; P < .001). Strain values in the nonpapillary muscle-related subregions were not different between the 2 groups (1.31 ± 1.04 vs 1.20 ± 1.03; P = .301).

Conclusions: Multiparametric strain analysis demonstrated severe normalized contractile injury in the papillary muscle-related LV subregions in patients with ischemic MR. The mean degree of normalized injury approached 2 standard deviations and was significantly worse than the levels seen in ischemic no-MR patients.

Keywords: ischemic mitral regurgitation; myocardial mechanics; regional contractile injury; strain mapping.

FIGURE 1.

The steps involved in obtaining the strain measurements in this study. A, A representative short-axis magnetic resonance imaging (MRI) tagged image. B, A standardized 18-region finite element model showing MRI measured displacements. C, A color contour plot showing multiparametric z scores obtained by comparison to the normal strain database.

FIGURE 2.

Box plots of normalized multiparametric strain z score values by left ventricular (LV) subregion for ischemic no mitral regurgitation (MR) versus ischemic MR patient groups, organized by nonpapillary muscle-related subregions (left) and papillary muscle-related subregions (right). Boxes represent 25th to 75th percentile, whereas error bars represent minimum and maximum values in the dataset. P values represent ischemic no-MR versus ischemic MR comparison within the nonpapillary and papillary subregion groups. BPS, Basilar posteroseptal; BAS, basilar anteroseptal; BA, basilar anterior; MPS, mid posteroseptal; MAS, mid anteroseptal; MA, mid anterior; APS, apical posteroseptal; AAS, apical anteroseptal; AA, apical anterior; AAL, apical anterolateral; APL, apical posterolateral; AP, apical posterior; BAL, basilar anterolateral; BPL, basilar posterolateral; BP, basilar posterior; MAL, midanterolateral; MPL, midposterolateral; MP, midposterior.

FIGURE 3.

By averaging multiparametric strain z scores in all patients in each group at every left ventricular (LV) grid point, a topographic map of average regional normalized contractile injury distribution for each group is uniquely visualized. These images represent the normalized contractile injury distribution of an average patient from each group. Shown are 4-quadrant endocardial views of the composite 3-dimensional LV color contour maps of the ischemic no mitral regurgitation group (A) and ischemic mitral regurgitation group (B). The color scale represents a 2.5 standard deviation range. Black ovals represent approximate papillary muscle insertion sites. PS, Posteroseptal; P, posterior; PL, posterolateral; A, anterior; AL, anterolateral; AS, anteroseptal.

FIGURE 4.

The overarching goal of this study was to visually demonstrate the differences in normalized contractile injury topographic distribution between those patients with coronary artery disease who have ischemic mitral regurgitation (MR) and those who do not. Shown here are 4-quadrant endocardial views of a subtraction 3-dimensional left ventricular (LV) color contour map demonstrating differences in LV strain distribution between ischemic MR and ischemic no-MR groups. This unique visualization is only possible because of the availability of group average multiparametric strain z score values at each of 15,300 points in a uniform, standardized grid in both patient groups, which can therefore be subtracted from each other. These 4 views of this composite LV mapping of the subtraction differences between the groups demonstrate the normalized contractile injury distribution that is responsible for the occurrence of MR in this ischemic coronary artery disease patient population. The color scale represents a 1.2 standard deviation range in subtraction differences between the 2 patient groups. Red regions represent > 1 full standard deviation increase in contractile injury in the ischemic MR group, whereas blue areas represent no difference between the 2 groups. Black ovals represent approximate papillary muscle insertion sites. PS, Posteroseptal; P, posterior; PL, posterolateral; A, anterior; AL, anterolateral; AS, anteroseptal.