Importance of the mitral subvalvular apparatus for left ventricular segmental systolic mechanics

Abstract

The relative importance of the anterolateral (ANTLAT) and posteromedial (POSTMED) papillary muscle (PM) chordae tendineae for left ventricular (LV) segmental wall function was assessed in 12 in situ ejecting canine hearts. Pairs of piezoelectric crystals were placed in the regions subtending PM insertions and the ANTLAT LV free wall to measure wall thickness. After mitral valve replacement with complete preservation of the subvalvular apparatus, chordal attachments to either the ANTLAT PM or POSTMED PM were randomly severed using exteriorized snares, followed by subsequent division of the remaining chordae tendineae. Segmental wall function in each region was determined at each stage by segmental preload recruitable stroke work (sPRSW, slope of the segmental stroke work-end-diastolic wall thickness relation). The order in which the chordae were severed was unimportant (p greater than 0.530 in all regions). When the ANTLAT PM chordae were severed first, there were significant declines in sPRSW without a change in the wall thickness intercept in both the ANTLAT (-71.0 +/- 18.3 vs. -57.7 +/- 16.8 mmHg, p less than 0.05) and POSTMED (-81.8 +/- 23.1 vs. -65.4 +/- 17.3 mmHg, p less than 0.05) PM insertion sites. No further significant reductions in sPRSW in either region were detected after severing the remaining chordal attachments to the POSTMED PM. sPRSW in the ANTLAT LV free wall decreased progressively, reaching statistical significance when both sets of chordae tendineae were divided (-88.3 +/- 14.3 vs. -74.0 +/- 15.2 mm Hg, p less than 0.05). When the POSTMED PM chordae were severed first, no significant changes in sPRSW or the wall thickness intercept in either region of PM insertion were detected. Subsequent division of the ANTLAT PM chordal attachments reduced sPRSW significantly in both the ANTLAT PM (-65.9 +/- 21.1 vs. -56.1 +/- 22.1 mm Hg, p less than 0.05) and POSTMED PM (-78.8 +/- 24.7 vs. -67.2 +/- 24.0 mm Hg, p less than 0.05) insertion sites, without a shift in the wall thickness intercept. In the ANTLAT LV free wall, sPRSW again fell progressively, achieving statistical significance only when both chordal attachments were severed (-78.6 +/- 14.8 vs. -62.2 +/- 13.7 mm Hg, p less than 0.05). In conclusion, division of the chordae tendineae resulted in a decline in segmental LV function not only in the areas subtending PM insertions but also in remote LV regions. Furthermore, the influence of the ANTLAT PM chordae predominated local LV systolic function at both PM insertion sites.(ABSTRACT TRUNCATED AT 400 WORDS)