Functional uncoupling of the mitral annulus and left ventricle with mitral regurgitation and dopamine.
BACKGROUND
The mitral annulus and left ventricle are generally thought to be functionally coupled, in the sense that increases in left ventricular (LV) size, as seen in ischemic mitral regurgitation (MR), or decreases in LV size, as seen with inotropic stimulation, are thought to increase or decrease annular dimensions in similar manner. The study aim was to elucidate the functional relationship between the mitral annulus and left ventricle during acute MR and inotrope-induced MR reduction.


METHODS
Radiopaque markers were implanted on the left ventricle and mitral annulus of five adult sheep. A suture was placed on the central scallop of the posterior mitral leaflet and exteriorized through the atrial-ventricular groove. Open-chest animals were studied at baseline (CTRL), at seconds after pulling on the suture to create moderate-severe 'pure' MR (PULL), and after titration of dopamine until the MR grade was maximally reduced (PULL+DOPA). This process was repeated two to three times for each animal.


RESULTS
The MR grade was increased with PULL (from 0.5 +/- 0.01 to 3.4 +/- 0.4, p < 0.01) and decreased after PULL+DOPA (from 3.4 +/- 0.4 to 1.5 +/- 0.9, p < 0.001). PULL resulted in an increase in mitral annular (MA) area, predominantly by an increase in the muscular mitral annulus. PULL+DOPA caused a decrease in MA area, but the LV volume and dimensions were not altered with either PULL or PULL+DOPA.


CONCLUSIONS
The acute geometric response to 'pure' MR and inotrope-induced MR reduction was limited to the mitral annulus. Surprisingly, the LV volume and dimensions did not change with acute MR or with inotrope-induced MR reduction. This suggests that, under these two conditions in an ovine model, the mitral annulus and left ventricle are functionally uncoupled.
Nguyen
Tom C
TC
Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, California 94305-5247, USA.
Itoh
Akinobu
A
Carlhäll
Carl J
CJ
Oakes
Robert A
RA
Liang
David
D
Ingels
Neil B
NB
Miller
D Craig
DC
D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology; D004195:Disease Models, Animal; D004298:Dopamine / Q000494:pharmacology; D006352:Heart Ventricles / Q000473:pathology*; D006439:Hemodynamics; D008944:Mitral Valve Insufficiency / Q000139:chemically induced / Q000473:pathology* / Q000503:physiopathology; D008955:Models, Cardiovascular; D012756:Sheep; D013536:Suture Techniques
D002316:Cardiotonic Agents; D004298:Dopamine