Left ventricular mechanics and myocyte function after correction of experimental chronic mitral regurgitation by combined mitral valve replacement and preservation of the native mitral valve apparatus.
BACKGROUND
Contractile function improves after correction of experimental mitral regurgitation, but ejection performance becomes depressed when mitral valve replacement involves chordal transection. A role for chordal transection in producing the depressed ejection performance was suspected but uncertain. Therefore, in this study, we tested two specific hypotheses: 1) that contractile function would improve and, in conjunction with chordal preservation, would allow for preserved ejection performance and 2) that improved left ventricular contractile function after surgery would be reflected in the function of myocytes isolated from the affected left ventricles.


RESULTS
We examined ventricular contractile function and ejection performance and isolated myocyte function after correction of experimental mitral regurgitation (chordal rupture) with mitral valve replacement that involved chordal preservation. After 3 months of chronic mitral regurgitation, the average regurgitant fraction of seven dogs was 0.77 +/- 0.04. End-diastolic volume had increased from 79 +/- 5 to 132 +/- 10 cm3 (p < 0.05). At that time, all indexes of left ventricular contractile function were depressed. Three months after mitral valve replacement with chordal preservation, end-diastolic volume fell to 100 +/- 4 cm3 (p < 0.05). At this time, all indexes of contractile function had returned to normal. End-systolic stress and ejection fraction after mitral valve replacement were similar to their baseline levels. Viscosity-velocity curves (analogous to force-velocity curves) of myocytes isolated from the affected left ventricles were similar to those of myocytes isolated from normal left ventricles.


CONCLUSIONS
We conclude that mitral valve replacement with chordal preservation allows ventricular contractile function to return to normal. Normal global ventricular function, in turn, is associated with normal function of the individual myocytes that compose the left ventricular chamber. Further, chordal preservation allowed for loading and ejection performance to return to premorbid levels.
Ishihara
K
K
Department of Medicine, Medical University of South Carolina, Charleston 29425-2221.
Zile
M R
MR
Kanazawa
S
S
Tsutsui
H
H
Urabe
Y
Y
DeFreyte
G
G
Carabello
B A
BA
D000818:Animals; D002815:Chordae Tendineae / Q000502:physiology*; D002908:Chronic Disease; D004285:Dogs; D006350:Heart Valve Prosthesis; D006439:Hemodynamics / Q000502:physiology; D008943:Mitral Valve; D008944:Mitral Valve Insufficiency / Q000503:physiopathology* / Q000601:surgery*; D009200:Myocardial Contraction / Q000502:physiology*; D013318:Stroke Volume / Q000502:physiology; D013997:Time Factors; D016277:Ventricular Function, Left / Q000502:physiology*