Effect of disrupting the mitral apparatus on left ventricular function in dogs.

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Abstract
BACKGROUND The importance of the mitral apparatus to left ventricular function has been suggested in clinical studies. The effect of disruption of the mitral apparatus on left ventricular diastolic and systolic properties has not been fully documented. METHODS AND RESULTS We investigated the end-diastolic and end-systolic pressure-volume and stroke work-end-diastolic volume relations and measured the isovolumic relaxation time constant (tau infinity) during nonfilling beats before and after disruption of the mitral apparatus under different loading conditions in 14 dogs using our recently developed volume-clamping technique for the in situ left ventricle. Disruption of the mitral apparatus increased left ventricular diastolic equilibrium volume (V0d) without changing the slope of the end-diastolic pressure-volume relation (Sd) and increased end-systolic pressure-volume relation dead volume (V0s) and volume-axis intercept of stroke work-end-diastolic volume relation (V0sw) without changing the slopes of these relations (maximum elastance, Ees, and Ssw). Disruption of the mitral apparatus increased tau infinity. CONCLUSION Disruption of the mitral apparatus increases the equilibrium volume without changing left ventricular diastolic stiffness or contractility and slows left ventricular relaxation. These results support and help explain the clinical observation that it is desirable to maintain the mitral apparatus during mitral valve replacement surgery.