Importance of the mitral apparatus for left ventricular function: an experimental approach

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Abstract
In an experimental study of 31 anesthetized dogs the importance of the mitral apparatus for the left ventricular function was investigated. During extracorporeal circulation bileaflet mitral valve protheses were implanted preserving the mitral subvalvular apparatus. Flexible wires were slung around the chordae tendineae and exteriorized through the left ventricular wall to cut the chordae by electrocautery from the outside when the heart was beating again. External and internal left ventricular dimensions were measured by sonomicrometry, left ventricular stroke volume by electromagnetic flowmeters around the ascending aorta, left ventricular end-diastolic volume by dye dilution technique, and left ventricular pressure by catheter tip manometers. Different preload levels were achieved by volume loading with blood transfusion before and after cutting the chordae tendineae. When the chordae had been divided peak systolic left ventricular pressure did not change. Heart rate only increased at the lowest left ventricular end-diastolic pressures of 3–4 mmHg, but remained unchanged at higher preload levels. Cardiac output decreased significantly up to −9% at left ventricular end-diastolic pressures of 5–10 mmHg, while left ventricular dpdtmax showed a consistent reduction of up to −15% at any preload level. Significant reductions were also seen in systolic shortening in the left ventricular major axis (by external measurements −27%, by internal recording −43%). Left ventricular end-diastolic dimensions increased in the major axis by +2% when recorded externally, by +10% when measured internally. Systolic and diastolic changes in the minor axis were not consistent and different in the external and internal recordings. Left ventricular end-diastolic volume was increased by +18% at any preload level, revealing an approximately parallel shift of the left ventricular end-diastolic pressure-volume relation to the right after severance of the chordae tendineae. It can be concluded that the mitral valve apparatus is of importance for the left ventricular function. Particularly in patients with chronic mitral valve disease and dilated hearts, preservation of the subvalvular mitral apparatus might be of benefit for the postoperative course and long-term functional result.