Significance of force transfer in mitral valve-left ventricular interaction: in vivo assessment.

OBJECTIVE

The objective of this study was to assess the combined force transfer from the papillary muscle tips to the mitral valve through the chordae tendineae in vivo, and thereby quantify the force transmitted through the papillary-chordal complex to augment left ventricular ejection.

METHODS

In an acute porcine model (n = 8), force transfer between papillary muscles and the mitral valve was recorded on the anterior and posterior papillary muscle tip using dedicated force transducers. Ultrasound sonomicrometry was utilized to record and calculate left ventricular long-axis shortening and mitral annular geometry. The closing force acting on the mitral valve leaflets was calculated as mitral annular area multiplied by the transmitral pressure difference throughout systole. Mitral valve competence was verified before measurements with color Doppler ultrasound.

RESULTS

Peak force in the anterior and posterior papillary muscle was 5.9 ± 0.6 N and 5.8 ± 0.7 N (mean ± standard error of the mean), respectively, and peak closing force was 6.8 ± 0.3 N all at a transmitral pressure of 90 mm Hg. Peak rate of left ventricular contraction coincided with peak papillary muscle force.

CONCLUSIONS

This study is the first to assess the magnitude and time course of the longitudinal force transmitted through the papillary-chordal complex to the left ventricular wall during ejection. The study also demonstrates a significant force transfer to the closing force acting on the mitral valve leaflets that constitutes an essential component of valvular-ventricular interaction to enhance left ventricular systolic pump performance. The magnitude of the combined papillary muscle force component emphasizes the crucial role of preserving mitral valve-left ventricular continuity in mitral valve surgery.