Ultrastructural quantification of collagen in human chordae tendineae.

OBJECTIVE To determine collagen fibril diameter distributions in the chordae tendineae and to see whether there are any differences between right and left sides of the human heart. DESIGN Collagen fibril diameters and the percentage volume occupied by collagen fibrils (as opposed to ground substance) were determined by means of a planimeter with a digitising tablet from electron micrographs printed at a magnification of 136; 000. MATERIAL Human chordae tendineae were obtained at postmortem examination from seven subjects aged 50-75 years. MEASUREMENTS AND MAIN RESULTS Histograms of collagen fibril diameter distributions showed a sharp, unimodal distribution. The mean collagen fibril diameters associated with the tricuspid and mitral valves were 41.1 nm and 40.5 nm respectively. The percentage volume occupied by collagen was about 39% for each valve. There were no significant differences for any of these values between the right and left sides of the heart. CONCLUSIONS The greater pressures present on the left side of the heart are not reflected in any difference in collagen fibril diameters within the chordae tendineae compared with the right side.