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In order to visualise the mammalian myocardial structure in its entirety, we distended excised porcine left ventricles by inflating the coronary arteries with compressed air, using rising pressures between 100 and 300 kPa. The ventricular walls became elongated, and left ventricular cavity widened with rising pressure albeit with insignificant changes in their mural thickness. High resolution computed tomographic analysis subsequent to pneumographic distension revealed a hierarchical structure. First, a feathered arrangement of the cardiomyocytes aggregated together mainly within the equatorial area of the ventricle, giving an overall appearance of systematically arranged spatially netted lamellar structures with pronounced local inhomogeneity. Second, histological examination in orthogonal planes, analysing samples dividing the ventricular walls into 18 segments, showed the lamellae themselves to be made up of aggregated chains of myocytes, the alignment of these chains producing the well-recognised change in so-called helical angle when traced through the thickness of the walls. Transmural length sections removed from the same positions in the ventricular walls showed inter-lamellar connections aligned in the direction from the ventricular base to the apex which were definitely longer than those we observed in transmural cross-sections. Electron-microscopy exposed the two compartments of interstitial connective tissue, suggesting the endomysium to bind long chains of myocytes to lamellar aggregates, while the loose perimysium strengthens the structure of the lubricating medium which eases the gliding of the lamellar aggregates relative to one another.
Lunkenheimer et al. (Mon,) studied this question.