Laminar structure of the heart: ventricular myocyte arrangement and
connective tissue architecture in the dog.
Legrice, I. J., B. H. Smaill, L. Z. Chai, S. G. Edgar, J. B. Gavin,
and P. J. Hunter.
Department of Physiology, Department of Pathology, School of
Medicine, University of Auckland, New Zealand, Department of
Engineering Science, School of Engineering, University of Auckland,
New Zealand
APStracts 2:0076H, 1995.
We have studied the three-dimensional arrangement of ventricular
muscle cells and the associated extracellular connective tissue
matrix in dog hearts. Four hearts were potassium-arrested, excised
and perfusion-fixed at zero transmural pressure. Full thickness
segments were cut from the RV and LV walls at a series of precisely
located sites. Morphology was visualized macroscopically and with SEM
in (i) transmural planes of section and (ii) planes tangential to the
epicardial surface. The appearance of all specimens was consistent
with an ordered laminar arrangement of myocytes with extensive
cleavage planes between muscle layers. These planes ran radially from
endocardium toward epicardium in transmural section and coincided
with the local muscle fibre orientation in tangential section.
Stereological techniques were used to quantify aspects of this
organization. There was no consistent variation in the cellular
organization of muscle layers (48.4 +/- 20.4[mu]m thick and 4 +/- 2
myocytes across) either transmurally or in different ventricular
regions (23 sites in 6 segments). But there was significant
transmural variation in the coupling between adjacent layers. The
number of branches between layers decreased twofold from
subepicardium to midwall, while the length distribution of perimysial
collagen fibres connecting muscle layers was greatest in the midwall.
We conclude that ventricular myocardium is not a uniformly branching
continuum, but a laminar hierarchy in which it is possible to
identify three axes of material symmetry at any point.
Received 21 September 1994; accepted in final form 2 March 1995.
APS Manuscript Number H852-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.