From the Department of Pathology, Faculty of Medicine of Ribeirão
Preto, University of São Paulo, Ribeirão Preto, SP, Brazil.
Correspondence to Professor Marcos A. Rossi, Department of Pathology, Faculty of Medicine of Ribeirão Preto, University of São Paulo, 140049-900 Ribeirão Preto, SP, Brazil. E-mail marossi{at}fmrp.usp.br
The stroma of the heart maintains the structure of the
myocardium, determining tissue tensile strength and
stiffness.1 In addition, it contributes to
ventricular function through the transmission of
myocyte-generated force to the atrial and ventricular
chambers and to the relengthening of myocytes in
diastole.2 The three-dimensional configuration
of cardiac collagen has been determined by scanning electron
microscopy3 4 5 : the epimysium envelops the entire cardiac
muscle; the perimysium, which is an extension of the epimysium, serves
to enwrap groups of myocytes; and the endomysium, as final arborization
of the perimysium, supports and connects individual cells. The
endomysial weave envelops each individual myocyte and is connected to
adjacent myocytes by lateral struts.
Because this knowledge was obtained through studies on whole fixed
myocardial tissue without removal of its nonfibrous elements, we
attempted to dissolve the cellular elements and leave behind a
noncollapsed matrix, aiming for a better three-dimensional view. For
this, we used a modification of the NaOH maceration technique reported
by Ohtani.6 This method was reported to be able to remove
cellular elements much more effectively than any other method. Small
fragments, 10x5x3 mm in size, of the anterior wall at the
midventricular region were obtained from three human
hearts, weighing between 300 and 350 g, without any pathological
changes. All samples were fixed in 10% neutral formalin. After being
rinsed in distilled water, the specimens were immersed in a 10% NaOH
solution for 4 to 6 days at room temperature and then rinsed in
distilled water until they became transparent. Then they were immersed
in 1% tannic acid for 4 hours. Subsequently, the specimens were rinsed
in distilled water overnight, rinsed, post-fixed in 1% osmium
tetroxide for 2 hours, dehydrated in graded concentrations of ethanol,
sectioned transversely or longitudinally with a very sharp, clean blade
under a dissecting microscope, freeze-dried, coated with gold, and
observed under a Zeiss 940-A scanning electron microscope.
The figure clearly shows, for the first
time, the three-dimensional architecture of collagen fibrils in human
myocardium after digestion of the cellular elements. This
is expected to contribute further to the understanding of the
morphology of the connective tissue skeleton of the heart.
Acknowledgments
Professor Rossi is Senior Investigator of the Conselho
Nacional de Desenvolvimento Científico e Tecnológico
(CNPq).
Footnotes
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke's Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
Circulation encourages readers to submit cardiovascular images to Dr Hugh A. McAllister, Jr, St Luke's Episcopal Hospital and Texas Heart Institute, 6720 Bertner Ave, MC1-267, Houston, TX 77030.
References
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© 1998 American Heart Association, Inc.
Images in Cardiovascular Medicine
Connective Tissue Skeleton of the Human Heart
A Demonstration by Cell-Maceration Scanning Electron Microscope Method
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Figure 1. Connective tissue skeleton of human heart sectioned
transversely. Its organization is quite similar to a honeycomb. The
perimysium (P) envelops groups of myocytes. The endomysium, as final
arborization of the perimysium, supports and connects individual cells.
The endomysial weave (W) envelops each individual myocyte and is
connected to adjacent myocytes by lateral struts (s) presenting
branches of variable size and extension. The range of length and
diameter of these struts is very wide. Collagen struts also connect
myocytes to interstitial microvessels (thin arrow) or
perimysium (thick arrow). A, Bar=20 µm; magnification x1415; B,
bar=10 µm, magnification x2830.
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