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Effects of obstruction of cardiac lymphatics
Effects of obstruction of cardiac lymphatics A study was undertaken in the dog to determine whether changes occurred in the lymphatics of the endocardium and myocardium of both ventricles after obstruction of the cardiac lymphatics. Other investigators have reported ventricular siibendocardial hemorrhage, increased elastic and fibrous tissue in the left ventricle endocardium, and opacification of the mitral valve leaflets. In 14 experiments the ventricular walls were injected with India ink. The efferent cardiac lymphatics were followed to their termination in the cardiac lymph node or nodes. These nodes were excised, as were afferent and efferent lymphatic trunks. After 4 to 16 weeks, with the aid of extracorporeal circulation and oxygenation, biopsies were taken of the myocardium and endocardium of the ventricles of the beating heart. Six animals were used as control subjects. Grossly, there were no changes in the endocardium, myocardium, or valve leaflets. Light and electron microscopy demonstrated no fibrosis or elastosis, and no lymphatics were identifiable. We were unable to establish evidence of permanent changes as a result of obstruction of the lymphatics of the dog heart.
Edward F. Parker, M.D., R. Randolph Bradham, M.D., Gordon R. Hennigar, M.D., and William B. Greene, B.S., Charleston, S. C.
A his study was undertaken to determine whether demonstrable changes occur in the lymphatics of the endocardium and myocardium of the right and left ventricles after obstruction of the cardiac lymphatics in dogs. There have been several other studies of the effect of obstruction of the cardiac lymphatics in dogs. Foldi and associates' made observations on the serum and enzyme changes following obstruction of the cardiac lymphatics. An elevation of the serum glutamic oxaloacetic acid transaminase was noted, but there was no change in activity of serum glutamic pyruvic acid transaminase. Rusznyak and colleagues- observed electrocardiographic signs of myocardial damage by obstruction of the cardiac lymphatics. They postulated that the presence of edema From the Departments of Surgery and Pathology, Roper Hospital and Medical University of South Carolina, Charleston, S. C. 29401. Supported by the John A. Hartford Foundation, Cardiovascular Research Laboratory, Roper Hospital, Charleston, South Carolina. Received for publication Aug. 5, 1974.
390
Table I. Electron microscopic findings in control and experimental animals Normal Hemorrhagic shock with typical zonal lesions Hemorrhagic shock without typical zonal lesions Fatty degeneration Separation of endocardial membrane Thickened but unseparated endocardial membrane Edematous fluid between membrane Evidence of trauma
13 8 6 2 10 1 2 1
resulted in diminished availability of oxygen for cellular metabolism. Miller's group 3 observed abnormalities in 17 of 22 dogs after production of long-term impairment of cardiac lymph flow. These changes included left and right ventricular subendocardial hemorrhages, increased elastic and fibrous tissue in the left ventricular endocardium, and opacification of the mitral valve leaflets. In other investigations, Miller and coworkers" found thin-walled vessels, pre-
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Fig. 1. Electron micrograph shows normal architecture of myocardium. The myofibrils, Z bands, intercalated discs, and mitochondria are within normal limits. (Control dog No. 4; original magnification xl2,500.)
sumably lymphatics, in the mitral valves of dogs. These vessels increased in number and caliber with impairment of the cardiac lymph flow. Symbas and associates5 obstructed the cardiac lymphatics and studied the effects on regeneration. They found that collaterals formed and lymphatic drainage to the cardiac lymph nodes was re-established after 16 days. Jellinek's group0 obstructed the cardiac lymphatics and observed collections of plasma in the wall of the coronary artery. These collections caused elevation of the endothelium and produced obstruction. Associated fibrinoid necrosis was also observed. In a separate set of experiments,
Bradham and associates7 were unable to reproduce these changes. Symbas and co-workers* interrupted the efferent cardiac lymphatics in dogs and found that the normal structure of the atrioventricular valves was altered: the tricuspid valves were more thickened than the mitral valves. The changes appeared to be due to accumulation of amorphous myxoid material. In the same dogs, no significant gross or microscopic changes were found in the endocardium or myocardium. Patek1* was unable to demonstrate lymphatics in the mitral and tricuspid valves, and Bradham and associates10 were able to do so only very infrequently. Because the results of cardiac lymphatic
The Journal of
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Parker et al.
Thoracic and Cardiovascular Surgery
Fig. 2. Electron micrograph of junction of left ventricular myocardium and endocardium shows reasonably normal mitochondria, banding, and intercalated disc. The subendocardial space shows low-density protein-like material and several free organelles. (Experimental dog No. 2; original magnification xlO,000.) obstruction in dogs have been so variable, we decided that further-experiments should be undertaken to observe changes in the lymphatics and other elements of the endocardium and myocardium, in particular. Methods Mongrel dogs were anesthetized with intravenous sodium pentobarbital. After a right thoracotomy was performed, respiration was maintained via a mechanical respirator with room air and intermittent positive pressure.
The pericardium was opened anteriorly for a short distance to allow visualization of the anterior walls of the left and right ventricles, which were injected with an aqueous suspension of India ink. Immediately or within a few minutes, the afferent cardiac lymphatics were visible and could be followed to the cardiac lymph node or nodes, which were usually situated between the vena cava and the ascending aorta, anterior to the trachea. The node or nodes were completely excised, and the efferent and
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Number 3
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March, 1975
&■*
y«
Fig. 3. Electron micrograph of left ventricular endocardium shows the typical zonal lesion of hemorrhagic shock: smudging of the Z bands and collapse of the myofibrils on either side of a flattened segment of intercalated disc. Elsewhere, mitochondria are disrupted and displaced. (Experimental dog No. 12; original magnification xl2,500.)
afferent trunks were identified and ligated singly or multiply. In numerous other experiments to study the cardiac lymphatics in dogs, the ability to recognize the cardiac lymphatics by the presence of dye within them was subject to varying degrees of filling and emptying, both spontaneously and on manipulation. After the above procedure, the lung was re-expanded and the thoracotomy wound was closed. The dogs were resuscitated and restored to normal for subsequent reoperation.
After an interval varying from 4 to 16 weeks, the second thoracotomy was performed via the same techniques; in addition, cardiopulmonary bypass with extracorporeal oxygenation and circulation was instituted after appropriate cannulations of the superior and inferior venae cavae and a femoral artery. Biopsies were obtained of the right ventricular endocardium and myocardium and of the left ventricular endocardium and myocardium. Afterward, the dogs were put to death. Fourteen experiments were per-
The Journal of
394
Parker et al.
Thoracic and Cardiovascular Surgery
Fig. 4. Electron micrograph of left ventricular endocardial membrane shows abundant connective tissue elements with slight edema underlying a normal flattened endothelial cell layer (arrows). The same changes were observed in the control animals. (Experimental dog No. 19; original magnification xl2,500.)
formed. In addition, exactly the same biopsies were obtained from 6 control animals not subjected to obstruction of the cardiac lymphatics. Tissue blocks from the 20 animals in the study were processed for examination by electron microscopy. In the first 5 experimental animals and the first 4 control animals, tissue blocks were taken from four areas from each heart: the right ventricular myocardium, right ventricular endocardium, left ventricular myocardium, and left ventricular endocardium. In the 11 remaining dogs, tissue blocks were taken from only the endocardium and immediately adjacent myocardium, totaling two sampling areas from the right and left ventricles.
There were 420 thick-sectioned blocks for light microscopic orientation. Recuts and deeper cuts brought the total number of toluidine blue slides to 680. Of these, 46 blocks were thin sectioned, stained, and examined with the electron microscope. Punch biopsies of the endocardium and adjacent myocardium were fixed in 4 per cent buffered glutaraldehyde for 30 minutes and then trimmed with the aid of a dissecting microscope, so that the endocardial membrane and the adjacent myocardial tissue would fall flat and be suitable for sectioning in cross section. These trimmed blocks remained in glutaraldehyde for an additional 60 minutes and were placed in buffered rinse overnight. The blocks were
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Number 3
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March, 1975
Fig. 5. Light micrograph of left ventricular endocardium shows edematous blebbing of the endocardial membrane. The same changes were observed in the control animals. (Experimental dog No. 12; original magnification xlOO.)
fixed in 2 per cent osmium tetroxide the following morning and were subsequently dehydrated and embedded in Epon. Parallel sections of all specimens submitted for electron microscopy were fixed in formalin and processed in paraffin for light microscopy. A total of 52 sections were cut and stained with hematoxylin and eosin. These were examined for proper orientation, and blocks were turned 90 degrees when necessary. A total of 160 slides were examined, including recuts and special stains. Results Grossly, there were no changes in the endocardium, myocardium, or valve leaflets. There was no fibrosis or elastosis, and no lymphatics were identifiable by light or electron microscopy. Electron microscopically, 8 animals had the typical zonal lesions of hemorrhagic shock with smudged Z banding at the intercalated disc.11 Six animals showed lesser evidence of hemorrhagic shock but had no typical zonal lesions. These changes included damaged mitochondria with myofibril dis-
ruption at the intercalated disc, contraction and smudging at the disc, and marked mitochondrial changes compatible with reduced blood volume. Some mitochondria showed effects of anoxia with no evidence of hemorrhagic shock. Fatty degeneration was present in 2 animals. The endocardial membrane was thickened and separated from the adjacent sarcolemma in 1 animal. There was slight separation but no thickening in 2 animals, thickening but no separation in 1, marked separation but no thickening in 1, edema fluid between the endocardium and sarcolemma in 1, and a mild degree of separation but no thickening in 7. The endocardial membrane was not seen in electron micrographs in 7 animals. Although some micrographs showed completely normal cardiac muscle architecture, no animal was completely free of some of the changes previously mentioned. The electron microscopic findings in both control and experimental animals, compiled from a total of 225 electron micrographs, are shown in Table I. The fact that more than one abnormality was frequently noted in the
The Journal of
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Parker et al.
same animal accounts for the number of abnormal findings exceeding the number of dogs. However, there was no difference in the incidence of changes in the experimental and the control animals. Representative changes observed by electron microscopy are illustrated in Figs. 1 through 4. The usual finding by light microscopy is illustrated in Fig. 5. Comment When one considers that previous investigators have described a rich and elaborate network of lymphatics in the endocardium and in the myocardium, it is surprising that none was identified by the criteria outlined by Leake. 1 - 11 One wonders if this is because, at the tissue planes under examination, lymph vessels as such may not be necessary for the transport of lymph or intracellular fluid to become lymph. Summary Because results of previous experiments by other investigators have varied, we performed 14 experiments to determine whether changes occurred in the lymphatics of the endocardium and myocardium of both ventricles in the dog after obstruction of the cardiac lymphatics. The ventricular walls were injected with India ink. The efferent cardiac lymphatics were traced to their termination in the cardiac lymph node or nodes, and the nodes were excised along with the efferent and afferent trunks. After 4 to 16 weeks, with the aid of extracorporeal circulation and oxygenation, biopsies were taken of the myocardium and endocardium of the ventricles of the beating heart for study by light and electron microscopy. Six control animals were used. Grossly, there were no changes in the endocardium, myocardium, or valve leaflets. Microscopic study revealed no fibrosis or elastosis, and no lymphatics were identifiable. We were unable to establish evidence of permanent changes as a result of obstruction of the lymphatics in the dog heart.
Thoracic and Cardiovascular Surgery
REFERENCES 1 Foldi, M., Braun, P., Papp, M., and Horvath, I.: Changes in Serum Transaminase Activity Following Myocardial Damage Due to Lymphatic Congestion, Nature (Lond.) 183: 1333, 1959. 2 Rusznyak, I., Foldi, M., and Szabo, G.: Lymphatics and Lymph Circulation: Physiology and Pathology, New York, 1960, Pergamon Press, Inc. 3 Miller, A. J., Pick, R., and Katz, L. N.: Ventricular Endomyocardial Pathology by Chronic Cardiac Lymphatic Obstruction in the Dog, Circ. Res. 8: 941, 1960. 4 Miller, A. J., Pick, R., and Katz, L. N.: Lymphatics of the Mitral Valve of the Dog: Demonstration and Discussion of the Possible Significance, Circ. Res. 9: 1005, 1961. 5 Symbas, P. N., Cooper, T., Gantner, G. E., Jr., and Willman, V. L.: Lymphatics of the Heart and Anatomic Effects Following Interruption of the Drainage of the Cardiac Lymph, Arch. Pathol. 81: 573, 1966. 6 Jellinek, H., Gabor, G., Solti, F., and Veress, B.: The Problem of the Coronary Changes Due to Disturbance of Vascular Wall Permeability, Angiology 18: 179, 1967. 7 Bradham, R. R., Parker, E. F., and Greene, W. B.: Lymphatics of the Atrioventricular Valves, Arch. Surg. 107: 210, 1973. 8 Symbas, P. N., Schlant, R. C , Gravanis, M. B., and Shepherd, R. L.: Pathological and Functional Effects on the Heart Following Interruption of the Cardiac Lymph Drainage, J. THORAC. CARDIOVASC. SURG. 57: 577,
1969.
9 Patek, P. P.: The Morphology of the Lymphatics of the Mammalian Heart, Am. J. Anat. 64: 203, 1939. 10 Bradham, R. R., Parker, E. F., Barrington, B. A., Webb, C. M., and Stallworth, J. M.: The Cardiac Lymphatics, Ann. Surg. 171: 899, 1970. 11 Martin, A. M., Greene, W. B., Simmons, R. L., and Soloway, H. B.: Human Myocardial Zonal Lesions, Arch. Pathol. 87: 339, 1969. 12 Leake, L. V., and Burke, J. F.: Fine Structure of the Lymphatic Capillary and the Adjoining Connective Tissue Area, Am. J. Anat. 118: 785, 1966. 13 Leake, L. B., and Burke, J. F.: Ultrastructural Studies on the Lymphatic Anchoring Filaments, J. Cell Biol. 36: 129, 1968. 14 Leake, L. V., and Burke, J. F.: Lymphatic Capillaries in Tail Fin of Amphibian Larva: An Electron Microscopic Study, J. Morphol. 125: 419, 1968.
Edward F. Parker, M.D., R. Randolph Bradham, M.D., Gordon R. Hennigar, M.D., and William B. Greene, B.S., Charleston, S. C.
A his study was undertaken to determine whether demonstrable changes occur in the lymphatics of the endocardium and myocardium of the right and left ventricles after obstruction of the cardiac lymphatics in dogs. There have been several other studies of the effect of obstruction of the cardiac lymphatics in dogs. Foldi and associates' made observations on the serum and enzyme changes following obstruction of the cardiac lymphatics. An elevation of the serum glutamic oxaloacetic acid transaminase was noted, but there was no change in activity of serum glutamic pyruvic acid transaminase. Rusznyak and colleagues- observed electrocardiographic signs of myocardial damage by obstruction of the cardiac lymphatics. They postulated that the presence of edema From the Departments of Surgery and Pathology, Roper Hospital and Medical University of South Carolina, Charleston, S. C. 29401. Supported by the John A. Hartford Foundation, Cardiovascular Research Laboratory, Roper Hospital, Charleston, South Carolina. Received for publication Aug. 5, 1974.
390
Table I. Electron microscopic findings in control and experimental animals Normal Hemorrhagic shock with typical zonal lesions Hemorrhagic shock without typical zonal lesions Fatty degeneration Separation of endocardial membrane Thickened but unseparated endocardial membrane Edematous fluid between membrane Evidence of trauma
13 8 6 2 10 1 2 1
resulted in diminished availability of oxygen for cellular metabolism. Miller's group 3 observed abnormalities in 17 of 22 dogs after production of long-term impairment of cardiac lymph flow. These changes included left and right ventricular subendocardial hemorrhages, increased elastic and fibrous tissue in the left ventricular endocardium, and opacification of the mitral valve leaflets. In other investigations, Miller and coworkers" found thin-walled vessels, pre-
Volume 69 Number 3
Obstruction of cardiac lymphatics
391
March, 1975
Fig. 1. Electron micrograph shows normal architecture of myocardium. The myofibrils, Z bands, intercalated discs, and mitochondria are within normal limits. (Control dog No. 4; original magnification xl2,500.)
sumably lymphatics, in the mitral valves of dogs. These vessels increased in number and caliber with impairment of the cardiac lymph flow. Symbas and associates5 obstructed the cardiac lymphatics and studied the effects on regeneration. They found that collaterals formed and lymphatic drainage to the cardiac lymph nodes was re-established after 16 days. Jellinek's group0 obstructed the cardiac lymphatics and observed collections of plasma in the wall of the coronary artery. These collections caused elevation of the endothelium and produced obstruction. Associated fibrinoid necrosis was also observed. In a separate set of experiments,
Bradham and associates7 were unable to reproduce these changes. Symbas and co-workers* interrupted the efferent cardiac lymphatics in dogs and found that the normal structure of the atrioventricular valves was altered: the tricuspid valves were more thickened than the mitral valves. The changes appeared to be due to accumulation of amorphous myxoid material. In the same dogs, no significant gross or microscopic changes were found in the endocardium or myocardium. Patek1* was unable to demonstrate lymphatics in the mitral and tricuspid valves, and Bradham and associates10 were able to do so only very infrequently. Because the results of cardiac lymphatic
The Journal of
392
Parker et al.
Thoracic and Cardiovascular Surgery
Fig. 2. Electron micrograph of junction of left ventricular myocardium and endocardium shows reasonably normal mitochondria, banding, and intercalated disc. The subendocardial space shows low-density protein-like material and several free organelles. (Experimental dog No. 2; original magnification xlO,000.) obstruction in dogs have been so variable, we decided that further-experiments should be undertaken to observe changes in the lymphatics and other elements of the endocardium and myocardium, in particular. Methods Mongrel dogs were anesthetized with intravenous sodium pentobarbital. After a right thoracotomy was performed, respiration was maintained via a mechanical respirator with room air and intermittent positive pressure.
The pericardium was opened anteriorly for a short distance to allow visualization of the anterior walls of the left and right ventricles, which were injected with an aqueous suspension of India ink. Immediately or within a few minutes, the afferent cardiac lymphatics were visible and could be followed to the cardiac lymph node or nodes, which were usually situated between the vena cava and the ascending aorta, anterior to the trachea. The node or nodes were completely excised, and the efferent and
Volume 69
Obstruction of cardiac lymphatics
Number 3
393
March, 1975
&■*
y«
Fig. 3. Electron micrograph of left ventricular endocardium shows the typical zonal lesion of hemorrhagic shock: smudging of the Z bands and collapse of the myofibrils on either side of a flattened segment of intercalated disc. Elsewhere, mitochondria are disrupted and displaced. (Experimental dog No. 12; original magnification xl2,500.)
afferent trunks were identified and ligated singly or multiply. In numerous other experiments to study the cardiac lymphatics in dogs, the ability to recognize the cardiac lymphatics by the presence of dye within them was subject to varying degrees of filling and emptying, both spontaneously and on manipulation. After the above procedure, the lung was re-expanded and the thoracotomy wound was closed. The dogs were resuscitated and restored to normal for subsequent reoperation.
After an interval varying from 4 to 16 weeks, the second thoracotomy was performed via the same techniques; in addition, cardiopulmonary bypass with extracorporeal oxygenation and circulation was instituted after appropriate cannulations of the superior and inferior venae cavae and a femoral artery. Biopsies were obtained of the right ventricular endocardium and myocardium and of the left ventricular endocardium and myocardium. Afterward, the dogs were put to death. Fourteen experiments were per-
The Journal of
394
Parker et al.
Thoracic and Cardiovascular Surgery
Fig. 4. Electron micrograph of left ventricular endocardial membrane shows abundant connective tissue elements with slight edema underlying a normal flattened endothelial cell layer (arrows). The same changes were observed in the control animals. (Experimental dog No. 19; original magnification xl2,500.)
formed. In addition, exactly the same biopsies were obtained from 6 control animals not subjected to obstruction of the cardiac lymphatics. Tissue blocks from the 20 animals in the study were processed for examination by electron microscopy. In the first 5 experimental animals and the first 4 control animals, tissue blocks were taken from four areas from each heart: the right ventricular myocardium, right ventricular endocardium, left ventricular myocardium, and left ventricular endocardium. In the 11 remaining dogs, tissue blocks were taken from only the endocardium and immediately adjacent myocardium, totaling two sampling areas from the right and left ventricles.
There were 420 thick-sectioned blocks for light microscopic orientation. Recuts and deeper cuts brought the total number of toluidine blue slides to 680. Of these, 46 blocks were thin sectioned, stained, and examined with the electron microscope. Punch biopsies of the endocardium and adjacent myocardium were fixed in 4 per cent buffered glutaraldehyde for 30 minutes and then trimmed with the aid of a dissecting microscope, so that the endocardial membrane and the adjacent myocardial tissue would fall flat and be suitable for sectioning in cross section. These trimmed blocks remained in glutaraldehyde for an additional 60 minutes and were placed in buffered rinse overnight. The blocks were
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Number 3
Obstruction of cardiac lymphatics
395
March, 1975
Fig. 5. Light micrograph of left ventricular endocardium shows edematous blebbing of the endocardial membrane. The same changes were observed in the control animals. (Experimental dog No. 12; original magnification xlOO.)
fixed in 2 per cent osmium tetroxide the following morning and were subsequently dehydrated and embedded in Epon. Parallel sections of all specimens submitted for electron microscopy were fixed in formalin and processed in paraffin for light microscopy. A total of 52 sections were cut and stained with hematoxylin and eosin. These were examined for proper orientation, and blocks were turned 90 degrees when necessary. A total of 160 slides were examined, including recuts and special stains. Results Grossly, there were no changes in the endocardium, myocardium, or valve leaflets. There was no fibrosis or elastosis, and no lymphatics were identifiable by light or electron microscopy. Electron microscopically, 8 animals had the typical zonal lesions of hemorrhagic shock with smudged Z banding at the intercalated disc.11 Six animals showed lesser evidence of hemorrhagic shock but had no typical zonal lesions. These changes included damaged mitochondria with myofibril dis-
ruption at the intercalated disc, contraction and smudging at the disc, and marked mitochondrial changes compatible with reduced blood volume. Some mitochondria showed effects of anoxia with no evidence of hemorrhagic shock. Fatty degeneration was present in 2 animals. The endocardial membrane was thickened and separated from the adjacent sarcolemma in 1 animal. There was slight separation but no thickening in 2 animals, thickening but no separation in 1, marked separation but no thickening in 1, edema fluid between the endocardium and sarcolemma in 1, and a mild degree of separation but no thickening in 7. The endocardial membrane was not seen in electron micrographs in 7 animals. Although some micrographs showed completely normal cardiac muscle architecture, no animal was completely free of some of the changes previously mentioned. The electron microscopic findings in both control and experimental animals, compiled from a total of 225 electron micrographs, are shown in Table I. The fact that more than one abnormality was frequently noted in the
The Journal of
396
Parker et al.
same animal accounts for the number of abnormal findings exceeding the number of dogs. However, there was no difference in the incidence of changes in the experimental and the control animals. Representative changes observed by electron microscopy are illustrated in Figs. 1 through 4. The usual finding by light microscopy is illustrated in Fig. 5. Comment When one considers that previous investigators have described a rich and elaborate network of lymphatics in the endocardium and in the myocardium, it is surprising that none was identified by the criteria outlined by Leake. 1 - 11 One wonders if this is because, at the tissue planes under examination, lymph vessels as such may not be necessary for the transport of lymph or intracellular fluid to become lymph. Summary Because results of previous experiments by other investigators have varied, we performed 14 experiments to determine whether changes occurred in the lymphatics of the endocardium and myocardium of both ventricles in the dog after obstruction of the cardiac lymphatics. The ventricular walls were injected with India ink. The efferent cardiac lymphatics were traced to their termination in the cardiac lymph node or nodes, and the nodes were excised along with the efferent and afferent trunks. After 4 to 16 weeks, with the aid of extracorporeal circulation and oxygenation, biopsies were taken of the myocardium and endocardium of the ventricles of the beating heart for study by light and electron microscopy. Six control animals were used. Grossly, there were no changes in the endocardium, myocardium, or valve leaflets. Microscopic study revealed no fibrosis or elastosis, and no lymphatics were identifiable. We were unable to establish evidence of permanent changes as a result of obstruction of the lymphatics in the dog heart.
Thoracic and Cardiovascular Surgery
REFERENCES 1 Foldi, M., Braun, P., Papp, M., and Horvath, I.: Changes in Serum Transaminase Activity Following Myocardial Damage Due to Lymphatic Congestion, Nature (Lond.) 183: 1333, 1959. 2 Rusznyak, I., Foldi, M., and Szabo, G.: Lymphatics and Lymph Circulation: Physiology and Pathology, New York, 1960, Pergamon Press, Inc. 3 Miller, A. J., Pick, R., and Katz, L. N.: Ventricular Endomyocardial Pathology by Chronic Cardiac Lymphatic Obstruction in the Dog, Circ. Res. 8: 941, 1960. 4 Miller, A. J., Pick, R., and Katz, L. N.: Lymphatics of the Mitral Valve of the Dog: Demonstration and Discussion of the Possible Significance, Circ. Res. 9: 1005, 1961. 5 Symbas, P. N., Cooper, T., Gantner, G. E., Jr., and Willman, V. L.: Lymphatics of the Heart and Anatomic Effects Following Interruption of the Drainage of the Cardiac Lymph, Arch. Pathol. 81: 573, 1966. 6 Jellinek, H., Gabor, G., Solti, F., and Veress, B.: The Problem of the Coronary Changes Due to Disturbance of Vascular Wall Permeability, Angiology 18: 179, 1967. 7 Bradham, R. R., Parker, E. F., and Greene, W. B.: Lymphatics of the Atrioventricular Valves, Arch. Surg. 107: 210, 1973. 8 Symbas, P. N., Schlant, R. C , Gravanis, M. B., and Shepherd, R. L.: Pathological and Functional Effects on the Heart Following Interruption of the Cardiac Lymph Drainage, J. THORAC. CARDIOVASC. SURG. 57: 577,
1969.
9 Patek, P. P.: The Morphology of the Lymphatics of the Mammalian Heart, Am. J. Anat. 64: 203, 1939. 10 Bradham, R. R., Parker, E. F., Barrington, B. A., Webb, C. M., and Stallworth, J. M.: The Cardiac Lymphatics, Ann. Surg. 171: 899, 1970. 11 Martin, A. M., Greene, W. B., Simmons, R. L., and Soloway, H. B.: Human Myocardial Zonal Lesions, Arch. Pathol. 87: 339, 1969. 12 Leake, L. V., and Burke, J. F.: Fine Structure of the Lymphatic Capillary and the Adjoining Connective Tissue Area, Am. J. Anat. 118: 785, 1966. 13 Leake, L. B., and Burke, J. F.: Ultrastructural Studies on the Lymphatic Anchoring Filaments, J. Cell Biol. 36: 129, 1968. 14 Leake, L. V., and Burke, J. F.: Lymphatic Capillaries in Tail Fin of Amphibian Larva: An Electron Microscopic Study, J. Morphol. 125: 419, 1968.