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Reversal of myocardial ischemia by arterialization of the coronary vein
Reversal of myocardial ischemia by arterialization of the coronary vein Ligation of the anterior descending coronary artery was done in 6 sheep, and marked S-T segment changes in epicardial electrograms were noted. In another group of 10 sheep, the coronary artery was also ligated, but the accompanying coronary vein was perfused with arterial blood from the internal mammary artery. The S-T segment changes in this group were minimal. Perfusion of the vein was stopped after 60 minutes while the artery remained occluded. S-T segment changes indicative of ischemia then occurred. In 7 animals, flows through the internal mammary artery were found to vary from 20 to 90 c.c. per minute. These findings suggest that retrograde flow of arterial blood through a coronary vein prevents the ischemia which otherwise follows coronary artery occlusion.
Joginder N. Bhayana, M.D., Donald B. Olsen, D.V.M., James P. Byrne, M.D., and Willem J. Kolff, M.D., Ph.D., Salt Lake City, Utah
SaPhenous vein grafts from the aorta to the coronary artery are being widely used to revascularize the ischemic myocardium.v 4, 10 These grafts will remain patent if there is distal run off. In a few patients with severe coronary atherosclerosis, the vessels are diseased to such an extent that no back flow is seen when an arteriotomy is done at the operating table. For these patients an alternative method for myocardial revascularization must be found. It is well known that coronary veins do not show atherosclerotic changes. The purpose of this study was to investigate the possibility of using the coronary vein that drains an ischemic area as a conduit for supplying arterial blood to the ischemic From the Division of Artificial Organs, Department of Surgery, and the Institute for Biomedical Engineering, University of Utah, Salt Lake City, Utah 84112. Supported in part by the National Institutes of Health via The National Heart and Lung Institute, Grant HL-13738, and by contributions to the Development Fund of the Division of Artificial Organs, among others, by Mrs. Mary Hercik, Received for publication July 3, 1973. Address for reprints: The Division of Artificial Organs, Building 518, Salt Lake City, Utah 84112.
myocardium. Preliminary studies in our laboratory were encouraging.': 15 This concept should not be confused with one proposed by Claude Beck." He recommended ligation of the coronary sinus and then arterialization, irrespective of the area of myocardial ischemia. With coronary angiography, the exact site of coronary artery disease can be determined. Thus it will be possible to arterialize the exact vein draining the ischemic area. The most crucial question is whether arterial blood delivered through the vein can, indeed, provide sufficient blood supply to the myocardium. If one first produces ischemic damage and then tries to repair it, one invites a number of difficulties and variables. Therefore, we took the opposite approach. We first tied off the artery and provided blood supply through the vein to the myocardium. We then proved that interruption of that blood supply resulted in ischemic damage. The efficacy of the oxygenated blood supply through the vein was evidenced by a normal S- T segment on the electrocardiogram, normal color of the heart
125
The Journol of
12 6
Bhayana et at.
Thorocic ond Cordiovosculor Surgery
CORONARY VEIN
LIGATED
Fig. 1. Technique of coronary vein perfusion with arterial blood from internal mammary artery.
muscle, normal contraction of the heart muscle, bright red color of the blood in the perfused vein, and actual measurement of the blood flow. After 1 hour of perfusion, when steady state was obtained, the flow into the vein was interrupted. The results were typical for ischemic damage to the pertaining area of the myocardium. Methods Sheep weighing from 62 to 72 kilograms were used. Anesthesia was induced by intravenous sodium methohexital* (5 mg. per kilogram of body weight) and scopolaminet (0.03 mg. per kilogram of body weight). An endotracheal tube was inserted and breathing was controlled with a pressurecycled respirator.j The left common carotid artery was cannulated for arterial pressure. The electrocardiogram and arterial pressure (with Statham pressure transducers§) were monitored on a multichannel Sanborn II recorder. Three sites were selected on the anterior surface of the left ventricle near the apex for epicardial electrocardiography. The electrodes were soldered wire loops, 4 mm. in diameter, and were sutured near the apex of the left ventricle. They were connected to *Brevane, Eli Lilly & Co., Indianapolis, Ind. tScopolamine hydrobrornide, Burroughs Wellcome & Co. (D. S. A.) Inc., Research Triangle Park, N. C. tBird Mark 10, the Bird Corporation Palm Springs. Calif. §Model dBd, Statham Instruments, Inc., Oxnard, Calif. [Model 7788 A, Hewlett-Packard, Division of Sanborn Co., Waltham, Mass.
the precordial terminal of a standard electrocardiograph, and the lead selector notch was in the V position. * Recordings were done at 1 mv. per millimeter, one tenth the electrocardiographic sensitivity that is used for external leads. The animals were divided into two groups. In the control group (6 sheep) only the left anterior descending artery was occluded. The artery was dissected near the middle of its course, at the point where it emerges from the myocardium. A heavy silk suture was passed around it and pulled through a tourniquet. Heparin, 2 mg. per kilogram of body weight, was given intravenously. Epicardial electrocardiograms were obtained before occlusion and then 5, 10, 15, and 20 minutes after occlusion. The tourniquet was removed, and epicardial electrocardiograms were recorded for 60 minutes after the arterial pressure had been stabilized to preocclusion level, by fluid infusion if necessary. Pressor drugs were not used. Maroko and colleagues" have shown that the magnitude of elevation of the S-T segment with epicardial electrodes correlates well with the depressed levels of myocardial creatine phosphokinase, and this is an indication of myocardial infarction. We used the magnitude of elevation of the S-T segment as an index of myocardial injury. In the second group of animals (23 sheep), the right internal mammary artery was dissected free and the left anterior descending coronary vein was surrounded with ligatures. A polyethylene catheter] of appropriate size was then introduced into the coronary vein after the proximal end had been ligated. After free flow of venous blood was obtained, the other end of the catheter was introduced into the internal mammary artery (Fig. 1). The anterior descending coronary artery was then ligated, and epicardial electrocardiograms were obtained every 5 minutes for the next 60 minutes. *Each electrocardiogram thus reflected potential differences between an epicardial electrode and a central terminal connection to right and left front and to left rear limb electrodes. tClay-Adams, Inc., Parsippany, New Jersey.
Volume 67
Myocardial ischemia
Number 1
1 27
January, 1974
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Fig. 4. Tracings from the same animal as in Fig. 3 after perfusion through the vein was stopped. ~ T segment elevation was present 10 and 20 minutes following termination of perfusion.
Table I. Flow studies 20
Animal No. 1 2
Fig. 2. S-T segment changes before ligation and 10 and 20 minutes after ligation of the coronary artery. The coronary vein was perfused.
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I Flow
range (c.c.Zmin .) 25-30 24-96 30-72 25-80 35-70 22-30 23-50
Legend : Range of flows recorded through mary artery during 60 minutes of coronary Flows varied with systemic blood pressure. artery was connected to the coronary vein , could flow only Into that vein .
internaJ mamvein perfusion . The mammary and the blood
Results
20
40
Fig. 3. Epicardial electrocardiograms from an animal with the left anterior descending artery ligated and the coronary vein perfused with arterial blood from the internal mammary artery. There is no elevation of SooT segment 10, 20, and 40 minutes after ligation of the artery C, Control.
The arterial pressure was monitored throughout the experiment and kept at preocclusion level. In a third group of 7 animals, flows through the internal mammary artery were measured during the 60 minutes of perfusion. We used electromagnetic flow probes and a direct readout recorder, * which was calibrated at the start of each experiment. 'Model SP 2206, Statham Instruments, Inc ., .Oxnard, Calif. Courtesy of Utah Biomedical Test Facility and Dr . Sam Topham .
Effects of occlusion of the left anterior descending coronary artery (control group). Following occlusion, an area of cyanosis with paradoxical motion was noted. The $-T segments in the electrograms were elevated over the control levels. The maximum changes were ' observed 20 minutes after occlusion (Fig. 2). Coronary vein perfusion group. Thirty animals were included in this group. Thirteen were not valid experiments due to technical problems. Electrograms only ·were done in 10 and flows were done in 7. In this group of animals, in which the coronary artery was occluded and the vein perfused with arterial blood from the internal mammary artery, several changes were seen: I. With the vein open but the artery occlud ed , an $-T segment elevation of only a few millimeters was noted in epicardial electrograrns when followed for up to 60 minutes after coronary occlusion (Fig; 3). Some $ - T segment elevation was present on the control electrocardiogram, presumably due
The Journal of Thoracic and Cardiovascular
Bhayana et at.
12 8
Surgery
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Fig. 5. Epicardial electrocardiograms from 10 animals showing the maximum S-T segment elevation occurring in each of three phases of the experiment. A, Control. B, After coronary artery ligation and during coronary vein perfusion. C, After termination of coronary vein perfusion. The artery remained ligated.
to myocardial injury associated with dissection of the artery and vein. After 60 minutes of perfusion, the cannula was clamped. The electrograms then showed elevation of the S-T segment similar to that seen in the control group when coronary artery ligation only was done (Fig. 4). Electrograms from 10 animals demonstrating maximal S-T segment elevation during the control period, coronary vein perfusion, and after termination of perfusion are shown in Fig. 5. 2. The usual cyanotic area at apex of the left ventricle, as seen in the control group, was absent. 3. Oxygenated blood could be visualized
Fig. 5. Coot'd. For legend, see opposite column.
in the coronary vein (Fig. 6), and contrasting venous blood could be seen when the internal mammary artery flow was interrupted (Fig. 7). 4. Flow studies were done in 7 animals and showed flow rates in the range of 20 C.c. to 90 c.c. per minute through the internal mammary artery (Table 1). The flow rate in each animal varied with the systemic blood pressure during the 60 minute observation period. Discussion
At present, direct methods of myocardial revascularization with saphenous vein grafts or internal mammary artery--coronary artery anastomosis are being widely used." Though the early results of saphenous
Fig. 6. Blood in the coronary vein is red, indicating origin from the internal mammary artery.
Fig. 7. With the perfusion cannula clamped, blood in the coronary vein that it is venous.
IS
blue, indicating
Volume 67 Number'1
Myocardial ischemia
131
January, 1974
vein graft procedures, including patency rates," flow rates.v ? and myocardial function studies," are extremely encouraging; these patients must be followed for a long time before the ultimate value of this operation can be proved. A number of problems, such as closure and intimal fibrosis in these grafts, are being noticed. The turbulence or flow related to use of a conduit of higher diameter than the natural coronary artery has been pointed out." Because of these problems, Green' proposed using the internal mammary artery as a conduit for arterial blood. Miller and associates> demonstrated the feasibility of using the internal mammary artery experimentally in 1959. The early results of this procedure are encouraging. Clinically it has been found that a number of patients have severely diseased distal coronary arteries. These patients have very low flows and high occlusion rates following saphenous vein graft procedures." We feel that in these patients the possibility of using the coronary vein as a conduit for arterial blood should be explored. We have utilized the technique of epicardial electrograms as an index of the extent and severity of myocardial ischemia.P A good correlation between the degree of S-T segment elevation and magnitude of myocardial ischemia has been pointed out by a number of workers.": 10 Sayen and his assocites'" found a good correlation between S-T segment elevation and intramyocardial oxygen tension after 5 minutes of coronary artery occlusion. It has also been pointed out that S-T segment elevation correlates well with depression of myocardial creatine phosphokinase activity. We found in these experiments that, if the left anterior descending coronary vein was perfused with arterial blood from the internal mammary artery, S-T segment changes were small compared to those associated with coronary artery ligation. If the perfusion was stopped, changes similar to those seen following corenary artery ligation alone were seen. These findings suggest that the myocardium receives oxygen from retro-
grade perfusion of the coronary vein with arterial blood. Similar findings in earlier experiments have been reported from this Iaboratory'> and also independently by Schultz and co-workers." Whether the coronary vein will show changes of sclerosis or atherosclerosis, as seen in saphenous vein grafts, is unknown. Long-term studies demonstrating patency of the internal mammary artery-coronary vein anastomosis and prevention of myocardial infarction are also necessary. REFERENCES
2 3
4 5
6
7 8
9
10
11 12
Arealis, E. G., Voider, J. G. R., and Kolff, W. J.: Letter to the Editor, Chest 63: 462, 1973. Beck, C. S., and Leighninger, D. S.: Scientific Basis for the Surgical Treatment of Coronary Artery Disease, J. A. M. A. 159: 1264, 1955. Effler, D. B., Favaloro, R. G., and Groves, L. K.: Coronary Artery Bypass Utilizing Saphenous Vein Grafts: Clinical Experience With 224 Operations, 1. THORAC. CARDIOVASC. SURG. 58: 178, 1969. Favaloro, R. G.: Direct and Indirect Coronary Surgery, Circulation 46: 197, 1972. Flemma, R. J., Johnson, W. D., Lepley, D., Tector, A., Walker, J., Gale, H., Beddingfield, G., Manley, J. C.: Late Results of Saphenous Vein Bypass Grafting for Myocardial Revascularization, Ann. Thorac. Surg. 14: 232, 1972. Furuse, A., Klopp, E. H., Brawley, R. K., Gott, V. L.: Hemodynamics of Aorta to Coronary Artery Bypass, Ann. Thorac. Surg. 14: 282, 1972. Green, G. E.: Internal Mammary Artery to Coronary Artery Anastomosis, Ann. Thorac. Surg. 14: 260, 1972. Grodin, C. M., Meere, C., Castonguay, Y. R., Lepage, G., and Grodin, P.: Blood Flow Through the Aorta to Coronary Artery Bypass Grafts and Early Postoperative Patency, Ann. Thorac. Surg. 12: 574, 1971. Grondin, C. M., Castonguay, Y. R., Lesperance, J., Bourassa, M. G., Campean, L., and Grondin, P.: Attrition Rate of Aorta to Coronary Artery Saphenous Vein Grafts After One Year, Ann. Thorac. Surg. 14: 223, 1972. Johnson, W. D., Flemma, R. J., and Lepley, D.: Direct Coronary Artery Surgery Utilizing Multiple Vein Bypass Grafts, Ann. Thorac. Surg. 9: 436, 1970. Loop, F.: Discussion of Internal Mammary Artery to Coronary Artery Anastomosis, Ann. Thorac. Surg. 14: 260, 1972. Manley, J. C., and Johnson, W. D.: Effects of Surgery on Angina (Pre and Postinfarction)
1 32
13
14
15
16
Bhayana et al.
and Myocardial Function, Circulation 46: 1208, 1972. Maroko, P. R., Kjekshus, J. K., Sobel, B. E., Watanabe, T., Covell, J. W., Ross, J., and Braunwald, E.: Factors Influencing Infarct Size Following Experimental Coronary Occlusion, Circulation 43: 67, 1970. Miller, E. W., Kolff, W. J., and Groves, L. K.: Experimental Coronary Artery Surgery in Dogs Employing a Pump Oxygenator, Surgery 45: 1005, 1959. Salaam, I. A., Olsen, D. B., and Kolff, W. J.: Arterialization of the Specific Vein That Drains an Acutely Ischemic Area of the Myocardium, Read before the British Surgical Research Society, Jan. 5, 1973. Sayen, J. J., Peiarie, G., Katchez, A. H., et al.: Correlation of Intramyocardium Electrocardiograms With Polarographic Oxygen and
The Journal 01 Thoracic and Cardiovascular Surgery
Contractility in the Nonischemic Left Ventricle, Circ. Res. 9: 1268, 1961. 17 Schultz, L. S., Ferguson, R., Pleain, M., and Lillehei, R. C.: Retrograde Perfusion as an Approach to Myocardial Revascularization, European Society for Experimental Surgery, Seventh Congress in Amsterdam, Netherlands, April II to 14, 1972. 18 Toyoshirna, H., Prinzmetal, M., Hosiba, M., et al.: The Nature of Normal and Abnormal Electrocardiograms: Relation of ST Segment and T Wave Changes to Intracellular Potential, Arch. Intern. Med. 115: 4, 1965. 19 Wegsia, R., Zegers, M., Keating, R. P., et al.: Relationship Between the Reduction in Coronary Flow and the Appearance of Electrocardiographic Changes, Am. Heart J. 38: 90, 1949.
Joginder N. Bhayana, M.D., Donald B. Olsen, D.V.M., James P. Byrne, M.D., and Willem J. Kolff, M.D., Ph.D., Salt Lake City, Utah
SaPhenous vein grafts from the aorta to the coronary artery are being widely used to revascularize the ischemic myocardium.v 4, 10 These grafts will remain patent if there is distal run off. In a few patients with severe coronary atherosclerosis, the vessels are diseased to such an extent that no back flow is seen when an arteriotomy is done at the operating table. For these patients an alternative method for myocardial revascularization must be found. It is well known that coronary veins do not show atherosclerotic changes. The purpose of this study was to investigate the possibility of using the coronary vein that drains an ischemic area as a conduit for supplying arterial blood to the ischemic From the Division of Artificial Organs, Department of Surgery, and the Institute for Biomedical Engineering, University of Utah, Salt Lake City, Utah 84112. Supported in part by the National Institutes of Health via The National Heart and Lung Institute, Grant HL-13738, and by contributions to the Development Fund of the Division of Artificial Organs, among others, by Mrs. Mary Hercik, Received for publication July 3, 1973. Address for reprints: The Division of Artificial Organs, Building 518, Salt Lake City, Utah 84112.
myocardium. Preliminary studies in our laboratory were encouraging.': 15 This concept should not be confused with one proposed by Claude Beck." He recommended ligation of the coronary sinus and then arterialization, irrespective of the area of myocardial ischemia. With coronary angiography, the exact site of coronary artery disease can be determined. Thus it will be possible to arterialize the exact vein draining the ischemic area. The most crucial question is whether arterial blood delivered through the vein can, indeed, provide sufficient blood supply to the myocardium. If one first produces ischemic damage and then tries to repair it, one invites a number of difficulties and variables. Therefore, we took the opposite approach. We first tied off the artery and provided blood supply through the vein to the myocardium. We then proved that interruption of that blood supply resulted in ischemic damage. The efficacy of the oxygenated blood supply through the vein was evidenced by a normal S- T segment on the electrocardiogram, normal color of the heart
125
The Journol of
12 6
Bhayana et at.
Thorocic ond Cordiovosculor Surgery
CORONARY VEIN
LIGATED
Fig. 1. Technique of coronary vein perfusion with arterial blood from internal mammary artery.
muscle, normal contraction of the heart muscle, bright red color of the blood in the perfused vein, and actual measurement of the blood flow. After 1 hour of perfusion, when steady state was obtained, the flow into the vein was interrupted. The results were typical for ischemic damage to the pertaining area of the myocardium. Methods Sheep weighing from 62 to 72 kilograms were used. Anesthesia was induced by intravenous sodium methohexital* (5 mg. per kilogram of body weight) and scopolaminet (0.03 mg. per kilogram of body weight). An endotracheal tube was inserted and breathing was controlled with a pressurecycled respirator.j The left common carotid artery was cannulated for arterial pressure. The electrocardiogram and arterial pressure (with Statham pressure transducers§) were monitored on a multichannel Sanborn II recorder. Three sites were selected on the anterior surface of the left ventricle near the apex for epicardial electrocardiography. The electrodes were soldered wire loops, 4 mm. in diameter, and were sutured near the apex of the left ventricle. They were connected to *Brevane, Eli Lilly & Co., Indianapolis, Ind. tScopolamine hydrobrornide, Burroughs Wellcome & Co. (D. S. A.) Inc., Research Triangle Park, N. C. tBird Mark 10, the Bird Corporation Palm Springs. Calif. §Model dBd, Statham Instruments, Inc., Oxnard, Calif. [Model 7788 A, Hewlett-Packard, Division of Sanborn Co., Waltham, Mass.
the precordial terminal of a standard electrocardiograph, and the lead selector notch was in the V position. * Recordings were done at 1 mv. per millimeter, one tenth the electrocardiographic sensitivity that is used for external leads. The animals were divided into two groups. In the control group (6 sheep) only the left anterior descending artery was occluded. The artery was dissected near the middle of its course, at the point where it emerges from the myocardium. A heavy silk suture was passed around it and pulled through a tourniquet. Heparin, 2 mg. per kilogram of body weight, was given intravenously. Epicardial electrocardiograms were obtained before occlusion and then 5, 10, 15, and 20 minutes after occlusion. The tourniquet was removed, and epicardial electrocardiograms were recorded for 60 minutes after the arterial pressure had been stabilized to preocclusion level, by fluid infusion if necessary. Pressor drugs were not used. Maroko and colleagues" have shown that the magnitude of elevation of the S-T segment with epicardial electrodes correlates well with the depressed levels of myocardial creatine phosphokinase, and this is an indication of myocardial infarction. We used the magnitude of elevation of the S-T segment as an index of myocardial injury. In the second group of animals (23 sheep), the right internal mammary artery was dissected free and the left anterior descending coronary vein was surrounded with ligatures. A polyethylene catheter] of appropriate size was then introduced into the coronary vein after the proximal end had been ligated. After free flow of venous blood was obtained, the other end of the catheter was introduced into the internal mammary artery (Fig. 1). The anterior descending coronary artery was then ligated, and epicardial electrocardiograms were obtained every 5 minutes for the next 60 minutes. *Each electrocardiogram thus reflected potential differences between an epicardial electrode and a central terminal connection to right and left front and to left rear limb electrodes. tClay-Adams, Inc., Parsippany, New Jersey.
Volume 67
Myocardial ischemia
Number 1
1 27
January, 1974
t;
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.
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Fig. 4. Tracings from the same animal as in Fig. 3 after perfusion through the vein was stopped. ~ T segment elevation was present 10 and 20 minutes following termination of perfusion.
Table I. Flow studies 20
Animal No. 1 2
Fig. 2. S-T segment changes before ligation and 10 and 20 minutes after ligation of the coronary artery. The coronary vein was perfused.
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I Flow
range (c.c.Zmin .) 25-30 24-96 30-72 25-80 35-70 22-30 23-50
Legend : Range of flows recorded through mary artery during 60 minutes of coronary Flows varied with systemic blood pressure. artery was connected to the coronary vein , could flow only Into that vein .
internaJ mamvein perfusion . The mammary and the blood
Results
20
40
Fig. 3. Epicardial electrocardiograms from an animal with the left anterior descending artery ligated and the coronary vein perfused with arterial blood from the internal mammary artery. There is no elevation of SooT segment 10, 20, and 40 minutes after ligation of the artery C, Control.
The arterial pressure was monitored throughout the experiment and kept at preocclusion level. In a third group of 7 animals, flows through the internal mammary artery were measured during the 60 minutes of perfusion. We used electromagnetic flow probes and a direct readout recorder, * which was calibrated at the start of each experiment. 'Model SP 2206, Statham Instruments, Inc ., .Oxnard, Calif. Courtesy of Utah Biomedical Test Facility and Dr . Sam Topham .
Effects of occlusion of the left anterior descending coronary artery (control group). Following occlusion, an area of cyanosis with paradoxical motion was noted. The $-T segments in the electrograms were elevated over the control levels. The maximum changes were ' observed 20 minutes after occlusion (Fig. 2). Coronary vein perfusion group. Thirty animals were included in this group. Thirteen were not valid experiments due to technical problems. Electrograms only ·were done in 10 and flows were done in 7. In this group of animals, in which the coronary artery was occluded and the vein perfused with arterial blood from the internal mammary artery, several changes were seen: I. With the vein open but the artery occlud ed , an $-T segment elevation of only a few millimeters was noted in epicardial electrograrns when followed for up to 60 minutes after coronary occlusion (Fig; 3). Some $ - T segment elevation was present on the control electrocardiogram, presumably due
The Journal of Thoracic and Cardiovascular
Bhayana et at.
12 8
Surgery
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Fig. 5. Epicardial electrocardiograms from 10 animals showing the maximum S-T segment elevation occurring in each of three phases of the experiment. A, Control. B, After coronary artery ligation and during coronary vein perfusion. C, After termination of coronary vein perfusion. The artery remained ligated.
to myocardial injury associated with dissection of the artery and vein. After 60 minutes of perfusion, the cannula was clamped. The electrograms then showed elevation of the S-T segment similar to that seen in the control group when coronary artery ligation only was done (Fig. 4). Electrograms from 10 animals demonstrating maximal S-T segment elevation during the control period, coronary vein perfusion, and after termination of perfusion are shown in Fig. 5. 2. The usual cyanotic area at apex of the left ventricle, as seen in the control group, was absent. 3. Oxygenated blood could be visualized
Fig. 5. Coot'd. For legend, see opposite column.
in the coronary vein (Fig. 6), and contrasting venous blood could be seen when the internal mammary artery flow was interrupted (Fig. 7). 4. Flow studies were done in 7 animals and showed flow rates in the range of 20 C.c. to 90 c.c. per minute through the internal mammary artery (Table 1). The flow rate in each animal varied with the systemic blood pressure during the 60 minute observation period. Discussion
At present, direct methods of myocardial revascularization with saphenous vein grafts or internal mammary artery--coronary artery anastomosis are being widely used." Though the early results of saphenous
Fig. 6. Blood in the coronary vein is red, indicating origin from the internal mammary artery.
Fig. 7. With the perfusion cannula clamped, blood in the coronary vein that it is venous.
IS
blue, indicating
Volume 67 Number'1
Myocardial ischemia
131
January, 1974
vein graft procedures, including patency rates," flow rates.v ? and myocardial function studies," are extremely encouraging; these patients must be followed for a long time before the ultimate value of this operation can be proved. A number of problems, such as closure and intimal fibrosis in these grafts, are being noticed. The turbulence or flow related to use of a conduit of higher diameter than the natural coronary artery has been pointed out." Because of these problems, Green' proposed using the internal mammary artery as a conduit for arterial blood. Miller and associates> demonstrated the feasibility of using the internal mammary artery experimentally in 1959. The early results of this procedure are encouraging. Clinically it has been found that a number of patients have severely diseased distal coronary arteries. These patients have very low flows and high occlusion rates following saphenous vein graft procedures." We feel that in these patients the possibility of using the coronary vein as a conduit for arterial blood should be explored. We have utilized the technique of epicardial electrograms as an index of the extent and severity of myocardial ischemia.P A good correlation between the degree of S-T segment elevation and magnitude of myocardial ischemia has been pointed out by a number of workers.": 10 Sayen and his assocites'" found a good correlation between S-T segment elevation and intramyocardial oxygen tension after 5 minutes of coronary artery occlusion. It has also been pointed out that S-T segment elevation correlates well with depression of myocardial creatine phosphokinase activity. We found in these experiments that, if the left anterior descending coronary vein was perfused with arterial blood from the internal mammary artery, S-T segment changes were small compared to those associated with coronary artery ligation. If the perfusion was stopped, changes similar to those seen following corenary artery ligation alone were seen. These findings suggest that the myocardium receives oxygen from retro-
grade perfusion of the coronary vein with arterial blood. Similar findings in earlier experiments have been reported from this Iaboratory'> and also independently by Schultz and co-workers." Whether the coronary vein will show changes of sclerosis or atherosclerosis, as seen in saphenous vein grafts, is unknown. Long-term studies demonstrating patency of the internal mammary artery-coronary vein anastomosis and prevention of myocardial infarction are also necessary. REFERENCES
2 3
4 5
6
7 8
9
10
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