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Anatomical Studies to Support the Expanded Use of the Internal Mammary Artery Graft for Myocardial Revascularization
ORIGINAL ARTICLES
Anatomical Studies to Support the Expanded Use of the fiternal Mammary Artery Graft for Myocardial Revascularization R. W. Landymore, M.D., F.R.C.S.C., and D. M. Chapman, Ph.D. ABSTRACT The internal mammary artery pedicle graft is frequently used for coronary bypass. Five internal mammary artery pedicle grafts, harvested but not utilized for coronary bypass, underwent histological examination. The histological studies demonstrated that the vasa vasorum were confined to the adventitia and did not penetrate the media of the internal mammary artery. These observations indicate that the media is nourished entirely from the lumen and suggest that harvesting the internal mammary artery as a free graft would not subject the wall of the artery to ischemic injury. Subsequent to these studies, we used the right internal mammary artery as a free graft to revascularize the distal circumflex coronary artery in 12 patients. The free graft was anastomosed to marginal branches of the circumflex and was then brought up to the left internal mammary artery pedicle graft and anastomosed end-to-side. This procedure has not resulted in excessive postoperative bleeding or sternal infections, and has relieved the anginal syndrome in all 12 patients.
went histological examination. The proximal portion of one mammary graft was damaged during the dissection, and the remaining four pedicle grafts were of inadequate length to bypass the obstructed coronary artery. All five pedicle grafts with a few millimeters of surrounding tissue were fixed in phosphate-buffered formaldehyde. The specimens were dehydrated in an alcohol series, cleared in xylol, and embedded in paraffin. Transverse and longitudinal sections 10 pm thick were stained by a variety of methods to demonstrate the tissue elements. Mayer's hemalundaqueous eosin or eriochrome cyanine were used for red blood cells, and elastin distribution was shown by orcein counterstained with orange G. Collagen was demonstrated with saffron and smooth muscle cells, with phloxine B (substituting for erythrosin). Multiple transverse sections were obtained from each of the five internal mammary pedicle grafts. The distance from the lumen to the outer aspect of the media was measured at 100-pm intervals around the entire circumference of each arterial cross section with a Zeiss IBAS 1B semiautomatic image-analysis computer system
The internal mammary artery and segments of autologous vein are routinely used to revascularize the ischemic myocardium. However, both grafts used for coronary bypass procedures have definite limitations. The internal mammary artery has excellent long-term patency but is of insufficient length to bypass the distal right coronary circulation and inferior marginal branches of the circumflex coronary artery. Autologous vein grafts, alternatively, are not limited by length but have disappointing long-term patency because they develop progressive intimal hyperplasia and typical atherosclerotic lesions, which ultimately result in graft failure [l-31. This report describes histological studies of five internal mammary pedicle grafts and the clinical use of the internal mammary artery as a free graft in 12 patients with coronary insufficiency.
141.
Material and Methods
Histological Studies Five internal mammary artery pedicle grafts harvested but not utilized for myocardial revascularization underFrom the Departments of Surgery and Anatomy, Dalhousie University, Halifax, NS, Canada. Accepted for publication Dec 16, 1986. Address reprint requests to DT. Landymore, Room 3065, R. C. Dickson Centre, Victoria General Hospital, Halifax, NS, Canada B3H 2Y9.
4 Ann Thorac Surg 44:4-6,July 1987
Clinical Studies The left internal mammary artery pedicle graft and right internal mammary artery free graft were used in 12 patients undergoing myocardial revascularization. Both mammary arteries were utilized in 3 patients because of the lack of autologous veins. One of these 3 patients had bilateral varicose veins, 1 had previously had bilateral varicose veins stripped, and 1 had had both leg veins removed during an earlier coronary artery bypass procedure. The remaining 9 patients had extremely small coronary arteries, particularly in the circumflex distribution. We thought that the use of autologous vein grafts in these patients would have resulted in a marked size mismatch, which would undoubtedly have led to early graft failure. In each patient, the left internal mammary artery was harvested as a pedicle graft and the right internal mammary artery was harvested as a free graft. The left internal mammary artery pedicle graft was utilized in each patient to revascularize the anterior circulation, and the free graft was anastomosed to one or more marginal branches of the circumflex coronary artery, the proximal anastomosis being secured in an end-to-side fashion to the left internal mammary artery pedicle graft. This procedure is not any more technically demanding than the use of the internal mammary artery as a pedicle graft,
5 Landymore and Chapman: Expanded Use of IMA Graft for Myocardial Revascularization
relieved in all patients, and postoperative exercise testing has been carried out in 8 patients, all of whom have a normal functional capacity.
Comment
Cross section of the internal mammary artery. (L = lumen; J = junction between the adventitia and the outermost portion of the media; v = venule; a = arteriole.) ( X 250 before 54%reduction.)
and provides sufficient length to revascularize the entire circumflex coronary artery.
Results
Histological Studies Histolopal examination of the internal mammary artery specimens indicated that the vasa vasorum were confined to the adventitia and did not penetrate the medial layer of the artery (Figure). The distance from the lumen to the outermost portion of the media measured 200 2 67 pm (mean t the standard error of the mean) (1,567 measurements). A detailed study of the microanatomy of 1 internal mammary artery was conducted. The mean thickness of the endothelium and subendothelial collagen was 2.5 pm, the internal elastic lamina measured 2.5 pm, and the media measured 180 pm. There were nine other elastic layers, each measuring 1.3 pm. Collagen and smooth muscle cells were dispersed between the elastic layers. The adventitia, which abutted the surrounding fat, had a thickness of 100 pm and consisted of longitudinal collagen fibers and fine longitudinal elastin fibrils. Clinical Studies The right internal mammary artery free graft was utilized to revascularize the circumflex coronary artery in 3 women and 9 men ranging in age from 48 to 66 years (mean, 57 years). Three patients had New York Heart Association Functional Class IV angina, and the remaining 9 patients were experiencing Class I11 symptomatology. Both internal mammary arteries were used to revascularize the left coronary circulation in all 12 patients, and segments of autologous vein were used in 3 patients with right coronary artery disease; 2 of these patients required right coronary endarterectomy. The clamp time ranged from 55 to 87 minutes (mean, 66 minutes). All 12 patients made an uneventful recovery and have been followed from 1 month to 7 months (mean, 5.9 months). The anginal syndrome has been
Single and bilateral internal mammary artery pedicle grafts are now routinely used for coronary bypass. The long-term patency of the mammary graft far exceeds the patency of the autologous vein graft and is becoming the graft of choice for myocardial revascularization [5-71. Although the internal mammary artery is usually used to revascularize a single coronary artery, there are reports describing the use of the internal mammary artery graft as a sequential graft to bypass one or more obstructed coronary arteries [8-111. The expanded use of the internal mammary graft is not a new concept; more than 10 years ago, Barner [12], Loop and colleagues [13], Schimert and co-workers [14], and Cheanvechai and associates [15] described the use of the internal mammary artery as a free graft in the aortocoronary position. Gold and colleagues [16] discussed the use of the internal mammary artery as a free sequential graft. They anastomosed a right internal mammary artery free graft to the distal end of a left internal mammary artery pedicle graft to extend the artery’s length for revascularization of the inferior branches of the circumflex coronary artery. This procedure was performed because of the unavailability of autologous vein grafts. In 1986, Sauvage and colleagues [17] reported using the right internal mammary artery free graft as a sequential graft in 5 patients and successfully used bilateral free grafts in a further 5 patients. These patients have no residual functional disability and have been followed for 11 to 18 months. Although the internal mammary artery has been used for many years, there has been considerable reluctance to select this conduit routinely for myocardial revascularization because some earlier observations suggested that it might not provide sufficient blood flow to the myocardium [18]. Subsequent experimental data [19] refuted these earlier observations and demonstrated that the internal mammary artery is capable of supplying sufficient blood flow to support the entire left coronary circulation. Furthermore, Singh [20], Loop [5], and their co-workers indicated that the mammary artery frequently enlarges with time and is capable of increasing its caliber in response to the demands of the coronary vascular bed. Clinical use of the internal mammary artery as a sequential conduit to revascularize one or more coronary arteries has resulted in the complete relief of angina in the majority of patients [8-11, 171, thus dispelling the belief that this small artery is not capable of providing adequate blood flow to the ischemic myocardium. Our histological studies and our early clinical experience support the use of the internal mammary artery as a free sequential graft. Geiringer (211 examined 300 aortas and 100 left anterior descending coronary arteries. He found that the media of large arteries was nourished
6 The Annals of Thoracic Surgery Vol 44 No 1 July 1987
by the vasa vasorum and also by diffusion from the lumen of the vessel and that smaller arteries may be nourished entirely from the lumen and are not dependent on an external blood supply. The presence of vasa vasorum that penetrate into the media appears to be dependent on the thickness of the wall of the artery, which is related to the overall diameter of the blood vessel. Geiringer showed that the critical distance from the lumen to the outermost media of a muscular artery is in the range of 350 pm. Arteries with a wall thickness of greater than 350 pm have vasa vasorum that penetrate and nourish the media while thinner-walled arteries are nourished entirely from the lumen. The distance from the lumen to the outer media of the internal mammary artery specimens examined in this study was less than 300 pm, which is well below the critical wall thickness indicated by Geiringer. Furthermore, we found that the vasa vasorum were confined to the adventitia, and that there were no blood vessels within the media of the internal mammary artery specimens. Our observations suggest, therefore, that the internal mammary artery is nourished entirely from the lumen, a finding that indicates that the artery could be harvested as a free graft without risking ischemic injury to the arterial wall. The report by Cheanvechai and colleagues [15] supports our histological observations and demonstrated that the patency of the internal mammary artery free graft is 89.8% at a mean of 11months. Sauvage and associates [17] reported a patency of 100%in 10 patients followed for 11 to 18 months. There can be very little doubt that in the future, the internal mammary artery will be the conduit of choice for myocardial revascularization. This artery appears to be capable of providing adequate flow for complete revascularization, is relatively immune to the development of atherosclerosis, and has excellent long-term patency. Our histological studies add further evidence to support the expanded use of this conduit to completely revascularize the ischemic myocardium.
References Geha A, Baue A: Early and late results of coronary revascularization with saphenous vein and internal mammary grafts. Am J Surg 137:456, 1979 Lytle B, Loop F, Thurer R, et al: Isolated left anterior descending coronary atherosclerosis: long-term comparison of internal mammary artery and venous autografts. Circulation 615369, 1980 Campeau L, Enjalbert M, Lesperance J, Bourassa MG: Arteriosclerosis and late closure of aortocoronary saphenous vein grafts: sequential angiographic studies 1 year, 5-7
years, and 10-12 years after surgery (abstract). Circulation 66:Suppl 294, 1982 4. Landymore RW, MacAulay M, Sheridan B, Cameron C: Comparison of cod-liver oil and aspirin-dipyridamole for the prevention of intimal hyperplasia in autologous vein grafts. Ann Thorac Surg 41:54, 1986 5. Loop F, Lytle B, Cosgrove D, et al: Influence of the internal mammary artery graft on 10 year survival and other cardiac events. N Engl J Med 314:1, 1986 6. Barner H, Standeven J, Reese J: Twelve-year experience with internal mammary artery for coronary artery bypass. J Thorac Cardiovasc Surg 90:668, 1985 7. Spencer FC: The internal mammary artery: the ideal coronary bypass graft? N Engl J Med 314:50, 1986 8. Kabbani SS, Hanna ES, Bashour TT, et al: Sequential internal mammary-coronary artery bypass. J Thorac Cardiovasc Surg 86:697, 1983 9. McBride LR, Barner HB: The left internal artery as a sequential graft to the left anterior descending system. J Thorac Cardiovasc Surg 86:703, 1983 10. Geha AS: Crossed double internal mammary to coronary artery grafts: indications, techniques and results. Arch Surg 111:289, 1976 11. Tector AJ, Schmahl TM: Techniques for multiple internal mammary artery bypass grafts. Ann Thorac Surg 38:281, 1984 12. Bamer H. The internal mammary artery as a free graft. J Thorac Cardiovasc Surg 66219, 1973 13. Loop FD, Spampinato N, Cheanvechai C, Effler DB: The free internal mammary artery bypass graft. Ann Thorac Surg 15:50, 1973 14. Schimert G, Vidne BA, Lee AB Jr: Free internal mammary artery graft: an improved surgical technique. Ann Thorac Surg 19:474, 1975 15. Cheanvechai C, Irarrazaval M, Loop F, et al: Aortacoronary bypass grafting with the internal mammary artery. J Thorac Cardiovasc Surg 70:278, 1975 16. Gold J, Shemin R, DiSesa V, et al: Multiple-vessel coronary revascularization with combined in-situ and free sequential internal mammary arteries. J Thorac Cardiovasc Surg 90:301, 1985 17. Sauvage LR, Wu H-D, Kowalsky TE, et al: Healing basis and surgical techniques for complete revascularization of the left ventricle using only the internal mammary arteries. Ann Thorac Surg 42449, 1986 18. Flemma RJ, Singh HM, Tector AJ, et al: Comparative hemodynamic properties of vein and mammary artery in coronary bypass operations. Ann Thorac Surg 20:619, 1975 19. Lee C, Orszulak T, Schaff H, Kaye M: Flow capacity of the canine internal mammary artery. J Thorac Cardiovasc Surg 91:405, 1986 20. Singh RN, Sosa JA: Internal mammary artery: a live conduit for coronary bypass. J Thorac Cardiovasc Surg 87:936, 1984 21. Geiringer E: Intimal vascularization and atherosclerosis. J Pathol Bacteriol 63901, 1951
Anatomical Studies to Support the Expanded Use of the fiternal Mammary Artery Graft for Myocardial Revascularization R. W. Landymore, M.D., F.R.C.S.C., and D. M. Chapman, Ph.D. ABSTRACT The internal mammary artery pedicle graft is frequently used for coronary bypass. Five internal mammary artery pedicle grafts, harvested but not utilized for coronary bypass, underwent histological examination. The histological studies demonstrated that the vasa vasorum were confined to the adventitia and did not penetrate the media of the internal mammary artery. These observations indicate that the media is nourished entirely from the lumen and suggest that harvesting the internal mammary artery as a free graft would not subject the wall of the artery to ischemic injury. Subsequent to these studies, we used the right internal mammary artery as a free graft to revascularize the distal circumflex coronary artery in 12 patients. The free graft was anastomosed to marginal branches of the circumflex and was then brought up to the left internal mammary artery pedicle graft and anastomosed end-to-side. This procedure has not resulted in excessive postoperative bleeding or sternal infections, and has relieved the anginal syndrome in all 12 patients.
went histological examination. The proximal portion of one mammary graft was damaged during the dissection, and the remaining four pedicle grafts were of inadequate length to bypass the obstructed coronary artery. All five pedicle grafts with a few millimeters of surrounding tissue were fixed in phosphate-buffered formaldehyde. The specimens were dehydrated in an alcohol series, cleared in xylol, and embedded in paraffin. Transverse and longitudinal sections 10 pm thick were stained by a variety of methods to demonstrate the tissue elements. Mayer's hemalundaqueous eosin or eriochrome cyanine were used for red blood cells, and elastin distribution was shown by orcein counterstained with orange G. Collagen was demonstrated with saffron and smooth muscle cells, with phloxine B (substituting for erythrosin). Multiple transverse sections were obtained from each of the five internal mammary pedicle grafts. The distance from the lumen to the outer aspect of the media was measured at 100-pm intervals around the entire circumference of each arterial cross section with a Zeiss IBAS 1B semiautomatic image-analysis computer system
The internal mammary artery and segments of autologous vein are routinely used to revascularize the ischemic myocardium. However, both grafts used for coronary bypass procedures have definite limitations. The internal mammary artery has excellent long-term patency but is of insufficient length to bypass the distal right coronary circulation and inferior marginal branches of the circumflex coronary artery. Autologous vein grafts, alternatively, are not limited by length but have disappointing long-term patency because they develop progressive intimal hyperplasia and typical atherosclerotic lesions, which ultimately result in graft failure [l-31. This report describes histological studies of five internal mammary pedicle grafts and the clinical use of the internal mammary artery as a free graft in 12 patients with coronary insufficiency.
141.
Material and Methods
Histological Studies Five internal mammary artery pedicle grafts harvested but not utilized for myocardial revascularization underFrom the Departments of Surgery and Anatomy, Dalhousie University, Halifax, NS, Canada. Accepted for publication Dec 16, 1986. Address reprint requests to DT. Landymore, Room 3065, R. C. Dickson Centre, Victoria General Hospital, Halifax, NS, Canada B3H 2Y9.
4 Ann Thorac Surg 44:4-6,July 1987
Clinical Studies The left internal mammary artery pedicle graft and right internal mammary artery free graft were used in 12 patients undergoing myocardial revascularization. Both mammary arteries were utilized in 3 patients because of the lack of autologous veins. One of these 3 patients had bilateral varicose veins, 1 had previously had bilateral varicose veins stripped, and 1 had had both leg veins removed during an earlier coronary artery bypass procedure. The remaining 9 patients had extremely small coronary arteries, particularly in the circumflex distribution. We thought that the use of autologous vein grafts in these patients would have resulted in a marked size mismatch, which would undoubtedly have led to early graft failure. In each patient, the left internal mammary artery was harvested as a pedicle graft and the right internal mammary artery was harvested as a free graft. The left internal mammary artery pedicle graft was utilized in each patient to revascularize the anterior circulation, and the free graft was anastomosed to one or more marginal branches of the circumflex coronary artery, the proximal anastomosis being secured in an end-to-side fashion to the left internal mammary artery pedicle graft. This procedure is not any more technically demanding than the use of the internal mammary artery as a pedicle graft,
5 Landymore and Chapman: Expanded Use of IMA Graft for Myocardial Revascularization
relieved in all patients, and postoperative exercise testing has been carried out in 8 patients, all of whom have a normal functional capacity.
Comment
Cross section of the internal mammary artery. (L = lumen; J = junction between the adventitia and the outermost portion of the media; v = venule; a = arteriole.) ( X 250 before 54%reduction.)
and provides sufficient length to revascularize the entire circumflex coronary artery.
Results
Histological Studies Histolopal examination of the internal mammary artery specimens indicated that the vasa vasorum were confined to the adventitia and did not penetrate the medial layer of the artery (Figure). The distance from the lumen to the outermost portion of the media measured 200 2 67 pm (mean t the standard error of the mean) (1,567 measurements). A detailed study of the microanatomy of 1 internal mammary artery was conducted. The mean thickness of the endothelium and subendothelial collagen was 2.5 pm, the internal elastic lamina measured 2.5 pm, and the media measured 180 pm. There were nine other elastic layers, each measuring 1.3 pm. Collagen and smooth muscle cells were dispersed between the elastic layers. The adventitia, which abutted the surrounding fat, had a thickness of 100 pm and consisted of longitudinal collagen fibers and fine longitudinal elastin fibrils. Clinical Studies The right internal mammary artery free graft was utilized to revascularize the circumflex coronary artery in 3 women and 9 men ranging in age from 48 to 66 years (mean, 57 years). Three patients had New York Heart Association Functional Class IV angina, and the remaining 9 patients were experiencing Class I11 symptomatology. Both internal mammary arteries were used to revascularize the left coronary circulation in all 12 patients, and segments of autologous vein were used in 3 patients with right coronary artery disease; 2 of these patients required right coronary endarterectomy. The clamp time ranged from 55 to 87 minutes (mean, 66 minutes). All 12 patients made an uneventful recovery and have been followed from 1 month to 7 months (mean, 5.9 months). The anginal syndrome has been
Single and bilateral internal mammary artery pedicle grafts are now routinely used for coronary bypass. The long-term patency of the mammary graft far exceeds the patency of the autologous vein graft and is becoming the graft of choice for myocardial revascularization [5-71. Although the internal mammary artery is usually used to revascularize a single coronary artery, there are reports describing the use of the internal mammary artery graft as a sequential graft to bypass one or more obstructed coronary arteries [8-111. The expanded use of the internal mammary graft is not a new concept; more than 10 years ago, Barner [12], Loop and colleagues [13], Schimert and co-workers [14], and Cheanvechai and associates [15] described the use of the internal mammary artery as a free graft in the aortocoronary position. Gold and colleagues [16] discussed the use of the internal mammary artery as a free sequential graft. They anastomosed a right internal mammary artery free graft to the distal end of a left internal mammary artery pedicle graft to extend the artery’s length for revascularization of the inferior branches of the circumflex coronary artery. This procedure was performed because of the unavailability of autologous vein grafts. In 1986, Sauvage and colleagues [17] reported using the right internal mammary artery free graft as a sequential graft in 5 patients and successfully used bilateral free grafts in a further 5 patients. These patients have no residual functional disability and have been followed for 11 to 18 months. Although the internal mammary artery has been used for many years, there has been considerable reluctance to select this conduit routinely for myocardial revascularization because some earlier observations suggested that it might not provide sufficient blood flow to the myocardium [18]. Subsequent experimental data [19] refuted these earlier observations and demonstrated that the internal mammary artery is capable of supplying sufficient blood flow to support the entire left coronary circulation. Furthermore, Singh [20], Loop [5], and their co-workers indicated that the mammary artery frequently enlarges with time and is capable of increasing its caliber in response to the demands of the coronary vascular bed. Clinical use of the internal mammary artery as a sequential conduit to revascularize one or more coronary arteries has resulted in the complete relief of angina in the majority of patients [8-11, 171, thus dispelling the belief that this small artery is not capable of providing adequate blood flow to the ischemic myocardium. Our histological studies and our early clinical experience support the use of the internal mammary artery as a free sequential graft. Geiringer (211 examined 300 aortas and 100 left anterior descending coronary arteries. He found that the media of large arteries was nourished
6 The Annals of Thoracic Surgery Vol 44 No 1 July 1987
by the vasa vasorum and also by diffusion from the lumen of the vessel and that smaller arteries may be nourished entirely from the lumen and are not dependent on an external blood supply. The presence of vasa vasorum that penetrate into the media appears to be dependent on the thickness of the wall of the artery, which is related to the overall diameter of the blood vessel. Geiringer showed that the critical distance from the lumen to the outermost media of a muscular artery is in the range of 350 pm. Arteries with a wall thickness of greater than 350 pm have vasa vasorum that penetrate and nourish the media while thinner-walled arteries are nourished entirely from the lumen. The distance from the lumen to the outer media of the internal mammary artery specimens examined in this study was less than 300 pm, which is well below the critical wall thickness indicated by Geiringer. Furthermore, we found that the vasa vasorum were confined to the adventitia, and that there were no blood vessels within the media of the internal mammary artery specimens. Our observations suggest, therefore, that the internal mammary artery is nourished entirely from the lumen, a finding that indicates that the artery could be harvested as a free graft without risking ischemic injury to the arterial wall. The report by Cheanvechai and colleagues [15] supports our histological observations and demonstrated that the patency of the internal mammary artery free graft is 89.8% at a mean of 11months. Sauvage and associates [17] reported a patency of 100%in 10 patients followed for 11 to 18 months. There can be very little doubt that in the future, the internal mammary artery will be the conduit of choice for myocardial revascularization. This artery appears to be capable of providing adequate flow for complete revascularization, is relatively immune to the development of atherosclerosis, and has excellent long-term patency. Our histological studies add further evidence to support the expanded use of this conduit to completely revascularize the ischemic myocardium.
References Geha A, Baue A: Early and late results of coronary revascularization with saphenous vein and internal mammary grafts. Am J Surg 137:456, 1979 Lytle B, Loop F, Thurer R, et al: Isolated left anterior descending coronary atherosclerosis: long-term comparison of internal mammary artery and venous autografts. Circulation 615369, 1980 Campeau L, Enjalbert M, Lesperance J, Bourassa MG: Arteriosclerosis and late closure of aortocoronary saphenous vein grafts: sequential angiographic studies 1 year, 5-7
years, and 10-12 years after surgery (abstract). Circulation 66:Suppl 294, 1982 4. Landymore RW, MacAulay M, Sheridan B, Cameron C: Comparison of cod-liver oil and aspirin-dipyridamole for the prevention of intimal hyperplasia in autologous vein grafts. Ann Thorac Surg 41:54, 1986 5. Loop F, Lytle B, Cosgrove D, et al: Influence of the internal mammary artery graft on 10 year survival and other cardiac events. N Engl J Med 314:1, 1986 6. Barner H, Standeven J, Reese J: Twelve-year experience with internal mammary artery for coronary artery bypass. J Thorac Cardiovasc Surg 90:668, 1985 7. Spencer FC: The internal mammary artery: the ideal coronary bypass graft? N Engl J Med 314:50, 1986 8. Kabbani SS, Hanna ES, Bashour TT, et al: Sequential internal mammary-coronary artery bypass. J Thorac Cardiovasc Surg 86:697, 1983 9. McBride LR, Barner HB: The left internal artery as a sequential graft to the left anterior descending system. J Thorac Cardiovasc Surg 86:703, 1983 10. Geha AS: Crossed double internal mammary to coronary artery grafts: indications, techniques and results. Arch Surg 111:289, 1976 11. Tector AJ, Schmahl TM: Techniques for multiple internal mammary artery bypass grafts. Ann Thorac Surg 38:281, 1984 12. Bamer H. The internal mammary artery as a free graft. J Thorac Cardiovasc Surg 66219, 1973 13. Loop FD, Spampinato N, Cheanvechai C, Effler DB: The free internal mammary artery bypass graft. Ann Thorac Surg 15:50, 1973 14. Schimert G, Vidne BA, Lee AB Jr: Free internal mammary artery graft: an improved surgical technique. Ann Thorac Surg 19:474, 1975 15. Cheanvechai C, Irarrazaval M, Loop F, et al: Aortacoronary bypass grafting with the internal mammary artery. J Thorac Cardiovasc Surg 70:278, 1975 16. Gold J, Shemin R, DiSesa V, et al: Multiple-vessel coronary revascularization with combined in-situ and free sequential internal mammary arteries. J Thorac Cardiovasc Surg 90:301, 1985 17. Sauvage LR, Wu H-D, Kowalsky TE, et al: Healing basis and surgical techniques for complete revascularization of the left ventricle using only the internal mammary arteries. Ann Thorac Surg 42449, 1986 18. Flemma RJ, Singh HM, Tector AJ, et al: Comparative hemodynamic properties of vein and mammary artery in coronary bypass operations. Ann Thorac Surg 20:619, 1975 19. Lee C, Orszulak T, Schaff H, Kaye M: Flow capacity of the canine internal mammary artery. J Thorac Cardiovasc Surg 91:405, 1986 20. Singh RN, Sosa JA: Internal mammary artery: a live conduit for coronary bypass. J Thorac Cardiovasc Surg 87:936, 1984 21. Geiringer E: Intimal vascularization and atherosclerosis. J Pathol Bacteriol 63901, 1951