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Progression of obstructive coronary artery disease after implantation of aorto-coronary saphenous vein bypass grafts
Progression of obstructive coronary artery disease after implantation of aorto-coronary saphenous vein bypass grafts Nineteen subjects with a total of 33 aorto-coronary saphenous vein bypass grafts were subjected to coronary and bypass graft angiography an average of 102 days after operation. There was a significant progression of coronary artery disease in both bypassed and nonbypassed coronary arteries. Net progression of disease was similar in both bypassed (/6 ± 12 per cent) and nonbypassed (12 ± 24 per cent) coronary arteries (p > 0.4). There was no significant difference between the mean net progression of disease in coronary arteries with patent grafts (16 ± 12 pel' cent) and those arteries with nonpatent grafts (/6 ± 13 per cent) (p > 0.8). We conclude that the progression of coronary arterial disease in patients subjected to the saphenous vein bypass procedures is a manifestation of the natural history of coronary artery disease and is rarely influenced per se by graft implantation.
Alberto Benchimol, M.D., F.A.C.C., Charles L. Harris, M.D., Harold Fleming, M.D., and Kenneth B. Desser, M.D., Phoenix, Ariz.
Rogression of obstructive atherosclerotic coronary arterial disease in subjects with aorto-coronary saphenous vein bypass grafts has recently been demonstrated by means of postoperative selective coronary arteriography.' As a result of these findings, some investigators have proposed that implantation of the aorto-coronary bypass graft may actually accelerate occlusive disease in the coronary circulation. We reported here a detailed analysis of the progression of coronary arterial disease in patients with aortocoronary saphenous bypass grafts. From the Institute for Cardiovascular Diseases. Good Samaritan Hospital, 1033 East McDowell Road, Phoenix, Ariz. 85006. Supported in part by the Nichols Memorial Fund. Received for publication April I, 1974. Address for reprints: Alberto Benchimol, M.D., Good Samaritan Hospital, P. O. Box 2989, Phoenix, Ariz. 85062.
Material and method
Nineteen subjects comprised the study group. There were I 8 men and 1 woman whose ages ranged from 34 to 62 with a mean of 51 years. All patients underwent implantation of aorto-coronary bypass grafts for angina pectoris considered refractory to treatment with coronary vasodilators, beta blocking agents, and other medication. Because 13 patients had multiple grafts, a total of 33 individual grafts were available for study. Aorto-coronary bypass of the right, left anterior descending, and left circumflex arteries was performed according to established technique. No subject underwent local or gas endarterectomy of the coronary arteries. The average time interval from initial coronary cineangiography to the operation was 26 days. The average postoperative interval from the day of operation to the
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date of restudy was 102 days. The mean interval from the date of the preoperative to postoperative study was 128 days. Selective coronary and aorto-coronary graft cineangiography was performed by the Sones technique with 75 per cent Hypaque. In addition to cineangiographic evaluation (fifty frames per second), rapid-sequence 14 by 14 inch roentgenograms of coronary arteries and grafts were obtained at a speed of six exposures per second during injection. Both the coronary arteries and the grafts were opacified in the right anterior and left anterior oblique projections, and an average of twelve coronary injections was performed in each patient. Aorto-coronary bypass grafts were considered patent if they were visualized during aortic root or selective opacification. For the purposes of this study, grafts were considered "definitely" occluded when a proximal segment of the saphenous vein was seen; they were "possibly" occluded if the grafts were not visualized during aortic root angiography, could not be selectively entered, or were not seen when the native coronary artery was filled in a antegrade or retrograde fashion. Coronary arteriograms were examined by three experienced cardiologists who carefully estimated the crosssectional diameter of partially occluded major vessels at the site of greatest luminal compromise. This diameter was then compared with a similar measurement in the proximal portion of the coronary artery, which was free of occlusive disease. In this manner, the per cent occlusion of a vessel was assessed and the preoperative and postoperative angiograms compared. A coronary artery was considered completely occluded if there was complete luminal obstruction during coronary arteriography and, if present, blockage of retrograde filling during aorto-coronary graft angiography. Results Aorto-coronary grafts. The anatomic distribution of bypass grafts was as follows: right coronary, 17; left anterior descending,
Thoracic and Cardiovascular Surgery
11; and left circumflex,S. Twenty-five (76 per cent) grafts were patent on postoperative study. Coronary arteries. The distal segments of three major coronary arteries were occluded prior to graft implantation. Of the 30 remaining bypassed coronary arteries, progression of disease rendered 15 (50 per cent) completely occluded (Fig. 1). Of 24 major coronary arteries which were not bypassed, 3 were completely occluded at the initial angiographic study. Disease in 3 of the 21 remaining, nonbypassed coronary arteries (14 per cent) progressed to 100 per cent obstruction. However, the degree of initial disease in those coronary arteries which were subsequently bypassed was greater than that in those arteries not operated upon; this comparison excludes arteries which were already occluded and therefore could not "progress" in terms of meaningful disease (mean per cent coronary obstruction ± 1 standard deviation prior to the operation: bypassed 76 ± 15 per cent, nonbypassed 42 ± 33 per cent [p < 0.001]). The extent of coronary arterial obstruction was similarly greater after operation in the bypassed arteries than in those vessels which did not receive grafts (per cent coronary obstruction after operation: bypassed 92 ± 10 per cent, nonbypassed 54 ± 35 per cent [p < 0.001]). Thus, there was significant progression of disease in both bypassed and nonbypassed native coronary arteries. The mean per cent obstruction in bypassed arteries was 76 ± 15 per cent before surgery and 92 ± 10 per cent (p < 0.001) after surgery. In nonbypassed arteries, the mean per cent. obstruction was 42 ± 33 per cent before surgery and 54 ± 35 per cent (p < 0.05) after surgery (Fig. 2). Net per cent progression in native coronary arteries. Twenty-four of 30 coronary arteries (70 per cent) which were bypassed became more obstructed. The average degree of progression in the 30 arteries as a group was 16 ± 12 per cent. Six of 21 patent, nonbypassed coronary arteries (29 per cent) were initially free of demonstrable disease.
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Fig. 1. Preoperative and postoperative selective coronary cineangiograms in the right and left anterior oblique projections. The patient was a 57-year-old man with coronary artery disease who underwent bypass grafting to the right coronary artery and left anterior descending coronary artery. Bottom panels demonstrate the selective aorto-coronary graft angiograms. Distal branches of the right coronary artery (RCA) developed complete obstruction in the interval between the two studies. Disease in the left anterior descending branch of the left coronary artery (LCA) progressed from 80 per cent obstruction to complete occlusion. The arrows in line drawings of the left coronary artery indicate the site of complete occlusion.
The development of coronary arterial disease was noted in 2 of the original 6 arteries after operation. One patient developed a 40 per cent localized luminal narrowing in a vessel previously free of disease. A 62-year-old man with grafts to the left anterior descending and left circumflex arteries later developed a new 100 per cent occlusion of the right coronary artery. The new occlusion was noted 8 months after the initial postoperative study. This zero to 100 per cent progression was the most striking change noted in the entire study group. Without the benefit of pathological study, it is impossible to designate this occlusion as a rapidly developing plaque or thrombosis arising as a result of the operation. Ten of 14 (71 per cent) nonbypassed coronary
arteries which were diseased on the preoperative arteriograms did not demonstrate progression of disease. Including the zero to 100 per cent occlusion described previously, there was no significant difference between the mean net per cent progression observed in bypassed and nonbypassed coronary arteries (bypassed 16 ± 12 per cent, nonbypassed 12 ± 24 per cent [p > 0.4]). Exclusion of the 100 per cent occlusion observed in the nonbypassed group resulted in a small but significant difference between the mean net per cent progression noted in the nonbypassed and the bypassed arteries (bypassed 16 ± 12 per cent, nonbypassed 7 ± 14 per cent [p < 0.05]). Progression of disease in coronary arteries with patent grafts and nonpatent grafts (pus-
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sibly or definitely occluded). The degree of coronary artery disease was significantly greater both before and after surgery in those vessels with patent grafts (before surgery: patent 80 ± 13 per cent and nonpatent 66 ± 16 per cent [p < 0.05]; after surgery: patent 96 ± 7 per cent and nonpatent 81 ± 13 per cent [p < 0.001]). The progression of disease in bypassed coronary arteries, both patent and nonpatent, was significant (patent: before surgery 80 ± 13 per cent and after surgery 96 ± 7 per cent [p < 0.001]; nonpatent: before surgery 66 ± 16 per cent and after surgery 81 ± 13 per cent [p < 0.02]). Interestingly, there was no significant difference between the net per cent progression in coronary arteries with patent and nonpatent grafts (patent 16 ± 12 per cent, nonpatent 15 ± 13 per cent, p > 0.8). Disease in 14 of 23 (61 per cent) coronary arteries bypassed with patent grafts progressed to 100 per cent occlusion. Only 1 of 7 arteries with non patent grafts was completely occluded on postoperative study. Discussion
Most investigations relating to aorto-coronary bypass grafts have engendered a certain degree of controversy and confusion. This latter appraisal can be amply applied to existing data on progressive disease in the native coronary circulation after operative intervention. Implicit in any discussion of the problem is the following question: Is the net per cent increase of disease in bypassed coronary arteries any different from that in arteries not bypassed in the same subject or that in subjects not operated upon? The initial study by Aldridge and Trimble! demonstrated progression of pre-existing coronary artery disease after implantation of bypass grafts. Of 8 coronary arteries with patent bypass grafts, 5 were noted to have developed total occlusion. No mention was made concerning progression of disease in nonbypassed native coronary arteries. Bousvaros and colleagues" provided findings in 4 patients who had 6 aorto-coronary bypass
Thoracic and Cardiovascular Surgery
grafts. Postoperative injection of 5 vessels that had previously been incompletely stenosed demonstrated complete occlusion when dye was introduced in an antegrade fashion. In 2 patients, however, graft opacification produced retrograde flow of dye up to and beyond the point of "obstruction" noted during standard arteriography. In their extensive review of the clinical response to bypass graft implantation, Alderman and associates" noted progression of pre-existing coronary artery disease as an incidental finding in 12 subjects. This acceleration of disease was noted in both bypassed and nonbypassed vessels. Griffith and co-workers I noted a 30 per cent incidence of progression of disease to total occlusion in bypassed coronary arteries with both patent and occluded grafts. The method for postoperative evaluation of coronary artery disease used by the latter authors reflected that reported in the existing literature, i.e., consideration of 50 or 100 per cent lumen obstruction. Since it is probable that luminal encroachment by atherosclerosis is a dynamic process which can occur in varying degrees, we accepted any decrease of lumen diameter as evidence of progression. Furthermore, the net progression of the occlusive process appeared to be a reasonable method for comparing the effects of the grafts per se on the native coronary circulation. This net measurement in no way assumes that the velocities of occlusive processes are stable; however, it does in part allow a more realistic comparison of the progression of disease in different arteries. On comparing the evolution of disease in the bypassed and nonbypassed coronary circulations, we found that the net increments of occlusion were comparable. The high prevalence of total occlusions in the bypassed group was a reflection of more severe preexisting disease. Exclusion of a single patient, in whom 100 per cent occlusion may have represented thrombosis, resulted in only a small difference (9 per cent) in net occlusive progression between the bypassed
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Fig. 2. Preoperative and postoperative selective coronary cineangiograms in a 56-year-old man with coronary artery disease who underwent aorto-right coronary artery bypass. Panels A and C demonstrate progression of disease in the left circumflex coronary artery (LC) from 40 to 80 per cent obstruction. Panels Band D show progression of 90 per cent obstruction to complete occlusion of the right coronary artery (RCA). Panel E shows the right graft angiogram.
and nonbypassed groups. Furthermore, the net per cent progression of disease in bypassed coronary arteries was identical in both patent and nonpatent groups. The total number of complete coronary occlusions was weighted in favor of the patent graft group , because those patients had more extensive disease before surgery. Utilizing serial coronary arteriography, Bemis and colleagues" have recently demonstrated that 52 per cent of their patients with coronary artery disease and no coronary grafts exhibited evidence of progression of the coronary arterial lesion. A 20 per cent decrease of luminal diameter was required as a requisite for progression. At this level of progression, their results are in accord with those described herein ; presumably, the number of subjects with progression might have been higher if lesser degrees of luminal reduction had been accepted . The findings presented in this study offer no basis for invoking pressure differentials, surgical manipulation of severely diseased coronary arteries, intraoperative myocardial infarction," or the duration of anoxic arrest
as mechanisms resulting in the progression of native coronary artery disease in our patients with aorto-coronary bypass grafts. In the overwhelming majority of subjects, the natural history of coronary artery disease would appear to be the most reasonable explanation for such progression . The more severe the pre-existing coronary artery disease, the more likely is the possibility that the lesion will progress to 100 per cent occlusion.. It is possible that functioning grafts permit longer survival into the postoperative period, with a higher prevalence of 100 per cent occlusion seen on follow-up angiographic study. REFERENCES Aldridge, H. E., and Trimble, A. S.: Progression of Proximal Coronary Artery Lesions to Total Occlusion After Aorta-Coronary Saphenous Vein Bypass Grafting, J. THORAC. CARDIOVASC. SURG. 62: 7, 1971. 2 Bousvaros, G., Chaudhry, M. A ., and Piracha, A. R.: Progression of Proximal Coronary Arterial Lesions to Total Occlusion After Vein Graft Surgery and Its Effects, Am . J. CardioI. 29: 255, 1972. 3 Alderman, E. i..., Matlof, H. J., Wexler, L.,
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The Journal 01 Thoracic and Cardiovascular Surgery
Shumway, N. E., and Harrison, D. C.: Results of Direct Coronary-Artery Surgery for the Treatment of Angina Pectoris, N. Engl. J. Med. 288: 535, 1973. 4 Griffith, L. S. C., Achuff, S. C., Conti, C. R., Humphries, J. 0., Brawley, R. K., Gott, V. L., and Ross, R. S.: Changes in Intrinsic Coronary Circulation and Segmental Ventricular Motion After Saphenous-Vein Coronary Bypass Graft Surgery, N. EngI. 1. Med. 288: 589, 1973.
5 Bemis, C. E., Gorlin, R., Kemp, H. G., and Herman, M. Y.: Progression of Coronary Artery Disease. A Clinical Arteriographic Study, Circulation 47: 455, 1973: 6 Brewer, D. L., Bilbro, R. H., and Bartel, A. G.: Myocardial Infarction as a Complication of Coronary Bypass Surgery, Circulation 47: 58, 1973.
Alberto Benchimol, M.D., F.A.C.C., Charles L. Harris, M.D., Harold Fleming, M.D., and Kenneth B. Desser, M.D., Phoenix, Ariz.
Rogression of obstructive atherosclerotic coronary arterial disease in subjects with aorto-coronary saphenous vein bypass grafts has recently been demonstrated by means of postoperative selective coronary arteriography.' As a result of these findings, some investigators have proposed that implantation of the aorto-coronary bypass graft may actually accelerate occlusive disease in the coronary circulation. We reported here a detailed analysis of the progression of coronary arterial disease in patients with aortocoronary saphenous bypass grafts. From the Institute for Cardiovascular Diseases. Good Samaritan Hospital, 1033 East McDowell Road, Phoenix, Ariz. 85006. Supported in part by the Nichols Memorial Fund. Received for publication April I, 1974. Address for reprints: Alberto Benchimol, M.D., Good Samaritan Hospital, P. O. Box 2989, Phoenix, Ariz. 85062.
Material and method
Nineteen subjects comprised the study group. There were I 8 men and 1 woman whose ages ranged from 34 to 62 with a mean of 51 years. All patients underwent implantation of aorto-coronary bypass grafts for angina pectoris considered refractory to treatment with coronary vasodilators, beta blocking agents, and other medication. Because 13 patients had multiple grafts, a total of 33 individual grafts were available for study. Aorto-coronary bypass of the right, left anterior descending, and left circumflex arteries was performed according to established technique. No subject underwent local or gas endarterectomy of the coronary arteries. The average time interval from initial coronary cineangiography to the operation was 26 days. The average postoperative interval from the day of operation to the
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date of restudy was 102 days. The mean interval from the date of the preoperative to postoperative study was 128 days. Selective coronary and aorto-coronary graft cineangiography was performed by the Sones technique with 75 per cent Hypaque. In addition to cineangiographic evaluation (fifty frames per second), rapid-sequence 14 by 14 inch roentgenograms of coronary arteries and grafts were obtained at a speed of six exposures per second during injection. Both the coronary arteries and the grafts were opacified in the right anterior and left anterior oblique projections, and an average of twelve coronary injections was performed in each patient. Aorto-coronary bypass grafts were considered patent if they were visualized during aortic root or selective opacification. For the purposes of this study, grafts were considered "definitely" occluded when a proximal segment of the saphenous vein was seen; they were "possibly" occluded if the grafts were not visualized during aortic root angiography, could not be selectively entered, or were not seen when the native coronary artery was filled in a antegrade or retrograde fashion. Coronary arteriograms were examined by three experienced cardiologists who carefully estimated the crosssectional diameter of partially occluded major vessels at the site of greatest luminal compromise. This diameter was then compared with a similar measurement in the proximal portion of the coronary artery, which was free of occlusive disease. In this manner, the per cent occlusion of a vessel was assessed and the preoperative and postoperative angiograms compared. A coronary artery was considered completely occluded if there was complete luminal obstruction during coronary arteriography and, if present, blockage of retrograde filling during aorto-coronary graft angiography. Results Aorto-coronary grafts. The anatomic distribution of bypass grafts was as follows: right coronary, 17; left anterior descending,
Thoracic and Cardiovascular Surgery
11; and left circumflex,S. Twenty-five (76 per cent) grafts were patent on postoperative study. Coronary arteries. The distal segments of three major coronary arteries were occluded prior to graft implantation. Of the 30 remaining bypassed coronary arteries, progression of disease rendered 15 (50 per cent) completely occluded (Fig. 1). Of 24 major coronary arteries which were not bypassed, 3 were completely occluded at the initial angiographic study. Disease in 3 of the 21 remaining, nonbypassed coronary arteries (14 per cent) progressed to 100 per cent obstruction. However, the degree of initial disease in those coronary arteries which were subsequently bypassed was greater than that in those arteries not operated upon; this comparison excludes arteries which were already occluded and therefore could not "progress" in terms of meaningful disease (mean per cent coronary obstruction ± 1 standard deviation prior to the operation: bypassed 76 ± 15 per cent, nonbypassed 42 ± 33 per cent [p < 0.001]). The extent of coronary arterial obstruction was similarly greater after operation in the bypassed arteries than in those vessels which did not receive grafts (per cent coronary obstruction after operation: bypassed 92 ± 10 per cent, nonbypassed 54 ± 35 per cent [p < 0.001]). Thus, there was significant progression of disease in both bypassed and nonbypassed native coronary arteries. The mean per cent obstruction in bypassed arteries was 76 ± 15 per cent before surgery and 92 ± 10 per cent (p < 0.001) after surgery. In nonbypassed arteries, the mean per cent. obstruction was 42 ± 33 per cent before surgery and 54 ± 35 per cent (p < 0.05) after surgery (Fig. 2). Net per cent progression in native coronary arteries. Twenty-four of 30 coronary arteries (70 per cent) which were bypassed became more obstructed. The average degree of progression in the 30 arteries as a group was 16 ± 12 per cent. Six of 21 patent, nonbypassed coronary arteries (29 per cent) were initially free of demonstrable disease.
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Fig. 1. Preoperative and postoperative selective coronary cineangiograms in the right and left anterior oblique projections. The patient was a 57-year-old man with coronary artery disease who underwent bypass grafting to the right coronary artery and left anterior descending coronary artery. Bottom panels demonstrate the selective aorto-coronary graft angiograms. Distal branches of the right coronary artery (RCA) developed complete obstruction in the interval between the two studies. Disease in the left anterior descending branch of the left coronary artery (LCA) progressed from 80 per cent obstruction to complete occlusion. The arrows in line drawings of the left coronary artery indicate the site of complete occlusion.
The development of coronary arterial disease was noted in 2 of the original 6 arteries after operation. One patient developed a 40 per cent localized luminal narrowing in a vessel previously free of disease. A 62-year-old man with grafts to the left anterior descending and left circumflex arteries later developed a new 100 per cent occlusion of the right coronary artery. The new occlusion was noted 8 months after the initial postoperative study. This zero to 100 per cent progression was the most striking change noted in the entire study group. Without the benefit of pathological study, it is impossible to designate this occlusion as a rapidly developing plaque or thrombosis arising as a result of the operation. Ten of 14 (71 per cent) nonbypassed coronary
arteries which were diseased on the preoperative arteriograms did not demonstrate progression of disease. Including the zero to 100 per cent occlusion described previously, there was no significant difference between the mean net per cent progression observed in bypassed and nonbypassed coronary arteries (bypassed 16 ± 12 per cent, nonbypassed 12 ± 24 per cent [p > 0.4]). Exclusion of the 100 per cent occlusion observed in the nonbypassed group resulted in a small but significant difference between the mean net per cent progression noted in the nonbypassed and the bypassed arteries (bypassed 16 ± 12 per cent, nonbypassed 7 ± 14 per cent [p < 0.05]). Progression of disease in coronary arteries with patent grafts and nonpatent grafts (pus-
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sibly or definitely occluded). The degree of coronary artery disease was significantly greater both before and after surgery in those vessels with patent grafts (before surgery: patent 80 ± 13 per cent and nonpatent 66 ± 16 per cent [p < 0.05]; after surgery: patent 96 ± 7 per cent and nonpatent 81 ± 13 per cent [p < 0.001]). The progression of disease in bypassed coronary arteries, both patent and nonpatent, was significant (patent: before surgery 80 ± 13 per cent and after surgery 96 ± 7 per cent [p < 0.001]; nonpatent: before surgery 66 ± 16 per cent and after surgery 81 ± 13 per cent [p < 0.02]). Interestingly, there was no significant difference between the net per cent progression in coronary arteries with patent and nonpatent grafts (patent 16 ± 12 per cent, nonpatent 15 ± 13 per cent, p > 0.8). Disease in 14 of 23 (61 per cent) coronary arteries bypassed with patent grafts progressed to 100 per cent occlusion. Only 1 of 7 arteries with non patent grafts was completely occluded on postoperative study. Discussion
Most investigations relating to aorto-coronary bypass grafts have engendered a certain degree of controversy and confusion. This latter appraisal can be amply applied to existing data on progressive disease in the native coronary circulation after operative intervention. Implicit in any discussion of the problem is the following question: Is the net per cent increase of disease in bypassed coronary arteries any different from that in arteries not bypassed in the same subject or that in subjects not operated upon? The initial study by Aldridge and Trimble! demonstrated progression of pre-existing coronary artery disease after implantation of bypass grafts. Of 8 coronary arteries with patent bypass grafts, 5 were noted to have developed total occlusion. No mention was made concerning progression of disease in nonbypassed native coronary arteries. Bousvaros and colleagues" provided findings in 4 patients who had 6 aorto-coronary bypass
Thoracic and Cardiovascular Surgery
grafts. Postoperative injection of 5 vessels that had previously been incompletely stenosed demonstrated complete occlusion when dye was introduced in an antegrade fashion. In 2 patients, however, graft opacification produced retrograde flow of dye up to and beyond the point of "obstruction" noted during standard arteriography. In their extensive review of the clinical response to bypass graft implantation, Alderman and associates" noted progression of pre-existing coronary artery disease as an incidental finding in 12 subjects. This acceleration of disease was noted in both bypassed and nonbypassed vessels. Griffith and co-workers I noted a 30 per cent incidence of progression of disease to total occlusion in bypassed coronary arteries with both patent and occluded grafts. The method for postoperative evaluation of coronary artery disease used by the latter authors reflected that reported in the existing literature, i.e., consideration of 50 or 100 per cent lumen obstruction. Since it is probable that luminal encroachment by atherosclerosis is a dynamic process which can occur in varying degrees, we accepted any decrease of lumen diameter as evidence of progression. Furthermore, the net progression of the occlusive process appeared to be a reasonable method for comparing the effects of the grafts per se on the native coronary circulation. This net measurement in no way assumes that the velocities of occlusive processes are stable; however, it does in part allow a more realistic comparison of the progression of disease in different arteries. On comparing the evolution of disease in the bypassed and nonbypassed coronary circulations, we found that the net increments of occlusion were comparable. The high prevalence of total occlusions in the bypassed group was a reflection of more severe preexisting disease. Exclusion of a single patient, in whom 100 per cent occlusion may have represented thrombosis, resulted in only a small difference (9 per cent) in net occlusive progression between the bypassed
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Fig. 2. Preoperative and postoperative selective coronary cineangiograms in a 56-year-old man with coronary artery disease who underwent aorto-right coronary artery bypass. Panels A and C demonstrate progression of disease in the left circumflex coronary artery (LC) from 40 to 80 per cent obstruction. Panels Band D show progression of 90 per cent obstruction to complete occlusion of the right coronary artery (RCA). Panel E shows the right graft angiogram.
and nonbypassed groups. Furthermore, the net per cent progression of disease in bypassed coronary arteries was identical in both patent and nonpatent groups. The total number of complete coronary occlusions was weighted in favor of the patent graft group , because those patients had more extensive disease before surgery. Utilizing serial coronary arteriography, Bemis and colleagues" have recently demonstrated that 52 per cent of their patients with coronary artery disease and no coronary grafts exhibited evidence of progression of the coronary arterial lesion. A 20 per cent decrease of luminal diameter was required as a requisite for progression. At this level of progression, their results are in accord with those described herein ; presumably, the number of subjects with progression might have been higher if lesser degrees of luminal reduction had been accepted . The findings presented in this study offer no basis for invoking pressure differentials, surgical manipulation of severely diseased coronary arteries, intraoperative myocardial infarction," or the duration of anoxic arrest
as mechanisms resulting in the progression of native coronary artery disease in our patients with aorto-coronary bypass grafts. In the overwhelming majority of subjects, the natural history of coronary artery disease would appear to be the most reasonable explanation for such progression . The more severe the pre-existing coronary artery disease, the more likely is the possibility that the lesion will progress to 100 per cent occlusion.. It is possible that functioning grafts permit longer survival into the postoperative period, with a higher prevalence of 100 per cent occlusion seen on follow-up angiographic study. REFERENCES Aldridge, H. E., and Trimble, A. S.: Progression of Proximal Coronary Artery Lesions to Total Occlusion After Aorta-Coronary Saphenous Vein Bypass Grafting, J. THORAC. CARDIOVASC. SURG. 62: 7, 1971. 2 Bousvaros, G., Chaudhry, M. A ., and Piracha, A. R.: Progression of Proximal Coronary Arterial Lesions to Total Occlusion After Vein Graft Surgery and Its Effects, Am . J. CardioI. 29: 255, 1972. 3 Alderman, E. i..., Matlof, H. J., Wexler, L.,
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Shumway, N. E., and Harrison, D. C.: Results of Direct Coronary-Artery Surgery for the Treatment of Angina Pectoris, N. Engl. J. Med. 288: 535, 1973. 4 Griffith, L. S. C., Achuff, S. C., Conti, C. R., Humphries, J. 0., Brawley, R. K., Gott, V. L., and Ross, R. S.: Changes in Intrinsic Coronary Circulation and Segmental Ventricular Motion After Saphenous-Vein Coronary Bypass Graft Surgery, N. EngI. 1. Med. 288: 589, 1973.
5 Bemis, C. E., Gorlin, R., Kemp, H. G., and Herman, M. Y.: Progression of Coronary Artery Disease. A Clinical Arteriographic Study, Circulation 47: 455, 1973: 6 Brewer, D. L., Bilbro, R. H., and Bartel, A. G.: Myocardial Infarction as a Complication of Coronary Bypass Surgery, Circulation 47: 58, 1973.