Occlusive changes at the coronary artery-bypass graft anastomosis

Occlusive changes at the coronary artery-bypass graft anastomosis Morphologic study of 95 grafts Ninety-five bypass graft anastomoses in 52 patients dying up to 4 years after direct coronary revascularization were studied at autopsy by angiograms and serial histologic sectioning of the graft-artery anastomosis. When new coronary occlusions and narrowings occurred, they were adjacent to either the proximal or distal ends of the anastomosis and were due to compression or loss of circumference of the arterial lumen (40 per cent), thrombus formation (40 per cent), mural dissection of the coronary wall (8 per cent), or the combination of compression and thrombosis (12 per cent). Small coronary artery diameter, local atheromas, and extension of the arteriotomy into a branch vessel were significant factors predisposing to occlusive changes. The findings emphasize the importance of careful artery selection for bypass, the need to avoid local vascular disease and branch-points, and the technical difficulties encountered in the presence of local vascular lesions or small coronary arteries.

Lawrence S. C. Griffith, M.D.,* Bernadine H. Bulkley, M . D . , Grover M. Hutchins, M . D . , and Robert K. Brawley, M . D . , Baltimore, Md.

.LVevascularization of the heart by direct anastomosis of either a vein graft or internal mammary artery to the coronary arteries has been successful in alleviating symptoms of angina pectoris in eighty-five to ninety per cent of patients. 2 " 5 Despite the symptomatic relief afforded by this procedure, approximately fifteen to thirty per cent of the bypass grafts are occluded one year after operation. 8 - 1 5 In addition, new total occlusions of the intrinsic coronary artery have been From the Cardiovascular Division of the Department of Medicine and the Departments of Pathology and Surgery, The Johns Hopkins Medical Institutions, Baltimore, Md. Supported by Grant P50-HL-17655-02 from the National Institutes of Health, Public Health Service, Department of Health, Education and Welfare, and the Stetler Research Fund for Women Physicians. This report was presented in part at the Twenty-third Annual Scientific Sessions of the American College of Cardiology, February, 1974.' Received for publication Dec. 23, 1976. Accepted for publication Feb. 7, 1977. Address for reprints: Dr. Grover M. Hutchins, Department of Pathology, The Johns Hopkins Hospital, Baltimore, Md. 21205. *Clayton Scholor of The Johns Hopkins University. 668

identified at postoperative catheterization in a large number of patients. 6 - 1 2 Many of these new occlusive changes were noted to begin or terminate at the bypass graft-to-coronary artery anastomosis site. 6 The nature of these occlusive changes has not been completely defined. On the basis of postoperative catheterization findings, at least four possible mechanisms have been suggested: progression or worsening of pre-existing atherosclerotic disease, thrombosis as a result of diminished volume and velocity of blood flow within the coronary segment proximal to the graftartery anastomosis, 1 6 - 1 7 turbulence within the coronary artery at the anastomotic site, or technical factors related to the construction of the anastomosis. In the present study, postmortem radiographic and histologic examinations of the bypass graft-tocoronary artery anastomosis were undertaken to define both the nature and frequency of these occlusive changes in autopsy material. This study will show that occlusive postoperative changes occur more commonly in coronary arteries with a small internal diameter, arteries that have required endarterectomy, or those in which the graft-artery anastomosis was made across a major branch-point of the coronary artery.

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Fig. I. Widely patent saphenous vein graft to coronary artery anastomosis. Top, Radiograph of tissue block containing the anastomosis. Bottom, Selected serial histologic transverse sections taken at the points indicated by the lettered arrows on the radiograph. A, The vein graft above and the coronary artery below. B, The proximal end of the anastomosis. C and D, The midportion of the anastomosis with the vein graft forming a roof over the opened artery below. The injection mass in the lumen stains dark. (Elastic stain. Original magnification x3.) Materials and methods The clinical and pathological features of the 52 patients in the autopsy files of The Johns Hopkins Hospital who had received one or more coronary artery bypass grafts between 1969 and September, 1975, were reviewed. The hearts had been studied by postmortem coronary arteriograms and bypass graft injection with a barium-gelatin-pigment injection mass.18 In all but 2 cases the hearts were fixed in formalin in a distended state prior to sectioning, and stereoscopic radiographs were prepared in at least two planes. The heart, radiographs, gross photographs, and a variety of histologic sections of the heart and the bypass grafts were available for review. The terminal portion of each bypass graft, including the distal anastomosis and part of the intrinsic coronary artery proximal and distal to the anastomosis, were removed "en bloc." Stereoscopic radiograms of each block were prepared in two planes. The block was then given light decalcification, routinely processed, and embedded in paraffin. The block was serially sectioned transversely at 8 fi beginning at the proximal end and every fifteenth section retained. Of the retained sections, every third was stained with hematoxylin and eosin, the second series of every third section was stained with an elastic stain, and the third series with

connective tissue or other stains as appropriate. Whenever a vein Y graft was present, the distal anastomosis of each limb was examined histologically in the same manner. The proximal anastomosis of the vein graft to the aorta was examined by serial histologic sections when any abnormality was noted on gross examination. Each case was then reviewed. Patency of the bypass graft and any occlusive change in the intrinsic coronary artery at the graft-artery anastomosis were determined from the radiographs, gross examination, and review of serial histologic sections. An example of a "satisfactory" vein graft-to-coronary artery anastomosis is shown in Fig. 1. Four sections were chosen for each anastomosis: the coronary artery about 5 mm. proximal to the proximal end of the arteriotomy, from which the caliber and extent of plaque in the coronary artery could be determined (A); the point of maximal narrowing of the coronary lumen at the proximal end of the arteriotomy (B); a similar point of maximal lumen narrowing at the distal end of the arteriotomy (D); and a section representative of the coronary lumen approximately 5 mm. beyond the distal end of the arteriotomy (E). In almost every case, the maximal narrowing of the intrinsic coronary artery occurred immediately at the terminal ends of the coronary arteriotomy.

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Table I. New occlusive narrowings in 95 coronary arteries at graft-coronary artery anastomosis Narrowed 70-90%

Narrowed or occluded 70-100%

Occluded 100%

Coronary artery bypassed

No.

No.

%

No.

%

No.

%

Proximal end* LAD RCA CIRC Totals

45 28 22 95

5 3 3 11

11 11 14 12

1 3 1 11

16 11 5 12

12 6 4 22

27 21 18 23f

Distal end* LAD RCA CIRC Totals

45 28 22 95

3 5 6 14

7 18 27 15

10 6 5 21

22 21 23 22

13 11 11 35

29 39 50 37t

Legend: LAD, Left anterior descending artery. RCA, Right coronary artery. CIRC, Left circumflex artery. *Proximal and distal: Location of occlusive change in coronary artery at either proximal or distal end of graft-artery anastomosis. tSignificant difference: p < 0.05.

Table II. Mechanisms of occlusive coronary artery change in 95 grafts Proximal No. Coronary arteries with new 70-100% occlusions Compression Thrombosis Dissection Compression and thrombosis

%

21 8 8 2 3

Proximal and distal

Distal No.

%

13 13 2 3

%

52

31 38 38 10 14

No.

42 42 6 10

21 21 4 6

40 40 8 12

Sections from the four locations were then projected, and outlines of the lumen, internal and external elastic lamina, and adventitia of the coronary artery were drawn on tracing paper.19 A calibrated millimeter grid was also projected and traced. The area of the entire cross-sectional coronary artery, as well as the area of the lumen, intima plus plaque, media, and adventitia were determined from the tracing by use of a planimeter. The diameter and circumference of the lumen and the entire coronary artery were calculated from the planimetered areas. The maximum reduction in crosssectional area of the coronary lumen at both the proximal and distal ends of the anastomosis was then calculated. The area of the coronary lumen at B was compared to the area at A, and the lumen area at D was compared to E. Reduction by more than 70 per cent of the lumen

area at B or D was considered significant. The postoperative occlusive changes were grouped as 100 per cent or total occlusion, 70 to 99 per cent occlusion, or 0 to 69 per cent occlusion. The per cent of atherosclerotic plaque present in the coronary artery at A and E was calculated by dividing the planimetered area of intima plus plaque by the planimetered area of the entire artery within the adventitia. In a final review of the pathological information, the mechanism of new significant occlusive changes was determined. Three mechanisms—compression or loss of circumference, thrombosis, and mural dissection—will be described in the Results section. Results General. The first bypass graft procedure was done at The Johns Hopkins Hospital in December of 1969. Operations for the first and last patients in this reported autopsy series were in June, 1970, and August, 1975, respectively. The hospital mortality rate at The Johns Hopkins Hospital for all patients who received at least one bypass graft between December, 1969, and December, 1975, was 10.5 per cent (65/621). If patients who had unstable angina pectoris, a myocardial infarction within 2 weeks of operation, or those who had combined operative procedures (bypass grafting plus either prosthetic valve replacement, aneurysmectomy, or closure of ventricular septal defect) are excluded, the hospital mortality rate in patients with stable angina during this same period was 4 per cent (16/391). The hospital mortality rate of patients with stable angina during 1974 and 1975 was 1.2 per cent (2/168). The mean age (±SEM) of the 52 patients included in this study was 55± 1 years (range 35 to 68). Thirty-nine (75 per cent) were men. Of the 95 bypass grafts placed, 91 were reversed saphenous vein and four were internal mammary artery grafts. All graft-to-coronary artery anastomoses were of the end-to-side type. Eighteen patients had one bypass graft placed, 26 patients had two, 7 patients had three, and one patient had four grafts. In 6 cases, prosthetic valve replacement was performed in addition to coronary artery bypass graft surgery. Of the 52 patients, 30 died intraoperatively or within 24 hours after operation (61 grafts), 14 died from one day to one month postoperatively (21 grafts), and 8 survived more than one month and up to 48 months (13 grafts). Frequency of occlusive changes. Examination of serial histologic sections of the bypass graft-to-coronary artery anastomosis revealed that most significant occlusive changes in the intrinsic coronary artery occurred immediately adjacent to either the proximal or distal ends of the graft-artery anastomosis (Fig.

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Occlusive changes in bypass grafts

Fig. 2. Saphenous vein graft-to-coronary artery anastomosis with an occlusion at the distal end of the anastomosis caused by compression. A, A widely patent graft above and coronary artery below filled with injection mass. B, The mid-portion of the anastomosis is also patent. C, The distal end of the anastomosis is completely occluded. Note that an atherosclerotic plaque is present here but not in A, proximal to the anastomosis. D, The area past the point of occlusion isfilledwith injection mass from collateral channels and shows a normal lumen. (Elastic stain. Original magnification x3.) 1). A new significant occlusive change was defined as a reduction of the cross-sectional area of the coronary artery lumen by 70 per cent or more. More new occlusive narrowings were found at the distal end of the anastomosis than at the proximal end (p < 0.05) (Table I). However, 29 per cent (10/35) of these significant changes at the distal end occurred in coronary arteries in which the anastomosis was made across a major branch-point and occlusion occurred in one of the two artery branches. (See Anastomosis across a branch-point section.) Mechanisms and frequency of occlusive change in coronary arteries. Three mechanisms of occlusive change in the coronary artery at the anastomosis site were identified: (1) compression or loss of circumference; (2) thrombosis: and (3) mural dissection. These mechanisms could occur separately or in combination. Compression or loss or circumference refers to the reduction in coronary artery lumen that occurs when part of the intrinsic coronary wall circumference is everted or compressed by suturing during construction of the graft-artery anastomosis. An example of compression or loss of circumference is shown in Fig. 2. A diagrammatic explanation of this mechanism is shown in Fig. 3. At operation, sutures are placed in both the bypass graft and coronary artery in such a manner as to evert both vessel walls and permit intima to intima

Table III. Frequency and mechanism of occlusive change depending on time of death after operation Time of death after operation Within 24 hr. (30 pts.)

Coronary arteries bypassed New 70-100% occlusion* Mechanism of artery narrowing Compression Thrombosis Dissection Compression and thrombosis Unknown

1-30 days (14 pts.)

1-48 mo. (8 pts.)

No.

%

No.

%

No.

%

61 31

51

21 9

43

13 8

62

14 8 3 2 4

45 26 10 6 13

5 1 1 2

56 11 11 22

1 6 1

13 75 13

-

-

*Only the most severe narrowing or occlusion of each bypassed artery (at either proximal or distal end of anastomosis) is recorded.

contact. In the midportion of the anastomosis (point C), the vein graft provides ample "roof" or gusset to more than compensate for any loss of circumference that occurs as a result of everting a portion of coronary wall. At the proximal and distal ends of the arteriotomy, the vein graft does not, however, provide any roof. Any portion of the arterial wall circumference immediately at or just beyond the apex of the arteriotomy that is

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Coronary

a.

© Fig. 3. Diagram showing mechanism of compression of coronary artery lumen during construction of anastomosis. /, Suture placement at terminal portions of arteriotomy. 2, First suture tied with eversion of coronary artery and graft walls by suture. 2a, Coronary artery wall everted; graft not drawn. 3, Anastomosis complete. Narrowings present at both ends of anastomosis owing to compression or loss of circumference (5 and D). 4, Sections through A, B, C, and D. Location of arteriotomy shown Y and Z are points where suture through wall enters coronary lumen. At both ends of anastomosis, Y and Z meet. See text for explanation. everted during construction of the anastomosis will directly reduce the coronary artery circumference and, hence, the cross-sectional area of the coronary lumen. The distance from the edge of the arteriotomy where each suture is placed through the coronary wall determines the width of artery wall that is everted. Hence, the internal circumference of the coronary artery at each end of the arteriotomy is reduced by the width of the everted segment on both sides of the arteriotomy. Thrombosis at the site of graft-to-coronary artery anastomosis is shown in Fig. 4. In this example, there was no appreciable loss of arterial circumference when

the anastomosis was made, yet the coronary artery at the proximal end is totally occluded and the distal artery is severely narrowed as a result of thrombus. Mural dissection of the coronary artery wall with a resulting significant decrease in cross-sectional area of the lumen was found in four bypassed arteries. Twenty-two of the 95 (23 per cent) bypassed coronary arteries were narrowed by 70 per cent or more at the proximal end of the anastomosis. Twenty-one of these 22 proximal narrowings were examined histologically and the mechanisms of new occlusive changes determined (Table II). Compression was responsible for

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67 3

Fig. 4. Saphenous vein graft-to-coronary artery anastomosis with occlusion of proximal and obstruction of the distal end by thrombosis. A, Vein graft above and patent artery below. B, Just proximal to the arteriotomy with patent graft above and occluded artery below. C and D, Near distal end of arteriotomy showing small channel through organized thrombus. (Elastic stain. Original magnification x4.) Table V. Internal diameter of coronary artery and new postoperative occlusive narrowings

Table IV. Characteristics of coronary artery at graft-artery anastomosis site

No. Anterior descending Proximal Distal Circumflex marginal Proximal Distal Right Proximal Distal

Internal diameter (mm.)

External diameter (mm.)

Plaque

(%)

40 36

1.6 ± 0 . 1 1.4 ± 0 . 1

2.4 ± 0.1 2.1 ± 0 . 1

31 ± 3 30 ± 3

20 15

1.7 ± 0 . 2 1.8 ± 0 . 2

2.5 ± 0.1 2.3 ± 0.1

24 ± 4 19 ± 6

20 14

1.6 ± 0 . 2 1.6 ± 0 . 1

3.2 ± 0.1 2.4 ± 0.2

53 ± 4 37 ± 5

or contributed to a sigrlificant new/ narrowingr of the coronary artery at the proximal end of the anastomosis in 11/95 (12 per cent) instances. Thirty-five (37 per cent) of the 95 bypassed arteries were narrowed by 70 per cent or more at the distal end of the anastomosis. Ten of these 35 significant distal narrowings occurred when the anastomosis extended across a major branch-point; here one branch was significantly narrowed or totally occluded and the other branch widely patent. (See Anastomosis across branch-point). Thirty-

Proximal Arteries (no.) New 70-100% occlusion Distal Arteries (no.) New 70-100% occlusion Combined proximal and distal Arteries (no.) New 70-100% occlusion

Small arteries (diam-

Large arteries (diam-

eters < 1.2 mm.)

eters a 1.3 mm.)

No.

%

No.

%

Difference

26 8

31

53 11

21

NS

20 12

*"

44 10

T*

p < 0 01

46 20

43

97 21

22

p < 0.01

one of the significant distal narrowings were examined histologically. Compression was responsible for or contributed to a new acute narrowing at the distal end of the anastomosis in 16 instances. Thrombosis was the important causative factor in an equal number of occlusive changes that occurred at either the proximal or distal ends of the anastomosis.

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Table VI. New occlusive changes in coronary arteries after bypass graft surgery

Patients restudied Johns Hopkins6 Montreal Heart7 New York Univ.8 Alabama9 Toronto General10 Univ. Oregon*11 Peter Bent Brigham12

HI

Patent bypass graft Grafts patent

Grafts placed

No.

%

Coronary arteries

New total occlusion

New (zz50%) Narrowing No.

%

No.

%

12 3 6 8 6t 9

20 40 38 59 37 35 35

29 39 44 40 34 48 52

7

264/652

40$

71 105 50 121 100 100 67

6 11 9 12 20 5 13

120 154 118 210 143 88 115

79 103 86 147 108 73 67

66 67 73 70 76 83 58

68 103 86 147 108 73 67

8 3 5 12 7

614

11.5

948

663

70

652

41/579

-

6

*Patency of bypass grafts and new occlusive changes in intrinsic coronary artery described only for arteries that filled antegrade on preoperative arteriogram. tNew narrowing or worsening s 2 5 per cent. ^Eighty-five per cent of new total occlusions were proximal to patent graft-artery anastomosis, and 15 per cent were distal to anastomosis. 6~8, 10~12

The influence that time of death after operation has on the frequency and cause of these occlusive narrowings is shown in Table III. In this table, only the most severe narrowing of a bypassed artery at either the proximal or distal end of the graft-artery anastomosis is recorded. Although a similar frequency of significant occlusive changes is found in the three postoperative periods, the mechanism of occlusion differs. Compression or loss of circumference was the principal mechanism of these changes observed up to 30 days after operation. Thrombosis was the major cause of occlusions observed in patients who died more than one month after operation. Characteristics of distal coronary artery at graft-artery anastomosis site. The features of the coronary artery that appear important in determining success or failure of the anastomosis are shown in Table IV. The internal and external diameters of the intrinsic coronary arteries that were available for histologic examination, as well as the per cent plaque present in the arterial wall, are recorded. The segment of coronary artery selected for measurement was approximately 5 mm. proximal and distal to where the graft-artery anastomosis began or ended. Excluded from this table are the measurements of coronary arteries subjected to endarterectomy and measurements at the distal end of any anastomosis where the arteriotomy was extended across a branch-point and down one branch. On the basis of external diameter, the distal right coronary artery was the largest of the three arteries usually bypassed. Because the distal right coronary artery had the most atherosclerotic plaque of the three arteries, the largest internal diameter was in the cir-

cumflex marginal coronary artery. The anterior descending had the smallest luminal diameter. Artery lumen size and prevalence of postoperative occlusive changes. The influence of size of the coronary artery lumen on the occurrence of either a new narrowing of <70 per cent or a new 100 per cent occlusion is examined in Table V. The diameter and cross-sectional area of the coronary artery lumen proximal and distal to the anastomosis were utilized to "size" the coronary segment at the proximal and distal ends of the anastomosis. A separation into favorable and less favorable groups appeared to occur if the internal coronary diameter was 1.3 mm. or more ("large" artery) or 1.2 mm. or less ("small" artery). More occlusive changes were found in "smaller" arteries than in "larger" arteries (Table V). This difference was significant at the distal end of the anastomosis and when the changes at both the proximal and distal ends were combined (p < 0.01). Anastomosis across a branch-point. There were 12 anastomoses in which the coronary arteriotomy was carried across a branch-point because the atherosclerotic plaque extended down one branch. This is schematically depicted in Fig. 5. The frequency of significant occlusive changes in both the arteriotomy branch and nonarteriotomy branch groups is also shown. Half of the branches in each group were narrowed by at least 70 per cent or were totally occluded. These occlusive changes began immediately distal to the branch-point. In those arteries in which histologic studies were available to determine the mechanism of these occlusions, 80 per cent of these significant occlusions were due to compression or loss of circumference and 20 per cent to thrombosis. Ten of the 12 arteries in

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Occlusive changes in bypass grafts

Occluded bypass graft

arteries 39 51 32 62 34 15 48 281

narrowing produced by thrombosis. There were no occlusive narrowings in the three Y grafts at the vein graft-to-vein graft anastomosis.

No bypass graft

New total occlusion

New total occlusion

No.

%

Coronary arteries

24 18 4 40 11 4 18

62 35 13 65 32 27 38

81 161 36 145 128 86 89

13 6 4 3 10 5 2

119/281

42

726

43

67 5

Discussion

No.

% 16 4 11 2 8 6 2

which the arteriotomy was extended across the branch-point demonstrated significant occlusive change in at least one of the two branches. An example of a branch-point occlusion is shown in Fig. 6. In other anastomoses in which the distal end of the arteriotomy ended just proximal to a branch-point, there were no occlusive changes. The circumference and diameter of a vessel are greatest just proximal to its flow divider,20 which may account for the better results seen in cases in which the arteriotomy ended immediately before a branch-point. Endarterectomy. An endarterectomy was performed at the time of bypass surgery in 12 coronary arteries. In six arteries, there was a significant new occlusion (narrowed 70 to 100 per cent) at one or both ends of the anastomosis. Three of these occlusions involved an anastomosis across a branch-point and one branch was occluded. No histologic material on late results of endarterectomy was available for study. Seven of these 12 patients died at operation and the remaining patients died within 2 days of the operation. Occlusive changes in bypass grafts. Of the 95 bypass grafts placed in these 52 patients, 88 (93 per cent) were patent and seven were occluded by thrombosis at the time of autopsy examination. Five of the seven arteries to which these occluded grafts were connected demonstrated a significant narrowing in the coronary artery at one or both ends of the anastomosis. One internal mammary artery graft was occluded as a result of mural dissection in the graft wall. In this situation, there was also mural dissection of the bypassed coronary artery. The aorta-vein graft anastomoses showed no occlusive narrowings except for one graft with a severe

Seven surgical centers, including The Johns Hopkins Hospital, have recorded complete postoperative catheterization findings in over 600 patients detailing not only bypass graft patency rates but also the frequency rates of new occlusive changes in the intrinsic coronary artery circulation.6-12 These data are shown in Table VI. The definition of a new total occlusion used in this table is failure to visualize a segment of coronary artery at postoperative catheterization that had been opacified before the operation. Despite some variability in the criteria for the selection of patients for postoperative catheterization, there is remarkable similarity in the frequency with which these occlusive changes were found at these seven institutions. These are the only major published reports that have compared pre- and postoperative coronary arteriograms. No surgical center has looked for these occlusive changes in the intrinsic coronary circulation and not found them in comparable frequency. By other criteria, such as operative mortality rate, 4, 14, 2 1 - 2 3 extent of postoperative symptomatic improvement in angina, 2-4, 23, 24 and the frequency of new Q waves after operation, 25-28 the surgical results of these seven institutions are similar to results from other institutions that have not reported postoperative arteriograms of the intrinsic coronary circulation. Occlusive changes in the intrinsic coronary circulation similar to those described at postoperative catheterization have been demonstrated in the present autopsy study. As suggested by catheterization studies,6 the most severe narrowings in the bypassed coronary artery occur immediately adjacent to both the proximal and distal ends of the anastomosis and not within the anastomosis. The incidence of significant occlusive changes (both new narrowings and new total occlusions) in bypassed coronary arteries is somewhat higher in the present autopsy material than in the postoperative catheterization data from the seven surgical centers (Table VII). This may be partially due to the increased sensitivity of pathological techniques to identify significant narrowings adjacent to the graft-artery anastomosis or simply to the bias of an autopsy population. The higher graft patency rate, more frequent >50 per cent narrowings, and less frequent new total occlusions in the autopsy material may be explained by the shorter interval from operation to postmortem examination of the patients in this series as compared to the time after

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NEW OCCLUSIVE CHANGES BRANCHES (NO.)

PLAQUE

NARROWED 70-99%

OCCLUDED 100%

NON-ARTERIOTOMY BRANCH

ARTERIOTOMY BRANCH ARTERIOTOMY

Fig. 5. Bypass graft anastomosis across branch-point. Diagram showing arteriotomy extended down one branch because of local plaque. Twelve anastomoses across branch-point found in autopsy material. Frequency of 70 to 99 per cent and 100 per cent occlusion found in arteriotomy and nonarteriotomy branches is noted.

Fig. 6. Saphenous vein graft-to-coronary artery anastomosis with occlusion of the distal end caused by thrombosis. The graft has been placed into a point of branching in the coronary artery and the arteriotomy extended into the branch occluded by thrombus. A, Across the patent portion of the anastomosis. B, At the point of branching of the coronary artery with a penetrating branch below and two superficial branches. C, The anastomosis continuing down a branch occluded by thrombus. The other branch isfilledwith injection mass. D, At the distal most end of the graft with the thrombosed (T) branch having a suture in its upper portion. As shown in the radiogram, the thrombosed vessel is filled by collaterals beyond the point of thrombosis. (Elastic stain. Original magnification x3.) operation that patients underwent postoperative catheterization. If the interval after surgery in the autopsy group had been longer, it is probable that some of the severe narrowings of the intrinsic coronary artery would have progressed to total occlusion. The similar frequency of occlusive changes in the catheterization and autopsy data suggest that the postmortem findings may not be unduly biased, i.e., representing only "poor" surgical results, because all of the patients died. Histologic examination of bypassed arteries demonstrated that these narrowings were the result of three

mechanisms: compression or loss of circumference, thrombosis, and mural dissection. Compression and thrombosis, which occurred with almost equal frequency, accounted for 90 per cent of these occlusive changes. Thrombosis was considered to be responsible for 33 per cent of the occlusive changes in patients dying within 30 days of operation and 75 per cent of the changes in patients who died more than one month after operation. McEnany and his associates29 have shown a higher graft patency rate (84 per cent) one year after surgery in patients treated with warfarin compared to the patency of a control group that received a placebo

Volume 73 Number 5 May, 1977

(72 per cent). If comparable data are shown for occlusive changes in the intrinsic coronary artery, it may be that anticoagulant therapy is advisable to prevent or minimize those occlusive changes that are secondary to thrombosis. Lumen size of the distal coronary segment and the presence of atherosclerotic plaque at this location appear to predispose to occlusive change after the operation. Compression and thrombosis were more common in those arteries with an internal diameter of 1.2 mm. or less than in arteries with a diameter of 1.3 mm. or more. These data suggest that a critical step in making the graft-coronary anastomosis relates to the width of arterial wall that is everted or used at both ends of the anastomosis. Because the bypass graft does not provide any roof or circumference at these two points, the width of arterial wall everted on both sides of the arteriotomy directly reduces the circumference of the intrinsic coronary artery. If the intrinsic coronary artery is large, reduction in circumference at either end of the anastomosis is not important. On the other hand, if the artery is small, everting a segment of arterial wall can significantly reduce the cross-sectional area of lumen. To illustrate the potential importance of coronary artery size, the reduction in lumen area for two coronary arteries, one with an internal diameter of 2 mm. and the other 1 mm. (Table VIII), can be calculated for two different suture bites. Given the internal lumen diameter, the lumen area for each artery can be calculated. For both arteries, two typical suture bites are shown, one 0.5 mm. back from the edge of the arteriotomy and the other 1.0 mm. The circumference of the coronary artery immediately at the apex of the arteriotomy may be reduced by an amount equal to the width of everted wall on both sides of the arteriotomy. In the 2 mm. artery, the two hypothetical suture bites will reduce the cross-sectional area of the coronary lumen either by 29 per cent or 54 per cent. In the smaller 1 mm. artery, the same two suture bites will reduce the cross-sectional area by 52 per cent and 89 per cent. This situation of necessity occurs only in case of eversion of the wall. The presence of extensive atherosclerotic plaque in the distal coronary segment also appears to predispose to occlusive changes in the intrinsic coronary artery. Plaque will diminish the internal circumference available for anastomosis and reduce the pliability of the coronary wall for suturing. If extensive, an endarterectomy may have to be done. If plaque extends down a major branch of the distal coronary artery, then it may be necessary to extend the arteriotomy and anastomosis down this branch. Previously, the surgical approach at

Occlusive changes in bypass grafts

67 7

Table VII. Frequency of postoperative occlusions in bypassed coronary arteries identified at catheterization and postmortem arteriography Postmortem arteriography

Postop. catheterization

%

No.

%

Difference

933 652 70 383 41 41 4* 424 45 11.5

95 88 29 19 48

93 31 20 51

p < 0.001 NS p < 0.05 NS

No. Arteries bypassed Patent grafts New 100% occlusion New 70-99% narrowing New narrowing 70-100% Postop. interval (mo.)

1.3

*New postoperative narrowing at catheterization is defined as ^50 per cent.

Table VIII. Decrease in cross-sectional area of intrinsic coronary artery adjacent to graft-artery anastomosis

Preop. dimensions Two millimeter artery Circumference (mm.) Diameter (mm.) Cross-sectional area (sq. mm.) Area reduction (%) One millimeter artery Circumference (mm.) Diameter (mm.) Cross-section area (sq. mm.) Area reduction (%)

Postop. dimensions: Width of everted wall 0.5 mm.

1.0 mm.

6.3 2.0 3.1

5.3 1.7 2.2 29

4.3 1.4 1.5 54

3.1 1.0 0.8

2.1 0.7 0.4 52

1.1 0.4 0.1 89

The Johns Hopkins Hospital was to incise directly into a distal plaque in an effort to roof this lesion and permit bidirectional flow both proximally and distally in the artery. If necessary, an endarterectomy would be done, and, if plaque extended across a branch-point, the arteriotomy would be extended down one branch. Our practice now is to avoid making an anastomosis at the site of recognized plaque. If necessary, we place separate grafts on either side of this plaque. The results of the present study emphasize that selection of patients for coronary bypass surgery should include not only consideration of their clinical status but also evaluation of the caliber of the distal coronary lumen and the extent and location of atherosclerotic plaque in this distal segment. These autopsy findings suggest that new postoperative occlusive changes in bypassed coronary arteries may be the consequence of

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The Journal of Thoracic and Cardiovascular Surgery

Griffith et al.

characteristics of the distal coronary segment. Smaller coronary arteries have more occlusive changes than larger arteries. The presence of atherosclerotic plaque in the distal coronary segment, especially if it involves a major branching point, is accompanied by more occlusive changes than if plaque is not present in this segment. Not only are more patients with more extensive distal plaque undergoing bypass surgery at this time, the surgical objective of complete revascularization includes bypassing into smaller secondary branches if there is a significant proximal narrowing. With currently available surgical techniques, smaller coronary arteries may have insufficient internal circumference to permit construction of the graft-artery anastomosis without creating a significant narrowing in the intrinsic coronary artery. In our opinion, the optimal magnification provided by the use of loups has permitted a greater frequency of satisfactory anastomoses in smaller coronary arteries. It is possible that greater magnification and even more meticulous suture techniques would diminish the frequency of significant occlusive changes in bypassed coronary arteries and increase the patency rates of conduits to these small coronary arteries.

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21 Alderman, E. L., Matloff, H. I., Wexler, L., Shumway, N. E., and Harrison, D. C : Results of Direct CoronaryArtery Surgery for the Treatment of Angina Pectoris, N. Engl. J. Med. 288: 535, 1973. 22 Reul, G. J., Morris, G. C , Jr., Howell, J. F., Crawford, E. S., and Stelter, W. J.: Current Concepts in Coronary Artery Surgery: A Critical Analysis of 1,287 Patients, Ann. Thorac. Surg. 14: 243, 1972. 23 Hall, R. J., Dawson, J. T., Cooley, D. A., Hallman, G. L., Wukasch, D. C , and Garcia, E.: Coronary Artery Bypass, Circulation 47, 48: 146, 1973 (Suppl. III). 24 Sabiston, D. C , Jr.: Direct Revascularization Procedure in the Management of Myocardial Ischemia, Circulation 43: 175, 1971. 25 Assad-Morell, J. L., Frye, R. L., Connolly, D. C , Gau, G. T., Pluth, J. R., Barnhorst, D. A., Wallace, R. B., Davis, G. D., Elveback, L. R., and Danielson, G. K.: Relation of Intraoperative or Early Postoperative Transmural Myocardial Infarction to Patency of Aortocoronary Bypass Grafts and to Diseased Ungrafted Coronary Arteries, Am. J. Cardiol. 35: 767, 1975.

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