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Does bilateral internal mammary artery grafting increase surgical risk?
J
THoRAc CARDIOVASC SURG
1988;95:850-6
Does bilateral internal mammary artery grafting increase surgical risk? The risk of bilateral internal mammary artery grafting was studied in three groups of patients who were computer matched for recognized risk factors: year of operation, age, gender, extent of coronary artery disease, left ventricular function, completeness of myocardial revascularization, and history of congestive heart failure. The patient groups differed in the fact that they received veins only, one internal mammary artery graft, or two internal mammary artery grafts. The operative mortality rates for these three groups were 1.8%,0.3%, and 0.9%, respectively (no significant difference). Analysis of perioperative morbidity demonstrated no significant differences except for a slight increase in transfusion requirements in the group receiving two internal mammary artery grafts (p = 0.04). None of the patients with only veingrafts had wound complications. One patient in the group with one internal mammary artery graft had a wound complication (0.03 %). Eight patients receiving two internal mammary artery grafts had wound complications (2.4 %) (p = 0.002). The prevalence of wound complications in patients with diabetes mellitus was 5.7% and in those without diabetes mellitus, 0.3% (p = 0.01). The prevalence of wound complications in patients less than 60 years of age was 0.2%, in patients in their 60s, 1.6%, and in patients older than 70, 3.1 % (p = 0.01). Multivariate logistic regression analysis identified diabetes mellitus and age and not bilateral internal mammary artery grafting as risk factors for wound complications. We conclude that bilateral internal mammary artery grafting does not increase surgical mortality and increases surgical morbidity by a slight increase in the mean transfusion requirement.
D. M. Cosgrove, MD, B. W. Lytle, MD, F. D. Loop, MD, P. C. Taylor, MD, R. W. Stewart, MD, C. C. Gill, MD, L. A. R. Golding, MD, and Marlene Goormastic, MPH, Cleveland, Ohio
h e internal mammary artery (IMA) has been established as the preferred conduit for myocardial revascularization. Its early patency rate exceeds that of vein grafts and long-term patency remains high, in contrast to vein grafts, which are subject to late closure as a result of progressive atherosclerosis. loS This superior long-term patency is reflected in improvement in longterm survival, decrease in the rate of reoperation, and improvement in reoperation-free survival and cardiac morbidity." To further enhance the results of myocardial revascularization, both IMAs have been used in an
Table I. Matching criteria
From the Departments of Thoracic and Cardiovascular Surgery and Biostatistics and Epidemiology. The Cleveland Clinic Foundation. Cleveland, Ohio.
attempt to bypass multiple vessels with this conduit. Technical maneuvers to maximize IMA length, enabling it to reach more distal branches of the right and circumflex coronary arteries, have been described," and the free IMA graft has been shown to have excellent long-term patency." No adverse effect on morbidity or mortality has
Read at the Thirteenth Annual Meeting of The Western Thoracic Surgical Association, Colorado Springs, Colo.. June 24-27. 1987. Address for reprints: Delos M. Cosgrove. MD, The Cleveland Clinic Foundation. 9500 Euclid Ave., Cleveland, OH 44106.
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Year of operation Age Gender Extent of disease Ventricular function Completeness of revascularization History of congestive heart failure
Within 1 year Within 2 years Male/female Single/double or triple/left main Normal/mild or maderate/ severe Complete/incomplete Yes/no
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Table II. Preoperative clinical characteristics
Year of operation' Age (yr)" Male' ('it,) Diabetes mellitus (%) Hypertension (%) History of CHF (%) CHF (%.) Cholesterol ::::250 mg/dl (%) Smoking (%)
Veins only
One IMA
Two IMAs
198 J.7 58.4 ± 8.0 283 (84.3) 38 (11.3) 85 (25.1) 11 (3.3) 4 (1.2) 157 (47.6) 162 (48.9)
1981.6 57.9 ± 7.9 283 (84.3) 32 (9.6) 81 (24.0) 11 (3.3) 1 (0.3) 149 (44.5) 151 (45.8)
1982.5 58.3 ± 7.9 283 (84.3) 36 (10.7) 65 (19.2) 11 (3.3) 2 (0.6) 140 (41.4) 131 (39.6)
CHF, Congestive heart failure. "Matching criteria.
Table
m. Angiographic extent of coronary artery
Table IV. Preoperative ventricular function
disease
,{ Single (%) Double (%) ,{ Triple (o/r) Left main disease (%)
Veins only IN = 338)
One IMA IN= 338}
Two IMAs IN= 338)
7 104 179 48
7 (2.1) 104 (30.8) 208 (61.5) 19 (5.6)
7 104 185 42
(2.1) (30.8) (53.0) (14.2)
(2.8) (30.8) (54.7) (12.4)
, { Normal (%) Mild (%) , { Moderate (%) Severe (%)
Veins only IN= 338}
One IMA IN = 338}
Two IMAs IN= 338}
174(51.5) 92 (27.2) 49 (14.5) 23 (6.8)
232 34 50 22
163 103 56 16
(68.6) (10.1) (14.8) (6.5)
(48.2) (30.5) (16.6) (4.7)
* Matching criteria.
"Matching criteria.
resulted from the use of one IMA graft. I I Surgeons, however, are concerned that the longer, more complicated, and technically more demanding procedure of bilateral IMA grafting may have an adverse effect on surgical morbidity and mortality. This study was undertaken to address these concerns. Patients and methods The first 500 patients who underwent elective bilateral IMA grafting at The Cleveland Clinic from 1972 through 1985 were identified with the aid of a computerized cardiovascular information registry. They provide the basis for this study. Excluded were patients undergoing reoperation and patients who had concomitant valve procedures, carotid endarterectomy, or aneurysmectomy. With the use of patient descriptors previously identified as operative risk factors, including year of operation, age, gender, extent of coronary artery disease, left ventricular function, completeness of revascularization, and history of congestive heart failure, it was possible to computer match groups of 338 patients." The groups differed in the fact that they received only vein grafts, one IMA graft, or two IMA grafts. Parameters for the matching criteria are shown in Table I. The computer-matched preoperative clinical characteristics of the three groups and other preoperative characteristics not computer matched were similar (Table II). The annual distribution of cases of the three groups was not significantly different (Fig. I). Computer matching for extent of coronary artery disease was done by using single- or double-vessel disease and triple-vessel or left main disease. In each group,
32.9% of the patients had single- or double-vessel disease and the remainder had triple-vessel or left main disease. The breakdown into single, double, triple, and left main disease is shown in Table III. Left ventricular function was matched by normal or mild ventricular dysfunction and moderate or severe ventricular dysfunction categories. Further stratification is shown in Table IV. The operative variables were remarkably similar although there was a trend toward an increasing number of grafts in the two-IMA group (Table V). Biostatistical method. Univariate analyses among the three groups were done by analysis of variance technique for continuous variables and XC test when appropriate for categorical variables. In cases in which the expected cell frequencies were small «5), Fisher's exact test was used to compare the groups. A t test was used to compare mean values for two groups. A stepwise logistic regression analysis was used to test independent association of multiple factors with wound complications." Results Mortality. There were 10 deaths in the entire group
(1.0%): six (1.8%) among patients receiving only vein grafts, one (0.3%) among patients receiving one IMA graft, and three (0.9%) among those receiving two IMA grafts. The differences were not statistically significant. The causes of death are listed in Table VI. Of the six deaths in patients undergoing saphenous vein grafts, three were related to preexisting conditions that dictated the choice for vein grafts as conduits. No deaths in any
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220 200 180 160 140
> o zw 120
o
;:)
aw
a:
100
VEINS ONLY
6. ONE IMA
e
IL
80
TWO IMAs
60 40 20 0 72
73
74
75
76
77
78
79
80
81
82
83
84
85
YEAR
Fig. 1. The annual distribution of cases in the three groups demonstrates the preponderance of patients who were operated on from 1982 through 1984.
group could be directly or indirectly attributed to the choice of conduit. Morbidity. The morbidity for the three groups is listed in Table VII. No significant trends emerged. Special attention was directed to complications related to the extent of the surgical procedure, including bleeding and wound complications. Table VIII shows the prevalence of hemorrhagic complications. Only mean transfusion requirements increased significantly in patients receiving bilateral IMA grafts. Wound complications were more common in patients with bilateral IMA grafts than in those with saphenous vein grafts or those receiving single IMA grafts. There were no complications in patients receiving only saphenous vein grafts, one (0.3%) in patients receiving one IMA graft, and eight (2.4%) in patients receiving two IMA grafts (p = 0.002). One patient in the single-IMA group (0.3%) required reoperation for wound complications whereas four (1.2%) patients with bilateral IMA grafts required some form of surgical intervention for management of wound complications. Further analysis of trends in wound complications with IMA grafts demonstrated women to have a higher incidence of wound complications (3/156 [5.7%]) than did men (6/1005 [1.4%]) (no significant difference). Among patients with bilateral IMA grafts, there were three wound complications in 53 women (5.7%) compared to five in 285 men (1.8%). These differences did not achieve statistical significance. More significant was the
decided increase in wound complications in patients with diabetes mellitus. In patients with single IMA grafts, there was one wound complication in 32 diabetic patients (3.1%) opposed to no wound complications in 303 nondiabetic patients. In patients who had two IMA grafts, there were two wound complications in 302 nondiabetic patients (0.7%) compared to six wound complications in 36 diabetic patients (16.7%) (p < 0.0001). Age influenced the incidence of wound complications. There was one wound complication in 562 patients less than 60 years of age (0.2%), six in 388 patients who were in their 60s (1.6%) and two in 62 patients age 70 years or older (3.1%) (p = 0.012). To identify and establish priorities for risk factors for wound complications, age, gender, diabetic status, and number of IMA grafts were entered into a multivariate logistic regression analysis. Diabetes mellitus (p < 0.001) and advanced age (p = 0.003) were the only statistically significant risk factors. Discussion The IMA graft has an early patency rate exceeding that of vein grafts.':" The difference in patency rates increases with time as vein grafts become stenotic and occluded as a result of progressive vein graft atherosclerosis, from which the IMA seems to be largely immune.'? Currently, vein graft failure is the major angiographic indication for reoperation, and it is increas-
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Table V. Operative variables Grafts (mean) Complete revascularization ('If) Cardioplegia ('Yr.)
Veins only
One IMA
Two IMAs
3.0 ± 0.9 286 (84.6) 288 (83.2)
3.2 ± 1.0 286 (84.6) 282 (83.4)
3.3 ± 1.0 286 (84.6) 290 (85.8)
inglyrecognized that stenotic vein grafts were associated with disastrous clinical histories." The IMA has the further advantage of not accelerating progression of atherosclerosis in the native circulation as rapidly as vein grafts." The clinical advantages of the superior long-term patency of the IMA graft are demonstrated in improvement in long-term survival, incidence of reoperation, reoperation-free survival, and hospitalization for cardiac events." If the long-term salutary effects of myocardial revascularization are to be sustained, it is essential that the conduit maintain its patency. Focus has turned to the IMA in an attempt to bypass the maximum number of vessels with a conduit demonstrated to have excellent long-term patency. Well have previously demonstrated in a large series of patients that there was no increased morbidity or mortality from using one IMA graft, but we have not demonstrated the safety of two IMA grafts. If this technique is to be widely adopted, it is important that its safety be documented and that any patient subsets with the increased potential for complications be identified. Previous analysis of the large patient groups operated on at one institution during this time frame have identified the major factors influencing operative mortality rate. Emergency operation, advanced age, poor ventricular function, female gender, incomplete revascularization, history of congestive heart failure, abnormal electrocardiogram, and congestive heart failure at the time of operation were the major risk factors during the 1980s when the majority of patients underwent operation. All but the latter two factors were taken into consideration in selection of matching criteria. Left main trunk disease was not separately matched as a risk factor, because since the mid-1970s this has ceased to be an independent risk factor and has an operative mortality rate similar to that of three-vessel disease." The similarity of patients matched in the three groups is demonstrated not only by statistical comparability of the matching criteria, but also for other preoperative descriptors such as preoperative hypertension, serum cholesterol levels greater than 250 mg/dl, history of smoking, diabetes mellitus, congestive heart failure, number of grafts, and use of cardioplegia.
Table VI. Causes of death Cause Veins only (N = 6) Hemorrhage Neurologic Infection Renal One IMA (N = I) Hemorrhage Two (MAs (N = 3) Cardiac Respira tory Multisystem failure
No. 2 2
Preexisting conditions that dictated the selection of veins as conduits probably accounted for the slightly higher operative mortality rate in patients in this group. Three patients died of preexisting conditions: renal failure, chronic lymphocytic leukemia, and refusal of a Jehovah's Witness to accept a transfusion. In these situations, surgeons selected vein grafts in the belief that the preexisting condition favored their use. In no cases could the cause of death be directly or indirectly attributed to the selection of one or more IMA grafts. The prolonged anesthesia time before the commencement of cardiopulmonary bypass provides an opportunity for undiagnosed ischemia to occur, which would result in increased perioperative infarctions. The fact that this did not occur is largely attributable to the increased sophistication of the cardiac anesthesiologist in maintaining the patient in a nonischemic state. The low incidence of perioperative myocardial infarction further attests to the ability of the IMA to provide blood flow sufficient to meet myocardial oxygen demands, as previously demonstrated by Schmidt and associates." The pleural space was opened during all IMA dissections. Previous reports suggest that respiratory function is impaired in patients when the pleural space is opened." In these three similar groups of patients, opening the pleural spaces did not significantly increase respiratory complications even when both pleural spaces were opened. Respiratory complications have previously been demonstrated to increase with age." The additional dissection associated with mobilization
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Table YD. Surgical morbidity
Myocardial infarction (%) Respiratory insufficiency (%) Stroke (%) IABP (%)
Veins only (N= 338)
OnelMA (N= 338)
2 (0.6) 12 (3.6) 7 (2.1) 2 (0.6)
3 (0.9) 6 (1.8) 4 (1.2) 1 (OJ)
Two IMAs (N= 338) 7 (2.1)
II (3.2) 8 (2.4) 2 (0.6)
IABP, Intra-aortic balloon pump.
Table VIll. Hemorrhagic complications
Reoperation for bleeding (%) Patients receiving blood (%) Mean transfusion (units) Mean transfusion of patients receiving blood (units)
of both IMAs increases the potential for postoperative bleeding and increased blood requirements. Well previously reported that this was not a problem in patients with one IMA graft. With bilateral IMA grafts, there was no increase in the incidence of reoperation for bleeding and only a marginally significant increase in the volume of blood transfused. This is in agreement with previously reported findings that preoperative red cell mass and age were the two best predictors of the necessity for and the amount of transfusion in patients undergoing myocardial revascularization." The duration of the operation and the number of grafts were not predictors of transfusion requirements. Thus it is not surprising that there was only a small difference in hemorrhagic complications in this carefully matched group of patients. Of greatest concern in the use of IMA grafts is the possibility of sternal wound infections. Originally, Culliford and associates'? noted that sternal wound infections developed in 1.1 % of the patients receiving only vein grafts, in 2.3% of the patients when the left IMA was used, and in 8.5% of the patients who had bilateral IMA grafting. Surgeons became concerned that dissection of both IMAs would devascularize the sternum and increase the number of wound complications. Our previous data comparing patients receiving saphenous vein grafts with patients receiving one IMA graft failed to demonstrate an increased incidence of wound problems associated with this procedure. I I In the present series of similar patients being treated by three different methods, there were no wound complications in patients receiving only vein grafts, one in patients receiving one
Veins only (N= 338)
OnelMA (N= 338)
Two IMAs (N= 338)
13 141 1.7 4.0
8 (2.7) 117 (34.6) 1.4 ± 2.7 4.0 ± 3.3
18 (5J) 140 (41.2) 2.0 ± 4.0 4.9 ± 5.6
(3.8) (41.7) ± 2.7 ± 2.9
IMA graft, and eight in patients receiving bilateral IMA grafts. Of the eight patients who underwent bilateral IMA grafting, four required a second operation (a prevalence of sternal wound complications necessitating reoperation of 1.2%). Although the wound complications were more common in patients with bilateral IMA grafts, the wound complication rate was substantially lower than that previously reported by Culliford and his colleagues. 19 Of equal importance is the fact that patients who had wound complications were older and more frequently female. This correlates with the previously demonstrated increased prevalence of wound complications in these two subsets. Most important is the high prevalence of wound complications in patients with diabetes mellitus who have undergone bilateral IMA grafting-16.7% compared with 0.7% for nondiabetic patients undergoing bilateral IMA grafting. Multivariate analysis identified diabetes mellitus and advanced age as the only significant risk factors for wound complications. Type of conduit and gender did not achieve statistical significance. Special consideration should be given to diabetic patients and elderly patients before bilateral IMA grafting. From this study we conclude that bilateral IMA grafting does not increase surgical mortality; however, it does increase surgical morbidity to a small degree. These findings should be reassuring to surgeons who are attempting to improve the long-term results of myocardial revascularization by using bilateral IMA grafts and help them to select the most appropriate patients in whom to practice this technique.
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REFERENCES 1. Loop FD, Irarrazaval MF, Bredee JJ, Siegel W, Taylor PC, Sheldon We. Internal mammary artery graft for ischemic heart disease: effects of revascularization on clinical status and survival. Am J Cardiol 1977;39:5I622. 2. Tector AJ, Schmahl TM, Janson B, Kallies JR, Johnson G. The internal mammary artery graft: its longevity after coronary bypass. JAMA 1981;246:2181-3. 3. Lytle BW, Loop FD, Cosgrove DM, Ratliff NB, Easley K, Taylor pe. Long-term (5-12 years) serial studies of internal mammary artery and saphenous vein bypass grafts. J THORAC CARDIOVASC SURG 1985;89:248-58. 4. Singh RN, Sosa JA, Green GE. Long-term fate of the internal mammary artery and saphenous vein grafts. J THoRAc CARDIOVASC SURG 1983;86:359-63. 5. Okies JE, Page US, Bigelow JC, Krause AH, Salomon NW. The left internal mammary artery: the graft of choice. Circulation 1984;70(Pt 2):1213-21. 6. LOOp FD, Lytle BW, Cosgrove DM, et al. Influence of the internal mammary artery graft on 10-year survival and other cardiac events. New Engl J Med 1984; 314:1-6. 7. Cosgrove DM, Loop FD, Lytle BW, et al. Determinants of 10-year survival after primary myocardial revascularization. Ann Surg 1985;202:480-90. 8. Cosgrove DM, Loop FD, Lytle BW, et al. Predictors of reoperation after myocardial revascularization. J THORAC CARDIOVASC SURG 1986;92:811-21. 9. Cosgrove DM, Loop FD. Techniques to maximize internal mammary artery length. Ann Thorac Surg 1985; 40:78-9. 10. Loop FD, Lytle BW, Cosgrove DM, Golding LAR, Taylor PC, Stewart RW. Free (aorta-coronary) internal mammary artery graft: late results. J THoRAc CARDIOVASC SURG 1986;92:827-31. 11. Cosgrove DM, Loop FD, Lytle BW, et al. Does mammary artery grafting increase surgical risk? Circulation 1985;72(Pt 2):11 170-4. 12. Cosgrove DM, Loop FD, Lytle BW, et al. Primary myocardial revascularization: trends in surgical mortality. J THoRAc CARDIOVASC SURG 1984;88:673-84. 13. Cox DR. The analysis of binary data. London: Methuen, 1970. 14. Lytle BW, Loop FD, Cosgrove DM, et al. Fifteen hundred coronary reoperations: results and determinants of early and late survival. J THoRAc CARDIOVASC SURG 1987;93:847-59. 15. Cosgrove DM, Loop FD, Saunders CL, Lytle BW, Kramer JR. Should coronary arteries with less than fifty percent stenosis be bypassed? J THORAC CARDIOVASC SURG 1981;82:520-30. 16. Schmidt DH, Blau F, Hellman C, Grzelak L, Johnson WD. Isoproterenol-induced flow responses in mammary and vein bypass grafts. J THoRAc CARDIOVASC SURG 1980;80:319-26. 17. Burgess GE, Cooper JR, Marino RJ, Peuler MJ, Mills
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NL, Ochsner JL. Pulmonary effect of pleurotomy during and after coronary artery bypass with internal mammary artery versus saphenous vein grafts. J THoRAc CARDIOVASC SURG 1978;76:230-4. 18. Cosgrove DM, Loop FD, Lytle BW, et al. Determinants of blood utilization during myocardial revascularization. Ann Thorac Surg 1985;40:380-4. 19. Culliford AT, Cunningham IN, Zeff RH, lsom OW, Teiko P, Spencer Fe. Sternal and costochondral infections following open-heart surgery: a review of 2,594 cases. J THORAC CARDIOVASC SURG 1976;72:714-26.
Discussion Dr. R. Leighton Fisk (Scottsdale. Ariz.). The cardiac surgeon is challenged to provide optimum myocardial revascularization based on available conduits and individual patient needs. Continuing commitment to improved surgical technique is imperative if the surgeon is to rescue patients from the adventures of his cardiology colleagues, armed with alternate means of palliation through advancing technology and experience. Dr. Cosgrove's report represents another benchmark, with its enviably low rate of morbidity and mortality with double IMA grafts. In a significant number of patients in three carefully matched groups under study, Cosgrove and coworkers have shown that the mortality rate is probably not increased and morbidity affected surprisingly little by the use of double IMA grafts. In the hands of the experienced, morbidity appears to be limited to sternal wound problems, and these occur predominantly in patients with diabetes, the very elderly, and three times more often in women than in men. The safety and theoretical superiority of single IMA grafting was presented many years ago. Original proponents fortunately persisted in their effort to successfully demonstrate the superiority of the single IMA graft over the saphenous vein graft with respect to long-term clinical results. Given this information, many surgeons who were reluctant to change are still working through their learning curve with the single IMA graft. Important for us now is the clear demonstration that double IMA grafts are significantly superior to single IMA grafts over the long term. Answers to a number of questions will be forthcoming, I hope by careful follow-up study on the part of those facile with the double IMA graft. Some of those questions are as follows: I. How much better is double IMA grafting? 2. Should double IMA grafting be reserved for those in whom "total" revascularization can be accomplished with only IMA conduits? 3. What are the preferred or optimal routes and configurations for extended revascularization with two IMAs? Long-term outcome of coronary artery bypass relates not only to graft patency and flow potential, but also to new disease and progression of disease in the native vessels. 4. What are the nature, frequency, and severity of complications attending reoperation after prior double IMA grafting? 5. Should one IMA perhaps be kept in reserve for future operation in certain subsets of patients, such as the younger
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Cosgrove et al.
patient? I have certainly been pleased to have IMAs available when reoperation is required. I congratulate the authors for clearly showing that double IMA grafting is a clinically safe and sound alternative. I will look forward to future work from this group evaluating the long-term outcome with their patients. I would like to close with four or five questions. Neither your abstract nor manuscript clarified that all IMA grafts were in situ, as distinguished from free IMA conduits. Could you please comment on this? Dr. Cosgrove. Free IMA grafts were included. This was done because we were interested in the morbidity and mortality associated with this revascularization attempt, not the long-term influence of an in situ graft versus a free graft. Dr. Fisk. In your experience with 500 double IMA grafts, 162 patients were excluded from this presentation, Do any of your experiences with these 162 patients provide you with anecdotal or collective observations that you would share with those of us who are inspired by your results? Dr. Cosgrove. The first 500 patients who received bilateral IMA grafts were selected, and we attempted to find matches for them. The only reason that patients were excluded is that we could not find matches for six descriptors for them. There was no other reason for exclusion. Dr. Fisk. In other words, you do not have any additional reservation or advice to offer. Dr. Cosgrove. Our experience now includes over 2000 cases, and the incidence of wound complications has remained about the same. We continue to be very concerned about the incidence of wound complications in diabetic patients. Dr. Fisk. I think that in part answers my next questions: Do you now avoid using double IMA grafts in your elderly, diabetic, female patients, and are there any other conditions for which you believe that double IMA grafting is at least relatively contraindicated? Dr. Cosgrove. We avoid using them in those situations, except when there is no other acceptable conduit. There is one other situation in which I would caution against use of an IMA~in a patient who has an atherosclerotic, stenotic vein graft to the left anterior descending coronary artery. I would not remove the vein graft and replace it with an IMA, because we have found through rather bitter experience that it does not immediately provide enough flow to replace the entire demands of the left anterior descending if the artery is completely occluded. Dr. Fisk. I appreciate that caution. You have had an exemplary experience with minimal blood use. How do you manage the patient undergoing elective operation who has been receiving anti platelet agents? Dr. Cosgrove. We discontinue aspirin preoperatively and try to avoid operation for at least 5 days. Dr. Fisk. Do you modify your enthusiasm for the double IMA graft in emergency situations, such as evolving myocardial infarction with or without immediately antecedent thrombolysis therapy? Dr. Cosgrove. In patients who are ischemic and cannot be relieved medically, we are much less apt to use IMA grafts. Dr. Harold V. Liddle (Salt Lake City, Utah). I would like to make two comments. The first has to do with restudies of IMAs. In my own experience, in a group of approximately 50 persons who have had IMA grafts for 15 years or longer, it is encouraging to find that only one IMA failed late and all the
Thoracic and Cardiovascular Surgery
remainder appear arteriographically to be very satisfactory grafts. The enduring quality of the IMA graft inspires me to use it on a regular basis. My question, however, concerns the use of both IMAs and the problems attendant to that use at the time of operation. I would like to know whether you and your group have any unique tricks or different techniques of anatomic location of the right IMA graft that obviate the problems attendant to a second sternotomy. Dr. Cosgrove. We do two things at the initial operation to avoid the problem. First, the more length there is in the graft, the more apt it is to fall away from the retrosternal area. Second, in young patients in whom there is a high probability of a reoperation, use of a free graft that does not cross the midline will avoid potential complications. At the time of reoperation, the lateral chest x-ray film provides a good idea of the location relative to the stenosis. In patients in whom it is immediately behind the sternum, we would expose the femoral vessels and be ready to go on cardiopulmonary bypass. We have, however, been able to successfully dissect out the patent IMAs crossing the midline, but there certainly is an attrition from injury. Dr. Murray I. Sheldon (Concord. Calif). I would like to focus on the diabetic patients with the high incidence of sternal wound infections. Are these infections different? Are there more gram-negative organisms? Is the sternal wound healing after infection different? Are you having more problems with eventual closure and granulation? What do you really think is the cause of this infection, and how can we best avoid it when we have to use bilateral IMAs in elderly diabetic patients? Dr. Cosgrove. I do not have the answer to all of your questions. Fifty percent of patients with wound complications require a second surgical intervention to close the wound, and that may mean anything from muscle flaps to omentum or just plain rewiring. I think the cause has to be related in some part to small-vessel disease associated with diabetes, which decreases the potential developing collateral blood flow. Dr. Sheldon. How necrotic is the sternum when you reoperate in these patients? Dr. Cosgrove. Not all of them are necrotic, but some are completely avascular and require extensive debridement and flap closure. Dr. Sheldon. What has been the mortality in those patients in whom you have had to reoperate to close the wound. Dr. Crosgrove. There have been no deaths in this group. In 2000 patients there have been some deaths. Dr. David M. Follette (Santa Monica. Calif). We have been concerned about adequate myocardial protection with bilateral IMA grafts. Your data showed a slight increase, but not a statistically significant difference, in the rate of infarction. Do you use any special strategy in terms of distribution of the cardioplegic solution or order of grafting to optimize the myocardial protection during the procedure? Dr. Cosgrove. No. What we have tried to do is to pick for our IMA recipients the vessels that we thought had the greatest influence on long-term survival by supplying the greatest myocardial mass. That usually involves the circumflex and almost always the left anterior descending. Our preference has been to do the IMA graft last. The reason is that, because it is a more fragile anastomosis, the potential for pulling on the anastomosis is greater while the heart is being moved around, and the damage is harder to repair.
THoRAc CARDIOVASC SURG
1988;95:850-6
Does bilateral internal mammary artery grafting increase surgical risk? The risk of bilateral internal mammary artery grafting was studied in three groups of patients who were computer matched for recognized risk factors: year of operation, age, gender, extent of coronary artery disease, left ventricular function, completeness of myocardial revascularization, and history of congestive heart failure. The patient groups differed in the fact that they received veins only, one internal mammary artery graft, or two internal mammary artery grafts. The operative mortality rates for these three groups were 1.8%,0.3%, and 0.9%, respectively (no significant difference). Analysis of perioperative morbidity demonstrated no significant differences except for a slight increase in transfusion requirements in the group receiving two internal mammary artery grafts (p = 0.04). None of the patients with only veingrafts had wound complications. One patient in the group with one internal mammary artery graft had a wound complication (0.03 %). Eight patients receiving two internal mammary artery grafts had wound complications (2.4 %) (p = 0.002). The prevalence of wound complications in patients with diabetes mellitus was 5.7% and in those without diabetes mellitus, 0.3% (p = 0.01). The prevalence of wound complications in patients less than 60 years of age was 0.2%, in patients in their 60s, 1.6%, and in patients older than 70, 3.1 % (p = 0.01). Multivariate logistic regression analysis identified diabetes mellitus and age and not bilateral internal mammary artery grafting as risk factors for wound complications. We conclude that bilateral internal mammary artery grafting does not increase surgical mortality and increases surgical morbidity by a slight increase in the mean transfusion requirement.
D. M. Cosgrove, MD, B. W. Lytle, MD, F. D. Loop, MD, P. C. Taylor, MD, R. W. Stewart, MD, C. C. Gill, MD, L. A. R. Golding, MD, and Marlene Goormastic, MPH, Cleveland, Ohio
h e internal mammary artery (IMA) has been established as the preferred conduit for myocardial revascularization. Its early patency rate exceeds that of vein grafts and long-term patency remains high, in contrast to vein grafts, which are subject to late closure as a result of progressive atherosclerosis. loS This superior long-term patency is reflected in improvement in longterm survival, decrease in the rate of reoperation, and improvement in reoperation-free survival and cardiac morbidity." To further enhance the results of myocardial revascularization, both IMAs have been used in an
Table I. Matching criteria
From the Departments of Thoracic and Cardiovascular Surgery and Biostatistics and Epidemiology. The Cleveland Clinic Foundation. Cleveland, Ohio.
attempt to bypass multiple vessels with this conduit. Technical maneuvers to maximize IMA length, enabling it to reach more distal branches of the right and circumflex coronary arteries, have been described," and the free IMA graft has been shown to have excellent long-term patency." No adverse effect on morbidity or mortality has
Read at the Thirteenth Annual Meeting of The Western Thoracic Surgical Association, Colorado Springs, Colo.. June 24-27. 1987. Address for reprints: Delos M. Cosgrove. MD, The Cleveland Clinic Foundation. 9500 Euclid Ave., Cleveland, OH 44106.
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Year of operation Age Gender Extent of disease Ventricular function Completeness of revascularization History of congestive heart failure
Within 1 year Within 2 years Male/female Single/double or triple/left main Normal/mild or maderate/ severe Complete/incomplete Yes/no
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Table II. Preoperative clinical characteristics
Year of operation' Age (yr)" Male' ('it,) Diabetes mellitus (%) Hypertension (%) History of CHF (%) CHF (%.) Cholesterol ::::250 mg/dl (%) Smoking (%)
Veins only
One IMA
Two IMAs
198 J.7 58.4 ± 8.0 283 (84.3) 38 (11.3) 85 (25.1) 11 (3.3) 4 (1.2) 157 (47.6) 162 (48.9)
1981.6 57.9 ± 7.9 283 (84.3) 32 (9.6) 81 (24.0) 11 (3.3) 1 (0.3) 149 (44.5) 151 (45.8)
1982.5 58.3 ± 7.9 283 (84.3) 36 (10.7) 65 (19.2) 11 (3.3) 2 (0.6) 140 (41.4) 131 (39.6)
CHF, Congestive heart failure. "Matching criteria.
Table
m. Angiographic extent of coronary artery
Table IV. Preoperative ventricular function
disease
,{ Single (%) Double (%) ,{ Triple (o/r) Left main disease (%)
Veins only IN = 338)
One IMA IN= 338}
Two IMAs IN= 338)
7 104 179 48
7 (2.1) 104 (30.8) 208 (61.5) 19 (5.6)
7 104 185 42
(2.1) (30.8) (53.0) (14.2)
(2.8) (30.8) (54.7) (12.4)
, { Normal (%) Mild (%) , { Moderate (%) Severe (%)
Veins only IN= 338}
One IMA IN = 338}
Two IMAs IN= 338}
174(51.5) 92 (27.2) 49 (14.5) 23 (6.8)
232 34 50 22
163 103 56 16
(68.6) (10.1) (14.8) (6.5)
(48.2) (30.5) (16.6) (4.7)
* Matching criteria.
"Matching criteria.
resulted from the use of one IMA graft. I I Surgeons, however, are concerned that the longer, more complicated, and technically more demanding procedure of bilateral IMA grafting may have an adverse effect on surgical morbidity and mortality. This study was undertaken to address these concerns. Patients and methods The first 500 patients who underwent elective bilateral IMA grafting at The Cleveland Clinic from 1972 through 1985 were identified with the aid of a computerized cardiovascular information registry. They provide the basis for this study. Excluded were patients undergoing reoperation and patients who had concomitant valve procedures, carotid endarterectomy, or aneurysmectomy. With the use of patient descriptors previously identified as operative risk factors, including year of operation, age, gender, extent of coronary artery disease, left ventricular function, completeness of revascularization, and history of congestive heart failure, it was possible to computer match groups of 338 patients." The groups differed in the fact that they received only vein grafts, one IMA graft, or two IMA grafts. Parameters for the matching criteria are shown in Table I. The computer-matched preoperative clinical characteristics of the three groups and other preoperative characteristics not computer matched were similar (Table II). The annual distribution of cases of the three groups was not significantly different (Fig. I). Computer matching for extent of coronary artery disease was done by using single- or double-vessel disease and triple-vessel or left main disease. In each group,
32.9% of the patients had single- or double-vessel disease and the remainder had triple-vessel or left main disease. The breakdown into single, double, triple, and left main disease is shown in Table III. Left ventricular function was matched by normal or mild ventricular dysfunction and moderate or severe ventricular dysfunction categories. Further stratification is shown in Table IV. The operative variables were remarkably similar although there was a trend toward an increasing number of grafts in the two-IMA group (Table V). Biostatistical method. Univariate analyses among the three groups were done by analysis of variance technique for continuous variables and XC test when appropriate for categorical variables. In cases in which the expected cell frequencies were small «5), Fisher's exact test was used to compare the groups. A t test was used to compare mean values for two groups. A stepwise logistic regression analysis was used to test independent association of multiple factors with wound complications." Results Mortality. There were 10 deaths in the entire group
(1.0%): six (1.8%) among patients receiving only vein grafts, one (0.3%) among patients receiving one IMA graft, and three (0.9%) among those receiving two IMA grafts. The differences were not statistically significant. The causes of death are listed in Table VI. Of the six deaths in patients undergoing saphenous vein grafts, three were related to preexisting conditions that dictated the choice for vein grafts as conduits. No deaths in any
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220 200 180 160 140
> o zw 120
o
;:)
aw
a:
100
VEINS ONLY
6. ONE IMA
e
IL
80
TWO IMAs
60 40 20 0 72
73
74
75
76
77
78
79
80
81
82
83
84
85
YEAR
Fig. 1. The annual distribution of cases in the three groups demonstrates the preponderance of patients who were operated on from 1982 through 1984.
group could be directly or indirectly attributed to the choice of conduit. Morbidity. The morbidity for the three groups is listed in Table VII. No significant trends emerged. Special attention was directed to complications related to the extent of the surgical procedure, including bleeding and wound complications. Table VIII shows the prevalence of hemorrhagic complications. Only mean transfusion requirements increased significantly in patients receiving bilateral IMA grafts. Wound complications were more common in patients with bilateral IMA grafts than in those with saphenous vein grafts or those receiving single IMA grafts. There were no complications in patients receiving only saphenous vein grafts, one (0.3%) in patients receiving one IMA graft, and eight (2.4%) in patients receiving two IMA grafts (p = 0.002). One patient in the single-IMA group (0.3%) required reoperation for wound complications whereas four (1.2%) patients with bilateral IMA grafts required some form of surgical intervention for management of wound complications. Further analysis of trends in wound complications with IMA grafts demonstrated women to have a higher incidence of wound complications (3/156 [5.7%]) than did men (6/1005 [1.4%]) (no significant difference). Among patients with bilateral IMA grafts, there were three wound complications in 53 women (5.7%) compared to five in 285 men (1.8%). These differences did not achieve statistical significance. More significant was the
decided increase in wound complications in patients with diabetes mellitus. In patients with single IMA grafts, there was one wound complication in 32 diabetic patients (3.1%) opposed to no wound complications in 303 nondiabetic patients. In patients who had two IMA grafts, there were two wound complications in 302 nondiabetic patients (0.7%) compared to six wound complications in 36 diabetic patients (16.7%) (p < 0.0001). Age influenced the incidence of wound complications. There was one wound complication in 562 patients less than 60 years of age (0.2%), six in 388 patients who were in their 60s (1.6%) and two in 62 patients age 70 years or older (3.1%) (p = 0.012). To identify and establish priorities for risk factors for wound complications, age, gender, diabetic status, and number of IMA grafts were entered into a multivariate logistic regression analysis. Diabetes mellitus (p < 0.001) and advanced age (p = 0.003) were the only statistically significant risk factors. Discussion The IMA graft has an early patency rate exceeding that of vein grafts.':" The difference in patency rates increases with time as vein grafts become stenotic and occluded as a result of progressive vein graft atherosclerosis, from which the IMA seems to be largely immune.'? Currently, vein graft failure is the major angiographic indication for reoperation, and it is increas-
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Table V. Operative variables Grafts (mean) Complete revascularization ('If) Cardioplegia ('Yr.)
Veins only
One IMA
Two IMAs
3.0 ± 0.9 286 (84.6) 288 (83.2)
3.2 ± 1.0 286 (84.6) 282 (83.4)
3.3 ± 1.0 286 (84.6) 290 (85.8)
inglyrecognized that stenotic vein grafts were associated with disastrous clinical histories." The IMA has the further advantage of not accelerating progression of atherosclerosis in the native circulation as rapidly as vein grafts." The clinical advantages of the superior long-term patency of the IMA graft are demonstrated in improvement in long-term survival, incidence of reoperation, reoperation-free survival, and hospitalization for cardiac events." If the long-term salutary effects of myocardial revascularization are to be sustained, it is essential that the conduit maintain its patency. Focus has turned to the IMA in an attempt to bypass the maximum number of vessels with a conduit demonstrated to have excellent long-term patency. Well have previously demonstrated in a large series of patients that there was no increased morbidity or mortality from using one IMA graft, but we have not demonstrated the safety of two IMA grafts. If this technique is to be widely adopted, it is important that its safety be documented and that any patient subsets with the increased potential for complications be identified. Previous analysis of the large patient groups operated on at one institution during this time frame have identified the major factors influencing operative mortality rate. Emergency operation, advanced age, poor ventricular function, female gender, incomplete revascularization, history of congestive heart failure, abnormal electrocardiogram, and congestive heart failure at the time of operation were the major risk factors during the 1980s when the majority of patients underwent operation. All but the latter two factors were taken into consideration in selection of matching criteria. Left main trunk disease was not separately matched as a risk factor, because since the mid-1970s this has ceased to be an independent risk factor and has an operative mortality rate similar to that of three-vessel disease." The similarity of patients matched in the three groups is demonstrated not only by statistical comparability of the matching criteria, but also for other preoperative descriptors such as preoperative hypertension, serum cholesterol levels greater than 250 mg/dl, history of smoking, diabetes mellitus, congestive heart failure, number of grafts, and use of cardioplegia.
Table VI. Causes of death Cause Veins only (N = 6) Hemorrhage Neurologic Infection Renal One IMA (N = I) Hemorrhage Two (MAs (N = 3) Cardiac Respira tory Multisystem failure
No. 2 2
Preexisting conditions that dictated the selection of veins as conduits probably accounted for the slightly higher operative mortality rate in patients in this group. Three patients died of preexisting conditions: renal failure, chronic lymphocytic leukemia, and refusal of a Jehovah's Witness to accept a transfusion. In these situations, surgeons selected vein grafts in the belief that the preexisting condition favored their use. In no cases could the cause of death be directly or indirectly attributed to the selection of one or more IMA grafts. The prolonged anesthesia time before the commencement of cardiopulmonary bypass provides an opportunity for undiagnosed ischemia to occur, which would result in increased perioperative infarctions. The fact that this did not occur is largely attributable to the increased sophistication of the cardiac anesthesiologist in maintaining the patient in a nonischemic state. The low incidence of perioperative myocardial infarction further attests to the ability of the IMA to provide blood flow sufficient to meet myocardial oxygen demands, as previously demonstrated by Schmidt and associates." The pleural space was opened during all IMA dissections. Previous reports suggest that respiratory function is impaired in patients when the pleural space is opened." In these three similar groups of patients, opening the pleural spaces did not significantly increase respiratory complications even when both pleural spaces were opened. Respiratory complications have previously been demonstrated to increase with age." The additional dissection associated with mobilization
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Table YD. Surgical morbidity
Myocardial infarction (%) Respiratory insufficiency (%) Stroke (%) IABP (%)
Veins only (N= 338)
OnelMA (N= 338)
2 (0.6) 12 (3.6) 7 (2.1) 2 (0.6)
3 (0.9) 6 (1.8) 4 (1.2) 1 (OJ)
Two IMAs (N= 338) 7 (2.1)
II (3.2) 8 (2.4) 2 (0.6)
IABP, Intra-aortic balloon pump.
Table VIll. Hemorrhagic complications
Reoperation for bleeding (%) Patients receiving blood (%) Mean transfusion (units) Mean transfusion of patients receiving blood (units)
of both IMAs increases the potential for postoperative bleeding and increased blood requirements. Well previously reported that this was not a problem in patients with one IMA graft. With bilateral IMA grafts, there was no increase in the incidence of reoperation for bleeding and only a marginally significant increase in the volume of blood transfused. This is in agreement with previously reported findings that preoperative red cell mass and age were the two best predictors of the necessity for and the amount of transfusion in patients undergoing myocardial revascularization." The duration of the operation and the number of grafts were not predictors of transfusion requirements. Thus it is not surprising that there was only a small difference in hemorrhagic complications in this carefully matched group of patients. Of greatest concern in the use of IMA grafts is the possibility of sternal wound infections. Originally, Culliford and associates'? noted that sternal wound infections developed in 1.1 % of the patients receiving only vein grafts, in 2.3% of the patients when the left IMA was used, and in 8.5% of the patients who had bilateral IMA grafting. Surgeons became concerned that dissection of both IMAs would devascularize the sternum and increase the number of wound complications. Our previous data comparing patients receiving saphenous vein grafts with patients receiving one IMA graft failed to demonstrate an increased incidence of wound problems associated with this procedure. I I In the present series of similar patients being treated by three different methods, there were no wound complications in patients receiving only vein grafts, one in patients receiving one
Veins only (N= 338)
OnelMA (N= 338)
Two IMAs (N= 338)
13 141 1.7 4.0
8 (2.7) 117 (34.6) 1.4 ± 2.7 4.0 ± 3.3
18 (5J) 140 (41.2) 2.0 ± 4.0 4.9 ± 5.6
(3.8) (41.7) ± 2.7 ± 2.9
IMA graft, and eight in patients receiving bilateral IMA grafts. Of the eight patients who underwent bilateral IMA grafting, four required a second operation (a prevalence of sternal wound complications necessitating reoperation of 1.2%). Although the wound complications were more common in patients with bilateral IMA grafts, the wound complication rate was substantially lower than that previously reported by Culliford and his colleagues. 19 Of equal importance is the fact that patients who had wound complications were older and more frequently female. This correlates with the previously demonstrated increased prevalence of wound complications in these two subsets. Most important is the high prevalence of wound complications in patients with diabetes mellitus who have undergone bilateral IMA grafting-16.7% compared with 0.7% for nondiabetic patients undergoing bilateral IMA grafting. Multivariate analysis identified diabetes mellitus and advanced age as the only significant risk factors for wound complications. Type of conduit and gender did not achieve statistical significance. Special consideration should be given to diabetic patients and elderly patients before bilateral IMA grafting. From this study we conclude that bilateral IMA grafting does not increase surgical mortality; however, it does increase surgical morbidity to a small degree. These findings should be reassuring to surgeons who are attempting to improve the long-term results of myocardial revascularization by using bilateral IMA grafts and help them to select the most appropriate patients in whom to practice this technique.
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REFERENCES 1. Loop FD, Irarrazaval MF, Bredee JJ, Siegel W, Taylor PC, Sheldon We. Internal mammary artery graft for ischemic heart disease: effects of revascularization on clinical status and survival. Am J Cardiol 1977;39:5I622. 2. Tector AJ, Schmahl TM, Janson B, Kallies JR, Johnson G. The internal mammary artery graft: its longevity after coronary bypass. JAMA 1981;246:2181-3. 3. Lytle BW, Loop FD, Cosgrove DM, Ratliff NB, Easley K, Taylor pe. Long-term (5-12 years) serial studies of internal mammary artery and saphenous vein bypass grafts. J THORAC CARDIOVASC SURG 1985;89:248-58. 4. Singh RN, Sosa JA, Green GE. Long-term fate of the internal mammary artery and saphenous vein grafts. J THoRAc CARDIOVASC SURG 1983;86:359-63. 5. Okies JE, Page US, Bigelow JC, Krause AH, Salomon NW. The left internal mammary artery: the graft of choice. Circulation 1984;70(Pt 2):1213-21. 6. LOOp FD, Lytle BW, Cosgrove DM, et al. Influence of the internal mammary artery graft on 10-year survival and other cardiac events. New Engl J Med 1984; 314:1-6. 7. Cosgrove DM, Loop FD, Lytle BW, et al. Determinants of 10-year survival after primary myocardial revascularization. Ann Surg 1985;202:480-90. 8. Cosgrove DM, Loop FD, Lytle BW, et al. Predictors of reoperation after myocardial revascularization. J THORAC CARDIOVASC SURG 1986;92:811-21. 9. Cosgrove DM, Loop FD. Techniques to maximize internal mammary artery length. Ann Thorac Surg 1985; 40:78-9. 10. Loop FD, Lytle BW, Cosgrove DM, Golding LAR, Taylor PC, Stewart RW. Free (aorta-coronary) internal mammary artery graft: late results. J THoRAc CARDIOVASC SURG 1986;92:827-31. 11. Cosgrove DM, Loop FD, Lytle BW, et al. Does mammary artery grafting increase surgical risk? Circulation 1985;72(Pt 2):11 170-4. 12. Cosgrove DM, Loop FD, Lytle BW, et al. Primary myocardial revascularization: trends in surgical mortality. J THoRAc CARDIOVASC SURG 1984;88:673-84. 13. Cox DR. The analysis of binary data. London: Methuen, 1970. 14. Lytle BW, Loop FD, Cosgrove DM, et al. Fifteen hundred coronary reoperations: results and determinants of early and late survival. J THoRAc CARDIOVASC SURG 1987;93:847-59. 15. Cosgrove DM, Loop FD, Saunders CL, Lytle BW, Kramer JR. Should coronary arteries with less than fifty percent stenosis be bypassed? J THORAC CARDIOVASC SURG 1981;82:520-30. 16. Schmidt DH, Blau F, Hellman C, Grzelak L, Johnson WD. Isoproterenol-induced flow responses in mammary and vein bypass grafts. J THoRAc CARDIOVASC SURG 1980;80:319-26. 17. Burgess GE, Cooper JR, Marino RJ, Peuler MJ, Mills
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NL, Ochsner JL. Pulmonary effect of pleurotomy during and after coronary artery bypass with internal mammary artery versus saphenous vein grafts. J THoRAc CARDIOVASC SURG 1978;76:230-4. 18. Cosgrove DM, Loop FD, Lytle BW, et al. Determinants of blood utilization during myocardial revascularization. Ann Thorac Surg 1985;40:380-4. 19. Culliford AT, Cunningham IN, Zeff RH, lsom OW, Teiko P, Spencer Fe. Sternal and costochondral infections following open-heart surgery: a review of 2,594 cases. J THORAC CARDIOVASC SURG 1976;72:714-26.
Discussion Dr. R. Leighton Fisk (Scottsdale. Ariz.). The cardiac surgeon is challenged to provide optimum myocardial revascularization based on available conduits and individual patient needs. Continuing commitment to improved surgical technique is imperative if the surgeon is to rescue patients from the adventures of his cardiology colleagues, armed with alternate means of palliation through advancing technology and experience. Dr. Cosgrove's report represents another benchmark, with its enviably low rate of morbidity and mortality with double IMA grafts. In a significant number of patients in three carefully matched groups under study, Cosgrove and coworkers have shown that the mortality rate is probably not increased and morbidity affected surprisingly little by the use of double IMA grafts. In the hands of the experienced, morbidity appears to be limited to sternal wound problems, and these occur predominantly in patients with diabetes, the very elderly, and three times more often in women than in men. The safety and theoretical superiority of single IMA grafting was presented many years ago. Original proponents fortunately persisted in their effort to successfully demonstrate the superiority of the single IMA graft over the saphenous vein graft with respect to long-term clinical results. Given this information, many surgeons who were reluctant to change are still working through their learning curve with the single IMA graft. Important for us now is the clear demonstration that double IMA grafts are significantly superior to single IMA grafts over the long term. Answers to a number of questions will be forthcoming, I hope by careful follow-up study on the part of those facile with the double IMA graft. Some of those questions are as follows: I. How much better is double IMA grafting? 2. Should double IMA grafting be reserved for those in whom "total" revascularization can be accomplished with only IMA conduits? 3. What are the preferred or optimal routes and configurations for extended revascularization with two IMAs? Long-term outcome of coronary artery bypass relates not only to graft patency and flow potential, but also to new disease and progression of disease in the native vessels. 4. What are the nature, frequency, and severity of complications attending reoperation after prior double IMA grafting? 5. Should one IMA perhaps be kept in reserve for future operation in certain subsets of patients, such as the younger
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patient? I have certainly been pleased to have IMAs available when reoperation is required. I congratulate the authors for clearly showing that double IMA grafting is a clinically safe and sound alternative. I will look forward to future work from this group evaluating the long-term outcome with their patients. I would like to close with four or five questions. Neither your abstract nor manuscript clarified that all IMA grafts were in situ, as distinguished from free IMA conduits. Could you please comment on this? Dr. Cosgrove. Free IMA grafts were included. This was done because we were interested in the morbidity and mortality associated with this revascularization attempt, not the long-term influence of an in situ graft versus a free graft. Dr. Fisk. In your experience with 500 double IMA grafts, 162 patients were excluded from this presentation, Do any of your experiences with these 162 patients provide you with anecdotal or collective observations that you would share with those of us who are inspired by your results? Dr. Cosgrove. The first 500 patients who received bilateral IMA grafts were selected, and we attempted to find matches for them. The only reason that patients were excluded is that we could not find matches for six descriptors for them. There was no other reason for exclusion. Dr. Fisk. In other words, you do not have any additional reservation or advice to offer. Dr. Cosgrove. Our experience now includes over 2000 cases, and the incidence of wound complications has remained about the same. We continue to be very concerned about the incidence of wound complications in diabetic patients. Dr. Fisk. I think that in part answers my next questions: Do you now avoid using double IMA grafts in your elderly, diabetic, female patients, and are there any other conditions for which you believe that double IMA grafting is at least relatively contraindicated? Dr. Cosgrove. We avoid using them in those situations, except when there is no other acceptable conduit. There is one other situation in which I would caution against use of an IMA~in a patient who has an atherosclerotic, stenotic vein graft to the left anterior descending coronary artery. I would not remove the vein graft and replace it with an IMA, because we have found through rather bitter experience that it does not immediately provide enough flow to replace the entire demands of the left anterior descending if the artery is completely occluded. Dr. Fisk. I appreciate that caution. You have had an exemplary experience with minimal blood use. How do you manage the patient undergoing elective operation who has been receiving anti platelet agents? Dr. Cosgrove. We discontinue aspirin preoperatively and try to avoid operation for at least 5 days. Dr. Fisk. Do you modify your enthusiasm for the double IMA graft in emergency situations, such as evolving myocardial infarction with or without immediately antecedent thrombolysis therapy? Dr. Cosgrove. In patients who are ischemic and cannot be relieved medically, we are much less apt to use IMA grafts. Dr. Harold V. Liddle (Salt Lake City, Utah). I would like to make two comments. The first has to do with restudies of IMAs. In my own experience, in a group of approximately 50 persons who have had IMA grafts for 15 years or longer, it is encouraging to find that only one IMA failed late and all the
Thoracic and Cardiovascular Surgery
remainder appear arteriographically to be very satisfactory grafts. The enduring quality of the IMA graft inspires me to use it on a regular basis. My question, however, concerns the use of both IMAs and the problems attendant to that use at the time of operation. I would like to know whether you and your group have any unique tricks or different techniques of anatomic location of the right IMA graft that obviate the problems attendant to a second sternotomy. Dr. Cosgrove. We do two things at the initial operation to avoid the problem. First, the more length there is in the graft, the more apt it is to fall away from the retrosternal area. Second, in young patients in whom there is a high probability of a reoperation, use of a free graft that does not cross the midline will avoid potential complications. At the time of reoperation, the lateral chest x-ray film provides a good idea of the location relative to the stenosis. In patients in whom it is immediately behind the sternum, we would expose the femoral vessels and be ready to go on cardiopulmonary bypass. We have, however, been able to successfully dissect out the patent IMAs crossing the midline, but there certainly is an attrition from injury. Dr. Murray I. Sheldon (Concord. Calif). I would like to focus on the diabetic patients with the high incidence of sternal wound infections. Are these infections different? Are there more gram-negative organisms? Is the sternal wound healing after infection different? Are you having more problems with eventual closure and granulation? What do you really think is the cause of this infection, and how can we best avoid it when we have to use bilateral IMAs in elderly diabetic patients? Dr. Cosgrove. I do not have the answer to all of your questions. Fifty percent of patients with wound complications require a second surgical intervention to close the wound, and that may mean anything from muscle flaps to omentum or just plain rewiring. I think the cause has to be related in some part to small-vessel disease associated with diabetes, which decreases the potential developing collateral blood flow. Dr. Sheldon. How necrotic is the sternum when you reoperate in these patients? Dr. Cosgrove. Not all of them are necrotic, but some are completely avascular and require extensive debridement and flap closure. Dr. Sheldon. What has been the mortality in those patients in whom you have had to reoperate to close the wound. Dr. Crosgrove. There have been no deaths in this group. In 2000 patients there have been some deaths. Dr. David M. Follette (Santa Monica. Calif). We have been concerned about adequate myocardial protection with bilateral IMA grafts. Your data showed a slight increase, but not a statistically significant difference, in the rate of infarction. Do you use any special strategy in terms of distribution of the cardioplegic solution or order of grafting to optimize the myocardial protection during the procedure? Dr. Cosgrove. No. What we have tried to do is to pick for our IMA recipients the vessels that we thought had the greatest influence on long-term survival by supplying the greatest myocardial mass. That usually involves the circumflex and almost always the left anterior descending. Our preference has been to do the IMA graft last. The reason is that, because it is a more fragile anastomosis, the potential for pulling on the anastomosis is greater while the heart is being moved around, and the damage is harder to repair.