CORONARY

INTRODUCTION

ARTERY

BYPASS

SURGERY

AND HISTORY

Coronary bypass surgery is a unique operation. It is complex microsurgery requiring a large, highly trained surgical team, extracorporeal circulation, and intensive care unit resources. Despite this complexity, despite its expense, and after being subjected to the most intense scrutiny any treatment has ever received, bypass surgery has become a very common operation. It has become common because it is a successful therapy for coronary atherosclerosis, a prevalent disease in Western society. Today bypass surgery is performed in 1 of every 1,000 persons in the United States of America each year, and it is as close to a public health measure as any operation has ever been. In this review, we will examine the current status of coronary bypass surgery as a treatment for patients with isolated coronary artery disease. Modern coronary bypass surgery is the result of a stepwise series of intellectual and technologic advances that extend back to the early years of this century (Table 11.’ Alexis Carrel performed experimental coronary bypass grafts in 1910. Subsequently, a number of schemes for indirectly increasing myocardial oxygen supply and treating angina pectoris, including cetvical sympathectomy, arterialization of the coronary sinus, coronary sinus ligation, per&u-dial and epicardial scarring operations, and ligation of the internal mammary arteries (IMAs), were attempted experimentally and clinically? 3 But the first operation that was documented to increase myocardial perfusion was Vineberg’s concept of implanting mammary arteries into the myocardium with the hope that communications with the coronary arteries would develop.4 Those communications sometimes did develop and some patients did experience relief of angina, but revascularization was inconsistent and was not immediate. The first direct approach to increasing coronary blood flow that was successful was coronary endarterectomy, performed clinically by Bailey in 1957.5 Another direct operation was patch repair of coronary stenoses, used successfully by both Senning and Effler in 196Z6

Curr

Probl

Surg,

October

1992

743

TABLE 1. Early History of Coronary Bypass Surgery’-3 Experimental 1910 Alexis Carrel. Carotid artery graft from descending 1950 1954 1956 1960 1961 1961 1964 Clinical 1906 1946 1946 1953 1957 1962 1962 1964

thoracic aorta to left comnary

Murray et al. Interposition vein grafts to coronary arteries Murray et al. Carotid artery graft from ascending aorta to coronary artery Thai et al. Mammary artery gratt to comnary artery Goetz et al. Mammary artery graft to left coronary system Mamiya et al. Left subclavian artery graft to left coronary artery Mamiya et al. Mammary artery gratI to right coronary artery Spencer et al. Mammary artery graft to circumflex comnaty artery Goyanes. Popliteal aneurysm replacement with venous graft Vineberg. Left mammary artery myocardial implantation Kunlin. Saphenous vein bypass grafting of lower-extremity atherosclerosis Gibbon. Cardiopulmonary bypass Bafly. Coronary endartemctomy Effler and Senning. Patch repair of coronary artery stenosis Sabiston. Saphenous vein graft to right coronary artery Garrett et al. Successful saphenous vein graft to left anterior descending coronary

1964 Kolessov. Mammary artery graft to left anterior descending comnaty artery (without coronary arterfography) 1967 Favalom. Saphenous vein graft to right comnaty artery 1968 Favalom and Johnson et al. Saphenous vein grafts to left coronary artery 1968 Green et al. Mammary artery graft to left coronary system

Two steps were essential in the development of bypass surgery as a widely used surgical treatment for coronary artery disease. One was the development of coronary arteriography by Sones and others.’ Although the initial demonstration of coronary anatomy by arteriography was somewhat serendipitous, Sones immediately recognixed the importance of this technique for the diagnosis and treatment of ischemic heart disease and applied it in the investigation of large numbers of patients. Also important were the careful follow-up studies by Proudfit and others, which demonstrated that the probability of complications of coronary atherosclerosis could be predicted by determining the location and severity of coronary artery lesions and left ventricular function.6-1o Once it became possible to de&e the anatomy of coronary artery disease and to determine its impact on prognosis, direct anatomic approaches to the treatment of coronary atherosclerosis were inevitable. The second critical advance was the development of cardiopulmonary bypass, used clinically by Gibbon in 1953. Although it has been possible to perform limited operations for bypass gmfting without cardiopulmonary bypass, the precise reconstructions needed to treat extensive coronary 744

Curr mob1 surg.

October 1992

artery disease would not have been possible without cardiopulmonary support. Vascular surgeons had used saphenous vein grafts for the treatment of lower-extremity arterial stenoses as early as 1948, and in 1962 Sabiston, at the Johns Hopkins Hospital, extended these concepts to the coronary arteries when he performed a saphenous vein graft from the aorta to the right coronary artery.’ Unfortunately, the patient died, delaying the further use of bypass surgery at this institution. Garrett and DeBakey successfully used a saphenous vein graft to the left coronary system as a “bailout” procedure in 1964 when an attempt at an endarterectomy failed but did not continue with bypass surgery until a number of years later.” In the Soviet Union, Kolessov performed an IMA graft to the left anterior descending (LAD) coronary artery in 1966 for the treatment of angina but without the benefit of coronary arteriography.” In 1967, Favalom revived the use of the saphenous vein graft when he performed a graft to the right coronary artery.13 The contributions of Favalom, Effler, Sones, and the Cleveland Clinic team were twofold: (1) bypass surgery was performed as a planned procedure to treat specific comnary stenoses that had been documented by arteriography, and (2) they kept doing it. Within a year the Cleveland Clinic team and Johnson and colleagues in Milwaukee had extended saphenous vein-grafting techniques to the left coronary system and Green had used the left IMA as a coronary bypass graft.‘4-16 The floodgates opened. Angiographic follow-up studies documented that many coronary bypass grafts remained patent, and the effectiveness of bypass surgery in relieving angina was soon obvibypass ous.l’, la Within a few years many centers were performing surgery, and by the early 1970s the techniques that form the basis of bypass surgery todaysaphenous vein grafting, IMA artery grafting, and coronary endarterectomy-were well established. Since then, the fundamental reconstructive techniques used in coronary surgery have changed very little. Conversely, major changes have taken place in techniques for protecting the patient and the myocardium during and after the operation. In addition, the assessment of the long-term results of bypass surgery and the more precise recognition of the subgroups of patients with coronary atherosclerosis who can benefit most from operation have been more fully documented. From the start, the results of coronary bypass surgery were carefully scrutinized. By 1975, three large, multicenter, prospective, randomized studies concerning coronary bypass surgery had been initiatedthe Veterans Administration Cooperative Study Gmup for Surgery for Coronary Arterial Obstructive Disease (VA study),“’ ” the European Coronary Surgery Study tECSSl?l and the Coronary Artery Surgery Study (CASS)?2 These studies evaluated the strategy of immediate surgery versus initial medical management followed by SUP Cum

Probl

Suv

October

~%a

746

gery if symptoms worsened. The study design and results of these trials were variable, and they all sparked debate. However, despite their design and the limited spectrum of patients examined, the randomized studies provided an enormous amount of information and established a foundation for the ongoing study of the efficacy of coronary artery surgery. All of these studies showed that some subgroups of patients have improved survival with surgery. No other operation has been evaluated with the same intensity as has coronary bypass surgery. At present the major issues that face surgeons concerning coronary bypass surgery are myocardial protection, noncardiac perioperative morbidity and mortality, long-term vein graft patency, the use of arterial bypass grafts, and the indications for reoperation.

CZSIIVGZNG PATIENT POPULATION One of the salient features of the practice of coronary bypass surgery is that the patient population has changed with time. Table 2 lists characteristics for the first 1,000 patients undergoing primary isolated elective bypass surgery each year at The Cleveland Clinic Foundation during selected years from 1967 to 1990. When compared with patients operated on in the early years of bypass surgery, patients today are older, less often men, and more likely to have

TABLE 2. Preoperative Clinical Characteristics Elective Primary Isolated Corunary Clinical

Variable

Age (yr, median) Men (W) Severe angina (% 1 Diabetes (% 1 Hypertension (96 1 Hypercholesterulemia (W / Age z 7oy-r (%I Single-vessel disease’ I% ! Double-vessel disease’ (% 1 Triple-vessel disease* (% I L&t main coronary stenosis (2 50%) 1%) Left venticuIar asynergv (% 1)

for the First 1,000 Patients per Year Undergoing Bypass Grafting (The Cleveland Clinic Foundation)

1967-1970 50 85 19 7 10 35 0.2 56 31 13 9 41

The terms single-, double-, and triple-vessel vessels (left anterior descending, circumflex,

746

1973

1976

1979

1982

1985

1988

1990

53 89 21 7 9 33 0.5 17 33 50 8

55 89 24 6 7 47 3 1.5 28 57 12

56 88 20 7 9 46 4 10 28 62 12

59 84 17 9 8 49 10 8 25 67 12

6.2 80 23 13 4 37 17 5 25 71 13

64 78 26 19 3 23 26 3 19 78 16

65 76 34 24 14 21 32 5 25 70 17

41

45

54

55

56

57

51

disease refer to the number of the three main coronary and right coronary arteries) that have stenoses z 50%.

Curr

Probl

Surg,

October

1992

triple-vessel disease, left main coronary artery stenosis, abnormal left ventricular function, severe angina, peripheral vascular disease, diaFurthermore, an increasing proportion betes, and hypertension.23-28 of patients have had previous interventions to treat coronary disease, either percutaneous transluminal coronary angioplasty PICA) or bypass surgery.Z5S 27-30 These changes in patient characteristics are the result of multiple forces. One important factor has been the recognition by surgeons and cardiologists that bypass surgery can be performed with relatively low risk for patients with extensive cardiac and noncardiac disease. In addition, both observational and randomized trials of bypass surgery have demonstrated that the survival advantage of surgery over medical therapy is greatest for patients with the worst ischemic heart disease: triple-vessel and left main coronary stenoses, abnormal left ventricular function, and severe angina. In other words, not only is it possible to perform bypass surgery for patients with more complex disease, but also they are the subset with the most to gain from the operation. The advent of FICA has had a complex effect on bypass surgery. Today, patients with limited coronary disease are often treated with PICA. Surgery for single-vessel disease is now uncommon, and in our practice the number of patients who undergo bypass surgery for double-vessel disease has also declined (see Table 21. However, this trend was evident before FTCA appeared. Although PTCA has subtracted some patients from the surgical population, many patients who now undergo PICA would not be surgical candidates. The presence of PTCA seems to have made it more likely that a patient with symptoms referable to ischemic heart disease will undergo coronary angiography. In addition, the use of PICA has resulted in an increased number of hospitals that perform bypass surgery (Fig l&F7 An interventional cardiology program requires surgical support, and in a competitive environment fewer and fewer hospitals are willing to forgo both surgery and PICA. Overall, the number of patients nationwide who undergo bypass surgery has continued to increase (Fig 1,B).27 The number of patients undergoing bypass surgery has increased, in part, because the age criterion for the invasive treatment of coronary artery disease has been eliminated.2”~ 31-33 Whereas in the early years bypass surgery was extremely uncommon in patients over 65 years of age, that currently is the median age of patients undergoing primary operation at our institution. The age of the surgical population is increasing because the age of the U.S. population is increasing. In addition, attitudes of physicians and patients regarding surgery for the elderly have changed. Elderly patients are increasingly unwilling to accept that they are too old to have surgery.

Curr

Probl

Surg.

October

1992

747

TOTAL NUMBER OF HOSPITALS PERFORMING BYPASS SURGERY PER YEAR loool

01

72

74

76

70

00

02

04

06

08

TOTAL NUMBER OF PROCEDURES PERFORMED PER YEAR

B

’

76

78

80

02

84

88

FIG 1. Data from The National Center for Health Statistics. A, number of hospitals performing coronary artery bypass surgery (CASG) has continued to increase and that increase accelerated with the appearance of percutaneous transluminal coronary angioplasty (PTCA) in the early 1960s. 8, numbers of coronary bypass operations and PTCA procedures continue to increase. (From Lytle BW, Cosgrove D, Loop FD: Cardiovasc C/in 1991; 21(2):265. Used by permission.)

SURGICAL TECHNIQUE

Innumerable modifications of the basic techniques of coronary bypass grafting have been used successfully. In this section we outline our approach. Virtually all isolated bypass operations are performed through a median stemotomy. The left IMA graft is prepared by dissection of a thin pedicle from the seventh or eighth intercostal space to the superior border of the first rib, and the pedicle is wrapped in a papaverine-soaked sponge. When the right IMA is to be used, that graft is prepared next. Simultaneously with IMA dissection, the greater saphenous vein is dissected out atraumatically by surgical assistants using noncontinuous incisions in the leg. The branches of the saphenous vein are tied with 4-0 silk ties. Overdistension of the 74s

Curr Prwbl surg#October lea2

vein is avoided, and it is stored in a balanced salt solution at room temperature. When the gastroepiploic artery is used as a graft, it usually can be prepared simultaneously with IMA dissection. The dissection of the gastroepiploic pedicle is accomplished by placing clips on the branches to the omentum and ties on the branches to the stomach. The dissection extends from the pylorus up the greater curvature of the stomach to the point where the vessel becomes less than 1 mm in diameter. Once the grafts are prepared, the pericardium is opened, heparin is given, and an arterial cannula is placed in the ascending aorta along with a single two-stage venous cannula in the right atrium (Fig 2). The IMAs are then divided distally, and flow is assessed visually. If the IMA flow is not satisfactory, the sternal retractor is closed 6 to i’ cm because excessive spreading may kink the IMA. If the flow is still not adequate, the IMA is examined for the inadvertent placement of a hemoclip. If flow is still unsatisfactory, the IMA is not used for a graft.

FIG 2. Cannulation for coronary bypass grafting usually includes an arterial cannula in the cending aorta, a two-stage venous cannula draining the right atrium and extending the inferior vena cava, a catheter in the ascending aorta for the antegrade delivery of dioplegic solution and for venting of the aorta, and a balloon catheter inserted through right atrial purse-string suture into the coronary sinus for the retrograde delivery of dioplegic solution.

asinto cara car-

Curr

749

Probl

Surg,

October

ICIW

Immediately before cardiopulmonary bypass, a balloon catheter for retrograde delivery of cardioplegic solution is placed into the coronary sinus through a purse-string suture in the right atrium. Cardiopulmonary bypass is then established, and volume is sequestered in the cardiotomy reservoir until the heart stops ejecting. An aortic crossclamp is then placed and cardioplegic solution is infused into the aortic root through a needle, then through the coronary sinus catheter. Infusion of cardioplegic solution is repeated after each distal anastomosis. During construction of the distal anastomoses, blood is vented from the aortic root through Y tubing connected to the aortic root needle. Distal vein graft to coronary anastomoses are completed first, usually using interrupted 7-O silk sutures. The effectiveness of this interrupted technique has been validated with postoperative angiograms in more than 5,000 vein grafts. Although many surgeons use some type of continuous suture technique with excellent results, there is no substitute for the documentation of postoperative results by angiography. We use sequential vein grafts when the amount of vein is limited, when small (< 1.25 mm) coronary vessels are to be grafted, or when aortic atherosclerosis limits the sites on the aorta where a proximal anastomosis can be performed (Fig 3). When performing sequential grafting, we place the most distal anastomo-

FIG 3. A left IMA graft branches.

750

to the LAD

coronary

artery

and

a sequential

vein

Cur-r

graft

Probl

to two

Surg.

circumflex

October

mgz

sis of the sequential graft to the largest coronary vessel. Another solution to the situation where aortic atherosclerosis limits the number of sites for proximal vein anastomoses is to perform one proximal anastomosis and then to connect the other vein grafts to that vein (Y grafts) (Fig 4). We try to avoid this because of adverse results early in our experience with occlusion of the secondary limbs of the graft. When we are forced into this situation, we use the largest-diameter segment of vein for the aortic anastomosis and make the secondary vein anastomoses as proximal as possible. We use a single period of aortic crossclamping for completion of all anastomoses, and once the distal anastomoses of the vein grafts are completed, the anastomoses to the aorta (proximal anastomoses) are done, usually with a continuous technique using 5-0 monofilament suture. When all vein anastomoses are completed, the distal arterial graft anastomoses are done. We use the left IMA to graft the most important left coronary vessel, which usually is the LAD coronary artery. When the right IMA is used as a graft, it is usually crossed anterior to the aorta to graft the most important circumflex branch (Fig 5). If the right IMA will not reach the target vessel as an in situ graft (left attached to the subclavian artery), it can be divided from its subclavian origin and used as an aorta-to-coronary (free) graft. The proxi-

FIG 4. A left IMA graft to the LAD cumflex, right, and diagonal

Curr

Probl

Surg,

October

coronary coronary

1992

artery and arteries.

Y grafts

with

saphenous

veins

to the cir-

761

FIG 5. Bilateral IMA grafting, with the left IMA going to the LAD coronary artery and the right IMA to the circumflex as an in situ graft. The posteriorly directed incisions in the pericardium allow the IMAs to take a direct route to the coronary artery and to fall posteriorly so that they do not become adherent to the chest wall after surgery.

mal anastomoses of free arterial grafts are constructed with an interrupted technique. Once all anastomoses are completed, the crossclamp is removed from the aorta. When blood cardioplegia is used, a warm reperfusion dose of cardioplegic solution is given before unclamping. When the heart has regained a vigorous contraction and systemic warming is completed, cardiopulmonary bypass is discontinued and protamine is given to reverse the effects of heparin. Hemostasis is obtained. The pericardium is incised in a posterior direction so that the in situ IMA grafts are routed to the heart through those incisions. The pericardial flap is placed over the right ventricle, but the pericardium is not closed nor are pericardial substitutes used. If the pleura has been opened, a chest tube is placed. Mediastinal chest tubes are always used. Sternal closure is accomplished with stainless-steel wire, and the subcutaneous and subcuticular layers are closed with absorbable suture. Throughout the operation careful attention is paid to blood conservation. Before heparinization and after reversal with prommine, shed blood is collected with a regionally heparinized collection system and is retransfused after surgery. An asanguineous pump prime

is used. 762

Curr

Probl

Surg.

October

1%~

PEFUOPERATIVE IN-HOSPITAL

RISK

MORTALITY

The overall in-hospital mortality associated with primary bypass surgery has been fairly stable at most institutions. Our period of lowest risk for elective surgery at The Cleveland Clinic Foundation occurred in the late 1970s and early 1980s when the positive effects of increased experience, effective myocardial protection, and blood conservation had not yet been counteracted by a dramatic increase in patient age and the severity of comorbid conditions (Tables 2 and 3). The slight increase in perioperative mortality we have witnessed in the last 5 years reflects the changing patient population. Jones and associates, in a study from Emory University, noticed an increased mortality rate (1.2% to 3.1%) and stroke rate (1.4% to 1.8%) from 1981 to 1987 and attributed these complications to a changing patient population.34 Kirklin and coworkers studied the results of bypass surgery from six different institutions including four community hospitals, the University of Alabama-Birmingham, and Katholicke Universiteit in Leuven, Belgium.35 An important observation was that the “early phase” of risk for death after bypass surgery extended for at least 2 months after surgery. Preoperative risk factors that increased the risk of early death included stenosis of the left main coronary artery, the number of stenotic coronary vessels, severe angina pectoris, unstable angina, acute myocardial infarction within 30 days of surgery, decreased left ventricular function, preoperative hemodynamic instability, older age, diabetes mellitus, and peripheral vascular disease. Factors related to the operation that increased mortality included the institution, the surgeon, not using the IMA for a bypass

TABLE 3. Morbidity Isolated

and Mortality (WI for First 1,000 Patients per Year Coronary Bypass Grafting: 1967-1990 (The Cleveland 1967-1979

Pertoperative infarction Postoperative bleeding Blood (units)’ Respiratory insufficiency Cerebmvascular accident Gastrointestinal bleeding Wound complication Mortality ‘Mean units of blood transfused

Curr

Probl

Surg,

October

7.1 10.1 11.0 5.0 2.0 1.2 2.0 3.0 Per patient.

1992

Undergoing Elective Clinic Foundation)

Primary

1973

1976

1979

1982

1985

1988

1989

1990

3.9 3.9 6.4 1.6 1.9 0.2 0.7 0.4

2.7 7.3 5.7 0.9 0.9 0.1 0.4 0.6

1.6 2.4 1.3 0.6 2.0 0.2 0.8 0.9

0.5 1.9 0.7 1.9 1.8 0.1 0.4 0.5

0.9 5.1 1.4 3.1 1.1 0.2 0.8 0.9

1.7 2.9 2.1 4.6 2.0 0.1 0.6 1.5

1.4 4.7 2.4 5.0 2.4 0.2 0.2 1.8

2.7 3.3 2.6 4.9 2.1 0.1 1.3 1.4

763

graft, the method of myocardial protection, and the myocardial ischemit time. In a study of 24,672 patients at The Cleveland Clinic Foundation who underwent primary isolated coronary bypass surgery from 1970 to 1982, cos ve and coworkers noted an overall in-hospital mortality of 1.2%. 3P For the entire group, the factors associated with increased mortality were emergent surgery, preoperative congestive heart failure, stenosis of the left main coronary artery, female sex, abnormal electrocardiogram (ECG), advanced age, lack of cardioplegia for myocardial protection, and an increasing number of bypass grafts. Data from the CASS Registry regarding nonrandomized patients who underwent primary coronary bypass surgery from 1974 through 1979 documented an overall operative @O-day) mortality rate of 2.37%~.~’ Factors that were found to have a strong P < .OOOl) association with increased operative mortality included age, sex (female > male), class III or IV angina, congestive heart failure, the number of stenotic coronary vessels, left ventricular wall motion, left ventricular end-diastolic pressure, unstable angina, height and weight (smaller patients were at increased risk), and emergency operation. Increased experience and evolving technology have changed some of the determinants of in-hospital mortality. In Cosgrove’s analysis, the patients who underwent surgery in the later years of the study (1980 to 19821 were examined as a separate subset. Their mortality rate was 0.8%. Stenosis of the left main coronary artery, the number of grafts performed, the number of diseased vessels, and abnormal angiographic left ventricular function were no longer associated with increased mortality. We attributed the ablation of these risk factors to more effective intraoperative myocardial protection. Emergency operation, advanced age, female sex, and clinical congestive heart failure persisted as risk factors. Cardiac causes accounted for 59% of deaths in the 1980 to 1982 time period, and stroke accounted for 20%. More recent data concerning the 8,545 patients who underwent primary isolated bypass surgery from 1985 through 1989 at The Cleveland Clinic Foundation document an in-hospital mortality of 1.8% and a strong association between increasing age and mortality (Table 4). Cardiac causes were considered to have led to 59% of deaths overall, but for patients over 70 years of age, more than half of the deaths stemmed from noncardiac complications. The increased mortality in elderly patients from noncardiac causes appears to result in part from a higher incidence of preexisting comorbid conditions. Loop and associates reviewed elderly patients undergoing surgery at The Cleveland Clinic Foundation from 1976 to 1986 and noted an increased incidence of diabetes, peripheral vascular disease, prior stroke, and cigarette smoking in the el754

Curr

Probl

SW5

October

ISSZ

TABLE 4. Primary Isolated Bypass Surgery of In-hospital Death and Cause

at The Cleveland of Death According

Clinic Foundation to Age Group

(1985-1989); Cause

Age W

No. of Patients

< 50 50-5s 60-69 70-79 2 80 Total

No. of In-hospital

1,066 2,371 3,377 1,606 125 8,545

10 18 67 53 7 155

Deaths

(0.94% ) (0.76%) (1.98%) (3.30% 1 (5.30%) (1.8% 1

Risks

of Death

Cardiac

Noncardiac

7 13 45 23 4 92

3 5 22 30 3 63

170%) (72%) (67%) (43% 1 157%) (59% 1

(30%)

GS%1 133% (57% (43% 141%

) 1 1 )

derly.Z6 In addition, the postoperative complications that were more frequent in the elderly tended to be noncardiac. Perioperative myocardial infarction and wound complications were not more common in the elderly, but stroke, reoperation for bleeding, respiratory distress, and renal failure were more frequent. Figure 6 shows the occurrence of fatal and nonfatal stroke and fatal and nonfatal perioperative myocardial infarction according to age group in The Cleveland Clinic Foundation 1985 to 1989 primary bypass surgery group. The incidence of stroke shows a steady, significant rise with increasing age, whereas no significant association was seen between age and the risk of perioperative myocardial infarction. Horneffer and

0

40

50-59

60-69

70-79

>=80

AGE DECADE

FIG 6. incidence of fatal and nonfatal cardiovascular accident (CVA) and perioperative myocardial infarction (Ml) for 8,545 patients undergoing primary isolated bypass grafting at The Cleveland Clinic Foundation (1985 to 1989) according to age group. CVA was significantly (P < 901) associated with older age whereas MI was not. Curr

Probl

Surg,

October

1992

755

colleagues at Johns Hopkins University have also noted a high incidence of noncardiac complications for patients over 70 years of age, which contributed to the 9.3% mortality for that subgroup compared with 2.2% for younger patients.33 In addition to preexisting conditions, it appears that the operative insult, and in particular cardiopulmonary bypass, carries more hazards for the elderly. Embolization of atherosclerotic debris, probably originating in the aorta, is a serious cause of noncardiac perioperative morbidity and mortality. Blauth and coworkers reviewed autopsy studies regarding 221 patients at The Cleveland Clinic Foundation who died in the hospital after cardiac surgery between 1982 and 1989.38 Atheroembolism was identified in 48 (22%) patients and involved multiple-organ systems in 62%. Atheroembolic phenomena were noted in 26% of autopsied patients who had undergone coronary bypass operations, and strong positive correlations were found between atheroembolism, increased age, and severe atherosclerosis of the ascending aorta. We have also identified atheroembolization as a cause of fatal perioperative myocardial infarction, and are continuing to study this problem. Atheroembolism appears to be the result of trauma to the ascending aorta from aortic clamping and, possibly, from the “jet effect” of flow through an arterial cannula in the ascending aorta. Other investigators have noted this problem, and ultrasonic characterization of the ascending aorta has been evaluated as a means of identifying patients at high risk.3s

MYOCARDLAL PROTECTION MYOCAKDLAL INFARCTION

AND PERZOPERATIVE

Because at least 50% of deaths after bypass surgery still result from cardiac-related causes, a fundamental principle of decreasing the morbidity and mortality associated with coronary bypass surgery is to minimize perioperative myocardial damage. However, not only must the heart be protected, but also the surgeon has to be able to conduct an expeditious, effective operation that corrects the pathologic conditions in coronary anatomy and decreases noncardisc morbidity associated with prolonged cardiopulmonary bypass and aortic manipulation. Effective myocardial protection begins before surgery. Patients who undergo surgery when they have myocardial ischemia or evolving myocardial infarction are at higher risk for perioperative myocardial damage compared with those undergoing elective surgery. The increased sophistication of the medical management of unstable angina has diminished the need for emergency operation as a treatment for ongoing ischemia. We continue the pharmacologic treatment of unstable angina, beta blockade, calcium channel blockers, 766

Cur-r

Probl

Surg,

October

1992

venous and arterial vasodilators, and heparin into the operating room. The increased sophistication of anesthetic management has helped to decrease the incidence of intraoperative myocardial ischemia before the onset of cardiopulmonary bypass and has allowed surgeons to take more time for preparation of multiple arterial graft conduits before bypass, allowing more complex operations. AU patients receive continuous intraoperative ECG and arterial pressure monitoring, and most have a pulmonary arterial catheter that provides continuous pulmonary arterial pressure monitoring and intermittent cardiac output determinations by use of thermodilution techniques. However, the phrase “myocardial protection” most commonly refers to strategies for management during cardiopulmonary bypass. The goals of this management are not only to protect the myocardium but also to create an immobile dry surgical field that will allow a precise operation to be performed. Multiple approaches have been used with clinical success. Cardiopulmonary bypass is a form of myocardial protection because it decreases myocardial work and myocardial oxygen consumption. Cardiopulmonary bypass combined with local occlusion of the coronary vessel can be used to construct some distal anastomoses, usually to the proximal right or anterior descending artery. However, local myocardial ischemia is produced, and the surgical field is suboptimal. The initial means of myocardial management used at The Cleveland Clinic Foundation was intermittent aortic crossclamping and normothermic anoxic arrest for construction of the distal graft to coronary anastomosis. The aortic crossclamp was removed, and a partial occluding clamp was used for construction of proximal anastomoses. The intermittent myocardial reperfusion was used to repay the “oxygen debt.” Disadvantages of this technique include the need for multiple clampings of the aorta, which increases trauma to the aorta, and interruption of the conduct of the operation to allow reperfusion, a disadvantage that was most noticeable when multiple grafts were performed. Despite these disadvantages, this strategy provided good results during the early years of bypass surgery, when most patients were relatively young and when most revascularization procedures were not complex. Furthermore, some surgeons have continued to use a similar type of myocardial protection, and favorable results have been reported.40 Another technique used frequently in the past was the strategy of not crossclamping the aorta but using systemic hypothermia and topical hypothermia to create cold fibrillatory arrest. With this scheme, local occlusion of the coronary arteries is used to create a dry surgical field. The disadvantages of this technique are the lack of myocardial relaxation that can make grafting to the circumflex coroCurr

Probl

Surg,

October

19%~

767

nary artery and to intramyocardial vessels more difficult, and experimental data that appear to indicate that cold fibrillation is associated with subendocardial ischemia despite the maintenance of perfusion through the major coronary arteries. On the other hand, some surgeons have continued to use this technique routinely with good clinical results.4’ Currently, we use cold fibrillatory arrest for myocardial protection when severe atherosclerosis of the ascending aorta makes any clamping of the aorta hazardous. The systemic temperature is lowered to 22” C, and a left atrioventricular vent is placed through the left superior pulmonary vein. Once fibrillation has occurred, elastic bands are placed around the coronary artery proximal and distal to the anastomotic site to limit flow through the coronary artery, and the distal anastomoses are constructed (Fig 7). Proximal anastomoses are constructed to the aorta with the use of 2to 4-minute periods of circulatory arrest. Today, the most commonly used method of myocardial protection is a single period of aortic crossclamping with intermittent infusion of cold cardioplegic solution designed to arrest the heart and create a metabolic environment that minimizes myocardial damage.42-46 Buckberg listed the goals of pharmacologic cardioplegia as arresting the heart safely, allowing continued energy production, and avoiding the negative aspects of ischemia.42’ 43 The steps used to achieve these goals include immediate cardiac arrest, hypothermia, provi-

FIG 7. Strategy for performing bypass surgery while not placing aorta. In addition to arterial and right atrial cannulation, a left via the right superior pulmonary vein to avoid left ventricular moses are constructed with local coronary occlusion, and ses are constructed during brief periods of circulatory arrest.

any clamp on the ascending atrioventricular vent is placed distension. The distal anastoproximal vein graft anastomo-

758

Curr

Probl

Surg,

October

19~2

sion of substrate to allow for a low level of energy production during arrest, maintenance of a normal or slightly alkaline pH, addition of agents to provide membrane stabilization, and the avoidance of myocardial edema. A variety of schemes for cardioplegia have been shown experimentally to maintain a favorable metabolic environment and have been used clinically with good success. The disadvantages of the use of cardioplegia are a slight increase in expense (particularly for the hardware required for blood cardioplegia) and a requirement for aortic crossclamping. The greatest advantage of cardioplegia is that the flaccid, arrested heart provides excellent surgical exposure. Initially, cardioplegic solutions were asanguineous and were based on a high-potassium or low-calcium solution to arrest the heart and a low temperature (5’ to 10’ Cl to lower the metabolic rate of the myocardium.4Z-46 Our use of asanguineous cardioplegia involved the high-potassium cardioplegic solution developed by Hearse and associates.a,45 Subsequently, some investigators added oxygen dissolved in the crystalloid solution to provide substrate for the low level of myocardial metabolic activity that is maintained during aortic crossclamping. Experimental data seemed to show an advantage to adding oxygen, and a clinical study by Guyton and coworkers confirmed that advantage in patients undergoing coronary bypass graIXng?7~ 48 Other additives to asanguineous cardioplegic solution have included buffers and oxygen radical scavengers. We found that when compared with normothermic anoxic arrest, the use of cold, asanguineous, multidose, potassium-based cardioplegic solution lowered the in-hospital mortality associated with isolated coronary bypass grafting and bypass grafting combined with aortic valve replacement .36,4s Cardioplegia in which blood is used to deliver oxygen has been gaining in popularity. We use a blood cardioplegia protocol outlined solution is accomplished by Buckberg.42, 5o Delivery of cardioplegic via a pump and heat exchanger connected to the cardiopulmonary bypass circuit. For the induction of atrest, final concentrations of constituents include blood (hematocrit, 20% to 30%), potassium chloride (10 to 20 mEq/L), tromethamine (pH 7.5 to 7.61, glucose P400 mgdl, > 400 mOsm), and citrate-phosphate-dextrose (50 ml in induction dose). Delivery is given according to time rather than volume. Maintenance of arrest is accomplished by repeat doses 15 to 20 minutes apart of cardioplegic solution containing less potassium chloride 00 to 15 mEq/Ll. Both asanguineous and blood cardioplegia provide effective myocardial protection, and the results achieved clinically by asanguineous cardioplegia are good enough that incremental improvement with the use of blood in the cardioplegic solution has not been easy to demonstrate. However, multiple authors have reported experiCurr

Probl

Surg,

October

19%

769

mental data that do appear to demonstrate superiority for blood cardioplegia, and in a clinical study of patients undergoing bypass grafting, Fremes and associates showed that patients who received blood cardioplegia had a lower rate of myocardial infarction, less enzyme release, and improved myocardial performance compared with patients receiving nonoxygenated asanguineous cardioplegia.51 Christakis and colleagues studied patients undergoing surgery for unstable angina and also found that blood cardioplegia lowered the rates of intraoperative myocardial infarction, postoperative lowoutput syndrome, and enzyme release. Multivariate techniques were used to identity blood cardioplegia as an incremental factor decreasing morbidity.52 Increasing emphasis has been placed on controlling the circumstances of re erfusion of ischemic myocardium to minimize reperfua sion injury.” ir’ 53 In the Buckberg protocol for blood cardioplegia, reperfusion solution is infused immediately prior to aortic uncrossclamping. This reperfusion solution contains 8 to 10 mEq/L of potassium to maintain electromechanical arrest; is normothermic to increase myocardial metabolic activity; and contains oxygen, glucose, and the Krebs cycle intermediates aspartate and glutamate to provide substrate and to replace intermediates lost during anaerobic metabolism. The idea of this normothermic “hot shot” of cardioplegia is to allow a few minutes of nonworking metabolic activity to enable myocardial reparative processes to go on. The principles of reparative reperfusion have been extended to the induction of cardioplegia in patients who are thought to have myocardial ischemia present at the initiation of aortic crossclamping, for example, patients undergoing surgery for evolving myocardial infarction or with prebypass ECG changes that suggest myocardial ischemia. Experimental data support this concept of the use of substrate-enhanced warm cardioplegic solution during cardioplegic induction in patients with ischemia, and the small number of clinical data that exist is encouraging.s4 For patients undergoing surgery for the treatment of coronary stenoses, distribution of cardioplegic solution is an important issue. The same coronary stenoses that limit blood flow can also limit the distribution of cardioplegic solution given antegrade through that stenotic coronary circulation. Solutions to the problem of nonuniform myocardial cooling during the institution of cold cardioplegia have included topical hypothermia with cold slush and perfusion of cardioplegic solution down completed vein grafts. However, cold solutions in the pericardium have been associated with phrenic nerve injury, and extensive use of in situ arterial grafts does not allow perfusion of cardioplegic solution through those grafts. A major advance in techniques for the distribution of cardioplegia has been the perfusion of cardioplegic solution through the coro7eo

Cur-r

Probl

Surg,

October

IWZ

nary sinus, a maneuver that allows the solution to reach the myocardium retrograde through the coronary venous system.55’ 56 We currently use a balloon catheter placed through the right atrium to achieve retrograde cardioplegic perfusion in the majority of patients and this technique is particularly useful during coronary reoperations. Right ventricular protection is inconsistent with retrograde cardioplegia alone,57 and we use a combination of antegrade and retrograde delivery. Recently the use of continuous, low-flow normothermic cardioplegic perfusion both antegrade and retrograde was reported, with excellent myocardial protection .being achieved in small numbers of patients. One major advantage of this concept is maintenance of systemic normothermia.58# 5g Disadvantages of continuous cardioplegia for patients undergoing coronary artery surgery include the presence of blood in the coronary arteries during the construction of the distal anastomosis and uneven distribution of cardioplegia if the solution is given only antegrade through stenotic coronary vessels. The use of retrograde cardioplegic delivery systems would appear to solve distribution problems, but it is not yet clear that retrograde perfusion alone will provide consistent, continuous cardioplegic distribution because of vagaries in the anatomy of the coronary venous system and problems with the practical mechanics of keeping a retrograde cardioplegia cannula in place. Despite the advances in myocardial protection during bypass surgery, myocardial infarction still occurs, probably for reasons related to coronary anatomy. Incomplete revascularization of preexisting diseased coronary arteries may result in perioperative myocardial infarction. In addition, technical errors involving graft anastomotic technique, graft thrombosis, perioperative rupture of atherosclerotic plaques, localized trauma to coronary vessels, embolization of atherosclerotic debris from atherosclerotic vein grafts, the aorta and, possibly, the native coronary circulation, endarterectomy, air embolization, and coronary artery spasm may singly or in combination contribute to perioperative myocardial infarction. Coronary artery spasm has been thought to be a cause of perioperative myocardial infarction, and we have documented severe postoperative coronary spasm angiographically. Because spasm is prone to occur in patients who have been treated before surgery with large doses of calcium channel blockers, these medications must be continued during and after the operation. However, we believe that significant perioperative coronary artery spasm is not common and that perioperative myocardial infarctions attributed to spasm are more likely due to other causes, particularly atheroemboli. Other uncommon causes for perioperative myocardial infarction that we have seen anecdotally include plaque rupture in native coronary vessels or IMA grafts and failure of the preoperative angiogram Curr

Probl

Surg.

October

1992

761

to demonstrate a significant coronary stenosis. In situations where ventricular function is worse after the bypass than before, it is important to keep in mind that the anatomy demonstrated by the preoperative angiogram may not be the same as the coronary anatomy present after cardiopulmonary bypass. When an apparent decrement is seen in left ventricular function, the use of intraoperative echocardiography can help define the location of the problem. Not only can echocardiography identify new wall-motion abnormalities, but it may also help in the diagnosis of previously unsuspected left ventricular outflow tract obstruction or mitral insufficiency. If we tind evidence of a new wall-motion abnormality by echocardiography, attention is directed to the vascular supply of that area. Grafts previously constructed are probed. If the vessel supplying the area has not been grafted, we graft it. A detailed discussion of postoperative hemodynamic management is beyond the scope of this review, but we think that there are two important principles. If the patient’s postoperative ventricular function is equivalent to the preoperative ventricular function, we use inotropic support or vasoactive drugs to make any desired alteration in postoperative hemodynamics. If we think the patient has had a perioperative decrement in myocardial function, we place an intraaortic balloon pump.” This balloon pump is particularly useful for patients with extremely diffuse coronary artery disease. The major disadvantage of the intraaortic balloon pump is the occurrence of vascular complications, which may develop in as many as 20% of patients ?

CEREBROVASCULAR ACCIDENT The risk of a cerebrovascular accident (CVA) associated with bypass surgery depends in part on its definition. Figure 6 details the rate of occurrence of any focal postoperative neurologic deficit, even if it was temporary, whereas CVA in Table 3 refers to a permanent neurologic deficit. Overall the risk of a permanent neurologic deficit after bypass surgery appears to be between 1% and 3% and is highly age related.“Z-64 Perioperative CVA has multiple causes, some of which are well known. Embolization of atherosclerotic debris as a cause of CVA has been discussed. Embolization of mural thrombus from the left ventricle may also cause a CVA. France and coworkers showed that when preoperative left ventriculography appeared to show the presence of a mural thrombus, the risk of CVA in patients who had cardiac surgery was 9.6% .65 We, therefore, perform a left ventriculotomy to remove any mural thrombi that are identified by ventriculography or echocardiography. Air embolization appears to be a rare cause of 762

Curt-

m-ubl

sur5

October

ISWZ

CVA for patients undergoing isolated bypass surgery, but attention must be paid to removing air from the aortic root. We also have noted postoperative CVA associated with transient episodes of atrial fibrillation. The role of carotid stenoses in causing perioperative CVA and the management of those stenoses are complex issues. Severe carotid stenoses clearly can cause intraoperative watershed-type CVAs or postoperative CVAs in patients who have initially come through the operation neurologically intact. On the other hand, it has not been clearly established that simultaneous carotid endarterectomy decreases the risk of CVA for patients with carotid lesions undergoing bypass surgery. Patients with carotid stenoses are also more likely to have aortic atherosclerosis and diffuse vascular disease and the CVAs that occur in those patients are not always caused by their carotid lesions. Hertzer and associates conducted a study of 275 Cleveland Clinic Foundation patients (2.8% of the 9,714 patients undergoing isolated coronary bypass surgery from 1983 to 1986) who required carotid endarterectomy in addition to bypass grafting because of symptoms 030 patients) or severe (270% ) carotid stenoses confirmed by angiography.66 When compared with the general population of patients undergoing bypass surgery at our institution during those years, the patients with carotid lesions were older, had more angina, and had a higher prevalence of triple-vessel disease (81%1, stenosis of the left main coronary artery (23%), and abnormal left ventricular function (72% 1. The treatment strategies that were used and in-hospital results are listed in Table 5. Group I patients were judged to be at low cardiac risk and underwent preliminary carotid endarterectomy followed by elective bypass surgery. Group II consisted of 129 patients judged to be at high cardiac risk who had asymptomatic, unilateral carotid stenoses of 70% or more of the vessel diameter. They were randomly assigned to receive either simultaneous carotid endarterectomy and bypass surgery (group IIA) or bypass surgery followed by delayed carotid endarterectomy @oup IIB). Group III patients had symptomatic or bilateral carotid lesions and, for the most part, were at high cardiac risk. They were treated with a variety of strategies. Examination of the distribution of the perioperative CVAs showed that of 6 that occurred during coronary bypass operations for patients with untreated carotid lesions, 4 were appropriate for that carotid lesion. Most of the CVAs in patients undergoing combined procedures involved watershed zones. This study did not identify an optimal management strategy, but some conclusions can be made. The overall operative mortality was 4% (111274) and the CVA rate was 5.8%. These rates can be compared with a mortality for isolated coronary bypass grafting of 1.3% and a CVA rate of 2% for isolated carotid endarterectomy during the peCurr

Probl

&n-g,

October

IWZ

763

TABLE 5. Management and Carotid

Strategies Stenoses””

and

Results

for Patients

Preoperative Treatment Group

No. of Patients

Group

I

24

Gmup

II

129

A

Risk

Carotid Status

Standard

Mixed

High

Asymptomatic unilateral stenosis z7ow

risk

58 III

122

A

60

B

9

C

30

D

23

CE = carotid

High

endarterectomy;

risk

Combined

Coronary

Status

71

B Gmup

Cardiac

With

Symptomatic or bilateral stenosis ?70%

artery bypass

Disease

Perioperative

Results

Management

Stroke

Death

CE, then CAB Randomized

1 (4.2%)

1 (4.2%)

CFJCAB

2 (2.8%)

3 (4.2%)

8 (14%)

3 L5.3%)

7 (7.1% I

6 (6.1%)

5 (8.3%)

4 (6.7% J

combined CAB, then CE Not randomized

Combined CE/CAB CE, then combined CEXAB Combined cI?JcAB, then CE CAB, then CE CAB = comnaly

Artery

0

2 122%)

2

5 (16.7%)

3 112.9%)

0

grafting

riod of the study. Regardless of management strategy, patients with combined coronary and carotid pathologic conditions were at relatively high risk. A trend was seen toward a lower risk of CVA for patients undergoing combined procedures. Patients who underwent bypass surgery with an uncorrected carotid lesion had a higher risk of CVA and about the same mortality when compared with other subgroups. In addition to advanced age, the factor that corresponds most directly with the occurrence of a perioperative CVA is history of a preoperative CVA.“, 63 Realizing that perfect management strategies have not yet been identified, surgeons still must choose one of the alternatives, and our tendencies are as follows. All patients with carotid bruits are evaluated with duplex scanning. Patients with severe bilateral carotid disease, carotid symptoms, or severe asymptomatic carotid stenoses are treated with initial carotid endarterectomy followed by de704

Curr

Pmbl

Surg.

October

1992

layed bypass surgery if it is our judgment that their cardiac disease will permit carotid endarterectomy. The current effectiveness of today’s anesthesia makes this approach more tenable. If the patient’s cardiac status is particularly precarious (unstable angina with left main coronary or triple-vessel disease), we prefer simultaneous endarterectomy and bypass grafting for patients with bilateral or symptomatic carotid disease. Patients with asymptomatic unilateral carotid stenoses and precarious coronary disease are treated with coronary revascularization followed by delayed carotid endarterectomy. We probably do not completely understand all the causes of perioperative CVA and it remains a formidable problem.

RESPIRATORY

COMPLZCATZONS

Virtually all patients undergoing coronary bypass surgery with the aid of cardiopulmonary bypass have changes in pulmonary function, but they are rarely serious, except in patients with significant preexisting pulmonary disease. Cardiopulmonary bypass produces complement activation, pulmonary sequestration of leukocytes, lysosomal enzyme release, endothelial cell damage, decreased alveolar epithelial integrity, and increased extravascular pulmonary water.67 Positive end-expiratory pressure and early postoperative diuresis are used to treat patients with an increased alveolar-arterial oxygen gradient . Severe pulmonary edema in the presence of a low left atrial pressure may occur in patients without preexisting pulmonary disease and has been attributed to the use of protamine.68 This rare complication appears to be associated with increased capillary permeability. Prolonged ventilator dependence is associated with prolonged cardiopulmonary bypass, preexisting pulmonary disease, advanced age, preoperative congestive heart failure, moperation, and emergency surgery.6g Loop and coworkers reported respiratory failure after bypass surgery in 1% of patients younger than 65 years of age, in 2.6% of patients between 65 and 74 years of age, and in 4.3% of patients over 75 years of age.Z6 Horneffer and associates noted a similar increase in respiratory complications in the elderly.33 We perform preoperative spirometry in patients with respiratory symptoms or evidence of chronic obstructive pulmonary disease on preoperative chest x-ray. Patients with an obstructive pattern are tested with bronchodilators and if their mechanics improve, they are treated with bronchodilators before, during, and after surgery. Phrenic nerve paralysis or paresis can significantly contribute to respiratory dysfunction. An association between the use of iced slush in the pericardium and phrenic nerve dysfunction has been Cur-r

Probl

Surg,

October

1992

766

reported and seems valid.70 Although phrenic nerve dysfunction is less common when slush is not used, it still can occur and probably has multiple causes. The influence of Ih4A dissection on phrenic nerve function has been a subject of concern. In experienced hands, dissection of the IMA rarely leads to direct phrenic nerve injury. We usually carry the IMA dissection only to the superior border of the first rib, a position where direct injury to the nerve is unlikely to occur. However, recent experimental work by O’Brien and colleagues in pigs appears to show that division of pericardiophrenic arterial branches of the IMA may lead to devascularization and ischemia of the phrenic nerve.‘l In a series of 500 patients receiving bilateral Ih4A grafts, we noted the need for prolonged ventilation (>48 hours) in 5%) a figure that may represent a slight increase over that expected for patients of comparable age not receiving bilateral IMA grafts.72 Phrenic nerve injury may also occur as a result of the trauma associated with the placement of central venous catheters. WOUND

COMPLICATIONS

In a comprehensive review of 6,504 consecutive patients who underwent isolated coronary bypass grafting at our institution during the years 1985 to 1987, Loop and coworkers noted a 1.1% incidence of major (mediastinitis, dehiscence, or both) perioperative or postoperative wound complications.73 Factors associated with an increased risk of this complication include increased operative time, obesity, and the number of units of blood transfused. Complication rates according to primary versus reoperative cases and the type of bypass grafts used are listed in Table 6. As an isolated variable, the types of conduits used did not significantly influence complication rates. However, we had previously identified a combination of bilateral IMA grafting and diabetes as being associated with an increased risk of wound complications, and when the subset of patients undergoing bilateral IMA grafting in this study was examined the presence of TABLE Wound

6. Complications

After

Isolated

Coronary Wound Rates

Grafts Vein One Two Total IMA

766

Used grafts only IMA f+- vein graftsi IMAs (k vein graft& = internal

rnarnmq

Bypass

Surgery:

Complication with Primary Oueration

W690 3013,480 19/1,199 5515,369

1985-1987”” Wound Complication Rates with ReoDeration

10.9% J (0.9%) (1.6%) (1.0% 1

5/395 S/593 4/147 1711,135

(1.3% I (1.3%) (2.7% 1 11.5% I

artery

Cur-r

Probl

Sur5

October

1992

diabetes was found to be associated with a fivefold increased risk of also noted by Galbut and wound complications,” 73 a relationship associates.74 Single IMA grafting did not increase the risk of wound complications in any patient subset. Factors cited by other authors as increasing the risk of mediastinitis that we did not identify include reexploration for postoperative hemorrhage, reoperation, low cardiac output, and respiratory complications.75’76 Wilson and colleagues also identified obesity as a risk factor.” Anatomic and physiologic studies have demonstrated that IMA dissection greatly decreases the blood supply to the ipsilateral side of the sternum.“’ ” After IMA dissection, immediate collateralization of the sternum appears to be poor. The lack of an increased risk of wound complications after single IMA dissection implies that some supply from the contralateral side of the sternum aids in sternal healing. It is remarkable that the sternum ever heals after bilateral IMA dissection. The residual vascular supply must be barely sufficient or, at times, the sternum may heal as a free bone graft. Of the total of 72 patients in Loop and colleagues’ study73 who had a major wound complication, 14% died in the hospital. Not only was the hospital mortality elevated, but also the economic implications associated with a wound complication were profound as the median length of hospital stay was 43 days and the hospital charges were three times that for patients who did not have a wound complication. Measures that we use to decrease the likelihood of a wound complication include a preoperative shower with a disinfectant, use of a clipper to remove hair, a short course of antibiotics started on arrival in the operating room, and wound surveillance by an epidemiologist. Intraoperative techniques include avoidance of cautery in the subcutaneous fat, dissection of a thin IMA pedicle, sparing use of the cautery during IMA dissection, and use of interrupted (nonstrangulating) absorbable sutures to close the subcutaneous fat and interrupted skin sutures in diabetic patients. The treatment of mediastinitis requires prompt recognition, debridement of infected and avascular tissue, and obliteration of any dead space with viable tissue. Two thirds of patients in our series were treated with debridement, closure of the sternum, and irrigation of the mediastinum with saline or povidone-iodine solution, Of patients treated with this “closed” method, 17% needed further procedures involving flap reconstruction. The remainder of the patients were treated with debridement and “open” packing of the mediastinum. Of 12 patients treated with the open method, 10 eventually underwent flap reconstruction. Mortality was approximately the same regardless of what treatment method was used, but patients treated by the open method had longer hospitalizations. Flaps that were used included rectus muscle, pectoralis major muscle, and omenCurr

Probl

Surg,

October

1932

767

turn. The rectus muscle covers defects in the lower mediastinum well but cannot be used if the ipsilateral IMA has been used for a graft. The pectoralis major muscle serves the upper mediastinum well, and the omentum can often cover the entire defect, although a laparotomy is required and an epigastric hernia may result.

BLEEDING Cardiopulmonary bypass deranges normal blood clotting in multiple ways, including activation of the intrinsic coagulation system and fibrinolytic system. In addition, cardiopulmonary bypass has an adverse influence on platelet function.67 Homologous transfusion of blood or blood components carries its own risks, including immunologic reaction and blood-borne infections .‘O*” In the late 1970s we instituted a multifaceted program of blood conservation that included preoperative blood donation, intraoperative blood salvage, asanguineous pump prime, careful intraoperative hemostasis, postoperative autotransfusion, and the acceptance of normovolemic anemia for hemodynamically stable patients. Prospective study in patients 65 years of age and younger who underwent primary isolated revascularization showed that with attention to these details almost all patients could undergo surgery without the need for blood transfusion.82 Unfortunately, such patients now make up a smaller proportion of surgical candidates and the mean number of units of homologous blood used per patient has risen steadily (see Table 31. Subsequent work showed that increased age and a small body surface area were associated with the use of more blood,83 and the current older population of patients that includes more women requires more blood. The need for postoperative reoperation to control bleeding or tamponade has ranged between 2% and 5%. Patients receiving bilateral IMA grafts may have a slightly higher incidence of significant bleeding. The use of aspirin, heparin, and thrombolytic agents in the medical management of patients with coronary artery disease complicates their management if surgery is needed. If bleeding complications develop, we use component therapy to correct the problem. Attempts to enhance the effectiveness of patients’ hemostatic mechanisms after surgery have included the use of desmopressin acetate and aprotinin. Desmopressin is a synthetic analogue of vasopressin that increases levels of factor VIII and von Willebrand factor and may increase the effectiveness of platelets.84 We have not been impressed with the effectiveness of desmopressin. Aprotinin is a protease inhibitor formerly used for the treatment of pancreatitis. Its exact mechanism of action is unknown, but when given before surgery it appears to protect platelet function during cardiopulmonary 768

Cut-r

Probl

surg,

October

msz

in experimental protocols and our bypass.85 We have used aprotinin impression is that blood clotting is improved if patients are given aprotinin. Aprotinin is not yet available for general clinical use. It is important to remember that our data regarding vein graft patency after operation are derived from situations where the early postoperative coagulation system is abnormal. Improving coagulation and platelet function early after an operation may have multiple effects, some of which may be undesirable. Work with heparin-bonded components for the cardiopulmonary bypass circuit is in its infancy, but may prove to be important. GRAFT

PATENCY

AND REVASC IJLWUZATION

STFIATEGIES

VEIN GRAFT PATENCY In most institutions the saphenous vein graft has been the mainstay of coronary bypass grafting. The patency rate of aorta-to-coronary saphenous vein grafts early after operation is good, but an important realization has been that the early patency rate of vein grafts is not stable. Patency rates from angiographic studies of vein grafts done at a variety of institutions are shown in Table 7, with grafts classed as either patent or totally occluded and grouped according to the postopera-

TABLE 7. Patency Between

Rates of Saphenous Vein Surgery and Postoperative No. of Vein Grafts

Bourassa 88

et

Fitzglbbon et al?’ Lawrie et ill?O The Cleveland Clinic Foundation