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Ann Thorac Surg 1996;61:552-557
© 1996 The Society of Thoracic Surgeons

Original Article: Cardiovascular

Can Patients With Left Main Stenosis Wait for Coronary Artery Bypass Grafting?

Donna E. Maziak, MDCM, Vivek Rao, MD, George T. Christakis, MD, Karen J. Buth, MSc, Jeri Sever, Stephen E. Fremes, MD, Bernard S. Goldman, MD

Division of Cardiovascular Surgery, Sunnybrook Health Science Centre and the University of Toronto, Toronto, Ontario, Canada


   Abstract
Top
 Footnotes
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Background. The economic impact of health care reforms may result in waiting lists for coronary artery bypass grafting. This study was designed to examine the clinical results of patients with left main stenosis who were placed on a triaged wait list for operation.

Methods. Data were collected prospectively on 2,145 patients undergoing isolated coronary artery bypass grafting between 1989 and 1994. Critical left main stenosis (LMS, 50% or more stenosis) was present in 281 patients, and 1,864 patients had no left main disease, or a left main stenosis of less than 50% (no LMS).

Results. The average time from angiography to operation was shorter in patients with LMS (LMS 38 ± 46 days versus no LMS 84 ± 71 days; p = 0.0001). Two patients in the LMS group died; they had declined operation. Four patients suffered non-Q wave myocardial infarctions, all of whom subsequently underwent operation with no perioperative complications. The presence of LMS did not influence operative mortality (LMS 2.8% versus no LMS 1.3%), the incidence of low output syndrome (LMS 8.3% versus no LMS 5.4%), or the incidence of perioperative myocardial infarction (LMS 3.8% versus no LMS 4.2%). To examine the effect of waiting time on outcomes, patients with LMS were divided into early (operation 10 days or less after angiography) and late revascularization groups (more than 10 days). Operative mortality, low output syndrome, and myocardial infarction were similar in the early and late groups. Patients in the early group were more likely to have New York Heart Association functional class IV symptoms (64% versus late 22%; p < 0.0001), unstable angina (87% versus late 65%; p < 0.0001), or a recent preoperative myocardial infarction (17% versus late 2%; p < 0.0001).

Conclusions. Carefully selected patients with significant left main stenosis can safely wait for operation with a low risk of complications. Early surgical intervention is allocated to patients with severe symptoms or recent preoperative myocardial infarction.


   Introduction
Top
 Footnotes
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
The traditional predictors of operative mortality after coronary artery bypass grafting include poor preoperative left ventricular function, age more than 70 years, redo operation, urgent operation for unstable angina, female sex, and the presence of left main stenosis [1, 2]. Several investigators have identified the presence of left main stenosis as a significant determinant of long-term survival [3–6]. The Veterans Administration Cooperative Study [7] demonstrated that bypass grafting conferred a significant survival benefit over medical therapy in patients with left main stenosis. However, the survival benefit did not become evident for at least 3 months after operation. A short period of delay between diagnosis of left main stenosis and surgical treatment may therefore be possible.

For editorial comment, see 513.

In the Canadian health care system, patients who are referred for coronary artery bypass grafting are triaged to a waiting list on the basis of urgency of symptoms and anatomy [8]. The urgency rating score [9] used by the Ontario Provincial Adult Cardiac Care Network confers priority to the symptomatic state of the patient over the patient's underlying anatomy. Thus, patients with noncritical coronary anatomy who present with unstable angina refractory to intravenous nitroglycerin undergo operation earlier than the asymptomatic patient with critical left main stenosis.

Impending health care reform in many industrialized Western countries with well-established health care delivery systems has prompted many investigators to devise indices to assess preoperative risk before coronary artery bypass grafting [10–13]. These indices of risk are then to be used as objective criteria to triage patients waiting for coronary artery bypass grafting.

The purpose of this study was to examine the effect of left main stenosis on operative morbidity and mortality. More specifically, we examined the relationship between waiting time (the time from diagnostic cardiac catheterization to operation) and postoperative clinical outcomes. In addition, we report the criteria that determined early versus late surgical intervention.


   Material and Methods
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 Acknowledgments
 References
 
Patient Population
Preoperative, perioperative, and postoperative data were collected prospectively on 2,145 consecutive patients undergoing isolated primary coronary artery bypass grafting between November 1989 and November 1994 at Sunnybrook Health Science Centre. There were 281Au: change OK?; same as abstract patients who had significant left main coronary artery disease (50% or more stenosis, LMS group) and 1,864 patients with either no left main disease or a stenosis of less than 50% (no LMS group).

Patients in the LMS group were then divided into two groups depending on the time from initial diagnostic cardiac catheterization to operation (wait). One hundred patients had a wait of 10 days or less (early group), whereas 181 patients had a wait of more than 10 days (late group).

To examine the criteria leading to earlier operation, we divided the LMS group into patients with 50% to 75% left main stenosis and 75% or more stenosis. In addition, each of these two groups were further divided on the basis of the presence of concomitant right coronary artery disease. Group 1 (n = 56) consists of patients with 50% to 75% left main stenosis with less than a 75% right coronary artery stenosis. Group 2 (n = 80) consists of patients with 50% to 75% left main stenosis in addition to severe (75% or more luminal narrowing) right coronary artery disease. Group 3 (n = 66) includes patients with 75% or more left main stenosis with less than 75% right coronary artery stenosis, whereas group 4 (n = 79) includes patients with severe left main disease and 75% or more right coronary artery stenosis.

Preoperative myocardial infarctions were defined as new ischemic changes on a surface 12-lead electrocardiogram accompanied by a serial cardiac enzyme rise within 30 days of operation. Postoperative myocardial infarctions were defined as a new Q wave found on the postoperative electrocardiogram. A myocardial infarction was also diagnosed if the postoperative electrocardiogram had a new left bundle branch block, loss of R wave progression, or new ST and T wave changes if accompanied by an increase in creatine kinase-MB level greater than 50 U/L and if the creatine kinase-MB to creatine kinase ratio was greater than 5%. This definition of perioperative myocardial infarction requires electrocardiographic changes and therefore, may underestimate the true rate of myocardial infarction.

Low output syndrome was diagnosed if the patient required inotropic medication to maintain the systolic blood pressure more than 90 mm Hg and the cardiac output more than 2.2 L • min-1 • m-2 for at least 30 minutes in the intensive care unit after correction of all electrolyte and blood gas abnormalities, and after adjusting the preload to its optimal value [14]. Operative mortality refers to all cause mortality within 30 days after operation or during the same hospital admission.

Statistical Analysis
Statistical analysis was performed with the SAS (SAS Institute, Cary, NC) and BMDP (BMDP Software, Los Angeles, CA) software programs. Categoric data were analyzed using {chi}2 test or Fisher's exact test where appropriate and are expressed as the percentage and absolute frequency for each variable. Continuous data were analyzed by two-tailed t tests and expressed as the mean ± standard deviation.


   Results
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 Acknowledgments
 References
 
Patient Population
The preoperative characteristics of the 2,145 consecutive patients are shown in Table 1Gotab 1. Patients in the LMS group were more likely to have peripheral vascular disease (17.4% versus no LMS 9.6%; p < 0.0001) and had a slightly higher incidence of preoperative strokes (7.8% versus no LMS 4.8%; p = 0.03). The time from diagnostic cardiac catheterization to operation (wait) was shorter in the LMS group (38 ± 46 days versus no LMS 84 ± 71 days). The median wait time in the LMS group was 20 days (range, 0 to 274 days), whereas the median wait time in the no LMS group was 73 days (range, 0 to 509 days). There were no differences between groups for other clinical characteristics.


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  		Table 1. . Left Main Disease Versus No Left Main Disease
 
Table 2Go illustrates the preoperative characteristics of patients on the basis of left main stenosis and right coronary artery stenosestab 2. Patients with severe right coronary artery disease were also more likely to have peripheral vascular disease (p = 0.03). There were no other clinical differences between the four groups. Patients with severe left main stenoses had a shorter mean wait (p = 0.05) and were more likely to be in the early group (p = 0.0001), irrespective of the degree of right coronary artery disease.


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  		Table 2. . Effect of Concomitant Right Coronary Artery Disease
 
Table 3Go illustrates the preoperative differences between patients who had a wait of 10 days or less versus more than 10 daystab 3. The mean wait in the early group was 5.7 ± 3.0 days versus 56.0 ± 48.1 days in the late group (p < 0.0001). Patients in the early group were more likely to be in New York Heart Association functional class IV (64.0% versus 21.5%; p < 0.0001), have preoperative congestive heart failure (7.0% versus 1.7%; p = 0.04), and were more likely to have suffered a preoperative myocardial infarct (17.0% versus 2.2%; p < 0.0001). In addition, patients in the early group were more likely to have a left main stenosis of 75% or more (72.0% versus 40.3%; p < 0.0001).


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  		Table 3. . Early Versus Late
 
Postoperative Outcomes
EFFECT OF LEFT MAIN STENOSIS.
The perioperative data and postoperative outcomes for the LMS and no LMS groups are illustrated in Table 4Gotab 4. Patients in the LMS group were more likely to have multiple (three or more) grafts compared with the no LMS group (86.82% versus 76.40%; p = 0.002). In addition, patients in the LMS group had longer aortic cross-clamp times (65 ± 19 minutes versus 58 ± 19 minutes; p < 0.0001), longer cardiopulmonary bypass times (103 ± 28 minutes versus 95 ± 29 minutes; p < 0.0001), and a longer hospital stay (7.9 ± 7.7 days versus 7.5 ± 8.6 days; p = 0.001).


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  		Table 4. . Perioperative Data: Left Main Disease Versus No Left Main Disease
 
The incidence of postoperative low output syndrome, operative mortality, and myocardial infarction were similar for LMS and no LMS.

EFFECT OF COMCOMITANT RIGHT CORONARY ARTERY STENOSIS.
Table 5Go displays the postoperative outcomes for patients with both significant left main stenosis and right coronary artery diseasetab 5. The extent of right coronary artery stenosis did not influence perioperative outcomes.


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  		Table 5. . Effect of Concomitant Right Coronary Artery Disease
 
EFFECT OF EARLY VERSUS LATE OPERATION.
Table 6Go illustrates the perioperative data and postoperative outcomes for the early and late groupstab 6. Patients in the early group were more likely to receive a preoperative intraaortic balloon pump (9.0% versus 0%; p < 0.0001). There were no other significant perioperative differences between the groups.


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  		Table 6. . Early Versus Late
 
MORBIDITY ATTRIBUTABLE TO WAITING TIME.
In the LMS group, there were two deaths on the waiting list. In both cases the patients had deferred operation for personal reasons and against medical advice. Twenty-one patients suffered a preoperative myocardial infarction (within 30 days of operation), but only 4 patients suffered an infarction while waiting for operation. All 4 patients subsequently underwent bypass grafting with no perioperative complications.


   Comment
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
Acknowledgments
 References
 
Several investigators have identified the presence of left main stenosis as an independent predictor of postoperative morbidity and mortality after coronary artery bypass grafting [1, 2, 7, 8, 11, 12]. Left main stenosis represents an anatomical indication for coronary artery bypass grafting regardless of symptomatology. The Coronary Artery Surgery Study [4, 15] and the Veterans Administration Cooperative Study [7] both revealed that coronary bypass grafting prolonged life in patients with left main stenosis. However, in the Veterans Administration study the benefit of bypass grafting over medical therapy alone did not become evident until 3 months after operation. Despite the results of the large Veterans Administration trial, the presence of left main stenosis has traditionally prompted surgeons to operate urgently on patients regardless of their symptomatic status. In the Ontario Provincial Health Care Network, a triage system exists for patients awaiting coronary artery bypass grafting. An urgency rating score is used to determine the optimum waiting time for patients needing operation [9]. In this index of severity, symptomatology is given priority over underlying anatomy. Therefore, patients without left main disease who have unstable angina refractory to medical therapy will receive priority over asymptomatic patients with left main disease. As a result of this triage system, 181 patients who had critical left main stenosis by angiographic criteria waited for more than 10 days before undergoing operation at our institution.

Impending health care reforms in the United States and other industrialized nations will force administrators to examine the delivery of health care services within their own institutions. The ability to predict accurately which patients can afford to wait for operation versus those who require immediate operation will enable health care providers to rationalize costs without jeopardizing patient care. The results of this study justify the use of a triage system even in patients with critical left main stenosis provided that these patients are carefully selected on the basis of symptomatic status.

Effect of Left Main Stenosis
Patients within the LMS group were similar to patients in the no LMS group in terms of their demographic profiles. There was a significantly higher proportion of patients with peripheral vascular disease in the LMS group, which was reflected in a slightly higher incidence of preoperative neurologic events. This finding probably reflects the aggressive nature or later stage of their atherosclerotic disease, and the presence of cerebrovascular disease. Previously it has been demonstrated that carotid artery disease is more prevalent among patients with left main stenosis [16]. Surprisingly, patients in the LMS group were not significantly different in terms of their symptomatic status before operation nor was there an increased incidence of preoperative myocardial infarctions. Nevertheless, patients with left main disease had significantly shorter waiting times than their cohorts in the no LMS group (38 ± 46 days versus 84 ± 71 days; p < 0.0001). The presence of left main disease resulted in more bypass grafts being constructed with a subsequent increase in both aortic cross-clamp times and cardiopulmonary bypass times. The difference in hospital stay was statistically significant (LMS, 7.9 ± 7.7 days versus no LMS, 7.5 ± 8.6 days; p = 0.001). Patients with left main stenosis did not suffer from an increased incidence of perioperative myocardial infarction, postoperative low output syndrome, or operative mortality. These univariate results confirm previous reports that left main stenosis is no longer an important predictor of operative mortality [8, 17].

Patients with concomitant right coronary artery disease (groups 2 and 4) were more likely to have peripheral vascular disease, presumably due to their generalized atherosclerotic disease. The presence of concomitant right coronary artery disease did not significantly reduce waiting time, nor did it increase operative morbidity and mortality.

Effect of Early Versus Late Operation
Approximately one third of the patients in the LMS group underwent operation with a wait time of less than 10 days. The patients in the early group were operated on primarily for symptoms as evidenced by the higher proportion of patients presenting with New York Heart Association functional class IV symptoms or with a recent preoperative infarct. The severity of the left main disease also influenced the wait time as patients with 75% or more left main stem stenosis were more likely to be in the early group.

The patients in the late group did not suffer from an increase in operative morbidity or mortality. Triage to the late group did not result in prolonged intensive care unit stay nor did it result in prolonged hospital stays. There were two patients in the late group who suffered perioperative strokes and required prolonged hospitalization for rehabilitation.

Summary
The present study reports the results of isolated coronary artery bypass grafting in patients with left main stenosis with an analysis of the effect of waiting time on postoperative outcomes. Several investigators have devised preoperative risk indices in an attempt to predict postoperative outcomes after coronary artery bypass grafting [10–13]. In Ontario, we use similar indices to triage patients waiting for bypass grafting. The emphasis in our triage system is placed on the symptomatic status of the patient and the underlying coronary anatomy is of secondary concern. As a result of this preference, some patients with critical left main stenosis are triaged to late operation. In fact, the mean wait time for patients with left main stenosis of more than 75% is still more than 3 weeks. This study demonstrates the safety of triaging patients for coronary artery bypass grafting. In particular, patients with left main stenosis can be triaged safely to late operation provided that they are carefully selected. We recommend that patients with a recent preoperative myocardial infarction or unstable angina refractory to medical therapy be triaged to early operation. We have not addressed the sociopsychological impact of waiting for operation or the long-term effect of those patients suffering complications while queuing for operation. Further analysis of the cost–risk interactions in triage systems is necessary.


   Acknowledgments
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
References
 
This study was supported by grant B2317 from the Heart and Stroke Foundation of Ontario.


   Footnotes
Top
 Footnotes
Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Presented at the Poster Session of the Thirty-first Annual Meeting of The Society of Thoracic Surgeons, Palm Springs, CA, Jan 30–Feb 1, 1995.

Address reprint requests to Dr Christakis, H-406, Sunnybrook Health Science Centre, 2075 Bayview Ave, Toronto, ON, Canada, M4N 3M5.


   References
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Kouchoukos NT, Oberman A, Kirklin JW. Coronary bypass surgery: analysis of factors affecting hospital mortality. Circulation 1980;62(Suppl 1):84–9.
  2. Kennedy JW, Kaiser GC, Fisher LD, et al. Multivariate discriminant analysis of the clinical and angiographic predictors of operative mortality from the Collaborative Study in Coronary Artery Surgery (CASS). J Thorac Cardiovasc Surg 1980;80:876–87.[Abstract]
  3. Chaitman BR, Davis KB, Kaiser GC, Mudd G. The role of coronary bypass surgery for left main equivalent coronary disease: the coronary artery surgery study registry. Circulation 1986;74(Suppl 3):17–25.
  4. Chaitman BR, Fisher LD, Bourassa MG, Davis KB, Mock MB. Effect of coronary bypass surgery on survival patterns in subsets of patients with left main coronary artery disease. Am J Cardiol 1981;48:765–77.[Medline]
  5. Farinka JB, Kaplan MA, Harris CN. Disease of the left main coronary artery: surgical treatment and long term follow-up in 267 patients. Am J Cardiol 1978;42:124–8.[Medline]
  6. Campeau L, Corbara F, Crochet D, Petitclerc R. Left main coronary artery stenosis. The influence of aortocoronary bypass surgery on survival. Circulation 1978;7:1111–5.
  7. Takaro T, Peduzzi P, Detre KM, et al. Survival in subgroups of patients with left main coronary artery disease. Circulation 1982;66:14–22.[Abstract/Free Full Text]
  8. Christakis GT, Ivanov J, Weisel RD, Birnbaum PL, David TE, Salerno TA, and the cardiovascular surgeons of the University of Toronto. The changing patterns of coronary artery bypass surgery. Circulation 1988;80(Suppl 1):51–61.
  9. Naylor CD, Baigrie RS, Goldman BS, et al. Assessment of priority for coronary revascularization procedures. Lancet 1990;335:1070–3.[Medline]
  10. Higgins TL, Estafanous FG, Loop FD, et al. Stratification of morbidity and mortality outcome by preoperative risk factors in coronary artery bypass patients: a clinical severity score. JAMA 1992;267:2344–8.[Abstract/Free Full Text]
  11. Tu JV, Mazer CD, Levinton C, et al. A predictive index for length of stay in the intensive care unit following cardiac surgery. Can Med Assoc J 1994;151:177–85.[Abstract]
  12. Parsonnet V, Dean D, Bernstein AD. A method of uniform stratification of risk for evaluating the results of surgery in acquired adult heart disease. Circulation 1989;79(Suppl 1): 3–12.
  13. Tu JV, Jaglal SB, Naylor CD. Multicenter validation of a risk index for mortality, intensive care unit stay and overall hospital length of stay after cardiac surgery. Circulation 1995;91:677–84.[Abstract/Free Full Text]
  14. Weisel RD, Burns RJ, Baird RJ, et al. Optimal postoperative volume loading. J Thorac Cardiovasc Surg 1983;85:552–63.[Abstract]
  15. Caracciolo EA, Davis KB, Sopko G, et al. Comparison of surgical and medical group survival in patients with left main coronary artery disease. Long-term CASS experience. Circulation 1995;91:2325–44.[Abstract/Free Full Text]
  16. Rizzo RJ, Whittemore AD, Couper GS, et al. Combined carotid and coronary revascularization: the preferred approach to the severe vasculopath. Ann Thorac Surg 1992;54:1099–109.[Abstract]
  17. Cosgrove DM, Loop FD, Lytle BW, et al. Primary myocardial revascularization. Trends in surgical mortality. J Thorac Cardiovasc Surg 1984;88:673–84.[Abstract]

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