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Ann Thorac Surg 1995;60:19-26
© 1995 The Society of Thoracic Surgeons
Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine and Barnes Hospital, St. Louis, Missouri.
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Abstract |
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 TopFootnotes Abstract IntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Methods. We examined our experience retrospectively in 3,942 patients who underwent CABG between 1986 and 1993, including 2,296 patients after acute MI.
Results. The operative mortality associated with increasing time intervals between MI and CABG were 9.1%, 8.3%, 5.2%, 6.5%, and 2.9%, for less than 6 hours, 6 hours to 2 days, 2 to 14 days, 2 to 6 weeks, and more than 6 weeks, respectively. In comparison, the operative mortality was 2.5% for patients with no history of acute MI. The incidence of permanent stroke and perioperative MI were greater and the length of postoperative hospitalization was longer for patients undergoing CABG early after MI. For patients undergoing operation electively, however, the operative mortality associated with increasing time intervals between MI and CABG were less, at 0.0%, 3.6%, 2.1%, 6.4%, and 2.1% for less than 6 hours, 6 hours to 2 days, 2 to 14 days, 2 to 6 weeks, and more than 6 weeks, respectively. For patients undergoing CABG within 14 days of MI, the operative mortality was 5.3% for those receiving an intraaortic balloon pump preoperatively for postinfarction angina, but 11.8% for those who underwent urgent/emergent operation without intraaortic balloon pump support.
Conclusions. Elective CABG can be accomplished with acceptable morbidity and mortality early after acute MI if an elective operation is possible. In addition, the intraaortic balloon pump should be used aggressively in patients with postinfarction angina to allow for elective rather than urgent/emergent operation.
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Introduction |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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The treatment of patients with acute myocardial infarction (MI) includes admission to the hospital, early administration of thrombolytic agents such as tissue plasminogen activator or streptokinase, intensive monitoring for acute complications of MI, efforts to reduce myocardial oxygen demand to salvage myocardial tissue at risk, and cardiac catheterization to document the presence of atherosclerotic coronary artery disease [1–4]. With approximately 1.5 million patients annually suffering an acute MI in the United States and nearly 25% of all deaths attributable to acute MI, this remains a major public health problem [5]. Options for myocardial revascularization include percutaneous coronary angioplasty (PTCA) or other endovascular interventions in the early postinfarction period or coronary artery bypass grafting (CABG) for suitable patients [6–18]. Although there was enthusiasm beginning in the 1970s for early or immediate CABG for acute MI, the currently accepted indications for early operative intervention after acute MI include mechanical complications related to the MI such as papillary muscle rupture, ventricular septal defect, or severe left ventricular mechanical dysfunction with congestive failure, as well as refractory postinfarction angina. In recent series reported from large medical centers, as many as 10% to 25% of all patients undergoing CABG procedures underwent operation within 4 weeks of an acute MI [13, 15]. Although the rationale for urgent or emergent operation is clear for patients with life-threatening complications of the MI, the optimal timing of CABG after uncomplicated MI for patients with documented atherosclerotic coronary artery disease remains controversial.
The objective of the present study was to determine the relationship between the timing of CABG after acute MI and short-term postoperative outcomes in a large, contemporary series of patients. A secondary objective was to document the outcomes of patients with acute MI treated before CABG with the intraaortic balloon pump (IABP) to determine, in particular, the benefits associated with the use of the IABP in patients with medically refractory postinfarction angina.
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Material and Methods |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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tab 1.
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The operative procedures were performed by a total of eight different surgeons using a variety of cannulation, cardioplegia, and grafting techniques. No distinction was made with regard to the types of conduit used for the revascularization. The most commonly used myocardial protection technique was the administration of antegrade, intermittent cold cardioplegia, but many patients also received retrograde, continuous, or blood cardioplegia. Operations were categorized as elective for patients who were hemodynamically stable at the time of operation and for whom the operation was undertaken as a procedure that could be scheduled more than 24 hours in advance. All other operations were categorized as urgent/emergent; this group included patients who were hemodynamically unstable at the time of operation and patients in whom operation was required for complications related to cardiac catheterization or failed PTCA or other endovascular interventions, and those in whom operation could not be planned more than 24 hours in advance.
Statistical Methods
Statistical calculations were made using SAS (PC version 6.0.4, SAS Institute, Cary, NC). Descriptive data are reported as mean ± one standard deviation. Comparisons between continuous variables were made using Student's t test. Comparisons between categoric variables were made using the 
2) or Fisher's exact test, as appropriate. Multiple group means were compared using analysis of variance. In all cases, differences were considered to be significant for a p value of 0.05 or less. Multiple logistic regression was performed in a positive, stepwise fashion with a significance level of p = 0.05 required for entry into the model.
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Results |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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) were similar in most, but not all respects. The mean age of patients in each of the five groups was not significantly different (p = 0.13). Likewise, the groups did not differ with respect to smoking history (p = 0.28), hypertension (p = 0.79), or the presence of peripheral vascular disease (p = 0.43). There were slight differences between patient groups with respect to the total number of previous MIs (p = 0.0001), but the number of previous MIs fell within a very narrow range between 1.3 and 1.5. There were also slight differences between groups with respect to the preoperative history of renal insufficiency (p < 0.0001), with a greater prevalence in patients undergoing CABG early after MI. The prevalence of diabetes mellitus was also nonuniform (p = 0.008), primarily because of a prevalence of 0.0% in the group of patients undergoing operation within 6 hours of MI. The frequency of urgent/emergent operation was greatest for patients undergoing operation early after acute MI. For patients undergoing CABG within 2 days of acute MI, the frequency of urgent/emergent operation ranged from 78.8% to 90.9%. In contrast, the frequency of urgent/emergent operation for patients more than 6 weeks after MI was only 15.7%. The number of distal bypass grafts performed was not uniform for each of the patient groups (p < 0.01). In particular, fewer grafts were performed for patients who underwent operation early after MI. The mean times required for cardiopulmonary bypass and aortic cross-clamping fell within a narrow range for the patient groups, from 109.2 to 124.2 minutes and 42.3 to 49.9 minutes, respectively. The IABP was used most frequently in association with operations performed early after MI, with as many as 43.9% of patients receiving an IABP if operation was undertaken between 6 hours and 2 days after MI. Similarly, intraoperative or postoperative use of the ventricular assist device was required most commonly in patients undergoing operation early after MI.
The primary short-term postoperative outcomes as they related to the timing of CABG after acute MI are summarized in Table 2. The operative mortality associated with CABG was not uniform among the patient groups (p < 0.001). The highest mortality was associated with operations undertaken early after MI (9.1% for patients undergoing operation within 6 hours of MI), with a gradual decrease in mortality as the interval between MI and CABG was longer. Even for patients (n = 1,284) with an interval of at least 2 weeks between MI and CABG, the operative mortality rate of 3.7% was still greater than the rate (2.1%) for patients (n = 1,646) who had no preoperative history of MI (p = 0.009). Considering an arbitrary cut-off of 2 days after MI, patients can be grouped into those undergoing operation within 48 hours of MI (n = 143) and those undergoing operation (n = 2,153) more than 48 hours after MI (Fig 1). The operative mortality for patients undergoing operation within 48 hours of MI (8.4%) was significantly greater than for patients undergoing operation more than 48 hours after MI (4.3%, p = 0.02).
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, categorized by the time interval between MI and CABG. The incidence of perioperative MI, permanent CVA, and atrial fibrillation were not uniform among the patient groups (p < 0.01, p < 0.05, and p < 0.05, respectively), being more common among patients undergoing operation early after MI. There was no difference in the incidence of transient postoperative CVA. The postoperative length of stay in the intensive care unit (p = 0.0001) was not uniform for the patient groups. There was no difference in the length of stay in the stepdown unit. In general, there was a longer intensive care unit stay for patients with short time intervals between MI and CABG.
Short-term postoperative outcomes are tabulated separately for elective and for urgent/emergent operations in Tables 3 and 4, respectively. For most patient groups, including those patients without preoperative MI as well as all patients collectively, the operative mortality associated with elective operation was less than for patients undergoing urgent/emergent operation. In addition, the operative mortality associated with CABG, regardless of the urgency of operation, was greater for patients with preoperative MI than for patients without preoperative MI. For most, but not all, patient groups (Tables 3 and 4), the incidence of perioperative MI and permanent CVA was increased for patients undergoing urgent/emergent operations compared with those undergoing elective operation. The incidence of atrial fibrillation, the incidence of transient CVA, as well as the length of hospital stay were not significantly different based on the urgency of operation.
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). Variables considered for the model included patient age, the number of previous MIs, smoking history, diabetes mellitus, renal insufficiency, hypertension, peripheral vascular disease, the time interval between MI and CABG, and the urgency of operation. Independent predictors of operative death, in order of decreasing importance, included urgency of operation (p = 0.0001), increasing patient age (p = 0.0001), renal insufficiency (p = 0.0001), number of previous MIs (p = 0.001), and hypertension (p = 0.013). Notably, when these other risk factors are controlled for, the time interval between MI and CABG per se was not a significant predictor of operative deaths.
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. For patients with a history of MI, the IABP was used more commonly in the preoperative period than in the intraoperative or postoperative periods. The IABP was used preoperatively in 27.2%, 39.4%, 13.2%, 5.0%, and 4.3% of patients with intervals between MI and CABG of less than 6 hours, 6 hours to 2 days, 2 to 14 days, 2 to 6 weeks, and more than 6 weeks, respectively. For patients undergoing CABG within 6 weeks of MI, the most common indication for the use of the IABP preoperatively was angina refractory to medical therapy.
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. For each patient group according to the time interval between MI and CABG, the operative mortality was greater for patients undergoing emergency operation without IABP support than for patients who received an IABP preoperatively for unstable angina. Although the trend is obvious and the magnitude of the differences in mortality are substantial, these differences did not reach statistical significance.
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. The operative mortality as well as the incidence of perioperative MI, perioperative CVA, and the need for the use of the ventricular assist device were greater for patients undergoing emergency operation without IABP support than for patients receiving an IABP preoperatively for angina, but these differences did not reach statistical significance given the small number of patients. There appeared to be no difference in the incidence of postoperative atrial fibrillation or the length of postoperative hospitalization.
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Comment |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Other investigators have advocated CABG within 4 to 6 hours after acute MI, documenting hospital mortality rates as low as 3.8% [19, 20]. These same investigators have also documented by comparison that the hospital mortality for patients treated medically without CABG approached 16% [20]. Nonetheless, immediate CABG has not become popular for patients with acute MI primarily because of the logistic difficulties associated with accomplishing transportation to the hospital, evaluation, and coronary arteriography in the first several hours after MI. Generally, we have been reluctant to perform CABG in the immediate period after acute MI and this reluctance is reflected in the small number of patients (n = 11) in our 8-year experience who underwent operation within 6 hours of acute MI. Most of these procedures were undertaken urgently or emergently in patients with hemodynamic instability or refractory postinfarction angina. Although the sample size was small there was, not surprisingly, a high associated operative mortality (9.1%) and a relatively high frequency of perioperative MI (9.1%) and stroke (9.1%). We believe the high associated morbidity and mortality may not be a reflection of the timing of CABG relative to the MI per se, but rather a reflection of the poor overall medical condition of our patients who have undergone operation in this situation.
Our experience suggests that when all patients are considered collectively, there is increased morbidity and mortality associated with CABG performed early after MI. These data confirm the findings of most [16, 18, 21] but not all previous investigators [22–24]. Notably, the increased operative risk, including operative mortality, perioperative MI, and perioperative CVA, appears to be present for patients undergoing CABG with intervals between MI and CABG of as long as 2 weeks and may continue to be present for patients undergoing CABG more than 6 weeks after MI. To help simplify the decision making for the patients, there appears to be a twofold increased risk for operative death in patients undergoing CABG within 2 days of MI compared with those who undergo operation later (see Fig 1).
Because of the obviously increased morbidity and mortality associated with CABG operations performed early after acute MI, there has been considerable interest in identifying groups of patients who might undergo CABG safely in the early postinfarction period. Previous studies have identified several potential groups of patients with better outcomes, including those with relative preservation of left ventricular ejection fraction [22–24], those who are not in shock at the time of operation [18, 22, 24], those with subendocardial versus transmural MI [16], male patients [11], those without left main coronary artery disease [11], and younger patients in general [13]. In the current study, we did not expressly consider the effect of ejection fraction or the presence of shock at the time of operation, but we have noted that patients who underwent CABG in what we consider an elective setting experienced better outcomes, in terms of both morbidity and mortality. There was less mortality and morbidity for each of the five time intervals considered between MI and CABG. Our use of the ``elective'' classification obviously subsumes several of the factors considered by other investigators, especially hemodynamic stability and freedom from angina at the time of operation. This is admittedly a heterogeneous group of patients and we have not considered the effects on postoperative outcomes of factors such as transmural versus subendocardial MI or the type of myocardial protection used during operation.
In most respects, the results of the multivariate logistic regression analysis should not be surprising. The identification of urgency of operation, increasing patient age, renal insufficiency, number of previous MIs, and hypertension as independent risk factors for an adverse outcome may be helpful in selecting patients for operation early after acute MI. Most notably, however, the time interval between MI and CABG was not significantly related to operative mortality when these other variables have been controlled. This suggests that the single variable that might be modified before operation is the urgency of operation. For that reason, it is important to identify strategies for facilitating elective rather than urgent/emergent operation.
Recently, we have reviewed our experience with application of the IABP in patients undergoing cardiac surgical procedures of all types and found a dramatic increase between 1986 and 1992 in the use of the IABP preoperatively for the indication of refractory angina [25]. There was markedly decreased morbidity and mortality among patients in whom perioperative IABP support was initiated early during the perioperative course. Among the patients in the current study, the IABP was commonly used preoperatively in patients undergoing CABG early after acute MI and particularly for those undergoing operation within 2 weeks of MI. In these patients, the most common indication for an IABP was refractory postinfarction angina. For patients who could be stabilized preoperatively with the IABP, elective operation might then become possible.
For patients receiving a preoperative IABP for refractory angina, the short-term postoperative outcomes were very favorable when compared to patients undergoing emergent operation without preoperative IABP support. In particular, the use of the IABP preoperatively for angina may lead to decreased mortality as well as decreased morbidity. Although the differences do not reach statistical significance because of the small number of patients, there is a remarkable trend toward less operative mortality, postoperative stroke, atrial fibrillation, and use of the ventricular assist device.
In summary, the data suggest that elective operation for CABG can be accomplished in the early postinfarction period with acceptable morbidity and mortality. Nonetheless, there appears to be a decrease in morbidity and mortality associated with increasing time intervals between MI and CABG for time periods of as long as 6 weeks. The greatest morbidity and mortality is associated with patients undergoing CABG in the early postinfarction period in an urgent or emergent setting. Indeed, the urgency of operation appears to be the single most important predictor of outcome in patients undergoing CABG after MI. For patients with refractory postinfarction angina, aggressive use of the IABP preoperatively to stabilize the patient before operation may allow elective, rather than urgent, operation and provide the opportunity for CABG in this setting to be accomplished with less morbidity and mortality.
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Acknowledgments |
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Footnotes |
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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Address reprint requests to Dr Rosenbloom, Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, 3108 Queeny Tower, Barnes Hospital, One Barnes Hospital Plaza, St. Louis, MO 63110.
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TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentAcknowledgmentsReferences |
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