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Original Articles: Adult Cardiac

Prior Inferior Myocardial Infarction Has Worse Early Outcomes in Patients Undergoing Coronary Artery Bypass Grafting Than Prior Anterior Myocardial Infarction

^a Department of Cardiovascular Surgery, Sakakibara Heart Institute, Tokyo, Japan
^b Department of Biostatistics and Epidemiology, Yokohama City University Medical Center, Yokohama, Japan

Accepted for publication October 21, 2008.

^_* Address correspondence to Dr Fukui, Department of Cardiovascular Surgery, Sakakibara Heart Institute, 3-16-1 Asahi-cho, Fuchu City, Tokyo, 183-0003, Japan (Email: tfukui-cvs{at}umin.ac.jp).

	Abstract

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Background: It is generally considered that patients with prior myocardial infarction (PMI) have worse outcomes than those without PMI after coronary artery bypass grafting (CABG). However, any difference in outcomes of patients with anterior or inferior PMI undergoing CABG has never been determined.

Methods: We retrospectively reviewed the records of 310 patients with anterior or inferior PMI who underwent isolated CABG between September 2004 and September 2008. Of these, 151 patients had anterior PMI (anterior group), and 159 patients had inferior PMI (inferior group). Preoperative and postoperative variables were compared between the groups. Multivariate logistic regression analysis was used to identify independent predictors of major postoperative complications including death.

Results: Patients of the inferior group were significantly older (68.3 ± 9.2 vs 65.5 ± 11.0; p = 0.015) and had more diseased vessels per patient (2.9 ± 0.3 vs 2.8 ± 0.5; p = 0.009) than the anterior group. A higher rate of mild or moderate mitral regurgitation was observed in the inferior group (18.2% vs 8.6%; p = 0.0209). The operative mortality was higher in the inferior group (5.0% vs 0%; p = 0.0073). Rates of respiratory failure (6.9% vs 0.7%; p = 0.0199) and requirement for hemodialysis (5.7% vs 0.7%; p = 0.0056) were higher in the inferior group. Multivariate analysis revealed inferior PMI (p = 0.0068) as the only independent predictor of major postoperative complications including death.

Conclusions: The present study indicates that patients with inferior PMI have poorer outcomes after isolated CABG than those with anterior PMI.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Since several treatments for acute myocardial infarction (AMI) have been established, mortality and morbidity have remarkably improved after AMI [1]. Therefore, the rate of patients with multivessel coronary artery disease with prior myocardial infarction (PMI) referred for coronary bypass surgery has increased. It is generally considered that patients with PMI have worse outcomes than those without PMI after coronary artery bypass grafting (CABG) [2]. However, to our knowledge, it has not previously been investigated whether there is a difference in outcomes after CABG between patients with anterior PMI and patients with inferior PMI.

The aim of the present study was to compare the outcomes after CABG in patients with anterior or inferior PMI. Furthermore, we aimed to identify the independent predictors of worse outcomes after CABG in patients with PMI.

	Patients and Methods

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Patient Population
Between September 2004 and September 2008, 782 patients underwent isolated CABG at the Sakakibara Heart Institute. Among these patients, 365 (46.7%) had PMI before surgery. Of these 365 patients, 310 had either anterior or inferior PMI, including 151 with anterior PMI and 159 with inferior PMI. Another 55 patients were excluded from this study because they had a lateral PMI or a combined history of both anterior and posterior PMI. In patients with inferior PMI, there were 151 (95.0%) whose inferior wall was supplied by the right coronary artery (right dominant system).

We compared the preoperative, intraoperative, and postoperative variables between the anterior and inferior groups. All data were collected prospectively and reviewed retrospectively. The board chairperson of the ethics committee at the Sakakibara Heart Institute approved this retrospective study and waived the need for patient consent.

The PMI was defined as a MI more than 30 days before surgery. The MI was treated with medication with or without percutaneous coronary intervention (PCI) during the acute phase. The PMI was confirmed with various examinations including an electrocardiogram, an echocardiogram, angiography, magnetic resonance imaging, and a scintigram, or a combination of these. Of these examinations, a thallium and meta-123I-iodobenzylguanidine scintigram was most often used to identify the MI lesion (68.7%). Magnetic resonance imaging was performed in 11.3% of patients for combined diagnosis with a scintigram. An electrocardiogram and echocardiogram were performed in all patients; however, they were used for identifying the MI lesion in only 31.3% of patients. Both non-Q-wave and Q-wave MI were included in this study.

Our strategy for isolated CABG was directed toward obtaining complete myocardial revascularization with an off-pump technique whenever feasible. Complete revascularization was defined as "traditional" completeness in this study. "Traditional" completeness was defined as all diseased arterial systems (stenosis >50%) receiving at least one graft insertion. The technique of off-pump CABG has been described previously [3]. We bypassed all significantly diseased coronary vessels (at least 50% diameter reduction) larger than 1 mm in diameter. If necessary, concomitant long segmental reconstruction (length more than or equal to 2.0 cm) of the left anterior descending artery with or without endarterectomy was performed in patients with a diffusely diseased left anterior descending artery [4]. Deep pericardial stay sutures were not used, and a commercially available heart positioner and stabilizer was applied in all cases. Cardiopulmonary bypass with or without cardiac arrest was used in patients who were not suitable for the off-pump technique (5.5%). Coronary artery bypass grafting with cardiopulmonary bypass was performed in patients with severely impaired left ventricular function, intramyocardial coronary arteries, or redo surgery.

Patients who had received mitral repair due to ischemic functional mitral regurgitation (MR) were not included in this study. We performed mitral repair in patients with moderate to severe or severe ischemic MR (IMR) [5]. Furthermore, patients who had received surgical left ventricular restoration due to left ventricular aneurysm and dilated ischemic cardiomyopathy were not included in this study. We performed surgical ventricular restoration in patients with a left ventricular end-systolic volume index of more than 100 cm³.

Nonelective operations included both emergency and urgent cases. Operative death was defined as death occurring during the same hospitalization or after discharge from the hospital, but within 30 days of the procedure. Low-output syndrome was defined as the need for adrenaline or more than 5 µg · kg^–1 · min^–1 of dopamine or dobutamine. Perioperative MI (POMI) was defined as a positive result for new Q waves in an electrocardiogram or a peak creatine kinase MB level of greater than 10% of the total creatine kinase. Respiratory failure was defined as requiring prolonged ventilation (>48 hours) or having pneumonia. A postoperative cerebrovascular accident was defined as having new stroke or intracranial bleeding, and was confirmed by computed tomography. In patients with preoperative stroke, postoperative stroke was defined as a worsening of the neurologic deficit with new radiologic findings. Major complications included low-output syndrome, POMI, severe ventricular arrhythmia, respiratory failure, requirement for hemodialysis, cerebrovascular accident, and mediastinitis.

Statistical Analysis
All statistical analyses were performed using the StatView 5.0 software package (SAS Institute, Cary, NC). Continuous variables are reported as the mean ± standard deviation. Continuous variables were compared by the Student t test, while discrete variables were compared by the ² test or Fischer exact test. Differences were considered significant at p less than 0.05.

A univariate analysis was drawn from the preoperative clinical variables listed in Table 1, anterior and inferior PMI. Then a multivariate logistic regression analysis was performed to determine the significant predictors of the combined endpoint of the operative death and major complications. Variables identified as having a p value of less than 0.1 on univariate analyses were considered for inclusion in the multivariate model.

	Results

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

Among these patients, 151 patients had anterior PMI (anterior group) and 159 had inferior PMI (inferior group). The preoperative characteristics of both groups are shown in Table 1. Mean age was significantly higher in the inferior group (68.3 ± 9.2 vs 65.5 ± 11.0; p = 0.015). The mean number of diseased vessels was significantly higher in the inferior group (2.9 ± 0.3 vs 2.8 ± 0.5; p = 0.009). Mean body surface area was larger in the anterior group (1.7 ± 0.2 vs 1.6 ± 0.2), but this was not statistically significant (p = 0.0815). In the anterior group, there were more patients who had diabetes (58.3% vs 44.0%; p = 0.0166). There was a significantly higher prevalence of having mild or moderate MR in the inferior group (18.2% vs 8.6%; p = 0.0209). Both groups of patients had slightly impaired left ventricular function. There was no difference regarding having a previous PCI between the groups (p = 0.6542). Furthermore, there were no differences regarding medications between the groups.

Pulmonary artery pressure (PAP) was measured preoperatively in 49 patients (32.5%) in the anterior group and 46 (28.9%) in the inferior group. There were no significant differences in systolic (30.0 ± 12.7 mm Hg in the anterior group versus 30.3 ± 10.5 in the inferior group; p = 0.8784), diastolic (12.7 ± 6.4 vs 13.5 ± 4.9 mm Hg; p = 0.5301), and mean PAP (19.5 ± 8.6 vs 20.2 ± 7.3 mm Hg; p = 0.6777) between the two groups.

The intraoperative and postoperative results are also listed in Table 1. There were no significant differences in the mean number of anastomoses per patients (4.2 ± 1.2 vs 4.3 ± 1.3; p = 0.5041) and the completeness of revascularization (95.9% vs 96.6%; p = 0.6768) between the inferior and anterior groups.

The grade of MR in patients who had had mild or moderate IMR preoperatively mostly improved in both groups. In the anterior group, the grade of MR of 10 patients (76.9%) improved postoperatively (one moderate MR to mild, and nine mild MR to trivial). In the inferior group, the grade of MR of 19 patients (65.5%) improved postoperatively (two moderate MR to mild, and 17 mild MR to trivial). No MR worsened in any patient after the operation.

Postoperative and preoperative ejection fractions were compared in each group using a paired t test. There were no significant differences in either group (pre 0.495 ± 0.119 vs post 0.503 ± 0.126 in the anterior group, p = 0.2500; pre 0.499 ± 0.117 vs post 0.501 ± 0.119 in the inferior group, p = 0.7862). In the inferior group, however, ejection fraction significantly improved after the operation in patients with improved MR (pre 0.419 ± 0.118 vs post 0.478 ± 0.137%; p = 0.0006), although this was not observed in patients with nonimproved MR (pre 0.380 ± 0.131 vs post 0.397 ± 0.112; p = 0.5531).

There were significantly more operative deaths among the inferior group (5.0% vs 0%; p = 0.0073). The causes of death of 8 patients in the inferior group were heart failure in 3 patients, respiratory failure in 4 patients, and mediastinitis in 1 patient. Furthermore, the number of patients with respiratory failure (6.9% vs 0.7%; p = 0.0056) and requirement for hemodialysis (5.7% vs 0.7%; p = 0.0199) was significantly higher in the inferior group. The combined endpoint of operative death and major complications was higher in the inferior group (18.9% vs 6.6%; p = 0.0023). We further assessed the outcome differences between the right dominant group (n = 151) and left dominant group (n = 8) in patients with inferior PMI. However, there were no differences in preoperative and postoperative variables between the groups.

From univariate analysis (Table 2), unstable angina (p = 0.0420), Canadian Cardiovascular Society class (p = 0.0291), creatinine (p = 0.0063), chronic obstructive pulmonary disease (p = 0.0413), and the inferior location of a previous MI (p = 0.0023) were significantly associated with operative death and major complications. Conversely, the anterior location of a previous MI was significantly observed in patients with no operative death or major complications (p = 0.0023). Whether CABG was on-pump or off-pump was not related to adverse outcome (p = 0.2516).

	Comment

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

Several studies of CABG in patients with AMI have described that perioperative mortality decreased as time elapsed [6–8]. Lee and colleagues [6] reported that a 3-day waiting period before CABG should be considered in the absence of absolute indications for emergency surgical intervention. It is suggested that reperfusion injury or whole body inflammatory states may lead to an increase in mortality during the acute phase after AMI [8]. Voisine and colleagues [7] reported that operative mortality significantly increased between 6 hours and 1 week after AMI. They also found that operative mortality was not influenced by a history of MI sustained more than 30 days prior to CABG, but perioperative mortality in patients over 65 years was significantly increased even after a 30-day waiting period when compared with that of patients without PMI. Similarly, Ketonen and colleagues [2] reported that having a history of MI prior to CABG was one of the predictors of an adverse long-term outcome after CABG. We can expect that patients with PMI may have cardiac dysfunction, dysrhythmia, or chronic heart failure that may lead to worse outcomes than patients without PMI.

Although previous studies demonstrated increases in long-term mortality with anterior MI over inferior MI [9], recent studies have reported that the long-term prognosis was not affected by the location of MI [10]. Furthermore, Gomez and colleagues [11] reported that inferior MI was associated with a significantly higher risk of mortality in the setting of a severely depressed ejection fraction. They speculated the reason for this was that an inferior MI usually causes a large area of myocardial damage and often involves the right ventricle, which is a factor influencing long-term prognosis. This may also have affected our results, though we did not examine right ventricular function preoperatively.

In the present study, patients in the inferior group were older than those in the anterior group. Older age has also been one of the predictors of worse outcome after CABG [2]. Furthermore, the diabetic state was worse in the inferior group as the rate of insulin usage was higher in this group, and peripheral vascular disease was more frequently observed in the inferior group. These variables were also predictors of worse outcomes after CABG. Thus, the preoperative status seemed to be worse in the inferior group in our study. However, age, insulin use, and peripheral vascular disease were not independent predictors of postoperative death and major complications in our study.

We included patients undergoing on-pump CABG in this study to compare the outcomes of on-pump patients with that of off-pump patients. However, univariate analysis did not identify a significant difference in outcomes between on-pump and off-pump CABG (p = 0.2516).

Patients with inferior PMI had a higher rate of IMR in our study. Kumanohoso and colleagues [12] revealed that the higher incidence of IMR in patients with inferior MI can be related to more severe geometric changes in the mitral valve apparatus with greater displacement of the posterior papillary muscle caused by localized inferior basal left ventricular remodeling. Although patients with moderate to severe or severe IMR were not included in the present study, because moderate to severe or severe MR was simultaneously repaired in our institution, there were more patients with mild or moderate IMR in the inferior group. However, multivariate analysis revealed that the IMR was not an independent predictor of the combined endpoint of death and major complications. Furthermore, the grade of MR improved in most patients after CABG and no MR deteriorated in any patients. The recovery of the myocardium of the inferior group may have contributed to the improvement of the grade of MR because a significant improvement in ejection fraction was observed in patients with improved MR after operation.

The reason why patients with inferior PMI had worse outcomes than patients with anterior PMI is unclear. However, we speculate that one of reasons may be because of right ventricular dysfunction. In necropsy studies, right ventricular infarction was seen in 14% to 60% of patients dying with inferior MI [13]. Not only left ventricular dysfunction but also potential right ventricular dysfunction may affect respiratory and renal function in patients with the inferior PMI.

Limitations
The limitations of this clinical study are as follows: (1) the number of patients was small; (2) we did not have information on PAP in all patients; (3) the results and conclusion of this study may not be generalized for female patients because the cohort only included 13% female patients; (4) we did not have a long-term clinical follow-up; (5) we did not distinguish the type of MI (non-Q-wave or Q-wave MI); and (6) the inability to match two groups (patients with inferior PMI were older and had more diseased vessels than patients with anterior PMI) perfectly weakens the outcome comparisons between CABG patients with anterior or inferior PMI. Small sample sizes inevitably limit the statistical power of our analysis. The use of a multicenter design will be necessary for accrual of a sample size necessary to generate the statistical power to truly evaluate the differences in operative death between the two groups.

Conclusion
The results of the present study showed that patients with inferior PMI have a poorer outcome than those with anterior PMI after isolated CABG. Further studies including larger sample size are needed.

	Acknowledgments

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
The authors gratefully thank Ko Bando, MD, for reviewing the article.

	References

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Toshihiro Fukui Tomoki Shimokawa Susumu Manabe Shuichiro Takanashi Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Fukui, T. Articles by Takanashi, S. Search for Related Content PubMed PubMed Citation Articles by Fukui, T. Articles by Takanashi, S. Related Collections Coronary disease