Asian Cardiovasc Thorac Ann 2008;16:231-235
© 2008 Asia Publishing EXchange Ltd
Gender Influence on Hospital Mortality after Coronary Artery Bypass Surgery
Mohammad H Mandegar, MD,
Mehrab Marzban, MD,
Amir H Lebaschi, MD,
Pouya Ghaboussi, MD,
Ali RA Alamooti, MD,
Ali Ardalan, MD
Tehran Heart Center, Tehran University of Medical Sciences Tehran, Iran
For reprint information contact: Amir H Lebaschi, MD Tel: 98 91 2315 9507 Fax: 98 21 6693 7185 Email: ah_lebaschi{at}razi.tums.ac.ir, Head Office of the Department of Surgery, Imam Medical Complex, Tehran University of Medical Sciences, Tehran, Iran.
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ABSTRACT
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There is still controversy about the influence of gender on hospital mortality after coronary artery bypass grafting. We analyzed various risk factors in 1,258 patients undergoing isolated on-pump coronary artery bypass, of whom 19 (1.5%) died in hospital. There were 937 men (74.5%) and 321 women (25.5%). Compared to men, women were older with a higher mean body mass index, twice as many were hypertensive and diabetic, and they had higher serum cholesterol and triglycerides. Men smoked more, had lower ejection fractions, more myocardial infarctions and poorer functional status. Female sex, congestive heart failure, low ejection fraction, diabetes, previous percutaneous interventions and chronic lung disease were more prevalent among the patients who died. These factors were used to form a logistic regression model in which sex did not have an independent influence on hospital mortality. The difference between men and women can be explained by differences in risk factor profile.
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INTRODUCTION
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Coronary heart disease is the leading cause of death among both men and women worldwide. It is still considered a disease of men, and there has been little recognition of its importance in women. Gender differences have been reported to exist in acute and chronic ischemia in terms of clinical manifestations, investigations and treatment.1 Coronary artery bypass grafting (CABG) has been shown to be effective for treating angina pectoris and prolonging life in patients with severe coronary artery disease.2 However, it has not yet been determined whether women benefit from this procedure to the same extent as men. Observational studies comparing outcomes between women and men after CABG have provided conflicting evidence as to whether or not sex is an independent predictor of death, especially in the early postoperative period. The purpose of this study was to investigate the influence of sex on hospital mortality after isolated first-time CABG.
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PATIENTS AND METHODS
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Between September 2004 and March 2005, data on patients who underwent first-time on-pump (conventional) CABG in Tehran Heart Center were collected prospectively. The inclusion criteria were isolated elective operations. For all patients, preoperative data including known major risk factors (cigarette smoking, diabetes mellitus, hypertension, cerebrovascular accidents, myocardial infarction, hypercholesterolemia, family history of cardiac disease) and other clinical conditions (chronic pulmonary disease, chronic renal failure, dysrhythmias) as well as history of previous vascular interventions (peripheral vascular surgery, carotid endarterectomy, and percutaneous coronary interventions) were recorded on a standard data form by trained data collectors on the day of admission. Objective data (lipid profile, ejection fraction, number of diseased vessels, and involvement of the left main coronary artery) were recorded after completion of the preoperative work-up, mainly the day before surgery. The definitions of various risk factors in the Society of Thoracic Surgeons Adult Cardiac Database were adopted in this study.3 After surgery, operative data were recorded on the data form, and the patients were followed up until the day of discharge. The discharge status or cause of death were also recorded.
Results are given as mean values with 95% confidence interval (CI). All data were entered into a dedicated database (Microsoft Access 2000) and analyzed with SPSS version 10.5 software (SPSS, Inc., Chicago, IL, USA). Quantitative values were compared using Student’s t test for independent groups. For categorical data, the chi-squared and Fisher’s exact tests were applied. Forward stepwise logistic regression was used to assess the independent effects of variables on hospital mortality.
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RESULTS
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At the end of the study period, data from 1,258 patients operated on by 6 surgeons had been collected. There were 937 men (74.5%) and 321 women (25.5%). The mean age was 58.7 years (range, 28 to 81 years), and 133 (10.6%) were aged 70 years or older. The mean weight was 73.49 kg (95% CI: 72.81–74.17), and mean height was 165.35 cm (95% CI: 164.82–165.88), giving a mean body mass index (BMI) of 27.01 kg·m–2 (95% CI: 26.69–27.33). The risk factors that differed between men and women are listed on Table 1
. Women were older and had higher BMIs. Twice as many women were hypertensive and diabetic compared to men. Mean serum cholesterol and triglyceride levels were higher in women. However, men had a much greater proportion of smokers and lower ejection fractions. Previous myocardial infarction and poor functional class were both more prevalent in men. Table 2 summarizes risk factors that had similar distributions in men and women.
Of the 1,258 patients who underwent CABG, 19 (1.5%) died in hospital. The causes of death were cardiac in 17 (89.5%), infection in 1 (5.3%) and neurologic in 1 (5.3%). Table 3 shows risk factors that had significantly different distributions in patients who died and those who were discharged alive. More men were discharged alive, and the survivors had lower BMIs. Congestive heart failure, low ejection fraction, diabetes mellitus, previous percutaneous interventions and chronic lung disease were more prevalent in patients who died. Risk factors that did not reach statistical significance in the differences between alive and dead patients are given in Table 4. Notable points are that more of those who died were aged > 75 years, had a higher mean BMI, greater incidence of cigarette smoking, worse functional status and more dysrhythmias. The extent of coronary disease was comparable among hospital survivors and those who died. In the next step, risk factors that were different in survivors and non-survivors and those with a p value of 0.1 or less were chosen for logistic regression analysis (Table 5). A forward stepwise method was used to enter these risk factors into the logistic regression model. Table 6 shows the risk factors that exerted independent effects on hospital mortality. According to this model, sex did not have an independent influence on hospital mortality.
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DISCUSSION
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In our preliminary univariate analysis, we found a sex difference between hospital survivors and non-survivors; women had a higher rate of hospital death than men. Comparison of various risk factors between men and women in this study showed differences: women were significantly less likely to have suffered a previous myocardial infarction or be in functional class III or IV, they also had significantly higher ejection fractions and greater BMIs. After recognizing other influencing factors, the logistic regression model indicated no independent role for sex in predicting hospital mortality. The implications of this finding may include the fact that mortality after CABG is not determined by sex and therefore non-modifiable, and there exist potentially modifiable risk factors for both sexes that if dealt with, may improve hospital outcome.
Reports concerning the influence of sex on hospital mortality after CABG have appeared for more than two decades. Earlier studies pointed to a higher hospital mortality rate in women.4–9 Older age, referral for surgery in more advanced stages of coronary artery disease, lower BMI and body surface area, and lower rate of internal mammary artery grafting have been proposed as probable causes for increased hospital mortality in women. More recent reports also identify female gender as a risk factor for hospital death.10–13 There are several other investigations that found no independent role for gender in hospital mortality after CABG. More frequent use of internal mammary artery grafts in women and overall refinement in the conduct of CABG have been suggested as influential in this regard.14–18 There are at least two reports that indicate a better outcome for women than men following CABG.19,20 In the study by Abramov and colleagues,19 women had a less favorable risk factor profile, nevertheless they had a better outcome. Analysis of the Bypass Angioplasty Revascularization Investigation (BARI) study showed similar early mortality rates after CABG in women and men but surprisingly, better late survival and freedom from myocardial infarction in women, after adjustment for other risk variables.
These contradictory results demonstrate the confusing nature of this issue. Many previous reports have incorporated large numbers of patients and utilized well-designed and well-managed databases. Apart from the special circumstances that surround each report, an important issue is the inherent differences among various populations studied. For example, a report from China pointed to higher hospital mortality among women, but our results and those from another western Asian country, Turkey, found no independent role for gender.10,16 Even this consideration cannot fully explain the contradictions because studies conducted in the same geographic area (e.g. North America) have produced different results. The authors hope that their report adds to the current knowledge of the role that gender plays in predicting hospital mortality, at least with respect to regional considerations, and helps clarify the current picture of CABG outcomes in Asia.
In our patients, women had a higher mean BMI than men, and this is particularly important because the early reports of higher mortality in women undergoing CABG suggested that this might be due to women’s smaller body size, and presumably smaller coronary arteries. Certainly, in older women undergoing mitral valve surgery, small size is associated with higher mortality, possibly because of poor energy reserves and less tolerance of stress. Body mass index is therefore a crucial part of this story. This unusual finding is presumably related to the ethnicity and country of origin of these women. If they had been smaller, they might have had a higher mortality. This study lends support to those who believe that sex is a risk factor only because women are smaller; perhaps it is no longer a risk factor if the size difference is eliminated.
This study suffered from some limitations. Although many preoperative variables were included, there may be important confounding factors unevaluated. The adequacy of preoperative medical therapy in women compared to that in men may be a confounding factor not addressed here because of data limitation. Also, we did not measure the extent, duration and severity of preoperative risk factors, which may also influence results. For example, there was no indication of the severity of diabetes mellitus or a measure of its adequacy of treatment. The focus of this investigation was preoperative risk factors, with no attempt to address possible confounding issues of intraoperative care or nonfatal perioperative morbid events and complications. Intraoperative care and perioperative events may relate more closely to immediate postoperative survival.
The increased proportion of some comorbidities in women observed in this study might have important implications for improving clinical management. The results indicate that regardless of gender, the fewer risk factors a patient has at surgery, the lower the risk of hospital death. Therefore, the focus of attention should be recognition and aggressive limitation of risk factors in women who are candidates for CABG.
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Impact of Gender on Outcome After Coronary Artery Bypass Surgery
Asian Cardiovasc Thorac Ann,
June 1, 2009;
17(3):
253 - 258.
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ABSTRACT
INTRODUCTION
