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Ann Thorac Surg 1999;68:625-626
© 1999 The Society of Thoracic Surgeons

Correspondence

Gender and coronary artery bypass mortality

Enrico Aidala, MDa, E. Lascala, MDa, Giuseppe Poletti, MDa

a Via Canova 46, 10126 Torino, Italy

To the Editor

We read with great interest the article by Edwards and colleagues [1] about the influence of gender on perioperative mortality after coronary artery bypass grafting. The purpose of that study is really a great challenge because of the contradictory conclusions of series found in the literature, showing the same or different mortality comparing men and women.

The great number of patients in the study, 97,153 female patients (28.17% of total population) is a factor allowing almost definitive results. There were significant differences between men and women, as always observed, being that the women were older, had a higher incidence of diabetes, hypertension, unstable angina, and nonelective operation. Therefore, to solve this discordance, it is useful to compare or group risk factors or stratify for identical predicted risk before statistical analysis. The article compared the two groups matched for age, first operation or reoperation and elective or nonelective procedure, and observed a higher mortality in women. Afterward, using the Bayesian risk model based on The Society of Thoracic Surgeons database [2], the investigators made an analysis of groups with the same predicted mortality, selected for clinical categories and for deciles having equal number of deaths; women were found again to have a significantly higher mortality, except for highest predicted risk categories.

In our institution we considered gender as an independent risk factor for perioperative mortality in a population of 917 patients (17% women) for an article published in 1997 [3]. The two groups showed similar differences for pre- and intraoperative characteristics; women were older, smaller (calculating body surface area), with higher incidence of diabetes and longer duration of angina, with worse ventricular function (using ejection fraction), and smaller size of left anterior descending artery.

At univariate analysis (we performed all statistical analysis with BMDP software) (BMDP Statistical Software Inc, Los Angeles, CA) female mortality was twice that of men (7.1% versus 3.7%; p = 0.045), but performing a multiple stepwise logistic regression gender did not reach statistical significance as an independent predictor of perioperative mortality. For a better evaluation of impact of risk (Aidala and associates, data not published), we then considered parameters emerged from multivariate and univariate analyses, coupling 114 men and 114 women for identical body surface area, age, ejection fraction, number of vessel disease, presence of diabetes, unstable angina, previous acute myocardial infarction, and emergency intervention.

The statistical analysis of perioperative mortality and morbidity (wound infection, postoperative acute myocardial infarction, resternotomy for bleeding, use of intraaortic balloon pump or inotropic agents, ventricular arrhythmias, and low cardiac output syndrome) demonstrated no significant differences (Table 1 ), excluding with greater validity gender as an independent risk factor for mortality.


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  		Table 1. Univariate Analysis in the Coupled Group ({chi}2test)

 
In addition, we performed a mean follow-up of 6 years (4 to 8 years) for these coupled patients. Using the Kaplan-Meyer method for actuarial curves and Breslow and Mantel-Cox models for time-related variables analyses, we estimated actuarial survival rate and actuarial freedom rate from myocardial infarction, reintervention (coronary artery bypass grafting or coronary angioplasty), and angina. There were no statistical differences, except for angina freedom rate, because at 6 years, 51.3% of women suffered from angina compared with 33.4% of men (p = 0.002 and p = 0.004, with Breslow and Mantel-Cox methods) (Table 2).


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  		Table 2. Actuarial Survival Rate and Events Freedom Rates in the Coupled Group

 
Although our population is small, we believe that risk factor pairing is useful to solve the initial answer. In fact it is possible that coupling for a small number of parameters leaves some elements of confusion, whereas stratification for predicted risk permits comparison of many variables whose sum of probability for the outcome is equal, but not necessarily the single parameter. Pairing for most of the risk factors with the only exception of gender is probably of great importance.

Even though studies with a large amount of patients are more impartial in their conclusions, we would like to point out that the purpose to define gender, as an independent factor for perioperative mortality, has not yet been definitively achieved.

References

  1. Edwards F.H., Carey J.S., Grover F.L., Bero J.W., Hartz R.S. Impact of gender on coronary bypass operative mortality. Ann Thorac Surg 1998;66:125-131.[Abstract/Free Full Text]
  2. Edwards F.H., Clark R.E., Schwartz M. Coronary artery bypass grafting. Ann Thorac Surg 1994;57:12-19.[Abstract]
  3. Bergerone S., Brscic E., Comoglio C., Aidala E., et al. Coronary artery bypass surgery. Cardiologia 1997;42:1257-1261.[Medline]

Related Article

Reply
Fred H. Edwards
Ann. Thorac. Surg. 1999 68: 626. [Extract] [Full Text] [PDF]




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