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Ann Thorac Surg 2001;71:507-511
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Improved in-hospital mortality in women undergoing coronary artery bypass grafting

^a Section of Cardiology, Veterans Affairs Hospital, White River Junction, Vermont, USA
^b Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire, USA
^c Beth Israel-Deaconess Medical Center, Boston, Massachusetts, USA
^d Fletcher Allen Health Care, Burlington, Vermont, USA
^e Maine Medical Center, Portland, Maine, USA
^f Catholic Medical Center, Manchester, New Hampshire, USA
^g Eastern Maine Medical Center, Bangor, Maine, USA
^h Center For the Evaluative Clinical Sciences, Dartmouth Medical School, Hanover, New Hampshire, USA

Accepted for publication June 13, 2000.

Address reprint requests to Dr O’Rourke, Medical Service-Cardiology, Veteran Affairs Medical Center, White River Junction, VT 05001
e-mail: Daniel.ORourke{at}Hitchcock.org

	Abstract

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Background. Few studies have examined the changes in in-hospital mortality for women over time. We describe the changing case mix and mortality for women undergoing coronary artery bypass grafting (CABG) from 1987 to 1997 in northern New England.

Methods. Data were collected on 8,029 women and 21,139 men undergoing isolated CABG. The study consisted of three time periods (1987 to 1989, 1990 to 1992, and 1993 to 1997) to account for regional efforts to improve quality of care that occurred during 1990 to 1992.

Results. Compared with 1987 to 1989, women undergoing CABG in 1993 to 1997 were older, had poorer ventricular function, and more often required urgent or emergency operations. The crude and adjusted mortality rates for both women and men decreased significantly over time. The absolute magnitude of the change in adjusted rates was greater for women (3.1%) than for men (1.5%). Although women represented only 28% of the study population, the decrease in their mortality accounted for 44% of the total decrease in adjusted mortality during the study period.

Conclusions. Over the last decade there has been a marked decrease in CABG mortality for women, despite a worsening case mix.

	Introduction

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Many studies of coronary artery bypass grafting (CABG) have compared the in-hospital mortality rates of men and women [1–8] and most have found women to be at higher risk for in-hospital death. There have been fewer studies that examined the changes over time in mortality [9–11] and only two that described specifically whether mortality was changing for women during the 1980s and early 1990s [9, 10]. However, these two studies came to different conclusions. Previously, we reported that in-hospital mortality in northern New England had decreased between 1987 and 1993 following an intervention to improve quality of care [12]. This finding was true across patient subgroups, including both men and women. In the present analysis, we sought to extend that finding by examining our more current regional experience through 1997 and more specifically, to describe the changing case mix and mortality for women undergoing isolated CABG in northern New England over the last decade. We described both the relative and absolute magnitude of the change and questioned how much of the overall change in in-hospital mortality observed during this time period was attributable to the changing outcomes for women.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Between July 1, 1987, and December 31, 1997, data were collected on 29,168 consecutive, isolated CABG procedures (21,139 men, 8,029 women) performed by the 31 surgeons at the five medical centers in Maine, Vermont, and New Hampshire who were the sole providers of open heart surgical procedures in the region. Of the 31 surgeons, 19 contributed data for the entire 10-year study period. Data were collected on patient demographics, comorbidities, prior cardiac history, cardiac anatomy and function, surgical indication and priority, procedural information, and outcomes, including in-hospital mortality [13].

A time period variable was created that included procedures performed (1) from 1987 to 1989 (N = 5,359), (2) from 1990 to 1992 (N = 8,414), and (3) from 1993 to 1997 (N = 15,395). Data from the first time period was the basis for several published reports [7, 13, 14] and represents a well-studied cohort. Beginning in 1990, a region-wide quality improvement effort was implemented to reduce CABG mortality that occupied much of 1990 to 1992 [12]. The improvement effort was a single intervention with three components aimed at reducing CABG mortality. The components included feedback of outcome data, training in continuous quality improvement techniques, and site visits to other medical centers. The first component, feedback of outcome data, consisted of reports of risk-adjusted outcome data that were distributed to participating clinicians three times each year. Each surgeon received three reports: his or her own outcomes, those of his or her medical center, and regional results. Anonymity of individual surgeons and participating institutions was preserved in the aggregate regional reports. Characteristics of patients and specific fatal and nonfatal outcomes were summarized. Three 2-day meetings each year provided a forum to discuss these results. The second component, continuous quality improvement training, consisted of a 2-day training session in which the theory and techniques of continuous quality improvement were presented and discussed. The third component consisted of site visits to observe the processes of CABG operation. Teams consisting of an industrial engineer and representatives of the medical, nursing, and perfusion staff undertook a "round-robin" observation schedule. The teams observed the entire CABG system, from the cardiac catheterization conference through the surgical procedure and postoperative care. The visitors focused on similarities and differences compared with their "home" medical center. Rather than recording and evaluating the entire day’s events, they paid greatest attention to their corresponding colleagues (e.g., the visiting surgeon monitored primarily the activities of the host surgeon). The third time period (1993 to 1997) represents the most current data in the registry and the "postintervention" period.

Standard statistical methods were used for the calculation of rates, proportions, and odds ratios. Parametric and nonparametric tests of the linear component of trend were used to evaluate change over time. Logistic regression was used to adjust mortality rates by time period. Both absolute and relative changes in mortality rates were calculated comparing the first and last time periods. (For example, mortality rates for all isolated CABG patients dropped from 4.3% in the first period to 3.0% in the last—an absolute change of 1.3%. This was a relative decline of 30.2% compared with the early mortality rate.) All analyses were performed using Stata Statistical Software [15] and Statistical Analysis System [16]. Statistical significance was defined as a two-tailed p value less than 0.05.

	Results

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Table 1 shows the change in patient characteristics over time for those variables associated with in-hospital mortality. The percentage of women undergoing bypass operation changed little over time, ranging from 26.6% in the early time period to 27.7% in more recent years. However, case mix and severity of illness for women did change. Over time, more women undergoing the operation were older than 75 years of age (p < 0.001), had depressed left ventricular ejection fractions (EF) (p = 0.055), and underwent CABG for urgent or emergent indications (p < 0.001). Similar changes were noted for men, who also showed a higher rate of left main stenosis (50% or more, p < 0.001).

View larger version (24K): [in this window] [in a new window]   Fig 1. Adjusted in-hospital mortality by time period for men and women. Mortality was adjusted for age, preoperative ejection fraction, preoperative left ventricular end-diastolic pressure, left main stenosis, and surgical priority.

	Comment

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

There have been two prior studies that examined the changes in case mix and outcome for women over time. In an earlier experience, Weintraub and coworkers [9] reported in more recent years that women undergoing CABG at Emory were older and sicker resulting in an increased mortality (1.0% in 1974 to 1979; 5.4% in 1988 to 1991). However, the increase in mortality was not fully explained by the changing case mix as female gender remained a multivariate risk factor for death even after accounting for the other risk factors. In contrast, Mickleborough and colleagues [10] from Toronto Hospital found that despite operating on an aging population with more comorbidities, the mortality rate for women decreased over time (2.4% in 1982 to 1984; 1.0% in 1991 to 1993). Although they were unable to clearly define the reasons for the improved mortality, they speculated that increased surgical experience and improvements in cardioplegia techniques likely contributed. Previously we had reported [14] fewer observed deaths in 1991 to 1993 when expected deaths were calculated from a 1987 to 1990 prediction rule; we attributed the decrease in mortality to a region-wide effort at quality improvement.

Why in-hospital mortality in northern New England has improved over time, especially for women, is likely multifactorial. It is unlikely these findings are a consequence of chance given the large size of our dataset. Bias is also unlikely because information was collected on consecutive patients for all surgeons operating in the region and the information was validated by comparison with an administrative dataset. Confounding by case mix is also not an obvious explanation. Though mortality rates decreased, the patient population had more comorbidities and a greater severity of illness over time. We adjusted for many of the common covariates recommended by the Working Group Panel of the Cooperative CABG Database Project [17]. Further, there was no significant difference over time in the association between the risk variables (age, preoperative EF, preoperative LVEDP, left main stenosis, and priority at operation) and in-hospital mortality. Increased surgical volume does not appear to be an explanation for the change. Over the 10-year study period, 19 of the 31 surgeons contributed data during all three study periods. The average increase in the volume of procedures for the 19 surgeons was less than 2%. The increased volume of procedures was achieved primarily by new surgeons joining the medical centers in the later years. However, the addition of the new surgeons does not explain the decline in mortality either, as the mortality rates for the 19 surgeons operating during the entire study period were nearly identical to all surgeons operating during the study period.

There are several areas in which improvement efforts would be expected to affect women more directly. Previously we had reported that patients with smaller body surface area, and thus smaller coronary vessels, were at higher mortality risk [7, 18]. It is possible that changes in surgical techniques related to small coronary vessels resulted from this study. Other examples include work in the more acute populations (i.e., unstable angina) in which women are overrepresented; efforts to reduce hemodilutional anemia, which is a problem in small patients and women; and the reduction in the proportion of patients with high preinduction heart rates (more than 80 beats per minute), which includes a higher percentage of women.

There were some identifiable changes in surgical technique during the study period that could be related to the reduction in mortality. The use of the internal mammary artery graft (IMA), which we have shown is related to in-hospital mortality [19], increased, at least during the time period from 1992 to 1995 [20], as did the number of distal anastomoses. However, these changes occurred with equal frequency in men and women and therefore do not explain the greater decrease in mortality for women. Additionally, the decline in mortality among women receiving an IMA graft was almost identical to the decline observed among women who did not receive an IMA graft. In recent years, the major changes in surgical technique that have occurred in this region have been off-pump bypass CABG including minimally invasive direct CABG and the use of non-IMA arterial grafts. However, the off-pump technique did not begin to be used significantly until 1998, which is beyond the study period. It is, therefore, unlikely that these changes alone are responsible for the decline in mortality.

As important as these identifiable changes in surgical technique might seem, equally important is the observation that the reduction in mortality rate was associated temporally with a three-component regional intervention that included feedback of outcome data, training in continuous quality improvement techniques, and "benchmarking" site visits to other medical centers [12]. These efforts led to a multitude of changes in the technical aspects of patient care, the process and organization of hospital care, personnel organization and training, and in the methods of evaluating care and making treatment decisions—changes that differed from hospital to hospital and surgeon to surgeon. We cannot attribute the improvement in mortality specifically to any one of these changes and believe it is most likely that multiple changes in the detailed process of care is what led to the improvement in the in-hospital mortality.

Our study has several limitations. Our results reflect surgical revascularization as practiced in northern New England, which is known to be more conservative in patient selection and to have lower per capita rates of revascularization than other areas of the country. Whether our experience can be generalized remains to be seen. We cannot state expressly what changes in process and practice led to the region-wide improvement in outcomes. However, it is noteworthy that New York state and northern New England, two areas with active efforts at quality improvement in open heart operation, had greater average annual declines in surgical mortality between 1987 and 1992 than any other state or area in the nation [21]. Clearly, there is something to be learned by groups of physicians examining their process and outcomes.

The mortality for women after CABG has been an important issue for three decades. Our study showed that despite worsening case mix, there has been a decrease in in-hospital mortality for women having bypass operations in northern New England during the past 10 years that has accounted for 44% of the decrease in overall mortality for the entire CABG population. Hopefully, ongoing efforts at improving the outcome of surgical revascularization for coronary artery disease will lead to further declines in adverse outcomes for both women and men.

	Acknowledgments

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
This study was supported by the American Heart Association, Dallas, Texas.

	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): John H. Sanders, Jr Stephen J. Lahey Mitchell Norotsky Reed D. Quinn Yvon R. Baribeau Felix Hernandez, Jr Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by O’Rourke, D. J. Articles by O’Connor, G. T. Search for Related Content PubMed PubMed Citation Articles by O’Rourke, D. J. Articles by O’Connor, G. T. Related Collections Coronary disease