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(Circulation. 1997;96:1575-1579.)
© 1997 American Heart Association, Inc.
Articles |
Effect of Cardiac Surgery Patient Characteristics on Patient Outcomes From 1981 Through 1995
From Emory Healthcare, Atlanta, Ga.
Correspondence to Christi D. Warner, PhD, RN, School of Nursing, Emory University, 531 Asbury Circle, Atlanta, GA 30322. E-mail cwarner{at}nurse.emory.edu
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Abstract |
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 Top Abstract IntroductionMethodsResultsDiscussionReferences |
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Background Previous studies have demonstrated increased risk in patients undergoing coronary artery bypass surgery (CABG), but the effect of this increasing risk on outcomes has not been well documented. The purposes of this study were (1) to evaluate patients who had CABG from 1993 to 1995 (group III) and compare them with patients from 1981 through 1987 (group I) and 1988 through 1992 (group II) to determine if the trend toward higher-risk patients continued and (2) to evaluate what effect risk had on in-hospital outcomes.
Methods and Results Data were collected prospectively on patients undergoing CABG. Patients from the three time periods were compared by use of univariate and multivariate statistics. Risk models for mortality were developed by use of logistic regression. Significant changes were noted in the three time periods, with risk increasing over time. Increased risk was associated with increased mortality in group II, but mortality declined in group III despite the continued increase in patient risk. Group II had an increase in complications, with little change in group III. The actual mortality rate was lower than predicted in group III.
Conclusions Patients undergoing CABG are increasingly high risk. In-hospital mortality rates declined during the period from 1993 through 1995 and were lower than predicted despite the increase in risk. This decreased mortality rate may reflect greater experience in providing care to high-risk patients and improved myocardial protection and surgical and anesthetic techniques. Although continued analysis of patient risk and benefit is needed, researchers must be cognizant of the rapid changes in technology and knowledge and should correlate changes in the process of care with outcomes.
Key Words: cardiopulmonary bypass • patients • surgery • risk factors • survival
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Coronary artery bypass graft surgery is an important and effective intervention for revascularization in patients with coronary artery disease. The number of CABG procedures performed yearly has increased steadily since the early 1980s,1 and the benefits of surgery have been extended to patients previously judged as "too sick" or "too old." Studies have documented an increase in the mean age of patients undergoing CABG and in the percentage of octogenarians having cardiac surgery.2 3 4 5 It has also been noted that improvements in medical therapy and technological advances in coronary angioplasty have changed the referral patterns for surgical revascularization so that more of the referrals are high-risk patients.6
Previously published data from Emory Healthcare indicated that CABG patients through 1991 were getting older and that correlates of in-hospital death and complications (such as increased age) were becoming more common.7 8 This trend, if it continues, has implications for health policy, costs, and the outcomes of care. The purposes of this study were (1) to evaluate the characteristics of patients undergoing CABG during a later time period (1993 through 1995) and compare them with patients from earlier time periods (1981 through 1987 and 1988 through 1992) to determine if the trend toward older and sicker patients was continuing and (2) to evaluate what effect the trend toward higher-risk patients has had on in-hospital patient outcomes.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Patient Population
The study population comprised 23 512 patients who had CABG from 1981 through 1995. Group I (1981 through 1987) consisted of 12 088 patients, group II (1988 through 1992) comprised 7298 patients, and group III (1993 through 1995) comprised 4126 patients. Patients undergoing concomitant valve repair or other types of cardiac surgery were excluded from this analysis.
Definitions
Angina class was defined by the Canadian
Cardiovascular Society classification9 and
congestive heart failure by the New York Heart Association
classification system.10 Information such as history of
diabetes, heart failure, hypertension, and previous MI were obtained
from each patient's history and physical examination. Surgery was
classified prospectively as elective, urgent, or emergent by the
operator. Complications were also classified by the operator and
included sternal or leg-wound infections, pneumonia, postoperative MI,
adult respiratory distress syndrome, major arrhythmias (atrial
fibrillation, ventricular dysrhythmias, and
bradyarrhythmias requiring pacemaker intervention),
postoperative angina, and neurological events (stroke, transient
ischemic attack, and prolonged depressed mental
state).
Data Analysis
Data were collected prospectively on patients undergoing cardiac
surgery and were entered into a computerized database. Patients in the
three groups were compared by use of Pearson's 
2
statistic for categorical variables and ANOVA procedures for
continuous variables. The 
-level of significance was established
as .05 for the overall three-group comparisons and as .025 for
comparisons between groups I and II and groups II and III.
Multivariate analysis of mortality and
development of risk-adjusted models for mortality were done with the
use of logistic regression. All statistical analyses were
performed with BMDP statistical software.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Significant changes in group characteristics were noted in the three time periods (Table 1
), with
patient risk significantly increasing over time. The greatest change
occurred between groups I and II, but there was continuing change
toward a higher-risk profile between groups II and III on several
measures. Mean age and the percentage of patients older than 65 years
were significantly higher in group II than group I
(P<.0001) but showed very little change from group II to
group III. However, the oldest patients (those 
80 years) increased
significantly from group I to group II and again from group II to group
III (both P<.0001).
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The percentage of patients with diabetes, hypertension, hyperlipidemia, nonelective surgery, and class III and IV angina all increased significantly from group I to group II (all P<.0001). Significant increases also occurred in the percentage of patients with diabetes, hypertension, and hyperlipidemia between groups II and III (all P<.001). The percentage of patients with heart failure increased from 12% to 14% between groups II and III (P<.002).
Mean EF decreased over the three time periods between groups I and II
and between groups II and III (P<.0001). The percentage of
patients with an EF 
35% increased significantly from group I to
group II (P<.0001) and from group II to group III
(P<.0004). The percentage of CABG patients who were women
increased significantly from group I to group II (P<.0001)
with no further increase in group III. Cigarette smoking declined
significantly from group I to group II (P<.0001), but the
decline reversed in group III (P<.0001).
Along with the change in patient characteristics among the three time
periods, there were accompanying changes in patient outcomes (Table 2). The most significant change was the
difference in mortality rates found among the three groups. The
increased risk profile in group II was associated with an increase in
the mortality rate over that of group I (P<.0001). However,
despite a continuing increase in patient risk, mortality declined
slightly although not significantly in group III.
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Other perioperative complications showed some change
among the three groups. As can be seen in Table 2
, there was a decrease
in postoperative MI and wound infections from group I to group II (
both P.0001), but other complications showed increases.
Most notably, rates of pneumonia, sternal wound infections,
postoperative angina, arrhythmias, and neurological events
increased from group I to group II (all P<.0002). Use of an
IABP also increased from group I to group II.
In contrast, many complications showed either no change or decreased
from group II to group III. Group III did show an increase in pneumonia
and use of an IABP, but these increases were not statistically
significant. The incidence of arrhythmias (atrial fibrillation
or flutter, ventricular dysrhythmias, and
bradyarrhythmias requiring pacing) changed only minimally over
time. The incidence of postoperative atrial fibrillation alone was
14% at all time periods.
When female and male mortality rates were analyzed separately,
significant change was found across the three time periods (Table 3). Similar to the overall mortality
rate, death rates for women and men increased in group II and declined
in group III, although the latter difference was not significant.
Female mortality rates were also significantly higher than male
mortality rates for all three time periods (P.0005). Given
that the percentage of patients aged 80 years increased in groups II
and III, mortality was analyzed separately for these patients
within each group. After a >3-fold increase in mortality in group II
compared with group I, mortality for the oldest patients declined in
group III.
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The incidence of any complication in the oldest patients (80 years)
was significantly higher than for younger patients at all three time
periods (P.0005) (Table 4).
Patients aged 80 years had total complication rates of 29%, 39%,
and 38% for the three time periods, respectively, compared with 18%,
24%, and 23% for the younger patients. Neurological events were
higher in those aged 80 years in group I (P<.0001), and
arrhythmias occurred more frequently in the oldest patients in
group III (P<.0006). Both neurological events and pneumonia
increased in frequency over the three time periods for the oldest
patients and those aged <80 years, although neurological events did
not increase significantly in patients aged 80 years. Although the
use of an IABP increased in both age groups, the biggest trend was seen
in the group III patients who were 80 years old. There was no
significant difference in the overall incidence of complications other
than death between women and men for any of the time periods.
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Given the changes in outcomes, we analyzed which
characteristics in each time period were significantly associated with
higher mortality. The univariate odds ratios for dying were
significantly higher for all three time periods for those patients who
were older than 65 years, were female, had nonelective surgery, and had
hypertension. Heart failure and diabetes had higher odds ratios for
mortality in groups I and II, and patients in groups II and III aged
80 years had an increased odds ratio for dying. An EF of 35% had
an odds ratio for mortality of >2 in groups I and III. The combined
odds ratios and 95% CIs are given in Table 5.
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Multivariate analysis using logistic regression
was used to determine the preoperative predictors of mortality for each
group. For group I, nonelective surgery, age >65 years, EF 35%,
female sex, hypertension, heart failure, and diabetes mellitus were
associated with mortality. Group II variables changed slightly from
group I: EF was no longer a predictor and, as might be predicted from
the univariate analysis, reoperation and age 80
years were significant predictors. Group III included reoperation,
nonelective status, age >65 years, female sex, EF 35%, and
hypertension as the significant variables. Odds ratios and 95% CIs
for the multivariate analyses are found in
Table 6.
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The multivariate analysis was also run using
the entire data set. The total mortality rate was 2.8%. A variable
for the time period was included as a preoperative characteristic. The
following variables were found to be associated with higher
mortality rates: nonelective status, age >65 years, reoperation, heart
failure, diabetes, hypertension, EF 35%, female sex, membership in
group II, and age 80 years.
Given the changes in patient risk and mortality over time, a
risk-adjusted model for mortality was developed using the
multivariate predictors in group I. Because there were
very few reoperations in group I, the group I risk model was used to
predict the mortality rate in patients undergoing first CABG in groups
II and III. In group II, the predicted mortality rate was lower than
the actual mortality rate, but in group III, it was higher than the
actual rate. Reoperation had significant univariate and
multivariate odds ratios for death in both groups II
and III, and therefore a second risk-adjusted model was developed that
was based on the multivariate predictors in group II.
This model was used to predict mortality in group III, and again, the
predicted mortality rate was higher than the actual mortality rate.
These data are presented in Table 7.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The trend toward extending the benefits of CABG to patients who are older and at higher risk appears to be continuing. Patient risk increased most sharply from group I to group II, but group III showed continuing increases in the percentage of patients with lower EFs, hypertension, and diabetes and those undergoing reoperation. Although initially an increase in mortality rate accompanied the increase in high-risk patients, data from later years (1993 through 1995) indicate that mortality rates tended to decline. This is an important finding because it demonstrates that the benefits of surgery can be extended to patients who may be most in need of revascularization. The decrease in mortality in group III is gratifying and may be reflective of greater experience in providing care to high-risk patients and improved myocardial protection and surgical and anesthetic techniques, coupled with better postoperative medical and nursing care.
The continuing high-risk profile of patients from 1993 through 1995 also demonstrates that changes in healthcare economics (eg, decreased reimbursement for CABG through global package pricing and other arrangements and increasing surveillance of outcomes of care) have not necessarily increased the incentive to select lower-risk patients. Although it is true that complications and the complexity of care required for high-risk patients increase the length of stay and the cost associated with CABG,11 12 13 economic pressures have not contributed to the selection of low-risk or "ideal" patients at this academic medical center.
Complications
Changes in complication rates among the three time periods are
interesting. Higher rates of some complications (notably neurological
events, pneumonia, sternal wound infection, postoperative angina, and
use of an IABP) occurred in group II, and a few complications decreased
(leg-wound infection and postoperative MI). There were no significant
increases in complications found between groups II and III. Some
investigators contend that an increased rate of complications may be
unavoidable to some extent with higher-risk patients and that the
mortality rate remains the best indication of quality of
care.14 A previous study found that there was a poor
correlation between hospital rankings based on complications and
hospital rankings based on mortality. Mortality rate and a measure
defined as "failure to rescue" were appropriately associated with
other quality-of-care indicators, but complication rates were
not.14 Others have argued that adverse events after
cardiac surgery are a more sensitive measure of quality of care than
mortality rates.15
The incidence of any complication was higher in the patients aged 80
years for all three time periods, a not- unexpected finding. Other
studies4 5 16 have documented higher complication rates
and higher costs associated with CABG in the elderly. Weintraub et
al7 8 found that increasing age was a
multivariate correlate of in-hospital stroke and
increased incidence of wound infection, although another
study17 did not find age to be associated with increased
risk of stroke. Neurological events were higher in the oldest patients
for all three time periods, although this was statistically significant
only in group I. Rates of pneumonia, arrhythmias, and use of an
IABP were also higher in the oldest patients. Leg-wound infection rates
were slightly higher in the patients aged 80 years, but the
differences were not significant.
Age and Sex
Patients aged 80 years made up almost 5% of the patients in
group III, a substantial increase from group I. In a previous report,
Weintraub et al8 reported on the trend toward older and
increasingly ill patients from 1981 to 1989. In that earlier
analysis, it was found that only 1% of the patients in the
sample were >80 years of age. Two other studies from the 1980s to the
early 1990s documented that patients 80 years old made up 1% of
cardiac surgery patients and 2.2% of CABG patients.4 5
The present study found that there was a >3-fold increase in the
number of patients aged 80 years from group I (1.3%) to group III
(4.6%). Although the mortality rate was significantly higher in the
patients aged 80 years for groups II and III, which is
consistent with previous studies,4 5 8 the
mortality rate for the oldest patients followed the same trend and also
declined in group III. Although long-term outcomes were not measured in
the present study, other studies have reported that selected
patients aged 80 years do benefit from cardiac surgery despite higher
mortality and morbidity rates. The majority of these patients have been
reported to experience significant symptom relief, improved
performance status and activity levels, and an acceptable
quality of life with follow-up to 3 years after
surgery.4 5 18
Mortality for women remained significantly higher than for men for all three time periods. The female-male difference in mortality rate is consistent with previously published reports7 and remained significant even when controlling for other variables in this analysis. Although age and comorbidities such as heart failure were controlled in the multivariate analysis, our analysis did not control for body surface area, which has been shown to negate the gender effect in some studies.6
Risk-Adjusted Mortality
Mortality in group II for patients undergoing first CABG was
higher than predicted by a risk-adjustment model that used
multivariate predictors from group I. Inclusion in
group II also appeared as a multivariate predictor of
mortality when logistic regression was performed for the entire data
set. Although it is impossible to determine the reason from these data,
it may represent a learning curve associated with the change
toward higher-risk patients. Alternatively, other important risk
factors may not have been included in the regression analysis
that could have decreased the predicted mortality rate. The modest
trend toward an overall lower mortality rate in group III becomes even
more salient in light of the difference between the predicted and
actual mortality rates in groups II and III. Although the absolute
decline in the mortality rate in group III is small, it is lower than
the predicted mortality rate by both risk models. It is interesting to
speculate that a learning-curve phenomenon and improved intraoperative
and postoperative therapies have reversed a trend toward higher
mortality rates associated with higher patient risk. Other researchers
have correlated improvements in myocardial protection techniques with
both a decrease in mortality rate and improved regional
contractility in patients undergoing emergency surgical
revascularization after failed
angioplasty.19 The improved outcomes in that study
occurred despite an increasingly high-risk profile of the patients.
Limitations
The limitations of this retrospective study include the fact that
outcomes beyond the initial hospitalization were not evaluated, and
despite consistent definitions, there is the potential for
change in how specific variables were valued over the time frames
used. Data completion on potentially important variables such as
cerebrovascular disease, preoperative cardiogenic shock, and renal
disease were insufficient during the earlier time frames to allow for
meaningful comparisons. The potential contribution of these
variables to mortality could not be analyzed. It is
possible that the predicted mortality rate was therefore
underestimated, but this would enhance the finding that the actual
mortality rate was lower than predicted in group III. These changes in
outcomes have not been correlated with specific changes in myocardial
protection, operative technique, or postoperative care. The data
presented here reflect the experience of one academic
healthcare system and thus may not be applicable to other settings.
Patients undergoing CABG are increasingly high risk by accepted risk factors such as older age, lower EF, reoperation, nonelective status, and preoperative comorbidities. This trend continues despite economic pressure in the healthcare system and increasing scrutiny of procedural outcomes. It is noteworthy that in-hospital mortality rates declined during the period from 1993 through 1995 and were lower than predicted despite the increase in high-risk patients undergoing CABG. More information is needed on the long-term outcomes of high-risk patients, including functional status and quality of life. Continued study and consideration are needed to monitor the increasing risk profile of CABG patients and to maintain a balance between risk and benefit. However, any analysis must be cognizant of the rapid changes in technology and knowledge occurring in cardiovascular surgery and should attempt to correlate changes in the process of care with patient outcomes.
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Selected Abbreviations and Acronyms |
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Received February 19, 1997; revision received March 31, 1997; accepted April 2, 1997.
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