Long-Term Outcome of Isolated Coronary Artery Bypass
Surgery in Patients With Severe Left
Ventricular Dysfunction
Jehangir Appoo, MD; Colleen Norris, MSc, PhD; Sabrina Merali, Michelle M. Graham, MD;
Arvind Koshal, MD; Merril L. Knudtson, MD; William A. Ghali, MD, MPH
Downloaded from http://circ.ahajournals.org/ by guest on June 15, 2017
Background—Coronary artery bypass grafting (CABG) is indicated in patients with coronary artery disease and impaired
ventricular function. However, earlier studies have suggested that prognosis of patients with severe left ventricular
dysfunction is extremely poor. We used the APPROACH registry to derive contemporary estimates of prognosis
associated with CABG for this high-risk patient population.
Methods and Results—The study group consisted of 7841 patients who had isolated CABG in the province of Alberta,
Canada between 1996 and 2001. Patients with markedly reduced left ventricular function (ejection fraction [EF] ⬍30%,
Lo EF, n ⫽430) were compared with those with moderate reduction in ventricular function (EF 30% to 50%, Med EF,
n ⫽2581) and those with normal left ventricular function (EF ⬎50%, normal [Nl] EF, n⫽4830). The operative mortality
was higher in the patient group with Lo EF (4.6%) compared with Med EF and Nl EF groups (3.4% and 1.9%,
respectively, P⬍0.001). At 5 years, survival was 77.7% for Lo EF patients compared with 85.5% and 91.2% for Med
EF and Nl EF patients, respectively (P⬍0.001). After controlling for other independent variables, the adjusted hazard
ratio for death was 1.98 (95% CI, 1.49 to 2.62) for Lo EF relative to Nl EF. The mortality rate at 1 year was significantly
lower for Lo EF patients who underwent CABG than it was for nonrevascularized Lo EF patients (risk-adjusted odds
ratio, 0.36; 95% CI, 0.24 to 0.55).
Conclusions—In the modern era of cardiac surgery, CABG can be performed in Lo EF cases with an acceptable
perioperative mortality risk. Our estimate of 5-year survival in this high-risk group is better than previously reported in
the literature from earlier periods. (Circulation. 2004;110[suppl II]:II-13–II-17.)
Key Words: coronary disease 䡲 heart failure 䡲 surgery 䡲 survival
M
In the past decade, some investigators have evaluated the
results of CABG in patients with LVD, but the number of
patients studied was limited8 –10 and tended to be single
surgeon experiences.11–13 These studies indicate that angina
class, coronary heart failure class, quality of life, and ventricular function do improve after CABG in patients with
LVD, but they also report a very high short-term mortality
risk, as well as rather poor longer-term survival after CABG.
More data on a larger cohort of patients are needed to derive
contemporary estimates of survival in patients with severe
LVD undergoing CABG.
In the present study, the long-term results of CABG in 430
patients with severe LVD were studied using a prospectively
compiled province-wide database. To our knowledge, this
reflects the largest experience of long-term follow-up of
patients with LVD undergoing CABG. The survival curves of
patients with severe LVD (Lo ejection fraction [EF]) were
edical therapy in patients with coronary artery disease
(CAD) and advanced left ventricular dysfunction
(LVD) carries a poor long-term survival.1,2 Coronary artery
bypass grafting (CABG) in these patients is associated with
improved survival compared with medical treatment. Historically, CABG in patients with LVD has been associated with
high perioperative mortality.3,4 However, advances in surgical technique and myocardial protection have lead to improved outcomes, allowing CABG to now be a relatively safe
procedure in select patients at high risk.5–7 The number of
patients with advanced LVD undergoing CABG has increased in the past few years. Although surgical revascularization may be successful in the short-term, little is known
about the long-term follow-up of patients with CAD and
severe LVD who undergo “successful” CABG. Death in these
patients may be caused by progression of heart failure,
ventricular arrhythmias, and recurrent ischemia.
From the Department of Surgery (J.A., S.M., A.K.), Faculty of Nursing (C.N.), and Department of Medicine (M.M.G.), University of Alberta,
Edmonton, Canada; the Departments of Medicine (M.L.K., W.A.G.) and Community Health Sciences (W.A.G.), and the Centre for Health and Policy
Studies, University of Calgary, Calgary, Alberta, Canada.
Correspondence to William A. Ghali, University of Calgary, Community Health Services Department, 3330 Hospital Drive North West, Calgary,
Alberta, Canada T2N 4N1. E-mail [email protected]
APPROACH is supported by donations from a variety of industrial sponsors (see Acknowledgements). W.A.G. is supported by supported by a
Government of Canada Research Chair and by a Health Scholar Award from the Alberta Heritage Foundation for Medical Research.
© 2004 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
DOI: 10.1161/01.CIR.0000138345.69540.ed
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Circulation
September 14, 2004
compared with patients with moderate LVD (Med EF) or
normal ventricular function (Nl EF) and hazard ratios derived
to identify the prognostic relevance of Lo EF on long-term
survival. To further characterize the prognosis associated
with Lo EF, we also compared survival in Lo EF patients who
underwent CABG with survival in Lo EF patients who were
only treated medically.
Methods
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All data were derived from the Alberta Provincial Project for
Outcome Assessment in Coronary Heart Disease (APPROACH), a
prospective data collection initiative that captures detailed clinical
information on all patients undergoing coronary angiography in
Alberta, Canada, a province with a population of ⬇3.2 million
people. Patients are enrolled into the registry at the time of
angiography and are followed-up prospectively for outcomes, including subsequent revascularization and death. Details of this
database have been previously described.14
At the time of coronary angiography, demographic data are
collected, including age and sex, and the presence of the following
medical conditions is determined: diabetes, peripheral vascular
disease, chronic lung disease, cerebrovascular disease, congestive
heart failure, hypertension, hyperlipidemia, liver or gastrointestinal
disease, neoplastic disease, and previous CABG surgery, angioplasty, myocardial infarction, or thrombolytic therapy for myocardial
infarction. The indication for angiography is categorized as stable
angina, myocardial infarction (within 8 weeks of angiography),
unstable angina, and other. The results of the coronary angiography,
specifically left ventricular ejection fraction and coronary anatomy,
are also recorded. In describing coronary anatomy, a vessel is labeled
as “diseased” when it contains a lesion causing ⱖ50% stenosis.
Patient survival and time from catheterization until death are
ascertained through semiannual linkage to Alberta Vital Statistics
records. The APPROACH study protocol was reviewed and approved by the Ethics Review Boards of the University of Calgary and
the University of Alberta.
All patients whose EF was measured (at cardiac catheterization or
by echocardiography) before surgery and who had isolated CABG in
Alberta between January 1, 1996 and December 31, 2001 were
eligible. Patients undergoing concomitant cardiac surgical procedures such as valve repair/replacement, automatic implantable cardioverter defibrillator implantation, aneurysmectomy, or other open
heart procedures were excluded. Patients with markedly reduced LV
function (EF ⬍30%, Lo EF) were compared with those with
moderate reduction in LV function (EF 30% to 50%, Med EF) and
those with normal LV function (EF ⬎50%, Nl EF). Death occurring
within 30 days after CABG was classified as operative death.
Results
Baseline Characteristics
The study sample consisted of 7841 patients who underwent
isolated CABG, of whom 430 (5.5%) had known Lo EF
preoperatively. These patients were compared with 2581
patients who had moderate EF reduction (EF 30% to 50%,
and referred to as Med EF throughout this report) and 4830
patients with normal EF (EF ⬎50%). Clinical variables are
summarized in Table 1. The difference in age among groups
was not significant. Patients with Lo EF had a significantly
greater prevalence of adverse clinical risk factors, including
TABLE 1. Baseline Characteristics of 7865 Patients Who
Underwent Isolated CABG
Independent Variables
Lo EF
Med EF
Nl EF
(N⫽430) (N⫽2581) (N⫽4830)
P
Females, %
13.0
16.6
22.4
⬍0.001
Age, mean
64.5
65.1
65.1
0.450
Body mass index,* mean
31.8
33.1
31.2
0.217
Pulmonary disease, %
15.6
9.1
9.0
⬍0.001
Cerebrovascular disease, %
9.1
7.6
6.9
0.185
Renal disease, %
4.2
2.1
1.4
⬍0.001
Heart failure, %
40.7
16.8
5.9
⬍0.001
Diabetes mellitus, %
25.1
19.1
15.4
⬍0.001
Smoker ever, %
68.1
65.0
61.4
0.001
1.6
1.2
1.0
0.315
Hypertension, %
57.0
57.2
59.2
0.198
Hyperlipidemia, %
48.6
58.0
62.6
⬍0.001
Dialysis, %
Liver/gastrointestinal disease, %
1.4
4.1
3.3
0.010
Malignancy, %
1.6
3.1
3.4
0.115
Previous CABG, %
Previous myocardial infarction, %
Previous PCI, %
Peripheral vascular disease, %
4.4
6.5
4.7
0.002
72.6
66.3
41.7
⬍0.001
9.5
15.3
16.8
⬍0.001
11.2
11.0
8.5
0.001
⬍0.001
Indication for catheterization
Myocardial infarction, %
34.0
30.3
18.2
Unstable angina, %
30.2
31.1
35.3
Statistical Analysis
Stable angina, %
22.1
31.2
41.3
Baseline categorical variables were compared among the 3 EF
groups (Lo EF versus Med EF versus Nl EF) by means of the ␹2 test.
Overall survival after CABG was estimated by use of the Kaplan–
Meier method. A Cox proportional hazards analysis was used to
compare survival up to 7 years after CABG across EF groups while
adjusting for other recorded variables, and hazard ratios were
reported for survival in Lo EF and Med EF groups relative to the Nl
EF group.
␹2 tests were also used to compare the baseline characteristics of
CABG-treated versus medically treated Lo EF patients. We then
performed logistic regression to compare the mortality rate at 1 year
in CABG-treated versus medically treated patients while controlling
for any potential differences in baseline characteristics. We extended
this multivariable analysis to also control for the propensity of being
selected for CABG. This was performed by first using logistic
regression to model predictors of undergoing CABG surgery among
all patients. The resulting model was used to calculate a probability
(ie, propensity) of being selected for CABG that was included as a
covariate in a our final multivariable analysis assessing the association between CABG surgery and mortality at 1 year.
Other, %
13.7
7.5
5.2
Low risk, %
6.5
10.0
13.9
High risk, %
73.3
74.6
71.1
Left main, %
19.8
14.9
14.4
0.5
0.6
0.6
Coronary anatomy
Missing, %
⬍0.001
Urgency
Emergency
7.4
4.3
4.3
Urgent in-house
57.4
55.1
52.2
Urgent out-of-house
26.7
28.0
28.0
Elective
8.1
11.9
14.8
Missing
0.2
0.6
0.6
⬍0.001
*Body mass index information was available for 196 patients in the Lo EF
group, 1209 patients in the Med EF group, and 2547 patients in the Nl EF
group.
Appoo et al
Long-Term Outcome of CABG
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Survival after CABG for the entire study population, with ventricular function stratified according to EF. Patients with markedly low EF
had significantly lower survival rates than those with normal EF and moderately reduced EF before CABG.
peripheral vascular disease, renal insufficiency, diabetes mellitus, congestive heart failure, and previous myocardial infarction. They also had a higher prevalence of multivessel and
left main coronary artery disease, and a tendency toward a
more acute indication for surgical revascularization, such as
recent myocardial infarction.
Operative Mortality
Operative mortality (ie, mortality within 30 days) in the Lo
EF group was 4.4% versus 3.4% and 1.9%, respectively, in
the Med EF and Nl EF groups (P⬍0.001).
Postoperative Survival
Figure 1 shows the Kaplan–Meier survival curves for the 3
different EF groups. At 3 years, Kaplan–Meier estimated
survival of Lo EF patients was 84.7% compared with 90.0%
and 94.5% for Med EF and Nl EF patients, respectively
(P⬍0.001 from log rank test). At 5 years, Kaplan–Meier
estimated survival of LoEF patients was 77.7% compared
with 85.5% and 91.2% for Med EF and Nl EF patients,
respectively (P⬍0.001).
The crude (ie, unadjusted) hazard ratio for Lo EF relative
to Nl EF was 2.75 (95% CI, 2.15 to 3.51) (Table 2). After
controlling for all other known independent variables, the
adjusted hazard ratio for Lo EF was 1.95 (95% CI, 1.49 to
2.55) relative to Nl EF.
Comparison of Surgical Revascularization Versus
Medical Treatment
Recognizing that Lo EF patients have poorer survival than
patients with Med EF or Nl EF, we also considered it
relevant to compare survival in Lo EF patients who
underwent CABG with survival of other Lo EF patients
who did not undergo surgery. The 430 patients with Lo EF
who underwent isolated CABG were thus compared with
1739 patients in the database with Lo EF who proceeded to
cardiac catheterization but did not undergo revascularization for a combination of possible reasons. Table 3
demonstrates that medically treated patients with Lo EF
were more likely to have a clinical diagnosis of congestive
heart failure and to have had a previous CABG procedure.
The profile of indications for catheterization differed
somewhat between the 2 groups, and the extent of coronary
artery disease was greater in the CABG group, with more
3-vessel disease and left main disease in surgically treated
Lo EF patients.
The unadjusted mortality rates at 1 year in the surgical and
medical treatment groups were 8.6% versus 14.3%, respectively (P⫽0.002). A multivariable logistic regression analysis
controlling for differences between groups in the baseline
characteristics shown in Table 3 reveals an odds ratio of 0.36
(95% CI, 0.24 to 0.55) for CABG-treated patients relative to
medically treated patients. When we additionally controlled
for the propensity to be selected for CABG surgery, the
adjusted odds ratio for CABG relative to medical therapy was
0.26 (95% CI, 0.17 to 0.41).
Discussion
The present study, encompassing the largest published
follow-up of CABG and low EF, shows that patients with this
syndrome have higher operative and postoperative long-term
II-16
TABLE 2.
Circulation
September 14, 2004
Hazard Ratios for Death by EF Group
Crude HR
(95% CI)
Nl EF (reference group)
*Adjusted HR
(95% CI)
1.0
1.0
Med EF
1.70 (1.44, 1.96)
1.46 (1.24, 1.72)
Lo EF
2.75 (2.15, 3.51)
1.95 (1.49, 2.55)
*Adjusted risk indicates risk after controlling for other independent variables
including age, sex, pulmonary disease, cerebrovascular disease, renal disease,
heart failure, diabetes, dialysis, hypertension, hyperlipidemia, liver/gastrointestinal disease, malignancy, previous CABG, previous PCI, previous MI, peripheral
vascular disease, indication for catheterization, coronary anatomy, jeopardy
score, and urgency of operation.
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mortality rates than patients with milder or no decrease in EF.
However, in Lo EF patients, the operative mortality rate,
although increased, is not overwhelmingly so (4.4% versus
1.9%). An operative mortality rate of 4.4% is consistent with
recently published data on the topic and is a marked improvement from previous reports indicating a prohibitive operative
mortality in the range of 10% to 50%.3 The definition of low
EF is somewhat variable across studies. To isolate patients
with severe left ventricular dysfunction in this study, low EF
was defined as an EF ⬍30% and patients with ejection
fractions of 30% to 35% were grouped with the medium EFs.
Thus, we can conclude that the 430 study patients comprised
a high-risk group of patients given the presence of multiple
comorbidities combined with a marked reduction in ventricular function.
Contrary to other published series, this study does not
reflect a single surgeon experience. The operative mortality
of 4.4% and 5-year estimated survival of 77.7% was achieved
on a regional basis, involving many different surgeons, 3
surgical centers, and uncontrolled techniques of myocardial
protection and surgery (ie, no imposed care protocol). Therefore, we conclude that an operative mortality rate of ⬍5%
with 5-year survival close to 80% is likely to be achievable in
other centers in the current era of cardiac surgery.
Late survival, although reduced when compared with
patients with milder or no decrease in EF, remains high, with
estimated 3- and 5-year survival of 84.7% and 77.7%,
respectively, in patients with preoperative low EF undergoing
isolated CABG. Thus, it is reassuring to know that once these
sick patients are through the perioperative course, they
continue on a survival path indicating a reasonably favorable
prognosis. When compared with normal EF, however, patients with low EF had an adjusted hazard ratio of 1.95,
indicating that EF is still a significant independent risk factor
for long-term outcome after CABG. Death in these patients
may be caused by progression of heart failure, ventricular
arrhythmias, and recurrent ischemia.
Newer medical and surgical therapies are being targeted
toward this high-risk subgroup of patients. The role of
aneurysmectomy and LV remodeling surgery as an adjunct to
CABG in this subgroup of patients is currently being investigated as one arm of a National Institutes of Healthsponsored multicenter study (STICH Trial). Recent evidence
from the MADIT II trial15 indicates that patients with previous myocardial infarction and EF ⬍30% derive a survival
benefit at 20 months with prophylactic AICD implantation.
Cell-based myocardial regeneration therapies (ie, stem cell
transplantation16 and/or gene therapy17) may also assume a
role in the management of such patients. Future studies will
determine whether these adjunctive measures will lead to
even further improvement in long-term survival in patients
with coronary artery disease and severe left ventricular
dysfunction. The results from this study serve as a good
reference point to compare the results of adjuvant treatments
versus isolated coronary artery surgery.
The survival comparison of Lo EF patients treated with
CABG relative to those treated medically is also notable. It
demonstrates that although the prognosis associated with Lo
EF is generally poor (relative to patients with better EF),
undergoing CABG is associated with better outcomes than
those seen in Lo EF patients who are medically managed.
This latter finding underlines the point that Lo EF alone
should not be used as a criterion to turn patients away from
CABG surgery in anticipation of poor surgical prognosis that
earlier studies might have suggested. Our combined findings
of acceptable short-term and long-term prognosis in Lo EF
patients undergoing CABG and poor prognosis in Lo EF
patients treated medically argue for an aggressive surgical
approach to CAD patients with Lo EF.
TABLE 3. Baseline Characteristics of 2169 Patients With Low
EF Treated With CABG vs Medical Management
Independent Variables
Medical
(N⫽1739)
CABG
(N⫽430 )
P
Females, %
22.7
13.0
⬍0.001
Age, mean
63.8
64.5
0.259
Pulmonary disease, %
18.5
15.6
0.163
7.8
9.1
0.394
Cerebrovascular disease, %
Renal disease, %
3.7
4.2
0.664
Heart failure, %
56.7
40.7
⬍0.001
Diabetes mellitus, %
26.6
25.1
0.54
Smoker ever, %
63.9
68.1
0.103
0.889
Dialysis, %
1.7
1.6
Hypertension, %
49.2
57.2
0.005
Hyperlipidemia, %
36.5
48.6
⬍0.001
3.9
1.4
0.011
Liver/gastrointestinal disease, %
Malignancy, %
3.3
1.6
0.070
Previous CABG, %
13.6
4.4
⬍0.001
Previous myocardial infarction, %
57.5
72.3
⬍0.001
7.5
9.5
0.156
10.2
11.2
0.573
23.8
18.6
18.7
38.9
34.0
30.2
22.1
13.7
18.9
32.1
43.7
5.3
6.5
73.0
19.8
0.7
Previous PCI, %
Peripheral vascular disease, %
Indication for catheterization
Myocardial infarction, %
Unstable angina, %
Stable angina, %
Other, %
⬍0.001
Coronary anatomy
Low risk, %
High risk, %
Left main, %
Missing, %
⬍0.001
Appoo et al
Study Limitations
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Preoperative EF was not standardized for this study but rather
was measured by different techniques in the context of usual
care (ie, echocardiography, calculated planimetry on catheterization, and visual estimation at time of catheterization).
EF was not available for every patient preoperatively; 280
patients were classified as “missing EF” and 470 patients
were classified as “EF not done due to instability.” These 2
groups were left out of the eventual analysis, because we did
not want to incorrectly classify cases with, for a variety of
reasons, unmeasured EF values. A second limitation is that
we do not have information on left ventricular volumes that
can provide prognostic information over and above EF
values. A third limitation is that we have focused on mortality
and late survival as the outcomes of interest. Other outcomes
such as resource use (eg, costs, readmissions for cardiovascular problems), recurrent nonfatal events, functional status,
and quality of life also warrant future study. A final caveat is
that the comparison of the CABG-treated and medically
treated Lo EF patients needs to be viewed with some caution.
Our multivariable risk adjustment and propensity analyses
provide partial adjustment for baseline differences and selection factors that would otherwise preclude a meaningful
comparison between groups. Even with such analyses, however, the CABG versus medical group comparison needs to
be interpreted carefully. We certainly do not present this
analysis to imply that all of the medically treated patients
should have had a CABG procedure. The analysis does,
however, demonstrate that the prognosis associated with Lo
EF in a contemporary CABG surgery population is quite
favorable relative to contemporary patients with Lo EF who
are treated medically rather than with CABG (for a variety of
reasons).
Conclusions
Despite these limitations and caveats, this study provides
important insights into the prognosis of patients with low EF
who undergo CABG. Patients with severe CAD and markedly
reduced EF represent a high-risk group that can undergo
isolated CABG safely. Long-term survival is statistically
significantly reduced when compared with patients with
milder or no decrease in EF, but 5-year survival is still very
good relative to previous published reports on prognosis in
such patients. Advances in adjuvant medical and surgical
therapies may further improve survival in this high-risk group
of patients.
Acknowledgments
Dr. Ghali is supported by a Government of Canada Research Chair
and by a Health Scholar Award from the Alberta Heritage Foundation for Medical Research. Dr. Norris was support by fellowships
from the Canadian Cardiovascular Outcomes Research Team
(CCORT) and Tomorrow’s Outcome Researchers in Cardiovascular
Long-Term Outcome of CABG
II-17
Health (TORCH) during the preparation of this manuscript. The
APPROACH initiative was originally funded in 1995 by a grant from
the Weston Foundation. The ongoing operation of the project is
supported by Merck Frosst Canada Inc, Monsanto Canada Inc,
Searle, Eli Lilly Canada, Guidant Corporation, Boston Scientific Ltd,
Hoffmann–La Roche Ltd, and Johnson and Johnson Inc–Cordis. We
appreciate the assistance of the Calgary Regional Health Authority
and the Capital Health Authority in supporting online data entry by
cardiac catheterization laboratory personnel. Members of the APPROACH project Clinical Steering Committee are, in Edmonton, Dr.
Stephen Archer, Dr. Arvind Koshal, Dr. William Hui, Dr. Ross
Tsuyuki, and Dr. Colleen Norris; and, in Calgary, Dr. L. Brent
Mitchell, Dr. Andrew Maitland, Dr. Michael Curtis, Dr. Merril L.
Knudtson, Dr. William A. Ghali, and Ms. Diane Galbraith.
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Long-Term Outcome of Isolated Coronary Artery Bypass Surgery in Patients With Severe
Left Ventricular Dysfunction
Jehangir Appoo, Colleen Norris, Sabrina Merali, Michelle M. Graham, Arvind Koshal, Merril L.
Knudtson and William A. Ghali
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Circulation. 2004;110:II-13-II-17
doi: 10.1161/01.CIR.0000138345.69540.ed
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