Journal of the American College of Cardiology
© 2002 by the American College of Cardiology Foundation
Published by Elsevier Science Inc.
Vol. 40, No. 3, 2002
ISSN 0735-1097/02/$22.00
PII S0735-1097(02)01969-1
Diabetes Mellitus Increases Short-Term
Mortality and Morbidity in Patients
Undergoing Coronary Artery Bypass Graft Surgery
Jeffrey L. Carson, MD,* Peter M. Scholz, MD,† Anita Y. Chen, MS,‡
Eric D. Peterson, MD, MPH, FACC,‡ Jeffrey Gold, MD, FACC,§㛳 Stephen H. Schneider, MD¶
New Brunswick, New Jersey; Durham, North Carolina; and New York, New York
The aim of this study was to determine the impact of diabetes mellitus (DM) on short-term
mortality and morbidity in patients undergoing coronary artery bypass surgery (CABG).
BACKGROUND Diabetes mellitus is present in approximately 20% to 30% of patients undergoing CABG, and
the impact of diabetes on short-term outcome is unclear.
METHODS
We performed a retrospective cohort study in 434 hospitals from North America. The study
population included 146,786 patients undergoing CABG during 1997: 41,663 patients with
DM and 105,123 without DM. The primary outcome was 30-day mortality. Secondary
outcomes were in-hospital morbidity, infections and composite outcomes of mortality or
morbidity and mortality or infection.
RESULTS
The 30-day mortality was 3.7% in patients with DM and 2.7% in those without DM; the
unadjusted odds ratio was 1.40 (95% confidence interval [CI], 1.31 to 1.49). After adjusting
for other baseline risk factors, the overall adjusted odds ratio for diabetics was 1.23 (95% CI,
1.15 to 1.32). Patients treated with oral hypoglycemic medications had adjusted odds ratio
1.13; 95% CI, 1.04 to 1.23, whereas those on insulin had an adjusted odds ratio 1.39; 95%
CI, 1.27 to 1.52. Morbidity, infections and the composite outcomes occurred more commonly
in diabetic patients and were associated with an adjusted risk about 35% higher in diabetics
than nondiabetics, particularly among insulin-treated diabetics (adjusted risk between 1.5 to
1.61).
CONCLUSIONS Diabetes mellitus is an important risk factor for mortality and morbidity among those
undergoing CABG. Research is needed to determine if good control of glucose levels during
the perioperative time period improves outcome. (J Am Coll Cardiol 2002;40:418 –23)
© 2002 by the American College of Cardiology Foundation
OBJECTIVES
Diabetes mellitus (DM) is a major risk factor for cardiovascular disease, and arteriosclerosis is responsible for 80% of
deaths in patients with DM. Approximately 20% to 30% of
patients undergoing coronary artery bypass surgery (CABG)
have DM. With one exception (1) studies are consistent in
documenting a 50% to 90% increase in long-term mortality
rates in diabetics (2– 8). This most likely is a result of
accelerated arteriosclerosis associated with diabetes.
institution, and few studies were large enough to comprehensively evaluated postoperative morbidity.
We performed a large multicenter cohort study using
detailed information on preexisting illness, cardiac status,
mortality and morbidity collected at 434 institutions under
the direction of the Society of Thoracic Surgeons. The aims
of our analysis were to determine if DM is independently
associated with 30-day mortality and morbidity and to
characterize the causes of death.
See page 424
METHODS
The impact of diabetes on short-term mortality and
morbidity in patients undergoing CABG is unclear. The
best evidence (9) suggests that in-hospital mortality is
elevated in DM, although the results are inconsistent
(3,6,7,10 –17). Only one study evaluated the cause of
long-term mortality (3). Most studies were from a single
From the Divisions of *General Internal Medicine and ¶Endocrinology, †Department of Medicine, and Division of Cardiothoracic Surgery, ‡Department of Surgery,
University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical
School, New Brunswick, New Jersey; §Outcomes Research and Assessment Group,
Duke Clinical Research Institute, Duke University, Durham, North Carolina; and
㛳Division of Cardiovascular Surgery, Albert Einstein College of Medicine, New York,
New York. Support was provided internally by the Society of Thoracic Surgery
National Cardiac Database.
Manuscript received October 10, 2001; revised manuscript received January 31,
2002, accepted April 30, 2002.
Study design and population. We performed a retrospective cohort study of patients undergoing coronary artery
bypass surgery from the U.S. and Canada that are included
in the 1997 STS national database. We included patients
undergoing both first and reoperations. We excluded patients who underwent simultaneous valvular heart surgery,
patients with DM treated with diet alone, or in whom the
treatment was unknown, and those with missing information on the presence of DM.
Outcome variables. The primary outcome was 30-day
mortality. Secondary outcomes were in-hospital morbidity,
infections and composite outcomes of mortality or morbidity and mortality or infection.
We defined in-hospital infection as deep sternum infection, leg infection, septicemia, urinary tract infection or
JACC Vol. 40, No. 3, 2002
August 7, 2002:418–23
Abbreviations and Acronyms
CABG ⫽ coronary artery bypass grafting
CI
⫽ confidence interval
CK
⫽ creatine kinase
DM
⫽ diabetes mellitus
LDH ⫽ lactase dehydrogenase
MI
⫽ myocardial infarction
pneumonia. The criteria for a deep sternum infection of the
muscle, bone and/or mediastinum included either wound
opened with excision of tissue, positive culture or treatment
with antibiotics. The criteria for infection of the leg vein
harvest site included either wound opened with excision of
tissue, positive culture or treatment with antibiotics. The
criteria for septicemia required positive blood culture. The
criteria for urinary tract infection required a positive urine
culture. The criteria for pneumonia were positive cultures of
sputum, blood, pleural fluid, empyema fluid, transtracheal
fluid or transthoracic fluid, consistent with the diagnosis
and clinical findings of pneumonia. Pneumonia is also
defined as a chest radiograph diagnostic of pulmonary
infiltrates.
We defined in-hospital morbidity as infections (as defined above), myocardial infarction (MI), renal failure,
stroke or multisystem failure. Postoperative MI required
two of the following four criteria: prolonged (⬎20 min)
typical chest pain not relived by rest and/or nitrates; enzyme
level elevation with either creatine kinase (CK)-MB ⬎5%
of total CK, CK greater than twice normal, lactase
dehydrogenase (LDH) subtype 1 ⬎ LDH subtype 2, or
troponin ⬎0.2 ␮g/ml; new wall motion abnormalities; or
serial electrocardiogram (at least two) showing changes from
baseline or serially in ST-T and/or Q waves that are 0.03 s
in width and/or plus one-third of the total QRS complex in
two or more contiguous leads. Renal failure required either
an increase of serum creatinine ⬎2.0 mg/dl, a 50% or
greater increase in creatinine over the baseline preoperative
value or a new requirement for dialysis. Stroke was defined
as a persistent central neurological deficit lasting ⬎72 h.
Multisystem failure was defined as two or more major organ
systems suffering compromised function.
Definition of DM. We defined DM as a history of
diabetes currently receiving treatment with either oral medications or insulin. We further subclassified DM based on
method of glucose control, including oral medication or
insulin, at time of surgery.
Data collection. The data were collected as part of the
National Database of the Society of Thoracic Surgeons,
including approximately 65% of all cardiac surgery programs
across North America. Data were collected using standardized data collection instruments and prospectively defined
explicit data definitions. The data are harvested semiannually and electronically transmitted to the Duke Clinical
Research Institute. It is then cleaned for predetermined
standards and analyzed. Data managers receive biannual
Carson et al.
Outcomes in Patients With Diabetes Undergoing CABG
419
training and updates on STS data definitions and procedures. Sites also receive biannual reports on data quality and
completeness. The data collection instruments included
questions regarding demographic characteristics, preoperative risk factors, previous interventions, preoperative cardiac
status, cardiac catheterization results, medications, intraoperative management and postoperative complications.
Statistical analysis. All statistical analyses were performed
using SAS version 8.0. First, we used simple 2 ⫻ 2 tables to
examine the univariate relation between diabetes status and
each outcome. Then we used multivariate analyses to
examine the independent effect of DM after controlling for
other known baseline predictors of surgical risk for potential
confounding. We performed separate multiple logistic regression models for the primary outcome and each secondary outcome. For the first set of multivariate analyses, we
examined the diabetes dichotomous variable to determine
its significance after adjusting for covariates. For the second
set of multivariate analyses, we dichotomized diabetes patients into two treatment groups—patients treated with
medications or patients treated with insulin. We then
examined the differential effect of each diabetes treatment
group to determine its significance after adjusting for
covariates. We did not examine confounding using propensity scores because developing a model predicting the
presence or absence of DM had little face validity.
All models included independent patient variables found
to be risk factors for mortality in previous modeling efforts
in this database (17). These variables included: demographic
(age, gender, race), preoperative risk factors (renal failure,
renal failure-dialysis, cerebrovascular accident—when,
chronic lung disease, peripheral vascular disease, cerebrovascular disease, last creatinine preop, body surface area),
previous interventions (number of prior cardiac operations
requiring bypass, prior percutaneous catheter angioplasty/
including balloon, atherosclerosis, and/or stent interval),
preoperative cardiac status (congestive heart failure, MI,
cardiogenic shock, arrhythmia, New York Heart Association classification), preoperative medications (diuretics, corticosteroids, digitalis, intravenous nitrates), preoperative
hemodynamics and catheterization hemodynamic data
(ejection fraction, number of diseased coronary vessels, left
main disease ⬎50%), operative (status of the procedure),
cardiopulmonary bypass and support (intra-aortic balloon
pump).
The data were collected as part of the National Database
of the Society of Thoracic Surgeons after approval by the
Institutional Review Board of Duke University.
RESULTS
There were 156,046 patients who underwent coronary
artery bypass surgery. We excluded 4,564 patients with DM
treated only with diet, 2,143 patients in whom the treatment was unknown and 2,553 patients who were missing
information on DM status. The final study population
420
Carson et al.
Outcomes in Patients With Diabetes Undergoing CABG
JACC Vol. 40, No. 3, 2002
August 7, 2002:418–23
Table 1. Description of Study Population
No DM
DM-Total
DM-Oral Medication
DM-Insulin
Risk Variable
(N ⴝ 105,123)
%
(N ⴝ 41,663)
%
(N ⴝ 25,003)
%
(N ⴝ 16,660)
%
Age (mean ⫾ SD)
Gender (male)
Race
Caucasian
Black
Other/missing
Smoker
Family history of CAD
Hypercholesterolemia
Renal failure
Dialysis
Hypertension
Cerebrovascular accident
Peripheral vascular disease
Respiratory failure/COPD
Previous CABG
Prior PTCA interval
ⱕ6 months
⬎6 months
Prior myocardial infarction
ⱕ6 h
⬎6 h but ⬍24 h
1 to 7 days
8 to 21 days
ⱖ21 days
Congestive heart failure
Beta-blocker use
Preoperative intraaortic balloon
Internal mammary artery use
Number of distal anastomoses
(mean ⫾ SD)
Pump time (mean ⫾ SD)
65.1 (⫾ 1.09)
77,761
74.0
64.7 (⫾ 10.2)
26,236
63.0
65.4 (⫾ 9.8)
17,013
68.0
63.8 (⫾ 10.2)
9,223
55.4
93,066
3,420
8,637
64,718
52,271
55,077
3,313
607
67,235
5,861
13,327
15,928
7,559
88.5
3.3
8.2
61.6
49.7
52.4
3.2
0.6
64.0
5.6
12.7
15.2
7.2
34,278
2,591
4,794
22,664
18,638
21,569
3,347
910
31,757
3,961
8,348
6,025
2,686
82.3
6.2
11.5
54.4
44.7
51.8
8.0
2.2
76.2
9.5
20.0
14.5
6.5
20,829
1,270
2,904
14,085
11,357
13,093
1,239
239
19,000
2,144
4,177
3,446
1,618
83.3
5.1
11.6
56.3
45.4
52.4
5.0
1.0
76.0
8.6
16.7
13.8
6.5
13,449
1,321
1,890
8,579
7,281
8,476
2,108
671
12,757
1,817
4,171
2,579
1,068
80.7
7.9
11.3
51.5
43.7
50.9
12.7
4.0
76.6
10.9
25.0
15.5
6.4
1,442
9,695
1.4
9.2
295
3,861
0.7
9.3
190
2,293
0.8
9.2
105
1,568
0.6
9.4
1,531
1,950
17,156
4,341
22,665
10,766
55,840
10,099
19,936
3.4 (⫾ 1.2)
1.5
1.9
16.3
4.1
21.6
10.2
53.1
9.6
19.0
447
619
6,760
2,094
10,476
8,907
20,788
4,073
7,965
1.1
1.5
16.2
5.0
25.1
21.4
49.9
9.8
19.1
288
374
4,097
1,109
6,208
4,542
13,008
2,406
4,590
3.5 (⫾ 1.2)
1.2
1.5
16.4
4.4
24.8
18.2
52.0
9.6
18.4
159
245
2,663
985
4,268
4,365
7,780
1,667
3,375
3.4 (⫾ 1.1)
1.0
1.5
16.0
5.9
25.6
26.2
47.2
10.0
20.3
97.7 (⫾ 40.0)
101.1 (⫾ 38.9)
102.3 (⫾ 40.3)
CABG ⫽ coronary artery bypass grafting; CAD ⫽ coronary artery disease; COPD ⫽ chronic obstructive pulmonary disease; DM ⫽ diabetes mellitus; PTCA ⫽ percutaneous
catheter angioplasty.
included 146,786 patients, 105,123 without DM and
41,663 (28.4%) patients with DM. Of the patients with
DM, 16,660 (40.0%) used insulin, and 25,003 (60.0%) used
oral medications. The mean age of the study population was
65.0 (SD ⫾ 10.7). The clinical characteristics of the study
population are described in Table 1.
Mortality. Overall, the 30-day mortality was 3.74% in
patients with DM and 2.70% in those without DM (Table
Table 2. Outcomes Stratified by DM and Treatment
Outcome
No DM
(N ⴝ 105,123)
DM (Total)
(N ⴝ 41,663)
DM-Oral
Medications
(N ⴝ 25,003)
DM-Insulin
(N ⴝ 16,660)
30-day mortality
Morbidity
Myocardial infarction
Stroke
Renal failure
Multiple system failure
Infection
Pneumonia
Urinary tract infection
Sternum
Leg
Septicemia
Mortality or morbidity
Mortality or infection
2,843 (2.7)
9,602 (9.1)
1,303 (1.2)
1,472 (1.4)
3,072 (2.9)
592 (0.6)
5,449 (5.2)
2,512 (2.4)
1,337 (1.3)
480 (0.5)
1,175 (1.1)
938 (0.9)
10,920 (10.4)
7,605 (7.2)
1,559 (3.7)
5,793 (13.9)
487 (1.2)
937 (2.3)
2,246 (5.4)
336 (0.8)
3,287 (7.9)
1,182 (2.8)
847 (2.0)
431 (1.0)
938 (2.3)
596 (1.4)
6,445 (15.5)
4,420 (10.6)
800 (3.2)
3,005 (12.0)
272 (1.1)
535 (2.1)
1,066 (4.3)
173 (0.7)
1,713 (6.9)
653 (2.6)
431 (1.7)
203 (0.8)
480 (1.9)
287 (1.1)
3,348 (13.4)
2,318 (9.3)
759 (4.6)
2,788 (16.7)
215 (1.3)
402 (2.4)
1,180 (7.1)
163 (1.0)
1,574 (9.4)
529 (3.2)
416 (2.5)
228 (1.4)
458 (2.7)
309 (1.9)
3,097 (18.6)
2,102 (12.6)
DM ⫽ diabetes mellitus.
Carson et al.
Outcomes in Patients With Diabetes Undergoing CABG
JACC Vol. 40, No. 3, 2002
August 7, 2002:418–23
421
Table 3. Unadjusted and Adjusted Risk Associated With Diabetes Mellitus Overall and Stratified by Type of Treatment*
A.
Operative Death
Unadjusted
Morbidity
Adjusted
Unadjusted
Infection
Adjusted
Unadjusted
Adjusted
1.57 (1.50–1.64)
1.35 (1.27–1.42)
1.91 (1.80–2.02)
1.36 (1.30–1.43)
1.24 (1.17–1.31)
1.55 (1.46–1.66)
Odds Ratio (95% Confidence Interval)
Diabetes (overall)
Oral medication
Insulin
1.40 (1.31–1.49)
1.19 (1.10–1.29)
1.72 (1.58–1.86)
1.23 (1.15–1.32)
1.13 (1.04–1.23)
1.39 (1.27–1.52)
B.
1.61 (1.55–1.66)
1.36 (1.30–1.42)
2.00 (1.91–2.09)
1.38 (1.33–1.44)
1.25 (1.19–1.30)
1.61 (1.53–1.69)
Mortality/Morbidity
Unadjusted
Mortality/Infection
Adjusted
Unadjusted
Adjusted
Odds Ratio (95% Confidence Interval)
Diabetes (overall)
Oral medication
Insulin
1.58 (1.53–1.63)
1.33 (1.28–1.39)
1.97 (1.88–2.06)
1.37 (1.32–1.42)
1.23 (1.18–1.28)
1.59 (1.52–1.67)
1.52 (1.46–1.58)
1.31 (1.25–1.37)
1.85 (1.76–1.95)
1.33 (1.27–1.38)
1.22 (1.16–1.28)
1.50 (1.42–1.59)
*Variables controlled in logistic regression model included: demographic (age, gender, race), preoperative risk factors (renal failure, renal failure dialysis, cerebrovascular
accident—when, chronic lung disease, peripheral vascular disease, cerebrovascular disease, last creatinine preop, body surface area), previous interventions (number of prior cardiac
operations requiring bypass, prior percutaneous catheter angioplasty/including balloon, atherosclerosis, and/or stent interval), preoperative cardiac status (congestive heart failure,
myocardial infarction—when, cardiogenic shock, arrhythmia, New York Heart Association classification), preoperative medications (diuretics, corticosteroids, digitalis,
intravenous nitrates), preoperative hemodynamics and catheterization hemodynamic data (ejection fraction, number of diseased coronary vessels, left main disease ⬎50%),
operative (status of the procedure), cardiopulmonary bypass and support (intraaortic balloon pump—when).
2); the unadjusted odds ratio was 1.40 (95% confidence
interval [CI], 1.31 to 1.49). After adjusting for other
baseline risk factors, the adjusted odds ratio was 1.23 (95%
CI, 1.15 to 1.32). The impact of DM on mortality is similar
to gender (adjusted odds ratio for female gender ⫽ 1.31),
race (adjusted odds ratio for Caucasian ⫽ 0.89), peripheral
vascular disease (adjusted odds ratio ⫽ 1.36) and chronic
lung disease (adjusted odds ratio ⫽ 1.33) but is less
important than preexisting renal failure or dialysis (adjusted
odds ratio ⫽ 1.73), preoperative cardiogenic shock (adjusted
odds ratio ⫽ 2.68) and reoperation (adjusted odds ratio ⫽
2.87).
When the analysis was stratified by diabetes treatment
and adjusted for confounders, patients treated with insulin
(adjusted odds ratio 1.39; 95% CI, 1.27 to 1.52) had a
significant elevation in risk associated with 30-day mortality
(Table 3). Those on oral medications also had a significant,
but small, increase in 30-day mortality (adjusted odds ratio
1.13; 95% CI, 1.04 to 1.23).
The distributions of causes of death are described in
Table 4. The majority of patients died from cardiac causes.
The other most common causes of death were neurologic,
pulmonary disease and infection. Compared with patients
without DM, infections were the cause of death more often
in patients with DM treated with insulin (p ⫽ 0.033).
However, infections were not a more common cause of
death in patients with DM (treated with oral medication
and insulin) than patients without DM (p ⫽ 0.22). Neurologic causes of death occurred more frequently in DM
patients overall (p ⫽ 0.01) and in DM patients treated with
oral medications (p ⬍ 0.005).
Morbidity, infection and composite outcomes.
Morbidity (13.9% vs. 9.1%), infections (7.9% vs. 5.2%) and
the composite outcomes of death or morbidity (15.5% vs.
10.4%) and death or infection (10.6% vs. 7.2%) occurred
more commonly in diabetic patients (Table 2). For each of
these outcomes, the adjusted risk was about 35% higher in
diabetics than nondiabetics (Table 3, A and B). Diabetic
patients using insulin had the highest risk of mortality and
morbidity compared with diabetic patients who were treated
Table 4. Causes of Death Stratified by Treatment for DM
No DM
(N ⴝ 105,123)
DM Total
(N ⴝ 41,663)
DM-Oral Medication
(N ⴝ 25,003)
DM-Insulin
(N ⴝ 16,660)
Cause of Death
n
%
n
%
n
%
n
%
Cardiac
Neurologic
Renal
Vascular
Infection
Pulmonary
Valvular
Other
Total cause of death recorded
Cause of death missing
Total deaths
1,864
263
54
35
153
181
3
176
2,729
115
2,844
68.30%
9.64%
1.98%
1.28%
5.61%
6.63%
0.11%
6.45%
2.60%
986
182
36
15
98
97
3
82
1,499
60
1,559
65.78%
12.14%
2.40%
1.00%
6.54%
6.47%
0.20%
5.47%
3.60%
503
100
18
9
41
49
3
37
760
40
800
66.18%
13.16%
2.37%
1.18%
5.39%
6.45%
0.39%
4.87%
3.04%
483
82
18
6
57
48
0
45
739
20
759
65.36%
11.10%
2.44%
0.81%
7.71%
6.50%
0.00%
6.09%
4.44%
DM ⫽ diabetes mellitus.
2.70%
3.74%
3.20%
4.55%
422
Carson et al.
Outcomes in Patients With Diabetes Undergoing CABG
with oral medications (Table 3, A and B). The adjusted risk
for each of these outcomes was 50% to 61% higher for
insulin-treated diabetics compared with nondiabetics for
each outcome.
Length of hospital stay. The median length of hospital
stay was 7.0 days (interquartile range; 5, 10) in patients
without DM and 8.0 (interquartile range; 6, 11) in patients
with DM (p ⬍ 0.001). The length of hospital stay was 7.0
days (interquartile range; 6, 11) in patients with DM treated
with oral medication and 8.0 days (interquartile range; 6,
12) in patients with DM treated with insulin. The length of
stay was significantly longer in patients treated with insulin
compared with patients treated with oral medication and
patients without DM (p ⬍ 0.001).
DISCUSSION
Summary of findings. This study of 146,786 patients
undergoing coronary artery bypass surgery found that patients with DM had a 23% to 37% increase in 30-day
mortality and in-hospital morbidity compared with patients
without DM. The increased risk of death (39%) or postoperative complications (50% to 61%) occurred most commonly in diabetic patients treated with insulin. Cardiac
disease was the most common mode of death in DM
patients, although neurological, pulmonary and infectious
disorders were relatively common modes of death.
Previous studies had conflicting results, although most
did not identify a significantly elevated risk of death in
patients with DM (3,6,7,10 –12). Two studies have found
associations between short-term mortality and DM. One
study based on data from 25 years ago found higher
mortality in DM with preserved left ventricular function,
although no differences were found in patients with poor
ventricular function, and confounding was not adjusted for
(13). A recent large study included 2,278 patients with DM
and 9,920 patients without DM (9). Short-term mortality
was significantly higher in DM (3.9% vs. 1.6%) after
controlling for other risk factors for death. This study was
limited by the fact that data were not contemporary (1978 to
1993), year of surgery was not controlled for, infections were
not reported and cause of death was not evaluated. Nearly
all of the studies that developed predictive indexes for
mortality after CABG surgery included DM in the regression model (14 –17).
This is the first study to contrast the causes of death in
patients with diabetes and patients without diabetes. Most
patients died from cardiac disease, although neurological
causes were very common. Infection was a more common
cause of death only in insulin-treated diabetics compared
with patients without DM.
This study further clarifies the risk of postoperative
complications in patients with diabetes undergoing coronary
artery bypass surgery. Prior studies that evaluated postoperative complications largely focused on individual diseases
and were much too small to detect differences in morbidity
JACC Vol. 40, No. 3, 2002
August 7, 2002:418–23
outcomes (6,7,9 –12,18 –20). We chose to evaluate complications grouped together because most individual diseases
were very uncommon. We demonstrate that the risk of
infection and other serious life-threatening complications is
36% to 38% higher in diabetics after adjusting for differences in risk factors. Similar to the analysis of death,
insulin-treated diabetics had the highest risk of serious
complications.
Possible explanations for poor outcome in DM. There
are a number of possible explanations for the relation
between DM and increased mortality and morbidity after
CABG. The most obvious explanation is that patients with
DM have more comorbidity or more advanced cardiac
disease at the time of surgery. While we controlled for many
known risk factors previously demonstrated to be associated
with mortality (demographic characteristics, preoperative
risk factors including most common comorbidities, previous
interventions, preoperative cardiac status, preoperative medications, preoperative hemodynamics and catheterization
data, and operative information), it is still possible there is
residual confounding. Other potential limitations include
incomplete 30-day follow-up for mortality, although a
validation study suggests that this information is accurate
(21), and difficulty in distinguishing pneumonia from congestive heart failure in postoperative coronary artery bypass
surgery patients. Neither of these potential problems should
have biased the results of the study because it is unlikely that
there are differential misclassifications between patients
with and without DM.
It is also interesting to consider the possibility that the
metabolic abnormalities associated with DM are responsible
for some of the increased mortality and morbidity. Dehydration and electrolyte disturbances as a result of uncontrolled hyperglycemia could contribute. Free fatty acids
levels are elevated after major surgery and could suppress
cardiac function, increase myocardial oxygen demand and
may be arrhythmogenic (22–25).
Hyperglycemia per se could impact on perioperative
mortality and morbidity by a number of mechanisms.
Hyperglycemia interferes with the function of polymorphonuclear leukocytes predisposing to infection and may impair
wound healing (10,11,26 –29). Some studies suggest a
relation between improved glucose control in the perioperative period and lower rates of wound infection and dehiscence (30 –32). Hyperglycemia could contribute to increased
platelet activity and disordered coagulation and fibrinolytic
function (33) as well as abnormalities in lipid metabolism.
Hyperglycemia may also adversely affect endothelial function (34). The few clinical trials of more intensive insulin
therapy of hyperglycemia during and after a MI (35–38) and
in intensive care unit patients (39) suggest improved outcomes.
Our data suggest that patients with DM are at significantly greater risk of death or suffering a serious postoperative complication when compared with nondiabetics. Diabetic patients represent 28% of all patients undergoing
JACC Vol. 40, No. 3, 2002
August 7, 2002:418–23
CABG. While the absolute difference in mortality and
morbidity between patients with and without DM is modest, the absolute difference is substantial when comparing
patients with insulin-treated DM to those without DM; the
difference in mortality is 1.9%, mortality or morbidity is
8.2%, and mortality or infection is 5.4%. There are also
significant healthcare costs associated with these poor outcomes (40).
Reprint requests and correspondence: Dr. Jeffrey L. Carson,
Robert Wood Johnson Medical School, 125 Paterson Street, New
Brunswick, New Jersey 08903. E-mail: Carson@umdnj.edu.
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