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19 декабря 2001 00:00   |   Reginald Abraham, MD,1 Hratch L. Karamanoukian, MD, 1 Mark R.

Does Avoidance of Cardiopulmonary Bypass Decrease the Incidence of

 
 
ABSTRACT
Background: The adverse effects of diabetes mellitus on the coronary
circulation and the higher incidence of cardiovascular events in 
 
diabetic patients are well documented [Johnson 1982]. Improvements
in myocardial protection, revascularization techniques, and 
 
anesthetic management have had favorable impacts on coronary artery
bypass grafting (CABG) outcome in diabetic patients. Despite that,
diabetic patients are significantly more likely to have a prior
history of myocardial infarction, congestive heart failure,
peripheral vascular disease, and hypertension, as well as having a 
 
significantly greater baseline serum creatinine. The aim of our 
 
study was to record, compare, and analyze the stroke rate among
patients with a history of preoperative diabetes undergoing
«off-pump» CABG (OPCAB) with conventional cardiopulmonary bypass
(CPB) CABG to determine whether the stroke rate in this higher risk 
 
population could be decreased by off-pump techniques.
Methods: The records of 1,227 patients with a pre-operative history
of diabetes undergoing conventional CABG (973 patients, 79.3%) using
cardiopulmonary bypass and off-pump CABG 254 (20.7%) were analyzed
from 1995 through 1999. There were no differences in age, sex, or 
 
elective/urgent status of patients. Preoperative risk factors
(gender distribution, carotid disease, ejection fraction, CHF,
hypertension, previous MI) were identical in both groups. The goal 
 
of the operations were complete revascularization, which was 
 
achieved via median sternotomy in both groups.
Results: Our reported series reveals a stroke rate of 3.6% in the 
 
CPB group and 1.2% in the off-pump group. This evidence alone was 
 
not statistically significant, but two other high-risk criteria for 
 
stroke, re-do CABG and calcified aortas, revealed that the off-pump
series had a higher percentage of each (26.4% redos in off-pump vs.
8.7% CPB redos, p < 0.005; 7.1% calcified aorta cases in the 
 
off-pump group vs. 2.9% in the CPB group, p < 0.004). The threefold
reduction in stroke may be clinically significant in light of the 
 
higher-risk profile of the off-pump group. The limitations of this 
 
study are that it was retrospective, there were a small number of 
 
events, and different surgeons were involved in the two different
approaches to these patients.
Conclusions: Improvements in myocardial protection,
revascularization techniques, and anesthetic management have made 
 
significant, favorable impacts on CABG outcome in diabetic patients.
New diagnostic and therapeutic strategies must be developed to 
 
lessen the medical and economic implications of stroke. A larger
series or a more effective way of analyzing preoperative risk may 
 
well have shown a statistically significant difference in the stroke
incidence given the differences in preoperative risk factors/stroke
predictors. Until such advances occur, a threefold reduction of 
 
stroke incidence using OPCAB certainly makes this technique a 
 
favorable one for high-risk diabetics requiring coronary
revascularization.
INTRODUCTION
The adverse effects of diabetes mellitus on the coronary circulation
and the higher incidence of cardiovascular events in diabetic
patients are well documented [Johnson 1982]. Improvements in 
 
myocardial protection, revascularization techniques, and anesthetic
management have had favorable impacts on coronary artery bypass
grafting (CABG) outcome in diabetic patients. Despite that, diabetic
patients are significantly more likely to have a prior history of 
 
myocardial infarction, congestive heart failure, peripheral vascular
disease and hypertension, as well as having a significantly greater
baseline serum creatinine [Stewart 1998]. Diabetic patients have 
 
overall longer ICU and hospital stays, and Herlitz [Herlitz 1996]
and Morris [Morris 1991] agree with Stewart [Stewart 1998] that 
 
diabetes is an independent risk factor for mortality following CABG.
Stroke is the third leading cause of death in the United States and 
 
continues to be a challenging problem as the population ages. Stroke
and neurologic complications occur in up to 6% of patients following
CABG. The incidence of cognitive and neuropsychological
complications are much higher and may exceed 60% [Almassi 1999].
Patients who undergo myocardial revascularization procedures, now 
 
more than 800,000 per year throughout the world, are particularly
prone to stroke, encephalopathy, and other neurologic dysfunction
because they are relatively old and have atherosclerotic heart
disease. With longer ICU stays, hospitalization, and overall
increased consumption of resources, estimates worldwide of the added
in-hospital cost are upwards of $800 million annually [Roach 1996].
These patients are also subject to marked hemodynamic fluctuations,
cerebral embolization of atherosclerotic plaque, air, fat, and 
 
platelet aggregates, cerebral hyperthermia after discontinuation of 
 
cardiopulmonary bypass (CPB), and other inflammatory and 
 
neurohormonal derangements associated with surgery [Roach 1996].
Hodgman and Eversman [Hodgman 1981] found a stroke incidence of 4.6%
in diabetics versus 1.6% in non-diabetics. Johnson et al. [Johnson
1982] observed five fatal strokes in their series of patients
concluding that diabetic patients may be more susceptible to stroke.
The aim of our study was to record, compare, and analyze the stroke
rate among patients with a history of pre-op diabetes undergoing
off-pump CABG (OPCAB) with conventional CPB CABG to determine
whether the stroke rate in this higher risk population could be 
 
decreased by off-pump techniques. Stroke was defined as any new 
 
global or focal neurological deficit lasting more than 24 hours that 
 
was confirmed by head CT scan and/or neurology evaluation during
that hospital stay.
MATERIALS AND METHODS
The records of 1,227 patients with pre-operative history of diabetes
undergoing conventional CABG (973 patients, 79.3%) using
cardiopulmonary bypass and «off-pump» CABG 254 (20.7%) were analyzed
from 1995 through 1999. The goal of the operations was complete
revascularization, but in the early phase of OPCAB surgery this goal 
 
was not always accomplished. Since 1997, complete revascularization
was accomplished routinely in the OPCAB patients. Revascularization
was achieved via median sternotomy in both groups. Aortic
calcification was assessed primarily by chest x-ray and CT scan and 
 
intraoperative palpation. Chest CT was utilized only if the chest
x-ray was suspicious for extensive lesions. Data was compared to the 
 
NY State database.
RESULTS
There were no differences in age, sex, or elective/urgent status. A 
 
higher proportion of the off-pump group were «re-do» cases compared
to the CPB group (26.4% off-pump vs. 8.7% CPB, p < 0.005), and the 
 
incidence of calcified aorta was higher in the off-pump group (7.1%
off-pump vs. 2.9% CPB, p < 0.04). Preoperative risk factors (gender
distribution, carotid disease, ejection fraction, CHF, hypertension,
previous MI) were identical in both groups. There was a higher
percentage of patients in the off-CPB group with preoperative
congestive heart failure (CHF) (18.5% off-pump vs. 12.8% CPB, p =
0.025) and who were also on IV nitroglycerin 24 hours pre-op (21.3%
off-pump vs. 15.2% CPB). The risk-adjusted mortality for both groups
was statistically the same (1.8% off-CPB vs. 2.6 % CPB, p = NS).
There was no significant difference in postoperative stroke rates
(1.2% off-pump vs. 3.6% CPB, p = NS). While the off-pump stroke rate 
 
represents one-third of the stroke rate in the CPB group, the 
 
difference was not statistically significant. Postoperative
complications (transmural MI, deep sternal wound infection,
bleeding, renal and respiratory failure) were identical in both
groups.
It is important to keep in mind some of the technical milestones
[Bergsland 1998], such as stabilizers (1997) and the LIMA stitch
[Bergsland 1999], that took place during the time frame of this 
 
study. Median sternotomy was the exposure technique of choice in 
 
most instances for complete myocardial revascularization in both 
 
groups. Revascularization of the marginal branches of the circumflex
artery was not considered a contraindication to off-pump coronary
grafting. Technical considerations included the use of the single
suture (LIMA) stitch technique in the oblique sinus of the posterior
pericardium to obtain exposure [Herlitz 1993] and mechanical
stabilization with an epicardial foot plate to reduce heart motion.
Ischemic preconditioning, especially of the LAD vessels, was routine
for 3−5 minutes and this was the first vessel grafted during
off-pump cases. Intracoronary shunts were used to reestablish flow 
 
during construction of the distal anastamoses, the details of which
have been previously described [Rivetti 1998]. A CO2 blower/saline
aerosolizer was used to maintain a bloodless field of vision
[Bergsland 1999]. All off-pump grafts were evaluated via transit
time flow meter [Bergsland 1999].
All relevant information, which included demographic data,
preoperative risk factors and comorbid conditions, angiographic data 
 
with severity and distribution of significant coronary artery
disease, and morbidity and mortality rates were recorded [Bergsland
1998]. The severity of angina was categorized according to the 
 
Canadian Cardiovascular Society (CCS) classification. The left 
 
ventricular ejection fraction (LVEF) was determined in all cases by 
 
left ventriculography during coronary angiography. The type of 
 
operative priority was defined as emergent when severity and 
 
distribution of coronary pathology in combination with hemodynamic
instability mandated immediate intervention. The management of some 
 
of these patients had included vasopressors, intra-aortic balloon
counterpulsation, and cardiopulmonary resuscitation. Patients in 
 
whom surgical intervention was promptly undertaken in the face of 
 
ongoing ischemia, or failed angioplasty, or as a result of 
 
unfavorable anatomy (i.e., left main disease), were referred to as 
 
urgent. The data collected from both study groups were statistically
analyzed and compared. Statistical analysis was conducted using Epi 
 
Info, version 6. Continuous normally distributed variables were 
 
contrasted using the Student's t test. The Fisher exact test was 
 
used when the expected value of a cell was less than 5. Differences
between variables were considered significant when the p value was
less than 0.05.
DISCUSSION
The negative impact of diabetes on survival following coronary
angioplasty was demonstrated by the Bypass Angioplasty
Revascularization Investigation (BARI) [BARI 1996]. Five-year
survival in diabetics assigned to multivessel angioplasty (65.5%)
was significantly lower than five-year survival in non-diabetics
treated similarly (91.1%). In addition, a reduced five-year survival
was observed in diabetics assigned to CABG (80.6%) versus that seen 
 
in non-diabetics undergoing CABG (91.4%) [BARI 1996].
Not all diabetics are the same. Lawrie et al. reported that 
 
diabetics controlled through diet had a prognosis indistinguishable
in all respects from non-diabetics [Lawrie 1986]. Those receiving
insulin had a substantially worse long-term survival, although their
early prognosis was identical. Patients receiving oral hypoglycemic
agents had an intermediate prognosis. Controlled diabetes is not 
 
sufficient reason to avoid surgery for severe coronary artery
disease. Five-year survival in diabetics after coronary surgery
still exceeds survival of any reported series of medically treated
patients with comparable disease [Johnson 1982].
An increasing proportion of high-risk patients are offered
revascularization because of signs and symptoms of ischemic heart
disease. Patients with a history of diabetes constitute one such 
 
high risk group. While we did not observe a statistically
significant difference in the mortality rate between the off-CPB and 
 
the CPB diabetic cohorts, others have reported very high mortality
rates among diabetics [Herlitz 1993, Zuanetti 1993, Herlitz 1996].
Herlitz et al. found that diabetics required more reoperation and 
 
had a higher incidence of peri- and post-operative neurological
complications [Herlitz 1996]. They also concluded that the mortality
rate during the two-year period after CABG was approximately twice
that of non-diabetic patients. The mechanism underlying higher
mortality in diabetic patients is thought to be existence of more 
 
extensive coronary artery disease, which compromises myocardial
function. From these and other similar studies, diabetes, after
multivariate analysis, still appears to be an independent predictor
of mortality. Diabetics have a higher risk of reinfarction compared
to non-diabetics, and the risk of thromboembolic complications in 
 
patients with diabetes was higher in comparison to non-diabetic
cohorts [Herlitz 1993, Herlitz 1996].
Advanced age is associated with an inhomogeneous reduction in gray 
 
matter flow, and this progressive reduction in regional blood flow 
 
and cerebrovascular collateral reserve may play a role in the 
 
increased incidence of postoperative stroke in the elderly,
especially when hypotension or a low flow state occurs during or 
 
after CPB [Calafiore 1997]. In an ever-aging population presenting
for CABG surgery with a myriad of medical problems, understanding
the physiology and pathophysiology of cerebral blood flow and the 
 
factors that may compromise it is essential.
Advances in surgical technique, anesthesia management, and CPB have 
 
all contributed to reductions in morbidity and mortality during
cardiac surgical procedures. However, the incidence of neurologic
injury, in particular neuropsychologic impairment, remains high 
 
after CPB [Taylor 1999]. Several studies have reported that 50%−70%
of patients exhibit cognitive deficits one week after coronary
bypass operations and approximately 30% of patients exhibit
long-term neuropsychologic impairment. The possibility of a lower
threshold to ischemic insult of any kind--whether microemboli, low 
 
flow, or other--suggests a more tenuous state that precludes safe 
 
use of CPB with its inherent sources of emboli and hemodynamic
changes, as demonstrated by Taylor et al. [Taylor 1999]. In the same 
 
paper, Taylor et al. observe one-third of patients exhibiting
long-term cognitive deficits after CPB. The principal cause of 
 
neuropsychologic impairment was thought to be diffuse microischemia
secondary to cerebral microemboli. Taylor et al. studied
interventions on-pump and correlated cerebral microemboli with 
 
transcranial doppler studies. They identified at least nine 
 
sources/points from which patients were at risk of showering emboli
and found the greatest number of emboli occurring during
interventions by the perfusionist (blood sampling and drug 
 
injections), although these were often correctable when detected.
Various authors and investigators have attempted to identify risk 
 
factors and preoperative predictors of perioperative stroke
following CABG, and at least two authors [Higgins 1992,
Mickleborough 1996] have proposed and developed severity scores and 
 
indices. Of the many risk factors examined by investigators,
preoperative stroke demonstrates the highest risk of development of 
 
postoperative neurologic events. Causes of stroke are 
 
multifactorial. Some generally accepted risk factors are age, length
of CPB and cross-clamp time, urgency of operation, calcified
aortas/generalized atherosclerosis, combined valve repair
(especially mitral) and CABG, and hypertension. Factors that are 
 
less generally accepted as predictors for stroke include female
gender, atrial fibrillation, and pulmonary disease [Higgins 1992,
Mickleborough 1996, McKhann 1997, Almassi 1999, Taylor 1999].
Central nervous system complications of CPB are very common. These
range from subtle neuropsychiatric abnormalities detected only with 
 
sophisticated tests (e.g., saccadic eye movements) to frank and 
 
clinically evident neurologic deficit. A permanent neurologic
deficit or stroke occurs in up to 6% of patients undergoing cardiac
surgery Lynn 1992, Roach 1996, Almassi 1999]. Hodgman and Eversman
[Hodgman 1981] found a stroke incidence of 4.6% in diabetics versus
1.6% in non-diabetics and observed five (1.9%) fatal strokes in 
 
their 261 patients. They concluded from this evidence that diabetic
patients are more susceptible to stroke.
Our reported series reveals a stroke rate of 3.6% with CPB and 1.2%
in the off-pump group. This evidence alone was not statistically
significant, but two other high-risk criteria for stroke, re-do CABG 
 
and calcified aortas, revealed that the off-pump series had a higher
percentage of each (26.4% redos in off-pump vs. 8.7% CPB redos, p <
0.005; 7.1% calcified aorta cases in the off-pump vs. 2.9% in the 
 
CPB group, p < 0.004). There was also a higher incidence of CHF on 
 
admission in the off-CPB group (18.5% vs. 12.8% in the CPB group, p 
 
= 0.025). This threefold reduction in stroke, therefore, is 
 
clinically significant in light of the higher risk profile of the 
 
off-pump group.
The limitations of this study are that it was retrospective, there
were a small number of events, and different surgeons were involved
in the two different approaches to these patients. Clearly, as this 
 
field of study broadens, more accurate risk stratification (NIH,
Mathews', Murkins' scales) [Higgins 1992, BARI 1996] can be utilized
as well as uniform definitions and applications of 
 
neuropsychological injury applied and followed long-term. More 
 
sensitive and consistent means of identifying aortic lesions (CT or 
 
epi-aortic scanning) may also identify high-risk individuals [Rao
1995, Calafiore 1997].
CONCLUSION
Improvements in myocardial protection, revascularization techniques,
and anesthetic management have made significant, favorable impacts
on CABG outcome in diabetic patients. New diagnostic and therapeutic
strategies must be developed to lessen the medical and economic
implications of stroke. To that end, we have explored the use of 
 
coronary revascularization techniques without extracorporeal
circulation (i.e., off-pump or beating heart surgery) to determine
the extent to which neurologic events and their consequences can be 
 
attenuated. A larger series or a more effective way of analyzing
preoperative risk may well have shown a statistically significant
difference in the stroke incidence given the differences in 
 
preoperative risk factors/stroke predictors. Such analytical tools
might include computer matching and subsequent logistic regression,
and identifying hazard criteria with appropriate confidence
intervals from univariate and multivariate analysis. Until such 
 
advances occur, a threefold reduction of stroke incidence using
OPCAB certainly makes this technique a favorable one for high-risk
diabetics requiring coronary revascularization.
 
APPENDIX
 
 
View Appendix
AUTHOR/ARTICLE INFORMATION
Submitted January 25, 2001; accepted January 29, 2001.
Address correspondence and reprint requests to: Hratch L.
Karamanoukian, MD, Kaleida Health-Buffalo General Hospital Site, 100 
 
High Street, Buffalo, N.Y. 14203, Phone: (716) 859−1080, Fax: (716)
859−4687, Email: lisbon5@yahoo.com
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