Adverse Neurologic Sequelae Associated with Coronary Bypass Grafting
February 1, 1997
Adverse Neurologic Sequelae Associated with Coronary Bypass Grafting
ABSTRACT & COMMENTARY
Synopsis: High-risk patients can be identified for both focal or diffuse cerebral injury and risk stratification should be used by clinicians in patients undergoing bypass surgery.
Source: Roach GW, et al. N Engl J Med 1996;335: 1857-1863.
The incidence of stroke or serious neuro- psychological dysfunction associated with coronary bypass surgery is variably reported in different studies. The Cardiac Surgery study, a part of the Multicenter Study of Perioperative Ischemia, was a prospective observational study designed to assess the incidence of adverse neurologic outcomes after bypass surgery; assess risk factors for poor outcome; and analyze the effect of these complications on the use of health care resources. The study consisted of 2100 patients from 24 U.S. hospitals, each of whom prospectively enrolled approximately 100 patients between 1991 and 1993. Patients were assessed for new perioperative neurologic findings, with the charts reviewed by six investigators. Outcome classifications were in two categories: Type I was fatal or non-fatal stroke, TIA, or coma at the time of discharge; a Type II outcome was defined as new deterioration in intellectual function, confusion, disorientation, etc., without evidence of focal neurologic injury. It was hypothesized that these two types of outcomes had different etiologies and possibly different risk factors. A variety of potential preoperative predictors of adverse neurologic outcome were assessed, as were several intra-operative and post-operative factors. Resources were categorized on the basis of length of ICU and hospital stay, and whether or not a patient was discharged to home or an intermediate or long-term care facility.
The baseline population of 2100 subjects who had predictable clinical characteristics: one-third older than 70 years; more than half had a history of hypertension. Fifty percent had unstable angina and myocardial infarction; 10-15% had prior bypass grafting or peripheral vascular disease. One-quarter had congestive heart failure, and 25% had diabetes. The primary outcome of adverse cerebral sequelae was present in 6.1% of patients, divided equally between Type I and Type II outcomes. Univariant analysis and logistic regression assessment identified eight predictors for Type I outcome. The most significant predictor (4.5 times increased risk) was proximal aortic atherosclerosis as palpated by the surgeon; a history of neurological disease imported a three-fold risk. A history of hypertension, pulmonary disease, or diabetes more than doubled the risk, and use of intra-aortic balloon pumping resulted in almost a three-fold increase in the likelihood of adverse neurologic events. A history of unstable angina also was associated with increased risk. For Type II outcomes, seven predictors were identified, including a history of heavy alcohol use, prior bypass surgery, cardiac arrhythmias, peripheral vascular disease, and the presence of heart failure. Age and pulmonary disease were associated with a two-fold increased risk. The most severe category was associated with a ten-fold increase in hospital mortality, and a Type II outcome was associated with a five-fold increase in hospital mortality. Of the entire cohort, those without any cerebral event had a 2% hospital mortality vs. 21% death rate for Type I subjects and 10% for Type II subjects. Length of stay was related to an adverse cerebral vascular outcome, averaging 25 days for Type I patients, 20 days for Type II patients, and 10 days for those without any adverse event. ICU stays were proportionately lengthened as well. Ninety percent of those without adverse event were discharged to home, compared with 60% of Type II patients and only 32% of Type I patients.
The authors concluded that adverse cerebral outcomes were significantly related to increased mortality and use of medical resources. Type II outcomes had not been previously specifically studied and were clearly associated with increased mortality and a considerable increased use of hospital resources. High-risk factors that related to adverse results included advanced age, proximal aortic atherosclerosis, pre-existing neurologic disease, pulmonary disease, and a history of hypertension. Conservative cost analyses were used based solely on ICU and total hospital stay. It was estimated that Type I neurologic events were responsible for an additional $10,000 in hospital costs, and Type II for $6,000 per patient. Using an estimate of 800,000 patients throughout the world who undergo bypass surgery, the authors suggest that the true additional in-house costs of adverse cerebral outcomes worldwide could be $400,000,000! They believe that their estimates substantially underestimate the actual costs, which probably run into several billions of dollars.
The authors note that the presence of proximal aortic atherosclerosis is associated with a four-fold increased risk for Type I events, and they speculate that these strokes are caused by emboli from atherosclerotic plaques "liberated by surgical manipulation of the aorta." Such atherosclerosis was detected in 12% of all patients and 20% of those over 70 years of age. No transesophageal echo (TEE) studies were reported. History of prior neurologic abnormalities, particularly stroke or TIA, was also significantly related to an adverse outcome, as was diabetes. Of interest, proximal aortic atherosclerosis was not associated with Type II outcomes. Advanced age and pulmonary disease are two significant factors, as is hypertension. Carotid artery disease was not carefully assessed in this trial. The authors conclude that high risk patients can be identified for both focal or diffuse cerebral injury, and that risk stratification should be used by clinicians in patients undergoing bypass surgery. Serious adverse outcomes occurred in 6% of such patients and were associated with substantial increases in mortality and morbidity.
COMMENT BY JONATHAN ABRAMS, MD
This carefully designed study provides useful information to clinicians evaluating individuals for bypass surgery with respect to the overall risk of the procedure, irrespective of coronary artery disease severity or left ventricular function. The fact that age is a strong predictor of adverse outcome is not surprising, but the relationship of pulmonary disease and hypertension, each imparting a two- to three-fold increased likelihood of a Type II outcome, is of great interest. Furthermore, the finding that a history of alcohol abuse imparts a great two- to three-fold increased risk for a Type II outcome (presumed diffuse cerebral vascular dysfunction) has not been emphasized previously. The interesting observation that surgical palpation of atheroma in the ascending aorta is strongly associated with perioperative stroke raises the question of whether individuals without history of cerebral vascular disease should undergo transesophageal echo, particularly if they have other risk factors as identified in this study such as hypertension, pulmonary disease, or advanced age. While the use of TEE in the operating room has become quite popular, it is doubtful that most routine coronary bypass cases utilize ultrasound aortic assessment.
This study supports use of TEE for an increased evaluation of aortic atherosclerosis. Cardiac surgeons could decrease the likelihood of Type I events with changes in technique if proximal aortic atherosclerosis was identified. For instance, left ventricular venting and use of intra-aortic balloon pumping was associated with adverse outcomes in this trial; the authors suggest that alterations in surgical technique for high-risk patients might include adjustments of the site for aortic cross clamping and cannulation, the increased use of arterial conduits to avoid proximal aortic anastomoses, use of hypothermic arrest to avoid aortic cross pumping, or even replacement of diseased aorta in individuals. For the cardiologist and internist, this report provides important and useful information with respect to risk stratification, although there is relatively little information as to how to avoid adverse neurologic outcomes other than superb clinical care and possibly the increased use of TEE in older patients.
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