Predicting Neurologic Outcome After CABG

Abstracts & Commentary

Sources: Stamou SC, et al. Stroke after coronary artery bypass. Incidence, predictors, and clinical outcome. Stroke. 2001;32:1508-1513; Silver B. Editorial comment. Stroke. 2001;32:1512-1513.

Stamou and colleagues studied the incidence, predictors, and early clinical outcome of stroke after coronary artery bypass grafting (CABG) over a 10-year period at Washington DC Hospital Center. A multivariate logistic regression analysis identified independent predictors of in-hospital stroke.

Postoperative strokes (n = 333) occurred in 2% of more than 16,000 consecutive patients who underwent CABG between 1989 and 1999. Stroke patients were older, more frequently women, more likely to have diabetes, hypertension, congestive heart failure, recent myocardial infarct, previous stroke, carotid atherosclerosis, chronic renal insufficiency, an ejection fraction less than 34%, and unstable angina (see Table).

Operative variables also influenced stroke occurrence: significant atherosclerosis of the ascending aorta was more frequent in stroke patients (P = 0.005) and cross-clamp time was higher in stroke patients (46 ± 19 minutes) vs. nonstroke patients (42 ± 25 minutes, P < 0.001). Cardiopulmonary bypass time was significantly prolonged for stroke patients (77 ± 59 minutes) vs. non-stroke patients (67 ± 40 minutes, P < 0.001).

Among postoperative variables, new-onset atrial fibrillation and low cardiac output syndrome were associated with a higher risk of postoperative stroke (see Table).

Table
Independent Correlates of Stroke After CABG
Preoperative Variables Odds Ratio P

Chronic renal insufficiency 2.8 < 0.001
Recent myocardial infarct 2.5 0.01
Previous stroke 1.9 < 0.001
Carotid artery atherosclerosis 1.9 < 0.001
Hypertension 1.6 < 0.001
Diabetes 1.4 0.001
Age > 75 years 1.4 0.0008
Left ventricle dysfunction 1.3 0.01
 
Postoperative Variables

Low cardiac output 2.1 < 0.001
Atrial fibrillation 1.7 < 0.001

Twenty-one patients with carotid artery disease developed stroke after CABG. In 16 the stroke was ipsilateral and in 5 contralateral to the diseased carotid artery. Two patients had bilateral infarcts.

Patients who developed stroke after CABG had a significantly increased length of hospital stay and a 5-fold higher rate of in-hospital mortality than patients without stroke (14.4% vs 2.7%).

Commentary

As noted by Silver in his editorial comment, an estimated 650,000 CABG operations are performed in the United States each year. The incidence of clinical stroke postCABG is reported to be between 1% and 5% and was 2% in the article reviewed here; therefore, CABG surgery is the single largest cause of iatrogenic stroke in this country.

A recent study suggested that patients who undergo minimally invasive "off-pump or beating heart" bypass surgery have a lower risk for stroke and cognitive impairment (Bhashe Rao B, et al. J Card Surg. 1998; 13:27-31). The study of Stamou et al determined the occurrence of clinically obvious stroke and did not consider postoperative delirium and cognitive impairment that contribute to the considerable cerebral morbidity of CABG procedures. Nevertheless, this study is a benchmark against which the outcome of patients who have CABG without cardiopulmonary bypass must be compared. We must await evidence from a randomized comparison of the 2 surgical techniques before concluding that "off pump" CABG is better for the brain. —John J. Caronna