Coronary artery bypass grafting for unstable angina pectoris: risk analysis

Unstable angina pectoris is a broad, nonspecific diagnosis encompassing a wide variety of clinical syndromes. The intravenous administration of nitroglycerin preoperatively is indicative of a more acute clinical situation, and allows for selection and analysis of a more homogeneous patient population. We reviewed the results of coronary artery bypass grafting for unstable angina defined as angina necessitating intravenous administration of nitroglycerin preoperatively. There were 129 patients (83 men and 46 women) with a mean age of 63.2 years (range, 36 to 86 years). Complications included operative death in 6.2%, postoperative low cardiac output in 11%, and perioperative myocardial infarction in 9%. Twenty perioperative variables were analyzed to identify risk factors for these end points. For operative death, age (p less than 0.05), cross-clamp time (p less than 0.05), and cardiopulmonary bypass time (p less than 0.001) were significant in the univariate analysis, but only age (p less than 0.05, F = 4.6) was an independent predictor using multivariate analysis (stepwise linear regression). For low cardiac output, univariate analysis demonstrated that cross-clamp time (p less than 0.01), preoperative use of an intraaortic balloon for angina (p less than 0.05), left ventricular score (p less than 0.05), number of diseased coronary vessels (p less than 0.05), and cardiopulmonary bypass time (p less than 0.001) were significant variables. However, only use of an intraaortic balloon for angina (p less than 0.0001, F = 14.3) and left ventricular score (p less than 0.005, F = 11.1) were significant independent predictors in the multivariate model. For perioperative myocardial infarction, only diabetes requiring insulin (p less than 0.005) was a significant predictor.