IMPACT OF MAMMARY GRAFTS ON CORONARY-BYPASS OPERATIVE MORTALITY AND MORBIDITY

The internal mammary artery is frequently used as a coronary artery by pass graft conduit because of superior long-term patency. The purpose of this study was to determine if there was also an advantage to the i nternal mammary artery in terms of operative mortality and morbidity. The Department of Veterans Affairs Cardiac Surgery Database was review ed for two separate time periods, April 1987 through March 1989 and Oc tober 1990 through September 1991. During these periods, 14,172 patien ts underwent coronary artery bypass grafting. Univariate and multivari ate logistic regression analyses were used to determine preoperative v ariables predictive of operative mortality and morbidity, with the ind ependent variable of use of the internal mammary artery added to previ ously determined indicators. The total group was analyzed in risk quar tiles according to expected mortality. Univariate analysis revealed an operative mortality of 6.8% in the early period and 6.5% in the latte r period for the saphenous vein groups compared with 3.7% and 3.2%, re spectively, for the internal mammary artery groups (p = 0.000). Multiv ariate analysis revealed an odds ratio of operative death with use of the internal mammary artery graft versus use of vein grafts of 0.78 du ring the first period and 0.72 during the second period, reductions of 22% and 28%, respectively. There were 29% and 37% reductions in the o dds of operative mortality in the highest-risk quartile group of patie nts using the internal mammary artery graft. The odds ratio of develop ing mediastinitis with one internal mammary artery graft was 1.84 (p < 0.01) in the first time period and 1.11 in the second time period (p = not significant). However, with multiple mammary bypass grafts, the odds ratios were 3.70 (p < 0.01) and 2.96 (p < 0.01) in the respective time periods. On the basis of this study, it is concluded that intern al mammary artery grafts in addition to providing superior long-term p atency also decreased operative mortality after adjustment for patient risk factors. Use of the mammary artery does not consistently increas e operative complications with the exception of mediastinitis when bot h internal mammary arteries are employed.