Despite regional improvement in beta blocker usage, post-operative MI rate did not decrease, perhaps due to preoperative beta blocker doses that did not change heart rate, according to “unexpected” study results presented June 12 at the Society of Vascular Surgery (SVS) in Boston.
Brian W. Nolan, MD, from the vascular surgery department at Dartmouth-Hitchcock Medical Center, Lebanon, N.H. , and colleagues undertook the study to determine if a regional quality improvement effort can increase preoperative beta blocker usage and decrease post-operative MI rate.
An effort to increase beta blocker utilization was implemented in 2003 at 11 centers participating in the Vascular Study Group of New England. A 90 percent target was set and feedback given at bi-annual meetings.
The researchers prospectively collected data on beta blocker usage (less than one month, preoperative versus chronic rates) and post-operative MI rates among patients undergoing open abdominal aortic aneurysm (AAA) repair (926 patients) and lower extremity bypass (LEB) (2,123 patients) from 2003 through 2008. Predictors of post-operative MI were determined using multivariate logistic regression.
They also analyzed rates of beta blocker utilization and post-operative MI over time across strata of patient risk based on a multivariate model.
According to Nolan and colleagues, the overall beta blocker utilization was 86 percent (AAA 90 percent, LEB 84 percent), and in-hospital post-operative MI occurred in 5.5 percent of patients (AAA 7.6 percent, LEB 4.6 percent).
They also found that preoperative beta blocker usage increased in low risk and chronic beta blocker usage increased in medium- to high-risk patients, but post-operative MI rates did not change over time.
The researchers reported that for patients who were older than 70 (OR 2.1) positive stress test (OR 2.2), congestive heart failure (OR 1.7), chronic beta blocker (OR 1.7), resting heart rate were independent predictors of post-operative MI; and for patients younger than 70 (OR 1.8) and diabetes (OR 1.6) were independent predictors of post-operative MI. Resting heart rate was 67, 70, 70 for patients on chronic beta blocker, preoperative beta blocker and no beta blocker.
The authors concluded that negative impact of chronic beta blocker use on post-operative MI was “unexpected and requires further investigation.”