Postoperative atrial fibrillation (AF) is a common complication of heart surgery, affecting 20–40% of patients. In recent guidelines of the American Heart Association and the European Society of Cardiology, β blocker (BB) treatment has been recommended as a first line choice for the prevention of postoperative AF.1 Although the efficacy of re-administration of BB to post-cardiac surgery patients has been evaluated, the effectiveness of prophylactic BB in patients without prior BB treatment has not been adequately studied.
In order to evaluate whether preoperative BB use affects the outcome of prophylactic BB treatment after heart surgery, an analysis was performed using the data of the largest double blind, placebo controlled, randomised trial of prophylactic BB treatment (metoprolol) for reduction in hospital length of stay following heart surgery, known as the β blocker length of stay (BLOS) study.2
In the BLOS study 1000 patients undergoing elective open heart surgery were randomised equally to metoprolol (100–150 mg/day) or double blind placebo, started within 12 hours of arrival in the intensive care unit (ICU) after surgery. The patients were followed for postoperative AF, length of hospital stay, and cost of in-hospital care. A third party payer prospective (Ministry of Health of Canada) was chosen for the cost analysis; costs are quoted in Canadian dollars.
The central question this study addresses is: “Does the therapeutic effect of prophylactic metoprolol use differ according to preoperative BB usage?” Multiple linear regression was used for quantitative outcomes such as length of stay, and multiple logistic regression was used for discrete outcomes such as AF. Tests of interaction were done to assess whether the effect of treatment differed significantly between two different groups of patients. Fisher’s exact test and Student’s t test (both two sided) were used to compare baseline characteristics between the two preoperative BB usage groups.