Perioperative Intra-Aortic Balloon Pump (IABP) in Coronary Artery Bypass Grafting (CABG) Operations in Patients With Severely Depressed Left Ventricular Function

Overview

Since its first introduction in humans in 1962, Intra-Aortic Balloon Pump (IABP) is now the most commonly used therapeutic option to support failing heart in cardiac surgery. The main effects of IABP are an increase in diastolic blood pressure and therefore an improvement in coronary perfusion and a reduction of ventricular after load, thus increasing stroke volume and cardiac output. IABP-related complications include limb ischemia, bleeding at the site of IABP insertion, infection, and aortic dissection. IABP could be used preoperatively, intraoperatively, or postoperatively. However, despite the wide use of the device, the optimal timing and use of IABP in high-risk patients undergoing cardiac surgery remains controversial. Time of insertion has been showed to affect hospital mortality, ranging from 18.8% to 19.6% for preoperative insertion, from 27.6% to 32.3% for intraoperative insertion, and from 39% to 40.5% for postoperative insertion. Several studies, randomized and non-randomized, have been conducted to address the impact of preoperative use of IABP on the outcome, each study including a relative small number of patients. In an effort to increase the strength of the results, two meta-analysis have been conducted and published in 2008. The objectives of both were to assess the effect on mortality and morbidity of using IABP preoperatively in high-risk patients undergoing coronary artery bypass grafting (CABG). Surprisingly, the meta-analysis from Field and co-workers was conducted on four randomized controlled trials (for a total of 193 patients included) published by the same author from the same institution, making the results not conclusive although favourable toward a beneficial effect of the preoperative use of IABP. Moreover, two of the randomized trials conducted by Christenson and co-workers and included in the above mentioned meta-analysis, were excluded from the meta-analysis from Dyub and co-workers because considered duplicates. Unfortunately, one study by Christenson and co-workers and included in the meta-analysis from Dyub was conducted on off-pump surgery, introducing another bias in the criteria of eligibility. At present it is unclear whether the preoperative use of IABP in high-risk coronary patients scheduled for CABG operations leads to a better outcome. The experimental hypothesis of the present randomized, controlled trial (RCT) is that the placement of IABP immediately before beginning the surgical procedure induces a reduction of major morbidity after the operation.

RCT including patients scheduled for elective CABG surgery (with or without associated procedures) and having a left ventricular ejection fraction \< 0.35. Exclusion criteria: age \< 18 years, no patient's consent, contra-indications to the use of IABP (severe peripheral arteropathy; endovascular abdominal aortic prostheses). Patients will be randomly allocated to either a control group or a treatment group. Patients in the control group will not receive an IABP preoperatively, and patients in the treatment arm will receive an IABP positioned immediately after the induction of anesthesia and before beginning surgery. Randomization will be performed the day before the operation. Primary endpoint: reduction of major morbidity rate (defined as either prolonged (\> 48 hours) mechanical ventilation, acute renal failure, mediastinitis, surgical revision, stroke). Secondary endpoint: reduction in inotropic drug use, shortening of mechanical ventilation and ICU stay. Interim analyses and stopping rules: interim analyses will be done at half (80 patients)and 2/3 (106 patients) of recruitment. The trial could be prematurely stopped in case of a difference in the primary endpoint reaching a P value of 0.005 at the first analysis, and 0.01 at the second.A specific stopping rule is settled for operative mortality (30 days) at 0.01 at the first interim analysis and 0.05 at the second interim analysis. Given the invasive nature and the costs of the intervention, a stopping rule for futility was settled in case of a lack of difference for the primary outcome. This was settled at a relative risk for the primary outcome not including the hypothesized value of 0.5 within 99% CI at the first interim analysis and 95% CI at the second.