Safety and Effectiveness of the Medtronic Resting Heart Bypass System in Heart Surgery Patients

Overview

The purpose of this study is to determine if the Medtronic Resting Heart Bypass system is safer and results in less inflammatory reaction than traditional bypass machines used in coronary artery bypass surgery. We hypothesize that the new Medtronic Resting Heart System is safer and results in much less systemic inflammatory reaction in comparison to the standard cardiopulmonary bypass systems currently in use.

Cardiopulmonary bypass (CPB) has played an extremely crucial role in coronary artery bypass grafting (CABG) surgery for the past five decades. During CABG, the CPB machine enables the surgeon to stop the heart and perform the surgery in a bloodless operating field. The CPB machine essentially takes over the job of the heart by oxygenating the blood and then perfusing the entire body. In patients undergoing CABG surgery with CPB, a systemic inflammatory reaction occurs when the blood is taken out of the body and circulated through the CPB machine. This inflammatory reaction is believed to increase postoperative morbidity and prolong hospital stay. The systemic inflammatory reaction results in activation of the complement, coagulation, fibrinolytic and kallikrein cascades, it activates leukocytes and endothelial cells causing expression of adhesion molecules and results in the release of inflammatory mediators such as cytokines. This inflammatory reaction during CPB leads to vasodilation, increased interstitial fluid and can affect organs such as the heart, lungs, brain and kidneys resulting in their dysfunction(s). Elimination of CPB in patients undergoing CABG surgery has resulted in reduction of this inflammatory response. Unfortunately, not all patients are able to undergo CABG without the use of CPB. Most conventional CPB systems also use cardiotomy suction which returns all the blood collected in the operative field back to the CPB reservoir and then eventually returns it to the patient. This blood is rich in inflammatory mediators and small particles because it has been activated by surgical trauma and by the proteins lining the wound cavity. Returning this blood back into the CPB circuit results in further circulation of inflammatory mediators. Removal of the cardiotomy suction from the CPB system could potentially decrease the inflammatory mediators and reduce the inflammatory response during CPB. Recently, there have been attempts to decrease the inflammatory reaction caused by the use of CPB by developing better, more effective systems. The Medtronic Resting Heart System is very similar to conventional CPB systems and has been approved for clinical use both in Canada and the United States. It has some potential advantages over traditional bypass machines which include; 1)a fully closed-to-air system that does not allow an air-blood interface which could prevent blood activation, 2)it does not have cardiotomy suction and therefore prevents air, lipids or particulate emboli from being re-introduced into the patient's circulation, 3)it minimizes hemodilution by using smaller and low-prime circuits, possibly decreasing the need for postoperative blood transfusion, 4)the CPB circuit, which is the blood-contacting surface, is coated with Carmeda Bioactive Surface (a heparin bioactive surface), that mimics critical characteristics of vascular endothelium and may prevent further blood activation, and 5)it has an active venous air detector and removal device (VARD) that detects venous air and automatically removes the air which may prevent blood activation. All of these elements are potential benefits which may further reduce the morbidity and inflammation associated with CABG surgery. Thus far to our knowledge, there have been no studies looking at the inflammatory reaction and morbidity in patients undergoing CABG procedures using more improved cardiopulmonary bypass machines. We are therefore proposing a prospective, randomized trial of the safety and effectiveness of the Medtronic Resting Heart system in CABG surgery.