Effect of Remote Ischemic Preconditioning in Patient Undergoing Cardiac Bypass Surgery

Overview

During coronary artery bypass graft surgery, injury occurs to the heart muscle. Some of this injury is due to the deprivation of oxygen and nutrients to the heart (a process called ischemia) during the surgery itself. The objective of this study is to examine whether remote ischaemic preconditioning (RIPC), in which the application of transient ischemia to the forearm and thigh (through the inflation of blood pressure cuffs placed on the right upper arm and upper thigh) may reduce the injury to the heart muscle sustained during cardiac surgery. The study hypothesis is: remote ischemic preconditioning will protect the heart and improve short-term clinical outcomes during coronary artery bypass graft surgery.

Ischemic heart disease (IHD) is currently the leading cause of morbidity and mortality in the developed world, and is set to become the leading cause of death in the world by the year 2020, according to the World Health Organisation. Patients with severe IHD that require coronary artery bypass graft (CABG) surgery, although protected by techniques such as cross-clamp fibrillation and cardioplegia, still sustain significant myocardial injury as evidenced by perioperative troponin T or I or CK-MB release. Novel treatment strategies are required to limit the myocardial injury sustained by patients undergoing CABG surgery in order to improve the clinical outcomes of this patient group. One such cardioprotective strategy is remote ischemic preconditioning(RIPC) which describes the cardioprotection obtained from inducing ischemia in tissue or an organ remote from the heart. Our laboratory and others have established RIPC using forearm ischemia (induced by an automated cuff applied to the upper arm) as an effective cardioprotective intervention in children undergoing corrective cardiac surgery for congenital heart disease and in adults undergoing CABG surgery. In this study we investigate whether simultaneous inflation/deflation of cuffs placed on the upper arm and thigh can reduce peri-operative myocardial injury and improve short-term outcomes in patients undergoing CABG surgery. Eligible patients will be those patients undergoing elective CABG surgery who are \>18 years old, with no significant renal or hepatic disease, and have not had a recent AMI (within 1 month). Consented patients will randomized to RIPC treatment or control.The RIPC protocol will comprise simultaneous 2 x 5 minutes of forearm and lower leg ischemia (with an automated pressure cuff inflated to 200 mmHg) with an intervening 5 minutes of reperfusion (during which the cuff is deflated) between each inflation. The control protocol will comprise a deflated cuff being placed on the upper arm and thigh for 20 minutes. The RIPC protocol will be implemented after the patients have been anesthetized and immediately prior to CABG surgery. The measured endpoint of cardioprotection will be troponin-T release at 0, 12, 24, 48 and 72 hours following CABG surgery.