Optimal myocardial protection strategy for coronary artery bypass grafting without cardioplegia: prospective randomised trial

Although hypothermia and ischaemic preconditioning (IP) are independently recognised mechanisms of cardioprotection, interactions between myocardial temperature and preconditioning have not been investigated. Therefore, this study explored the possibility of inducing IP during hypothermia and quantifying its effects at two temperature regimens commonly used in clinical practice. One hundred and four patients undergoing coronary artery bypass grafting (CABG) with intermittent cross-clamping and ventricular fibrillation were randomised to four groups: N=normothermia (36.5+/-0.5 degrees C); NP=normothermia+preconditioning, H=hypothermia (31.5+/-0.5 degrees C), HP=hypothermia+preconditioning. The primary outcome measure was release of cardiac Troponin I (cTnI), measured at 6 time points from pre- to 72 h after the end of CPB. There were no hospital deaths and no significant differences in pre- and intra-operative variables (P>or=0.05). There were significant differences in cTnI release between all groups, as follows: N: 117+/-12 microg/l (P<or=0.05 vs. all groups), NP: 87+/-8 microg/l (P<or=0.05 vs. groups N and HP), H: 76+/-6 microg/l (P<or=0.05 vs. groups N and HP), HP: 44+/-6 microg/l (P<or=0.05 vs. all groups). In conclusion, IP can be induced at both normothermia and moderate hypothermia, where it significantly reduces myocardial damage. Further studies are warranted to investigate the effects of the addition of hypothermia to pharmacological myocardial preconditioning.