LONDON -- Ischemia from three five-minute squeezes of the right upper arm just before an elective coronary artery bypass graft may help stave off myocardial injury, suggested investigators here.
LONDON, Aug. 17 -- Ischemia from three five-minute squeezes of the right upper arm just before an elective coronary artery bypass graft may help stave off myocardial injury, suggested investigators here.
In the study of 57 CABG patients, the 27 who received ischemic preconditioning showed significant reductions in levels of troponin T, starting six hours after CABG compared with the 30 controls, reported Derek J. Hausenloy, Ph.D., of University College London Hospital, and colleagues, in the Aug. 18, issue of The Lancet
The protocol in the proof-of-concept study consisted of three five-minute cycles of ischemia induced by an automated cuff-inflator placed on the right upper arm and inflated to 200 mm Hg. After each cycle, the cuff the cuff was deflated for five minutes.
By contrast, controls had a deflated cuff placed on their right arm for 30 minutes. The ischemic preconditioning was applied following anesthesia and before CABG.
Levels of troponin T were measured before surgery and six, 12, 24, 48, and 72 hours following surgery. Baseline concentrations of troponin T were less than 0.01 ug/L before surgery in both groups.
Total troponin T levels released 72 hours after surgery were reduced from 36.12 ug/l (SD 26.08) in the control group to 20.58 ug/l (SD 9.58) in the group that received the preconditioning.
This equated to a mean difference of 15.55 ([SD 5.32];95% CI 4.88-26.21; P=0.005). The total area under the curve was reduced by 43%, the study showed. This reduction first became significant at six hours. None of the patients were taking drugs that could have aped or inhibited the ischemic preconditioning.
Exactly how restricting blood flow to the arm protects the myocardium during CABG is not clear, but researchers suspect that it is mediated through either a humoral or hormonal factor such as adenosine, bradykinin or opioids or perhaps the recruitment of a neuronal pathway.
Now the researchers are conducting a trial looking at whether the same preconditioning protocol may benefit patients receiving only cardioplegia during the time of their CABG surgery.
In an accompanying commentary, Henry Purcell, M.D., and John Pepper, M.D., of Royal Brampton Hospital in London, pointed out that the study attempts to answer a "provocative and appealing question," but left some questions and there were caveats.
Namely, there is no information on how the conditioning would affect C-reactive protein or other inflammatory markers. They also noted that it is not possible to infer that a reduction in concentration of troponin T would lead to short term or long term reduction in cardiovascular events. In addition, the study was conducted in a single tertiary care center, and the patients were undergoing elective CABG.
The findings need to be replicated by other doctors in other institutions on larger numbers of patients, but "if intermittent limb occlusions are consistently shown to reduce myocardial injury during cardiac revascularization, the implications for practice are immense," they wrote.