Coronary artery bypass grafting, known in the medical parlance as 'CABG,' is often a very big operation but one with lifesaving potential for folks who have lengthy and/or multiple blockages of their coronary arteries, which supply the heart muscle itself. Since its inception some 50+ years ago, various modifications of CABG have been developed and attempted, including so called 'off-pump' surgery, where the heart isn't stopped to allow the new vessels to be sewn in place. Now comes a novel idea, at least to me, that Rick and I discuss on PodMed this week: remote ischemic preconditioning prior to CABG, as appears in the Lancet.
So what in the world is remote ischemic preconditioning? Remote refers to a body part far from the heart, ischemic refers of course to drastically reducing the blood supply to that body part, and preconditioning is undertaking this strategy prior to the CABG operation. In this study 329 patients who were scheduled to undergo first-time, elective cardiac bypass surgery of three vessels were randomized to remote ischemic preconditioning or not. Those who underwent preconditioning received three consecutive inflations of a blood pressure cuff in the left upper extremity for five minutes duration, followed by five minutes of reperfusion, where the cuff was deflated and blood allowed back into the arm. These cycles took place after anesthesia induction.
The main outcome measure was cardiac troponin, an indicator of heart muscle damage, in the first 72 hours after surgery. Mortality differences between the two groups were also compared. Cardiac troponin measured an average of 266 ng/ml in the treated group versus 321 ng/ml in the control group. The difference persisted and reductions in all-cause mortality were also seen at the conclusion of 4 years of follow-up. The authors conclude that this is a promising and simple means of potentially improving outcomes for people who elect to undergo on-pump CABG, and that since this is an increasingly challenging population, often with multiple comorbidities, clearly deserving of further study. They do offer the caveat that propofol should not be used as an anesthetic agent since it appears to abrogate the benefits of ischemic preconditioning. Well.
What is the possible mechanism whereby ischemia induced in the arm would benefit damage to the heart muscle during bypass surgery? For the nerds among us, it turns out that the technique was pioneered in 1986 in dogs by Murray et al, where the observation of a cardioprotective effect with regard to infarct size was made in dogs subjected to ischemia prior to occlusion of a coronary artery. The exact mechanism(s) are still not understood. I'd still like to know who made the original observation, since as Rick opines, they're looking pretty smart right now.
Other topics this week include insoles for knee osteoarthritis in JAMA, the low risk ankle rule in the Canadian Medical Association Journal, and overcoming one's genetic risk for diabetes with diet in Diabetes Care . Until next week, y'all live well.