Columns, Patient Care

Remote Ischemic Conditioning Helps STEMI Patient Outcomes

Issue 11 and Volume 39.

The Research
Sloth AD, Scmidt MR, Munk K, et al. Improved long-term clinical outcomes in patients with ST-elevation myocardial infarction undergoing remote ischaemic conditioning as an adjunct to primary percutaneous coronary intervention. Eur Heart J. 2014;35(3):168–175.

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The Science
Before describing this study, let’s review what remote ischemic conditioning (RIC) is. It’s obtained by applying a blood pressure cuff to either arm in a patient experiencing a myocardial infarction and pumping it up to 200 mmHg and leaving it there for five minutes. The cuff is deflated to zero and left for five minutes. This procedure is repeated three more times.

This study is a follow-up of the authors’ parent study that demonstrated that RIC significantly reduced the size of a myocardial infarction.

Patients identified by EMS as having an ST elevation myorcardial infarction (STEMI) were randomized to have RIC plus percutaneous coronary intervention (PCI) or PCI alone (control group). The study examined 333 patients.

Using a national database that provides all citizens a unique identifier, the authors determined the rate of major adverse cardiovascular and cerebrovascular events (MACCE) over a five-year period.

MACCE occurred in 17 (13.5 %) patients in the RIC + PCI group and in 32 (25.6%) patients in the control group. All-cause mortality was reduced in the RIC + PCI group compared with the control group (5 deaths [4.0%] vs. 15 deaths [12.0%]).

The authors concluded, “RIC before primary percutaneous coronary intervention seemed to improve long-term clinical outcomes in patients with STEMI.”

Doc Keith Wesley Comments
I must admit that when I read this study I simply couldn’t believe the results. So, I pulled a dozen papers dating back as far as 1997 and educated myself.

During organ ischemia, the cells move into anaerobic metabolism and major disruptions in membrane permeability make the cell extremely vulnerable to circulating toxins. When perfusion to the organ is reestablished, these injured cells lack their normal protective mechanisms to filter out toxins. This reperfusion injury results in the death of a larger number of cells.

An ischemic organ initially releases a whole host of chemicals to improve cellular integrity. They include adenosine, bradykinin, nitric oxide and many others. It’s been demonstrated that inducing ischemia in an organ near the organ of concern results in an increased concentration of these protective chemicals in the bloodstream and a reduction in the reperfusion injury.

So, that explains how an adjacent organ can help the organ become reperfused, but how does cycling a blood pressure cuff on the arm accomplish the same thing?

It appears the ischemia doesn’t have to be near the organ of concern. This 20-minute period of ischemia in the arm results in the same release of protective chemicals as well as other reflex pathways that condition the ischemic heart muscle to the oncoming reperfusion.

Frankly, this is amazing! A procedure that’s noninvasive and free, yet can significantly reduce myocardial infarct size and long-term mortality and morbidity? It’ll never fly!

Oh wait, I envision new ads for auto-cycling blood pressure cuffs for an introductory price of $2,500. There may be hope after all.

Medic Karen Wesley Comments
The “amazing human machine” again puts me in a state of awe. I was more interested in the process of homeostasis demonstrated by this study than I was in the use of cycling a blood pressure cuff.

There are several old and very odd treatments still used in medicine today, and most don’t have a prehospital indication. This technique does apply to street medicine, and I believe more research is needed to determine its success in a larger patient group.

With EMS and cardiac centers working closely to identify and treat STEMI patients, this is something that, along with early notification and 12 leads, could be coordinated for patients meeting the criteria.

As Doc stated, not every effective procedure needs to have a price tag. Anything we can do to mimic the natural homeostatic response of our bodies during the insult of medical and traumatic emergencies should be targeted.

Again Doc, thanks for the physiology lesson you brought forth. That knowledge for providers is likely as valuable as the study itself.