Research published this week in JACC Intervention shows the results of a clinical trial which studied patients admitted to hospital with STEMI type heart attacks. The patients were treated with primary PCI but also had a blood pressure cuff placed on their arm. In half the patients the cuff was inflated to 200mmHg pressure for 5 minutes then released for 5 minutes and this was repeated 3 times, in the other half the cuff was left un-inflated. The idea behind this intervention was to produce a phenomenon known as Remote Ischaemic Post-Conditioning. The trial results showed that cuff inflation reduced the amount of heart muscle damage based on troponin rise and measured by MR scans. The cuff inflation also reduced the amount of oedema or swelling in the heart.
There has been huge interest in developing drugs which might protect the heart during this reperfusion period but although many have shown promise in the laboratory this has not been translated into benefit when tested in patients. The only treatment to have crossed this translational canyon is one called ischaemic conditioning.
Nearly 30 years ago Murry et al. showed that four cycles of 5 minutes of coronary artery occlusion and 5 minute reperfusion protected the heart from a subsequent longer period of sustained occlusion. This effect was called ischaemic pre-conditioning. Although interesting it is difficult to see how it could be applied in clinical practice. Other studies later showed however that ischaemic conditioning could be delivered after the initial period of ischaemia and still be protective. This was called ischaemic post-conditioning and whilst not as potent as pre-conditioning the effect was still important.
A breakthrough came in 1993 it was shown that the ischaemic signal for this pre and post-conditioning did not need to be delivered at the site of the subsequent injury to be effective. So for example it was possible to make the arm or leg ischaemic and to protect the heart. This was called remote ischemic conditioning and it was this which led to the clinical trial described above.
Like many of these types of trials the numbers of patients and the size of the effect is small. It is more hypothesis generating that a game changer but it does pave the way for larger studies to investigate this effect.