No evidence of benefit from distal embolic protection in acute MI: EMERALD published

March 01, 2005

New York The results of the Enhanced Myocardial Efficacy and Recovery by Aspiration of Liberated Debris (EMERALD) study are now published in the March 2, 2005 issue of the Journal of the American Medical Association and show that distal embolic protection with a balloon-occlusion and aspiration device (GuardWire Plus, Medtronic, Santa Rosa, CA) failed to improve microvascular flow and reperfusion success, reduce infarct size, or enhance event-free survival in acute-MI patients undergoing primary PCI.[1]

"I think this study teaches us a lot about the pathophysiology of acute MI," Dr Gregg W Stone (Colombia University Medical Center, New York, NY) told heart wire . "We can't make any assumptions, and we can never practice anecdotal medicine. Major questions, theories, and hypotheses need to be tested in appropriately designed prospective randomized trials, such as EMERALD, and the results of these studies should guide our thinking. Before this study, we were doing a lot of distal protection in acute MI, and now we're not anymore. I think we should be pleased that we conducted a very good, well-run study that showed that this therapy, while it is safe and didn't do any harm, was just not effective."

I think we should be pleased that we conducted a very good, well-run study that showed that this therapy, while it is safe and didn't do any harm, was just not effective.

In an editorial accompanying the published study, Drs Albert Schömig and Adnan Kastrati (Deutsches Herzzentrum, Munich, Germany) echo that sentiment. They credit the EMERALD investigators for the first randomized trial of the usefulness of distal protection during PCI in acute-MI patients but agree the results do not lend support to the use of distal embolic protection in this setting.[2]

"They [the results] show, in addition, that neither the attractiveness of the therapeutic concept nor the enthusiasm generated by observations from a limited number of patients can replace the need for well-designed randomized clinical trials before advocating the widespread application of new technology," write the editorialists.

Attractive concept but no benefit

The EMERALD trial was a multicenter, prospective, randomized study designed to measure infarct size five to 14 days after primary angioplasty in 501 acute-MI patients randomized to distal protection and PCI or PCI without embolic protection. Investigators also sought to compare the incidence of complete ST-segment resolution between the two study arms. Secondary end points included frequency of grade-3 myocardial blush and 30-day major adverse cardiac events (MACE).

Investigators effectively removed atherothrombotic debris in 73% of patients using the distal-embolic-protection device. However, removal of debris did not have any significant effect on the primary end points. Complete ST-segment resolution was achieved in a similar proportion of patients reperfused with and without the protection device. Left ventricular infarct size was similar in both groups. There were no significant differences between study arms in the frequency of myocardial blush, and there was no improvement in event-free survival for those treated with embolic protection.

Stone told heart wire that he was surprised by the results. While the EMERALD investigators posited numerous theories as to why distal microcirculatory protection failed in this studyincluding a slightly prolonged time to reperfusion with the devicehe said he suspects the intervention may be "too little, too late." He said embolic-protection devices might not be able to achieve meaningful myocardial salvage in a disease characterized by inflammation and endothelial dysfunction, capillary leakage, and reperfusion injury.

Commenting on the results for heart wire , Dr Jay Yadav (Cleveland Clinic, OH) said that he thinks the conclusions reached by the investigators may be too broad. Instead of "throwing the baby out with the bathwater," Yadav said he suspects the problem may be specific to the device, as distal-balloon-occlusion devices fail to protect side branches from dislodged emboli.

"This is a good device, but it has certain performance characteristics," he said. "It was developed for use in the carotid artery where there are no side branches. The carotid artery is like a saphenous vein graft; it also has no branches. You can put the distal-balloon-occlusion device anywhere in those segments and you're protecting all of the runoff. But when you get into the coronaries, this is not the case. There are lots of branches, particularly in the LAD [left anterior descending artery]."

Yadav pointed out that in the Saphenous Vein GraftAngioplasty Free of EmboliRandomized (SAFER) trial, the use of distal-balloon-occlusion protection was effective and associated with a 42% relative reduction in MACE.[3]

In their paper, the EMERALD investigators note that despite the visible debris extracted from 73% of patients, embolization may still have occurred at the time of lesion crossing or debris may have moved into unprotected proximal side branches. They report, however, that there was no angiographically apparent increase in side-branch occlusion in the embolic-protection group.

Editorialists look for convincing explanations, too

In the editorial, Schömig and Kastrati question whether a filter-based protection device might be more effective. Yadav told heart wire that he believes that while a filter would not catch all the emboli, the device would not shunt blood directly into the proximal vessels and would be more effective than a balloon-occlusion device in the coronary arteries. Proximal-balloon-occlusion devices might be another option in embolic protection, he said.

I think a key concept to remember is that we are going to need embolic protection devices for specific organs and anatomies.

"Newer embolic-protection devices are being developed specifically for the coronary arteries. I think a key concept to remember is that we are going to need embolic protection devices for specific organs and anatomies," said Yadav. "It doesn't make sense to generalize to every territory, which is what has been done here with this early technology."

Schömig and Kastrati also attempt to reconcile the lack of efficacy in the distal-protection strategy. They write that vessel occlusion and aspiration of emboli may not have been complete and also note that the device is not able to impede soluble mediators. Like Yadav, they also point out that the time to treatment is likely not a factor, as there was no benefit seen even in patients treated within one hour after symptom onset.

"The difficulty in finding convincing explanations for the lack of efficacy of the distal-protection strategy used in the EMERALD trial may simply imply that both the relevance and nature of the mechanisms interfering with microcirculatory function in AMI need to be reassessed," they conclude.

Medtronic Corp funded the EMERALD study. Lead investigator Stone has served as a financial consultant to Medtronic Corp. Yadav is the inventor of the Angioguard, a guidewire-based, filter-type embolic-protection device. Yadav was a shareholder in Angioguard at the time of its purchase by Johnson & Johnson in 1999 but no longer owns any shares of stock in Johnson & Johnson.


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