Mesh-Covered Stent Results in More Complete ST-Segment Resolution in STEMI

October 29, 2012

MIAMI — A novel stent that also acts as an embolic-protection device resulted in more complete ST-segment resolution when compared with patients treated with a conventional bare-metal stent or drug-eluting stent (DES) [1].

The MGuard (InspireMD) device, a novel polyethylene micronet mesh-covered stent, is designed to trap and exclude thrombus, as well as atheromatous debris, that can result in distal embolization when physicians stent coronary lesions. The MASTER study, led by Dr Gregg Stone (Columbia University, New York) and presented during a morning press conference by Dr Sigmund Silber (Heart Center, Munich, Germany) at TCT 2012, included patients with ST-segment elevation MI (STEMI) treated at 50 clinical centers in nine countries.

"The STEMI patients have a lot of thrombus in the artery, and the problem is that sometimes the artery is occluded or very narrow, but it's not a stable lesion," Silber told heartwire . "It's highly thrombotic, so if you push a balloon through this thrombus you have a risk of dislocating the thrombus to the peripheral vessels. There's nothing you can do about it. Once you dislodge a thrombus and the thrombus goes downstream, there's no intervention to heal this. So you have to prevent it."

The MASTER investigators randomized 217 patients to the thin-strut MGuard stent and 216 to the control arm that included treatment with DES and bare-metal stents. In terms of the primary end point, 57.8% of patients who received the MGuard stent had complete ST-segment resolution compared with 44.7% of patients in the control arm, an absolute 13.2% difference that was statistically significant (p=0.008). In terms of clinical follow-up at 30 days, no patients treated with the MGuard stent died, compared with four patients in the control arm (p=0.06). There was no difference in other clinical events, including reinfarction, target lesion revascularization, stent thrombosis, stroke, or TIMI major or minor bleeding.

For a Difference to Be a Difference

In a magnetic resonance imaging (MRI) substudy, there was no reported difference between groups in terms of left ventricular myocardial mass, infarct size, or microvascular obstruction. Press conference moderator Dr Roxana Mehran (Mount Sinai School of Medicine, New York) said that that the MRI results, obtained at three to five days in 30 patients in each arm, are likely taken too early to determine the benefits of the MGuard stent, given that a large amount of edema surrounds the myocardial necrosis at this time. "The lack of a benefit at three to five days doesn't concern me personally," she said. "The ST-segment resolution is a good marker of mortality--we've shown that in the HORIZONS-AMI study--but we have to prove this in a mortality study."

Dr Bernard Gersh (Mayo Clinic, Rochester, MN), who was not involved in the MASTER trial, said that it is not yet known how much of a difference in ST-segment resolution between treatments is needed to translate into a clinical benefit. For example, is the 13.2% absolute difference between the MGuard stent and control stents sufficient to translate into a reduction in mortality? he asked. "For a difference to be a difference, there really has to be a difference," said Gersh. Silber said the "bigger the better," but he is confident about the MGuard stent, given that there was an observed trend toward improved mortality at 30 days.

For a difference to be a difference, there really has to be a difference

Speaking with the media, Silber said the study reiterates the importance of embolic protection in STEMI patients. The present device differs from distal embolic-protection devices, which have not been successful in preventing distal embolization during PCI of diseased vessels, as it does not cross the lesion to use an "umbrella" to catch fragmented thrombus. Instead, predilation with the device traps the thrombus and atheromatous debris before it is embolized downstream to the distal vasculature. "The major goal is not just to open the vessel to get a beautiful result," he said. "The point is, did you open the artery without any embolic events in the periphery?"

Silber said that he hopes another study will be performed to address hard clinical outcomes, but as of yet no study is planned, given the small size of the company and costs of such a trial. During the TCT presentation, Stone said that he would like to see the result confirmed in a larger clinical trial, as well as a large morbidity and mortality trial, but if the ST-segment-resolution improvements are validated in other trials, he would consider such an stent/embolic protection device worthy of use in clinical practice.

Stone is a consultant to Boston Scientific, Abbott Vascular, Medtronic, InspireMD, Atrium, Eli Lilly, and Daiichi Sankyo. Silber has received research grants from InspireMD.