Dislodgement of atheromatous (an abnormal fatty deposit in an artery) and thrombotic (blood clot) material ("debris") during percutaneous coronary intervention (PCI) following a heart attack is common. This debris may travel to more distal smaller vessels (beyond the site of arterial blockage) and may result in microcirculatory dysfunction. Prevention of this "distal embolization" may improve reperfusion success, reduce the damage caused by a blocked artery, and enhance event-free survival.
A procedure commonly used with PCI involves use of a specialized guidewire and catheter device to collect liberated embolic debris in the artery. Pilot studies and small randomized trials have demonstrated that distal (situated beyond the point in the obstructed artery) protection of the microcirculation during primary PCI retrieves embolic debris in most patients and may result in greater rates of normal blood flow, improved left ventricular function, and enhanced event-free survival compared with controls.
Gregg W. Stone, M.D., of Columbia University Medical Center and Cardiovascular Research Foundation, New York, and colleagues performed a clinical trial to evaluate the usefulness of distal microcirculatory protection during mechanical reperfusion therapy in acute myocardial infarction (AMI). The randomized controlled trial was conducted at 38 academic and community-based institutions in 7 countries, enrolling 501 patients aged 18 years or older with ST-segment elevation myocardial infarction (STEMI) presenting within 6 hours of symptom onset and undergoing primary PCI or rescue intervention after failed thrombolysis.
The patients were randomized between May 20, 2002, and November 21, 2003 to receive PCI with a balloon occlusion and aspiration (removal by suction of dislodged debris) distal microcirculatory protection system vs. angioplasty without distal protection.
Among 252 patients assigned to the distal protection group, aspiration was performed in 97 percent (242/251), all angioplasty balloon inflations were fully protected in 79 percent (193/245), and visible debris was retrieved from 73 percent (182/250). Complete ST-segment resolution (STR) was achieved in a similar proportion reperfused with vs. without the distal protection device (63.3 percent vs. 61.9 percent, respectively; and left ventricular infarct size was similar in both groups. Major adverse cardiac events at six months occurred with similar frequency in the distal protection group and in the control group.
"We did not identify clinical usefulness of distal microcirculatory protection in AMI, and its routine use in patients undergoing mechanical reperfusion therapy cannot be recommended.
Multiple explanations may be proposed as to why distal microcirculatory protection failed to enhance myocardial reperfusion success, reduce infarct size, or improve clinical outcomes in the present trial. First, the device may not have been efficient enough in aspirating liberated atherothrombotic debris," the authors write. "Second, the additional median 21-minute delay to angioplasty in the distal protection group or the several extra minutes of additional balloon occlusion may have increased infarct size and worsened clinical outcomes, offsetting the potential benefit of emboli removal, though most prior studies have suggested that this degree of delay at a median reperfusion time of 3.6 hours would be unlikely to affect myocardial salvage or survival."
(JAMA. 2005;293:1063-1072. Available post-embargo at JAMA.com)
Editor's Note: This study was funded by Medtronic Corp, Santa Rosa, Calif. Dr. Stone has served as a consultant for Medtronic Inc; co-authors Drs. Kalynych and Dulas own stock in Medtronic; and co-author Dr. Lansky has received research support from Medtronic. No other authors reported financial disclosures.
Editorial: Distal Embolic Protection in Patients With Acute Myocardial Infarction - Attractive Concept But No Evidence of Benefit
In an accompanying editorial, Albert Schömig, M.D., and Adnan Kastrati, M.D., of Technische Universität, Munich, Germany, discuss the findings by Stone et al.
"Numerous explanations may be given for the surprising lack of efficacy of the distal protection device used in this study. Placement of the protection device and inflation of the distal occlusion balloon prolonged the time to reperfusion, thus having the potential to abrogate the beneficial effects of rapid mechanical revascularization. The device itself could have led to embolization during the attempts to cross the thrombotic lesion or by contact with less severely diseased portions of the infarct-related vessel or its side branches. Vessel occlusion or aspiration of embolizing material may not have been complete; also, the protection device is not able to impede the release of soluble mediators."
"The difficulty in finding convincing explanations for the lack of efficacy of the distal protection strategy used in the [Stone et al] trial may simply imply that both the relevance and the nature of the mechanisms interfering with microcirculatory function in AMI need to be reassessed," the editorialists write. "Stone and colleagues deserve credit for having conducted the first randomized trial of the usefulness of distal protection devices during PCI in patients with AMI. The results of this well-designed trial do not lend support to the use of these devices in this setting. They 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 technologies."
(JAMA. 2005;293:1116-1118. Available post-embargo at JAMA.com)