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Review
The Role of Percutaneous Thrombectomy in the Contemporary Treatment of Acute Myocardial Infarction
September 2004
The following special CME section is underwritten through an educational grant from Possis Medical, Inc.
Learning objectives. At the conclusion of this activity, the participant should be able to: 1) describe the impact of thrombus on percutaneous coronary revascularization during acute myocardial infarction; 2) discuss various clinical tools available for the assessment of myocardial reperfusion; and 3) describe the current data on the use of mechanical thrombectomy in acute myocardial infarction.
Activity instructions. Successful completion of this activity entails reading the article, answering the test questions and obtaining a score of over 70%, and submitting the test and completed evaluation form to the address listed on the form. Tests will be accepted until the expiration date listed below. A certificate of completion will be mailed to you within 60 days.
Estimated time to complete this activity: 1 hour
Initial release date: September 30, 2004 Expiration date: September 30, 2005
Target audience. This educational activity is designed for cardiologists, nurses and cardiovascular technologists.
Accreditation statements. Physicians: This activity is sponsored by the North American Center for Continuing Medical Education (NACCME). NACCME is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. NACCME designates this continuing medical education activity for a maximum of 1 category 1 credits toward the AMA Physician’s Recognition Award. Each physician should claim only those credits that he/she actually spent in the educational activity.This activity has been planned and produced in accordance with the ACCME Essential Areas and Policies. The American Medical Association has determined that non-US licensed physicians who participate in this CME activity are eligible for AMA PRA category 1 credit.
Nurses: The North American Center for Continuing Medical Education is an approved provider of continuing nursing education by the Pennsylvania State Nurses Association, an accredited approver by the American Nurses Credentialing Center’s Commission on Accreditation. This continuing nursing education activity was approved for 1 contact hour(s).
Provider approved by the California Board of Registered Nursing (Provider Number 13255) for 1 contact hours.
ASRT. Radiologic Technologists: Activities approved by the American Medical Association (AMA Category 1) are eligible for ARRT Category B credit as long as they are relevant to the radiologic sciences. Radiologic Technologists, registered by the ARRT, may claim up to 12 Category B credits per biennium.
SICP. This activity is approved for 1 contact hour by the Society of Invasive Cardiovascular Professionals.
Commercial support disclosure. This educational activity has been supported by an educational grant from Possis Medical, Inc.
Faculty disclosure information. All faculty participating in Continuing Medical Education programs sponsored by The North American Center for Continuing Medical Education are expected to disclose to the meeting audience any real or apparent conflict(s) of interest related to the content of their presentation. Dr. Ali discloses he is a member of the speakers’ bureau and has received a research grant from Possis Medical, Inc. Dr. Schreiber has no real or apparent conflicts of interest.
This article contains discussion of published and/or investigational uses of agents that are not indicated by the FDA. Neither North American Center for Continuing Medical Education nor Possis Medical, Inc. recommends the use of any agent outside of the labeled indications. Please refer to the official prescribing information for each product for discussion of approved indications, contraindications and warnings.
Introduction
Atherosclerotic coronary plaque rupture with superimposed thorombosis is responsible for vessel occlusion in acute myocardial infarction (AMI). Rapid restoration of normal antegrade coronary flow is associated with better preservation of myocardial function and improves long-term prognosis.1
Although early reperfusion can be accomplished with pharmacologic thrombolysis, percutaneous transluminal coronary angioplasty (PTCA) and stenting are associated with higher reperfusion rates than pharmacological therapy.2 However, primary percutaneous coronary intervention (PCI) carry higher risk of reocclusion, recurrent infarction, and restenosis compared with elective angioplasty.3-5 The presence of thrombus in acute MI is recognized as a major predictor of these complications.6,7
Arterial patency and restoration of normal epicardial (Thrombolysis In Myocardial Infarction [TIMI] flow grade 3) flow has served as the gold standard to assess the success of reperfusion therapy. Recently the focus has shifted downstream from epicardial flow. Studies have demonstrated that despite achieving TIMI flow grade 3 in majority of AMI patients, reduced myocardial perfusion is often documented.8-12 Various modalities available for the assessment of myocardial perfusion are shown in Table 1.
Given the risk associated with the presence of coronary thrombus, intense efforts have been focused on developing pharmacological and mechanical strategies to enhance the clinical success of primary PCI. Although the beneficial role of glycoprotein IIb/IIIa receptor antagonists in elective PCI has been established, there is only a modest amount of data supporting the use of intravenous GP IIb/IIIa receptor inhibitors as supportive antiplatelet therapy in patients undergoing primary PCI.13-15
Mechanical thrombectomy with various devices has shown promising results in thrombus reduction prior to definitive PCI. Another evolving strategy involved use of distal embolic protection devices to reduce procedural complication in high risk thrombotic lesions. The purpose of this review is to describe the use of mechanical thrombectomy in the treatment of AMI.
Mechanical Thrombectomy. Several devices have been developed for mechanical thrombectomy. These include transluminal extraction atherectomy (TEC catheter, Interventional Technologies, San Diego, Calif.); AngioJet rheolytic thrombectomy (Possis Medical, Minneapolis, Minn.) and the X-sizer catheter system (EndiCOR Medical Inc, San Clemente, Calif.). All these devices aspirate and actively remove thrombus. Another device, the Acolysis® Ultrasound Thrombolysis System (Vascular Solutions, Inc., Minneapolis, Minn.) is designed to disrupt and disintegrate thrombus. Rheolytic thrombectomy is the only FDA-approved thrombectomy system available in the U.S. for coronary and peripheral use.
Table 1. Clinical modalities available to assess myocardial perfusion
1. TIMI flow grade and frame count
2. TIMI myocardial perfusion (TMP) grade
3. ST-segment resolution on 12-lead EKG
4. Doppler coronary flow velocity & flow reserve (CFV)
5. Nuclear myocardial perfusion imaging
6. Myocardial contrast Echocardiography.
Rheolytic Thrombectomy. AngioJet rheolytic thrombectomy (RT) is a catheter-based method for thrombus removal. The catheter is attached to a drive unit with a piston pump that generates a high-pressure pulsed flow rate of 10,000 psi at 60 cc/min through a hypotube. The hypotube ejects its saline at a loop in the catheter tip. The jets of high-velocity saline are directed back into an exhaust lumen. This creates a vortex, or Venturi effect tip (Bernoulli effect) that fragments and aspirates thrombus and loose debris (Figure 1). Transient bradycardia develops with RT catheter activation, particularly in right coronary or dominant circumflex lesions, and a right ventricular temporary pacemaker is recommended. The bradycardia is thought to be caused by the active release of adenosine from hemolyzed red cells. Transient ST elevation noted on the electrocardiogram during pump activation is usually due to the release of potassium from red cells, and not active ischemia.16
A variety of RT catheters are available for clinical use in large and small native coronary vessels (XMI®), large SVGs (XVG®), and peripheral arteries(Xpeedior®).The coronary catheter is deliverable through 6 French (Fr) guiding systems, and is associated with no evidence of perforation in vessels > 2.0 mm in size.
In the Vein Graft Angio-Jet Study (VeGAS-2) trial, 350 patients were randomized to RTC versus a urokinase infusion for additional 6 to 30 hours. The study showed less bleeding, myocardial infarctions (mostly NSTEMI 12% vs. 25%, p 17 Silva et al. reported the use of RT in 70 patients with AMI (16% with cardiogenic shock) and with angiographically evident thrombus who were treated with AngioJet rheolytic thrombectomy followed by immediate definitive treatment. Procedure success (residual diameter stenosis = 2 after final treatment) was achieved in 93.8%. Clinical success (procedure success without major in-hospital cardiac events) was achieved in 87.5%, with an in-hospital mortality rate of 7.1%. Final TIMI 3 flow was achieved in 87.7%.18
In another small series of 19 patients with cardiogenic shock treated with RT, procedure success (final diameter stenosis or = 2) was achieved in 95%, with final TIMI 3 flow in 89%. Clinical success (procedure success without major in-hospital cardiac events) was achieved in 68%.19 We compared the outcome of 97 patients undergoing RT for AMI with 88 patients treated with standard PCI at a single center. There was a higher incidence of diabetes mellitus in the RT group (31% vs. 14%, p 20
X-Sizer Catheter System. The X-sizer catheter system consists of a helical cutter and dual lumen catheter connected to an external passive vacuum source allowing removal of intracoronary thrombotic material. Once activated the cutter is spun at 2,100 RPM by a motor drive unit. As the catheter is advanced in a slow fashion, the thrombus load is aspirated through various ports at the head of the catheter.
In the XTRACT randomized study, 797 patients were randomized to stenting with and without prior thrombectomy. Although the device reduced the thrombotic burden, there was no difference in myocardial infarction (15.8% vs. 16.6%, p = NS) with the procedure using the thrombectomy catheter. All cause MACE was no different with the dual lumen catheter than standard medical therapy alone (16.8% vs. 17.1%, p = NS) at 30 days and continued at one year. However, there was a reduction in “large” myocardial infarctions (MIs) in patients treated with the thrombectomy.21
In a randomized trial, Antoniucci et al. compared RT before direct infarct artery stenting with direct infarct artery stenting alone in 100 patients with a first acute myocardial infarction (AMI). The primary end point of the study was early ST-segment elevation resolution, and the secondary end points were corrected Thrombolysis In Myocardial Infarction (TIMI) frame count, infarct size, and 1-month clinical outcome. The primary end point rates were 90% in the thrombectomy group and 72% in the placebo group (p 22 suggesting better myocardial perfusion. In a retrospective analysis of 118 AMI patients, our group compared the impact of RT on ST-segment resolution. RT was performed in 61 patients and 57 patients had standard PCI. GP IIb/IIIa inhibitors were used in all patients. ST-segment resolution from baseline was stratified into 3 categories (complete resolution, > = 70%; partial resolution = 30%; and no resolution, 50% was observed in 83% of X-sizer-treated patients and in 52% of controls (p 24
Conclusion. All these studies are suggestive of the fact that removal of the thrombus burden prior to definitive PCI in AMI is useful to prevent embolization and may result in better preservation of microvascular function and improved myocardial salvage during epicardial revascularization. The Angiojet in Myocardial Infarction (AiMI) study is a randomized study of 480 patients undergoing catheter-based reperfusion therapy. This study is designed on the premises that RT prior to definitive PCI in these patients will result in better myocardial preservation, as assessed by final infarct size . Enrollment was recently completed and final results are expected to be presented at Transcatheter Cardiovascular Therapeutics 2004.
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