Cath Lab Digest - March 2008 - (Page 38)

CLINICAL UPDATE MARCH Invasive Imaging Tools for Optimizing Coronary Stent Deployment Michael C. McDaniel, MD, Habib Samady, MD, FACC Emory University School of Medicine, Atlanta, Georgia Dr. McDaniel discloses no conflict of interest regarding the content herein. Dr. Samady discloses that he has given talks on the PressureWire supported by Radi Medical Systems. y significantly reducing restenosis rates, drug-eluting stents (DES) have allowed interventional cardiologists to approach longer and more complex lesions, as well as multi-vessel disease patients. This dramatic reduction in restenosis has led to the adoption of DES as the dominant percutaneous coronary intervention (PCI) strategy in catheterization laboratories in the United States during the past 5 years. However, in the last 18 months, reports of late stent thrombosis have raised concerns about the long-term safety of DES. Some studies have suggested that late (>30 days to 1 year) and very late (>1 year) stent thrombosis rates may be higher with DES compared with bare-metal stents (BMS).1-3 Autopsy studies have indicated that the mechanism of late stent thrombosis may involve lack of complete endothelialization of DES struts and placement of DES edges in the necrotic core segment of atherosclerotic plaque.4 Furthermore, in contrast to BMS, DES have been associated with a paradoxical vasoconstriction response to acetylcholine at the proximal and distal stent edge, indicating dysfunctional endothelium immediately upstream and downstream from the stent.5-7 This delayed and/or diminished endothelialization has necessitated long-term dual anti-platelet therapy. Thus, the overall benefit of DES over BMS relates to the balance between reduction in restenosis, the cost differential (accounting for increased upfront cost and fewer repeat revascularizations), the increased bleeding risks associated with long-term dual anti-platelet therapy, and the possible increased risk of late stent thrombosis. Such complex revascularization decisions are often made by the treating cardiologist in the cath lab and require careful consideration of the clinical picture, angiographic analysis and increasingly, use of invasive imaging tools such as fractional flow reserve (FFR) and intravascular ultrasound (IVUS). The interventionalist has to address three important questions that help guide revascularization: 1) does the lesion(s) need revascularization?; 2) if PCI is to be performed, should DES or BMS be used?; and 3) are the stents optimally deployed for best short- and long-term outcomes? 1. Does the lesion need revascularization? While revascularization improves survival in a subgroup of patients — those with ST-elevation myocardial infarction, cardiogenic shock, severe left main and triple-vessel disease with depressed ventricular function — the majority of PCIs are performed for relief of anginal symptoms or treatment of inducible ischemia. Therefore, in the setting of stable syndromes, if there is doubt about the hemodynamic significance of lesions, it is incumbent on the interventionalist to ascertain this before proceeding with PCI. The best way to avoid short- and longterm stent complications is not to deploy stents unless indicated! Even an experienced interventional cardiologist can not accurately assess the hemodynamic significance of moderate (40–70%) lesions by visual angiographic analysis.8 Furthermore, a homogeneously diseased vessel may appear angiographically normal because no segment is worse than its adjacent reference segment. These limitations of angiography are compounded in overlapped, tortuous, eccentric, calcified lesions, as well as ostial and bifurcation lesions. Additionally, significant inter- and intra-observer variability exists in the angiographic interpretation of lesion severity.9-11 Given these limitations of angiography, physiologic techniques and IVUS have emerged as important adjunctive tools. Several physiologic measures of stenosis severity have been developed: FFR, coronary flow reserve (CFR), and hyperemic stenosis resistance (HSR). FFR was developed as a pressure index of epicardial stenosis severity and is defined as the ratio of the maximal blood flow achievable in an epicardial coronary artery with a stenosis relative to the maximal flow in the same vessel without the stenosis.12-16 A lesion with an FFR <0.75, in a patient with normal myocardium, is considered hemodynamically significant and identifies inducible ischemia with high overall accuracy (93%).16 FFR is relatively independent of loading conditions or myocardial contractility and FFR ≤ 0.78 has been shown to accurately reflect hemodynamic lesion severity even in patients with recent infarction or with elevated left ventricular mass index.17,18 Coronary flow reserve is defined as the ratio of hyperemic blood velocity to the resting blood velocity. The CFR value ≤ 2.0 predicts inducible myocardial ischemia on stress testing with good predictive accuracy (89% to 96%).8,16,19-22 However, CFR reflects both the epicardial and the microvascular resistance, therefore, conditions such as diabetes, myocardial infarction, ventricular hypertrophy, and advanced age can impair microvascular function and reduce CFR independent of the epicardial stenosis severity. To overcome this limitation, the concept of relative CFR (rCFR) was introduced. The rCFR is obtained by dividing the CFR of the “culprit” vessel by the CFR of an adjacent “normal” vessel. A rCFR 0.8mmHg/cm/sec has been shown to be predictive of reversible ischemia on stress testing and may be particularly helpful for assessing hemodynamic severity of a stenosis in patients with microvascular disease. However, there are no prospective studies evaluating the deferral of PCI based on HSR and further research is needed before HSR can be widely adopted. Several studies have demonstrated that PCI with BMS can be safely deferred for FFR > 0.75 and CFR values greater than 2.0.16 The largest of these studies, the randomized Deferral of PTCA Versus Performance of PTCA (DEFER) trial, demonstrated that deferred PCI based on an FFR >0.75 confers no adverse prognosis compared to routine PCI using BMS.25 In fact, at five years, there was a non-significant trend toward lower rates of cardiac death and myocardial infarction in the “defer group” compared to the “perform group” (3.3 vs. 7.9%, p = 0.21).26 In addition to accurately determining the hemodynamic severity of focal lesions, FFR may be particularly useful in guiding revascularization in more complex subsets of patients such as serial stenoses, diffuse disease, ostial and bifurcation disease, and multivessel disease. For serial lesions or diffuse disease, a pressure pullback during intravenous (IV) adenosine infusion can be useful.16,27 Pressure loss due to focal stenosis can be differentiated by an abrupt increase in pressure during a pullback. This technique may help avoid unnecessary revascularization using longer or overlapping DES, which are known to increase the risk of both restenosis and thrombosis.2 Ostial lesions are notoriously difficult to accurately gauge angiographically and can easily be interrogated with FFR. The angiographic assessment of the ostia of side branches of bifurcation lesions after PCI is difficult.28–30 In addition, off-label use of DES in bifurcation lesions is associated with increased rates of restenosis and stent thrombosis.2 Despite severe angiographic appearance in the ostium of “jailed” bifurcations, more than 70% to 80% of these bifurcation lesions are not hemodynamically significant by FFR.31 Thus, “jailed” side-branch lesions are often not functionally significant and PCI of the side branch can often be deferred. This single stent technique with provisional stenting of the side branch only if hemodynamically significant can improve shortand long-term outcomes of bifurcation PCI. Finally, a retrospective study of multi-vessel disease indicated that an

Table of Contents Feed for the Digital Edition of Cath Lab Digest - March 2008

Cath Lab Digest - March 2008 Are You Being Paid Fair Market Value in 2008? A Cardiac Cath Lab Professionals Survey by Cath Lab Digest and the Society of Invasive Cardiovascular Professionals Saint Joseph’s Hospital Invasive Imaging Tools for Optimizing Coronary Stent Deployment Contents Clinical Editor’s Corner A Workflow Revolution in Cath Lab Reporting Advantages of a New Digital Lab at Baystate Medical Center Cardiac Computed Tomography: What Does it Mean for the Cath Lab? The Latest in Cardiac Magnetic Resonance Imaging (MRI) Cellular Cardiomyoplasty and Cardiac Regeneration Intravascular Ultrasound in the Cath Lab: A Powerful — and Underutilized — Tool to Improve Patient Outcomes The Stentplus™ Patient Success Program Cardiac Cath Lab Clutter — or, Spring into Action! Groin Bleeds and Other Hemorrhagic Complications of Cardiac Catheterization: A List of Relevant Issues Ask the Clinical Instructor: A Q&A Column for Those New to the Cath Lab What Do You Think? Experience with a New Guidewire: The Terumo Runthrough NS The Ostial Pro™ Stent Positioning System: Perfecting Aorto-Ostial Stent Placement Precious Minutes The Ten-Minute Interview with…Mark Bowles, BSN, CCRN Vascular Care in the Cath Lab: Planning a Smooth Transition Cath Laughs CMS 2008 OPPS Final Rule Review An Extensive Set of Review Courses for the CCI Basic Science, Non-Invasive Echocardiography and Vascular, and ARDMS Ultrasound Exams Meetings Calendar CEU Education Center Clinical & Industry News STEMI Interventions Classifieds Advertisers Index

Cath Lab Digest - March 2008

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