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March/April 2011
New Frontiers in Transradial Intervention
A present-day assessment of three important clinical issues.
By Adhir Shroff, MD, MPH, FACC, FSCAI, and Sunil V. Rao, MD, FACC, FSCAI
Transradial angiography and intervention is widely practiced throughout the world1 but accounts for a minority of cardiac procedures in the United States.2 Although the transradial approach offers many clinical and economical advantages, the most tangible benefit is a reduction in vascular access site bleeding complications after percutaneous coronary intervention (PCI).3 Recently, the science of transradial PCI has been advanced with the publication of several studies pertaining to radial artery access,4-6 right versus left radial artery approaches,7 and understanding the mechanisms of transradial PCI failure.8 Despite this, there remain several unanswered questions. What is the best anticoagulation strategy for transradial PCI? Is there a role for transradial access in the treatment of acute myocardial infarction? How can radial artery patency be maintained for future procedures? This article summarizes the state of evidence that is available to answer each of these questions and proposes recommendations based on consensus where evidence is lacking.
WHAT IS THE OPTIMAL ANTITHROMBOTIC STRATEGY FOR TRANSRADIAL PCI ?
The past decade has seen vast changes to the anticoagulation landscape for PCI. Commonly used regimens include unfractionated heparin (UFH) with or without a glycoprotein inhibitor (GPI), low-molecular-weight heparin with or without GPI, and bivalirudin. Although the specific data supporting each regimen are beyond the scope of this article, each medication(s) received approval based on demonstrating a favorable clinical benefit-to-risk relationship and, in particular, minimizing periprocedural or 30-day ischemic endpoints in patients with acute coronary syndromes (ACS).9-13 In each of these landmark trials, vascular and bleeding complications were considered in determining the net clinical utility of each treatment strategy. It is important to note that all of these landmark studies predominantly used a femoral approach to access.
Because transradial PCI is associated with a < 1% vascular access complication rate,14 it is reasonable to reconsider the traditional antithrombotic paradigm. Although access site bleeding and vascular complications are nearly eliminated with transradial access, non–access site bleeding continues to be an appreciable risk. It is clear that the risk of non–access site bleeding varies with the population studied and the antithrombotic regimens used.15 For example, in patients undergoing PCI, access site bleeding accounts for the majority of bleeding events; in contrast, non–access site bleeding predominates in patients with non–ST-segment elevation ACS because a significant proportion of them do not undergo PCI. In a recent retrospective analysis of > 17,000 PCI patients, non–access site bleeding accounted for more than half of all bleeding events.16 Genitourinary, gastrointestinal, and head/neck bleeding were the most common sources of non–access site bleeding.
The relative impact of the radial approach on bleeding associated with a particular antithrombotic therapy is difficult to assess due to the rarity with which transradial PCI is represented in published trials. The prevalence of transradial PCI in the ACUITY trial of bivalirudin was 6.2%.17 Although the radial approach was associated with a significant reduction in ACUITY-defined major bleeding compared with the femoral approach, the impact of bivalirudin over heparin/enoxaparin plus GPI was attenuated by the use of radial access such that the type of anticoagulant was no longer significant for access site bleeding. Similarly, the radial approach accounted for only 4.4% of cases in the SYNERGY trial of enoxaparin for ACS treatment18 but accounted for 67% of the patients in the ATOLL trial of intravenous enoxaparin in primary PCI for ST-segment elevation myocardial infarction (STEMI).19 Intravenous enoxaparin was associated with a significant reduction in major bleeding over UFH when used with femoral access in the STEEPLE trial;13 however, the high use of transradial PCI negated the bleeding advantage of intravenous enoxaparin in the ATOLL trial. The use of transradial PCI was rare in the pivotal trials of GPI.9,11,20,21 However, the advantage of a radial approach on bleeding complications in the context of GPI has been reported in studies that have compared radial with femoral PCI.3,4
Interestingly, from the recently published survey of global practice patterns among transradial operators, there does not seem to be a consensus on the antithrombotic strategy used for PCI.1 For elective and low-risk PCI cases, a majority of operators in the United States use bivalirudin (53.2%), whereas in other countries, UFH alone is most commonly used. For ACS patients, UFH with or without GPI is frequently used outside of the United States. In the United States, UFH with or without GPI and bivalirudin with or without GPI regimens are similarly used (Figure 1).
Given the available data, it is difficult to make a strong evidence-based recommendation for any particular regimen. What does appear important is an adoption of approaches that reduce both access site and non–access site bleeding. As previously mentioned, radial access nearly eliminates access site bleeding but would not be expected to reduce non–access site bleeding. Concomitant pharmacological approaches are necessary to accomplish “global” reduction in bleeding risk. Therefore, combining transradial PCI with appropriate dosing of antithrombin and antiplatelet agents,22 or with bivalirudin or intravenous enoxaparin, appears to be a reasonable approach until further data are available.
TRANSRADIAL ACCESS FOR STEMI
The treatment of STEMI has evolved over time23 such that outcomes have significantly improved.25 Despite this improvement, patients with STEMI undergoing PCI have higher acute mortality rates, lower procedural success rates, higher resource utilization, and more bleeding complications compared with patients undergoing elective PCI or PCI for non–ST-segment elevation ACS.26-29 Bleeding in particular appears to be a major risk factor that is linked to subsequent mortality in the STEMI population, and strategies associated with a reduction in bleeding risk are also related to decreased mortality.30 Transradial access offers another approach to lowering bleeding risk in this highrisk cohort of patients. A meta-analysis of radial primary PCI studies showed an association between transradial primary PCI and reduced mortality,24 which was ostensibly driven by limiting postprocedural vascular and bleeding complications (Figure 2).
Given the learning curve that is associated with adopting transradial PCI35 and the clinical priority given to door-to-balloon times, starting a transradial primary PCI program should be reserved for those operators and catheterization laboratory staff who are experienced with complex transradial PCI. No clear guidelines are available, and each operator's learning will likely differ. In addition, the catheterization laboratory staff, who are an integral part of the STEMI team,36 must be proficient with the patient setup, equipment, and postprocedure care that are unique to radial procedures.
There are certain principles that can facilitate the performance of transradial primary PCI in the context of current door-to-balloon time pressures. First, tests for determining dual circulation to the hand (eg, Allen's test, Barbeau test37) can be performed quickly either in the emergency department or immediately upon arrival in the procedure area. Second, radial access can be achieved simultaneously with patient setup because fluoroscopy is usually not necessary. Third, it is important to have a bailout strategy in case radial access, traversing the arm or chest vasculature, or engaging the coronary arteries creates a delay to prompt reperfusion. Another strategy that has been described is the routine use of the left radial approach for primary transradial PCI due to a lower incidence of subclavian tortuosity compared with the right side.38 Subclavian tortuosity has been described as the cause of transradial PCI procedural failure in up to 18% of cases.8 This may be even more relevant among elderly patients and those of short stature; therefore, either a routine left radial approach or a selective left radial approach in older patients and those who are < 65 inches in height may reduce primary transradial PCI procedural failure.7,8,38
There are several reports in the literature that have demonstrated the feasibility of using the radial approach for the treatment of STEMI (Table 1). Given the relatively localized expertise with this technique, these studies are limited to a few centers. Each of these studies required the operators to have performed >100 transradial PCI procedures. In these studies, they were able to achieve similar procedural success rates with less bleeding complications when compared to the transfemoral approach. In some cases, the door-to-reperfusion time was increased by a few minutes, whereas in other cases, there was no difference between transradial and transfemoral access. The recently completed RIVAL trial will report on major adverse cardiac outcomes between STEMI patients who were randomized to radial or femoral approaches to primary PCI and will provide further data on the efficacy and safety of primary transradial PCI.
RADIAL ARTERY OCCLUSION
Radial artery occlusion after transradial PCI has been shown to occur in up to 8% of patients. Although the pathogenesis is not well understood, it is likely related to arterial injury during catheter manipulation that leads to spasm and thrombosis.39 The current literature suggests that most radial artery occlusion is clinically silent,4,40,41 but most studies have not routinely surveyed patients for this event and often exclude patients that lack dual circulation to the hand. Importantly, there is inconsistent evidence supporting the utility of the Allen's test for identifying patients who are at risk of developing symptomatic radial artery occlusion.42,43 Further, many patients who develop radial artery occlusion will often recanalize their radial artery at 30 days.4 Risk factors for radial artery occlusion include high ratio of the arterial sheath diameter to the radial artery diameter,46 lack of systemic anticoagulation during transradial procedures,35 multiple arterial accesses in the same artery,47 and prolonged occlusive arterial compression.48
Given these risk factors, several strategies can be adopted to minimize the risk of radial artery occlusion (Table 2). These include the use of systemic anticoagulation (either UFH, low-molecular-weight heparin,44 or bivalirudin45), minimizing arterial sheath size, and using patent hemostasis (Figure 3).4,41 The concept of patent hemostasis revolves around maintaining antegrade flow in the radial artery while achieving hemostasis (Table 3). This technique is of paramount importance and has been shown to significantly decrease the rate of radial artery occlusion—almost tenfold in one study.41
CONCLUSION
As transradial PCI gains worldwide popularity, developing a strong evidence base for the individual aspects of the procedure has become a priority. Three areas of interest include antithrombotic strategies for transradial PCI, transradial primary PCI, and prevention of radial artery occlusion. Although definitive data on the optimal antithrombotic regimen for transradial PCI have not yet emerged, attention must be paid to both access site and non–access site bleeding. The radial approach addresses the former but not the latter. Combining radial and pharmacological approaches may achieve the lowest bleeding risk. With respect to primary PCI, transradial access is associated with reduced mortality but should only be adopted by experienced operators and catheterization laboratory staff. Finally, radial artery occlusion is a major complication of transradial PCI, and operators should adopt preventive strategies.
Adhir Shroff, MD, MPH, FACC, FSCAI, is Associate Professor of Medicine, University of Illinois–Chicago Medical Center, and he has a dual appointment at the Jesse Brown VA Medical Center in Chicago, Illinois. Dr. Shroff has disclosed that he is a paid consultant to and receives grant/research funding from Terumo Interventional Systems and The Medicines Company. He further disclosed that he receives grant/research funding from Abiomed. Dr. Shroff may be reached at (312) 996-9086; arshroff@uic.edu.
Sunil V. Rao, MD, FACC, FSCAI, is Associate Professor of Medicine, Duke University Medical Center in Durham, North Carolina. He has disclosed that he is a paid consultant to AstraZeneca, Bristol-Myers Squibb, Daiichi Sankyo/Lilly, Sanofi-Aventis, Terumo Interventional Systems, and The Medicines Company. Dr. Rao may be reached at rao00010@dcri.duke.edu.
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