Association of dual-antiplatelet therapy with reduced major adverse cardiovascular events in patients with symptomatic peripheral arterial disease

Association of dual-antiplatelet therapy with reduced major adverse cardiovascular events in patients with symptomatic peripheral arterial disease Ehrin J. Armstrong, MD, MS,a David R. Anderson, MD,b Khung-Keong Yeo, MBBS,b Gagan D. Singh, MD,b Heejung Bang, PhD,c Ezra A. Amsterdam, MD,b Julie A. Freischlag, MD,d and John R. Laird, MD,b Denver, Colo; and Sacramento, Calif Objective: This study was conducted to determine whether there is additive benefit of dual-antiplatelet therapy (DAPT) with aspirin (acetylsalicylic acid [ASA]) and clopidogrel compared with ASA monotherapy among patients with symptomatic peripheral arterial disease. Methods: This was an observational cohort analysis that included 629 patients with claudication or critical limb ischemia. The prevalence of patients taking ASA monotherapy vs DAPT was assessed monthly for up to 3 years. A propensity model was constructed to adjust for baseline demographic characteristics and to assess the effect of DAPT on major adverse cardiovascular events (MACEs) and major adverse limb events. Results: At baseline, 348 patients were taking DAPT and 281 were taking ASA monotherapy. During 3 years of follow-up, 50 events (20%) occurred in the DAPT group vs 59 (29%) in the ASA monotherapy group. After propensity weighting, DAPT use was associated with a decreased risk of MACEs (adjusted hazard ratio [HR], 0.65; 95% confidence interval [CI], 0.44-0.96) and overall mortality (adjusted HR, 0.55; 95% CI, 0.35-0.89). No association was found between DAPT use and the risk of major amputation (adjusted HR, 0.69; 95% CI, 0.37-1.29). In a subgroup of 94 patients who underwent point-of-care platelet function testing, 21% had decreased response to ASA and 55% had a decreased response to clopidogrel. No association was found between a reduced response to ASA or clopidogrel and adverse events at 1 year. Conclusions: DAPT may be associated with reduced rates of MACEs and death among patients with symptomatic peripheral arterial disease. (J Vasc Surg 2015;-:1-9.)

Patients with peripheral arterial disease (PAD) are at increased risk of major adverse cardiovascular events (MACEs) and overall mortality.1-3 A number of medical therapies have been shown to reduce cardiovascular mortality among patients with PAD, including statins, angiotensin-converting enzyme (ACE) inhibitors, and abstention from smoking.4-10 Antiplatelet agents also reduce MACEs in patients with symptomatic PAD, with a small additional benefit of clopidogrel relative to aspirin (acetylsalicylic acid [ASA]) monotherapy.11-13 There are little data, however, regarding the possible additive benefit From the Division of Cardiology, University of Colorado, and Veterans Affairs Eastern Colorado Health Care System, Denvera; and the Vascular Center and Division of Cardiovascular Medicine, Department of Internal Medicine,b Division of Biostatistics, Department of Public Health Sciences,c and Department of Surgery,d University of California, Davis, Sacramento. E.J.A. is supported by American Heart Association grant 11CRP7260031. Author conflict of interest: J.R.L. is a consultant for Boston Scientific, Covidien, Abbott, Bard, and Medtronic. E.J.A. is a consultant for Abbott, Medtronic, and Spectranetics. Additional material for this article may be found online at www.jvascsurg.org. Reprint requests: John R. Laird, MD, UC Davis Medical Center, 4860 Y St, Ste 3400, Sacramento, CA 95817 (e-mail: [email protected]). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest. 0741-5214 Copyright Ó 2015 by the Society for Vascular Surgery. Published by Elsevier Inc. http://dx.doi.org/10.1016/j.jvs.2015.01.051

of dual-antiplatelet therapy (DAPT) in this patient population. A subgroup analysis of the Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management, and Avoidance (CHARISMA) trial suggested that DAPT use may be associated with a reduction in myocardial infarction (MI) and hospitalization for ischemic events in patients with PAD.14,15 However, DAPT vs ASA monotherapy has not been systematically studied among a group of patients with more advanced PAD, including severe lifestyle-limiting claudication or critical limb ischemia (CLI). These patients represent a high-risk cohort of patients with PAD who may be most likely to benefit from more intensive antiplatelet therapy. In this study, we assessed the relationship between DAPT and subsequent mortality, MACEs, and limbrelated outcomes among a cohort of patients with moderate to severe claudication or CLI treated at a multidisciplinary vascular center. We also studied the association between antiplatelet resistance and outcomes among a subgroup of these patients. METHODS The University of California (UC), Davis Medical Center Institutional Review Board approved the study protocol with a waiver of informed consent. Study design and data sources. We conducted a cohort study using data from the UC Davis PAD Registry. This registry comprises all patients with a clinical diagnosis of PAD who underwent diagnostic angiography or 1

2 Armstrong et al

therapeutic endovascular intervention, or both, at the UC Davis Medical Center between June 2006 and May 2013, as previously described.16 At the time of data extraction, the registry included 1201 patients who underwent 1897 procedures. A total of 753 patients presented with claudication or CLI and were included in this study; the other patients in the registry included those presenting with acute limb ischemia, carotid artery stenosis, subclavian artery stenosis, or renal artery stenosis. The median length of patient follow-up was 3.2 years. All patients in the registry with symptomatic PAD defined by claudication or CLI were included in the study cohort. All patients underwent diagnostic or interventional lower extremity angiography at the UC Davis Medical Center. Data collection was based on detailed electronic medical records and angiographic review. Baseline demographic, clinical, laboratory, and procedural data were obtained through preprocedure clinical notes, admission history, and in-patient documentation. Prescriptions for ASA, clopidogrel, ticlopidine, and prasugrel were verified by pharmacy prescriptions during the month before the procedure and at 1-month intervals during 36 months of follow-up. All records were reviewed by trained chart abstractors and verified by a board-certified cardiologist. During the study period, 753 patients with claudication or CLI underwent lower extremity angiography; of these, 96 patients were prescribed warfarin before the procedure, and 28 were not taking any antiplatelet therapy, leaving 629 patients in the analysis cohort. Patients were categorized as taking ASA monotherapy if they were prescribed ASA without concomitant clopidogrel, ticlopidine, or prasugrel. Patients were categorized as taking DAPT if they were prescribed ASA and clopidogrel (n ¼ 342), ticlopidine (n ¼ 1), or prasugrel (n ¼ 5). Continued antiplatelet therapy use was assessed every month after lower extremity angiography for up to 3 years. Use of ASA and other antiplatelet agents was determined by the electronic medical record, prescribing records, and clinic visit notes. Data definitions. MACEs were defined as MI, stroke, or death. MI was defined as symptoms of chest pressure and elevation of troponin with evidence of infarct by myocardial perfusion imaging or cardiac catheterization. Stroke was defined as focal neurologic deficit with computed tomography or magnetic resonance imaging evidence of cerebral ischemic or hemorrhagic infarct. All deaths were confirmed via direct record documentation or the Social Security Death Index, with most cases determined via the Social Security Death Index.17 Because a combination of data sources was used for mortality determination, only all-cause mortality is reported. Major adverse limb events (MALEs) were defined as major lower extremity limb amputation above the level of the ankle joint, thrombolysis, or surgical bypass.18 Claudication was classified as Rutherford category 1 to 3 disease (mild, moderate, or severe claudication, respectively), and CLI was classified as Rutherford category 4 to 6 disease (ischemic rest pain, minor tissue loss, or major tissue loss, respectively).19

JOURNAL OF VASCULAR SURGERY --- 2015

Measurement of antiplatelet resistance. Testing for antiplatelet resistance was performed in a subset of 94 patients as part of an Institutional Review Boardapproved study that included provision of informed consent by participants. This was a separately funded study conducted during 2011 to 2012. All patients underwent lower extremity intervention for claudication or CLI. If patients were taking clopidogrel preprocedure, blood was drawn at the start of the procedure. For patients who started taking ASA or clopidogrel during the procedure, blood was drawn at least 5 hours after the initial dosing. Blood was then tested #2 hours using the VerifyNow assay (Accumetrics, San Diego, Calif) for ASA or thienopyridine resistance. ASA resistance was defined as aspirin reaction units $550 based on prior studies,20 and thienopyridine resistance was defined as P2Y12 reaction units (PRU) $235.21 Outcomes. The primary outcome of the study was the occurrence of MACEs during the 3-year follow-up period. Loss to follow-up during the 3 years consisted of 68 of 348 patients (19.5%) in the DAPT group and 56 of 281 (20%) in the ASA monotherapy group, suggesting that there was not any differential censoring. Prespecified secondary outcomes included the occurrence of MALEs, the individual components of MACEs and MALEs, and the combined incidence of death or major amputation during the 3-year follow-up period. For the subgroup of patients with testing performed for antiplatelet resistance, a combined end point of death, MI, stroke, major amputation, surgical bypass, or repeat revascularization was used. Statistical analysis. Means with standard deviations are used to describe continuous variables and frequencies and percentages are used for categoric variables. Continuous variables were compared using the Wilcoxon rank sum test and categoric values using c2 or Fisher exact tests. Propensity scores were developed to adjust for covariates that may influence the decision to prescribe ASA monotherapy vs DAPT.22 A comprehensive set of baseline covariates was included in the propensity model: age, sex, patient-reported race/ethnicity (Caucasian, Hispanic, African American, Asian), body mass index, glomerular filtration rate, history of diabetes, congestive heart failure, coronary artery disease, prior MI, smoking status (active, former, or never), hypertension, stroke, carotid artery disease, chronic obstructive pulmonary disease, malignancy, abdominal aortic aneurysm, prior gastrointestinal bleeding, prior above-ankle amputation, left ventricular ejection fraction (in 5% increments from #10% to $65%), Rutherford score (1-6), and prescription of concomitant medications, including statin medications, b-blockers, and ACE inhibitors. Diagnostic tests to demonstrate balance of the covariates after inverse probability of treatment weighting (IPTW) included calculation of the standardized difference before and after weighting and visual inspection of a kernel density plot to verify propensity score overlap between groups (Supplementary Table I, online only). Visual inspection of propensity scores by treatment group before

JOURNAL OF VASCULAR SURGERY Volume -, Number -

Armstrong et al 3

Fig 1. Propensity scores for dual-antiplatelet therapy (DAPT) use (red bars) compared with aspirin (acetylsalicylic acid [ASA]) monotherapy (blue bars). The propensity score for DAPT use is the probability, given baseline covariates, that any patient in either group is prescribed DAPT.

weighting also suggested adequate overlap in the two cohorts (Fig 1). Proportional hazards models using antiplatelet therapy as a time-varying exposure were then developed using weighted regression with IPTW to estimate the association of DAPT with subsequent outcomes.23 Unadjusted survival curves were estimated using the Kaplan-Meier method, and adjusted survival curves were estimated using IPTW weighting.24 To account for baseline patient characteristics that may have led to the decision to perform a major amputation or lower extremity bypass in the first 30 days after diagnostic angiography, rates of major amputation, MALEs, and death/major amputation were calculated using a landmark analysis beginning at 30 days after the initial angiogram.25 Several sensitivity analyses were also performed to assess the relationship between DAPT and cardiovascular outcomes. Hazard ratios (HRs) were recalculated using time-varying Cox proportional hazard models that adjusted for the same covariates included in the propensity model. Propensity modeling was also performed using nearestneighbor matching and after trimming the propensity scores to minimize possible effects from outliers (Supplementary Tables II and III, online only). All analyses were performed using Stata 11.2 software (StataCorp LP, College Station, Tex). HRs are provided with 95% confidence intervals (CIs). For all tests, a P value of <.05 was considered significant. RESULTS Among the overall group of 629 patients, 348 (55%) were prescribed DAPT and 281 (45%) were prescribed ASA monotherapy (Table I). The cohort was a mean age of 67 years (range, 28-92 years), and 44% of the patients

were women. An endovascular intervention was performed in 603 patients (80%), including 201 aortoiliac interventions, 218 femoropopliteal interventions, 70 infrapopliteal interventions, and 114 multilevel interventions. Most patients in each group (54% in ASA monotherapy and 56% in DAPT) presented with CLI. Patients prescribed DAPT were more likely to have a history of diabetes (54% vs 45%; P ¼ .02), coronary artery disease (56% vs 45%; P ¼ .007), and be prescribed a b-blocker medication (55% vs 48%; P ¼ .05). The rates of statin prescription, ACE inhibitor use, and abstention from smoking were not significantly different between the groups. A history of gastrointestinal bleeding was present in 8% of patients in the ASA monotherapy group compared with 4% in the DAPT group (P ¼ .06). Antiplatelet prescriptions were verified every month during the 3-year follow-up, and the percentage of patients prescribed DAPT during that time period varied from 55% to 59% of the cohort available for follow-up at each assessment. During the 3-year follow-up period (Table II), patients prescribed DAPT had significantly lower unadjusted Kaplan-Meier estimated rates of MACEs (20% vs 28%; P ¼ .03) and overall mortality (11% vs 21%; P ¼ .01). DAPT was not associated significantly with unadjusted rates of major amputation (9% vs 7%; P ¼ .7) or MALEs (14% vs 14%; P ¼ .5), but was associated with lower rates of death or major amputation (18% vs 27%; P ¼ .01) in unadjusted analyses, primarily because of the reduction in mortality with this combined end point. After propensity weighting using monthly prescription records to account for the duration of DAPT, DAPT use remained associated with a significantly lower risk of MACEs (adjusted HR, 0.65; 95% CI, 0.44-0.96), overall

JOURNAL OF VASCULAR SURGERY --- 2015

4 Armstrong et al

Table I. Baseline demographics Variablesa Age, years Male sex Race/ethnicity Caucasian Hispanic African American Asian Body mass index, kg/m2 Tobacco use, former or current Congestive heart failure Diabetes mellitus GFR, mL/min Hypertension Coronary artery disease Ejection fraction COPD History of Stroke/TIA MI Abdominal aortic aneurysm Carotid stenosis Gastrointestinal bleeding Contralateral amputation Medication use Statin ACE inhibitor b-blocker Rutherford classification 1 2 3 4 5 6 Ankle-brachial index

DAPT (n ¼ 348)

ASA monotherapy (n ¼ 281)

67 6 12 195 (56)

67 6 14 157 (56)

274 (78) 34 (10) 29 (8) 11 (3) 28 6 5 265 (77) 68 (20) 187 (54) 70 6 37 299 (86) 195 (56) 56 6 16 61 (18)

234 (83) 22 (8) 21 (7) 4 (1) 27 6 7 212 (77) 59 (21) 126 (45) 73 6 44 236 (84) 126 (45) 52 6 17 41 (15)

54 74 20 54 15 24

(16) (21) (6) (16) (4) (7)

45 43 13 37 22 22

P value .7 .9 .4

.2 .8 .7 .02 .4 .5 .007 .07 .3

(16) (15) (5) (14) (8) (8)

.8 .06 .5 .5 .06 .4

245 (70) 222 (64) 193 (55)

183 (65) 168 (60) 134 (48)

.2 .3 .05 .8

14 (4) 72 (21) 65 (19) 35 (11) 133 (38) 28 (8) 0.51 (0.39-0.66)

11 44 56 32 113 26 0.53

(4) (16) (20) (12) (40) (9) (0.40-0.69)

.2

ACE, Angiotensin-converting enzyme; ASA, acetylsalicylic acid (aspirin); COPD, chronic obstructive pulmonary disease; DAPT, dual-antiplatelet therapy; GFR, glomerular filtration rate; MI, myocardial infarction; TIA, transient ischemic attack. a Continuous data are shown as mean 6 standard deviation or mean (range) and categoric variables as number (%).

mortality (adjusted HR, 0.55; 95% CI, 0.34-0.84), and amputation-free survival (adjusted HR, 0.53; 95% CI, 0.34-0.80; Fig 2). Similar point estimates were obtained using a time-varying Cox proportional hazard model and after several sensitivity analyses (Table II; Supplementary Tables II and III, online only). There was no significant association between DAPT use and target vessel revascularization over time. Point-of-care testing for resistance to ASA and clopidogrel at the time of the lower extremity intervention was performed in a subgroup of 94 patients. The prevalence of ASA resistance at baseline was 21%, as defined by an aspirin reaction units $550, whereas the prevalence of clopidogrel resistance was 55%, as defined by a PRU $235. No significant association was found between clopidogrel resistance (HR, 1.6; 95% CI, 0.7-3.6) or ASA resistance (HR, 1.1; 95%, CI 0.5-2.8) and the combined end point of death, MI, stroke, major amputation, or target vessel revascularization at 1 year. Analysis of PRU values by quartile also did not demonstrate a difference in 1-year outcomes based on the

PRU value at the time of the lower extremity intervention (Fig 3). DISCUSSION In this study, we report the association between DAPT and cardiovascular outcomes among a cohort of patients with lifestyle-limiting claudication or CLI. Our main finding was that DAPT was associated with significantly lower rates of subsequent MACEs and overall mortality compared with ASA monotherapy. There was no significant association of DAPT use with limb-related outcomes, suggesting that the primary benefit of more intensive antiplatelet therapy may be due to a reduction of cardiovascular outcomes in other vascular beds. In a subgroup of patients who were tested for antiplatelet resistance, there was no association between the presence of ASA or thienopyridine resistance and subsequent combined cardiovascular or limb-related outcomes. Antiplatelet therapy and MACEs among patients with PAD. ASA and clopidogrel have each been studied extensively among patients with asymptomatic and

JOURNAL OF VASCULAR SURGERY Volume -, Number -

Armstrong et al 5

Table II. Three-year outcomes of dual-antiplatelet therapy (DAPT) vs acetylsalicylic acid (ASA [aspirin]) monotherapy Outcomes rates,a No. (%) Variables MACE Death MI Stroke MALE Lower extremity bypass Major amputation Death or major amputation

DAPT (n ¼ 348) 50 29 19 8 33 16 20 55

(20) (11) (9) (4) (14) (7) (9) (18)

ASA (n ¼ 281) 59 42 14 7 26 13 12 65

(28) (21) (7) (4) (14) (7) (7) (27)

Unadjusted HR (95% CI) 0.67 0.54 1.07 0.90 0.85 0.84 1.13 0.63

(0.46-0.97) (0.34-0.87) (0.53-2.13) (0.32-2.47) (0.51-1.42) (0.41-1.75) (0.55-2.31) (0.44-0.91)

Cox PH adjusted P .03 .01 .8 .8 .5 .6 .7 .01

HR (95% CI) 0.63 0.56 0.88 1.0 0.72 0.63 0.77 0.54

(0.43-0.93) (0.34-0.92) (0.43-1.81) (0.34-2.96) (0.42-1.22) (0.30-1.34) (0.39-1.45) (0.35-0.84)

IPTW adjusted P

.02 .02 .7 .9 .2 .2 .4 .006

HR (95% CI) 0.65 0.55 0.96 0.93 0.67 0.59 0.69 0.53

(0.44-0.96) (0.34-0.89) (0.47-1.97) (0.34-2.60) (0.40-1.13) (0.28-1.25) (0.37-1.29) (0.34-0.80)

P .03 .02 .9 .9 .1 .2 .3 .003

CI, Confidence interval; HR, hazard ratio; IPTW, inverse probability treatment weighting; MACE, major adverse cardiovascular event; MALE, major adverse limb event; MI, myocardial infarction; PH, proportional hazard. a Rates of lower extremity bypass, major amputation, MALE, and death or major amputation are based on landmark analysis beginning 30 days after angiography. Outcomes rates are reported as total events in each column, followed by the Kaplan-Meier estimate of the event rate for each group to account for censoring.

symptomatic PAD. Although ASA monotherapy for patients with subclinical PAD remains controversial, it is a class I recommendation among patients with symptomatic PAD.26-28 The recommendation for clopidogrel monotherapy in patients with PAD is based primarily on the results of the Clopidogrel Versus Aspirin In Patients At Risk Of Ischaemic Events (CAPRIE) trial, in which patients at high risk for atherothrombotic events (including history of recent stroke, MI, or symptomatic PAD) were randomized to daily ASA (325 mg) or clopidogrel (75 mg). At a mean follow-up of 1.91 years, patients randomized to clopidogrel had a relative risk reduction of 8.7% in MACEs although the absolute difference in event rates was low (5.32% vs 5.83%). The subgroup of patients with PAD had the greatest benefit from clopidogrel, with a 23.8% relative risk reduction (absolute event rate of 3.71% vs 4.86%) relative to ASA monotherapy. More intensive combined antiplatelet therapy for patients with PAD was also studied in the CHARISMA trial, which randomized patients with cardiovascular disease or multiple risk factors to DAPT or ASA monotherapy.14 Although the primary end point of the study was negative, patients with a history of clinically evident atherothrombosis had a statistically significant relative risk reduction of 12% with DAPT. A subgroup analysis of patients with PAD enrolled in the CHARISMA trial found that PAD patients prescribed DAPT had lower rates of subsequent MI (2.3% vs 3.7%) and hospitalization for ischemic events (16.5% vs 20.1%), but the overall rates of MACE were not significantly different (7.6% vs 8.9%; P ¼ .18).15 We, however, found a significantly lower rate of MACEs among our study cohort. These differential findings may be partly due to inclusion of a higher-risk group of patients with severe PAD, with more than half of the patients presenting with CLI. Consistent with these differences, the overall event rates in our cohort were much higher (20% vs 28% at 3 years). In comparison, some patients in the PAD subgroup in the CHARISMA trial were asymptomatic, and the patients primarily with

symptomatic PAD had claudication with an anklebrachial index of #0.85 or a history of previous vascular intervention rather than CLI. Because more intensive antiplatelet therapy may be of greatest benefit among patients with more advanced vascular disease, we believe that our findings are more relevant and generalizable to patients with moderate to severe claudication or those with CLI. Importantly, we were only able to determine overall mortality, rather than causespecific mortality. Although prior studies have shown that most of the excess events among patients with PAD are due to cardiovascular disease and cardiovascular mortality, this study could not definitively identify cause of death. Antiplatelet therapy and limb-related outcomes. Compared with the significant reduction in overall mortality and MACEs observed with DAPT, we did not find any association between DAPT and the limb-related outcomes of major amputation or MALEs. Although many patients are prescribed clopidogrel after an endovascular intervention, most endovascular interventions use balloon angioplasty or bare-metal stents, where the primary benefit of clopidogrel is to prevent thrombosis before reendothelialization. DAPT may not have a lesion-specific benefit in this population when prescribed for a longer duration. DAPT use among patients with CLI undergoing surgical lower extremity bypass is associated with a reduction in MI size at the expense of higher bleeding rates.11 In a larger randomized study of patients undergoing belowknee surgical bypass for the treatment of claudication or CLI, DAPT use improved graft patency among patients undergoing placement of prosthetic grafts but had no effect on patency of vein conduits.29 A recent meta-analysis suggested a possible reduction in the need for subsequent limb revascularization among patients taking antiplatelet therapy, but many of these revascularizations were elective and may have been related to disease progression rather an effect on sites of previous intervention.30 Although DAPT had not been shown to definitively affect limb-related outcomes, inhibition of other antiplatelet

6 Armstrong et al

JOURNAL OF VASCULAR SURGERY --- 2015

Fig 2. Major adverse cardiovascular events (MACEs) and limb outcomes among patients prescribed dual-antiplatelet therapy (DAPT; red line) vs aspirin (acetylsalicylic acid [ASA]; blue line) monotherapy. Patients prescribed DAPT had significantly lower rates of (A) MACEs, (B) overall mortality, and (C) major amputation or death. D, There was no significant association between DAPT and major adverse limb events (MALEs).

pathways may have benefit in the treatment of patients with PAD. A recent subgroup analysis of the Thrombin Receptor Antagonist in Secondary Prevention of Atherothrombotic Ischemic Events-Thrombolysis in Myocardial  Infarction 50 (TRA2 P-TIMI 50) trial of vorapaxar vs placebo reported that patients with PAD randomized to vorapaxar had significantly lower rates of acute limb ischemia and peripheral artery revascularization.31 Vorapaxar is an antagonist of protease-activated receptor 1, the main platelet receptor for thrombin. Inhibition of additional signaling pathways for platelet activation may be associated with this specific benefit on limb outcomes. Protease-activated receptor 1 is also expressed on other cell types, including smooth muscle and endothelial cells, so it is possible that the benefit of vorapaxar is related to on-target effects of other cell types, including reduction in smooth muscle cell proliferation.32 Whether more intensive antiplatelet therapy with ticagrelor improves limb outcomes relative to clopidogrel monotherapy will also be an end point of the ongoing A Study Comparing

Cardiovascular Effects of Ticagrelor and Clopidogrel in Patients With Peripheral Artery Disease (EUCLID) trial (clinicaltrials.gov identifier NCT01732822). Antiplatelet resistance and cardiovascular outcomes. Multiple studies have shown that clopidogrel at standard dosing leads to variable inhibition of platelet responsiveness among patients undergoing coronary percutaneous intervention.33,34 The reasons for this variability include differences in drug absorption, metabolism, and genetic predisposition.35 Insufficient inhibition of platelet activation is a risk factor for future atherothrombotic events because platelets mediate many of the early steps in thrombosis.36 In patients with PAD, incomplete platelet inhibition has also been shown to be associated with greater circulating levels of platelet activation markers, including b-thromboglobulin and CD40 L.37 Whether adjusting the dose of clopidogrel to achieve greater platelet inhibition among patients with PAD could reduce cardiovascular events remains uncertain, because recent studies in patients undergoing percutaneous coronary intervention

JOURNAL OF VASCULAR SURGERY Volume -, Number -

Armstrong et al 7

Fig 3. Aspirin (acetylsalicylic acid [ASA]) and clopidogrel resistance among patients treated with dual-antiplatelet therapy (DAPT). There was no significant association between (A) clopidogrel resistance (P2Y12 reaction units [PRU], <235 [blue line] vs $235 [red line]) or (B) aspirin (ASA) resistance (aspirin reaction units [ARU], <550 [blue line] vs $550 [red line]) and the combined end point of death, myocardial infarction (MI), stroke, or target vessel revascularization.

have failed to show an effect of tailored antiplatelet dosing on subsequent outcomes.38,39 One study of platelet responsiveness monitored 100 patients for 1 year after femoropopliteal angioplasty and stenting.21 Division of patients into quartiles of PRU values demonstrated significantly increased event rates among patients in the third and fourth quartiles. Of note, all but two of the events driving that study end point were target vessel revascularization, as only one death and one major amputation occurred during follow-up. In comparison, the rates of reintervention in our substudy cohort were low (12 revascularizations at 1 year) because the initial interventions involved a combination of aortoiliac and femoropopliteal target vessels. Our cohort of 94 patients may have therefore been underpowered to detect an effect of clopidogrel resistance. However, we also did not find any trend between quartiles of platelet reactivity and outcomes. Despite the lack of association with clinical outcomes, the prevalence of clopidogrel resistance was similar to that of other recent studies that included patients with PAD, which has been reported between 30% and 51%.40 Further studies are necessary with larger cohorts to determine the relationship between on-treatment platelet reactivity and outcomes as well as the optimal cutoff point to define antiplatelet resistance. Limitations. This study has several limitations. First, this was an observational cohort study and is therefore subject to possible residual confounding. We used propensity scores to minimize confounding based on measured covariates as well as several sensitivity analyses that reached consistent results (eg, similar point estimates) for all measured outcomes. Because DAPT duration may vary significantly, we also used a time-varying methodology to account for changes in antiplatelet prescriptions over time.

Second, this was a single-center study with a relatively small cohort. A larger, multicenter study should be conducted to confirm these findings in other patient populations. Third, we could not rigorously identify postprocedural bleeding outcomes with our study design or determine transfusion requirements. It is possible that patients prescribed DAPT had significantly higher rates of bleeding. However, previous randomized trials have shown that DAPT is associated with a higher rate of minor bleeding but no significantly increased risk of major bleeding.14 Fourth, we could not determine the cause of death in most cases because the Social Security Death Index was used to determine long-term mortality. Some prospective randomized trials have used cardiovascular mortality, rather than overall mortality, as a component of the overall end point. However, prior studies of claudication and CLI have shown that most deaths are due to cardiovascular causes.41 Fifth, the lack of an association between resistance to antiplatelet agents and outcomes may be related to the small sample size of that subgroup. Sixth, we relied on pharmacy prescribing records to assess antiplatelet use, but we were unable to assess medication refills, which may be a measure of compliance to prescribed therapy. Additional studies with larger cohorts should be performed to further delineate the relationship between antiplatelet resistance and outcomes among patients with PAD. CONCLUSIONS We found that DAPT is associated with reduced rates of MACEs and mortality among patients with severe symptomatic PAD compared with ASA monotherapy. These results suggest that DAPT may provide an additional long-term reduction in cardiovascular events among

8 Armstrong et al

patients with lifestyle-limiting claudication or CLI. Additional randomized studies are warranted to assess the additive benefit of more intensive and DAPT among patients with advanced PAD. AUTHOR CONTRIBUTIONS Conception and design: EA, DA, DC, GS, HB, EA, JF, JL Analysis and interpretation: EA, DA, DC, GS, HB, EA, JF, JL Data collection: EA, DA, DC, GS Writing the article: EA, DA, JL Critical revision of the article: EA, DA, DC, GS, HB, EA, JF, JL Final approval of the article: EA, DA, DC, GS, HB, EA, JF, JL Statistical analysis: EA, HB Obtained funding: Not applicable Overall responsibility: JL REFERENCES 1. Criqui MH, Langer RD, Fronek A, Feigelson HS, Klauber MR, McCann TJ, et al. Mortality over a period of 10 years in patients with peripheral arterial disease. N Engl J Med 1992;326:381-6. 2. Criqui MH, Ninomiya JK, Wingard DL, Ji M, Fronek A. Progression of peripheral arterial disease predicts cardiovascular disease morbidity and mortality. J Am Coll Cardiol 2008;52:1736-42. 3. Welten GM, Schouten O, Hoeks SE, Chonchol M, Vidakovic R, van Domburg RT, et al. Long-term prognosis of patients with peripheral arterial disease: a comparison in patients with coronary artery disease. J Am Coll Cardiol 2008;51:1588-96. 4. Heart Protection Study Collaborative Group. Randomized trial of the effects of cholesterol-lowering with simvastatin on peripheral vascular and other major vascular outcomes in 20,536 people with peripheral arterial disease and other high-risk conditions. J Vasc Surg 2007;45: 645-54. 5. Yusuf S, Sleight P, Pogue J, Bosch J, Davies R, Dagenais G. Effects of an angiotensin-converting-enzyme inhibitor, ramipril, on cardiovascular events in high-risk patients. The Heart Outcomes Prevention Evaluation Study Investigators. N Engl J Med 2000;342:145-53. 6. Jonason T, Bergström R. Cessation of smoking in patients with intermittent claudication. Effects on the risk of peripheral vascular complications, myocardial infarction and mortality. Acta Med Scand 1987;221:253-60. 7. Pande RL, Perlstein TS, Beckman JA, Creager MA. Secondary prevention and mortality in peripheral artery disease: National Health and Nutrition Examination Study, 1999 to 2004. Circulation 2011;124: 17-23. 8. Feringa HH, van Waning VH, Bax JJ, Elhendy A, Boersma E, Schouten O, et al. Cardioprotective medication is associated with improved survival in patients with peripheral arterial disease. J Am Coll Cardiol 2006;47:1182-7. 9. Kumbhani DJ, Steg PG, Cannon CP, Eagle KA, Smith SC, Goto S, et al. Statin therapy and long-term adverse limb outcomes in patients with peripheral artery disease: insights from the REACH registry. Eur Heart J 2014;35:2864-72. 10. Westin GG, Armstrong EJ, Bang H, Yeo KK, Anderson D, Dawson DL, et al. Association between statin medications and mortality, major adverse cardiovascular event, and amputation-free survival in patients with critical limb ischemia. J Am Coll Cardiol 2014;63: 682-90. 11. Catalano M, Born G, Peto R. Prevention of serious vascular events by aspirin amongst patients with peripheral arterial disease: randomized, double-blind trial. J Intern Med 2007;261:276-84.

JOURNAL OF VASCULAR SURGERY --- 2015

12. Antithrombotic Trialists’ Collaboration. Collaborative meta-analysis of randomised trials of antiplatelet therapy for prevention of death, myocardial infarction, and stroke in high risk patients. BMJ 2002;324: 71-86. 13. CAPRIE Steering Committee. A randomised, blinded, trial of clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE). CAPRIE Steering Committee. Lancet 1996;348:1329-39. 14. Bhatt DL, Fox KA, Hacke W, Berger PB, Black HR, Boden WE, et al. Clopidogrel and aspirin versus aspirin alone for the prevention of atherothrombotic events. N Engl J Med 2006;354:1706-17. 15. Cacoub PP, Bhatt DL, Steg PG, Topol EJ, Creager MA, Creager MA. Patients with peripheral arterial disease in the CHARISMA trial. Eur Heart J 2009;30:192-201. 16. McCoach CE, Armstrong EJ, Singh S, Javed U, Anderson D, Yeo KK, et al. Gender-related variation in the clinical presentation and outcomes of critical limb ischemia. Vasc Med 2013;18:19-26. 17. Hill ME, Rosenwaike I. The Social Security Administration’s Death Master File: the completeness of death reporting at older ages. Soc Secur Bull 2001;64:45-51. 18. Conte MS, Geraghty PJ, Bradbury AW, Hevelone ND, Lipsitz SR, Moneta GL, et al. Suggested objective performance goals and clinical trial design for evaluating catheter-based treatment of critical limb ischemia. J Vasc Surg 2009;50:1462-73. e1-e3. 19. Rutherford RB, Baker J, Ernst C, Johnston K, Porter JM, Ahn S, et al. Recommended standards for reports dealing with lower extremity ischemia: revised version. J Vasc Surg 1997;26:517-38. 20. Chen WH, Lee PY, Ng W, Tse HF, Lau CP. Aspirin resistance is associated with a high incidence of myonecrosis after non-urgent percutaneous coronary intervention despite clopidogrel pretreatment. J Am Coll Cardiol 2004;43:1122-6. 21. Spiliopoulos S, Pastromas G, Katsanos K, Kitrou P, Karnabatidis D, Siablis D. Platelet responsiveness to clopidogrel treatment after peripheral endovascular procedures: the PRECLOP Study: clinical impact and optimal cutoff value of on-treatment high platelet reactivity. J Am Coll Cardiol 2013;61:2428-34. 22. Curtis LH, Hammill BG, Eisenstein EL, Kramer JM, Anstrom KJ. Using inverse probability-weighted estimators in comparative effectiveness analyses with observational databases. Med Care 2007;45: S103-7. 23. Robins JM, Hernán MA, Brumback B. Marginal structural models and causal inference in epidemiology. Epidemiology 2000;11:550-60. 24. Cole SR, Hernán MA. Adjusted survival curves with inverse probability weights. Comput Methods Programs Biomed 2004;75:45-9. 25. Dafni UU. Landmark analysis at the 25-year landmark point. Circ Cardiovasc Qual Outcomes 2011;4:363-71. 26. Fowkes FG, Price JF, Stewart MC, Butcher I, Leng GC, Pell AC, et al. Aspirin for prevention of cardiovascular events in a general population screened for a low ankle brachial index: a randomized controlled trial. JAMA 2010;303:841-8. 27. Belch J, MacCuish A, Campbell I, Cobbe S, Taylor R, Prescott R, et al. The prevention of progression of arterial disease and diabetes (POPADAD) trial: factorial randomised placebo controlled trial of aspirin and antioxidants in patients with diabetes and asymptomatic peripheral arterial disease. BMJ 2008;337:a1840. 28. 2011 Writing Group Members, 2005 Writing Committee Members, ACCF/AHA Task Force Members. 2011 ACCF/AHA focused update of the guideline for the management of patients with peripheral artery disease (updating the 2005 Guideline): a report of the American College of Cardiology Foundation/American Heart Association Task Force on practice guidelines. Circulation 2011;124: 2020-45. 29. Belch JJ, Dormandy J. Results of the randomized, placebo-controlled clopidogrel and acetylsalicylic acid in bypass surgery for peripheral arterial disease (CASPAR) trial. J Vasc Surg 2010;52:825-8.e2. 30. Wong PF, Chong LY, Mikhailidis DP, Robless P, Stansby G. Antiplatelet agents for intermittent claudication. Cochrane Database Syst Rev 2011:CD001272. 31. Bonaca MP, Scirica BM, Creager MA, Olin J, Bounameaux H, Dellborg M, et al. Vorapaxar in patients with peripheral artery disease: results from TRA20P-TIMI 50. Circulation 2013;127:1522-6.

JOURNAL OF VASCULAR SURGERY Volume -, Number -

32. Martorell L, Martínez-González J, Rodríguez C, Gentile M, Calvayrac O, Badimon L. Thrombin and protease-activated receptors (PARs) in atherothrombosis. Thromb Haemost 2008;99:305-15. 33. Serebruany VL, Steinhubl SR, Berger PB, Malinin AI, Bhatt DL, Topol EJ. Variability in platelet responsiveness to clopidogrel among 544 individuals. J Am Coll Cardiol 2005;45:246-51. 34. Bliden KP, DiChiara J, Tantry US, Bassi AK, Chaganti SK, Gurbel PA. Increased risk in patients with high platelet aggregation receiving chronic clopidogrel therapy undergoing percutaneous coronary intervention: is the current antiplatelet therapy adequate? J Am Coll Cardiol 2007;49:657-66. 35. Angiolillo DJ, Ferreiro JL, Price MJ, Kirtane AJ, Stone GW, Angiolillo DJ, et al. Platelet function and genetic testing. J Am Coll Cardiol 2013;62:S21-31. 36. Mega JL, Close SL, Wiviott SD, Shen L, Hockett RD, Brandt JT, et al. Cytochrome p-450 polymorphisms and response to clopidogrel. N Engl J Med 2009;360:354-62. 37. Tepe G, Bantleon R, Brechtel K, Schmehl J, Zeller T, Claussen C, et al. Management of peripheral arterial interventions with mono or dual antiplatelet therapydthe MIRROR study: a randomised and doubleblinded clinical trial. Eur Radiol 2012;22:1998-2006.

Armstrong et al 9

38. Collet JP, Cuisset T, Rangé G, Cayla G, Elhadad S, Pouillot C, et al. Bedside monitoring to adjust antiplatelet therapy for coronary stenting. N Engl J Med 2012;367:2100-9. 39. Price MJ, Berger PB, Teirstein PS, Tanguay JF, Angiolillo DJ, Spriggs D, et al. Standard- vs high-dose clopidogrel based on platelet function testing after percutaneous coronary intervention: the GRAVITAS randomized trial. JAMA 2011;305:1097-105. 40. Karnabatidis D, Spiliopoulos S, Pastromas G, Kitrou P, Christeas N, Katsanos K, et al. Prevalence of nonresponsiveness to aspirin in patients with symptomatic peripheral arterial disease using true point of care testing. Cardiovasc Intervent Radiol 2014;37:631-8. 41. Faglia E, Clerici G, Clerissi J, Gabrielli L, Losa S, Mantero M, et al. Long-term prognosis of diabetic patients with critical limb ischemia: a population-based cohort study. Diabetes Care 2009;32: 822-7.

Submitted Oct 19, 2014; accepted Jan 21, 2015.

Additional material for this article may be found online at www.jvascsurg.org.

JOURNAL OF VASCULAR SURGERY --- 2015

9.e1 Armstrong et al

Supplementary Table I (online only). Standardized differences in covariates before and after propensity weighting

Supplementary Table II (online only). Propensity matched analysis of cardiovascular outcomesa HR (95% CI)

Standardized difference, % Variable Ejection fraction Coronary artery disease Diabetes b-Blocker Gastrointestinal bleeding MI Body mass index Statin Prior cancer GFR ACE inhibitor COPD Carotid artery disease Caucasian Hypertension AAA Rutherford score Age Congestive heart failure Prior amputation Current smoker Stroke/TIA Sex

Before adjustment

After adjustment

27.9 18.4 14.6 12.8 12.6 12.4 10.3 9.3 8.9 7.7 6.8 6.3 5.3 5.1 4.4 4.3 4.3 3.1 3.0 2.8 2.3 1.1 1.0

5.7 0.4 1.6 1.0 0.3 1.1 1.7 0.7 0.3 1.2 0.3 1.1 1.2 1.0 0.4 0.7 5.6 1.0 0.8 0.6 0.4 0.6 1.6

AAA, Abdominal aortic aneurysm; ACE, angiotensin-converting enzyme; COPD, chronic obstructive pulmonary disease; GFR, glomerular filtration rate; MI, myocardial infarction; TIA, transient ischemic attack.

Outcome MACE MALE Death Amputation/death

Unadjusted 0.63 0.72 0.56 0.54

(0.43-0.93) (0.42-1.22) (0.34-0.92) (0.35-0.84)

Adjusted 0.68 0.95 0.61 0.56

(0.52-0.90) (0.62-1.46) (0.44-0.84) (0.43-0.74)

CI, Confidence interval; HR, hazard ratio; MACE, major adverse cardiovascular event; MALE, major adverse limb event. a Nearest-neighbor matching was performed using a caliper width equal to 0.25  the standard deviation of the propensity score. Unadjusted HRs represent rates of MACE, MALE, death, and amputation/death before adjustment of baseline covariates. Adjusted HRs were calculated using the same covariates included in the main propensity model.

Supplementary Table III (online only). Propensity weighted outcomes after trimminga HR (95% CI) Outcome MACE MALE Death Amputation/death

Unadjusted 0.63 0.72 0.56 0.54

(0.43-0.93) (0.42-1.22) (0.34-0.92) (0.35-0.84)

Adjusted 0.66 0.87 0.61 0.60

(0.47-0.92) (0.51-1.48) (0.41-0.89) (0.43-0.83)

CI, Confidence interval; HR, hazard ratio; MACE, major adverse cardiovascular event; MALE, major adverse limb event. a After trimming propensity weights with values <0.1, 340 patients were prescribed dual-antiplatelet therapy (DAPT) and 270 were prescribed acetylsalicylic acid (ASA [aspirin]) monotherapy. Unadjusted HRs represent rates of MACE, MALE, death, and amputation/death before adjustment of baseline covariates. Adjusted HRs were calculated using the same covariates included in the main propensity model.