FUNDAMENTO: O papel dos testes de reatividade plaquetária (RP) na predição de eventos em longo prazo em pacientes latino-americanos tratados com stents farmacológicos (SF) não foi estabelecido. OBJETIVOS: Analisar o papel dos testes de RP na predição de eventos após a implantação de SF. MÉTODOS: De maio de 2006 a janeiro de 2008, foram incluídos 209 pacientes brasileiros que se submeteram a tratamento eletivo com SF. A RP foi avaliada 12 a 18 horas após o procedimento, por agregometria de transmitância de luz com 5µM de ADP. Os pacientes foram acompanhados prospectivamente por até 4,8 anos. Dezessete (8%) dos indivíduos foram perdidos durante o acompanhamento e a coorte final foi composta de 192 pacientes. A curva ROC foi utilizada para determinar o melhor ponto de corte de 5µM de ADP para prever eventos. O endpoint primário foi uma combinação de morte cardiovascular, infarto agudo do miocárdio, trombose definitiva de stent, e revascularização de artéria alvo.Modelos de risco proporcional de Cox foram utilizados para determinar as variáveis independentemente associadas com o tempo até o primeiro evento. RESULTADOS: O melhor ponto de corte de 5µM de ADP foi de 33%. Cento e sete (55,7%) pacientes apresentaram 5mM de ADP > 33%. A taxa de sobrevivência livre de eventos em 1.800 dias foi de 55% contra 70% para os indivíduos com ADP5 acima e abaixo desse ponto de corte, respectivamente (p = 0,001). Preditores de tempo independentes para o primeiro evento foram tabagismo atual (HR 3,49, IC95%: 1,76-6,9, p = 0,0003), ADP 5mM > 33% (HR 1,95, IC95%: 1,09-3,51, p = 0,025) e idade (HR 1,03 IC 95%: 1,0-1,06, p = 0,041). CONCLUSÕES: Neste estudo, 55,7% dos pacientes apresentaram alta reatividade plaquetária durante tratamento. 5µM de ADP > 33% foi um preditor independente de eventos em longo prazo.
ARTIGO ORIGINAL
ANGIOPLASTIA COM E SEM STENT
IUniversidade Federal Fluminense, Programa de Pós-Graduação em Ciências Cardiovasculares, Niterói, RJ
IICasa de Saúde São José, Rio de Janeiro, RJ - Brasil
Em pacientes tratados com stents farmacológicos (SF), a dupla terapia antiplaquetária é obrigatória e tratamento com clopidogrel e aspirina tem sido o procedimento mais utilizado na prática clínica1. No entanto, muitos indivíduos respondem mal ao clopidogrel quando avaliados por testes de reatividade plaquetária (TRP)2-4. Uma série de estudos tem demonstrado uma associação entre a reatividade plaquetária no tratamento em um único momento durante a terapia com clopidogrel e o risco de eventos cardíacos em pacientes caucasianos que foram submetidos à intervenção coronária percutânea (ICP)5-10. No entanto, o papel desses testes em pacientes latino-americanos tratados com SF não está claro. Essa é uma questão importante, pois a resposta ao clopidogrel pode ser influenciada por fatores genéticos, tais como polimorfismos P45011-15 e a distribuição destes polimorfismos genéticos pode ser diferentes entre os grupos étnicos. Por exemplo, o CYP2C19*2 com perda de função é comum em diversas populações e ocorre em 24% dos indivíduos caucasianos. No entanto, a frequência desse alelo é um pouco menor em mexicanos-americanos (18%), maior em afro-americanos (33%), e significativamente maior em populações asiáticas (51%)16-18. Além disso, a força do efeito do CYP2C19*2 na resposta ao clopidogrel pode depender de outros fatores, tais como herança genética ou exposições ambientais, que podem diferir entre as etnias. Dessa forma, os TRP podem ter desempenhos diferentes de acordo com a origem étnica.
Neste estudo, buscou-se avaliar o papel da reatividade plaquetária durante o tratamento medida pela agregometria óptica na previsão de longo prazo de eventos cardiovasculares em pacientes brasileiros tratados com SF.
Este estudo foi aprovado pelo Comitê de Ética Médica do nosso hospital e segue a Declaração de Helsinki. Todos os pacientes forneceram consentimento informado por escrito. O estudo foi financiado pela nossa instituição.
Esse foi um estudo de coorte observacional, prospectivo. De maio de 2006 a janeiro de 2008, foram prospectivamente incluídos 209 pacientes brasileiros consecutivos que foram submetidos à ICP eletiva com implante de SF em um hospital cardiológico. A média de idade foi de 67 ± 10,4 anos e 142 (74%) eram do sexo masculino. Todos os pacientes apresentavam doença arterial coronária estável. A indicação de ICP foi deixada a critério do médico assistente. Dados clínicos basais foram coletados imediatamente antes da intervenção. Antes da ICP, os pacientes foram tratados com clopidogrel de acordo com nosso protocolo institucional. Pacientes virgens de clopidogrel foram tratados com uma dose de ataque de 600 mg, duas horas antes do procedimento. Os pacientes que já estavam usando clopidogrel por pelo menos cinco dias não receberam a dose de ataque. O tipo do stent foi o Cypher em 117 (56%) pacientes, Taxus em 86 (41%), Endeavour em 10 (4,7%), e outros em seis (2,8%) indivíduos.
A reatividade plaquetária foi avaliada em um único ponto no tempo em todos os pacientes, de 12 a 18 horas após a ICP através de agregometria por transmissão de luz com 5µM de ADP. Na alta hospitalar, todos os pacientes estavam em tratamento com aspirina 100 mg e 75 mg de clopidogrel por dia, e foram mantidos com esse tratamento durante pelo menos um ano. Todas as decisões sobre questões terapêuticas foram deixados a critério do médico assistente.
O acompanhamento foi feito através de entrevistas telefônicas e complementado com informações dos médicos responsáveis e registros hospitalares. Foram coletados dados do estado clínico e sobre o regime medicamentoso, incluindo o uso de clopidogrel. Os pacientes foram acompanhados por até 4,8 anos (média de 2,2 ± 1,2 anos). Dezessete (8%) pacientes foram perdidos no acompanhamento e a coorte final foi composta de 192 pacientes.
As amostras de sangue (5 tubos com 4,5 mL) foram coletadas de todos os pacientes 12 a 18 horas após a ICP. A função plaquetária foi avaliada através de agregometria por transmissão de luz. Plasma rico em plaquetas foi preparado por centrifugação de amostras de sangue a 250 x g por 10 min. Estudos de agregação foram realizados com um agregômetro Chrono-log óptico (Chrono-log Corporation, EUA) e o AGGRO / LINK software ® 810-CA para Windows. Foram utilizados como agonistas 5µM de ADP e ácido araquidônico (1µM).
O endpoint primário foi uma combinação de morte cardiovascular, infarto do miocárdio não-fatal, trombose definitiva de stent e revascularização percutânea da artéria alvo. A trombose definitiva foi considerada como síndrome coronariana aguda com uma angiografia mostrando trombose de stent. De acordo com o tempo de ICP, foi classificada em aguda (
As variáveis categóricas são expressas como frequências e percentuais. As variáveis contínuas foram analisadas para uma distribuição normal com o teste de Kolmogorov-Smirnoff. Variáveis distribuídas normalmente são apresentadas como média ± desvio padrão. A curva ROC foi utilizada para determinar o ponto de corte ótimo de 5µM de ADP para predizer eventos. Curvas de sobrevida livre de eventos de Kaplan-Meier foram construídas e o teste log-rank foi utilizado para avaliar as diferenças entre as curvas. Modelos de risco proporcional de Cox foram usados para determinar as variáveis independentemente associadas com tempo até o primeiro evento. As covariáveis incluídas nessa análise foram: idade, sexo, histórico de hipertensão, histórico de diabetes mellitus, histórico de dislipidemia, tabagismo atual, infarto do miocárdio prévio, revascularização coronária prévia, ICP prévio, aspirina, betabloqueadores, inibidores da enzima de conversão da angiotensina, bloqueadores dos receptores da angiotensina, estatinas, regime periprocedimento com clopidogrel, uso de clopidogrel por mais de um ano após a ICP, stent implantado na artéria descendente anterior (ADA), ICP multiarterial, número de stents implantados, diâmetro mínimo do stent, comprimento total do stent, ácido araquidônico, e 5µM de ADP. As variáveis foram selecionadas utilizando-se o método
O ponto de corte ótimo de 5µM ADP, conforme determinado pela análise da curva ROC, foi de 33%, com a área sob a curva (AUC) de 0,58 (intervalo de confiança de 95%, 0,49-0,67). A sensibilidade, especificidade, valor preditivo positivo e valor preditivo negativo foram, respectivamente, 66,7%, 48,2%, 31,8% e 80%. Usando esse ponto de corte, a alta reatividade plaquetária (ARP) durante o tratamento estava presente em 107 (55,7%) dos 192 pacientes incluídos na análise. As características basais dos pacientes com ARP em comparação com os pacientes com reatividade plaquetária baixa são mostradas na
Durante o acompanhamento, 51 (26,5%) pacientes atingiram o endpoint primário. A média de 5µM ADP foi superior nesses pacientes, em comparação com aqueles sem endpoints (37 ± 13,5
As taxas de sobrevida livre de eventos foram menores para fumantes atuais e pacientes com ARP (
A principal descoberta do presente estudo foi que a ARP medida pela agregometria por transmissão da luz estava independentemente associada com eventos cardiovasculares em pacientes brasileiros com doença arterial coronária estável submetidos a ICP com implante de SF. O ponto de corte ótimo para 5µM ADP nessa análise foi de 33%. Nosso estudo é o primeiro a incluir apenas pacientes latino-americanos do Brasil e confirmou que os TRP são úteis na previsão de resultados em longo prazo nesse cenário, como demonstrado com pacientes caucasianos.
A função plaquetária pode ser avaliada por diferentes métodos. A agregometria por transmissão da luz tem sido utilizada por outros autores para tratar o valor desse teste na predição de eventos cardiovasculares após implante de stent coronário5-7. Esses estudos demonstraram que a avaliação da função plaquetária foi capaz de identificar pacientes de alto risco. No entanto, eles forneceram informações apenas depois de 30 dias, 6 meses e 1 ano de acompanhamento. A esse respeito, nosso estudo adiciona informações aos estudos anteriores utilizando agregometria por transmissão de luz, uma vez que fornece dados em acompanhamento de longo prazo, demonstrando que os TRP podem identificar pacientes em risco além de um ano após o implante de SF. Mais recentemente, um novo método utilizado para avaliar a função plaquetária foi introduzido. O Multiplate Analyser é teste laboratorial remoto que tem mostrado ser superior à agregometria convencional por transmissão de luz19.
Uma comparação direta dos testes de função plaquetária foi relatada em apenas um estudo. O estudo POPULAR6 comparou a capacidade de seis TRPs diferentes em prever eventos aterotrombóticos em pacientes pré-tratados com clopidogrel submetidos a ICP com implante de stent. Apenas agregometria por transmissão de luz, VerifyNow, e Plateletworks foram significativamente associados com o endpoint primário. O IMPACT-R, Dade PFA colágeno / ADP, e Inovance PFA P2Y não foram capazes de discriminar entre pacientes com e sem eventos em 1 ano de acompanhamento. Digno de nota, embora os três testes anteriores tenham sido capazes de identificar pacientes em risco, a área sob a curva foi modesta (0,63, 0,62, e 0,61, respectivamente). No presente estudo, isso também foi verdade. A área sob a curva para o 5µM ADP > 33% foi de apenas 0,58. Da mesma forma, observou-se um bom valor preditivo negativo, mas baixo valor preditivo positivo, como também foi observado no estudo POPULAR. Uma possível explicação para esse achado é que em todos estes estudos, incluindo o nosso, a função plaquetária foi avaliada em um único momento. De fato, tem sido demonstrado que, em pacientes recebendo clopidogrel, a função plaquetária varia ao longo do tempo e, portanto, as medições seriadas melhoram a precisão desses testes20. Usando o ensaio VerifyNow P2Y12, Campo et al. demonstraram que a reatividade das plaquetas diminuiu do valor basal para um mês em pacientes com clopidogrel, melhorando a área sob a curva de 0,69 no valor basal a 0,87 em 30 dias. Com clopidogrel, a reatividade plaquetária em 1 mês foi o mais forte preditor de resultados adversos20.
Outra preocupação em relação às medidas da função plaquetária nesse cenário refere-se ao ponto de corte ótimo para a previsão de eventos. Alguns estudos têm utilizado pontos de corte pré-especificados, enquanto outros usaram curvas ROC para determinar o ponto de corte ideal. Dois estudos que utilizaram 5µM ADP sugeriram pontos de corte de 42,9% e de 46% com base nas curvas ROC6,21. Encontramos um ponto de corte inferior de 33%. Isto pode ser explicado por um maior tempo de acompanhamento em nosso estudo e diferenças na gravidade da doença. Além disso, estudos recentes têm encontrado pontos de corte mais baixos do que os sugeridos por estudos anteriores. Por exemplo, no estudo GRAVITAS, o teste VerifyNow P2Y12 foi utilizado para identificar pacientes com ARP22. Um ponto de corte preestabelecido de 240 PRU foi utilizado com base em dados anteriores23. Pacientes com ARP foram randomizados para um tratamento fixo com alta dose de clopidogrel (600 mg, seguido de 150 mg por dia durante 6 meses) ou a dose padrão de clopidogrel (75 mg por dia). Não houve diferenças entre os desfechos dos dois tratamentos. No entanto, em uma subanálise deste estudo, o ponto de corte pré-especificado de 240 PRU não foi associado com eventos isquêmicos no acompanhamento. Pelo contrário, um ponto de corte post-hoc de 208 PRU avaliado de 12 a 24 h após a PCI ou em 30 dias foi associado com o endpoint primário24. Digno de nota, usando esse ponto de corte inferior, a proporção de pacientes com ARP era muito semelhante à observada no nosso estudo (49,6% e 55,7%, respectivamente).
Embora a maioria dos estudos tenha mostrado que os testes de reatividade plaquetária são úteis na predição de eventos em pacientes tratados com implante de stent, um estudo recente usando o ensaio VerifyNow P2Y12 não mostrou qualquer benefício25. Uma possível explicação para esse achado é que as taxas de eventos foram menores do que o esperado. Taxas de eventos de dois anos em pacientes com e sem ARP foram de 2,8% e 2,4%, muito menor do que a observada em nosso estudo. Isso também poderia estar relacionado com as diferenças raciais ou étnicas, uma vez que esse estudo foi realizado em uma população asiática, em contraste com uma população predominantemente ocidental em outros estudos.
Metade dos endpoints em nosso estudo ocorreu após 1 ano de acompanhamento. Esta é uma descoberta importante, já que a terapia antiplaquetária dupla em pacientes com SF tem sido recomendada por até 1 ano. Demonstramos que muitos eventos ainda ocorrem depois desse ponto no tempo e os pacientes em risco, apesar da utilização de aspirina e clopidogrel, podem ser identificados através de TRP. Entre 5 tromboses definitivas de stent, duas ocorreram 2 e 3,6 anos pós-ICP, em pacientes recebendo terapia antiplaquetária dupla. Por outro lado, um aumento "rebote" transitório na reatividade plaquetária 3 meses após a interrupção do clopidogrel já foi observada26 e pode explicar o aumento nos eventos isquêmicos que ocorrem imediatamente após a descontinuação do clopidogrel27,28, embora alguns acreditem que esses eventos são apenas um resultado de epitelização tardia do stent29. O tempo ideal da terapia antiplaquetária dupla pós-implantação de stent é uma questão de debate e merece mais estudos. No entanto, tivemos a oportunidade única de estudar pacientes que estavam em uso de clopidogrel por mais de um ano após a intervenção, a critério de seus médicos responsáveis. Nossos dados sugerem que pacientes com ARP têm risco aumentado de eventos, mesmo se persistirem com clopidogrel além de 1 ano pós-ICP.
O mais forte preditor de eventos cardiovasculares nesse estudo foi o tabagismo atual. Embora o tabagismo tenha sido relacionado à trombose tardia29,30, poucos estudos têm abordado a associação entre o tabagismo, a análise da função plaquetária e prognóstico nesse cenário. Em alguns estudos, uma proporção maior de fumantes foi observada em pacientes com baixa reatividade plaquetária5,22. Em outros, o oposto7 ou nenhuma diferença foi observada6. No entanto, o chamado paradoxo do fumante tem sido descrito. De acordo com esta hipótese, o fumo estimula o CYP1A2 no citocromo P450, resultando em maior produção do metabólito ativo do clopidogrel e em menor trombose do stent31. Nossos resultados não apoiam essa teoria. Mais importante, em no nosso estudo 5µM ADP > 33% previu eventos cardíacos, independentemente do tabagismo atual.
A melhor estratégia para o manejo de pacientes com alta reatividade plaquetária em tratamento não está clara. A estratégia de tratamento fixo com alta dose de clopidogrel, testada no estudo GRAVITAS, não foi superior ao tratamento com dose padrão22. Alternativamente, pode-se escolher um dos novos fármacos antiplaquetários, prasugrel ou ticagrelor, que têm demonstrado serem superiores ao clopidogrel em ensaios clínicos, no contexto de síndromes coronárias agudas32,33.
Embora a maioria dos autores concorde que as evidências disponíveis atualmente apoiam o conceito de um limite para a reatividade plaquetária durante o tratamento que pode ser usado para estratificar o risco do paciente para eventos isquêmicos após ICP34, as diretrizes não recomendam testes de função plaquetária de forma rotineira1,35-37. Isto pode ser devido a alguns inconvenientes relacionados a esses testes. Até o momento não há ensaios clínicos em grande escala, demonstrando que o ajuste da terapia antiplaquetária com base em qualquer desses pontos de corte melhora os resultados clínicos. Questões adicionais são a falta de consenso sobre o melhor método para avaliar a ARP e o valor do ponto de corte associado com o risco clínico. No entanto, acreditamos que tais testes são de particular importância em pacientes que tenham sofrido síndrome coronária aguda. As diretrizes recomendam que esses pacientes sejam mantidos em terapia antiplaquetária dupla idealmente por um ano. Na verdade, a incidência de trombose muito tardia no estudo HORIZONS-AMI30 foi elevada, independente do tipo de stent, justificando o monitoramento desses pacientes com TRP ao longo do tempo.
Este estudo tem algumas limitações. Em primeiro lugar, esse é um estudo de centro único relativamente pequeno e nossos resultados devem ser generalizados com cautela. Apesar disso, o estudo apresentou poder suficiente para detectar diferenças entre os grupos, devido ao longo tempo de acompanhamento. Não foram coletados dados sobre eventos hemorrágicos, que são endpoints importantes relacionados com a mortalidade. Não foram realizadas medições em série da função plaquetária, que têm demonstrado um aumento da precisão do teste. E, finalmente, os nossos dados referem-se principalmente à primeira geração de stents e não podem ser aplicados aos stents de nova geração.
Neste estudo, um valor de corte de 33% para 5µM ADP foi associado com eventos em longo prazo em pacientes brasileiros com doença arterial coronária estável tratados com SF. Usando esse ponto de corte, 55,7% dos pacientes apresentaram alta reatividade plaquetária durante o tratamento. O tabagismo atual foi o mais forte preditor de eventos cardiovasculares, seguido pela ARP e idade. A ARP previu eventos em longo prazo, independentemente da manutenção do clopidogrel por mais de 1 ano.
Esse trabalho foi financiado por nossas instituições e nenhuma fonte financeira externa foi fornecida.
Concepção e desenho da pesquisa: Villacorta AS, Villacorta Junior H, Helmuth B; Obtenção de dados: Villacorta AS, Batista MJS, Gomes RV, Macedo LA; Análise e interpretação dos dados: Villacorta AS, Villacorta Junior H, Mesquita ET; Análise estatística: Villacorta Junior H; Redação do manuscrito: Villacorta AS; Revisão crítica do manuscrito quanto ao conteúdo intelectual: Villacorta Junior H, Batista MJS, Gomes RV, Mesquita ET, Helmuth B.
Declaro não haver conflito de interesses pertinentes.
O presente estudo não teve fontes de financiamento externas.
Este artigo é parte de dissertação de Mestrado de Aline Sterque Villacorta pela Universidade Federal Fluminense.
1. Levine GN, Bates ER, Blankenship JC, Bayley SR, Bittl JA, Cercek B, et al; American College of Cardiology Foundation; American Heart Association Task Force on Practice Guidelines; Society for Cardiovascular Angiography and Interventions. 2011 ACCF/AHA/SCAI Guideline for Percutaneous Coronary Intervention. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Society for Cardiovascular Angiography and Interventions. J Am Coll Cardiol. 2011;58(24):e44-122.
2. Gurbel PA, Bliden KP, Hiatt BL, O'Connor CM. Clopidogrel for coronary stenting: response variability, drug resistance, and the effect of pretreatment platelet reactivity. Circulation. 2003;107(23):2908-13.
3. 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(2):246-51.
4. Heptinstall S. Variable therapeutic effectiveness of clopidogrel in acute coronary syndromes. J Thromb Haemost. 2006;4(3):539-41.
5. Buonamici P, Marcucci R, Migliorini A, Gensini GF, Santini A, Paniccia R, et al. Impact of platelet reactivity after clopidogrel administration on drug-eluting stent thrombosis. J Am Coll Cardiol. 2007;49(24):2312-7.
6. Breet NJ, van Werkum JW, Bouman HJ, Kelder JC, Ruven HJ, Bal ET, et al. Comparison of platelet function tests in predicting clinical outcome in patients undergoing coronary stent implantation. JAMA. 2010;303(8):754-62.
7. Hochholzer W, Trenk D, Bestehorn HP, Fischer B, Valina CM, Ferenc M, al. Impact of the degree of peri-interventional platelet inhibition after loading with clopidogrel on early clinical outcome of elective coronary stent placement. J Am Coll Cardiol. 2006;48(9):1742-50.
8. Price MJ, Endemann S, Gollapudi RR, Valencia R, Stinis CT, Levisay JP, et al. Prognostic significance of post-clopidogrel platelet reactivity assessed by a point-of-care assay on thrombotic events after drug-eluting stent implantation. Eur Heart J. 2008;29(8):992-1000.
9. Gurbel PA, Bliden KP, Guyer K, Cho PW, Zaman KA, Kreutz RP, et al. Platelet reactivity in patients and recurrent events post-stenting: results of the PREPARE POST-STENTING Study. J Am Coll Cardiol. 2005;46(10):1820-6.
10. Geisler T, Langer H, Wydymus M, Gohring K, Zurn C, Bigalke B, et al. Low response to clopidogrel is associated with cardiovascular outcome after coronary stent implantation. Eur Heart J. 2006;27(20):2420-5.
11. 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(4):354-62.
12. Shuldiner AR, O'Connel JR, Bliden KP, Gandhi A, Ryan K, Horenstein RB, et al. Association of cytochrome P450 2C19 genotype with the antiplatelet effect and clinical efficacy of clopidogrel therapy. JAMA. 2009;302(8):849-57.
13. Hulot JS, Collet JP, Silvain J, Pena A, Bellemain-Appaix A, Barthélémy O, et al. Cardiovascular risk in clopidogrel-treated patients according to cytochrome P450 2C19*2 loss-of-function allele or proton pump inhibitor coadministration: a systematic meta-analysis. J Am Coll Cardiol. 2010;56(2):134-43.
14. Bouman HJ, Schömig E, van Werkum JW, Velder J, Hackeng CM, Hirschhäuser C, et al. Paraoxonase-1 is a major determinant of clopidogrel efficacy. Nat Med. 2011;17(1):110-6.
15. Kassimis G, Davlouros P, Xanthopoulou I, Stavrou EF, Athanassiadou A, Alexopoulos D. CYP2C19*2 and other genetic variants affecting platelet response to clopidogrel in patients undergoing percutaneous coronary intervention. Thromb Res. 2012;129(4):441-6.
16. Luo HR, Poland RE, Lin KM, Wan YJ. Genetic polymorphism of cytochrome P450 2C19 in Mexican Americans: a cross-ethnic comparative study. Clin Pharmacol Ther. 2006;80(1):33-40.
17. Xiao ZS, Goldstein JA, Xie HG, Blaisdell J, Wang W, Jiang CH, et al. Differences in the incidence of the CYP2C19 polymorphism affecting the S-mephenytoin phenotype in Chinese Han and Bai populations and identification of a new rare CYP2C19 mutant allele. J Pharmacol Exp Ther. 1997;281(1):604-9.
18. Takakubo F, Kuwano A, Kondo I. Evidence that poor metabolizers of (S)-mephenytoin could be identified by haplotypes of CYP2C19 in Japanese. Pharmacogenetics. 1996;6(3):265-7.
19. Johnston LR, Larsen PD, La Flamme AC, Harding SA. Methodological considerations for the assessment of ADP induced platelet aggregation using the Multiplate® analyser. Platelets. 2012 Jun 11. [Epub ahead of print].
20. Campo G, Parrinello G, Ferraresi P, Lunghi B, Tebaldi M, Miccoli M, et al. Prospective evaluation of on-clopidogrel platelet reactivity over time in patients treated with percutaneous coronary intervention relationship with gene polymorphisms and clinical outcome. J Am Coll Cardiol. 2011;57(25):2474-83.
21. Gurbel PA, Antonino MJ, Bliden KP, DiChiara J, Suarez TA, Sigla A, et al. Platelet reactivity to adenosine diphosphate and long-term ischemic event occurrence following percutaneous coronary intervention: a potential antiplatelet therapeutic target. Platelets. 2008;19(8):595-604.
22. Price MJ, Berger PB, Teirstein PS, Tanguay JF, Angiolillo DJ, Spriggs D, et al; GRAVITAS Investigators. Standard- vs high-dose clopidogrel based on platelet function testing after percutaneous coronary intervention: the GRAVITAS randomized trial. JAMA. 2011;305(11):1097-105.
23. Price MJ, Berger PB, Angiolillo DJ, Teirstein PS, Tanguay JF, Kandzari DE, et al. Evaluation of individualized clopidogrel therapy after drug-eluting stent implantation in patients with high residual platelet reactivity: design and rationale of the GRAVITAS trial. Am Heart J. 2009;157(5):818-24.
24. Price MJ, Angiolillo DJ, Teirstein PS, Lillie E, Manoukian SV, Berger PB, et al. Platelet reactivity and cardiovascular outcomes after percutaneous coronary intervention: a time-dependent analysis of the Gauging Responsiveness with a VerifyNow P2Y12 assay: Impact on Thrombosis and Safety (GRAVITAS) trial. Circulation. 2011;124(10):1132-7.
25. Park DW, Lee SW, Yun SC, Song HG, Ahn JM, Lee JY, et al. A point-of-care platelet function assay and C-reactive protein for prediction of major cardiovascular events after drug-eluting stent implantation. J Am Coll Cardiol. 2011;58(25):2630-9.
26. Mylotte D, Peace AJ, Tedesco AT, Mangiacapra F, Dicker P, Kenny D, et al. Clopidogrel discontinuation and platelet reactivity following coronary stenting. J Thromb Haemost. 2011;9(1):24-32.
27. Ho PM, Peterson ED, Wang L, Magid DJ, Fihn SD, Larsen GC, et al. Incidence of death and acute myocardial infarction associated with stopping clopidogrel after acute coronary syndrome. JAMA. 2008;299(5):532-9.
28. Schulz S, Schuster T, Mehilli J, Byrne RA, Ellert J, Massberg S, et al. Stent thrombosis after drug-eluting stent implantation: incidence, timing, and relation to discontinuation of clopidogrel therapy over a 4-year period. Eur Heart J. 2009;30(22):2714-21.
29. Ellis SG, Colombo A, Grube E, Popma J, Koglin J, Dawkins KD, et al. Incidence, timing, and correlates of stent thrombosis with the polymeric paclitaxel drug-eluting stent: a TAXUS II, IV, V, and VI meta-analysis of 3,445 patients followed for up to 3 years. J Am Coll Cardiol. 2007;49(10):1043-51.
30. Dangas GD, Caixeta A, Mehram R, Parise H, Lansky AJ, Cristea E, et al; Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction (HORIZONS-AMI) Trial Investigators. Frequency and predictors of stent thrombosis after percutaneous coronary intervention in acute myocardial infarction. Circulation. 2011;123(16):1745-56.
31. Park KW, Kang SH, Kang J, Jeon KH, Park JJ, Han JK, et al. Enhanced clopidogrel response in smokers is reversed after discontinuation as assessed by VerifyNow assay: additional evidence for the concept of 'smokers' paradox'. Heart. 2012;98(13):1000-6.
32. Wiviott SD, Braunwald E, McCabe CH, Montalescot G, Ruzyllo W, Gottlieb S, et al. Prasugrel versus clopidogrel in patients with acute coronary syndromes. N Engl J Med. 2007;357(20):2001-15.
33. Wallentin L, Becker RC, Budaj A, Cannon CP, Emanuelsson H, Held C, et al. Ticagrelor versus clopidogrel in patients with acute coronary syndromes. N Engl J Med. 2009;361(11):1045-57.
34. Bonello L, Tantry US, Marcucci R, Blindt R, Angiolillo DJ, Becker R, et al; Working Group on High On-Treatment Platelet Reactivity. Consensus and future directions on the definition of high on-treatment platelet reactivity to adenosine diphosphate. J Am Coll Cardiol. 2010;56(12):919-33.
35. Hamm CW, Bassand JP, Agewall S, Bax J, Boersma E, Bueno H, et al; ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation: The Task Force for the management of acute coronary syndromes (ACS) in patients presenting without persistent ST-segment elevation of the European Society of Cardiology (ESC). Eur Heart J. 2011;32(23):2999-3054.
36. Wright RS, Anderson JL, Adams CD, Bridges CR, Casey Jr DE, Ettinger SM, et al. 2011 ACCF/AHA focused update of the Guidelines for the Management of Patients with Unstable Angina/Non-ST-Elevation Myocardial Infarction (updating the 2007 guideline): a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines developed in collaboration with the American College of Emergency Physicians, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2011;57(19):1920-59.
37. Mattos LA, Lemos Neto PA, Rassi A Jr, Marin-Neto JA, Sousa AG, Devito FS, et al. Diretrizes da Sociedade Brasileira de Cardiologia - Intervenção coronária percutânea e métodos adjuntos diagnósticos em cardiologia intervencionista (II Edição - 2008). Arq Bras Cardiol. 2008;91(6 supl.1):1-58.
Humberto Villacorta Junior R. Visconde de Silva, 154/402, Humaitá CEP 22271-090, Rio de Janeiro, RJ - Brasil E-mail:
Artigo recebido em 20/06/12, revisado em 26/08/12, aceito em 29/10/12.
ADP = adenosina difosfato
AUC = área sob a curva
SF = stents farmacológicos
ARP = alta reatividade plaquetária no tratamento
ICP = intervenção coronária percutânea
TRP = testes de reatividade de plaquetas
ROC = receiver operating curve
BACKGROUND: The role of platelet reactivity (PR) tests in the prediction of long-term events in Latin-American patients treated with drug-eluting stents (DES) has not been established. OBJECTIVES: To assess the role of PR tests in the prediction of events after DES implantation. METHODS: From May 2006 through January 2008, 209 Brazilian patients who underwent elective treatment with DES were included. PR was assessed 12 to 18h after the procedure by light transmittance aggregometry with 5µM of ADP. Patients were prospectively followed for up to 4.8 years. Seventeen (8%) individuals were lost to follow-up and the final cohort comprised 192 patients. Receiver operating curve (ROC) was used to determine the best 5µM of ADP cutoff to predict events. The primary endpoint was a combination of cardiovascular death, acute myocardial infarction, definite stent thrombosis, and target-artery revascularization. Cox proportional hazard models were used to determine the variables independently associated with the time to the first event. RESULTS: The best ADP 5µM cutoff was 33%. One hundred and seven (55.7%) patients had ADP 5µM >33%. Event-free survival rate at 1,800 days was 55% vs. 70% for individuals with ADP5 above and below such cutoff, respectively (p=0.001). Independent predictors of time to first event were current smoking (HR 3.49; 95% CI 1.76-6.9; p=0.0003), ADP 5µM >33% (HR 1.95; 95% CI 1.09-3.51; p=0.025) and age (HR 1.03; 95% CI 1.0-1.06; p=0.041). CONCLUSIONS: In this study, 55.7% of the patients had high on-treatment platelet reactivity. ADP 5µM >33% was an independent predictor of long-term events.
IUniversidade Federal Fluminense, Programa de Pós-Graduação em Ciências Cardiovasculares, Niterói, RJ
IICasa de Saúde São José, Rio de Janeiro, RJ - Brasil
RESULTS: The best ADP 5µM cutoff was 33%. One hundred and seven (55.7%) patients had ADP 5µM
CONCLUSIONS: In this study, 55.7% of the patients had high on-treatment platelet reactivity. ADP 5µM
In patients treated with drug-eluting stents (DES), dual antiplatelet therapy is mandatory and treatment with clopidogrel and aspirin has been the most frequent regimen used in clinical practice1. However, a great number of individuals are poor responders to clopidogrel as assessed by platelet reactivity tests (PRT)2-4. A number of studies have demonstrated an association between on-treatment platelet reactivity at a single time point during clopidogrel therapy and the risk of cardiac events in Caucasian patients who have undergone percutaneous coronary intervention (PCI)5-10. However, the role of such tests in Latin-American patients treated with DES is not clear. This is an important issue, as response to clopidogrel may be influenced by genetic factors such as P450 polymorphisms11-15 and the distribution of these genetic polymorphisms may differ among ethnic groups. For instance, the loss-of-function CYP2C19*2 is common in diverse populations and occurs in 24% of Caucasian individuals. Nevertheless, the frequency of this allele is somewhat lower in Mexican-Americans (18%), higher in African-Americans (33%), and markedly higher in Asian populations (51%)16-18. Furthermore, the strength of effect of CYP2C19*2 on clopidogrel response may depend on other factors, such as genetic background or environmental exposures, which may differ among ethnicities. Therefore, PRT may have different performances according to the ethnic background.
In this study, we sought to assess the role of on-treatment platelet reactivity measured by optical aggregometry in the prediction of long-term cardiovascular events in Brazilian patients treated with DES.
This study was approved by the Medical Research Ethics Committee of our hospital and conformed to the Declaration of Helsinki. All patients provided written informed consent. The study was funded by our institution.
This was an observational, prospective cohort. From May 2006 through January 2008, 209 consecutive Brazilian patients who underwent elective PCI with DES implantation in a cardiology hospital were prospectively included. Mean age was 67±10.4 years and 142 (74%) were males. All patients had stable coronary artery disease. The indication of PCI was left to the primary physician's discretion. Baseline clinical data were collected immediately before the intervention. Before PCI, patients were treated with clopidogrel according to our institution protocol. Clopidogrel-naive patients were treated with a loading dose of 600 mg 2 h before the procedure. Patients who were already on clopidogrel for at least five days did not receive the loading dose. The type of stent was Cypher in 117 (56%) patients, Taxus in 86 (41%), Endeavour in 10 (4.7%), and others in 6 (2.8%) individuals.
Platelet reactivity was assessed at a single-time point in all patients, 12 to 18 h after PCI by light transmittance aggregometry with 5µM of ADP. At discharge, all patients were on aspirin 100mg and clopidogrel 75 mg per day and were maintained on this regimen for at least one year. All decisions regarding therapeutic issues were left at the discretion of the primary physician.
Follow-up was achieved by telephone interviews and was complemented with information from primary physicians and hospital records. Data on clinical status and on drug regimen, including the use of clopidogrel, were collected. Patients were followed for up to 4.8 years (mean 2.2±1.2years). Seventeen (8%) patients were lost to follow-up and the final cohort comprised 192 patients.
Blood samples (5 tubes with 4.5 mL) were collected from all patients 12 to 18 h after PCI. Platelet function was assessed by light transmittance aggregometry. Platelet-rich plasma was prepared by centrifuging blood samples at 250xgfor10min. Aggregation studies were performed with a Chrono-log optical aggregometer (Chrono-log Corporation, USA) and the AGGRO/LINK® 810-CA software for Windows. ADP 5µM and arachidonic acid (1 µM) were used as agonists.
The primary endpoint was a combination of cardiovascular death, nonfatal myocardial infarction, definite stent thrombosis, and percutaneous target-artery revascularization. Definite thrombosis was considered as acute coronary syndrome with an angiogram showing stent thrombosis. According to time from PCI, it was classified into acute (
Categorical variables are expressed as frequencies and percentages. Continuous variables were analyzed for a normal distribution with the Kolmogorov-Smirnoff test. Normally distributed variables are presented as mean ± standard deviation. Receiver operating curve (ROC) was used to determine the optimal ADP 5µM cutoff to predict events. Kaplan-Meier event-free survival curves were constructed and log-rank test was used to assess differences between curves. Cox proportional hazard models were used to determine the variables independently associated with time to first event. Covariates included in this analysis were age, gender, history of hypertension, history of diabetes mellitus, history of dyslipidemia, current smoking status, prior myocardial infarction, prior coronary artery bypass graft, prior PCI, aspirin, beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, statins, periprocedural clopidogrel regimen, use of clopidogrel for more than 1 year after PCI, stent implanted in the left anterior descending (LAD) coronary artery, multivessel PCI, number of stents implanted, minimal stent diameter, total stent length, arachidonic acid, and ADP 5µM. Variables were selected using the stepwise forward method. A p value < 0.05 was considered statistically significant. The analysis was performed using the statistical software SAS® System, version 6.11 (SAS Institute, Inc., Cary, North Carolina).
ADP 5µM optimal cutoff as determined by ROC curve analysis was 33%, with the area under the curve (AUC) of 0.58(95% confidence interval, 0.49-0.67). Sensibility, specificity, positive predictive value and negative predictive value were, respectively, 66.7%, 48.2%, 31.8%, and 80%. Using this cutoff, high on-treatment platelet reactivity (HPR) was present in 107(55.7%) out of 192 patients included in the analysis. Baseline characteristics of patients with HPR as compared with patients with low platelet reactivity are shown in
During follow-up, 51 (26.5%) patients reached the primary endpoint. Mean ADP 5µM was higher in these patients as compared with those without endpoints (37±13.5vs.32.8±14.1, p = 0.06). The cardiovascular events observed were 34 (17.7%) target-artery percutaneous revascularizations, 23 (12%) acute myocardial infarctions, 10 (5.2%) cardiovascular deaths, and 5 (2.6%) definite stent thrombosis. Median time to first event was 371 days (interquartile range 180-732 days). Of note, 51% of the events occurred after one year of follow-up. Acute stent thrombosis was observed in 2 patients, subacute in 1, and very late in 2 patients (2 and 3.6 years post-stent implantation). Among these 5 cases, 3 (60%) resulted in death. All patients who experienced stent thrombosis were on dual antiplatelet therapy at the moment of the event. In all but one patient ADP 5µM was above the optimal cutoff, indicating HPR. The only patient with ADP 5µM below the cutoff had acute stent thrombosis.
Event-free survival rates were lower for current smokers and patients with HPR (
The primary finding of the present study was that HPR as measured by light transmittance aggregometry was independently associated with long-term cardiovascular events in Brazilian patients with stable coronary artery disease who underwent PCI with DES implantation. The optimal cutoff level for ADP 5µM in this analysis was 33%. Our study is the first one to include only Latin-American patients from Brazil and confirmed that PRT are useful in predicting long-term outcomes in this scenario as demonstrated with Caucasian patients.
Platelet function can be assessed by different methods. Light transmittance aggregometry has been used by other authors to address the value of such test in the prediction of cardiovascular events after coronary stent implantation5-7. These studies demonstrated that platelet function assessment was able to identify high-risk patients. However, they only provided information after 30-day, 6-month, and 1-year follow-up. In this regard, our study adds information to the previous studies using light transmittance aggregometry, as it provides data on long-term follow-up, demonstrating that PRT can identify patients at risk beyond one year after DES implantation. More recently, a new method used to assess platelet function has been introduced. The Multiplate Analyser is a point of care test that has been shown to be superior to the conventional light transmittance aggregometry19.
Head-to-head comparison of platelet function tests has been reported in only one study. The POPULAR study6 compared the ability of six different PRTs in predicting atherothrombotic events in clopidogrel-pretreated patients undergoing PCI with stent implantation. Only light transmittance aggregometry, VerifyNow, and Plateletworks were significantly associated with the primary endpoint. The IMPACT-R, Dade PFA collagen/ADP, and Inovance PFA P2Y were unable to discriminate between patients with and without events at 1-year follow-up. Of note, although the 3 former tests were able to identify patients at risk, the area under the curve was modest (0.63, 0.62, and 0.61, respectively). In the present study this was also true. The area under the curve for ADP 5µM >33% was only 0.58. Likewise, we observed a good negative predictive value, but low positive predictive value as was also observed in the POPULAR study. A possible explanation for this finding is that in all these studies, including ours, platelet function was assessed in a single time point. As a matter of fact, it has been demonstrated that in patients on clopidogrel, platelet function varies over time and, therefore, serial measurements improve the accuracy of these tests20. Using the VerifyNow P2Y12 assay, Campo et al. demonstrated that platelet reactivity decreased from baseline to one month in patients on clopidogrel, improving the area under the curve from 0.69 at baseline to 0.87 at 30 days. On-clopidogrel platelet reactivity at 1 month was the strongest predictor of adverse outcomes20.
Another concern regarding platelet function measurements in this setting refers to the optimal cutoff level for event prediction. Some studies have used prespecified cutoffs, while others have used ROC curves to determine the optimal cutoff. Two studies using ADP 5µM have suggested cutoffs of 42.9% and 46% based on ROC curves6,21. We found a lower cutoff of 33%. This may be explained by a longer follow-up in our study and differences in disease severity. Furthermore, recent studies have found lower cutoffs than those suggested by previous studies. For example, in the GRAVITAS study, the VerifyNow P2Y12 test was used to identify patients with HPR22. A prespecified cutoff of 240 PRU was used based on previous data23. Patients with HPR were randomized to either a fixed regimen of high-dose clopidogrel (600 mg followed by 150 mg daily for 6 months) or the standard-dose clopidogrel (75 mg daily). No differences in outcomes were observed between the two regimens. However, in a subanalysis of this study, the prespecified cutoff of 240 PRU was not associated with ischemic events in the follow-up. On the contrary, a post-hoc cutoff of 208PRU assessed at 12 to 24 h after PCI or at 30 days was associated with the primary endpoint24. Of note, using this lower cutoff, the proportion of patients with HPR was very similar to the one observed in our study (49.6% and 55.7%, respectively).
Although most of the studies have shown that platelet reactivity tests are useful in predicting events in patients treated with stent implantation, a recent study using the VerifyNow P2Y12 assay failed to show any benefit25. A possible explanation for this finding is that event rates were lower than expected. Two-year event rates in patients with and without HPR were 2.8% and 2.4%, much lower than that observed in our study. This could also be related to racial or ethnic differences, since this study was carried out in an Asian population, in contrast with a predominantly western population in other studies.
Half of the endpoints in our study occurred after 1 year of follow-up. This is an important finding, as dual antiplatelet therapy in patients with DES has been recommended for up to 1 year. We demonstrated that many events still occur after that time point and patients at risk, despite the use of aspirin and clopidogrel, can be identified by PRT. Among 5definite stent thromboses, 2 occurred at 2 and 3.6 years post-PCI, in patients on dual antiplatelet therapy. On the other hand, a transitory 'rebound' increase in platelet reactivity within 3months after clopidogrel discontinuation has been observed26 and may explain the increase in ischemic events that occur early after clopidogrel discontinuation27,28, although some believe that these events are rather a result of late stent epithelization29. The ideal time on dual antiplatelet therapy post-stent implantation is a matter of debate and deserves further studies. Nevertheless, we had the unique opportunity to study patients who were on clopidogrel for more than 1year after the intervention, at the discretion of their primary physicians. Our data suggest that patients with HPR have increased risk of events even if they persist on clopidogrel beyond 1 year post-PCI.
The strongest predictor of cardiovascular events in this study was current smoking. Although smoking has been related to late stent thrombosis29,30, few studies have addressed the association between smoking, platelet function analysis, and prognosis in this scenario. In some studies, a greater proportion of smokers was observed in patients with low platelet reactivity5,22. In others, the opposite7 or no difference was observed6. However, the so-called smoking paradox has been described. According to this hypothesis, smoking stimulates the CYP1A2 at the cytochrome P450, resulting in higher production of the active clopidogrel metabolite and less stent thrombosis31. Our findings do not support this theory. Most importantly, in our study ADP 5µM>33% predicted cardiac events regardless of current smoking.
The best strategy for the management of patients with high on-treatment platelet reactivity is not clear. The strategy of fixed regimen of high-dose clopidogrel, tested in the GRAVITAS STUDY, was not superior to the standard-dose regimen22. Alternatively, one may choose one of the new antiplatelet drugs, prasugrel or ticagrelor, which have been found to be superior to clopidogrel in clinical trials, in the context of acute coronary syndromes32,33.
Although most authors agree that currently available evidence supports the concept of a threshold for on-treatment platelet reactivity that may be used to stratify patient risk to ischemic events following PCI34, guidelines have not recommended platelet function tests on a routine basis1,35-37. This may be due to some drawbacks related to these tests. There have been no large-scale clinical trials to date demonstrating that the adjustment of antiplatelet therapy based on any of these cutoffs improves clinical outcomes. Additional issues are the lack of consensus on the optimal method to evaluate HPR and the cutoff value associated with clinical risk. However, we believe such tests are of particular importance in patients who have suffered an acute coronary syndrome. The guidelines recommend that these patients be kept on dual antiplatelet therapy ideally for one year. In fact, the incidence of very late thrombosis in the HORIZONS-AMI30 study was elevated, regardless the type of stent, justifying monitoring these patients with PRT overtime.
This study has some limitations. First, this is a relatively small single-center study and one should generalize our findings with caution. In spite of that, the study had enough power to detect differences between groups due to the very long follow-up. We did not collect data on bleeding events, which are important endpoints related to mortality. We did not perform serial measurements of platelet function, which has been shown to improve the test accuracy. And finally, our data refers mostly to first-generation stents and may not apply to new generation stents.
In this study, a cutoff value of 33% for ADP 5µM was associated with long-term events in Brazilian patients with stable coronary artery disease treated with DES. Using this cutoff, 55.7% of patients had high on-treatment platelet reactivity. Current smoking was the strongest predictor of cardiovascular events, followed by HPR and age. HPR predicted long-term events independently of clopidogrel maintenance beyond 1 year.
This work was supported by our institutions and no external financial source was provided.
Conception and design of the research: Villacorta AS, Villacorta Junior H, Helmuth B; Acquisition of data: Villacorta AS, Batista MJS, Gomes RV, Macedo LA; Analysis and interpretation of the data: Villacorta AS, Villacorta Junior H, Mesquita ET; Statistical analysis: Villacorta Junior H; Writing of the manuscript: Villacorta AS; Critical revision of the manuscript for intellectual content: Villacorta Junior H, Batista MJS, Gomes RV, Mesquita ET, Helmuth B.
No potential conflict of interest relevant to this article was reported.
There were no external funding sources for this study.
This article is part of the thesis of master submitted by Aline Sterque Villacorta, from Universidade Federal Fluminense.
1. Levine GN, Bates ER, Blankenship JC, Bayley SR, Bittl JA, Cercek B, et al; American College of Cardiology Foundation; American Heart Association Task Force on Practice Guidelines; Society for Cardiovascular Angiography and Interventions. 2011 ACCF/AHA/SCAI Guideline for Percutaneous Coronary Intervention. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Society for Cardiovascular Angiography and Interventions. J Am Coll Cardiol. 2011;58(24):e44-122.
2. Gurbel PA, Bliden KP, Hiatt BL, O'Connor CM. Clopidogrel for coronary stenting: response variability, drug resistance, and the effect of pretreatment platelet reactivity. Circulation. 2003;107(23):2908-13.
3. 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(2):246-51.
4. Heptinstall S. Variable therapeutic effectiveness of clopidogrel in acute coronary syndromes. J Thromb Haemost. 2006;4(3):539-41.
5. Buonamici P, Marcucci R, Migliorini A, Gensini GF, Santini A, Paniccia R, et al. Impact of platelet reactivity after clopidogrel administration on drug-eluting stent thrombosis. J Am Coll Cardiol. 2007;49(24):2312-7.
6. Breet NJ, van Werkum JW, Bouman HJ, Kelder JC, Ruven HJ, Bal ET, et al. Comparison of platelet function tests in predicting clinical outcome in patients undergoing coronary stent implantation. JAMA. 2010;303(8):754-62.
7. Hochholzer W, Trenk D, Bestehorn HP, Fischer B, Valina CM, Ferenc M, al. Impact of the degree of peri-interventional platelet inhibition after loading with clopidogrel on early clinical outcome of elective coronary stent placement. J Am Coll Cardiol. 2006;48(9):1742-50.
8. Price MJ, Endemann S, Gollapudi RR, Valencia R, Stinis CT, Levisay JP, et al. Prognostic significance of post-clopidogrel platelet reactivity assessed by a point-of-care assay on thrombotic events after drug-eluting stent implantation. Eur Heart J. 2008;29(8):992-1000.
9. Gurbel PA, Bliden KP, Guyer K, Cho PW, Zaman KA, Kreutz RP, et al. Platelet reactivity in patients and recurrent events post-stenting: results of the PREPARE POST-STENTING Study. J Am Coll Cardiol. 2005;46(10):1820-6.
10. Geisler T, Langer H, Wydymus M, Gohring K, Zurn C, Bigalke B, et al. Low response to clopidogrel is associated with cardiovascular outcome after coronary stent implantation. Eur Heart J. 2006;27(20):2420-5.
11. 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(4):354-62.
12. Shuldiner AR, O'Connel JR, Bliden KP, Gandhi A, Ryan K, Horenstein RB, et al. Association of cytochrome P450 2C19 genotype with the antiplatelet effect and clinical efficacy of clopidogrel therapy. JAMA. 2009;302(8):849-57.
13. Hulot JS, Collet JP, Silvain J, Pena A, Bellemain-Appaix A, Barthélémy O, et al. Cardiovascular risk in clopidogrel-treated patients according to cytochrome P450 2C19*2 loss-of-function allele or proton pump inhibitor coadministration: a systematic meta-analysis. J Am Coll Cardiol. 2010;56(2):134-43.
14. Bouman HJ, Schömig E, van Werkum JW, Velder J, Hackeng CM, Hirschhäuser C, et al. Paraoxonase-1 is a major determinant of clopidogrel efficacy. Nat Med. 2011;17(1):110-6.
15. Kassimis G, Davlouros P, Xanthopoulou I, Stavrou EF, Athanassiadou A, Alexopoulos D. CYP2C19*2 and other genetic variants affecting platelet response to clopidogrel in patients undergoing percutaneous coronary intervention. Thromb Res. 2012;129(4):441-6.
16. Luo HR, Poland RE, Lin KM, Wan YJ. Genetic polymorphism of cytochrome P450 2C19 in Mexican Americans: a cross-ethnic comparative study. Clin Pharmacol Ther. 2006;80(1):33-40.
17. Xiao ZS, Goldstein JA, Xie HG, Blaisdell J, Wang W, Jiang CH, et al. Differences in the incidence of the CYP2C19 polymorphism affecting the S-mephenytoin phenotype in Chinese Han and Bai populations and identification of a new rare CYP2C19 mutant allele. J Pharmacol Exp Ther. 1997;281(1):604-9.
18. Takakubo F, Kuwano A, Kondo I. Evidence that poor metabolizers of (S)-mephenytoin could be identified by haplotypes of CYP2C19 in Japanese. Pharmacogenetics. 1996;6(3):265-7.
19. Johnston LR, Larsen PD, La Flamme AC, Harding SA. Methodological considerations for the assessment of ADP induced platelet aggregation using the Multiplate® analyser. Platelets. 2012 Jun 11. [Epub ahead of print].
20. Campo G, Parrinello G, Ferraresi P, Lunghi B, Tebaldi M, Miccoli M, et al. Prospective evaluation of on-clopidogrel platelet reactivity over time in patients treated with percutaneous coronary intervention relationship with gene polymorphisms and clinical outcome. J Am Coll Cardiol. 2011;57(25):2474-83.
21. Gurbel PA, Antonino MJ, Bliden KP, DiChiara J, Suarez TA, Sigla A, et al. Platelet reactivity to adenosine diphosphate and long-term ischemic event occurrence following percutaneous coronary intervention: a potential antiplatelet therapeutic target. Platelets. 2008;19(8):595-604.
22. Price MJ, Berger PB, Teirstein PS, Tanguay JF, Angiolillo DJ, Spriggs D, et al; GRAVITAS Investigators. Standard- vs high-dose clopidogrel based on platelet function testing after percutaneous coronary intervention: the GRAVITAS randomized trial. JAMA. 2011;305(11):1097-105.
23. Price MJ, Berger PB, Angiolillo DJ, Teirstein PS, Tanguay JF, Kandzari DE, et al. Evaluation of individualized clopidogrel therapy after drug-eluting stent implantation in patients with high residual platelet reactivity: design and rationale of the GRAVITAS trial. Am Heart J. 2009;157(5):818-24.
24. Price MJ, Angiolillo DJ, Teirstein PS, Lillie E, Manoukian SV, Berger PB, et al. Platelet reactivity and cardiovascular outcomes after percutaneous coronary intervention: a time-dependent analysis of the Gauging Responsiveness with a VerifyNow P2Y12 assay: Impact on Thrombosis and Safety (GRAVITAS) trial. Circulation. 2011;124(10):1132-7.
25. Park DW, Lee SW, Yun SC, Song HG, Ahn JM, Lee JY, et al. A point-of-care platelet function assay and C-reactive protein for prediction of major cardiovascular events after drug-eluting stent implantation. J Am Coll Cardiol. 2011;58(25):2630-9.
26. Mylotte D, Peace AJ, Tedesco AT, Mangiacapra F, Dicker P, Kenny D, et al. Clopidogrel discontinuation and platelet reactivity following coronary stenting. J Thromb Haemost. 2011;9(1):24-32.
27. Ho PM, Peterson ED, Wang L, Magid DJ, Fihn SD, Larsen GC, et al. Incidence of death and acute myocardial infarction associated with stopping clopidogrel after acute coronary syndrome. JAMA. 2008;299(5):532-9.
28. Schulz S, Schuster T, Mehilli J, Byrne RA, Ellert J, Massberg S, et al. Stent thrombosis after drug-eluting stent implantation: incidence, timing, and relation to discontinuation of clopidogrel therapy over a 4-year period. Eur Heart J. 2009;30(22):2714-21.
29. Ellis SG, Colombo A, Grube E, Popma J, Koglin J, Dawkins KD, et al. Incidence, timing, and correlates of stent thrombosis with the polymeric paclitaxel drug-eluting stent: a TAXUS II, IV, V, and VI meta-analysis of 3,445 patients followed for up to 3 years. J Am Coll Cardiol. 2007;49(10):1043-51.
30. Dangas GD, Caixeta A, Mehram R, Parise H, Lansky AJ, Cristea E, et al; Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction (HORIZONS-AMI) Trial Investigators. Frequency and predictors of stent thrombosis after percutaneous coronary intervention in acute myocardial infarction. Circulation. 2011;123(16):1745-56.
31. Park KW, Kang SH, Kang J, Jeon KH, Park JJ, Han JK, et al. Enhanced clopidogrel response in smokers is reversed after discontinuation as assessed by VerifyNow assay: additional evidence for the concept of 'smokers' paradox'. Heart. 2012;98(13):1000-6.
32. Wiviott SD, Braunwald E, McCabe CH, Montalescot G, Ruzyllo W, Gottlieb S, et al. Prasugrel versus clopidogrel in patients with acute coronary syndromes. N Engl J Med. 2007;357(20):2001-15.
33. Wallentin L, Becker RC, Budaj A, Cannon CP, Emanuelsson H, Held C, et al. Ticagrelor versus clopidogrel in patients with acute coronary syndromes. N Engl J Med. 2009;361(11):1045-57.
34. Bonello L, Tantry US, Marcucci R, Blindt R, Angiolillo DJ, Becker R, et al; Working Group on High On-Treatment Platelet Reactivity. Consensus and future directions on the definition of high on-treatment platelet reactivity to adenosine diphosphate. J Am Coll Cardiol. 2010;56(12):919-33.
35. Hamm CW, Bassand JP, Agewall S, Bax J, Boersma E, Bueno H, et al; ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation: The Task Force for the management of acute coronary syndromes (ACS) in patients presenting without persistent ST-segment elevation of the European Society of Cardiology (ESC). Eur Heart J. 2011;32(23):2999-3054.
36. Wright RS, Anderson JL, Adams CD, Bridges CR, Casey Jr DE, Ettinger SM, et al. 2011 ACCF/AHA focused update of the Guidelines for the Management of Patients with Unstable Angina/Non-ST-Elevation Myocardial Infarction (updating the 2007 guideline): a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines developed in collaboration with the American College of Emergency Physicians, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2011;57(19):1920-59.
37. Mattos LA, Lemos Neto PA, Rassi A Jr, Marin-Neto JA, Sousa AG, Devito FS, et al. Diretrizes da Sociedade Brasileira de Cardiologia - Intervenção coronária percutânea e métodos adjuntos diagnósticos em cardiologia intervencionista (II Edição - 2008). Arq Bras Cardiol. 2008;91(6 supl.1):1-58.
Humberto Villacorta Junior R. Visconde de Silva, 154/402, Humaitá Postal Code 22271-090, Rio de Janeiro, RJ – Brazil E-mail:
Manuscript received June 20, 2012, revised manuscript August 26, 2012, accepted October 209, 2012.
ADP = adenosine diphosphate
AUC = area under the curve
DES = drug-eluting stents
HPR = high on-treatment platelet reactivity
PCI = percutaneous coronary intervention
PRT = platelet reactivity tests
ROC = receiver operating curve