CLINICAL RESEARCH: INTERVENTIONAL CARDIOLOGY
Temporal Pattern of Ischemic Events in Relation to Dual Antiplatelet Therapy in Patients With Unprotected Left Main Coronary Artery Stenosis Undergoing Percutaneous Coronary Intervention
Tullio Palmerini, MD*,*,
Antonio Marzocchi, MD*,
Corrado Tamburino, MD ,
Imad Sheiban, MD ,
Massimo Margheri, MD ,
Giuseppe Vecchi, MD||,
Giuseppe Sangiorgi, MD¶,
Andrea Santarelli, MD#,
Antonio L. Bartorelli, MD**,
Carlo Briguori, MD, PhD,
Luigi Vignali, MD,
Francesco Di Pede, MD,
Angelo Ramondo, MD||||,
Luigi Inglese, MD¶¶,
Marco De Carlo, MD##,
Leonardo Bolognese, MD***,
Alberto Benassi, MD,
Cataldo Palmieri, MD,
Vincenzo Filippone, MD,
Diego Sangiorgi, MSc*,
Fabio Barlocco, MD||||||,
Giulia Lauria, MD* and
Stefano De Servi, MD||||||
* Istituto di Cardiologia, Policlinico S. Orsola, Università di Bologna, Bologna, Italy
Dipartimento di Cardiologia, Ospedale Ferrarotto, Università di Catania, Catania, Italy
Divisione di Cardiologia, Università di Torino, Torino, Italy
Dipartimento Cardiovascolare, Ospedale Careggi, Università di Firenze, Firenze, Italy
|| Dipartimento di Cardiologia, Ospedale S. Maria delle Croci, Ravenna, Ravenna, Italy
¶ Centro Emocolumbus, Milano, Italy
# Dipartimento di Cardiologia, Ospedale degli Infermi, Rimini, Italy
** Centro Cardiologico Monzino, Università di Milano, Milano, Italy
Dipartimento di Cardiologia, Clinica Mediterranea, Napoli, Italy
Unità Operativa di Cardiologia, Azienda Ospedaliero-Universitaria, Parma, Italy
Dipartimento di Cardiologia, Azienda Ospedaliera, Mestre, Italy
|||| Dipartimento di Scienze Cardiovascolari, Università di Padova, Padova, Italy
¶¶ Cardiovascular Interventional Radiology Department, IRCCS Policlinico S. Donato, S. Donato Milanese, Milano, Italy
## Dipartimento Cardio-Toracico, Ospedale Cisanello, Pisa, Italy
*** Dipartimento Cardiovascolare, Ospedale S. Donato, Arezzo, Italy
Dipartimento di Cardiologia, Hesperia Hospital, Modena, Italy
Istituto Fisiologia Clinica, CNR, Massa, Italy
Dipartimento Cardiovascolare, Ospedale Cervello, Palermo, Italy
|||||| Dipartimento di Malattie Cardiovascolari, Ospedale Civile, Legnano, Italy
Manuscript received October 9, 2008;
revised manuscript received December 1, 2008,
accepted December 2, 2008.
* Reprint requests and correspondence: Dr. Tullio Palmerini, Istituto di Cardiologia, Università di Bologna, Policlinico S. Orsola, Via Massarenti 9, 40 138 Bologna, Italy. (Email: tulliopalmerini{at}hotmail.com).
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Abstract
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Objectives: The aim of this study was to investigate whether there is a temporal pattern of ischemic events in relation to dual antiplatelet therapy in patients with unprotected left main coronary artery (ULMCA) stenosis treated with percutaneous coronary intervention (PCI).
Background: Identifying which periods during follow-up of patients with ULMCA stenosis treated with PCI are associated with higher risk of clinical events might help to improve therapeutic strategies.
Methods: We analyzed data from 15 centers involved in an observational study conducted by the Italian Society of Invasive Cardiology on patients with ULMCA stenosis treated with PCI. Eight hundred ninety-four patients were enrolled.
Results: At 30-day follow-up, the rate of cardiac mortality and myocardial infarction (MI) was 5.4%. In patients still taking dual antiplatelet therapy, the adjusted incidence rate ratio/10,000 patient-days of the combination of cardiac mortality and MI in the 31- to 180-day interval compared with the 181- to 360-day interval after PCI was 3.64 (p = 0.035). This risk was particularly high in patients with acute coronary syndromes. After stopping clopidogrel, the adjusted incidence rate ratio of cardiac mortality and MI in the 0- to 90-day interval compared with the 91- to 180-day interval was 4.20 (p = 0.009).
Conclusions: In patients with ULMCA stenosis taking dual antiplatelet therapy there is an increased hazard of cardiac mortality and MI between 31 and 180 days compared with 181 to 360 days. Furthermore, there is an increased hazard of cardiac mortality and MI in the first 90 days after stopping clopidogrel.
Key Words: antiplatelet therapy • left main • stent
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Abbreviations and Acronyms
| | MI = myocardial infarction | | PCI = percutaneous coronary intervention | | ULMCA = unprotected left main coronary artery |
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The introduction of stents and, more recently, drug-eluting stents has renewed the interest in the percutaneous treatment of unprotected left main coronary artery (ULMCA) stenosis (1). Several studies have reported very favorable outcomes that are competitive with surgery, especially for ostial and midshaft lesions (2–5). In particular all studies have consistently shown that the procedural risk of percutaneous coronary intervention (PCI) in elective patients is, in general, low and comparable to that of surgery. However, the risk of sudden death and of major ischemic events during follow-up raises some concerns and limits the widespread use of PCI in this context (6). A more comprehensive understanding of risks during follow-up and in particular of the timing of the risk of ischemic events in relation to the duration and time of discontinuation of clopidogrel therapy might help to improve therapeutic strategies and thus clinical outcomes of these patients. Therefore, we investigated how the risk of cardiac mortality and myocardial infarction (MI) is distributed over the course of the first year in patients with ULMCA stenosis treated with PCI while they were still taking dual antiplatelet therapy. Moreover, we also assessed the incidence of cardiac mortality and MI in the first 9 months after stopping clopidogrel.
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Methods
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Patients and definitions.
The characteristics of the GISE-SICI (Gruppo Italiano Studi Emodinamici) survey on ULMCA stenosis have been already reported in detail (7). Briefly, this survey was a multicenter, retrospective, observational study performed in patients with ULMCA stenosis treated with PCI. All interventional high-volume centers performing >800 PCIs/year in Italy and affiliated with GISE-SICI were asked to participate in the survey by providing demographic, clinical, procedural, and follow-up data on consecutive patients with ULMCA stenosis treated with PCI between January 2002 and December 2006. For the purpose of this study, we included only those centers that systematically collected data on dual antiplatelet therapy (15 centers). Patients taking warfarin therapy and those with antiplatelet therapies different from clopidogrel and aspirin were excluded. Clinical follow-up was performed through office visits, telephone interviews, or—when patients could not be contacted either way—by consulting civil registries of mortality.
We defined as the clinical end point of interest the occurrence of cardiac mortality or MI. In the computation of this end point, events were counted only once (whichever occurred first). Other definitions of the study have been already published in detail (7). The study was approved by the local ethics committees of each participating center.
Statistical analysis.
The primary object of the study was to evaluate the association between time interval after PCI and the incidence of cardiac mortality and MI while patients were still taking dual antiplatelet therapy. In this analysis, to eliminate periprocedural factors or other conditions associated with the risk of early mortality or MI, we did not consider events occurring in the first 30 days after PCI, censoring all patients who died or had an MI in this interval of time. Four periods of interest were considered: 31 to 90, 91 to 180, 181 to 270, and 271 to 360 days after PCI. Unadjusted incidence rates of the clinical end point in the various intervals of time were compared with the Fisher exact test. The incidence rate was calculated considering the number of events/10,000 patient-days of treatment. To minimize possible selection bias, we used a Poisson regression multivariable analysis in which the variable of interest was the risk of the clinical end point in the interval of time between 31 and 180 days after PCI compared with 181 to 360 days. The following variables were included in the model: age, renal dysfunction, acute coronary syndrome, and left ventricular ejection fraction. To determine risk adjusted instantaneous incidence rates of events during the period of dual antiplatelet therapy, we performed a multivariable Cox regression analysis, adjusting for the same variables as specified in the preceding text and using kernel hazard functions.
Furthermore, we also investigated the association between the time interval after stopping clopidogrel and the incidence of cardiac mortality and MI. After stopping clopidogrel, 3 periods of interest were considered: 0 to 90, 91 to 180, and 181 to 270 days. We performed a Fisher exact test to compare incidence rates in the various intervals of time, a Poisson regression analysis to assess the risk of cardiac mortality and MI in the first 90 days, and a Cox regression analysis using kernel hazard functions to determine the risk-adjusted instantaneous incidence rates of events. Statistical analyses were performed with SPSS version 12.0 for Windows (SPSS Inc., Chicago, Illinois) and STATA/SE version 9.2 for Windows (Statacorp, College Station, Texas). A value of p < 0.05 was considered statistically significant.
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Results
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30-day clinical outcomes.
Clinical characteristics of the general cohort of patients, of patients suitable for analyses on dual antiplatelet therapy, and of patients suitable for analyses after clopidogrel discontinuation are shown in Table 1. At 30-day follow-up there were 48 clinical end point events (5.4%). We observed 30 cardiac deaths (3.3%) and 19 MIs (2.1%). The incidence rate of cardiac mortality and MI per 10,000 patient-days was 19.1.
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Table 1 Clinical Characteristics of the General Cohort of Patients Enrolled in the Study, of the Cohort of Patients Selected for Analyses on Dual Antiplatelet Therapy, and of the Cohort of Patients Selected for Analyses After Clopidogrel Discontinuation
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Clinical outcomes on clopidogrel treatment after 30-day follow-up.
After eliminating patients who died or had an MI in the first 30 days, patients who were prescribed 1-month dual antiplatelet therapy, those who were lost to follow-up before 30 days, or those who were treated with a combination of dual antiplatelet therapy different from aspirin and clopidogrel, 765 patients remained available for the evaluation of the clinical outcome on dual antiplatelet therapy. There were 12 clinical end point events (44%) between 31 and 90 days, 12 events in the period between 91 and 180 days, 3 events (12%) between 181 and 270 days, and no events between 271 and 360 days (Table 2). The unadjusted incidence rate of the clinical end point per 10,000 patient-days was 2.7 for the 31- to 90-day period, 2.3 for the 91- to 180-day period, 1.03 for the 181- to 270-day period, and 0 for the 270- to 360-day period (p = 0.029). Figure 1, which represents the instantaneous incidence of the clinical end point, shows an increased risk of events between 30 and 180 days, this risk abruptly declined thereafter. Therefore, in the multivariable analysis we considered 2 periods at risk: between 31 and 180 days and between 181 and 360 days. The unadjusted incidence rates per 10,000 patient-days in these 2 periods were 2.5 and 0.6, respectively (p = 0.008). In the multivariable analysis (Table 3), the incidence rate ratio of the clinical end point between 31 and 180 days compared with between 181 and 360 days was 3.64 (95% confidence interval: 1.09 to 12.16; p = 0.035). As shown in Figure 2, in stable patients the incidence rate of the primary end point per 10,000 patient-days was 0.2 between 31 and 180 days and 0 between 181 and 360 days (p = NS). In patients with acute coronary syndromes the incidence rate was 4.2 in the first period and 1.1 in the second period (p = 0.01).
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Table 2 Number of Cardiac Deaths, MIs, and the Combination of Cardiac Death or MI While Patients Were Taking Dual Antiplatelet Therapy
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Figure 1 Adjusted Instantaneous Incidence Rate/Patient-Days of Cardiac Mortality and MI During the First Year of Follow-Up in Patients Taking Dual Antiplatelet Therapy
The risk of cardiac mortality and myocardial infarction (MI) was concentrated between 31 and 180 days; this risk abruptly declined thereafter.
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Table 3 Poisson Multivariable Analysis Assessing the Incidence Rate Ratio of Cardiac Mortality and MI During the Course of Dual AP and After Clopidogrel Discontinuation
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Figure 2 Incidence Rate of Cardiac Mortality and MI Between 31 and 180 Days Compared With 181 and 360 Days in Stable Patients or Those With ACS
In stable patients there was 1 event between 31 and 180 days of dual antiplatelet treatment and no events thereafter. In patients with acute coronary syndrome (ACS) there were 23 events between 31 and 180 days and only 3 thereafter. MI = myocardial infarction.
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Clinical outcome after stopping clopidogrel.
For this analysis we excluded patients who presented an event in the first 30 days, patients with events while taking dual antiplatelet therapy, and patients who were still taking dual antiplatelet therapy at the time of the last contact. A total of 641 patients were suitable for this analysis. During the 9-month follow-up, after stopping clopidogrel there were 27 clinical end point events (17 cardiac deaths and 12 MIs). Twenty (74%) of these events (13 cardiac deaths and 8 MIs) occurred 0 to 90 days, 5 (19%) occurred 91 to 180 days (3 cardiac deaths and 3 MIs), and 2 (7%) occurred 181 to 270 days after stopping clopidogrel (1 cardiac death and 1 MI). The unadjusted incidence rate of the clinical end point per 10,000 patient-days was 3.88 between 0 and 90 days, 1.11 between 91 and 180 days, and 0.49 between 181 and 270 days (p = 0.0001). Although most of the events observed between 0 and 90 days after stopping clopidogrel occurred in patients treated with dual antiplatelet therapy for a period <6 months; a similar pattern of events clustering in the first 3 months after clopidogrel discontinuation was also observed for patients treated with clopidogrel for 6 months and in those treated for more than 6 months (Table 4). Figure 3, which represents the instantaneous incidence of the clinical end point after clopidogrel discontinuation, shows that the risk of events was concentrated in the first 90 days, abruptly declining thereafter. In the multivariable analysis (Table 3), including adjustment for total duration of clopidogrel treatment, the incidence rate ratio of the clinical end point in the interval of 0 to 90 days compared with the interval of 91 to 180 days was 4.20 (95% confidence interval: 1.43 to 12.30; p = 0.009).
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Table 4 Incidence of Cardiac Mortality and MI After Stopping Clopidogrel in Relation to Dual Antiplatelet Therapy Duration
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Figure 3 Adjusted Instantaneous Incidence Rate/Patient-Days of Cardiac Mortality and MI After Clopidogrel Discontinuation
The risk of cardiac mortality and myocardial infarction (MI) was concentrated between 0 and 90 days; this risk abruptly declined thereafter.
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Discussion
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In this study we report the clinical outcome of 894 patients with ULMCA stenosis treated with PCI. At the 30-day follow-up, we observed a 3.3% incidence of cardiac mortality and a 2.1% incidence of MI, which favorably compare with early clinical outcomes of high-risk patients with ULMCA stenosis treated with surgery (8). In contrast, this rate of 30-day mortality was slightly higher if placed in the context of the general stent experience reported in randomized trials (9). However, we must emphasize that not only patients enrolled in this study had ULMCA stenosis, which represents a risk factor per se, but they also presented high-risk clinical features because of old age, clinical presentation, high Euroscore, the presence of several comorbidities, and high incidence of bifurcation lesions. Not surprisingly, we observed that the highest incidence rate of cardiac mortality and MI occurred at 30-day follow-up, a finding that is in line with the concept that the period immediately after stenting is the most critical, because of periprocedural complications and stent thrombosis. However, the aim of this study was to investigate whether there were other periods at increased risk of cardiac mortality and MI in patients taking dual antiplatelet therapy and after clopidogrel discontinuation, independent from the 30-day clinical outcome. For this reason, we excluded from the statistical analyses all patients who died or had an MI in the first 30 days. After censoring these patients, we performed 2 kinds of analyses: the first considered the time course of clinical events during the first year of follow-up in patients taking dual antiplatelet therapy, and the second considered the time course of clinical events after clopidogrel discontinuation. The main finding of this study is that after 30-day follow-up there are 2 periods at higher risk of cardiac mortality and MI: the first occurs when patients are still taking dual antiplatelet therapy and spans the interval between 31 and 180 days after PCI; the second occurs in the first 3 months after stopping clopidogrel.
This is the first study to report an uneven distribution of events in patients with ULMCA stenosis treated with PCI during the first year of follow-up while they are still taking dual antiplatelet therapy. This uneven distribution of the clinical end point was independent from the 30-day clinical outcome. Patients with ULMCA stenosis represent a high-risk cohort of patients; furthermore, most of our patients presented with acute coronary syndromes and had other high-risk clinical features. Because our patient population was highly peculiar, further investigations should assess whether these findings are limited to patients with ULMCA stenosis or might be extrapolated to other categories of patients.
The results of our study might have important clinical implications. The observation that the risk of cardiac mortality and MI was not evenly distributed over time during aspirin and clopidogrel treatment but was concentrated in the first 6 months warrants a careful surveillance of these patients in this period of time and should prompt the development of new therapeutic strategies that reduce the risk in this specific interval of time. The end point of this study was the occurrence of cardiac mortality and MI, events in which platelet activation might play a major role (10). The occurrence of thrombotic events while patients were still taking dual antiplatelet therapy raises the hypothesis that a more intense antiplatelet regimen than that currently used might be necessary in this time period (11). This hypothesis is also confirmed by the observation that the uneven distribution of events was observed only in patients with acute coronary syndromes. Whereas patients with stable coronary artery disease fared well, presenting with 1 clinical end point event between 31 and 180 days and no events thereafter, patients with acute coronary syndromes presented with 23 events between 31 and 180 days and only 3 thereafter. Recurrences in patients with acute coronary syndromes have been correlated with a persistent activation of the coagulation system (12) that might last several months after the first qualifying episode (13). In this context of increased thrombin generation and consequent platelet hyper-reactivity, the standard maintenance dose of clopidogrel might not guarantee an adequate platelet inhibition (14) and more powerful antiplatelet drugs might be necessary.
Another intriguing finding of our study was the observation of a cluster of ischemic events in the first 3 months after clopidogrel suspension. Although most of the events observed between 0 and 90 days after clopidogrel suspension were in patients who underwent dual antiplatelet therapy for a period <6 months, the multivariable analysis showed that their occurrence was independent from duration of dual antiplatelet therapy. Similar findings were observed by Ho et al. (15), who reported an increased incidence of death and MI in the initial 90 days after stopping clopidogrel among both medically and PCI-treated patients with acute coronary syndrome. Although the cause of this phenomenon remains unclear, it might be argued that clopidogrel suspension is associated with a rebound hyperthrombotic state that might be responsible for the increased risk of cardiac mortality and MI (16,17). If the results of our study are confirmed by other studies, the modality of drug cessation should be reconsidered and alternative strategies such as tapering of clopidogrel or increasing the dose of aspirin should be evaluated, at least in high-risk patients like those included in this analysis.
Study limitations.
This study suffers all limitations common to other retrospective studies. The classification of events was made at the individual sites without an adjudication committee. We do not have data on stent thrombosis according to the Academic Research Consortium definition. We observed a relative low number of events and therefore cannot exclude overfitting of the statistical models.
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Footnotes
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Dr. Ramondo is a Tutor of CoreValve.
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References
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