(Circulation. 2000;101:751.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Baylor College of Medicine, Houston, Tex (N.S.K.); Cleveland Clinic Foundation, Cleveland, Ohio (A.M.L., E.J.T.); University of Missouri, Columbia, Mo (G.C.F.); Duke Clinical Research Institute, Durham, NC (K.S.P., L.G.B., R.M.C., R.A.H.); Queens Medical Centre, Nottingham, UK (R.G.W.); COR Therapeutics, South San Francisco, Calif (T.J.L.); Onassis Cardiac Surgery, Athens, Greece (D.V.C.); and University Hospital, Rotterdam, Netherlands (M.L.S., E.B.).
| Abstract |
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Methods and ResultsPURSUIT patients were treated with the GP IIb/IIIa antagonist eptifibatide or placebo; PCIs were performed according to physician practices. In 2253 of 9641 patients (23.4%), PCI was performed by 30 days. Early (<72 hours) PCI was performed in 1228 (12.7%). In 34 placebo patients (5.5%) and 10 treated with eptifibatide (1.7%) (P=0.001), MI preceded early PCI. In patients censored for PCI across the 30-day period, there was a significant reduction in the primary composite end point in eptifibatide patients (P=0.035). Eptifibatide reduced 30-day events in patients who had early PCI (11.6% versus 16.7%, P=0.01) and in patients who did not (14.6% versus 15.6%, P=0.23). After adjustment for PCI propensity, there was no evidence that eptifibatide treatment effect differed between patients with or without early PCI (P for interaction=0.634). PCI was not associated with a reduction of the primary composite end point but was associated with a reduced (nonspecified) composite of death or Q-wave MI. This association disappeared after adjustment for propensity for early PCI.
ConclusionsEptifibatide reduced the composite rates of death or MI in PCI patients and those managed conservatively.
Key Words: platelets coronary disease eptifibatide
| Introduction |
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Antagonists of GP IIb/IIIa given during and after PCI can reduce the likelihood of periprocedural MI 2 3 4 5 6 11 12 13 14 15 and long-term mortality.16 Thus, it is appealing to treat ACS patients with a GP IIb/IIIa antagonist as part of a strategy that includes aggressive early intervention (during GP IIb/IIIa inhibition). We reviewed a large trial of the GP IIb/IIIa antagonist eptifibatide (Integrilin) in ACS patients to determine the effects in those who had PCI and in those who were managed conservatively and whether early PCI as part of a strategy that included GP IIb/IIIa antagonism could reduce the risk of death or MI compared with delayed management.
| Methods |
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24 hours of ischemic chest discomfort and had either
ST-segment or T-wave deviation or elevation of the creatine kinase MB
fraction without sustained (>30 minutes) ST elevation. Patients were
randomized to either placebo or intravenous eptifibatide as
a 180-µg/kg bolus followed by a 1.3- or 2-µg ·
kg-1 · min-1
infusion for a maximum of 72 hours. After review of the first 2000
patients by the data and safety monitoring board, the lower infusion
rate was stopped, in accord with the study protocol. In patients who
had PCI during the first 72 hours (early PCI), study drug infusion was
to continue through the intervention and a minimum of 24 hours
afterward to 96 hours maximum. All other treatment decisions, including
angiography and PCI, were left to the treating physician. When PCI was
planned, investigators were encouraged (but not required) to perform it
within 72 hours of randomization. The present analysis is
restricted to patients treated with the higher dose versus
placebo. The primary end point was the composite of death or MI within 30 days. Death or MI among patients who had PCI within the first 72 hours was a secondary end point, because the timing would capture those who had intervention while taking the study drug. The hospital and study records of patients suspected of having new MIs were reviewed and classified by a blinded adjudication committee.4 Investigators were also asked to report whether the patient had had an MI.
Statistical Methods
Modeling Techniques
Statistical comparisons of the rates of death or MI for
interventional subgroups were made by logistic regression modeling.
To estimate the difference in 30-day outcomes for the treatment arms during the period when patients were managed medically only, we did a censored analysis using Cox regression survival modeling. For each patient, we calculated the time until death, MI, or last follow-up (within 30 days). For those who had PCI, follow-up was censored at intervention; thus, survival information only during the period of purely medical treatment was used.
We estimated the relation between early (
72 hours) PCI and event-free
survival with Cox regression modeling techniques using time-dependent
covariates. Although these techniques do not prove causality, we have
referred to association with a reduced event rate as "protective"
and association with an increased event rate as "detrimental." We
also made models for the main effect of randomized treatment and the
main effect and interaction terms of randomized treatment with PCI.
Adjustment for Selection Bias
We developed a propensity score for the likelihood of
PCI17 18 19 by identifying baseline factors to predict PCI.
The PCI probability was determined for each patient by use of a
logistic model. The time-dependent models were applied again with the
inclusion of the propensity score, which allowed us to estimate the
association of PCI or eptifibatide with clinical outcomes and the
interaction of the 2 after adjustment for PCI selection bias.
We also used a second approach to adjust for PCI selection bias. The proportion of patients who had early PCI ("PCI use") was calculated for each center. We then calculated the rates and odds ratios for death or MI within each tertile of PCI use for all patients in the 2 treatment arms. Because eptifibatide treatment was randomly allocated within each center, we could estimate the treatment effect for sites likely to use early PCI versus those unlikely to.
| Results |
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In eptifibatide patients, 282 PCIs (26%) were urgent, compared with 328 (28%) in placebo patients (P=0.25). Intracoronary stents were placed in 51% of PCIs in eptifibatide patients and 50% of PCIs in placebo patients (P=0.81).
Across the 30 days when patients were censored for PCI, there was a
significant reduction in the primary composite end point in
eptifibatide patients (P=0.035, Table 2
). The reduction approached significance
when patients who had PCI or bypass surgery (CABG) were censored
(P=0.058).
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Propensity to Perform PCI
The propensity score was highly predictive of the likelihood of
PCI (
2=837) (Figure 2
). Younger patients with less
comorbidity and patients in North America were more likely to have PCI.
The propensity score includes an interaction between sex and treatment.
PCI use was not different for men and women assigned to eptifibatide.
However, among placebo patients, men were more likely to undergo PCI
(OR 1.32, 95% CI 1.091.59).
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Patients Who Had Early PCI
Among the 1228 early PCI patients, 1105 (91%) were taking the
study drug at the time of the intervention. Study drug was continued a
median of 26 hours after initiation of PCI. Abciximab was used in 116
(9.5%) of the patients who had early PCI: 40 (34%) were assigned to
eptifibatide and 76 (66%) to placebo. Of 622 placebo-treated patients
who had early PCI, 156 (25%) had recurrent ischemia and 34
(5%) suffered an MI before the procedure, compared with 112 (18%) and
10 (1.7%), respectively, of 606 eptifibatide patients.
Kaplan-Meier survival estimates for patients who had early PCI are
shown in Figure 3
and Table 3
. Eptifibatide-treated patients who had
early PCI experienced a significant (P<0.01) decrease in
events during 30-day follow-up. Among patients randomized to placebo,
the rates of death or MI were higher in patients who had early PCI than
in those managed conservatively or by a delayed invasive strategy. In
eptifibatide-treated patients, these rates were similar regardless of
the strategy chosen, indicating that eptifibatide blunted the early
hazard associated with PCI. Eptifibatide reduced the composite of death
or MI before and after early PCI (Figure 4
). This reduction was present when
the analysis was restricted to events after PCI in patients who
received intracoronary stents (Table 4
).
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Eptifibatide Effect in Early PCI Versus Delayed Invasive or
Conservative Strategy
In PURSUIT, the PCI use analysis showed that the
eptifibatide effect was greatest in the tertiles of centers with the
highest likelihood of early PCI
(Table 5
). Unadjusted event rates showed a
greater effect for eptifibatide in early PCI patients than in those
treated conservatively or with a delayed invasive strategy (51 versus
11 events prevented/1000 patients treated). However, after adjustment
for differing clinical characteristics using the propensity score, this
difference disappeared (20 versus 18 events prevented/1000 patients
treated, P for interaction=0.634).
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Early PCI and Clinical Outcome
Table 6
shows time-dependent
covariate analyses for the associations between PCI and the
30-day composite of death or MI. Early PCI had little relation to the
likelihood of death or MI (hazard ratio 0.889, P=0.205)
either before or after statistical adjustment. Similar results were
seen for the end point of death or investigator-determined MI. However,
early PCI was associated with a lower composite rate of death or Q-wave
MI (hazard ratio=0.493, P<0.001; Figure 5
).
After adjustment for treatment and
propensity, the association with early PCI remained but was of
borderline significance (hazard ratio=0.669, P=0.044). For
each of the 3 end points, the eptifibatide benefit was still
significant after adjustment for the propensity score and PCI use. The
hazard ratio for death or MI was 0.75 (P=0.008), for death
or Q-wave infarction 0.782 (P=0.031), and for death or
investigator-determined infarction 0.77 (P<0.001). The
interaction between PCI and randomized eptifibatide treatment was also
sampled after each statistical adjustment and did not reach
significance, indicating that the effect of eptifibatide was not
limited to either group.
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| Discussion |
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Eptifibatide in Patients Managed Invasively
Although eptifibatide reduced the overall rates of death or MI in
patients managed aggressively or conservatively, the reduction appeared
to be greater in patients who had early PCI. When events preceding PCI
were excluded, there was a 31% relative reduction in events at 30 days
in patients who underwent PCI within 72 hours; the reduction was 6% in
patients who had not had PCI during this period. A similar effect was
seen when centers were grouped according to their propensity to perform
PCI within the first 72 hours (use analysis). Conversely,
baseline patient characteristics were quite different between the
management groups, and correction of the event rates using the
propensity score indicated that the adjusted benefit of eptifibatide
did not differ between patients who did or did not have early PCI.
Unfortunately, no methods resolve these discrepancies precisely. Although treatment with eptifibatide or placebo was randomly assigned, PCI is inevitably determined by both preexisting patient characteristics (involving demographics, coronary anatomy, and physician biases) and postrandomization clinical events. We and others have observed that in patients with unstable syndromes, the characteristics differ in those who had or did not have PCI.20 21 22 Attempts to provide clinically meaningful approaches to this issue require adjustment for the characteristics that affect an individual patients propensity to undergo PCI. The propensity score has been validated as a useful instrument to test therapies not randomly assigned.23 Adjustment according to the propensity score indicated no difference in the effects of eptifibatide between patients who had PCI and those managed medically. Thus, selecting ACS patients for PCI may also select a group likely to benefit from a GP IIb/IIIa antagonist.
Effect of PCI on Outcome
The concept of early PCI in ACS patients is theoretically
attractive for many reasons, including the hope that increasing the
vascular luminal diameter may prevent subsequent ischemia and
infarctions. However, before the era of GP IIb/IIIa antagonism and
aggressive PCI with stent placement, 2 randomized
trials9 10 and a recent registry study24
failed to confirm this. Other trials indicate that an
intravenous GP IIb/IIIa antagonist is
beneficial during PCI. Very recently, the FRISC-2 investigators showed
a reduction in death or MI in patients assigned to early
revascularization; how this balance would be
affected by early treatment with a GP IIb/IIIa antagonist
is not known.25
The association of PCI with an early increase in the rate of enzymatically detected MI11 24 may obscure conclusions about the ultimate benefit of PCIs. Using Kaplan-Meier estimates of event rates, we saw that the composite of death or MI at 30 days was more common among patients who had PCI. However, the analysis also suggested that early PCI may be associated with a reduction in a composite of death or Q-wave infarction. Although not drawn from a randomized cohort, the data raise the possibility that PCI is associated with an early hazard and with a reduction in later, more significant events. Interestingly, this hazard was present primarily in placebo patients and was blunted by eptifibatide.
Limitations
Selection bias is the major study limitation. Although
patients were randomized to placebo or eptifibatide, selection for PCI
was an operator-dependent decision, often based on events after
randomization. In addition, the decision for early PCI is likely to
accompany a variety of other practice patterns, which may confound the
outcomes of GP IIb/IIIa antagonist treatment. Thus, seeing
these findings as hypothesis-generating is important. The use
analysis partly circumvented these problems by comparing
treatments in each tertile according to the likelihood of PCI at a
given center, although other medical practices may also vary between
centers in different tertiles. Factorial randomization between
eptifibatide and placebo and between early invasive and conservative
management would have provided a clearer answer to the interaction
between the treatment modes. However, such a design would help assess
the interaction between GP IIb/IIIa inhibition and a
revascularization strategy rather than a particular
procedure (such as PCI), because the latter depends primarily on
anatomic substrates rather than randomized treatment assignment.
Limitations include the difficulty in diagnosing periprocedural MI in patients who have early PCI while cardiac enzymes from enrollment are still elevated. The 24-hour infusion required after PCI may result in a further advantage for eptifibatide treatment. Finally, this analysis does not account for CABG, although the censored survival analysis suggests a reduction in events preceding bypass similar to that seen preceding PCI.
Clinical Implications
Our findings offer important insights into the interaction between
PCI and GP IIb/IIIa antagonism in ACS patients. In many centers, such
patients undergo early angiography and anatomically directed PCI to
reduce the degree of narrowing associated with a culprit lesion. Our
findings suggest that the 2 approaches are not competitive and may, in
fact, be complementary, because eptifibatide treatment prevented events
both before and after PCI. Therefore, even in the patient being
considered for early PCI, very early treatment with a GP IIb/IIIa
antagonist most likely forms a useful part of a larger
comprehensive strategy.
| Acknowledgments |
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| Footnotes |
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Guest Editor for this article was David P. Faxon, MD, USC School of Medicine, Los Angeles, Calif.
Dr Lorenz is an employee of Cor Therapeutics, Inc, the manufacturer of Integrilin, the form of eptifibatide used in this study.
Received March 9, 1999; revision received September 9, 1999; accepted September 23, 1999.
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