(Circulation. 2000;102:1893.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Brigham and Womens Hospital (F.M.S., E.B.), Harvard Medical School (F.M.S., E.B.), and Harvard School of Public Health (F.M.S.), Boston, Mass; National Heart Foundation (A.M.T.), Melbourne, Australia; University of Glasgow (J.S., S.C., C.P.), Glasgow, Scotland; University of Texas School of Public Health, Houston (C.M.H.); University of Sydney (A.K., J.S.), Sydney, Australia; and Wake Forest University (R.B., C.D.F.), Winston Salem, NC.
Correspondence to Dr F. Sacks, Nutrition Department, Harvard School of Public Health, 665 Huntington Ave, Boston, MA 02115. E-mail fsacks{at}hsph.harvard.edu
| Abstract |
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Methods and ResultsThe data from 3 large randomized trials with
pravastatin 40 mg were pooled and analyzed with the
use of a prospectively defined protocol. Included were 19 768
patients, 102 559 person-years of follow-up, 2194 primary end points
(coronary death or nonfatal myocardial infarction), and 3717
expanded end points (primary end point, CABG, or PTCA).
Pravastatin significantly reduced relative risk in younger
(<65 years) and older (
65 years) patients, men and women, smokers
and nonsmokers, and patients with or without diabetes or hypertension.
The relative effect was smaller, but absolute risk reduction was
similar in patients with hypertension compared with those without
hypertension. Relative risk reduction was significant in predefined
categories of baseline lipid concentrations. Tests for interaction were
not significant between relative risk reduction and baseline total
cholesterol (5% to 95% range 177 to 297 mg/dL, 4.6 to
7.7 mmol/L), HDL cholesterol (27 to 58 mg/dL, 0.7 to
1.5 mmol/L), and triglyceride (74 to 302 mg/dL, 0.8 to
3.4 mmol/L) concentrations, analyzed as continuous
variables. However, for LDL cholesterol, the
probability values for interaction were 0.068 for the prespecified
primary end point and 0.019 for the expanded end point. Relative risk
reduction was similar throughout most of the baseline LDL
cholesterol range (125 to 212 mg/dL, 3.2 to 5.5
mmol/L) with the possible exception of the lowest quintile of
CARE/LIPID (<125 mg/dL) (relative risk reduction 5%, 95% CI 19% to
-12%).
ConclusionsPravastatin treatment is effective in reducing coronary heart disease events in patients with high or low risk factor status and across a wide range of pretreatment lipid concentrations.
Key Words: coronary disease drugs lipids lipoproteins meta-analysis
| Introduction |
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For these reasons, the investigators of the 3 large randomized trials with pravastatin1 2 3 initiated a pooling project shortly after the individual trials started. The present report is a study of relative risk reduction in coronary events with pravastatin in patient groups defined on the basis of baseline characteristics, including CHD risk factors and plasma lipids, in the pooled data from 3 large trials with a total of 19 768 patients, 102 559 person-years of follow-up, 2194 primary coronary end points (CHD death and nonfatal MI), and 3717 expanded coronary events (CHD death, nonfatal MI, CABG, and PTCA).
| Methods |
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The primary outcome variable for analysis of treatment effects in the subgroups was coronary death or nonfatal MI. The secondary outcome, not prespecified in the protocol, was an expanded end point that included the primary end point, CABG or PTCA. This end point provided additional events and hence was considered useful in the investigation of risk reduction in subgroups in which there were few events and in further exploration of possible interactions identified in the prespecified analyses. Coronary death was defined as fatal MI, fatal coronary artery disease, or sudden death. The diagnosis of definite nonfatal MI required either (1) typical symptoms of acute MI and elevation of serum creatine kinase concentration or its MB isoform, (2) unequivocal ECG evidence (eg, development of new pathological Q waves), or (3) typical symptoms with strong ECG evidence.
Statistical analyses were performed at Wake Forest University (R.B.; Winston-Salem, NC) independently of the sponsor. The protocol specified analyses of risk reduction in the 3 trials combined and in CARE and LIPID. The intention-to-treat model of analysis was used. Primary analysis involved use of the Cox proportional hazards model, with trial as a covariate, and was unadjusted for baseline covariates. Participant differences in study duration or underlying expected event rates were adjusted for by including a main effect for "study" in each model. Ancillary analysis included the baseline risk factors of age, sex, smoking, diabetes, hypertension; LDL cholesterol, HDL cholesterol, and triglyceride levels; and qualifying coronary event (MI, unstable angina, no coronary event) as covariates. An examination of effect modification according to patient characteristics involved the use of a Cox proportional hazards model with the "trial" and the patient factor as a covariate and the appropriate treatment interaction terms. The relationship between baseline plasma lipid concentrations and coronary event reduction with pravastatin was investigated with the lipids as continuous variables in the Cox model, as prespecified, with a linear interaction term. Risk reduction was first investigated in the prespecified lipid categories and subsequently explored in quintiles of the lipid distributions. Relationships between follow-up event rates and baseline cholesterol levels were assessed with generalized linear models5 to predict events. A probability value of <0.05, 2-sided, was reported as significant. No formal adjustment was made for multiple comparisons (per protocol), and appropriate allowance for this is needed in interpreting results.
| Results |
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Pravastatin reduced the risk of coronary events
significantly and similarly in patients with manifest CHD, either MI or
unstable angina, and in those without manifest CHD (Tables 2
and 3
).
Relative risk reductions in the primary and expanded end points in the
pravastatin group were highly statistically significant for
patients <55 years, 55 to 64 years, and 65 to 75 years old. Women and
patients with diabetes assigned to receive pravastatin
experienced a highly significant reduction in risk for the expanded end
point. Risk reductions in the primary end point for women and diabetic
patients were similar to those in the expanded end point, although the
probability value for the primary end point was borderline due to the
smaller number of events. In women, after adjustment for baseline risk
factors, the risk reduction for the primary end point was 22%
(P=0.045). In other instances, the inclusion of baseline
coronary risk factors as covariates did not affect the
magnitude of the relative risk reductions or the significance of the
interaction testing.
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There was no evidence for a different relative effect of
pravastatin according to age of the patients, in men
compared with women, in diabetic compared with nondiabetic patients,
and in smokers compared with nonsmokers (Tables 2
and 3
).
Pravastatin significantly reduced the risk of the primary
and expanded end points in patients who reported a history of
hypertension, although the magnitudes of the reductions were
significantly less than those for the patients who did not report
hypertension (14% versus 33%, P interaction=0.003 for the
primary end point, and 16% versus 29%, P interaction=0.013
for the expanded end point) (Tables 2
and 3
). These
differences were slightly diminished when the analysis was
restricted to CARE and LIPID (14% versus 31%, P
interaction=0.2 for the primary end point, and 17% versus 26%, P
interaction=0.09 for the expanded end point) and were not affected by
the inclusion of baseline risk factors and the use of antihypertensive
medications as covariates in the multivariate
analysis. In further multivariate
analysis, the relative risk reductions for patients who did not
report a history of hypertension but who were taking antihypertensive
medications for indications other than hypertension such as angina
pectoris or congestive heart failure (n=5245 CARE/LIPID) were 31% for
the primary end point and 24% for the expanded end point. Thus, the
use of antihypertensive medications per se appears not to have been
responsible for the difference in risk reduction between hypertensive
and nonhypertensive patients. There also was no effect of
pravastatin on blood pressure levels in these trials.
Risk reductions were highly significant for the primary and expanded
end points in all of the categories of total cholesterol,
LDL cholesterol, and HDL cholesterol that were
prespecified in the protocol (Tables 4
and 5
). For triglycerides,
risk reductions for the primary and expanded end points were
significant in the lower and intermediate prespecified categories
(<133 and 133 to 219 mg/dL); in the higher category (
220 mg/dL),
risk reduction was borderline in significance for the primary end point
(P=0.057) and significant for the expanded end point
(P=0.029). Event rates were lower in the
pravastatin group than in the placebo group across the
range of total cholesterol (Figure 1
, top), HDL cholesterol
(Figure 2
, top) and
triglyceride (Figure 2
, bottom) concentrations.
There was no significant difference in the effect of
pravastatin on the relative reduction of coronary
risk according to baseline total cholesterol, HDL
cholesterol, or triglyceride levels, as shown
by a nonsignificant probability value in tests for interaction with
these lipid concentrations treated as continuous variables (Tables 4
and 5
). For the expanded end point, the P
value for interaction between baseline triglycerides and
risk reduction was borderline (P=0.055). However, risk
reduction was nearly identical for the lowest quintile of
triglycerides (<98 mg/dL [1.1 mmol/L], risk
reduction expanded end point 20%) compared with the highest quintile
(>207 mg/dL [2.4 mmol/L], risk reduction 18%) (Figure 2
). Thus, the evidence is weak, at best, for modification of the
effect of pravastatin by triglyceride
concentrations.
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For LDL cholesterol, risk reduction for the primary end
point was 22% in the lowest prespecified category of <135 mg/dL
(4.5 mmol/L) (P=0.005), 23% in the middle category of
135 to 174 mg/dL (4.5 to 5.5 mmol/L) (P<0.001), and
32% in the highest category of
175 mg/dL (5.5 mmol/L)
(P<0.001) and for the expanded end point (17%, 23%, and
30%, respectively) (Tables 4
and 5
). Test for a
difference in risk reduction according to baseline LDL
cholesterol concentration, considered as a continuous
variable, was borderline for the primary end point
(P=0.068) and significant for the expanded end point
(P=0.019). An exploratory analysis of this finding
in the CARE/LIPID pooled population showed that event rates increased
continuously over the range of LDL cholesterol levels in
the placebo group but not in the pravastatin group (Figure 1
, bottom). Risk was reduced significantly in all except the
lowest quintile of <125 mg/dL (RR for primary end point 0.96 [0.77 to
1.19], RR for expanded end point 0.95 [0.81 to 1.12]) (Figure 1
, bottom).
| Discussion |
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Remaining weaknesses of this pooling project are the relatively small numbers of women and patients with diabetes, which did not provide sufficient statistical power for definitive results on risk reduction for the prespecified primary end point. When the sensitivity of the study was increased by adding revascularization procedures to the primary end point, event reduction due to pravastatin for women and diabetics was highly significant, providing evidence that strongly favored an interpretation that pravastatin therapy prevents coronary events in women and diabetics. A similar situation occurred in the evaluation of whether baseline LDL cholesterol concentrations influenced the effect of pravastatin on the primary end point. The P value for interaction between baseline LDL cholesterol and coronary events was borderline for the primary end point but significant for the expanded end point.
In older patients, aged 65 to 75 years at the beginning of the trial in which they were enrolled and 70 to 80 years at its end (not included in WOSCOPS), relative risk reduction was highly significant, and there was no evidence that relative risk reduction differed according to age. Trials that used clofibrate and niacin6 or simvastatin7 and included patients up to the age of 70 years found that risk reduction was significant in those of age 60 to 70 years and similar to that in the younger patients. Because three fourths of deaths from MI in the United States occur in patients older than 65 years,8 these results should support the use of pravastatin to reduce overall coronary disease in the population.
Pravastatin significantly reduced coronary events in patients with a history of hypertension. However, the relative risk reduction was less than that in patients who did not report a history of hypertension. This finding is unexpected because no individual trial of pravastatin or of other statins showed reduced efficacy in hypertensives. We have identified no explanation for the difference in relative risk reduction between hypertensives and nonhypertensives, and this finding may be due to chance and the testing of multiple subgroups. No formal adjustment of multiple comparisons was made among the 10 prespecified subgroups, and one might expect a false-positive result on average with every 20 independent tests. Furthermore, this interpretation is in part supported by the weakening of the significance level for the difference in relative risk reduction in the expanded end point compared with the primary end point. If the difference were real, then one might anticipate that the statistical significance would increase as the number of events included in the analysis increases. We further emphasize that absolute risk reduction is substantial with pravastatin in the hypertensives in view of their high rate of recurrent coronary events. For example, the number of patients needed to be treated to prevent a coronary event (coronary death, MI, CABG, or PTCA) was 21 among hypertensive patients compared with 20 in the overall CARE/LIPID population.
Baseline total cholesterol, HDL cholesterol, and triglyceride concentrations did not significantly affect relative risk reduction with pravastatin. This is consistent with the individual results of the 3 pravastatin trials2 9 10 ; Scandinavian Simvastatin Survival Study (4S), a secondary prevention trial with simvastatin11 ; and Air Force/Texas Coronary Atherosclerosis Prevention Study (AFCAPS/TexCAPS), a primary prevention trial with lovastatin.12
Relative risk reduction was significant in each prespecified category of baseline LDL cholesterol concentration. However, an interaction test for an effect of baseline LDL cholesterol on relative risk reduction, also prespecified, showed a trend for the primary end point (P=0.068) that increased in significance with the expanded end point (P=0.019). The finding was explored by an analysis of LDL quintiles, suggesting a possible diminished risk reduction only in the lowest quintile of the CARE and LIPID range (ie, <125 mg/dL [3.2 mmol/L]). An LDL cholesterol of 125 mg/dL corresponds to approximately the 30th percentile of the middle-age and older population in the United States.13 Possible explanations include a threshold below which there is no risk reduction, a curvilinear relationship with diminishing risk reduction as baseline LDL cholesterol decreases, or simply chance. A contributing factor could be the effect of the diminished absolute LDL cholesterol reduction observed with lower baseline LDL cholesterol concentration.10 Besides CARE and LIPID,1 2 no other clinical end point trials of statins investigated patients in this range of baseline LDL cholesterol concentrations and thus do not contribute data to this topic.3 11 12 Finally, a conclusive investigation would require a still larger number of patients and events than exist in CARE and LIPID in the lower part of the range of LDL cholesterol concentrations.
In conclusion, the PPP demonstrates remarkable uniformity of relative risk reduction in primary and secondary prevention in men and woman, in older and younger patients, and in diabetic and nondiabetic patients; across the population ranges of total cholesterol, HDL cholesterol, and triglycerides; and in most of the LDL cholesterol range. Absolute risk reduction by pravastatin is then driven by the level of risk in the patient groups and is large in those with high event rates, such as older patients, diabetic patients, smokers, and those with high total or LDL cholesterol concentrations. These considerations should weigh strongly in determination of the appropriateness of this treatment for primary prevention.14 Finally, these findings support a policy of near-universal treatment of patients with clinical evidence of CHD.
| Acknowledgments |
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Received January 6, 2000; revision received May 31, 2000; accepted May 31, 2000.
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