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(Circulation. 2000;102:1503.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the University of Michigan Medical Center (B.P.); Wake Forest University School of Medicine (R.P.B., C.D.F., M.E.M., W.R.); University of Minnesota Hospital/Clinic (D.B.H.); and University of British Columbia (G.B.J.M.).
Correspondence to Bertram Pitt, MD, Department of Internal Medicine, Division of Cardiology, University of Michigan Medical Center, 1500 East Medical Center Drive, 3910 Taubman Center, Ann Arbor, MI 48109-0366.
| Abstract |
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Methods and ResultsThe Prospective Randomized Evaluation of the Vascular Effects of Norvasc Trial (PREVENT) was a multicenter, randomized, placebo-controlled, double-masked clinical trial designed to test whether amlodipine would slow the progression of early coronary atherosclerosis in 825 patients with angiographically documented coronary artery disease. The primary outcome was the average 36-month angiographic change in mean minimal diameters of segments with a baseline diameter stenosis of 30%. A secondary hypothesis was whether amlodipine would reduce the rate of atherosclerosis in the carotid arteries as assessed with B-mode ultrasonography, which measured intimal-medial thicknesses (IMT). The rates of clinical events were also monitored. The placebo and amlodipine groups had nearly identical average 36-month reductions in the minimal diameter: 0.084 versus 0.095 mm, respectively (P=0.38). In contrast, amlodipine had a significant effect in slowing the 36-month progression of carotid artery atherosclerosis: the placebo group experienced a 0.033-mm increase in IMT, whereas there was a 0.0126-mm decrease in the amlodipine group (P=0.007). There was no treatment difference in the rates of all-cause mortality or major cardiovascular events, although amlodipine use was associated with fewer cases of unstable angina and coronary revascularization.
ConclusionsAmlodipine has no demonstrable effect on angiographic progression of coronary atherosclerosis or the risk of major cardiovascular events but is associated with fewer hospitalizations for unstable angina and revascularization.
Key Words: amlodipine atherosclerosis angiography ultrasonics trials angina revascularization
| Introduction |
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Amlodipine besylate (Norvasc) is a long-acting dihydropyridine calcium channelblocking agent that is lipophilic, has antioxidant effects, and prevents experimental atherosclerosis.6 We postulated that amlodipine would alter the progression of coronary and carotid artery atherosclerosis and therefore reduce the risk of events without the major adverse clinical effects found in previous studies of dihydropyridine calcium channelblocking agents.1 2 7 8 This report describes the results of the Prospective Randomized Evaluation of the Vascular Effects of Norvasc Trial (PREVENT).
| Methods |
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30% diameter stenosis
(nonintervened and noninfarcted) and the presence of
1 lesion with a
5% to 20% stenosis (judged qualitatively) that was not in a
vessel with a
60% lesion. Other eligibility criteria included
diastolic blood pressure of <95 mm Hg, total
cholesterol of <325 mg/dL, and fasting blood glucose of
<200 mg/dL. Randomization was stratified according to clinical center
and history of PTCA. Study medication was initiated at 5 mg QD and increased to 10 mg QD after 2 weeks if tolerated. The final study angiogram was scheduled 36 months after randomization, 7 to 10 days after the study medication was stopped. If a patient had a cardiac procedure performed during follow-up, an "interim" angiogram obtained before the procedure could serve as the final film if a 36-month film could not be obtained and if the interim film occurred no earlier than 35 months after randomization.
Angiographic Methods and Outcomes
The primary objective was to determine whether amlodipine would
reduce the progression of early atherosclerotic segments as measured on
the basis of a change in mean minimal diameter with quantitative
coronary angiography (QCA).9 10 Atherosclerotic
segments were defined as coronary segments with a diameter
stenosis of
30% at baseline. Up to 12 coronary
segments were used in the analysis of disease
progression.6 Vessels that underwent a procedure at or
before baseline were excluded from the analyses. The baseline
and follow-up films were centrally read pairwise by a certified reader
who was blinded to treatment assignment and the temporal sequencing of
films.
Ultrasonographic Methods and Outcomes
A secondary hypothesis tested whether amlodipine reduced the
progression of atherosclerosis in the carotid arteries
as assessed with B-mode ultrasonography. Progression was based on the
mean of the 3-year regression slopes of the maximum IMT measurements
estimated in each of the 12 separate wall segments (near and far walls
of the common carotid, bifurcation, and internal carotid arteries, on
the right and left sides of the neck).11 This outcome
required fewer participants (377) than the angiographic outcome (825).
There were 2 ultrasound examinations at baseline and 1 every 6 months
thereafter for 36 months. Certified readers who were blinded to
treatment assignment centrally read videotapes.
Monitoring for Clinical Events and Adverse Experiences
The prespecified clinical events were all-cause mortality and
the occurrence of major fatal/nonfatal vascular events or procedures.
Death, myocardial infarction, stroke, hospitalized heart failure, and
hospitalized episodes of unstable angina were classified by an external
events classification committee blinded to treatment assignment with
the use of definitions that were used in other
studies.12 13 14 Confirmation of unstable angina required
hospitalization for typical chest pain and either evidence of
myocardial ischemia (ECG or stress test evidence, or new
angiographic findings of disease) or an indication that this pain was
similar to that of previously documented evidence of ischemia.
The PREVENT adverse experience database was retrospectively reviewed
for terms that suggest cancer or bleeding. All suspected cancers were
classified by an external oncology committee. The a priori
definition for an incident cancer was a new pathologically confirmed
cancer diagnosed at least 1 year postrandomization.
Statistical Analyses
Analysis of the primary end point was performed with a
mixed-effects ANCOVA model that accounted for correlation among
segments measured within patients.15 Treatment effects are
presented in terms of the mean difference and 95% CIs in
3-year change for both minimum diameter and percent diameter
stenosis. In addition to treatment group assignment, the
mixed-effects model included effects that represent segments,
clinical centers, PTCA status at baseline, and random effects for
participants. Secondary analyses of 3-year change in minimal
diameter and percent diameter stenosis were performed within
predefined subgroups after stratification of segments by baseline
stenosis of 0%, >0% to
30%, >30% to 50%, >50%, and
all segments. For analysis of all segments, baseline
stenosis was included as a covariate. Correlation among
segments was accounted for by fitting models to allow different
variances for each segment and a common covariance between
segments (heterogeneous compound symmetry). Segments having
undergone revascularization during follow-up were
excluded from analyses of 36-month angiograms.
The progression of atherosclerosis in the carotid arteries was measured on the basis of the slope of the maximum IMT measurements averaged over 12 separate wall segments as a function of time.11 For this analysis, a mixed-effects model was fit to the maximum IMT measured within each segment at each follow-up. In addition to including random intercepts and slopes for participants, this model contained fixed effects for clinic, treatment, segment, time, and a timextreatment interaction. Treatment effects are presented in terms of the mean difference and 95% CIs on the mean difference in 36-month change in maximal IMT. Analyses of time until the occurrence of clinical outcomes were carried out by log-rank statistics and proportional hazards models to adjust for covariates.16 For clinical outcomes, treatment effects are presented in terms of hazard ratios (HRs) and associated 95% CIs. Simple tests of proportions and means were conducted to evaluate treatment group differences in baseline characteristics. HRs and associated 95% CIs were used to estimate treatment group differences in the 36-month occurrence of adverse events, including cancer and bleeding episodes.
To protect against the increased probability of a type I error, tests of statistical significance were performed at the 0.05 level for the primary angiographic outcome and the overall ultrasound analysis. Because the 5 clinical event outcomes were selected at least in part to address safety concerns,1 2 14 hypothesis tests were interpreted at the 0.05 level so potentially important differences would not be overlooked. In contrast, 95% CIs of treatment effects were calculated for all other secondary outcomes.
| Results |
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Angiographic Results
Evaluable follow-up angiograms were obtained from 82% (678 of
825) of the participants. There was no evidence that any baseline
characteristic was distributed differentially between treatment groups.
For the primary outcome measure (mean 3-year change in the minimum
diameter in segments of
30% stenosis), the placebo and
amlodipine groups had nearly identical average reductions in the
minimal diameter: 0.084 versus 0.095 mm, respectively
(P=0.38, Table 2
).
Amlodipine also failed to show any significant effect for each of the
other angiographic outcomes.
|
Ultrasonographic Results
In contrast, amlodipine had a significant effect on the
progression of carotid atherosclerosis (Table 3
): the placebo participants had a
0.033-mm increase in IMT during 3-years of follow-up, and the
amlodipine participants had a 0.013-mm decrease (P=0.007).
When stratified according to carotid segment, the estimated 3-year
changes in the common carotid were -0.046-mm regression for amlodipine
versus +0.011-mm progression for placebo (95% CI on difference -0.090
to -0.024 mm).
|
Clinical Event Results
Table 4
presents the rates and
Figure 1
presents the life-table
curves for the major clinical events by treatment group. Vital status
was unknown for 2 placebo and 4 amlodipine patients. Amlodipine had no
effect on all-cause mortality. When fatal and nonfatal coronary
and cerebrovascular events are combined, there were 23 amlodipine and
28 placebo participants who experienced an event (HR 0.82 [95% CI
0.47 to 1.42]). Amlodipine reduced the occurrence of the combination
of hospitalized nonfatal congestive heart failure and unstable angina
(61 amlodipine versus 88 placebo, HR 0.65 [0.47 to 0.91]), a
difference primarily due to a reduction in the rate of unstable angina
(60 versus 85, HR 0.67 [0.48 to 0.93]). Amlodipine also reduced
coronary revascularizations (53 versus 86,
HR 0.57 [0.41 to 0.81]) regardless of the use of ß-blocker,
nitrates, or lipid-lowering therapy. When the major and other events
and procedures were combined, there were fewer events in the amlodipine
group (86 versus 116, HR 0.69 [0.52 to 0.92]), mostly attributable to
a difference in unstable angina and
revascularization.
|
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Table 5
presents adverse experiences
for which there was a treatment group difference with a nominal
P value of
0.10. Twenty-three confirmed incident cancers
were reported during the second and third years of follow-up: 15
amlodipine and 8 placebo (HR 2.13 [0.90 to 5.21]). In the first year
postrandomization, there were 7 and 4 cancers, respectively. This
treatment difference is consistent with reports from
observational studies that link calcium channel blockers to an
increased risk of cancer during the long term, although other studies
have not reported an association.7 There were 10
participants who were hospitalized for bleeding: 5 in each group. All
were on their study medications within 3 days of the hospitalization,
none were on an open-labeled calcium channel blocker, and 1 amlodipine
patient was on warfarin. During follow-up, 40 amlodipine and 28 placebo
participants reported at least 1 bleeding episode, mostly nosebleeds
(HR 1.42 [0.88 to 2.30]), similar to the bleeding risk reported from
larger observational studies.8
|
Other Follow-Up Results
Pill count compliance was 79% for amlodipine versus 83% for
placebo. After 4 months of treatment, both systolic and
diastolic blood pressures were lower in the amlodipine
group compared with the placebo group (122/75 versus 130/79
mm Hg, respectively). Although the use of calcium channel blockers and
ACE inhibitors was discouraged during follow-up, 91
amlodipine and 120 placebo patients were receiving a nonstudy calcium
channel blocker for at least some portion of follow-up, and 32
amlodipine and 67 placebo group participants were receiving an ACE
inhibitor. The use of diuretics was almost equal
between treatment groups during follow-up: 111 amlodipine and 93
placebo. After the Scandinavian Simvastatin Survival Study
(4S) results,17 an effort was made to get appropriate
participants to use lipid-lowering agents. The use of statins increased
from 27% at baseline (Table 1
) to 52% for any use during the
course of follow-up (50% amlodipine versus 54% placebo).
| Discussion |
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In contrast, amlodipine had a significant effect on the progression of carotid artery atherosclerosis, as assessed with B-mode ultrasonography. One explanation for this discrepancy may be a difference in the sensitivity of B-mode ultrasonography and coronary angiography for the detection of early arterial disease. Experimental studies show that the growth of atherosclerotic lesions initially affects the vessel wall or external arterial diameter without encroachment on the lumen.18 Another explanation is that the blood pressurelowering action of amlodipine: reduction in wall stress may have different effects on the carotid and coronary circulation. Regardless, the extent of carotid atherosclerosis as measured by B-mode ultrasonography is associated with increased risk of cardiac mortality and morbidity.19 20 21
Amlodipine had no effect on the risk of all-cause mortality or major cardiovascular events (myocardial infarctions and strokes). However, the statistical power for the detection of a treatment difference in mortality and major morbidity rates was low because of the relatively low incidence rates (eg, <2%/y for myocardial infarction or death).
Of possible importance is the finding that amlodipine significantly reduced the rates of unstable angina and coronary revascularization. An improvement in coronary vasomotor tone could be due to a direct effect on vascular smooth muscle or endothelial function. These reductions in hospitalization for angina pectoris and revascularization were seen in patients on a ß-blocker, nitrate, or lipid-lowering agent. A reduction in the incidence of unstable angina pectoris could result in lower rates of coronary angiography and revascularization. These beneficial effects were not seen in previous angiographic trials with nifedipine or nicardipine in patients with stable coronary artery disease, even though these agents have proved antianginal effects, suggesting that amlodipine may have additional effects.
Of additional importance is the finding that the event curves for
unstable angina pectoris and coronary
revascularizations diverge early. Although lipid
lowering with statins and ACE inhibition with ramipril have reduced
total mortality rates, nonfatal myocardial infarction, and
revascularizations in patients with stable
coronary artery disease,17 22 23 24 there is a lag
of
1 year before the event curves for these strategies diverge. The
addition of amlodipine could produce an early benefit and further
reduce revascularization and hospitalization for
unstable angina. It may be hypothesized that this would allow statins
or ACE inhibitors a chance to reduce "hard"
ischemic events by altering the underlying pathophysiology of
atherosclerosis, plaque rupture, or thrombosis and
thereby possibly avoid coronary
revascularization. Thus, amlodipine might further
reduce the need for coronary
revascularizations observed in previous randomized
trials of medical therapy versus coronary angioplasty, such as
Randomised Intervention Treatment of Angina (RITA-2) and Atorvastatin
Versus Revascularization Treatment
(AVERT).25 26 This strategy, however, requires prospective
testing.
| Acknowledgments |
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| Footnotes |
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Drs Pitt, Byington, and Miller serve as consultants to Pfizer; Dr Hunninghake currently works on various other research projects supported by Pfizer and serves on the Pfizer Speakers Bureau; and Dr Mancini serves as a consultant to both Merck and Parke-Davis.
| Appendix 1 |
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|
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Steering Committee Cochairmen
Curt D. Furberg, MD, PhD (Wake Forest University School of
Medicine); Bertram Pitt, MD (University of Michigan Medical
Center).
Angiography Reading Center
G.B. John Mancini, MD (University of British Columbia).
Ultrasound Reading Center
Ward Riley, PhD (Wake Forest University School of Medicine).
Data Coordinating Center
Robert P. Byington, PhD, Michael E. Miller, PhD (Wake Forest
University School of Medicine).
Central Laboratory
Smithkline Beecham Clinical Laboratories.
Sponsor
Pfizer, Inc/US Pharmaceuticals Group: Robert Scott, MD, Ethel
Buebendorf, RN.
Received January 11, 2000; revision received April 26, 2000; accepted May 2, 2000.
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