Author + information
- Received July 14, 1998
- Revision received November 10, 1998
- Accepted January 20, 1999
- Published online May 1, 1999.
- Odd Johansen, MD∗,* (, )
- Magne Brekke, MD†,
- Ingebjørg Seljeflot, PhD‡,
- Michael Abdelnoor, MPH, PhD‡ and
- Harald Arnesen, MD, PhD∗
- ↵*Reprint requests and correspondence: Dr. Odd Johansen, Department of Cardiology, Ullevaal University Hospital, N-0407 OSLO, Norway
The aim of the study was to investigate whether omega-3 fatty acids (n-3 FA) reduce the occurrence of restenosis after percutaneous transluminal coronary angioplasty.
Meta-analyses have shown significant reduction of restenosis after coronary angioplasty upon supplementation with n-3 FA.
In a prospective, placebo-controlled, double-blind study, 500 patients were randomly allocated to treatment with n-3 FA (Omacor™, Pronova AS, Oslo, Norway) 5.1 g/day or corn oil (placebo) starting at least two weeks prior to elective coronary angioplasty. The treatment was continued until restenosis evaluation by quantitative coronary angiography after six months. Stenosis was defined as a minimal luminal diameter (MLD) <40% of the reference diameter. Successful coronary angioplasty was defined as ≥20% acute gain in MLD and a residual stenosis <50%. Restenosis was defined as ≥20% late loss of diameter and stenosis >50% or an increase in stenosis of ≥0.7 mm. Three-hundred ninety-two patients fulfilled the criteria for initial stenosis and successful coronary angioplasty, and, except four patients who died, none were lost for follow-up.
Restenosis occurred in 108/266 (40.6%) of the treated stenoses in the Omacor group and in 93/263 (35.4%) in the placebo group (odds ratio [OR] 1.25, 95% confidence interval [CI] [0.87–1.80] p = 0.21). In the Omacor group one or more restenoses occurred in 90/196 (45.9%) patients as compared with 86/192 (44.8%) in the placebo group (OR 1.05, 95% CI [0.69–1.59] p = 0.82).
Supplementation with 5.1 g n-3 FA/day for six months, initiated at least two weeks prior to coronary angioplasty did not reduce the incidence of restenosis.
Percutaneous transluminal coronary angioplasty was introduced in 1977 (1)and has become the most used invasive procedure for myocardial revascularization. This procedure gives high initial success rate with an immediately good blood flow in the affected artery (2). The major concern is the high incidence of restenosis, which has recently been documented to be as high as 45% four to six months after coronary angioplasty, when measured with quantitative coronary angiography (3,4). The process of restenosis is initiated by injury of the vessel wall with the subsequent release of thrombogenic, vasoactive and mitogenic factors (5).
Endothelial and deep-vessel wall injury lead to platelet aggregation, fibrin formation, inflammation and activation of macrophages and vascular smooth-muscle cells. These events induce the production and release of growth factors and cytokines (6), resulting in the migration of smooth muscle cells from their usual location in the arterial media to the intima. At the same time they change to a synthetic phenotype, produce extracellular matrix and proliferate (7,8). This process eventually results in lumen narrowing and represents the restenosis. In addition, remodelling of the vascular wall seems to play a role for the ultimate degree of restenosis (9).
With focus on smooth muscle cell proliferation and matrix formation, numerous pharmacological approaches have been evaluated in an attempt to prevent restenosis. Except for promising results with the antioxidant probucol (10), no single principle has consistently shown a reduction in angiographically defined restenoses at six months. Omega-3 fatty acids (n-3 FA) have been proposed to be antiatherogenic through a variety of mechanisms, like decrease in membrane arachidonic acid and thromboxane A2 formation with decreased platelet aggregation, decreased production of platelet derived growth factor in endothelial cells (11)and anti-inflammatory properties (12). Furthermore, reduction of intimal hyperplasia and coronary atherosclerosis in animal models has been observed upon administration of n-3 FA (13–15), as well as reduced incidence of aortocoronary vein graft occlusion in humans (16). However, clinical trials previously conducted to determine the effect of n-3 FA on the restenosis rate after coronary angioplasty have produced conflicting results (3,4,17–25).
Two meta-analyses have been published (26,27), concluding with a small to moderate benefit of n-3 FA on restenosis. In 1994 Leaf et al. published a large multicenter, double-blind, placebo-controlled study. They concluded that 8 g/day of n-3 FA failed to prevent the high rate of restenosis after coronary angioplasty (4).
We report the results of a prospective randomized, placebo-controlled, double-blind trial (the Coronary Angioplasty Restenosis Trial, CART) designed to test the hypothesis that a dietary supplementation of n-3 FA given daily from two weeks before through six months after angioplasty will reduce the frequency of restenosis.
Study design and patient population
From April 1992 through February 1996, 500 patients accepted for elective percutaneous transluminal coronary angioplasty were scheduled to receive a daily dietary supplement of 3 × 1 g gelatin capsules twice daily, starting at least two weeks prior to coronary angioplasty and continued until follow-up angiography regularly six months after the angioplasty. Each capsule containing 84% ethyl esters of n-3 polyunsaturated fatty acids (0.45 g eicosapentaenoic acid [EPA] and 0.39 g docosahexaenoic acid [DHA] with the addition of 4 mg alpha-tocopherol) (Omacor™, Pronova AS, Oslo, Norway) or an equal amount of ethyl ester of corn oil as placebo. Randomization was undertaken using consecutively numbered sealed envelopes. Both the patients and the investigators were blinded with regard to the treatment given. Compliance with the study medication was assessed by determination of serum phospholipid fatty acids before and at the end of the study period and by capsule counts.
A previously validated individual diet questionnaire (28)was obtained from 261 consecutively included patients. All patients were recruited from a single center, and they were treated with other medication as prescribed by their physician. At randomization, users of fish oil supplementation were asked to stop the additional intake during the study period. The major type (29)and the location of the index lesion in the vessel were characterized. All treated lesions were in vessels with a diameter above 1.5 millimeters (mm), and the mean value was 2.7 mm. No differences in the diameter of treated vessels were found between the treatment groups. Patients who were scheduled for elective coronary angioplasty for one or more lesions in native coronary arteries who had not undergone prior angioplasty and were willing to participate were candidates for inclusion.
Exclusion criteria were: questionable patient compliance; treatment with steroid or immunosuppressive drugs; poorly controlled, sustained hypertension; pregnancy; unstable angina pectoris; bleeding disorder documented by laboratory tests; or other serious illnesses with expected survival of less than two years. Angiographic reasons for exclusion were diffuse lesions (>2 cm long), excessive tortuosity of proximal segment, extremely angulated segments (>90°) or chronic (>3 months) total occlusions. Stent implantation was reason for exclusion because of the special therapeutic regimen given after this procedure.
Coronary angioplasty procedure
All patients underwent coronary angioplasty from the right femoral artery using a rapid exchange system. A standard regimen of drug treatment was instituted before the procedure. The patients were started or maintained on aspirin 160 mg once daily, and those who did not use any calcium channel blocking drugs received 20 mg nifedipine twice daily at least from the day before angioplasty. Patients were in the fasting state. They were also pretreated with an infusion of glyseroltrinitrate 12–25 μg per min which was continued throughout the procedure, and the patients were heparinized with a bolus dose of 10,000 I.E. intra-arterially followed by 5,000 I.E. every hour during the angioplasty. Thereafter intravenous infusions of heparin 1,000 I.E./h, and glyseroltrinitrate 12 μg per min were continued until the next day.
Coronary cineangiograms of the lesion on the affected vessels were obtained using two orthogonal views. (General Electric CGR DX HILINE Buc, France). To enable replication, all angles and positions of gantry were noted in a specific protocol. The angiograms performed before coronary angioplasty, immediately after coronary angioplasty and at follow-up examinations were obtained in the same catheterization site with the same angiographic equipment and the same image intensifier magnification.
Each cardiac catheterization procedure was standardized, and only two experienced radiologists were involved in the study. Quantitative measurements were calibrated using the guiding catheter as the reference dimension. The localization of the marker of minimal luminal diameter (MLD) was determined by the radiologist according to the lowest figure of MLD given by the computer. In addition to the standard projections, the best camera angles for visualization of stenotic areas were recorded for reproducible positioning on subsequent filming. Angiographic controls between the angioplasty and the study end point, was not conducted unless recurrence of severe ischemic symptoms emerged. In all other patients repeated angiography was performed at six months. If a repeat angiogram was indicated at four months or later, no further angiogram was requested at six months.
On discharge after the coronary angioplasty the patients were maintained on trial medication and other therapy as individually indicated for the following six months. Interpretation of the angiographies was undertaken without knowledge of the patients assigned treatment.
A qualifying stenosis was defined as an atherosclerotic lesion in the coronary arteries equal to or more than 60% stenosis as measured by quantitative coronary angiography. The degree of stenosis was calculated on the basis of the MLD of the stenosis as compared with the reference diameter of the vessel, that is, the closest vessel diameter judged to be normal. A successful angioplasty was defined as less than 50% residual stenosis and at least 20% reduction of original stenosis.
We defined restenosis as less than 50% luminal diameter remaining and: 1) at least 20% increase of the stenosis, or 2) a loss of 0.7 mm or more of the vessel diameter as measured by quantitative coronary angiography at six months follow-up procedure when compared with the post-coronary angioplasty angiography. Acute gain was defined as the difference between MLD after and before coronary angioplasty, and late loss was defined as the difference between MLD after coronary angioplasty and at follow-up procedure.
Blood samples after overnight fasting were obtained 14 and 1 day before, and 3 and 6 months after balloon treatment.
Serum total cholesterol and triglyceride levels were analyzed by enzymatic colorimetric methods (Boehringer Mannheim GmbH, Mannheim, Germany). Serum high-density lipoprotein cholesterol was determined in the supernatant after precipitation with phosphotungstic acid and magnesium chloride (30). Serum samples were kept frozen at −70°C until analyzed for phospholipid fatty acids. For each subject, samples obtained at different times were analyzed in batch. Serum lipids were extracted with n-butanol after addition of an internal standard (phosphatidyl-choline diheptadecanoyl, Sigma, St. Louis, Missouri). An antioxidant (2,6,-di-tert.-butyl-p-kresol, Fluka AG, Buchs, Switzerland) was added to the n-butanol before extraction. Phospholipids were isolated from the total lipid extracts by solid-phase extraction on aminopropyl columns (Varian, Harbour City, California) and transmethylated. The phospholipid fatty acids were quantified by gas chromatography. FAME mixture Me-81- added C17:0 methylester (Larodan, Malmø, Sweden) was used as an external standard. A human serum pool sample was included as a control to monitor the analytic performance. The day-to-day coefficients of variation in this serum pool for C16:0, C18:2n-6, C20:5n-3 and C22:6n-3 were 3.7%, 4.1%, 5.2%, and 4.8%, respectively (n = 91). The results were quantified as milligrams of phospholipid fatty acid per liter of serum. All sera measured had been frozen only once. The protocol was approved by the Regional Ethics Committee, and all patients gave their informed consent.
The primary end point of the study was restenosis as determined with quantitative coronary angiography six months after coronary angioplasty. We assumed a restenosis rate of 30% per patient in the placebo group. A sample size of 480 patients was calculated to detect a 40% relative reduction by fish oil supplementation with a type I error of 0.05 and a power of 80%.
An increasing use of stenting at the time the study was designed contributed to the decision to expand the sample size to 500 patients because stenting was one reason for exclusion from the study. Analyses were performed after the intention-to-treat principle. To adjust for interdependency between multiple restenoses in the same patient, we also analyzed data with regard to the number of patients with ≥1 restenoses within each group.
Variables on categorical data were evaluated by Mantel-Haenszel test and differences between continuous variables by the Mann-Whitney Utest. A two-sided p value ≤0.05 was considered statistically significant. Estimation of the adjusted effect was done by controlling for discrepancies in risk factors using the multivariate logistic model (31). The EPI Info software program (32)was used throughout. No interim analyses were performed.
Table 1shows the floating scheme of patients throughout the study. Of the 500 randomized patients, the finally evaluable population represented 388 patients, 196 assigned to receive active treatment and 192 constituting the placebo group. Five patients were withdrawn before admittance to the catheterization laboratory and 103 patients were disqualified during the coronary angioplasty procedure. The main reason for this was stenting, which was performed in 54 patients, 25 in the Omacor group and 29 in the placebo group. In 23 patients the indication for balloon treatment was not confirmed when the coronary angiogram was reevaluated immediately before the planned angioplasty. Nonsuccessful coronary angioplasty according to the study protocol was encountered in 23 patients. In addition two patients were excluded for angiographic reasons (chronic occlusion, diffuse lesion more than 2 cm) and one patient because of an alternative treatment.
Finally, four patients died during the study period, two had acute myocardial infarction before they died, and two suffered sudden death. The total number of stenoses evaluable in the study was 529, 266 in the Omacor group and 263 in the placebo group. As a mean 1.4 stenoses were treated per patient. One stenosis occurred in 271 patients, 93 patients had two stenoses and 24 patients had three stenoses.
From Table 2, which shows the baseline characteristics of the evaluated patients, we learn that there were no significant differences between the two groups concerning age, gender, smoking habits, diabetes mellitus, hypertension, previous myocardial infarction, angina pectoris New York Heart Association (NYHA) class distribution, left ventricular ejection fraction, systolic and diastolic blood pressure. The only statistically significant difference was in body mass index (p = 0.02).
The locations of the index lesions in the coronary arteries (Table 3)were left anterior descending or one of its side branches in 39.5%, left circumflex including the intermediary artery in 34.8% and the right coronary artery in 25.7%. Lesions in the right coronary artery were somewhat more frequent in the Omacor than in the placebo group. This slightly skew distribution did not influence the results of the trial as the restenosis rates were equal in all locations (data not shown). There were no group differences in the major types of lesions (A, B1, B2 and C) when characterized by the American College of Cardiology/American Heart Association classification (29).
With respect to the use of relevant drugs at the time of inclusion, we found no statistically significant differences between the two groups, with the exception of statins, which were more frequently used in the placebo group (Table 4). When the latter difference was analyzed in a multivariate logistic model, no influence on the crude effect of Omacor versus placebo on the OR for restenosis was found.
Table 5summarizes the dietary intake of energy and main nutrients at baseline according to a standardized dietary questionnaire in 261 of the patients. As can be seen the patients were on a moderate lipid lowering diet with no clinically important group differences.
When considering serum phospholipid fatty acids and serum lipids before, two weeks after start of therapy, and six months after coronary angioplasty (Table 6), EPA, DHA and total n-3 FA showed significantly increased values in the Omacor group when compared with the placebo group. This difference was present already after two weeks. Linoleic acid, arachidonic acid and total n-6 fatty acids were reduced in the Omacor group. At the same time a considerable and expected reduction in triglycerides was encountered in the Omacor group whereas no group differences were found for total cholesterol or high density lipoprotein cholesterol.
Except for arachidonic acid at two weeks in the placebo group, total cholesterol at six months in both groups and triglycerides at six months in the placebo group, all intragroup differences from baseline were statistically highly significant (p < 0.01).
Table 7shows the restenosis rate per patient in the Omacor group versus the placebo group. As can be seen, no difference in the incidence of restenoses between the two groups (46% vs. 45%) was found. The odds ratio (OR) was 1.05 with a 95% confidence interval (CI) ranging from 0.69 to 1.59 (p = 0.82).
The restenosis rates per treated lesion are also shown in Table 7. We found the number of restenoses to be 108 (40.6%) in the Omacor group and 93 (35.4%) in the placebo group, giving an OR of 1.25 with a 95% CI from 0.87 to 1.80 (p = 0.21). Thus, no difference in the occurrence of restenosis between Omacor and placebo was found as far as number of treated stenoses is concerned.
In Table 8the absolute values of the reference diameter and the MLD of the index arteries before coronary angioplasty, immediately after coronary angioplasty and at follow-up examination are given. In addition, the acute gain and late loss are listed. As can be seen no group differences were found.
Figure 1illustrates, by visualizing the cumulative distribution curves of the MLDs, that no group differences were encountered at any time during the study.
Other than three patients in the Omacor group and two patients in the placebo group with diarrhea or nausea, no obvious adverse effects to the capsules were noted.
Study population: demographics
The present study was a randomized, double-blind, placebo-controlled trial which finally evaluated 388 patients who had undergone successful coronary angioplasty six months earlier. Because of the study design with randomization at least two weeks before the coronary angioplasty and an increasing number of implanted stents, a 20% exclusion rate was calculated. Of the initially randomized 500 patients, 22.4% were excluded before or during the coronary angioplasty procedure. The main reasons were stent implantation (54 patients), lack of angiographic inclusion criterion on reevaluation before the coronary angioplasty (23 patients), or unsuccessful coronary angioplasty according to the study protocol (23 patients). The excluded patients were evenly distributed between the treatment groups. Except for four patients who died, no patient was lost for follow-up procedure. Of the finally evaluable 388 patients, 196 belonged to the n-3 FA treatment group and 192 to the corn oil placebo group.
The study population was representative of patients scheduled for elective coronary angioplasty with a mean age of 60 years, 78% being male, 19% present smokers, 9% diabetics, 34% treated hypertensives and 50% with previous myocardial infarction. Furthermore, more than 95% of the patients had angina pectoris in NYHA class II and III, and the demographic variables were altogether similar to those of the meta-analysis of O’Connor et al. (26)and the recent larger Enoxaparin MaxEPA Prevention of Angioplasty Restenosis (EMPAR) study (3).
The two groups were also similar in demographic values as well as in the use of additional drugs at baseline. The only difference of significance was that statins were used more often in the placebo group. In multivariate analysis, however, this difference did not influence the outcome of the trial with regard to the incidence of restenosis. This finding is also in accordance with two recent placebo-controlled studies, where statins were found to have no effect on the frequency of restenosis after coronary angioplasty (29,33).
Furthermore, the location and characteristics of the treated lesions visualize a typical patient population with severe coronary heart disease admitted for elective coronary angioplasty in Norway.
Restenosis: definition and effect of n-3 FA
Various definitions have been used to define restenosis after coronary angioplasty. The presently used definition with late loss of minimal luminal diameter of at least 20% or 0.7 mm and residual diameter of less than 50% have been generally accepted since the methodological work of Beatt et al. (34). The observed restenosis rates as judged by quantitative coronary angiography of approximately 38% when calculated per stenosis and about 45% per patient are consistent with those of recent literature and very similar to that obtained in the EMPAR study (3). This high incidence of restenosis points to a considerable clinical problem of angina pectoris after initially successful coronary angioplasty, although the proneness to plaque rupture and myocardial infarction is probably small in the cellular process of restenosis with abundant fibrillar collagen (35).
We could not demonstrate any effect on the restenosis rate of supplementation with 5.1 g/day of highly concentrated n-3 FA as compared with placebo. This is not in accordance with the two meta-analyses published when we started our study, where a certain positive effect on restenosis of n-3 FA was demonstrated (26,27). Thus, O’Connor et al. (26)found an OR of 0.71 with a 95% CI of 0.54–0.94 for restenosis when supplementation with n-3 FA was given. In the meta-analysis of Gapinski et al. (27), the positive effect of n-3 FA on restenosis was mainly present in the studies where angiographic evaluation of restenosis was performed and furthermore, positively related to the dosage of n-3 FA given. Thus, supplementation with more than 4 g per day was necessary to obtain a positive effect.
However, the results of two larger prospective randomized placebo-controlled trials on this topic have more lately been published. Thus, Leaf et al. (4)in their study of 447 evaluable patients and Cairns et al. (3)with 653 evaluable patients, did not show any effect of supplementation with 6.9 and 5.4 g/day of n-3 FA from one–two weeks before the coronary angioplasty on the frequency of restenosis after four to six months. Both studies also used corn oil as placebo, and their results are very similar to those of our study with regard to the incidence of restenosis and the lack of effects of supplementation with n-3 FA. Thus, the meta-analyses of seven smaller studies probably do not reflect the true effect of supplementation with n-3 FA on the incidence of restenosis after coronary angioplasty. This also stresses the necessity of performing large controlled trials, and visualizes the discrepancy that may occur between meta-analyses and larger clinical trials as recently highlighted by LeLorier et al. (36).
Bioavailability of n-3 FA
Concerning patient compliance to the study medication, the measurements of fatty acids in the serum phospholipids during the study period are of special value. The significant increase in EPA and DHA as well as in the total n-3 FA of 147%, 14% and 46%, respectively, already at the time of coronary angioplasty confirm an impressive degree of compliance in the actively treated patients as a group. For scientific documentation during supplementation with n-3 FA, such measurements should be advocated. Leaf et al. (4)obtained this compliance measure as well and showed that, whereas the n-3 FA were fully present in the plasma phospholipids after 12 days supplementation, the changes in arachidonic acid, EPA and DHA in the red cell membrane phospholipids were not yet completed. The lack of a positive effect of n-3 FA supplementation in our study may still be due to a to short period of pre-angioplasty supplementation. The study of Bairati et al. (18)in 119 patients showed a positive result when supplementation with 4.5 g/day was introduced three weeks before the coronary angioplasty. However, they did not measure the n-3 FA concentrations.
The total lack of effect of n-3 FA supplementation in the recent three large controlled studies (3,4)including our own, with pretreatment periods of about two weeks, possibly makes it unlikely that the difference in pretreatment time from two to three weeks plays a dominating role, although this possibility cannot be completely ruled out.
n-3 FA supplementation: concentrate versus diet
In the study of Bairati et al. (18)the restenosis rate after coronary angioplasty was further related to the intake of n-3 FA in the ordinary diet as evaluated by a quantitative food frequency questionnaire in 103 of the patients. They found a highly significant relation between the dietary n-3 FA and the frequency of restenosis with daily content of as little as 0.15 g or more (upper tertile) in the diet, giving an OR of only 0.20 for restenosis when compared with patients with a daily intake of less than 0.033 g/day (the lower tertile). This points to the possibility that n-3 FA, when part of the ordinary diet, may induce effects that are not visible after supplementation of n-3 FA in higher concentration. Whether this possibility will ever be scientifically focused in larger clinical trials on restenosis after coronary angioplasty is, however, doubtful.
The present randomized, placebo-controlled study does not support the hypothesis that supplementation with n-3 FA concentrate from two weeks before coronary angioplasty reduces the incidence of restenosis after six months.
We thank Norsk Hydro AS Research Center, Porsgrum, Norway, for performing the fatty acid analyses and the department of Clinical Chemistry, Ullevål University Hospital, Oslo for lipid measurements and for their cooperation.
Study committee members.
Ethics review committee: Jon Dale, MD, PhD, Kjell Midtbø, MD, PhD, Pål Smith, MD, PhD.
Steering committee: Harald Arnesen, MD, PhD, Knut Grønseth, MD, Knud Landmark, MD, PhD, Øyvind Skjæggestad, MD, PhD, Michael Abdelnoor, MPH, PhD.
☆ This study was supported in part by a research grant from Pronova AS Oslo, Norway.
- confidence interval
- Coronary Angioplasty Restenosis Trial
- docosahexaenoic acid
- eicosapentaenoic acid
- Enoxaparin MaxEPA Prevention of Angioplasty Restenosis
- minimal luminal diameter
- New York Heart Association
- odds ratio
- n-3 FA
- omega-3 fatty acids
- Received July 14, 1998.
- Revision received November 10, 1998.
- Accepted January 20, 1999.
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