Effects of Lipid Lowering by Pravastatin on Progression and Regression of Coronary Artery Disease in Symptomatic Men With Normal to Moderately Elevated Serum Cholesterol Levels
The Regression Growth Evaluation Statin Study (REGRESS)
Background Intensive lowering of serum cholesterol may retard progression of coronary atherosclerosis in selected groups of patients. However, few data are available on the potential benefit of serum cholesterol reduction in the broad range of patients with coronary atherosclerosis and normal to moderately elevated serum cholesterol levels who undergo various forms of treatment. The Regression Growth Evaluation Statin Study (REGRESS) addresses this group of patients.
Methods and Results REGRESS is a double-blind, placebo-controlled multicenter study to assess the effects of 2 years of treatment with the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor pravastatin on progression and regression of coronary atherosclerosis in 885 male patients with a serum cholesterol level between 4 and 8 mmol/L (155 and 310 mg/dL) by quantitative coronary arteriography. Primary end points were (1) change in average mean segment diameter per patient and (2) change in average minimum obstruction diameter per patient. Clinical events were also analyzed. Of the 885 patients, 778 (88%) had an evaluable final angiogram. Mean segment diameter decreased 0.10 mm in the placebo group versus 0.06 mm in the pravastatin group (P=.019): The mean difference between treatment groups was 0.04 mm, with a 95% CI of 0.01 to 0.07 mm. The median minimum obstruction diameter decreased 0.09 mm in the placebo group versus 0.03 mm in the pravastatin group (P=.001): The difference of the medians between the treatment groups was 0.06 mm, with a CI of 0.02 to 0.08 mm. At the end of the follow-up period, 89% (CI, 86% to 92%) of the pravastatin patients and 81% (CI, 77% to 85%) of the placebo patients were without new cardiovascular events (P=.002).
Conclusions In symptomatic men with significant coronary atherosclerosis and normal to moderately elevated serum cholesterol, less progression of coronary atherosclerosis and fewer new cardiovascular events were observed in the group of patients treated with pravastatin than in the placebo group.
Several studies have demonstrated that intensive lowering of serum total cholesterol or LDL cholesterol may retard progression of coronary atherosclerosis.1 2 3 4 5 6 7 8 9 10 11 12 13 14 However, most of these studies were either intentionally restricted to selected groups of patients, in particular patients with hypercholesterolemia,1 6 familial atherosclerosis,5 a previous history of coronary artery bypass graft surgery (CABG),3 or myocardial infarction,4 or unintentionally comprised a high proportion of a specific group of patients, such as patients with a previous history of percutaneous transluminal coronary angioplasty (PTCA).11 12 Other studies have used a combination of lipid lowering and lifestyle changes (including exercise programs), which makes it difficult to determine the effect of lipid lowering per se.7 13 Furthermore, only a few studies included patients with serum cholesterol levels <5.5 mmol/L (213 mg/dL), and in almost all studies, patients who underwent PTCA or CABG as primary treatment were excluded.
Little is known about the potential benefit of serum cholesterol reduction in the broader range of patients with coronary atherosclerosis who have normal to moderately elevated serum cholesterol levels and undergo various forms of primary treatment, in particular medical management, PTCA, or CABG. The Regression Growth Evaluation Statin Study (REGRESS) specifically addresses this large group of patients, which represents the majority of patients seen in clinical practice. The effect of lipid reduction by the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor pravastatin was assessed in a randomized study design using quantitative coronary arteriography (QCA) to determine the effect of 2 years of treatment on progression and regression of coronary atherosclerosis. This report focuses on the outcome of the analysis of primary end points and the occurrence of cardiac events.
REGRESS is a double-blind, placebo-controlled, multicenter study to assess the effect of 2 years of treatment with the HMG-CoA reductase inhibitor pravastatin on progression and regression of angiographically documented coronary atherosclerosis in male patients with a serum cholesterol between 4 and 8 mmol/L (155 and 310 mg/dL). The study was conducted under the auspices of the Interuniversity Cardiology Institute of the Netherlands (ICIN), Utrecht, Netherlands. Committees responsible for specific aspects of the study are presented in “Appendix A.”
Eleven hospitals in the Netherlands, 7 university and 4 nonuniversity hospitals, participated in the study. Each participating hospital appointed a center coordinator who was responsible for patient recruitment, conduct of the study, and data collection. The trial was approved by the ethics committees of each of the participating institutions. Written informed consent was obtained from each patient.
All male patients who, from a review of the records at the participating centers, were scheduled to undergo coronary arteriography were considered for entry into the study. The enrollment scheme is shown in Fig 1⇓. The center coordinator reviewed the patient chart to determine suitability on the basis of inclusion and exclusion criteria presented in “Appendix B.” Patients who had clinical evidence of coronary artery disease, had a screening cholesterol value ≥4.0 mmol/L (155 mg/dL) and <8.0 mmol/L (310 mg/dL), and met the other entry criteria were identified and approached by the center coordinator for informed consent. Occasionally a patient was approached before a cholesterol value was known, but in any case, informed consent had to be obtained before the first coronary arteriogram was performed so that special attention could be given to the angiographic procedure.
Potential candidates receiving therapy with lipid-lowering agents or drugs that could significantly affect serum lipid levels had their drugs withdrawn (at least 12 weeks for patients receiving HMG-CoA reductase inhibitors, clofibrate, or their analogues and at least 6 weeks for patients receiving bile acid sequestrants, nicotinic acid, or other prohibited drugs).
Directly after a patient was enrolled in the study, a dietician was consulted and a brochure issued by the Netherlands National Health Program entitled “Advice on Health and Diet” was given to the patient. Dietary advice comprised the following guidelines for percentage energy intake: 10% to 15% derived from protein intake, 30% to 35% derived from lipid intake, and 50% to 55% derived from carbohydrate intake. If a patient appeared to be a potential candidate for inclusion, a fasting blood lipid sample for analysis by the Lipid Reference Laboratory (Erasmus University and University Hospital “Dijkzigt,” Rotterdam, Netherlands) was obtained. Blood samples for determination of serum cholesterol, HDL cholesterol, and triglycerides were drawn after an overnight fast. For patients who had experienced a myocardial infarction, samples had to be obtained at least 8 weeks after the date of infarction. If the total cholesterol value in this qualifying specimen was also between 4.0 and 8.0 mmol/L (155 and 310 mg/dL) and the coronary arteriogram showed at least one lesion that narrowed the lumen diameter by ≥50% (visually assessed), the patient qualified for entry into the study.
All coronary arteriograms performed were first reviewed by the center coordinator and were subsequently sent to the Central Angiographic Core Laboratory at the ICIN, Utrecht, Netherlands, for assessment of quality according to standard guidelines. If the views obtained or the film quality was inadequate, the patient was excluded from the trial.
Baseline determinations of other study variables were made during the dietary stabilization or during the interval between arteriography and receipt of certification of the angiogram. This included a complete history and physical examination, a 12-lead ECG, and a chest radiograph if not on file from the last 6 months.
After certification, the patients were divided into one of three blocks according to the type of primary management elected at the participating center: a PTCA block, a CABG block, and a medical management block. In each block, patients were then randomized to receive pravastatin 40 mg once daily or placebo.
Patients and physicians were blinded to the result of randomization throughout the study.
Treatment and Follow-up
During the period of treatment, the patient was asked to stay on a stable diet, to take the study drug as prescribed, and to refrain from taking medications listed among the exclusion criteria. Patients were urged to report any adverse reaction and all other clinical events to the center coordinator at the hospital at which they were enrolled. The patients were seen regularly by the center coordinator. Smoking behavior was monitored during the trial. Follow-up lipid analyses and safety laboratory tests were performed at months 2, 4, 6, 12, 18, and 24. All lipid laboratory tests were carried out at the Lipid Reference Laboratory. Serum cholesterol, HDL cholesterol, and triglycerides were measured on fasting blood samples by standard techniques at all visits. Total cholesterol was measured with an enzymatic kit (Boehringer Mannheim) and calibrated with a human serum calibrator. HDL cholesterol was measured after precipitation of apolipoprotein B–containing lipoproteins with a 4% tungstate solution and centrifugation,15 and the triglycerides were analyzed enzymatically (Bayer/Technicon) by a technique that included free glycerol.16 LDL cholesterol was calculated according to the Friedewald formula.17
The Lipid Reference Laboratory is an international member of the USA National Cholesterol Reference Method Laboratory Network chaired by the Centers for Disease Control and Prevention (Atlanta, Ga).18 19 Pravastatin 40 mg once daily or placebo was administered at bedtime. Patients whose total cholesterol rose above 8.0 mmol/L (310 mg/dL) on repeated assessments and who did not respond to enhanced dietary effort were to have open-label cholestyramine added to their treatment. Patients whose total cholesterol decreased to <2.0 mmol/L (77 mg/dL) were to have the dose reduced by one half. Matching patients in the other cohort would have parallel changes in their treatment regimen. According to these guidelines, administration of cholestyramine was necessary in one patient (and matching control patient); dose reduction was never indicated.
Compliance was verified by tablet counts at each visit and averaged >90% for all participants. Compliance with the dietary guidelines was monitored regularly by dieticians and scored on standardized forms. Dietary adherence remained good throughout the study. The safety committee reviewed intercurrent events, adverse effects, laboratory results, and other relevant data at regular intervals during the trial. The safety committee, which was entitled to demand unblinded data, saw no reason to do so.
Follow-up coronary arteriography was scheduled for 24 months after the date of randomization and was actually performed after a mean±SD of 24.2±0.92 months. In 8 patients, a second angiogram was performed between 17 and 22 months after randomization because of progressive anginal complaints. These angiographic studies were performed according to the criteria set forth in the protocol, and the angiograms were therefore considered to be the final study angiogram.
Quantitative Coronary Arteriography
Quality assurance of catheterization laboratories and cine films was strictly maintained. Before the start of the study, the catheterization laboratory of each participating center was inspected by an experienced third party. During the first year of the study, this was repeated every 3 months; later, these inspections were carried out whenever a significant change in X-ray equipment was carried out or changes in film quality were noted at the Angiographic Core Laboratory. Among others, the following parameters were checked and corrected if necessary: rotation and skew angle indicators of the gantry, position of the isocenter, pincushion distortion, resolution of the X-ray system, and quality of film development. Only catheters approved for QCA were used.20 The distal tip of the catheter was cut off and sent to the QCA Core Laboratory for measurement and was used as a scaling device in the QCA analysis. Panning of the image had to be avoided as much as possible. The protocol required administration of coronary vasodilators (5 to 10 minutes before coronary arteriography, 5 to 10 mg isosorbide dinitrate was administered sublingually; this was repeated during the procedure if necessary). The exact filming sequence of the initial coronary cinearteriography and the precise rotational and angulational views as well as table height were noted; optimal projections were duplicated precisely at follow-up coronary cinearteriography. Baseline and follow-up coronary arteriograms were analyzed by QCA using the Cardiovascular Measurement System (CMS-MEDIS Medical Imaging Systems). This system uses a high-quality cine-video converter (CAP 35E) that allows a selected cine frame to be projected onto a digital camera through a zoom lens (usually the optical magnification used was ×2.3). The video signal of the magnified region of interest was subsequently digitized at a matrix size of 512×512×8 bits. For calibration, the boundaries of a nontapering part of the catheter were determined automatically over a length of approximately 2 cm. To determine the contours of the vessel, the user only had to indicate the beginning and end of the coronary segment to be analyzed, after which a path line was computed connecting these two points. The contours of the vessel were then computed in multiple iterations by the minimal-cost contour-detection technique. The edge strength of a point was based on the weighted sum of the first and second derivative functions; this edge strength was corrected for the limited resolution of the entire imaging chain, a procedure that is particularly important for the accurate measurement of small vessels. A diameter function was determined in absolute terms (in millimeters) by computing the shortest distances between the left and right contours along the vessel centerline. The reference diameter was defined as previously described.21 Left ventricular ejection fractions of baseline and follow-up angiograms were calculated according to the area-length method after manual contour tracing.
For QCA, the coronary tree was divided into 13 segments, according to the American Heart Association classification, excluding the posterolateral branches (Fig 2⇓).22 Obstructions within these segments were coded and analyzed separately if the diameter narrowing was ≥20% at either baseline or follow-up. As a result, obstruction data were always available in paired format (baseline and follow-up) with at least one of the two severities >20% diameter stenosis. Baseline and follow-up coronary arteriograms of each patient were viewed simultaneously on a double Tagarno projector (Tagarno A/S) by an experienced cardiologist blinded to treatment allocation. Matching segments and obstructions in both coronary arteriograms were carefully selected by use of identical projections. Preferably, end-diastolic frames were selected for QCA; if this was not feasible (for example, because of overlap with other branches), corresponding frames at another point in the cardiac cycle were selected. All QCA analyses were reviewed by a QCA expert and corrected if necessary.
If a segment or lesion was adequately visualized in two (preferably orthogonal) projections and free of significant foreshortening in both views, the average values of all parameters in both projections were calculated. Segments that were opacified solely by collateral circulation (generally distal to total occlusions) were excluded from QCA. In case of a new occlusion, the segment was measured by QCA only at baseline and in case of a recanalization, only at follow-up.
Visual analysis of all films was performed with consensus readings and a 38-segment coding system.23 Bypass grafts were coded according to a modified Coronary Artery Surgery Study (CASS) system.24 The result of visual analysis was considered a secondary end point.
End Points of the Trial
The angiographic end points of this trial were defined before the study was unblinded. The primary end point of the trial was a comparison between the pravastatin and placebo groups for (1) change in average mean segment diameter (MSD) on a per-patient basis and (2) change in average minimum obstruction diameter (MOD) on a by-patient basis. Fig 3⇓ shows a stylized diagram of a vessel indicating areas encompassing MSD and MOD. To calculate average MSD per patient, the MSDs of all qualifying segments were added and divided by the number of contributing segments; segments that were occluded or located distal to an occlusion at either baseline or follow-up were not included because no meaningful MSD value can be calculated for these cases. Calculations for average MOD were done in the same manner, except that obstructions that had progressed to occlusion or occlusions that had recanalized were not excluded (MOD of occlusion equals 0); segments distal to occlusions were also excluded from the MOD analysis, since no meaningful MOD can be calculated for segments distal to an occlusion. Thus, no data were inferred.
In addition, patients were categorized with regard to MOD and clinical events as regressors, stable patients, and progressors according to the following (prespecified) definitions. A progressor is a patient with at least one lesion worsening by ≥0.4 mm (2 times medium term variability)10 or development of a lesion that reduces the lumen diameter by ≥0.4 mm. A regressor is a patient with at least one lesion improving by ≥0.4 mm and no lesions worsening ≥0.4 mm. A stable patient is a patient with no lesions worsening or improving by ≥0.4 mm. Patients with regressing and progressing lesions were considered to be progressors because simultaneous progression and regression reflect an unstable process in coronary atherosclerosis. These definitions have been reviewed previously.10 If a patient had suffered a clinical event, he was considered to be a progressor irrespective of angiographic outcome.
Because PTCA and CABG procedures may influence progression considerably, we excluded in the primary analysis lesions and segments modified or conceivably modified by PTCA or CABG. In patients in whom PTCA was performed, the entire coronary artery in which the PTCA (and guide wire manipulation) was performed was excluded. To determine whether a particular segment was influenced by CABG, the following algorithm was used: If a particular segment in a coronary artery was grafted and no occlusions were present at baseline coronary arteriography, all segments in the same artery were considered to be influenced by the bypass graft. If occlusions were observed, all segments that were filled directly by the native system were considered to be not influenced by the bypass graft.
Clinical Events During the Trial
The following clinical events were analyzed. (1) Myocardial infarction (fatal or nonfatal): To establish a diagnosis of a new myocardial infarction, two of the following three criteria had to be met: characteristic angina ≥30 minutes in duration, new ischemic Q waves or ST-T–wave changes in the ECG, and elevation of serum creatine kinase–MB fraction to ≥3 times the upper limit of normal. (2) Coronary heart disease death (other than known fatal myocardial infarction): no known nonatherosclerotic cause and presence of cardiac symptoms within 72 hours of death. (3) Nonscheduled PTCA or CABG: PTCA and CABG not planned in the original block division of REGRESS (eg, PTCA in the medical management block, CABG in the PTCA block, second PTCA in the PTCA block, etc). (4) Stroke and transient ischemic attack (TIA): motor paralysis, sensory or speech dysfunction, diplopia, or visual disturbance lasting more (stroke) or less (TIA) than 24 hours. (5) Death (all other): acceptable documentation was obtained from hospital records, a death certificate, or autopsy report.
Criteria to include the events in the database were as follows: (1) In subjects who completed the study according to the protocol, all events after randomization until the time of the follow-up coronary arteriography were counted irrespective of whether the patient was on double-blind medication. Events occurring during or within 24 hours after a “block scheduled” PTCA or CABG and the follow-up angiogram were not counted. When a PTCA was performed instead of a scheduled CABG or a CABG instead of a scheduled PTCA, this procedure was not counted as a clinical event. (2) For the subjects in whom an emergency angiogram was performed before the end of the study because of symptoms, events were counted for the full 24-month treatment period, even if the emergency angiogram was considered to be the final study arteriogram. (3) In subjects who discontinued the study prematurely, without a final coronary arteriogram, and for whom no subsequent follow-up information was available, events were counted up until the discontinuation date.
All cardiovascular clinical events were evaluated and identified according to the above guidelines by two physicians for inclusion or exclusion in the clinical events analysis before unblinding took place.
A number of substudies were performed in addition to the angiographic main study. Substudies include B-mode ultrasound studies of the carotid and femoral arteries, ambulatory ECG monitoring, specialized lipid research, and DNA studies. The results of these studies will be reported separately.
Baseline characteristics of the different patient groups were compared and tested for balance with Pearson’s χ2test, Student’s t test, or one-way ANOVA, where appropriate. The effects of treatment on the lipid levels were assessed with mixed-model ANOVA with random patient effects and fixed treatment and time effects. Kaplan-Meier curves were used to estimate time to first coronary event or death, and the treatment groups were compared by the log-rank test and Cox regression model. Finally, the angiographic effect of treatment on MSD was assessed by ANCOVA, with baseline levels as covariates. The effect of treatment on MOD was analyzed with nonparametric methods (Mann-Whitney test, rank ANOVA) because of the extremely skewed distribution of MOD. Therefore, we presented the median MOD and the median change of the MOD to illustrate treatment effects. Differences between hospitals with respect to these effects were investigated by mixed-model ANOVA. A value of P≤.05 was considered to be significant. The spss and bmdp (1L, 2L, 5V) statistical packages were used to perform the calculations.
Study Population, Baseline Characteristics, and Adverse Events
Between December 1989 and December 1991, a total of 1068 patients were initially included and underwent a first coronary arteriography. Of these, 183 patients were not randomized (see Fig 4⇓): 42 patients because of nonqualifying lipid measurements, 4 patients because of other disqualifying laboratory tests, 77 patients because of nonqualifying coronary arteriograms, and 60 patients for a variety of other reasons. In all, 885 patients were randomized: 230 in the PTCA block, 282 in the CABG block, and 373 in the medical management block. In some cases, after randomization by the referring physician, a different primary treatment was chosen than was initially decided on (eg, PTCA instead of CABG). Excluding nonscheduled procedures during follow-up, a total of 221 (112 placebo and 109 pravastatin) patients underwent PTCA, 260 (124 placebo and 136 pravastatin) patients underwent CABG, and 403 (198 placebo and 205 pravastatin) patients received medication only. In total, 107 patients had no pair of matching angiograms, 48 in the placebo group and 59 in the pravastatin group. One patient in the placebo group withdrew his informed consent immediately after randomization and before medication was started. This patient was considered noncompliant. Except for lipid measurements, no data for this patient were available, and consequently this patient was not involved in the analyses. In the placebo group, for 4 patients the baseline angiograms were lost, 28 patients refused a second angiogram without a specific reason, and 8 patients died (1 patient subsequent to a failed, block-scheduled, PTCA). Because of adverse events, 10 placebo patients did not complete the study; the events were cancer (3), endocrine disorders (2), and severe viral infection, back pain, general unwellness, bilateral carotid artery stenosis, and raised hepatic transaminases (each 1 case). In the pravastatin group, for 1 patient the baseline angiogram was lost, 39 patients refused a second angiogram without a specific reason, and 5 patients died. Because of adverse events, 16 patients did not complete the study. The events were cancer (3), skin rash (2), abdominal cramps (2), and bilateral carotid artery stenosis, heart failure, bradycardia at first coronary arteriography, worsening vision, back pain, conjunctivitis, joint complaints, myalgia, and sleep disturbances (each 1 case).
Three patients stopped their study medication but had a follow-up angiogram performed. They were included for the angiographic analysis according to the intention-to-treat principle.
The biographical and baseline data of the study patients according to placebo or pravastatin treatment allocation are listed in Table 1⇓. Overall, the mean age ±SD was 56.2±8.1 years. Approximately half the patients had a history of previous myocardial infarction, and one third to one quarter were hypertensive and were current smokers. By the criterion of a stenosis of ≥50% being considered significant, approximately 60% of the patients had multivessel coronary disease. Panel visual analysis at the Central Core Laboratory revealed that some patients had no lesions with a diameter stenosis of ≥50%; in all these cases, however, there were (multiple) less severe lesions. Patients with <50% diameter stenosis were included in the group with single-vessel disease. The treatment groups were well balanced with respect to baseline characteristics, listed in Table 1⇓, and concomitant medication as shown in Table 2⇓.
Effect of Treatment on Serum Lipid Levels
The serum lipid levels for the two treatment groups at baseline and during the trial are listed in Table 3⇓. Lipid levels in the placebo group did not change markedly during the study. In the pravastatin group, maximum lipid reduction was achieved within 2 months. Total cholesterol and LDL cholesterol and triglycerides were lowered significantly, that is, total cholesterol dropped by 20% during the study period, LDL cholesterol dropped by 29%, and triglycerides dropped by 7%. HDL cholesterol increased significantly, by 10%, during the study period.
The clinical events of the study patients according to treatment allocation are listed in Table 4⇓. Of the 152 clinical events, 140 (92%) were cardiac events, 8 (5%) were of cerebrovascular origin, and 4 (3%) were noncardiovascular events. In the placebo group there were 12 and in the pravastatin group there were 7 nonfatal myocardial infarctions, a reduction of 42% (P=.24). In the placebo group 47 patients and in the pravastatin group 20 patients needed a nonscheduled PTCA (reduction, 57%; P=.004). The incidence of the other clinical events, including the noncardiac events, did not clearly differ between the two treatment groups. In Fig 5⇓, Kaplan-Meier curves are displayed (time to first clinical event) for the pravastatin and the placebo groups. After 2 years of treatment, 89% (95% CI, 86% to 92%) of the patients in the pravastatin group and 81% (CI, 77% to 85%) of the patients in the placebo group were without clinical events (P=.002). This effect in favor of pravastatin did not vary significantly among hospitals (P=.52).
Of the 885 patients enrolled in the trial, a second angiogram was obtained in 778 patients (88%), as shown in Fig 2⇑. For the primary analysis, the angiographic data of 125 patients (56 patients in the placebo group and 69 patients in the pravastatin group) could not be used because all coronary segments of these patients were considered to be influenced by a performed PTCA or CABG (see “End Points of the Trial” section). There were no differences in baseline characteristics between the patients with and those without a second angiogram (Table 5⇓), except for a slightly higher age, a somewhat larger proportion of patients with multivessel disease, and a higher New York Heart Association angina class in the group with a second (not informative) angiogram, which is to be expected. In total, 4209 coronary segments, with a mean±SD of 6.6±3.0 per patient, containing 4340 stenoses, with a mean of 6.8±4.0 per patient, were measured quantitatively and included in the primary analysis.
Primary End Points
Table 6⇓ shows the mean baseline and follow-up values and changes in quantitative estimates of MSD and MOD by treatment group. Baseline MSD and MOD did not differ significantly between the treatment groups. Both groups showed net progression, having smaller MSDs and MODs at follow-up than at baseline. However, in the placebo group, mean MSD decreased 0.10 mm, whereas in the pravastatin group, mean MSD decreased 0.06 mm (P=.019): The mean difference was 0.04 mm, with a 95% CI of 0.01 to 0.07 mm. MOD behaved similarly: In the placebo group, the median MOD decrease was 0.09 mm, whereas the median MOD decrease in the pravastatin group was 0.03 mm (P=.001): The difference of the medians was 0.06 mm, with a 95% CI of 0.02 to 0.08 mm. If new total occlusions were excluded from the MOD analysis (as was done for the MSD analysis), the difference between treatment groups was essentially the same. The treatment effects did not vary significantly among hospitals (P>.22).
Relation Between Baseline Lipid Levels, Change in MOD and MSD, and Occurrence of Clinical Events
In Table 7⇓, the median change of the MOD and the mean change of the MSD are given for patients (in quartiles) treated with placebo or pravastatin with respect to different levels of baseline total cholesterol, HDL cholesterol, LDL cholesterol, and triglycerides. In patients with a baseline LDL cholesterol <3.8 mmol/L (147 mg/dL), the median change of MOD was 0.10 mm in the placebo group and 0.03 mm in the pravastatin group. The effect of pravastatin could therefore be estimated as a reduction in progression of 0.07 mm in 2 years. In patients with a baseline LDL cholesterol between 3.8 and 4.3 mmol/L (147 and 166 mg/dL), the thus-defined pravastatin effect was 0.04 mm; in patients with a baseline LDL cholesterol between 4.3 and 4.8 mmol/L (166 and 186 mg/dL), 0.06 mm; and in patients with baseline LDL cholesterol levels >4.8 mmol/L (186 mg/dL), 0.04 mm. The effect of pravastatin did not differ significantly between the four subgroups with regard to LDL cholesterol levels (P>.38). For the other baseline lipid values, essentially the same results were obtained. With respect to MSD, the pravastatin effect also did not differ between the subgroups with regard to lipid levels.
No interaction could be demonstrated between baseline lipid levels, baseline patient characteristics, and the change in MOD-MSD or the occurrence of clinical events during the study.
Effects of Pravastatin on Change in MOD and MSD With Regard to the Different Randomization Blocks: Medical Management, PTCA, and CABG
The effect of pravastatin therapy on change of median MOD was 0.06 mm less progression for the medical management block, 0.08 mm less progression for the PTCA block, and 0.03 mm less progression for the CABG block. With respect to change of the mean MSD, the effect of pravastatin was 0.05 mm, 0.03 mm, and 0.05 mm less progression for the medical management block, PTCA block, and CABG block, respectively. The effect of pravastatin (restricted to segments not influenced by PTCA or CABG) did not differ significantly between the three randomization blocks (P=.34 for MOD and P=.54 for MSD).
Categorical Approach: Regressing, Stable, and Progressing Patients
Of the 885 randomized patients, 641 had an informative second arteriogram that could be used to determine whether the patient was angiographically a progressor or regressor. There were 323 angiographic progressors (142 pravastatin and 181 placebo patients). Of these patients, 41 (13%) had experienced a clinical event. There were 234 angiographically stable patients (118 pravastatin and 116 placebo patients) and 84 regressors (54 pravastatin and 30 placebo patients). Of these 318 patients, 47 (15%) experienced a clinical event, and thus, these 47 patients were considered (clinical) progressors. Of the remaining 244 patients without an informative second arteriogram, 39 experienced a clinical event, and these patients were also considered to be (clinical) progressors. The remaining 205 patients could not be classified as either progressing or regressing and were therefore excluded from the present analysis. In Table 8⇓, the regressing, stable, and progressing patients are compared with respect to the most relevant baseline characteristics. Progressing patients received pravastatin medication less often (P=.0035) and had somewhat larger baseline MSD and MOD values. No clear relation between other baseline characteristics, including lipid values, and fraction of progressing or regressing patients could be demonstrated (all P>.05).
In this study, pravastatin had a significant beneficial effect on both a priori established end points, that is, MSD and MOD. We elected to use two primary end points, since they reflect different manifestations of progression (or regression) of coronary atherosclerosis and it is conceivable that a drug has a beneficial effect in only one of these aspects. Changes in MSD reflect mainly changes that affect a coronary artery or segment in a diffuse manner, whereas changes in MOD reflect mainly changes in degree of narrowing of atherosclerotic lesions and the development of new lesions.
The differences between the placebo and the pravastatin groups were highly significant but small. However, these data should be interpreted with caution. Changes in average values between baseline and follow-up, even if used on a per-patient basis as was done in REGRESS, are very useful to show differences between groups but do not depict in any detail the changes that occur in individual patients in whom progression is often limited to one or a few segments or lesions. Thus, the effect on single segments or lesions may become “diluted” if average values for the entire coronary arterial tree are used. Furthermore, an interval of 2 years is a relatively short period of time in a chronic disease process like atherosclerosis, which often begins at a relatively young age. Many observational studies have shown that progression of coronary atherosclerosis is a time-related phenomenon.25 On the other hand, changes occurring over a certain period of time cannot simply be extrapolated to longer time intervals, because there are indications that progression, especially of individual lesions, may occur in bouts rather than as a continuous process.26
Although cardiac events did not represent a primary end point, we included cardiac events in this report because of their clinical significance and because they may influence the outcome of the analysis of progression. The latter is particularly true for patients who needed PTCA or CABG during follow-up. It is highly probable that progression in these patients with usually increasing (or at least not improving) symptoms was more pronounced than it was in patients in whom the clinical condition did not call for mechanical intervention (the fact that perhaps plaque instability and not gradual progression is the underlying cause in some of these patients is of secondary importance in this context). However, progression leading to initially nonscheduled interventions is not immediately apparent in the analysis of progression because segments in which PTCA is performed and segments influenced by bypass grafts should be excluded from primary analysis of progression and regression. There are two options to deal with this problem. The first option is to analyze angiograms made before the intervention. This, however, was not feasible in our study because, in many instances, these angiograms were not made according to the standards required for QCA follow-up angiograms. Furthermore, the variable time interval between baseline angiogram and preintervention angiogram would have made a correct interpretation of the findings very difficult. Therefore, we chose the second option, that is, we analyzed events separately for differences between the placebo and the pravastatin groups. Apart from being of direct clinical importance, the markedly lower event rate in the pravastatin group corroborates the angiographic finding of reduced progression.
Comparison With Other Studies
Quantitative comparison of REGRESS with other angiographic progression (or regression) studies is difficult because of the lack of uniformity in study design and interpretation of the angiographic data. An important aspect of study design concerns the administration of vasodilators before or during coronary arteriography. In many studies, vasodilators were not or not always used.1 3 4 5 7 8 10 Recently it has been shown that lowering of serum cholesterol may restore endothelial function and thus reduce vasomotor tone.27 28 If no endothelium-independent vasodilators are given, this could lead to differences in angiographic outcome between treatment groups that are not due solely to differences in progression or regression. Other problems relate to differences between studies in definition of angiographic end points and interpretation or exclusion of certain segments or lesions (eg, bypassed segments, lesions treated by PTCA, and occluded segments). In addition, it has been shown that different QCA systems may behave differently in absolute values. Whether this is also true for changes between baseline and follow-up has yet to be assessed, but the possibility should be considered.
Three angiographic progression trials using an HMG-CoA reductase inhibitor as monotherapy have been reported, namely, the Monitored Atherosclerosis Regression Study (MARS),9 the Canadian Coronary Atherosclerosis Intervention Trial (CCAIT),10 and the Multicentre Anti-Atheroma Study (MAAS).11 The first two studies used lovastatin, and the last study used simvastatin.
In MARS, the primary end point (change in mean percent diameter stenosis assessed by quantitative arteriography) was not statistically different between treatment groups; however, a subdivision showed a significant beneficial effect on stenoses that narrowed the lumen diameter >50%. These results are not entirely comparable with our results because we elected to use absolute diameters. Percentage stenosis may underestimate progression if diffuse luminal narrowing occurs that also reduces the reference diameter. In MARS, mean global change score, used as a secondary end point, showed a significant difference between the treatment groups.9
In CCAIT, the primary end point was change in minimal lumen diameter.10 This criterion is similar to the MOD used in REGRESS; furthermore, the same QCA system was used. In CCAIT, a mean difference between treatment groups of 0.04 mm in minimal lumen diameter was noted, which is on the same order as the difference of 0.06 mm in median MOD found in REGRESS and was also statistically significant. In MAAS, two arteriographic end points were used that were almost identical to the end points used in REGRESS; in a period of 4 years, the treatment effects were 0.06 and 0.08 mm for mean and minimum lumen diameter, respectively.11 All three studies (MARS, CCAIT, and MAAS) showed some reduction of cardiac events; in contrast to REGRESS, however, this did not reach statistical significance in any of these studies. The lack of statistical significance could be due to the smaller number of patients compared with REGRESS; however, the relative differences between placebo and treatment groups were also smaller. In the Pravastatin Limitation of Atherosclerosis in the Coronary Arteries (PLAC I) study (which has not yet been reported in extenso), a total of 408 patients was sufficient to show a statistically significant reduction in clinical events in favor of the pravastatin group.12 A significant reduction in the incidence of clinical events by pravastatin was also demonstrated in the Pravastatin Multinational Study.29 Apart from sample size, patient selection appears to be an important determinant in the occurrence of clinical events and the magnitude of the effect of therapy. In the relatively high-risk population of the Familial Atherosclerosis Treatment Study (FATS), a statistically significant reduction of clinical events was achieved by treatment with colestipol in combination with lovastatin or niacin in a series of only 146 patients.5 On the basis of presently available data, it is impossible to determine whether drug-specific factors play a role in the reduction of clinical events. In REGRESS, the effect on clinical events occurred earlier than would be expected on the basis of retardation of progression. We therefore hypothesize that factors other than cholesterol lowering may be involved, such as a direct effect on plaque structure and a direct or indirect effect on (fluctuations in) vascular tone.27 28 30 This aspect merits further investigation.
Limitations of the Study
In REGRESS, only men were included. We fully recognize the importance of obtaining data in women; however, it appeared practically impossible to include, in a reasonable period of time, a number of women high enough to be expected to show statistically significant differences between treatment groups for women only. The CCAIT study and MARS both included women and showed no marked differences between men and women; however, the numbers of women were too small to allow a meaningful separate statistical evaluation for the latter category.9 10 Even in the Scandinavian Simvastatin Survival Study (4S), which included 4444 patients, the number of women was apparently not high enough to show a beneficial effect on the primary end point (total mortality) in this group, although there was a significant reduction of major coronary events.31 Nevertheless, at present we would probably include women if we designed a similar trial.
REGRESS was designed to include medical management patients, PTCA patients, and CABG patients. This design was elected because PTCA and CABG represent therapeutic modalities that have become an integral part in the treatment of patients with coronary artery disease. Excluding these patients would have introduced a serious selection bias. However, their inclusion resulted in the problem that the angiographic data of 125 patients who underwent PTCA or CABG appeared unsuitable for analysis of the primary end points, because all available segments were influenced by the intervention. This appears to be an unavoidable problem. Because of the required study length in almost every angiographic intervention trial, there are scheduled and nonscheduled PTCA and CABG procedures that may influence the progression pattern. This problem can be solved in part only by comparing baseline characteristics of patients with suitable versus unsuitable angiograms, separate analysis of the segments influenced by mechanical intervention, and counting nonscheduled procedures as events. In REGRESS, the only differences in baseline characteristics concerned age and New York Heart Association functional class, which corroborates the supposition that exclusion of the 125 patients did not influence the outcome of the study significantly.
The retardation of progression and reduction of cardiac events that could be achieved by cholesterol reduction in a wide range of patients with normal to moderately elevated serum cholesterol levels raises the question whether cholesterol lowering should be an integral part in the management of patients with coronary atherosclerosis, regardless of initial serum cholesterol level. The present study and recently reported other studies justify at least serious consideration of this option. However, for several reasons, administration of lipid-lowering drugs on such a large scale may not be achievable, and therefore, future studies should be directed toward identifying patients who will benefit most.
Another question concerns the significance of the type of intervention by which cholesterol lowering is achieved. Apart from pravastatin and other HMG-CoA reductase inhibitors, diet (with or without reduction of other risk factors) and a variety of cholesterol-lowering drugs have been shown to have a beneficial effect on progression of coronary atherosclerosis.3 7 8 13 Most of these studies included selected groups of patients (eg, postinfarction patients, patients who had had bypass surgery) or used different angiographic end points and therefore, like the studies mentioned earlier, are difficult to compare with REGRESS. A risk factor reduction study that used angiographic methods and criteria that are very similar to those used in REGRESS is the Stanford Coronary Risk Intervention Project (SCRIP).13 In the risk reduction group of SCRIP, total cholesterol was lowered intentionally by diet and exercise from 6.03 mmol/L (233 mg/dL) to 5.03 mmol/L (195 mg/dL) (16.4% reduction), and per year there was 0.021 mm less decrease of minimal diameter than in the usual-care group. There were also fewer cardiac events in the risk reduction group than in the usual-care group (25 versus 44). However, this may not be interpreted as a beneficial effect of simple risk reduction because at the end of the study, 90% of the patients in the risk reduction group and 23% of the patients in the usual-care group used lipid-lowering drugs. It seems that the gain by a combination of measures was not greater than may be achieved by cholesterol lowering only.
In symptomatic men with significant coronary atherosclerosis and normal to moderately raised serum cholesterol, in the group of patients treated with pravastatin, less progression of coronary atherosclerosis and fewer new cardiovascular events were observed than in the placebo group. Pravastatin therapy was well tolerated. Further studies are required to determine the efficacy in women and to identify patients who will benefit most.
University Hospitals of Amsterdam (Free University and Academic Medical Center), Groningen, Leiden, Maastricht, Nijmegen, Utrecht. Nonuniversity hospitals: St Antonius, Nieuwegein; Medisch Centrum, Alkmaar; Medisch Spectrum, Enschede; and Reinier de Graaf Gasthuis, Delft.
Committees (per December 31, 1993)
Executive Committee. A.V.G. Bruschke, MD (principal investigator); K.I. Lie, MD (principal investigator); J.W. Jukema, MD (project manager); A.J. van Boven, MD; A.H. Zwinderman, PhD; F.M. van Rappard, PhD.
Steering Committee. A.V.G. Bruschke, MD (Leiden); K.I. Lie, MD (Groningen); J.W. Jukema, MD (Leiden); M. Bootsma, MD (Leiden); A.J. van Boven, MD (Groningen); E. de Groot, MD (Utrecht); M. Galjee, MD (AZVU, Amsterdam); J.A. Henneman, MD (Alkmaar); R.J.G. Peters, MD (AMC, Amsterdam); A.G.H. Kessels, PhD (Maastricht); A. Backx, MD (Nijmegen); E.G. Mast, MD (Nieuwegein); G.T. Meester, MD (Utrecht); G.P. Molhoek, MD (Enschede); J.H.C. Reiber, PhD (Leiden); R. Rienks, MD (Utrecht); F. Vermeer, MD (Maastricht); A.J.A.M. Withagen, MD (Delft); I. Hoogendam, MD (Bristol-Myers Squibb BV, Netherlands); ex officio: R. Belder, MD (Bristol-Myers Squibb Inc, Princeton, NJ); M. McGovern, MD (Bristol-Myers Squibb Inc, Princeton, NJ); R.L. Kirkeeide, MD (Houston, Tex).
Policy Advisory Board. H.J.J. Wellens, MD, chairman (Maastricht); J.C. Birkenhäger, MD (Rotterdam); M.R. Hayden, MD (Vancouver, BC, Canada); W.B. Kannel, MD (Boston, Mass); S.B. Knoebel, MD (Indianapolis, Ind); F. Sturmans, PhD (Maastricht); ex officio: M. McGovern, MD (Princeton, NJ); R.L. Kirkeeide, MD (Houston, Tex).
Safety Committee. E.L. Noach, MD (Leiderdorp); P.J. Hoedemaeker, MD (Leiden); A.E. Meinders, MD (Leiden); ex officio: A.V.G. Bruschke, MD (Leiden); K.I. Lie, MD (Groningen); G.T. Meester, MD (Utrecht).
Data Management Committee. G.T. Meester, MD, chairman (Utrecht); J.W. Jukema, MD (Leiden); W.A. Dijk, MSc (Groningen); N. Fineberg, MD (Indianapolis, Ind); A.G.H. Kessels, PhD (Maastricht); ex officio: B. Rodda, PhD (Princeton, NJ).
Angiography Committee. A.V.G. Bruschke, MD, chairman (Leiden); J.H.C. Reiber, PhD (Leiden); E.T. Bal, MD (Nieuwegein); F. Bär, MD (Maastricht).
Clinical Chemical Committee. H. Jansen, PhD, chairman (Rotterdam); G.J.M. Boerma, PhD (Rotterdam); J.J. van Doormaal, MD (Groningen); J.J.P. Kastelein, MD (Amsterdam); A. van der Laarse, MD (Leiden).
Technical Committee. N. Bom, chairman, PhD (Rotterdam); R.G.A. Ackerstaff, PhD (Nieuwegein); W.A.E.M. Aengevaeren, MD (Nijmegen); E.G. Mast, MD (Nieuwegein); R. Rienks, MD (Utrecht); F.W.A. Verheugt, MD (Amsterdam); J.W. Viersma, MD (Groningen).
Inclusion and Exclusion Criteria in the REGRESS Trial
1. Male patients <70 years old undergoing coronary cinearteriography to assess anginal complaints.
2. A qualifying baseline lipid and lipoprotein measurement by the Lipid Reference Laboratories, with a total cholesterol level between 4.0 and 8.0 mmol/L (155 and 310 mg/dL) after about 4 weeks or more of dietary advice. If the patient has incurred a myocardial infarction, approximately 8 weeks must elapse before the qualifying cholesterol level is measured. Patients undergoing CABG or PTCA procedure must have qualifying cholesterol before procedure or while on stable therapy of antianginal drugs.
3. At least one coronary stenosis ≥50% (visually assessed) in a major coronary artery. Cineangiograms must be certified by the Center Coordinator and one other qualified cardiologist to ensure that the film is of a quality that permits computerized quantitative analysis (QCA). The fact that the film has been certified will be recorded on the Case Report Form.
1. Age ≥70 years at entry at the initial coronary cinearteriography.
2. Inability or unwillingness to consent to and undergo a repeat coronary cinearteriography. Noncompliance with recommended treatment. Enrollment in another study protocol that includes a coronary cineangiogram and experimental drug therapy.
3. Fasting cholesterol <4.0 mmol/L (155 mg/dL) or ≥8.00 mmol/L (310 mg/dL), or triglycerides ≥4.0 mmol/L (354 mg/dL) as determined by the CORE lipid laboratory.
4. Life-threatening illnesses other than coronary artery disease in which life expectancy is less than the study duration, or one of the following conditions: (a) malignancy; (b) cardiac valve disease requiring valve replacement; (c) cardiomyopathy; (d) previous CABG; (e) previous PTCA within 1 year before randomization; (f) cardiac pacemaker implant; (g) clinical congestive heart failure after medical management, requiring diuretics (ejection fraction <0.3 if performed); (h) complete A-V block; (i) complete left bundle branch block; (j) Wolff-Parkinson-White syndrome.
5. Use of lipid-lowering drugs ≤6 weeks before qualifying lipid measurement (≤12 weeks for fibrates or HMG-CoA reductase inhibitor). History of poor response to other HMG-CoA reductase inhibitor (<15% decrease in total cholesterol at usual dose).
6. Immune disorder (systemic lupus, dysproteinemia, or major hypersensitivity or allergic disorders) or use of immunosuppressive therapy or corticosteroids.
7. Significant metabolic disease: (a) renal disease: nephrotic syndrome, decreased renal function with serum creatinine ≥150 μmol/L (2.5 mg/dL); (b) hepatobiliary disease with ASAT or ALAT >1.5×normal upper limit; (c) chronic or recurrent pancreatitis; (d) severe overweight (Quetelet index >30 kg/m2); (e) muscle disorders; (f) oral or insulin-dependent diabetes mellitus, uncorrected hypothyroidism or hyperthyroidism (a euthyroid patient on stable replacement of thyroid hormone is acceptable); (g) treatment with chronic corticosteroids or androgens; (h) porphyria.
8. Significant gastrointestinal disease or surgery that might interfere with drug absorption.
9. Excess ethanol consumption (>3 drinks/d) (1 drink=45 g of 40% liquor or equivalent).
The REGRESS study was sponsored by Bristol-Myers Squibb Co, Princeton, NJ.
- Received January 11, 1995.
- Accepted February 7, 1995.
- Copyright © 1995 by American Heart Association
Brensike JF, Levy RI, Kelsey SF, Passamani ER, Richardson JM, Loh IK, Stone NJ, Aldrich RF, Battaglini JW, Moriarty DJ, Fisher MR, Friedman L, Friedewald W, Detre KM, Epstein SE. Effects of therapy with cholestyramine on progression of coronary arteriosclerosis: results of the NHLBI type II coronary intervention study. Circulation. 1984;69:313-324.
Buchwald H, Varco RL, Matts JP, Long JM, Fitch LL, Campbell GS, Pearce MB, Yellin AE, Edmiston WA, Smink RD Jr, Sawin HS Jr, Campos CT, Hansen BJ, Tuna N, Karnegis JN, Sanmarco ME, Amplatz K, Castaneda-Zuniga WR, Hunter DW, Bissett JK, Weber FJ, Stevenson JW, Leon AS, Chalmers TC, and the POSCH Group. Effect of partial ileal bypass surgery on mortality and morbidity from coronary heart disease in patients with hypercholesterolemia. N Engl J Med. 1990;323:946-955.
Schuler G, Hambrecth R, Schlierf G, Niebauer J, Hauer K, Neumann J, Hoberg E, Drinkmann A, Bacher F, Grunze M, Kübler W. Regular physical exercise and low-fat diet: effects on progression of coronary artery disease. Circulation. 1992;86:1-11.
Blankenhorn DH, Azen SP, Kramsch DM, Mack WJ, Cashin-Hemphill L, Hodis HN, DeBoer LWV, Mahrer PR, Masteller MJ, Vailas LI, Alaupovic P, Hirsch LJ, and the MARS Research Group. The Monitored Atherosclerosis Regression Study (MARS): coronary angiographic changes with lovastatin therapy. Ann Intern Med. 1993;119:969-976.
Waters D, Higginson L, Gladstone P, Kimball B, Le May M, Buccuzzi SJ, Lespérance J, the CCAIT Study Group. Effect of monotherapy with an HMG-CoA reductase inhibitor on the progression of coronary atherosclerosis as assessed by serial quantitative arteriography: the Canadian Coronary Atherosclerosis Intervention Trial. Circulation. 1994;89:959-968.
Pitt B, Ellis SG, Mancini GBJ, Rosman HS, McGovern ME, for the PLAC I investigators. Design and recruitment in the United States of a multicenter quantitative angiographic trial of pravastatin to limit atherosclerosis in the coronary arteries (PLAC I). Am J Cardiol. 1993;72:31-35.
Haskell WL, Alderman EL, Fair JM, Maron JD, Mackey SF, Superko HR, Williams PT, Johnstone IM, Champagne MA, Krauss RM, Farquhar JW. Effects of intensive multiple risk factor reduction on coronary atherosclerosis and clinical cardiac events in men and women with coronary artery disease: the Stanford Coronary Risk Intervention Project (SCRIP). Circulation. 1994;89:975-990.
Warnick GR, Nguyen P, Albers JJ. Comparison of improved precipitation methods for quantitation of the high density lipoprotein cholesterol. Clin Chem. 1985;31:217-224.
Bucolo G, David H. Quantitative determination of serum triglycerides by use of enzymes. Clin Chem. 1973;19:475-482.
Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18:499-502.
Boerma GJM, Jansen AP, Jansen RTP, Leijense B, van Strik R. Minimizing interlaboratory variation in routine assay of serum cholesterol through the use of serum calibrators. Clin Chem. 1986;32:943-947.
Reiber JHC, van der Zwet PMJ, von Land CD, Koning G, van Meurs B, Buis B, van Voorthuisen AE. Quantitative coronary arteriography: equipment and technical requirements. In: Reiber JHC, Serruys PW, eds. Advances in Quantitative Coronary Arteriography. Dordrecht, Netherlands: Kluwer Academic Publishers; 1992:75-111.
Austen WG, Edwards JE, Frye RL, Gensini GG, Gott VL, Griffith LSC, McGoon DC, Murphy ML, Roe BB. A reporting system on patients evaluated for coronary artery disease: report of the Ad Hoc Committee for Grading of Coronary Artery Disease, Council on Cardiovascular Surgery, American Heart Association. Circulation. 1975;51:6-34.
James TN, Bruschke AVG, Böthig S, Dodu SRA, Gil JF, Kawamura K, Paulin SJ, Piessens J. Report of WHO/ISFC Task Force on Nomenclature of Coronary Arteriograms. Circulation. 1986;74:451A-455A.
Coronary Artery Surgery Study (CASS). A randomized trial of coronary artery bypass surgery: survival data. Circulation. 1983;68:939-950.
Bruschke AVG, Buis B. Progression of coronary artery disease. Curr Opin Cardiol. 1987;2:996-1001.
Harrison DG, Armstrong ML, Freimann PC, Heistad DD. Restoration of endothelium-dependent arterial relaxation by dietary treatment of atherosclerosis. Circulation. 1987;80:1808-1811.
Vita JA, Treasure CB, Nabel EG, McLenachan JM, Fish RD, Yeung AC, Vekshtein VI, Selwyn AP, Ganz P. Coronary vasomotor response to acetylcholine relates to risk factors for coronary artery disease. Circulation. 1990;81:491-497.
Fuster V, Badimon JJ, Badimon L. Clinical-pathologic correlations of coronary disease progression and regression. Circulation. 1992;86(suppl III):III-1-III-11.