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J Am Coll Cardiol, 1999; 33:909-915 © 1999 by the American College of Cardiology Foundation |
a Departments of Medical Cardiology, Medicine and Pathological Biochemistry and Statistics, University of Glasgow, Royal Infirmary, Glasgow, United Kingdom
Manuscript received April 1, 1998; revised manuscript received September 18, 1998, accepted December 4, 1998.
Reprint requests and correspondence: Dr. Stuart M. Cobbe, Department of Medical Cardiology, Royal Infirmary, 10 Alexandra Parade, Glasgow G31 2ER, United Kingdom.
stuart.cobbe{at}clinmed.gla.ac.uk
| Abstract |
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The purpose of the study was to assess the effect of lipid reduction with pravastatin on hospital admissions in middle-aged men with hypercholesterolemia in the West of Scotland Coronary Prevention Study.
BACKGROUND
A prospective, randomized controlled trial was undertaken in primary care centers in the West of Scotland.
METHODS
A total of 6,595 participants randomized to receive pravastatin 40 mg or placebo daily were followed up for a mean of 4.9 years (range 3.5 to 6.1 years). Analysis of hospital admissions was undertaken according to the "intention to treat" principle both for cardiovascular diseases and noncardiovascular diseases (including malignant neoplasms, psychiatric diagnoses, trauma and other causes). A secondary analysis of hospitalization in patients who were
75% compliant was performed.
RESULTS
During the trial, 2,198 (33%) of the 6,595 men were admitted to hospital on 4,333 occasions, of which 1,234 (28%) were for cardiovascular causes. Pravastatin reduced the number of subjects requiring hospital admission for cardiovascular causes by 21% (95% CI [confidence interval] 9 to 31, p = 0.0008) overall, and by 27% (95% CI 15 to 38) in compliant participants. The number of admissions per 1,000 subject-years for cardiovascular disease was reduced by 10.8 (95% CI 4 to 17.4, p = 0.0013) in all subjects, and by 15.6 (95% CI 8.3 to 23, p < 0.0001) in compliant participants. Pravastatin had no significant influence on hospital admission for any noncardiovascular diagnostic category. There were 13.4 fewer admissions per 1,000 subject-years for all causes in the pravastatin-treated group (95% CI 0.4 to 27.3, p = 0.076). No significant difference in duration of hospital stay was found between the pravastatin and placebo patients in any diagnostic group.
CONCLUSIONS
Pravastatin therapy reduced the burden of hospital admissions for cardiovascular disease, without any adverse effect on noncardiovascular hospitalization.
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| Methods |
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Participants were randomized to receive either pravastatin 40 mg or a placebo each evening. They were followed up every three months for a mean of 4.9 years (range 3.5 to 6.1 years), giving a total of 32,216 subject-years of observation. The dates of any hospital admission and discharge were obtained, with a copy of the hospital discharge summary, which documents the primary and secondary reasons for hospitalization.
Diagnoses were coded according to the International Classification of Diseases 8th Revision (ICD 8) and procedures according to the Office of Population Censuses and Surveys Revision 4 Coding (OPCS 4). In addition to direct reports of hospitalization from the trial participants, the occurrence of hospital admission was verified from central records using the Scottish Record Linkage System (10). We previously validated the accuracy of this system compared with hospital admission data obtained by direct patient enquiry (11). By means of direct contact and record linkage, we were able to obtain details of hospitalization both for subjects remaining in the trial and for those who had withdrawn from trial therapy and follow-up attendance. The study protocol was approved by the local research ethics committees in the West of Scotland.
Statistical methods. The primary analysis of hospital admissions was undertaken according to the "intention to treat" principle. Among cardiovascular causes for hospitalization, we determined separately admissions for atherosclerotic CHD, nonatherosclerotic heart disease, cerebrovascular disease and other vascular disease. Noncardiovascular hospital admissions were analyzed under the trial categories of malignancy (including lymphoma, myeloma and malignant melanoma but excluding minor skin cancers), psychiatric diagnoses, trauma and other causes. An individual may have experienced one or more hospital admissions for diagnoses within a given category, as well as admissions for problems in one or more categories. We also performed a more detailed cause-specific analysis of noncardiovascular hospital admissions based on the ICD 8 body systems classification.
We previously reported the influence of compliance on the reduction in coronary risk in subjects receiving pravastatin (12). A secondary analysis of the hospitalization data was performed for compliant patients, defined as in the previous report as those attending and being issued with trial medication at
75% of potential trial visits.
The intervals from randomization to first hospital admission for both cardiovascular and noncardiovascular categories were compared among treatment groups using the log-rank test and displayed as Kaplan-Meier plots. Comparisons among treatment groups of the proportion of subjects hospitalized were made using chi-square statistics and corresponding confidence intervals (CI) for risk ratios. The comparisons involving number of admissions and total days hospitalized were made using permutation tests. Approximate 95% CI for the differences in rates of these outcomes were calculated from the mean differences ± 1.96 standard error (SE). For those participants who were hospitalized, the duration of stay was compared among the treatment groups using a Wilcoxon rank-sum test.
To compare admission rates with respect to underlying risk of coronary events, participants were categorized according to quartiles of baseline five-year untreated risk of definite CHD death or nonfatal MI. These were calculated using a Cox proportional hazards survival model incorporating smoking, diabetes mellitus, nitrate consumption, angina pectoris, family history of CHD, widowhood, age, diastolic blood pressure and total/HDL (high density lipoprotein) cholesterol ratio, as previously reported (13). The numbers of patients admitted within each quartile for each treatment group were compared using the Fisher exact test. Differences in the effect of pravastatin across the quartiles were tested using a logistic regression model incorporating treatment, risk quartiles and their interactions. Statistical calculations were performed using SAS 6.12 for Windows.
Results are presented (unless otherwise indicated) as numbers of participants, numbers of admissions or total days hospitalized per 1,000 subject-years. The observed number of subjects, admissions or total days hospitalized can be recovered by multiplying the rates presented by the observed duration of follow-up in subject years and dividing by 1,000.
| Results |
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Number of trial subjects hospitalized. During the trial, 2,198 (33%) of the 6,595 men were admitted to hospital on one or more occasions. Cardiovascular disease was the principal cause of admission in 736 individuals. The number of participants (per 1,000) requiring hospitalization according to trial category is listed in Table 1, and the Kaplan-Meier curves for time to first cardiovascular and noncardiovascular admissions are illustrated in Figure 1A and B, respectively. Pravastatin reduced the number of participants requiring hospital admission for CHD by 29% (95% CI 16 to 41, p < 0.0001), and for all cardiovascular causes by 21% (95% CI 9 to 31, p = 0.0008). There was no significant difference between treatment groups in the number of subjects or time to first hospitalization for noncardiovascular causes.
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Number of hospital bed-days. Among participants who were hospitalized, no significant difference was seen in the median duration of hospital admission between those treated with pravastatin and the placebo in any diagnostic category (Table 1). The 736 patients hospitalized for cardiovascular causes occupied a total of 9,306 hospital bed days (median 7, IQR 3 to 13, range 1 to 520), which represented 31% of the 29,851 hospital-days for all causes. Pravastatin treatment reduced the number of hospital bed-days for CHD by 61.4 per 1,000 subject-years (95% CI 25.2 to 97.5, p = 0.001), but there was no influence on the number of bed-days for other cardiovascular diagnoses. The number of bed-days for noncardiovascular causes was reduced by 94 per 1,000 subject-years (95% CI 64.8 to 252.6, p = 0.28) in the pravastatin-treated group. This resulted in a nonsignificant overall reduction in hospital bed usage of 168.7 per 1,000 subject-years (95% CI 18.9 to 356.3, p = 0.086) in the pravastatin-treated group.
Effect of pravastatin therapy in compliant subjects.
For the participants with
75% compliance, there were 11,697 treatment-years of follow-up on 2,452 placebo-treated subjects, and 11,765 treatment-years on 2,450 pravastatin-treated individuals. Pravastatin treatment reduced the risk of compliant participants requiring hospital admission for atherosclerotic CHD by 35% (95% CI 19 to 47, p < 0.0001) and for all cardiovascular causes by 27% (95% CI 15 to 38, p = 0.0001). The number of compliant patients requiring hospital admission, the total number of admissions, the total hospital bed-days and the median length of stay are given in parentheses in Table 1. Compliant participants receiving the placebo had rates of hospitalization for cardiovascular causes that were similar to the total cohort, but had markedly lower rates of admission for malignancy and other noncardiovascular diagnoses. This is likely to be explained by the tendency of participants to discontinue preventive therapy for CHD in the event of diagnosis of an alternative life-threatening illness.
Effect of baseline risk. The number of hospital admissions for cardiovascular and noncardiovascular causes according to quartiles of baseline risk of the primary trial end point (definite CHD death or nonfatal MI) is illustrated in Figure 3. Pravastatin therapy resulted in reductions in cardiovascular hospitalizations in all quartiles of risk, with no evidence of a differential effect of treatment across the quartiles. The risk of noncardiovascular hospital admission also increased progressively from quartile 1 to quartile 4, but there was no trend towards any difference in noncardiovascular events between treatment groups.
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| Discussion |
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Unlike the report of the primary end points of the trial, based on a "time to first event" analysis, the current results permit assessment of the effect of pravastatin on the overall requirement for hospital admissions during the average five-year follow-up of the trial. By including the effects of second and subsequent admissions, the number of hospital admissions for analysis is nearly doubled. The effect of pravastatin in reducing total cardiovascular admissions is not offset by any increase in noncardiovascular hospitalizations. However, in this primary prevention population, the reduction in cardiovascular hospitalizations was diluted by the greater number of noncardiovascular events to the extent that the overall requirement for hospital admission was not significantly reduced, although a favorable trend was seen.
Duration of hospital stay. The results of our analysis differ from those presented by the Scandinavian Simvastatin Survival Study (SSSS) because we found no significant effect of therapy on duration of hospital admission for CHD (16). We also found the distribution of length of hospital stay to be skewed and therefore undertook a nonparametric analysis and expressed the duration of admission as the median (IQR) and range. In contrast, the SSSS investigators reported an "average" duration of hospital stay and used parametric statistics, although they did not report whether their data were normally distributed, nor how they dealt statistically with multiple hospitalizations in the same participant.
The analysis of hospital days takes into account the number of hospital admissions as well as the duration of admission. A powerful beneficial effect was noted in the pravastatin-treated group in respect to cardiovascular diseases. A nonsignificant reduction occurred in total hospital-days for noncardiovascular causes in the pravastatin group, resulting in a total reduction of 168.7 hospital-days per 1,000 subject-years for all diagnoses in the pravastatin-treated group. There is no clear explanation for the reduction in the number of hospitals-days for noncardiovascular causes in the pravastatin group. This analysis is influenced by a small number of patients who had very prolonged hospital admissions (>1 year) and should be viewed with caution. However, this reduction might be attributable to prevention of cardiovascular complications other than myocardial infarction in subjects initially hospitalized for noncardiovascular causes.
Effect of baseline risk. The finding that hospital admissions for cardiovascular causes were reduced by pravastatin therapy across all quartiles of risk is as expected. Our previous report had shown that the proportional effect of pravastatin in reducing risk was similar regardless of the baseline level of risk (13). The observation that the probability of noncardiovascular hospitalization also increased in parallel with the cardiovascular risk may appear surprising at first sight. However, it is explicable on the basis that the subjects in the higher quartiles of cardiovascular risk tended to be older and were more likely to be smokers, thus also increasing their risk of noncardiovascular diseases such as cancer and respiratory disease.
Conclusions. In summary, these results confirm the beneficial effects of pravastatin therapy on reducing health care costs attributable to hospital admission (17). They provide further reassurance that therapy did not produce any adverse effects on noncardiovascular events, particularly on cancers, trauma and psychiatric hospitalizations.
| Appendix |
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Data and Safety Monitoring Committee
Michael F. Oliver, MD (Chairman) (National Heart and Lung Institute, London, United Kingdom), Anthony F. Lever, MD (Dept. of Medicine and Therapeutics, Western Infirmary, Glasgow, United Kingdom), Byron W. Brown, PhD (Stanford University, Stanford, California), John G.G. Ledingham, MD (Nuffield Department of Clinical Medicine, John Radcliffe Hospital, Oxford, United Kingdom), Stuart J. Pocock, PhD (London School of Hygiene & Tropical Medicine, London, United Kingdom), Basil M. Rifkind, MD, PhD (National Institutes of Health, National Heart, Lung & Blood Institute, Bethesda, Maryland).
Cardiovascular Endpoints Committee
Stuart M. Cobbe, MD, Barry D. Vallance, MD (Department of Cardiology, Hairmyres Hospital, East Kilbride, United Kingdom), Peter W. Macfarlane, PhD.
Adverse Events Review Board
A. Ross Lorimer, MD, James H. McKillop, MD, PhD, David Ballantyne, MD (Department of Cardiology, Victoria Infirmary, Glasgow, United Kingdom).
Data Centre Staff
John Norrie, Liz Anderson, David Duncan, Sharon Kean, Audrey Lawrence, June McGrath, Vivette Montgomery, PhD (Robertson Centre for Biostatistics, Glasgow University).
Population Screening
Melvyn Percy (Minerva Medical plc, Glasgow, United Kingdom).
Clinical Coordination, Monitoring and Administration
Elspeth Pomphrey, MD, Andrew Whitehouse, MD, Patricia Cameron, Pamela Parker, Fiona Porteous, Leslie Fletcher, Christine Kilday (Glasgow Royal Infirmary).
Computerized ECG Analysis
David Shoat (deceased), Shahid Latif, Julie Kennedy (Glasgow Royal Infirmary).
Laboratory Operations
Margaret Anne Bell, Robert Birrell (Glasgow Royal Infirmary).
Company Liaison and General Support
Margot Mellies, MD, Joseph Meyer, MD, Wendy Campbell (Bristol-Myers Squibb Company, Princeton, New Jersey).
| Footnotes |
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* A list of members appears in the Appendix. ![]()
| References |
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This article has been cited by other articles:
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M. F Muldoon, S. B Manuck, A. B Mendelsohn, J. R Kaplan, and S. H Belle Cholesterol reduction and non-illness mortality: meta-analysis of randomised clinical trials BMJ, January 6, 2001; 322(7277): 11 - 15. [Abstract] [Full Text] [PDF] |
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Pravastatin Reduces Cardiovascular Admissions Journal Watch (General), April 6, 1999; 1999(406): 6 - 6. [Full Text] |
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