CARDIOVASCULAR DISEASES

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Cardiovascular Diseases Bulletin

Introduction

The original Protocols for Investment in Health Gain were written in the early 1990s to suggest areas where the introduction, or more widespread use, of certain practices could lead to worthwhile improvements in health for the people of Wales. The documents also highlighted current practices which were of questionable value. This revision has been prepared by reviewing the earlier Protocol for Investment in Health Gain: Cardiovascular Diseases to provide some clear, updated statements with a precise indication of the strength of the evidence and its sources for each statement; and to introduce new statements covering subjects of important current interest.

The statements represent a methodical summary of the evidence in this area found through a formal literature search across a wide range of sources. The evidence has been critically appraised using internationally accepted methods2, compiled into this technical document under the direction of a public health physician, and reviewed by a multidisciplinary team who are directly involved in patient care. In addition to this document, the information will be available electronically, via the NHS Cymruweb (http://cymruweb.wales.nhs.uk/pep) and the Internet (http://www.uwcm.ac.uk/pep). Information on the methodology adopted (including a copy of the documentation), the formats in which the document is issued and details of other publications in the series, are available on request.

The convention used in this document to indicate the type of evidence is:

‘Type I evidence’ - at least one good systematic review and meta-analysis

(including at least one randomised controlled trial).

‘Type II evidence’ - at least one good randomised controlled trial

‘Type III evidence’ - well designed interventional studies without randomisation

‘Type IV evidence’ - well designed observational studies

‘Type V evidence’ - expert opinion; influential reports and studies

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Many health issues do not lend themselves to investigation by randomised controlled trial. By valuing evidence from these trials more highly than observational studies there is a danger that interventions with limited effectiveness might be judged to be more worthy than those based on observation. Similarly, those observational studies which clearly prove effectiveness (and make a randomised trial unethical) might be undervalued. Randomised controlled trials are a valuable form of evidence and, when available, they are included. If not, high quality evidence has been sought within the other categories. Information assigned as Type V evidence may include expert opinion and narrative review of randomised controlled trials for clinical guideline development, important reports or recommendations which should rightly be highly regarded.

The health gain notation (used to indicate the potential benefit to health) is:

(1) ‘beneficial’ - effectiveness clearly demonstrated

(2) ‘likely to be beneficial’ - effectiveness not so firmly established

(3) ‘trade-off between beneficial and adverse effects’ - effects weighed according to individual circumstances

(4) ‘unknown’ - insufficient/inadequate for recommendation

(5 ‘unlikely to be beneficial’ - ineffectiveness is not as clearly demonstrated as for (6)

(6) ‘likely to be ineffective or harmful’ - ineffectiveness or harm clearly demonstrated

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It should be stressed that these gradings, while aiming to be impartial, represent only the best advice of the professionals involved in preparing the Bulletin. Although the statements are deliberately brief, statistically significant quantitative information has been provided where possible. This is usually given as Number Needed to Treat (NNT), Odds Ratio, Relative Risk or Proportional or Absolute % Risk Difference, together with 95% confidence intervals, as per the original source of the information. Issues of cost-effectiveness or cost-benefit are considered where evidence is available.

In keeping with the original Protocols, these revised documents are designed to assist Health Authorities in developing local strategies and in commissioning high quality health care. It is anticipated, however, that they will be of value to all health professionals in keeping abreast of the huge and increasing body of medical literature and can provide an agenda for future action in a wide variety of settings. It should be stressed that the publications will act as a supplement to, not a substitute for, clinical skills and experience. We anticipate that some of the conclusions reached will be controversial. Every effort has been made to include the best evidence within a subject area. Readers who are aware of any important studies that have been overlooked are encouraged to contact the project team4.

 

The Cardiovascular Diseases Health Evidence Bulletin

Diseases of the heart and circulation are the major cause of morbidity and mortality in Wales and the United Kingdom, with coronary heart disease still the single largest cause of death in Wales. The cardiovascular diseases included in this bulletin are coronary heart disease, heart failure, congenital heart disease, stroke and transient ischaemic attack (TIA), peripheral vascular disease and aortic aneurysm, varicose veins, leg ulcers and deep vein thrombosis, and the common arrhythmias.

There is a wealth of literature on the multifactorial and largely preventable risk factors for cardiovascular disease, mainly from large prospective cohort studies. They are reviewed in the chapter on primary prevention which cites some of the main historical studies to illustrate the most important population-based associations and reviews the evidence for the effectiveness of interventions in the primary prevention of cardiovascular disease. Lifestyle factor interventions to reduce cardiovascular risk at the level of the individual are reviewed in the Healthy Living Bulletin.

As in the original Protocol1, coronary heart disease is reviewed in sections of stable and unstable angina, and myocardial infarction. These are defined clinical entities and allow a more thorough assessment of the sub-groups of patients to whom the evidence is applicable, but inevitably some overlap across the sections will occur. Up-dated evidence for the common arrhythmias is reviewed in the most appropriate chapter.

New and increasingly complex diagnostic, therapeutic and technological interventions have generated a wealth of new evidence from randomised controlled trials since the original Protocol1 was published. Much of this new evidence relates to technical details of invasive management of patients. This bulletin focuses on the evidence of effectiveness of established interventions and in comparing new interventions, technologies and therapies to those established in clinical practice. Wherever possible, evidence from systematic reviews and meta-analyses has been cited. Many of these have been undertaken by the Cochrane Collaboration and published in the Cochrane Database of Systematic Reviews or critically appraised in the Database of Reviews of Effectiveness (DARE) in the Cochrane Library. Where a DARE report is available from the current edition of Cochrane Library, this is referenced together with the original journal article.

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Where systematic reviews have not been undertaken, evidence from individual randomised controlled trials has been cited. In the absence of Type I or II evidence, when necessary, well designed and conducted non-randomised trials, observational studies and expert opinion have been cited. The literature searches were complete to 30 September 1998 and The Cochrane Library 1998 Issue 4. With new systematic reviews, meta-analyses and randomised controlled trials published each month, some statements in this bulletin will soon become out of date. It is intended that the electronic version posted on the web will be regularly updated.

The statements made in this bulletin present a graded summary of the best available evidence of effectiveness across the spectrum of cardiovascular disease. The statements are intended to act as signposts to further sources of evidence, not as guidelines for clinical management of patients. To place the evidence in the clinical context, evidence-based clinical guidelines have been cited. It is hoped that this bulletin will facilitate evidence-based practice, which involves "integrating individual clinical expertise with the best available external clinical evidence from systematic research".

Dr David Fone, Team Leader. December 1998.

 

References

  1. Welsh Health Planning Forum.  Protocol for Investment in Health Gain - Cardiovascular Diseases.  Cardiff: Welsh Office NHS Directorate, May 1991.
  2. Barker J, Weightman AL, Lancaster J.  Project for the Enhancement of the Welsh Protocols for Investment in Health Gain: Project Methodology 2.  Cardiff: Duthie Library UWCM, 1997.
  3. See Contributers
  4. Contact: Protocol Enhancement Office, Duthie Library, UWCM, Heath Park, Cardiff, CF4 4XN.
  5. This table is adapted from the Bandolier system (derived from he work at McMaster University, Canada) using the NHS Centre for Reviews and Dissemination criteria for a systematic review.  See p.18 in ref.2 or http://www.jr2.ox.ac.uk/Bandolier/band6/b6-5.html and the Database of Abstracts of Reviews of Effectiveness (DARE) in the Cochrane Library.
  6. This Notation is modified from the tables used in Enkin M, Keirse MJNC, Renfrew M and Neilson J.  A guide to effective care in pregnancy and childbirth.  2nd ed. Oxford: Oxford University Press, 1995 pp. 389-90.
  7. Number Needed to Treat (NNT) = The number of patients to be treated to prevent the outcome of interest.

    Odds Ratio: If equal to 1, the effects of the intervention are no different from contol.   If the OR is greater (or less) than 1, then the effects of the intervention are more (or less) than control.  Note that the effect being measured may be adverse or desirable.

    Relative risk: Defined as the ration of the incidence of the outcome in the exposed or intervention group to the incidence in the control group.  Other comments as per odds ratio.

    95% confidence interval: The range of values within which we can be 95% certain that the true population value lies.
  8. Office for National Statistics.  1996 Mortality Statistics: Cause.  England and Wales.  Series DH2 No. 23.  London:HMSO, 1988.
  9. Healthy Living Health Evidence Bulletin - due for publication early 2000.
  10. Available on CD-ROM and floppy disc from Update Software, PO Box 696, Oxford OX2 7YX.
  11. Sackett DL, Richardson WS, Rosenburg W, Haynes RB.  Evidence- based Medicine.   Edinburgh: Churchill Livingstone, 1997.
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Health Evidence Bulletins: Wales, Duthie Library, UWCM, Cardiff CF14 4XN. e-mail: weightmanal@cardiff.ac.uk