SIGN guideline on cardiovascular disease aims to target resources towards risk group that will benefit most, says Dr Alan Begg

Having a shortage of clinical guidelines to follow is not something that is regularly complained about by GPs. One grievance that is voiced, however, is that inconsistencies can arise between guidelines on the same clinical topic, confusing the GP, who is struggling to meet the increasing demands of his or her patients. When a new guideline is published, what GPs want to know is:

  • what's new?
  • how does it differ from current guidance?
  • is a change in clinical practice required?
  • are other guidelines due to be published in the near future likely to endorse any suggested change?

To be credible, a guideline should be developed from the clinical evidence to a clearly defined and consistent methodology that has been tried and tested, is free of commercial influence, and clearly states where cost effectiveness matters have been taken into account. This is certainly the case with the Scottish Intercollegiate Guidelines Network (SIGN) national clinical guideline on Risk estimation and the prevention of cardiovascular disease, published on 6 February 2007.1

Risk assessment in CVD

Awareness of how much a patient may be at risk of developing the disease, especially in those without pre-existing cardiovascular disease (CVD), is essential for effective management and to ensure the maximum benefit from preventative drug treatment.

The SIGN guideline accepts the Joint British Societies' (JBS2) threshold for a first event (CVD risk ?20% over 10 years) as the level at which individuals should be considered high risk.2 The Framingham function, based on a selected American cohort, tends to underestimate the risk in populations with lower socioeconomic status, who tend to have higher rates of CVD.

The ASSIGN (ASsessing cardiovascular risk using SIGN guidelines to assess preventative treatment) score has been developed to take deprivation and family history (a history of proven CVD in a first-degree relative before the age of 60 years) into account. In doing so, it identifies the highest risk patients, who have most to gain and who can be targeted using the limited resources available.1

Pharmacological treatment

The calculated risk threshold is important in deciding whether patients without CVD should be treated with aspirin or a statin. Overall, it was felt that treatment with low-dose aspirin was associated with a reduction in the relative risk of cardiovascular events in both men and women. If the BP is <150/90 mmHg, then, using the ?20% threshold, the benefit of administering aspirin outweighs the risk of a major bleeding event, including cerebral haemorrhage.

All those over 40 years of age who are at a ?20% level of risk should be considered for treatment with simvastatin 40 mg/day,on the basis that the likelihood of a major coronary event occurring will be reduced by standard doses of statin therapy. This is a cost-effective approach, in line with NICE guidance on initiating statin therapy with a drug that has a low acquisition cost.3 In patients with established symptomatic CVD, an approach using more intensive statin therapy would, however, be more appropriate.

Lipid and cholesterol lowering

As yet, no clinical trials have evaluated the relative and absolute benefits of cholesterol lowering to different targets in relation to clinical events,2,4 so SIGN was unable to recommend specific targets for lipid lowering. This leaves uncertainty as to whether GPs should be aiming for the low targets advocated by JBS2.2

A meta-analysis of cholesterol-lowering trials has concluded that there is an approximately linear relationship between the absolute reductions in low density lipoprotein cholesterol achieved in the major statin trials, and the proportional reductions in cardiovascular events.5 However, the JBS2 guideline does point out that setting targets in guidelines is often a matter of judgement, based on the total CVD risk of the patients being considered for treatment.

Until the position is clearer, any change to the current cholesterol QOF target for CHD, stroke/transient ischaemic attack, or diabetes of 5 mmol/l is likely to remain unchanged.5 In day to day clinical practice, primary care teams are finding that in order to meet this level consistently, they have to aim for and achieve a lower target.

Hitting blood pressure targets

Achieving lower blood pressure levels can be difficult. The SIGN guideline gives an A-grade recommendation to lower levels (>140 mmHg systolic and/or >90 mmHg diastolic) for the initiation of blood pressure-lowering therapy in CVD patients without other target organ damage, than the levels presently specified in the QOF standards. The threshold is even lower (>130 mmHg systolic and/or >80 mmHg diastolic) if there is other target organ damage. This is important for GPs, who should not be satisfied with having met their QOF target in these high-risk patients but, rather, they should follow the SIGN guidance.

Cost assessment

Published in conjunction with the guideline is a resource impact assessment, which gives figures for the likely cost of increased statin prescribing that would result from lowering the risk threshold.7 Importantly for GPs, the additional unit costs to the practice of carrying out a full risk assessment and of managing these patients are also included—resources that are important if primary risk prevention is to have any impact on reducing first CVD events.

Conclusion

Two important NICE guidelines, MI: secondary prevention in primary and secondary care for patients following a myocardial infarction, and Cardiovascular risk assessment: the modification of blood lipids for the primary and secondary prevention of cardiovascular disease are due to be published this year, although this month's planned publication of the former has now been postponed until the end of the year.8 In view of the available evidence, their recommendations are unlikely to contradict those put forward by SIGN, and increased activity for primary care teams is inevitable.

  1. Scottish Intercollegiate Guidelines Network. Risk estimation and the prevention of cardiovascular disease (SIGN 97). A national clinical guideline. Edinburgh: SIGN, 2007.
  2. JBS 2: Joint British Societies' guidelines on prevention of cardiovascular disease in clinical practice. Heart 2005; 91 (suppl 5): v1–52.
  3. National Institute for Health and Care Excellence. Statins for the prevention of cardiovascular events. Technology appraisal 94. London: NICE, 2006.
  4. Hayward R, Hofer T, Vijan S. Narrative review: lack of evidence for recommended low-density lipoprotein treatment targets: a solvable problem. Ann Intern Med 2006; 145 (7): 520–530.
  5. Baigent C, Keech A, Kearney P, Cholesterol Treatment Trialists' (CTT) Collaborators et al. Efficacy and safety of cholesterol-lowering treatment: prospective meta-analysis of data from 90,056 participants in 14 randomised trials of statins. Lancet 2005; 366 (9493): 1267–1278.
  6. British Medical Association. Revisions to the GMS Contract, 2006/07. Delivering Investment in General Practice. London: BMA, 2006.
  7. Scottish Intercollegiate Guidelines Network. Management of Coronary Heart Disease. A national clinical and resource impact assessment. Edinburgh: SIGN, 2007.
  8. www.nice.org.ukG