Level 2: Mid-level evidence
Several guidelines and charts are available to estimate cardiovascular (CV) risk, which includes coronary heart disease (CHD) risk and cerebrovascular disease risk. Most of the data and guidelines focus on prevention of CHD because CV risk correlates with CHD risk and CV risk can be estimated by 4/3 CHD risk (e.g., if the CHD risk over five years is 15%, then the five-year CV risk is 20% [4/3 x 15 = 20]. A five-year CHD risk of 6% is roughly equal to a five-year CV risk of 8%.) (BMJ. 2000;320:659-661; full-text available online without charge at bmj.bmjjournals.com/cgi/content/full/320/7236/659. Accessed July 12, 2007). Basing risk-factor reduction treatments on absolute risk is important for strategies that may involve risk and/or cost, including treatment of hypertension, aspirin, or treatment of hyperlipidemia with medications. However, comparing study results and risk predictions can be confusing because of differences in end points. National guidelines developed in many countries differ in methods used for risk prediction and patient selection for preventive measures.
Six national guidelines (from Australia, Canada, the United States, Joint British Societies, and European societies) were evaluated in a modeling study based on 12,300,000 Canadian men and women aged 20-74 years (BMJ. 2006;332:1419; full-text available online without charge at bmj.bmjjournals.com/cgi/content/full/332/7555/1419. Accessed July 12, 2007). The New Zealand guidelines were more efficient (preventing the most deaths with the fewest patients treated) than five other national guidelines for selecting patients for statin therapy based on estimating CV risk. These guidelines would avoid 14,700 deaths while treating only 12.9% of the population. The New Zealand five-year CV-risk prediction charts and instructions for use are available online without charge at bmj.bmjjournals.com/cgi/content/full/320/7236/709 (accessed July 12, 2007).