Cardiovascular diseases (CVD) are currently the leading cause of death worldwide, and a major cause of disability. CVD, including supervision of risk factors with respect to prevention, have in recent decades become an increasingly important topic for general practice. These issues have also become prominent in public debate and health care policy. Specific strategies of individual prevention are to a large extent, at least in the Western world, in the hands of the general practitioners (GPs). In recent years, there has been much emphasis on clinical practice guidelines to aid GPs in their preventive work and guide them to the most cost-effective management. This refers both to recommendations on therapeutic options as well as methods to identify those who would benefit the most from preventive treatment. These guidelines can provide important and updated information for clinicians and function as an instrument for quality improvement and potentially also performance assessment in clinical practice. However, various studies have shown that GPs only follow the guidelines to a certain extent, and that recommended treatment goals are often not reached. Some authors have explained this in terms of physicians' inadequacy, whilst others have pointed out that at least part of the explanation is likely to lie in the nature of the guidelines as such. The quality and usefulness of clinical guidelines for prevention of CVD are of great importance to many, both on the level of individual health care and from the perspective of resource allocation.
The objective of this project was to study and discuss the validity and relevance of international CVD prevention guidelines for general practice. More specifically:
- To document the CVD risk profile of a general population as defined by selected, authoritative preventive clinical guidelines, by means of modelling studies.
- To estimate the workload associated with following the recommendations of the selected guidelines for a well-defined general population in whole.
- To identify potential causes of guidelines' overestimation of risk, focusing on individual risk factors.
Material and methods
This dissertation is based on analyses of data from the Norwegian HUNT 2 population survey, including roughly 65 000 participants. Two studies were conducted to document the CVD risk profile of this general population and to model the implications of implementing current clinical guidelines, regarding the proportion of the population identified at “increased risk”, and the clinical workload associated with following the guideline recommendations. Subsequently, two studies were conducted to analyse whether potential causes of guidelines' overestimation of CVD risk might stem from the way two individual risk factors, cholesterol and obesity, are handled in the guidelines. The dissertation further includes analysis and identification of additional factors potentially limiting the validity and relevance of preventive CVD guidelines.
If authoritative guideline recommendations for CVD prevention are literally applied, a vast majority of adults in Norway would exhibit “unfavourable” CVD risk profiles and thus be considered in need of individual, clinical attention and follow-up. The potential workload associated with implementing current European clinical guidelines could destabilise the healthcare system in Norway, one of the world's most long- and healthyliving nations, by international comparison.
Total cholesterol was not found to be as predictive of mortality as generally assumed. Thus, possible errors regarding the role of total cholesterol in the CVD risk algorithms of many clinical guidelines were identified. If our findings are generalisable, clinical and public health recommendations regarding the “dangers” of cholesterol should be revised.
Body mass index, the most widely recommended measure of obesity in preventive CVD guidelines, was found to be inferior to waist-to-hip ratio (WHR), waist-to-height ratio (WHtR), and waist circumference in relation to predicting mortality. WHR and WHtR exhibited the best predictive properties. It appears reasonable to recommend WHR as the primary clinical measure of body composition and obesity for preventive purposes.
There currently appears to be a range of factors limiting the validity and relevance of clinical practice guidelines on prevention of CVD, at least in Norway. Such limitations may have important effects on clinical practice and resource allocation, as well as population health. The guidelines appear to overestimate CVD risk and fail to correctly identify a manageable proportion of the population as “high-risk individuals”, for whom individual preventive strategies would be effective and beneficial. The strategy of targeting individuals at risk ends up being recommended at the level of mass strategy, which can hardly be regarded as sustainable or responsible. A number of factors potentially limiting the validity and relevance of current guidelines were identified. The dissertation includes a proposal of ways to improve the guidelines.