Cardiovascular disease (CVD), largely heart disease and stroke, accounts for almost half of all NCD-related deaths and is now the leading cause of death in low- and middle-income countries (LMIC). Nearly 58% of CVD deaths in LMICs are in those aged less than 60 compared with just 20% in high-income countries (HICs) [1, 2].
A reduction of CVD morbidity and premature mortality has been achieved through a combination of three strategies: population-level risk factor reduction strategies; individual-based primary prevention strategies targeted at high-risk groups to prevent the onset of CVD through risk factor reduction; and secondary prevention and treatment to prevent disease progression in people with established CVD . Research from several countries has consistently shown that treatments of established CVD explain less of the decline than reductions in risk factors to prevent development of cardiovascular disease. Between 42% and 60% of the decline in CVD deaths has been attributed to changes in risk factors including reduction in total cholesterol, systolic blood pressure and smoking prevalence, while 23% to 47% was attributed to treatments including secondary preventive therapies [4–9].
Individual-based primary prevention strategies can involve two approaches. First is the ‘vertical’ approach that involves management of each of the single risk factors such as hypertension or hypercholesterolemia according to pre-defined thresholds for treatment initiation irrespective of the presence or absence or levels of concomitant risk factors. The second approach calls for treatment decisions based on assessment of an individual’s “total’’ predicted risk of developing a cardiovascular event - such as myocardial infarction or stroke over next five or ten years. Total CVD risk is determined according to charts or equations that take into account the co-existence in an individual of a range of risk factors such as age, sex, tobacco use, body mass index, diabetes, raised blood pressure and a variety of biochemical indicators. Recent research suggests that compared with the vertical treatment approach, adopting pharmaceutical treatment strategies based on the total CVD risk assessment approach offers considerable savings [10, 11]. The 2007 WHO guidelines for primary prevention of CVD recommend the second approach by targeting limited healthcare resources most cost-effectively at high-risk groups to prevent CVD .
The total risk scores are based upon multivariate risk analyses of longitudinal cohorts that ascribe values to different risk factors . Since the publication of the first risk scores from the Framingham Heart Study in 1976 , many scores have been developed and are in use from other cohort studies, mainly in developed countries involving Caucasian populations [15–21]. The scores vary widely in terms of study characteristics, predictors and CVD outcomes investigated . Risk scores based upon studies conducted in HIC may not be suitable for use in low-resource settings. Therefore the World Health Organization and the International Society of Hypertension (WHO/ISH) developed sets of regional risk prediction charts based on fewer risk factors that can be assessed by physicians and non-physician health workers in primary care setting for CVD prevention in each of the fourteen WHO subregions .
Although the CVD risk scores are designed for use by clinicians for quick and consistent estimation of total CVD risk in ‘individuals’, these can also be used to estimate and monitor population distribution of CVD risk from cross-sectional survey of population samples [10, 11]. National health planners may use population-distribution of total CVD risk to assess total preventive needs and associated costs as well as to monitor net-effectiveness of interventions that affect multiple CVD risk factors by different magnitudes and direction .
Few LMIC currently have clinical guidelines either for screening or treatment of risk factors based on ‘total’ CVD risk scores and few have estimated population-distribution of CVD risk over time. Using nationally representative population data, this study provides first-ever estimates of population-distribution of CVD risk in three LMICs (Cambodia, Mongolia, and Malaysia) countries at different stages of socio-economic, demographic and epidemiological transition. The study assesses the population distribution of total CVD risk estimated using the WHO/ISH risk charts alone, and the effect that inclusion of different criteria has on those distribution estimates in all three countries. The paper considers the issues that may be associated with using the total risk approach both at a population- and at individual-level in low-income settings.
Malaysia is an upper middle-income country of some 28 million people, a newly industrialized market economy with GDP of 287.9 billion. Mongolia, one of the least densely populated countries with a population of less than 3 million, is a lower-middle-income country with GDP of 8.761 billion, is a country with a growing economy centered on agriculture and mining. Cambodia, a low-income country with GDP 12.83 billion and a country of more than 13 million people, remains largely agricultural and rural, although it has seen industrial and economic growth in recent years [24, 25]. In each of the countries the impact of NCDs is significant: NCDs account for more than 50% of life years lost in Malaysia and Mongolia and 31% in Cambodia . Life-expectancy at birth in Malaysia was 74 years as of 2011, whereas it was 68 and 63 years for Mongolia and Cambodia .