Primary Prevention of Cardio-Vascular Disease in Ethnic South Asians

• Adjusting Framingham Risk Estimate
• Issues to Consider When Adjusting Risk
• Consider Adjusting Risk for Additional Risk Factors by a Factor of 1.5-2.0.

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• South Asians
• The Importance of Conventional Risk Factors in South Asians- The INTER-HEART Study

Assessment and Management of Cardiovascular Risk

Adjusting Calculated Risk

Some publications report that, for some populations, the Framingham data now overestimates the risk. This may relate to the observation that rate of ischaemic cardiac events (based on mortality data) has been falling and this decline started before the more widespread use of many primary prevention measures.

In other words, if the incidence of new events falls independent of changes in factors used to estimate risk, then the risk calculations will be an overestimate.

Conversely, if the actual risk increases because of increased prevalance of important factors not included in the risk calculation (such as increasing obesity including increasing abdominal obesity in Asians), then the risk calculations will be an underestimate.

If some factors have a greater impact in some populations then a risk equation derived from the study of a different ethnic or racial group will underestimate risk. For example, if the relative risk of smoking was higher in a certain ethnic groups then the Framingham calculator would underestimate risk.

Even if the Framingham risk estimate is largely accurate, we might wonder if this risk estimate can be refined further. To do this we might measure some of the emerging risk factors. A new risk factor needs to be shown to provide additional information to the conventional risk factors. As evidence in favour of a new risk factor increases it may be categorised as an emerging risk factor.

Emerging risk factors may increase relative risk. Even if the relative risk increase is over two, if the emerging risk factor has a low prevalence, then routine measurements in all persons may not be that helpful or "cost-effective". If presence of an emerging risk factor only increases the absolute risk by a small amount then one might argue that there is no benefit from this measurement. For example, in persons with a five year risk of cardiovascular events of five percent, measurement of hs-CRP may still mean the person will fall below the pharmacological treatment threshold of the New Zealand Guidelines, even if one increases the absolute risk estimate by a factor of two. The same arguments apply to measurement of Lp(a). Unnecessary measurements of these risk factors may merely increase the costs of any screening program with little benefit- the selective us of these tests seems more reasonable.

With this in mind, we can appreciate the importance of the INTER-HEART study. published in The Lancet. It gives further insight into the importance of the established risk factors in different populations and whether we need to search for novel risk factors to refine our risk estimates or simply continue to measure conventional risk factors.

Hitesh Patel, Cardiologist
11th September, 2004