Risk Factor Interaction

Coronary artery disease, as has been explained, is a multifactorial disease with diverse risk factors coming together and interacting to produce the pathological changes. The presence of a number of risk factors in a single individual increases the risk many times. Studies such as the Framingham and the MRFIT have clearly shown that the coexistence of multiple risk factors confers a magnified risk which is ~nultiplicative rather than additive. It means that the various risk factors work synergistically to increase the coronary risk and mortality in an exponential manner. A smoker with modest elevations of cholesterol and blood pressure is at greater risk of coronary death than a non-smoker with severe Hypertension or marked hypercl~olesterolernia. A single risk factor is not sufficiently sensitive to identify all individuals at high risk of coronary artery disease. The b~ilk of CAD occur in individuals with only moderate elevatiolzs of a nunzber of risk jactors mther than in those who lie at the up per end of a single risk factor.Genesis of

Multiplicative effect of risk factors

The above picture gives us an idea about the lnultiplicative effect of various risk factors. The estimaled 10 yeas coronary risk show11 here is based on six risk Sactors- blood pressure, total cl~olesterol (TC), HDL cholesterol, diabetes, smoking and presence of vei~tricular enlargement. As can be seen, the 10 y e u risk in those withoul any of the risk factors is less than 10 per cenl. I1 increases to 20 per cent when the systalic BP rises to 160 mm Hg and TC becomes 260 rngldl. The risk increases f~uther to 30 per cent in presence of additional risk factors like diabetes and low HDL cholesterol. Cigarette smoking increases the risk furlher to 40 per cent whereas ill prcsence of cardiac e~llargen~ent risk rises steeply to aboul 60 per cent. This is an important principle Lo remember for preventive measures,because the benefit obtained by improviilg all the risk factors togelhcr, even masginally, is definitely larger than that of strictly controlling a singlc factor and not addressing the other ones. The demonstration of such ~nultiplicalive risk has given rise to the concept of "comprehensive Cardio-vascular risk" or "tolal risk",estimating the individual's ovcrdl risk of devcloping Cardio-vascular disease resulting fronl the co~lsortium of rislc factors. This is particulasly relevant in the Indian context because of the c l u s t e ~ i n oT ~ risk factors among ethnic Indians.