As far as CAD is concerned the people of South Asian region are at a veiy ndisadvantageous position. The term 'South Asians' includes persons that originated from nations of Indian subcontinent: India, Pakistan, Bangladesh,Nepal, Bhutan and Sri Lanka. They also include large and small iinrnigrant populations residing in different parts of the world. While differing in ethnic and socio-economic characteristics, they share a common characteristic - the highest predisposition to develop CAD - and in that the immigrant Indians share the major burden. Noimally CAD rates vary among different populations with first generation immigrants having rates intermediate between that of the country of origin and the host country. The CAD rates ultimately blend with the prevalent rates of the adopted country in two or three successive generations, depending on the rate of acculturation and adoption of lifestyle habits of the host country. While other imnigrant communities follow the same pattern, Indian immigrants are singular exception because they have higher rates of CAD than the native population of the adopted country.Epidemiology and Natural History of Heart Disease The magnitude of the problem can be understood by looking at the prevalence,severity, prematurity and ~liortality of CAD in South Asians, also called as Asian Indians
Prevalence
The first report to highlight the high prevalel~ce of CAD anioiig Indian expatriates came from an autopsy study done in Singapore. Coronary artery disease with myocardial involvelllent was seven times more common in Jndians when compared to Cliiilese males. Subsequcntly, other studies from Singaporc, Uganda,South Africa and Fiji confirmed a three-fold higher prevalence of CAD in Indians
compased to the respective native populations. In the Southall Study, the prevalence of CAD diagnosed by the presence of major Q waves was four per ccnt in Indiaborn nicn compn~.ccl to 2.3 per ccnt in Europeans. Physicians of Indian origin ('first generation Indians') who have migrated to thc West have Sour tinies higher prevalence of CAD ( 1 0 per cent) than that of general physicial~ population in USA. The age-adjusted prevnlence of myocardial infarction (MI) or angina was three times more in Indian men (mean age 46.4 years) compared to the inen in the Framinghaln Offspring St~ldy (7.2 per cent vs. 2.5 per cent).
While South Asians exhibit the highest prevalence of CAD and coroniily risk factors as conlpared with Caucasians, they even differ from the other Asians. CAD prevalence rates for them are six times higher than Chinese ant1 k ~ u r times higher than other Asian Americans. In contrast Japanese have the sirnilair prevalence rates as Whites. More 1.ecent1y the study of llealth Assessment and Risk in Ethnic groups (SHARE) from Canada showed that the overall prevalence of CAD was 10.7 per cent among South Asian Zndiai~s versus 4.6 per cent in Europeans and 1.7 per cent in Chinese population.
Severity and Extent of Lesion
Apart from the high prevalence, the other disturbing features of CAD in South Asians are the severity and extent of lesion. Generally Indians show more severe and extensive disease; quantitative analysis of corollary arlgiography reveals that more than twice the number of Asian Indians has triple vessel disease (TVD) compared to the Whites. In UK studies, Asian Indians as compared to Caucasians were found to have higher incidence of TVD (54 per cent vs, 21 per cent), high atheroma score (3.66 per cent vs. 1.97 per cent) and larger infarct size (massive infarction). On angiography, their coronay arteries are found to be more often smaller and tend to develop fewer collateral vessels as CAD progresses. Even many were found unsuitable for coronay artery bypass surgery (CABS) because of severity of lesions.
Prematurity
CAD in Indians tends to be more aggressive and manifests at a younger age.Generally CAD occurring before the age of 55 years in men and 65 years in women is defined as premature CAD. Any CAD before the age of 40 years is termed as CAD in young. It indicates extensive, accelerated and aggravated atherosclerosis - the most severe form of,CAD. In the Western countries incidence of young CAD is less than 5 per cent whereas in Asian Indians it is about 12-16 per cent. In a prospective study of 13 1 men, the rate of first MI was five times higher among Indian men compared to the Europeans. Further, the mean age at first MI was about five years lower for the Indian men (50.2 vs. 55.5 years). Even in India also the incidence of CAD in young is estimated to be as high as 12 per cent. It has been found that over half of myocardial infarctions (MI) occur in persons less than 55 years of age and up to 25 per cent of *MIS occur in persons less than 4 0 years of age.
The first report to highlight the high prevalel~ce of CAD anioiig Indian expatriates came from an autopsy study done in Singapore. Coronary artery disease with myocardial involvelllent was seven times more common in Jndians when compared to Cliiilese males. Subsequcntly, other studies from Singaporc, Uganda,South Africa and Fiji confirmed a three-fold higher prevalence of CAD in Indians
compased to the respective native populations. In the Southall Study, the prevalence of CAD diagnosed by the presence of major Q waves was four per ccnt in Indiaborn nicn compn~.ccl to 2.3 per ccnt in Europeans. Physicians of Indian origin ('first generation Indians') who have migrated to thc West have Sour tinies higher prevalence of CAD ( 1 0 per cent) than that of general physicial~ population in USA. The age-adjusted prevnlence of myocardial infarction (MI) or angina was three times more in Indian men (mean age 46.4 years) compared to the inen in the Framinghaln Offspring St~ldy (7.2 per cent vs. 2.5 per cent).
While South Asians exhibit the highest prevalence of CAD and coroniily risk factors as conlpared with Caucasians, they even differ from the other Asians. CAD prevalence rates for them are six times higher than Chinese ant1 k ~ u r times higher than other Asian Americans. In contrast Japanese have the sirnilair prevalence rates as Whites. More 1.ecent1y the study of llealth Assessment and Risk in Ethnic groups (SHARE) from Canada showed that the overall prevalence of CAD was 10.7 per cent among South Asian Zndiai~s versus 4.6 per cent in Europeans and 1.7 per cent in Chinese population.
Severity and Extent of Lesion
Apart from the high prevalence, the other disturbing features of CAD in South Asians are the severity and extent of lesion. Generally Indians show more severe and extensive disease; quantitative analysis of corollary arlgiography reveals that more than twice the number of Asian Indians has triple vessel disease (TVD) compared to the Whites. In UK studies, Asian Indians as compared to Caucasians were found to have higher incidence of TVD (54 per cent vs, 21 per cent), high atheroma score (3.66 per cent vs. 1.97 per cent) and larger infarct size (massive infarction). On angiography, their coronay arteries are found to be more often smaller and tend to develop fewer collateral vessels as CAD progresses. Even many were found unsuitable for coronay artery bypass surgery (CABS) because of severity of lesions.
Prematurity
CAD in Indians tends to be more aggressive and manifests at a younger age.Generally CAD occurring before the age of 55 years in men and 65 years in women is defined as premature CAD. Any CAD before the age of 40 years is termed as CAD in young. It indicates extensive, accelerated and aggravated atherosclerosis - the most severe form of,CAD. In the Western countries incidence of young CAD is less than 5 per cent whereas in Asian Indians it is about 12-16 per cent. In a prospective study of 13 1 men, the rate of first MI was five times higher among Indian men compared to the Europeans. Further, the mean age at first MI was about five years lower for the Indian men (50.2 vs. 55.5 years). Even in India also the incidence of CAD in young is estimated to be as high as 12 per cent. It has been found that over half of myocardial infarctions (MI) occur in persons less than 55 years of age and up to 25 per cent of *MIS occur in persons less than 4 0 years of age.
Mortality
Marked prematurity and extensive atherosclerosis leads to markedly higher mortality in young Asian Indians compared to other ethnic groups. In UK overall age standardised mortality mte (SMR) for CAD in South Asian men is 36 per cent higher than Caucasians - but 313 per cent higher in the age group of 20-29 years.Between 1970-72 and 1979-83, while all the other ethnic groups studied showed either no change or a decline in mortality due to CAD, immigrants from the Indim subcontinent experienced a tise in mortality (6 per cent in men and 13 per cent in women) despite having had the highest rates initially. In Singapore, SMR in South Asians as compared to other ethnic groups (Chinese) is higher; and the difference in mortality becomes more conspicuous with decreasing age. While in the age group of 60-69 years, the mortality is 300 per cent higher, it rises by 390 per cent in the age group of 50-59 years, by 500 per cent between 40-49 years and by 1250 per cent in the age group of 30-39 years. SMR for CAD among Asian Indian women in South Africa is four times higher than that of US women, 14 times higher than that of French, and 21 times higher than that of Japanese.
Marked prematurity and extensive atherosclerosis leads to markedly higher mortality in young Asian Indians compared to other ethnic groups. In UK overall age standardised mortality mte (SMR) for CAD in South Asian men is 36 per cent higher than Caucasians - but 313 per cent higher in the age group of 20-29 years.Between 1970-72 and 1979-83, while all the other ethnic groups studied showed either no change or a decline in mortality due to CAD, immigrants from the Indim subcontinent experienced a tise in mortality (6 per cent in men and 13 per cent in women) despite having had the highest rates initially. In Singapore, SMR in South Asians as compared to other ethnic groups (Chinese) is higher; and the difference in mortality becomes more conspicuous with decreasing age. While in the age group of 60-69 years, the mortality is 300 per cent higher, it rises by 390 per cent in the age group of 50-59 years, by 500 per cent between 40-49 years and by 1250 per cent in the age group of 30-39 years. SMR for CAD among Asian Indian women in South Africa is four times higher than that of US women, 14 times higher than that of French, and 21 times higher than that of Japanese.
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| Morbidity and mortality curve |
In summary
i)The prevalence of CAD among immigrant Indians is about three-fold higher than in comparable indigenous populations;
ii) CAD tends to occur earlier in life among people of Indian descent; extensive often involving multiple vessels
iii) The process is very severe, diff~~se, and runs an accelerated malignant course; and
iv) Moi-tality attributable to CAD is substantially higher among Indian immigrants across all age groups and is remarkably pronounced in the young.
i)The prevalence of CAD among immigrant Indians is about three-fold higher than in comparable indigenous populations;
ii) CAD tends to occur earlier in life among people of Indian descent; extensive often involving multiple vessels
iii) The process is very severe, diff~~se, and runs an accelerated malignant course; and
iv) Moi-tality attributable to CAD is substantially higher among Indian immigrants across all age groups and is remarkably pronounced in the young.
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