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At the heart of general practice since 1960

Assessing heart disease in your ethnic patients

Dr Ali Hamaad and Professor Gregory Lip discuss why ethnicity causes problems with the estimation of cardiovascular risk

dentifying at-risk individuals is central to prevention of cardiovascular disease, which remains the biggest killer in the Western world. Important ethnic variations in relative incidence and prevalence of coronary heart disease make the risk more difficult to assess.

The most widely used method for the assessment of coronary heart disease (CHD) and cardiovascular disease (CVD) risks is based upon equations derived from the Framingham Heart Study1, which used eight weighted risk factors (see box).

The Framingham risk estimation is based on the 10-year prospective experience of the Framingham cohort which consists exclusively of white, middle-class men and women aged 30-74 living in semi-urban Massachusetts in the US.

Cardiovascular risk profiles derived from the Framingham cohort cannot realistically be applied to ethnic minorities to attempt to predict their cardiovascular risk.

Ethnic minorities possess inherently different population and racial characteristics in CVD risk profiling.

Application of Framingham risk estimates to ethnic minorities has been shown to underestimate CVD risk. It is suggested GPs should use a lower threshold to manage the same overall vascular risk.

The Joint British Societies Coronary Risk Prediction Charts in the back of the British National Formulary are unfortunately also based on the Framingham equation, making them inaccurate when applied to ethnic minorities2.

There has been some headway in attempting to create a risk calculator applicable to ethnic minorities. A study3 in JAMA applied the Framingham equation to different ethnic cohorts in North America.

It found reasonable agreement between predicted and actual CHD event rates among certain ethnic groups that were subjects in other prospective cardiovascular studies.

Unfortunately the ethnic populations studied were black Americans, native Americans and Hispanics, inherently different ethnic subgroups to those present in the UK.

Family history has long been regarded an important factor in CVD, and rightly so. It does not feature in the Framingham or other derived risk equations.

It is important to consider family history when establishing the probability of a patient having CHD during current assessment of their symptoms, but it is not a factor in determining future risk of developing CHD and more weight should be given to established risk factors (see box).

Ethnic variations in CVD and risk

Risk of CVD varies among different ethnic groups. Relative to Caucasians, Afro-Caribbean people have a high incidence of stroke and end-stage renal failure, whereas risk of CHD is less common4.

South Asians (predominantly from the Indian subcontinent and east Africa) have a much higher incidence of CHD5. Ischaemic heart disease is highest in immigrants born in the Indian subcontinent whereas it is remarkably low in those born in the Caribbean.

Stroke incidence is high in people born in the Indian subcontinent and Caribbean, with highest rates among Caribbean women. Variations of mortality rates in ethnic subgroups internationally and in stark contrast to Caucasian populations suggest a complex interaction between environmental factors and underlying genetic susceptibility.

Traditional risk factors among ethnic minorities ­ smoking and raised cholesterol ­ are less prevalent when compared with the native European white population6. But south Asians do exhibit a tendency to lower HDL cholesterol and high triglyceride concentrations7.

Prevalence of hypertension in people of African descent (including Afro-Caribbeans) is high and may be up to four times more common than among whites8.

It is likely this contributes to the high incidence of stroke and end-stage renal failure in this ethnic group. South Asians also have a higher prevalence of hypertension than white people, though this is lower than that for populations of African descent7.

Diabetes is a particularly common risk factor in south Asians, for men and women, and is higher than in any other ethnic group9.

This may explain the high incidence of coronary disease in south Asians, mediated by hyperinsulinaemia and central adiposity. Diabetes is more prevalent among people of African descent, although this is less common than in the south Asian population.

Obesity may contribute to the higher prevalence of hypertension and diabetes10 among women of African descent,

from the Caribbean and from West Africa.

CHD in other ethnic groups

In the US, Hispanics make up a significant proportion of the ethnic population. Some evidence suggests Hispanics have a significantly lower prevalence of coronary heart disease compared with whites and Asian-Americans, and this difference persists even after controlling for cardiac risk factors11.

Data is sparse on Far Eastern populations, but rates of cardiovascular disease in these groups remain low.

Differing responses to treatment

Several drugs have been shown to help prevent CHD among at-risk individuals, and treatment is mainly targeted at controlling appropriate risk factors in these individuals.

Controlling hypertension is an important step, but there are well-recognised issues surrounding this in black populations of African descent.

?-blockers are generally less effective in black hypertensives12 so higher doses of ?-blockers may therefore be needed to achieve target blood pressure control, and younger black patients may be

more responsive than the elderly to

?-blockade13.

Addition of a diuretic has been shown to negate this differential effect of

?-blockers in blacks14. However, unless there are clear indications (such as following myocardial infarction)

?-blockers should not be considered as first-line monotherapy in black patients. ACE inhibitors also demonstrate a less-favourable antihypertensive response when used alone in black patients.

Again, addition of a diuretic eliminates this dampened response15.

Restricting salt is an important non-pharmacological step in the management of hypertensive disease in blacks (reducing daily sodium intake to less than 100mmol) in view of the 'salt sensitivity' exhibited by black hypertensives12.

Reduced responsiveness to ?-blockers and ACE-inhibitors is not exhibited by Asian patients. This ethnic group, however, do have other less well-recognised features when considering the management of cardiovascular risk. South Asians are less likely to be prescribed lipid-lowering drugs; surprising given the greater prevalence of coronary heart disease and dyslipidaemic states compared with the white population16.

Lifestyle differences are apparent among South Asians which may contribute to existing risk factors. Lack of physical activity among south Asian immigrants in the UK is the most obvious, aggravating insulin resistance, increasing body mass index and dyslipidaemia17.

Underestimation of CHD and CVD in ethnic subgroups has largely been attributed to the relative inaccuracy of Framingham risk when applied to these groups. It is important to recognise that

there are particular cardiovascular diseases and cardiovascular risk factors associated with certain ethnic groups, such as stroke and hypertension among blacks, and coronary heart disease, diabetes and dyslipidaemia among south Asians.

Treatment issues are also important, especially when considering commencing ?-blockers or ACE inhibitors in black patients, or lipid-lowering therapy in south Asians.

Weighted risk

factors used in

the Framingham

Heart Study

 · Age

 · Sex

 · Systolic or diastolic blood pressure

 · Serum total and

high density (HDL) cholesterol

 · Presence of left ventricular hypertrophy

 · Presence of diabetes mellitus

 · Cigarette smoking

Assessing heart disease in your ethnic patients

Cardiovascular diseases and risk factors according to ethnic group with associated therapeutic considerations

Most prevalent Common risk factors Therapeutic considerations

cardiovascular

diseases

Blacks of African 1 Stroke 1 Hypertension 1 ?-blockers and ACE inhibitors less effective

descent (African, 2 End-stage renal failure 2 Diabetes in managing hypertension

Afro-Caribbean) 3 CHD less common 3 Central adiposity 2 Sodium restriction important step in

managing hypertension

South Asians 1 CHD 1 Diabetes 1 Require more lipid lowering

2 Stroke 2 Central adiposity therapy, especially if CHD present

3 Low HDL cholesterol, 2 Encourage more physical activity

raised triglycerides

References

1 Anderson KM et al. Cardiovascular disease risk profiles. Am Heart J 1991;121:293-8

2 Joint British recommendations on prevention of coronary heart disease in clinical practice. Heart. 1998;s2:S1-S29

3 D'Agostino RB at al. Validation of the Framingham Coronary Heart Disease Prediction Scores: results of a multiple ethnic groups investigation.

JAMA. 2001;286:180-7

4 Raleigh VS. Diabetes and hypertension in Britain's ethnic minorities: implications for the future of renal services.

BMJ. 1997;314:209-13

5 Balarajan R. Ethnic differences in mortality from ischaemic heart disease and cerebrovascular disease in England and Wales. BMJ. 1991;302:560-4

6 Cruickshank JK et al. Ethnic differences in fasting plasma C-peptide and insulin in relation to glucose tolerance and blood pressure. Lancet. 1991;338:842-7

7 Bhopal R et al. Heterogeneity of coronary heart disease risk factors in Indian, Pakistani, Bangladeshi and European origin populations: a cross-sectional study. BMJ. 1999;319:215-20

8 Chaturverdi N et al. Resting and ambulatory blood pressure differences in Afro-Caribbeans and Europeans. Hypertension. 1993;22:90-6

9 Cruickshank JK et al. Heart attack, stroke, diabetes and hypertension in West Indians, Asians and Whites in Birmingham. BMJ. 1980;281:1108

10 McKeigue PM et al. Relation of central obesity and insulin resistance with high diabetes prevalence and cardiovascular risk in South Asians. Lancet.1991;337:382-6

11 Budoff MJ et al. Ethnic differences in coronary atherosclerosis. J Am Coll Cardiol. 2002;39:408-12

12 Gibbs CR et al. The management of hypertensive disease in black patients.

Q J Med. 1999;92:187-92

13 Abson CP et al. Once daily atenolol in hypertensive Zimbabwean blacks. A double-blind trial using two different doses. S Afr Med J. 1981;60:47-8

14 Veterans Administration Co-operative Study Group on Antihypertensive Agents. Efficacy of nadolol alone and combined with bendroflumethiazide and hydralazine for systemic hypertension. Am J Cardiol. 1983;52:1230-7

15 Drayer JIM, Weber MA. Monotherapy of essential hypertension with a converting enzyme inhibitor. Hypertension. 1983;5(s3):108-13

16 Patel MG et al. Prescribing of lipid-lowering drugs to south Asian patients: ecological study. BMJ. 2002;325:25-6

17 Dhawan J, Bray CL. Asian Indians, coronary artery disease and physical exercise. Heart. 1997;78:550-4

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