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Primary Prevention of Cardio-Vascular Disease

Assessment and Management of Cardiovascular Risk

Treatment Threshold in the United States of America

The New Zealand Guidelines are based on the Framingham data. The threshold for pharmacologic treatment is set at an estimated risk of cardiovascular events of 15% over five years.

It is worth remembering that the effect of this is that many younger persons with two risk factors may not exceed the treatment threshold even though they are at increased relative risk compared to their peers of the same age. In addition, it means that older persons with only one risk factor might exceed the pharmacologic treatment threshold.

The impact of any guidelines such as the New Zealand Guidelines is that the focus will shift towards reducing events in older persons, people whose life expectancy may not increase as much as younger persons after prevention of a cardiovascular event.

If one wanted to reduce the risk for more people, and if one assumed that the longer term benefits of risk factor modification is greater than implied by estimation of short-term risk (over five years) then one would set a lower threshold for treatment of various risk factors.

The United States of America's Guidelines (ATP III) take a slighty different approach, which will mean treatment with lipid modifying agents will be recommended for younger persons as well even though they are at lower absolute risk. For example, if a person has two or more risk factors other than LDL cholesterol, then it recommends:

  • estimation of ten year risk of coronary heart disease events (not cardiovascular events as in the NZ Guidelines) The risk estimate is higher for older persons.
  • if the calculated ten year risk is less than ten percent, the highest acceptable LDL cholesterol level is 4.1 mmol/l. For those who have a risk between 10 and 20 percent, the highest acceptable LDL cholesterol level is 3.3mmol/l.

Risk factors, other than LDL cholesterol, in the USA guidelines are:

  • smoking
  • any treated hypertension or blood pressure greater than 140/90;
  • HDL less than 1 mmol/l;
  • family history of ischaemic heart disease as defined in the NZ Guidelines;
  • and age (men aged more than 45 years and women aged more than 55 years)
    • .

Risk Category LDL Goal (mmol/l) Non-HDL Goal (mmol/l)
CHD and CHD Equivalent <2.5 <3.3
2 or more risk factors and ten year CHD risk less than 20 percent
<3.3 for risk >10%
<4.1 for risk <10%
<4.1 or 4.9

dependent on level of risk
0-1 risk factor <4.1 <4.9

If triglyeride levels are above about 6 mmol/l then the first goal is to lower this to reduce risk of pancreatitis. Statins, amongst other drugs, lower triglyeride levels.

Thus, for example, a male aged 45 years with mild hypertension, and who does not have any other risk factors, would get lipid modifying therapy if the LDL cholesterol is above 4.1 mmol/l, even though this person absolute risk may not be "high". This person would not receive treatment for mild hypertension or dyslipidaemia using the NZ Guidelines (unless these factors are severely raised).

The complete ATP III guidelines are readily available on the world wide web. The overall impression is that more people will qualify for lipid modifying therapy than if the NZ Guidelines were used. More younger persons who may be at lower absolute risk but are at higher relative risk compared with their peers will get lipid modifying therapy and this is likely to have a greater impact on preventing myocardial infarction in younger persons. As with most aspects of health care, the United States of America is able, it seems, to afford more health care.

The New Zealand Guidelines recommend lowering risk below fifteen percent even if the calculated risk for cardiovascular events exceeds 20 percent over five years. The guidelines from the USA, in contrast, would recommend these patients' LDL cholesterol is lowered to optimal levels just like patients with established coronary artery disease. The USA's guidelines also recommend a secondary target for treatment- non-HDL cholesterol

Hitesh Patel, Cardiologist
17 September, 2004

Reference:
Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). Final Report.

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