Dr. Michael Lim's Articles
At the heart of celebrations
With risk-scoring systems done by your doctor, you can take the guesswork out of heart disease. By Michael Lim
BEFORE you tuck into your favourite goodies during the upcoming festive period, you may want to know your risk of getting a heart attack or stroke. With an increased emphasis on preventive approaches to heart disease, physicians are being encouraged to use risk scoring systems (also termed global risk assessment) in an attempt to categorise patients into various risk levels for heart attack.
Global risk assessment of heart artery disease is a calculation of the risk of having a heart attack over a determined period. If you are told by your physician that you have a 20 per cent risk of a heart attack over the next 10 years, does it really mean that you have a one-in-five chance of getting a heart attack within the next 10 years if you do not change your lifestyle? According to the 2013 American College of Cardiology and American Heart Association Guideline on Assessment of Cardiovascular Risk, no one has 10 per cent or 20 per cent risk of a heart attack during a 10-year period.
What a 20 per cent 10-year risk means is that within a group of individuals with the same risk profile, for every 100 individuals, there will be 20 individuals who will develop a heart attack within the 10-year period. Only those who are predestined to have a heart attack will be able to have the heart attack event prevented by preventive measures. Hence, the scoring system serves mainly as a wake-up call to those with multiple risk factors.
Risk scoring systems are not the bible truth
Although physicians are encouraged to use risk scoring systems, the reality is that none of the global risk assessment systems have had their validity tested in well-designed trials. Data for the development of these risk-scoring systems have been obtained from long-term observations in specific population groups, and from trials which have very clear criteria as to what type of patients are included and excluded from the study.
Hence, they are generally not meant to be applied to different population groups with different ethnicity, cultural backgrounds and socio-economic conditions. At best, when applied to diverse populations which are different from the population from which the data is derived, they provide a rough estimate of the risk.
Even within a population cohort, individual differences can be very diverse. Risk-scoring systems use data which are averages of the population being studied and hence, it must be understood that there are limitations when one tries to use averages in a population to apply to individuals.
Potential benefit of global risk assessment
The largest benefit from global risk assessment is to help physicians gauge who are those who can potentially benefit from treatment and to sieve out those with low risks who not only won’t benefit from treatment but may suffer from unnecessary financial cost and side-effects of treatment. The key is to identify those who have the highest potential to benefit from treatment and the lowest risks of harm from treatment.
New global risk assessment system
The global risk assessment tool that has been most widely applied in many countries is the Framingham 10-year risk score for coronary heart disease. Significantly, the experts involved in the 2013 American College of Cardiology and American Heart Association Guideline on assessment of Cardiovascular Risk recognised the significant limitations of this system and did not recommend the continued use of this scoring system.
Key limitations of Framingham score is that the data has been obtained primarily by observing an exclusively White study population in the town of Framingham in Massachusetts, USA. The current risk-scoring systems suffer from using data from populations of limited ethnicity, non-representative populations, not historically updated and data based on endpoints which were subjective. There is very little data on the usefulness of risk-scoring systems but the limited data suggests that it may modestly modify patient knowledge and intention to change favourably. Despite this beneficial trend, there is currently no trial data on the impact of risk-scoring systems on heart attacks and strokes.
The Work Group for the 2013 American College of Cardiology and American Heart Association Guideline on assessment of Cardiovascular Risk proposed the use of a new risk-scoring system as part of a preventive strategy for early identification of the development of disease in arteries and the prevention of significant adverse outcomes such as heart attacks and strokes. The new global risk-assessment system proposed a 10-year risk and a lifetime risk calculation for heart attacks and strokes.
The 10-year risk was defined as the risk of developing a first heart attack or stroke, over a 10-year period among people free from arterial disease at the beginning of the period. This model has been developed for those from the ages of 40 to 79 years. A 10-year risk score of <7.5 per cent is considered as low risk. In addition to the risk score, there is a list of new risk identifiers to further assess in risk assessment. The list of new risk identifiers were carefully selected to ensure that they would be easily available, likely to be used by primary healthcare providers, cost-effective, reliable, and had low risks of requiring further testing for low-risk individuals.
If after your risk assessment, you fall into a borderline category and are wondering whether you really need to take medication, the new risk identifiers can help you decide whether you will benefit from treatment.
If a male family member had a heart attack before the age of 55 years, or a female family member had a heart attack before 65, you are more likely to benefit from treatment. You can discuss this with your physician to get some low-cost simple tests done, such as high sensitivity C-reactive protein (hs-CRP) to detect inflammation in the walls of the arteries, a CT scan of the heart arteries to assess the severity of calcium deposition (Coronary artery calcium or CAC) in the heart arteries which correlates with the degree of disease of the heart arteries or calculate the ratio of your systolic ankle pressure to your arm systolic pressure (ankle-brachial index or ABI) which is an indirect indicator of narrowing of the leg arteries.
Your risk is increased if the hs-CRP is >2 mg/L, the CAC is >300 Agaston units or the ABI is < 0.9 . Although it is not in the current guidelines, there are world renowned experts who advocate the use of ultrasound screening of the neck and groin arteries to detect early development of cholesterol deposition in the arterial system.
In addition to the 10-year risk calculator, the Work Group had also developed a lifetime risk estimation for all persons who are between 20 and 39 years of age and for those between 40 and 59 years of age, who are determined to be at low 10-year risk (<7.5 per cent).
How often should global risk assessment be performed
The latest recommendations consider it reasonable to perform assessment of risk factors for heart disease and stroke every four to six years in adults 20 to 79 years of age, who are free from arterial disease. For those of you who want to check yourselves before you plunge into the season of feasting, the new risk calculator can be downloaded from http://my.americanheart.org/cvriskcalculator.
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