CHOLESTEROL measurements are routinely done for those going for a general health check-up or an assessment of their risk of heart attack and stroke. Most people believe that the "bad" cholesterol (also termed low density lipoprotein cholesterol or LDL-C) will clog their arteries and the "good" cholesterol (also known as high density lipoprotein cholesterol or HDL-C) will protect them against heart disease.
For years, cholesterol guidelines have advised physicians to commence treatment of cholesterol with drugs once the "bad" LDL-C exceeds certain recommended targets. Physicians will also commonly tell their patients to embark on measures to elevate the "good" HDL-C in the belief that higher HDL-C protects the individual against heart disease. Recent guidelines and trials will change longstanding paradigms.
Treating risk and not numbers
What do the new guidelines say about who needs and who does not need cholesterol lowering medication (statin)? The latest cholesterol guidelines issued by the American Heart Association and the American College of Cardiology in November 2013 have attracted a storm of controversy for its paradigm shift.
While the new guidelines are not based on new trial data, it has taken a whole new approach to managing cholesterol. Instead of using LDL-C numbers generated from a blood test as the basis for decision-making, the new strategy takes a patient-centric approach by recommending the commencement of statins if an individual falls within one of four defined risk groups. The new guidelines define those who have heart artery disease, stroke or narrowing of the lower limb arteries as having atherosclerotic cardiovascular disease (ASCVD).
The four groups who are at risk of a stroke or heart attack are:
- those who already are known to have ASCVD;
- those with no known ASCVD but have LDL-C >190 mg/dl;
- diabetics from ages 40 to 75 years with LDL-C 70 mg/dl to 189 mg/dl; and
- those with no known ASCVD from the ages of 40 to 75 years with LDL-C 70 mg/dl to 189 mg/dl and a calculated 10-year risk of more than 7.5 per cent based on the new risk calculator.
Simply put, those with known arterial disease, severely elevated LDL-C, are middle-aged/elderly diabetics or those middle-aged/elderly with increased risk of ASCVD should be considered for statin consumption. It also means that if you are young and have no risk factors or known ASCVD, you do not need statin if the LDL-C is less than 190 mg/dl.
If you don't fall into the four defined risk groups but still have elevated LDL-C and are still uncertain about whether you should start on statins, here is another checklist that the newest guidelines provide. You need to discuss the necessity of taking statin with your physician if you have any one of the following:
- a strong family history of ASCVD in first-degree relatives (onset at more than 55 years in male and more than 65 years in female);
- abnormal test results showing excessive calcium in heart arteries (high calcium score of 300 or more Agaston units on computed tomography scans of the heart arteries);
- evidence of lower limb arterial blockage (ratio of ankle systolic blood pressure to arm systolic blood pressure of < 0.9);
- elevated C-reactive protein > 2mg/L on blood test, or
- have an LDL-C of 160 mg/dl due to genetically inherited cholesterol disorders. Some of the items on the checklist will require your physician to order these tests.
How low should 'bad' cholesterol go?
There is general consensus and an overwhelming scientific data to illustrate that lowering LDL-C is beneficial in preventing heart attack and stroke.
Unlike the existing guidelines which recommend achieving a target level of LDL-C < 100 mg/dl for those with known heart artery disease and multiple risk factors for heart disease, the new guideline takes the stand that while groups that are at risk of ASCVD should aim to lower the LDL-C levels, it does not recommend any specific LDL-C or HDL-C targets.
Although the new guideline does not make reference to any specific LDL-C target to achieve, it does however recommend that if the LDL-C < 40 mg/dl on two consecutive visits, the dose of the statin can be reduced.
This approach has stirred a storm of controversy and other experts have referred to previous cholesterol-lowering trials that have validated the target of LDL-C < 100 mg/dl. The most interesting thing about the issue of setting an LDL-C target is that the new recommendation of not fixing targets is not based on new data but is based on the same data which lets the earlier experts who were writing the existing guidelines to recommend the target of LDL-C < 100 mg/dl. Hence, physicians are most likely to continue to use the recommendations of achieving a target LDL-C < 100 mg/dl for those with known heart artery disease.
A new global risk assessment calculator was proposed about the time the new cholesterol guidelines were released to estimate the likelihood of getting a stroke or heart attack in 10 years or a lifetime.
Critics have commented that when the new risk calculator is applied to existing ongoing trial populations, it significantly overestimates risk. The data is based on an American population and is not meant to be applied to Asian populations.
Furthermore, one needs to understand the meaning of being at risk. When using a global risk assessment calculator and the risk score predicts that the person has a 20 per cent risk of a heart attack over the next 10 years, does it really mean that the person has a one in five chances of getting a heart attack within the next 10 years if he does not modify his 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 risk within a 10-year period 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 take steps to prevent the heart attack event. There is no evidence to support the use of risk calculators for guiding drug treatment. The new guideline clearly states that risk calculation should be more appropriately used to motivate therapeutic lifestyle change in younger individuals.
The right approach to cholesterol
Do not be alarmed when risk calculators estimate that your risk of heart attack or stroke is 20 per cent. What it means is that 80 out of 100 will not be at high risk. Using additional tests, doctors can sieve out the 20 out of 100 high-risk individuals who need treatment.
If you fall within the four risk groups defined in the new guideline, you will benefit from statin therapy. In principle, lowering the LDL-C is beneficial and if the LDL-C falls below 40 mg/dl on consecutive tests, the statin dose should be reduced. There are studies to validate the reduction of LDL-C to 100 mg/dl to reduce strokes and heart attacks for those with ASCVD and hence, it is reasonable to use this as a target despite the absence of fixed targets in the new guideline.
As statins do have potential side effects, including increasing the risk of diabetes in those who are predisposed, the general principle is to use the highest dose of statin to achieve the lowest LDL-C possible without any adverse effects.
- Dr Lim is medical director at the Singapore Heart, Stroke & Cancer Centre. He is also editor-in-chief, Heart Asia (a journal of the British Medical Journal Publishing Group); chairman, scientific advisory board, Asia Pacific Heart Association; and honorary professor and senior medical adviser, Peking University Heart Centre
- To read more of Dr Lim's previous health-related articles, please visit: http://www.btinvest.com.sg/specials/shscc
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