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Friday, April 15, 2011

Understanding Cardiovascular Risk

Many express hesitation when it comes to the idea of taking cholesterol medication, or “statins.” This is despite their well documented record of efficacy and safety in the prevention of cardiovascular disease (CVD).  Guidelines for the treatment of high cholesterol are based on one’s LDL (or “bad cholesterol”) level in combination with one’s determined CVD risk.  

According to the National Cholesterol Education Program’s most recent Adult Treatment Program Report (ATP III for those at lowest risk, medication may not be indicated until the LDL cholesterol is greater than 160 to 190. However, for those at highest risk, medication may be suggested when the LDL level is over 100, or even lower for some. 

Who is at highest risk and how should asymptomatic adults be screened for CVD?

Recent guidelines by ACCF and AHA have been issued in 2010. Those with existing cardiovascular disease (history stroke, aortic aneurysm, coronary artery disease or peripheral vascular disease) are at highest risk for future events.  Certain diseases are also considered “coronary artery disease equivalents,” because of the very high rates of cardiovascular disease in those affected. Diabetes and chronic renal insufficiency are the two most common conditions that fall into this category.  

One widely used CVD risk calculator is called the Framingham Risk Score (FRS).  Use of this tool is endorsed by the American Heart Association and the American College of Cardiology, and numerous other medical professional groups.  The FRS uses traditional cardiac risk factors to calculate a score of one’s ten year risk of having a cardiovascular event.  The major risk factors for CVD are: 
  • Cigarette smoking
  • Hypertension (BP greater than or equal to 140/90 mm Hg or on antihypertensive medication)
  • Low HDL cholesterol (less than 40 mg/dL),
  •  Family history of premature CHD (CHD in male first-degree relative less than 55 years; CHD in female first-degree relative less than 65 years)
  • Age (men greater than or equal to 45 years; women greater than or equal to 55 years)

High risk is defined as a person whose likelihood of having a cardiovascular event is over 20% within ten years.  Low risk is defined as a person whose likelihood of having a cardiovascular event is less than 10 %. Those at intermediate risk have a 10 to 20% chance of having a cardiovascular event within 10 years.  Some further stratify intermediate risk into moderate risk (FRS of <10% but two CHD risk factors) and moderately high risk (FRS >10% and two CHD risk factors). Furthermore, some use a cut-off of 6% as the upper limit of “low risk.”  

The Framingham Risk Score works well for those over 40 years old, and may work better for men than women.  The key is to identify those who are at higher risk and to take action to modify that risk—lowering their blood pressure and treating their cholesterol.  There are supplementary tests that can be particularly useful in patients who are intermediate risk and might benefit from more intense monitoring and intervention.

Here some tests that have clinical utility:

“HS-CRP” (C-reactive protein) is an inflammatory marker that may be helpful to guide decision-making for men over 50 and women over 60 who are at intermediate cardiac risk.  CRP can be lowered by interventions that improve other cardiovascular risk factors, such as exercise, weight loss, smoking cessation, statins, and antihypertensive treatments.  In the JUPITER trial rosuvastatin (Crestor) 20 mg/d versus placebo was studied in the primary prevention of cardiovascular events in men and women without diabetes with LDL cholesterol > 130 mg/dL and CRP > 2 mg/L.  After a median follow-up of 1.9 years, rosuvastatin was associated with a significant reduction in cardiovascular events.

Hemoglobin A1C
Hemoglobin A1C is a measure of glycemic control over several months.  It is most commonly used to diagnose and monitor diabetes. However, studies have shown that in non-diabetic patients increased hemoglobin A1C levels (even within normal range) are associated with increasing risk of cardiovascular disease. 

Urinalysis for the detection of microalbumin
Urine microalbumin detection is recommended annually in diabetic patients. The test is inexpensive and easy to perform. The presence of microalbuminuria has also been linked to increased cardiovascular risk in patients with hypertension and in asymptomatic adults who are at intermediate risk of cardiovascular disease.

Carotid Intima Media Thickness (IMT) by Ultrasound
This is the thickness of the vascular lining of the carotid artery. The risk of CHD events increases in a continuous fashion as carotid intima media thickness increases (RR increases approximately 15% per 0.10-mm increase in carotid IMT). This test is not performed at all centers.

Ankle Brachial Index (ABI)
The ABI is performed by doppler measurement of blood pressure in all 4 extremities at the brachial, posterior tibial, and dorsalis pedis arteries. The highest lower-extremity blood pressure is divided by the highest of the upper-extremity blood pressures, with a value of < 0.9 indicating the presence of peripheral arterial disease, which is defined as > 50% blockage. When defined in this way, the ABI has both a high sensitivity and specificity for anatomic blockage.  An abnormally low ABI has also been shown to be a predictor of cardiovascular events.

Exercise ECG
 An Exercise ECG, a form of cardiac “stress test,” may be useful for risk assessment in intermediate-risk asymptomatic adults (including sedentary adults considering starting a vigorous exercise program).  Probably the most powerful risk marker obtained during routine exercise testing is exercise capacity; studies have consistently found that depressed exercise capacity is associated with increased cardiovascular risk.

Computed Tomography for Coronary Calcium
A cardiac CT or EBCT may be used to detect and quantify coronary calcium (CAC), a marker of atherosclerosis.  It may be useful in persons at intermediate risk (6 to 20%). This test is not recommended for men less than 40 or for women less than 50 due to the very low prevalence of detectable calcium in these demographics. 

In pooled data from six clinical trials, study subjects who had calcium scores of zero were found to have a low rate of cardiovascular events (0.4%) over the subsequent 3 to 5 years after testing. In subjects with high calcium scores, 400 to 1000 and >1000, the rates of cardiovascular events over the 3 to 5 year period were 4.6% and 7.1% respectively.

The recently released EISNER study found that study subjects who received cardiac CT for coronary artery calcium score were more likely than control subjects who received counseling alone to modify their cardiovascular risk profile over a 4 year period.  In contrast study subjects who received calcium scoring by CT were not found to incur higher downstream medical testing or health care costs. The implication being that the test could be an effective strategy for early detection, without increasing overall cost. 

Cardiovascular disease remains the most common cause of death in the American population.  In the last century we have developed effective therapeutics that help prolong life, reduce and delay the risk of cardiovascular illness.  Doctors should help patients understand their individual risk profiles, which are not static, but worsen with age, so that appropriate behavioral change or medication is prescribed when it is indicated.

1 comment:

  1. Smoking has been incorporated to almost all of the diseases that involve the heart, the lungs and more. This is true since cigars contain a lot of harmful elements. Though this is just one of the risk factors that greatly affect the human's health, it still plays the biggest roles in the every one's health may it be a first handed smoker or a second handed smoker.