By Lance E. Sullenberger, MD. FACC, FACP, FSCCT*
We have all heard over the course of the last several decades that our cholesterol levels predict our risk of heart attack and stroke. Patients frequently ask me, “How could I have heart disease? My cholesterol level is normal.” Or they report to me, “I don’t have to worry because my good cholesterol is high.”
As a cardiologist, I have both bad and good news: Your cholesterol level does not matter! As you likely already know, cholesterol is a type of fat found within all cells and is free floating in blood on molecules called lipoproteins. The two most common of these lipoproteins containing cholesterol are low-density lipoprotein (also known as LDL), which carries cholesterol to the tissues (“bad cholesterol”), and high-density lipoprotein (also known as HDL), which carries cholesterol to the liver to be flushed from the body (“good cholesterol”).
Cholesterol carried by LDL can invade the walls of blood vessels and lead to inflammation within the walls of these blood vessels. Cholesterol in this way forms the main constituent of “plaque” that builds up within the walls of blood vessels, in particular within the walls of arteries that carry oxygen-containing blood to the organs such as your heart and brain. This plaque can increase in size to eventually lead to a “clogged” artery, or the plaque can “rupture,” which causes the blood near the ruptured plaque to clot. In the heart, these situations lead to chest pain (sometimes referred to as “angina”), shortness of breath, or a heart attack. In the head and neck, clogging or obstruction of an artery leads to stroke.
Why then does one’s cholesterol level not matter?
Cholesterol lipoprotein levels within the bloodstream are determined by two main factors. The first is the consumption of fats which alter levels of cholesterol metabolism—mainly saturated and trans-saturated fats. Saturated fats are found mainly within animal-based foods such as fatty meat, butter, and cheese. Trans-saturated fats are found within processed foods such as margarine. The other major determinant for cholesterol levels within an individual is from genetics, which determines how much cholesterol lipoproteins circulate mainly by how much cholesterol the liver is able to remove from the bloodstream.
Only 1 component of risk
Yet, we know from observational data that these levels are only one component of a patient’s overall risk of developing plaque within the arteries, also known as atherosclerosis. Some patients with what appears to be an advantageous cholesterol risk profile (low LDL, high HDL) still have heart attacks and strokes. On the other hand, we all know those people who have terrible lifestyle habits and poor cholesterol levels, but who still do not have any adverse effects. That is because neither dietary cholesterol changes nor genetic cholesterol metabolism alone can predict the predisposition of the artery wall to plaque formation, and it is the actual formation of plaque that really determines an individual patient’s risk of heart attack and stroke.
Thus, most physicians look for ways other than cholesterol levels alone to determine risk of plaque formation. A common method is with a “risk calculator,” a validated (proven by studies) method of estimating the individual risk of a patient using known risk factors for developing atherosclerosis. The most common risk calculator was updated in 2013 by the American College of Cardiology and American Heart Association, and it utilizes not only cholesterol levels, but also age, sex, ethnicity, blood pressure, smoking status, and diabetes to help better gauge individual risk of having a heart attack or stroke (cvriskcalculator.com).
When a patient’s risk is calculated to be over 7.5% (meaning the risk of having a heart attack or stroke is greater than 7.5% over the next 10 years), then most physicians will recommend that the patient consider starting a medication within the class known as statins to help lower the patient’s cholesterol level in order to alter his or her risk profile. Patients with what has been considered a normal cholesterol level can still be estimated to have a high enough risk based on other factors within the risk calculator that they would be told they need a statin! The issue is that, as a physician, I can only modify certain risk factors: I cannot change a patient’s age, sex, or ethnicity, but I can lower the cholesterol level—the basis of all plaque—and hopefully reduce the individual’s risk.
What does the scan show?
The second, more technological way, to determine risk is with an imaging study called a Coronary Calcium Scan. A Coronary Calcium Scan is a non-contrast, low-radiation, CT scan of the heart that takes about 30 seconds to acquire and costs about $50. The heart scan is then reviewed for evidence of calcium within the arteries of the heart; the plaque within the heart arteries calcifies or scars over time and is easily seen on these scans. Using a standardized software, the amount of calcified plaque is scored by an automated process. Coronary calcium scores range from zero (normal) to the low thousands. Because tens of thousands of patients with different scores have been followed for years, we know that a patient’s coronary calcium score directly correlates to risk over time. These scans are more predictive than risk calculators because they directly look for plaque formation within the artery walls. There is no test in the field of cardiology that can portend a better prognosis for a patient than a score of zero on a Coronary Calcium Scan. Coronary calcium scores over 300, on the other hand, are generally considered to be high-risk, and most physicians would agree that such a score warrants statin therapy.
It is an important point that a coronary calcium score of zero in most cases indicates a patient who does not need a statin medication, regardless of how high the measured cholesterol. Conversely, a high coronary calcium score indicates that a patient merits statin use, regardless of how low measured cholesterol levels are.
‘The book of your cardiac risk’
What to make of all of this? I find that many patients will tend to over-value their absolute cholesterol levels rather than the entirety of their risk profile. While these levels are important, they only tell one “chapter” in what is in essence “the book of your cardiac risk story.” Ultimately, you as the patient and I as the physician care about your risk of having a heart attack or stroke and care about taking steps to gauge that risk accurately. Those numbers on your cholesterol blood tests tell only a fraction of that risk. Whether through a risk calculator or through a Coronary Calcium Scan, risk assessment is an important step in helping to decide if your risk (not your cholesterol levels!) needs to be treated.
*Dr. Sullenberger of Capital Cardiology (capitalcardiology.com) is Board Certified in Internal Medicine, Cardiovascular Disease, and Advanced Heart Failure/Transplant Cardiology. He holds special certification in Echocardiography, Nuclear Cardiology, and CT Coronary Angiography and is a Fellow of the American College of Cardiology, Fellow of the American College of Physicians, and Fellow of the Society of Cardiovascular Computed Tomography. He is on staff at Albany Medical Center and St. Peters Hospital.