In my last post, I discussed the untimely death of Wake Forest Basketball coach Skip Prosser and the relationship of vulnerable plaque to sudden cardiac death and myocardial infarction. Only 14% of heart attacks are caused by a fixed artery blockage of 70% or greater. For 70% of heart attack patients, the blockage in the coronary artery is less than 50% (non-obstructive). A non-obstructive plaque causes no symptoms and usually would not produce a positive stress test. Since the 50% blockage typically causes no symptoms for 70% of myocardial infarction patients, the heart attack or sudden death is their first symptom.
How do we overcome this
We try to overcome this by using the Framingham risk score, assigning points for risk factors including HDL cholesterol, systolic blood pressure, age, total cholesterol, and smoking status. This is useful and helps to identify some high-risk patients, but still, we frequently miss people who go on to infarction. Our current system, based on risk scores, stress tests, coronary angiography, bypasses, and stents, has simply failed to identify too many patients with substantial risk.
Since the vast majority of heart attacks are not occurring at sites of fixed stenosis but rather at the site of a vulnerable plaque rupture, the question becomes how do we identify these high-risk patients and treat them aggressively. Patients who have established atherosclerotic arterial disease at any site should be treated as if they have coronary artery disease. Arterial disease is a diffuse process and any blockage anywhere indicates that most of the arteries are involved with atherosclerotic plaque. There is a dramatic correlation between type 2 diabetes and arterial disease. The same holds true for patients with kidney damage. Both of these patient classes should be treated with the same level of aggression as the patient with established vascular disease. Patients with a high Framingham Risk Score should be aggressively managed. The risk factor management targets for these patients are lower than those we normally are aiming for. The blood pressure should be less than 130 systolic (top number). The LDL cholesterol should be less than 70. The hemoglobin A1c should be under 6.5.
There are many patients at risk who fit none of these categories and currently, they are not being treated aggressively enough. Patients with strong family histories but low to intermediate risk scores are an example. Some people have intermediate risk scores but in actuality are very high risk—how do we identify them? Since the fundamental risk is the extent of plaque in the artery—specifically the amount of unstable plaque—the ideal way to identify high-risk patients would be to develop a methodology that allows us to identify patients with unstable plaque. The higher the amount of unstable plaque, the higher the risk.
The gold standard for directly examining the amount of plaque in the artery is coronary catheterization using intravascular ultrasound technology. This is an invasive technique that carries some risk and substantial expense. It is not routinely used even in patients having a heart catheterization. It is impractical for intermediate risk screening.
More studies are now available to help us understand the role of coronary artery calcium scoring. The American College of Cardiology and the American Heart Association have just published an expert consensus document on this technology. Atherosclerotic plaques are dynamic deposits in the arterial wall that go through progressive and predictable stages. Plaque “instability and rupture can be followed by calcification, perhaps to provide stability to an unstable plaque.” The authors state, “Radiographically detected coronary calcium can provide an estimate of total coronary plaque burden.” The authors go on to provide a further rationale for the use of this technology:
“Patients who have calcified plaque are also more likely to have non-calcified or ‘soft-plaque’ that is prone to rupture and acute coronary thrombosis… coronary artery calcium scoring may be able to globally define a patient’s CHD (coronary heart disease) event risk by virtue of its strong association with total coronary atherosclerotic disease burden, as shown by correlation with pathologic specimens. Perhaps even more convincing is the following:
‘Pathology studies have shown that the extent of coronary calcium within plaques tends to be related to healed plaque ruptures.’ We cannot identify the vulnerable plaque but we can quantify ruptured plaque history which tells us his risk for future plaque rupture and thrombotic obstruction. We cannot identify the vulnerable plaque, but we can identify the ‘vulnerable patient’.”
Even more impressive, when we combine the Framingham Risk Score and the Coronary Calcium Score, we have a system that is able to predict coronary risk in a very robust fashion. Any patient with a coronary calcium score over 100 should be considered to have coronary disease and should have risk factors reduced to those same aggressive targets.
Women are a special case here and for them, this technology may be even more important. Women are less likely to form focal narrowings in the arteries and so they are even more likely to have an infarction with a non-obstructive plaque (narrowing less than 50%). Women tend to deposit their plaque in a concentric, symmetrical fashion up and down the artery. In fact, women with recurrent chest pain and a normal heart catheterization still have a 20% six-year risk of sudden death, myocardial infarction, stroke, or congestive heart failure (WISE study). For this reason, I would not consider any woman’s cardiac workup to be complete until she had a calcium score. Too many women are told they have nothing to worry about after a normal heart catheterization. The woman with recurrent chest pain is still often high risk and in need of aggressive risk-factor management.
Here is the really amazing part. In spite of the extensive literature on the new science of risk assessment and the importance of vulnerable plaque, almost no insurance companies pay for the calcium score. In our group practice, we offer this test for $249.00. When you consider the information to be gained from the study, that seems very reasonable. This technology should be much more widely applied to identify high-risk patients and we should press the payors to allow this test in intermediate-risk patients.