CORONARY ARTERY DISEASE SCREENING

  Diabetes is arguably THE major risk factor for developing coronary artery disease (CAD) from atherosclerosis. Coronary artery disease results from blockage of the coronary blood vessels with deposits of cholesterol, fats and calcium in the walls of these blood vessels. Blocked coronary arteries impair blood flow to the heart and lead to heart attacks, heart failure and death. It’s important to understand that once well established, there is no data that says that CAD is fully reversible. Certainly once heart muscle cells die, they are lost forever. The damaged area of the heart will never regenerate. If the damage is severe enough or extensive enough, it will affect the heart’s ability to pump blood, and the patient will be left permanently crippled.

Why, then, shouldn’t your doctor ROUTINELY screen for CAD in his or her patients with diabetes? The answer to this question is that until recently we have had very few tests that were good screening tools to use for detecting early CAD. In fact, there are really just two.

The first is the traditional Graded Exercise Treadmill (GXT) test. GXTs have been done for more than 50 years, and we have a lot of experience with them. They are good at revealing ESTABLISHED CAD in patients. If a GXT is positive, its ability to correctly predict significant CAD is high. Unfortunately, however, if it is negative, it can be wrong (this is called a “false negative” or another term is “sensitivity”). That means that some people with significant CAD are inadvertently missed when the GXT is read as being negative. What is of more concern however, is that GXTs have NO reliability in detecting early CAD (the whole purpose of a screening test here is to detect early CAD, when it can be treated aggressively so to prevent the development of established or more severe CAD). Typically, GXTs are only used when patients have established symptoms that suggest CAD (The symptoms typically associated with CAD are mid-chest pressure or a sensation of tightness or heaviness in the chest. The discomfort classically is described as, “An elephant is sitting on my chest.” The discomfort can radiate down the left arm, go to the neck or back. Usually there is some associated shortness of breath. dizziness, sweating or palpitations also.) Under those circumstances, a GXT can be a pretty good test to pick up signs of a real problem underlying the symptoms.

The second tool we now have to screen for developing atherosclerosis is coronary artery calcium (CAC) scoring. This is a screening procedure that can be done with electron beam (EB) equipment or computed tomography (CT). Electron beam CAC scoring is an FDA-approved procedure and the “gold standard” for measuring coronary calcification and associated atherosclerosis. It can pick up atherosclerosis in its very early stages, long before a coronary angiogram, exercise treadmill or nuclear medicine heart study detects a problem. Unfortunately, General Electric, the largest manufacturer of CT scanners in the U.S., bought out the primary EB equipment manufacturerer, and is purposely killing that technology to eliminate competition for their CT scanning equipment.  EB scanning centers are becomming increasingly hard to find.  CT techniques are now more readily available, but arguably do not produce the high quality images seen with EB equipment. The only CT scanners that are really very good for this type of screening are dual source CT scanners that double the information gained from the study in the same time window.  The study itself takes about 15 minutes to complete. No injections are necessary, and no medication is given to complete the study.  This study does, however, expose the patient to radiation (A single chest X-ray exposes an individual to the equivalent radiation of living on earth for 2 1/2 days.  The radiation of this type of CT exposes an individual to the equivalent radiation of 150 to 500 chest X-rays.)  Because insurance companies consider this a screening procedure, they typically will not reimburse for it as a medical expense.

If you have a coronary artery calcium (CAC) score screening, what might it show? There are several possibilities. It could be completely negative. That means there are no calcium deposits in your coronary arteries, and by implication it is VERY likely that you do NOT have any significant problems with atherosclerosis leading to coronary artery disease.

Another possibility is that you have a relatively high CAC score. This means that it is VERY LIKELY that you DO have areas of significant blockage in your coronary arteries and you may be prone to a heart attack. This result would lead us to pursue further testing and include referral to a cardiologist for consultation. The good news here at least is that we may still be able to prevent a major problem before it actually occurs.

And the third possibility is that your CAC score indicates that you have some developing atherosclerosis but probably not of the degree that it will cause any symptoms. This is precisely the information that we need to know to give you the EARLY WARNING SIGN that something bad is going on and that it’s time to change things so that the process does not continue. Some types of coronary atherosclerosis appear to be reversible (so-called “soft” plaques). However, when calcium deposits occur in the vessel walls, this (hard plaque) does not appear to be correctable. Nonetheless, if lifestyle changes and medications (as necessary) halt the progression of atherosclerosis and these calcifications, we will have achieved the major goal of early screening. Serial CAC scoring can be done every few years and will provide us with the information we need to know to determine if our interventions are working.

Presently, I do believe that if you have diabetes, are under 65 years of age, and particularly if you have hypertension and/or elevated cholesterol, that you SHOULD consider getting a CAC score done. I would recommend you do this with an electron beam technology machine if one is available.  Otherwise a dual source CT scanner will work, but at the cost of some radiation exposure.  This will give you a specific risk score for having coronary artery disease. This can be used as a guide to help motivate you to better control risk factors for atherosclerosis and prevent problems before they occur.

Once a diagnosis of CAD is made, management will vary depending upon its perceived severity. If the patient is symptomatic, typically a GXT will be done to identify whether a serious blockage exists. If the GXT is positive, then the patient will be referred for heart catheterization with either the placement of stents to dilate the narrowed vessels and hold them open, or referral for heart surgery to replace the diseased vessels. If a screening test such as a CAC shows some atherosclerosis but the disease is asymptomatic, then aggressive medical therapy is indicated. This means controlling the diabetes as well as possible, aggressively lowering cholesterol levels, keeping the blood pressure under tight control, and lifestyle modifications such as weight loss and regular exercise. These interventions, particularly when used in combination, can show dramatic effects to reduce and probably even reverse the atherosclerotic process. The result is avoiding a heart attack or stroke and extending you life.

Revised 8/08

 

©Ted A. Tobey, M.D., Inc. ~ All Rights Reserved