Sunday, January 29, 2012

Back to basics: Coronary calcium

Back to basics: Coronary calcium

After having my attentions pulled a thousand different directions these past 6 months, with the release of Wheat Belly and all the wonderful media attention it has attracted, I’ve decided to pick up here with a series of discussions about the fundamental issues important to the Track Your Plaque program and prevention and reversal of coronary atherosclerotic plaque.

I fear the discussions at times have drifted off into the exotic. This is great because this is how we learn new lessons, but we can never lose sight of the basics, else we risk losing control over this disease.

Imagine you’ve got a beautiful new car. You wax it, gap the spark plugs, rotate the tires, etc. and it looks brand-new, just like it came off the dealer’s lot. 50,000 miles pass, however, and you realize you’ve forgotten to change the oil. Ooops! In other words, no matter how meticulous the attention to transmission, tires, and paint job, neglect of the most basic responsibility can ruin the whole thing. We can’t let that happen with heart health.

If we propose to reverse coronary atherosclerotic plaque, we’ve got to have something to measure. First, it tells us whether we have atherosclerotic plaque in the first place, the stuff that accumulates and blocks flow and causes anginal chest pains, and ruptures like a little volcano and causes heart attacks. Second, it gives us something to track over the years to know whether plaque has grown, stopped growing, or been reduced. Without such a measure, you will be driving without a speedometer or odometer, just guessing whether or not you’ve gotten to your destination.

Of course, the conventional approach to heart disease and heart attack is not to track atherosclerotic plaque in your coronary arteries, but to track some distant “risk factor” for atherosclerotic plaque, especially LDL cholesterol. But LDL cholesterol is flawed at several levels. First, it is calculated, not measured. The nearly 50-year old Friedewald equation used to calculate LDL cholesterol is based on several flawed assumptions, yielding a value that can be 20, 30, or 50% inaccurate as a rule, only occasionally generating a value close to the real value. (No point in publicizing this problem, of course: Why compromise a $27 billion annual cash cow?) It also ignores the effect of diet. (No, cutting fat does not reduce LDL for real, only the calculated value. Cutting carbohydrates, especially wheat–”healthy whole grains”–slashes measured LDL values like NMR LDL particle number and apoprotein B.)

But all risk factors are, at best, snapshots of the situation at that moment in time. They change from day to day, week to week, month to month, year to year. If you do something dramatic in health, like lose 50 pounds, you can substantially change your risk factors values, like LDL cholesterol and HDL cholesterol. But you may not modify the amount of atherosclerotic plaque in your heart’s arteries.

Measuring the amount of atherosclerotic plaque in your heart’s arteries is, in effect, a cumulative expression of the effects of risk factors up until the moment of measurement.

There are several stumbling blocks, however, in the concept of measuring coronary atherosclerotic plaque. We cannot measure all the unique components of plaque, such as fibrous tissue like collagen, or degradative enzymes like collagenases, or inflammatory proteins like matrix metalloproteinase, or the debris of hemorrhage and inflammation. We struggle to contemporaneously mix in measures of bloodborne inflammation, coagulation and viscosity, and physiological phenomena of the artery itself, like endothelial dysfunction, medial (muscle) tone, and adventitial fat.

So we are left with semi-static measures of total coronary atherosclerotic plaque like coronary calcium, obtainable via CT heart scans as a calcium “score.” No, it is not perfect. It does not reflect that moment’s blood viscosity, it does not reflect the inflammatory status of the one nasty plaque in the mid-left anterior descending, nor does it reflect the irritating sheer effects of a blood pressure of 150/95.

But it’s the best we’ve got.

If anyone has something better, I invite you to speak up. Carotid ultrasound, c-reactive protein, ankle-brachial index, stress nuclear studies, myoglobin, skin cholesterol, KIF6 genotype . . . none of them approach the value, the insight, the trackability of actually measuring coronary atherosclerotic plaque. And the only method we’ve got to gauge coronary atherosclerotic plaque that is non-invasive and available in 2012? Yup, a good old CT heart scan calcium score.


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