THE CLINIC: An In-Depth Look at Determining Coronary Fitness

Thu, 6 Sept. 2012 - 12:34 a.m. MT
Credit: ARA Staff - American Running Association

QUESTION:

I'm 52, 5’ 10“, and 150 lbs. In 2001 I had a CT scan to check for plaque build-up on my heart, and my cardiac calcium (CAC) score was 14. In 2008 my doctor insisted I

repeat it and now it's 114. My lipid profile is excellent, though, with a cholesterol of 179, HDL 93, LDL 72, and triglycerides 71. I run three times a week at fairly high intensity (my HR often reaches 170 or higher). I bike twice a week for about 45 minutes aTnd lift weights regularly. I also race, I have no symptoms, and my only risk factor, as far as I can see, is my parents' cardiac history. My mom and dad had coronary heart disease, which they acquired fairly early in life, but neither exercised or ate well. Both smoked and one was an alcoholic.

 

My cardiologist, who did not think a statin was necessary, gave me a stress test and advised that I take a baby aspirin daily. The stress test went well (10:50 at 18 METs) and the only finding was mild mitral and tricuspid regurgitation at rest and post-exercise. My blood pressure is normal, and I watch my sodium intake. My diet is mainly Mediterranean, with 8 to 12 ounces of wine daily. Since this recent CAC score I've added (almost every day) either fish or fish oil in 2-gram amounts. 

 

Now that I understand a little more about coronary heart disease, was there

any point in getting that repeat CAC, with all the attendant radiation? I had plaque then and some more now. From what I can see that's all it tells me. Does it matter whether it's 14 or 114 or 214? 

 

Also, I wonder whether the stress test was of  value. Polar states their monitors are 98 percent accurate. So my max rate should be above 180 just looking at my numbers from

training. The stress test was based on the 220 minus my age formula, which I

questioned at the time of the exam. I only reached 169. It was a very hard

effort but it was not natural, that is, I think I could have gone on but the

limiting factor was the extreme grade. I felt that my legs might give out

and I'd fall off. Is this a common complaint of someone like me who achieves

higher heart rates with pace over longer periods? Do other protocols

manipulate variables more familiar to the athlete (treadmill testing using

faster paces rather than extreme grades). Even if 185 is my max heart rate, is achieving 169 adequate? Or was the whole idea of a test pointless because I've given myself a stress test three times a  week for 20 years? 

 

Two other quick questions, on my supplements: Is taking aspirin helpful? What about the two grams daily of fish oil? Are there any risks that might offset the cardiac benefits? I just found out on a brain MRI (they were looking for an acoustic neuroma for complaint of tinnitus) that I have a venous angioma (with no cavernoma/AVM). Does that change the picture with regard to the use of aspirin and omega-3 supplements?

 

David Whittier

Reseda, CA

 

ANSWER:

First, you are to be commended for your healthy lifestyle.

 

With regard to your CAC question, I note that CT scanning has lots of controversy associated with it. I think that most reasonable people, as well as statements from professional organizations, would tell you that there was no point in getting either of your CT scans. Risk assessment for CAD needs to start somewhere and the recommended

starting point is clinical assessment. Most U.S. guidelines/position

statements recommend starting with the Framingham risk score. You can

Google “Framingham risk score” and plug in your numbers. The different web sites may give you different values because some scores are based on risk of a hard cardiac event (death or MI) and others are based on risk of all cardiac events (which includes development of angina as an endpoint, as well as the hard endpoints). 

 

At any rate, no matter which score you use, assuming a systolic BP of 120 mmHg, your risk score comes out to be about 2 percent. Remember that this is the risk over 10 years, so your annual risk would be about 0.2 percent. This places you into the "low-risk" category (usually defined as 10-year risk below 10 percent). Nobody, even the CT zealots, are advocating CT scanning for low-risk patients. The possible value of CT

scanning in intermediate or high-risk people is more controversial (a paper

by Phil Greenland suggested some additional risk stratification was possible

with CAC scoring in clinically intermediate-risk people). 

 

There are always caveats. The Framingham risk score does not address family history. But unless you have a very strong family history (parents, aunts, or uncles with CAD onset before age 50 or 60), this is unlikely to substantially alter your risk. Also,

"low-risk" never means zero percent risk. However, your risk is

so low on clinical grounds alone that it is extremely unlikely that any test in

people like yourself will reveal an abnormality that will alter your

risk--and it is certainly not cost-effective for society to apply screening tests

in people like you.  Just about all middle-aged men will have some

plaque, but the risk of rupture is very low. The increase in your score

from 14 to 114 over 7 years might be real, but there is substantial

variability in between-scan measurements. And even then, a score of 114 is

still pretty low. 

 

Having said all of this, the radiation exposure from CT calcium scanning is low. No one knows what the minimum radiation exposure risk is, but as far as is known, it is not likely that the amount of radiation exposure from two CAC scans is clinically meaningful. Just don't let anyone talk you into a CT coronary angiogram, where the radiation exposure is

significantly higher than it is for simple calcium scoring.

 

With regard to the stress test, I also see little value in it in your case, but

since you did it there is some useful information. The single strongest

prognostic value from a stress test is exercise duration, even more useful

from a prognostic standpoint than the echo imaging data. Your exercise

duration of 18 METs means that you are just about immortal. You will not

meet many people your age who can exercise to that high a workload. The

formula for predicting maximal heart rate of 220 minus your age works reasonably well

for populations but is not very accurate for an individual because of the

tremendous amount of variability around the regression line. Applying this

formulas reveals your predicted heart rate is 220 - 50 = 170. So your peak

heart rate of 169 by my calculation is 100 percent of that predicted. 

 

The more important issue is workload achieved--not maximum heart rate. So I wouldn't worry about any of this. From what you describe I suspect that the treadmill protocol that you performed consisted of skipping the first few stages of the Bruce protocol. Based on this assumption you were probably exercising at about a 20 percent grade in your final stage of exercise. As you note this is a very steep grade and difficult for most runners to

handle unless you have been doing interval hill training.  Predictably you

were more limited by quadriceps fatigue than general body fatigue. You

likely could have achieved a higher workload by customizing the treadmill

protocol to increase speed more than grade, but from a practical standpoint this

is not really necessary. The information from this test indicates that you

are in excellent physical shape and the prognostic information is very

reassuring.

 

In the Physicians Health Study, low-dose aspirin lowered MI risk. Entry age for this study was 35 years but as I recall a benefit was not seen until men were at least 50 years old. So based on this study you could make an argument for using aspirin. However, the American Heart Association does not recommend aspirin for people whose Framingham risk score is less than 10 percent over 10 years. Once again, your risk for MI is so low that the number of people with your characteristics whom you would have to treat with aspirin to prevent a single heart attack over a several-year period would be several hundred, if not thousands. I am not aware of any data that aspirin lowers stroke risk for men in the primary prevention setting (there is data for women).  

 

Aspirin is widely recommended because it is cheap and usually innocuous but there is a slight increased bleeding risk.  A couple of years ago the aspirin manufacturers went to the FDA to try to receive an indication for approval for cardiovascular disease prevention in the general population but the FDA turned down this request. 

 

And finally, fish oil seems to be the new "vitamin" for prevention of coronary artery disease (vitamin E was the wonder preparation a decade ago but now is in disfavor). Fish oil lowers triglycerides, has an anti-clotting effect, and may (although the literature

is more controversial) lower arrhythmia risk. However, there is very little evidence

that it is of any value in the general population. Eating fish is healthy

but this does not translate into taking fish oil supplements. 

 

I would continue your healthy Mediterranean eating, including

fish in the diet, low sodium, and moderate alcohol consumption. Keep up the exercise

program. I would not recommend either aspirin or fish oil supplements at

this time, not because these products represent any significant risk for you

(I doubt that your venous angioma represents a significant bleeding risk)

but because you are at such low risk on the basis of your lifestyle alone

that it is highly unlikely that aspirin or fish oil supplements will do you

any good at this time (unless your parents age of onset for CAD was very

young or there is additional worrisome family history in second degree

relatives). 

 

I would also avoid any additional cardiac testing for the next several years unless a good clinical reason emerges to indicate testing is warranted. It's important to remember that the single most important risk factor is age, more important than any of the other factors that receive so much more attention. Your risk increases as you get older, and somewhere in the future you may cross a threshold where your risk will be high enough

such that aspirin or some other preventive measure might be warranted.  But you are clearly not there at this time.  For what it's worth, our risk profiles are pretty

similar--yours is slightly more favorable than mine--and I have never had

any cardiac testing and don't take any medications or supplements.  

 

Todd Miller, MD

Rochester, MN


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(RUNNING & FITNEWS® November/ December 2008 • Volume 26, Number 6)




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