The New York Times today 6.29.08 published a long piece (NYTimes on Cardiac CTA) on the merits and overpromising of the cardiac CT angiogram (cardiac CTA), a chest CT with intravenous contrast that allows images of the coronary arteries themselves while the heart is beating. The images can demonstrate plaque or damaged areas in the arterial walls, whether calcified or not. Many cardiologists in the US are promoting this test as a routine study for risk evaluation. This article (http://www.nytimes.com/2008/06/29/business/29scan.html?pagewanted=all#) argues “not so fast.”
Many of my patients have had cardiac calcium scores upon my recommendation, which is also a CT of the chest to look at the coronary arteries. But there are important differences.
- The cardiac CTA requires an intravenous injection of contrast dye as well as a beta-blocker drug to slow the heart rate; the cardiac calcium score requires neither.
- The cardiac CTA, according to the NY Times article, has a substantial radiation exposure, which they quoted as about 21 mSv. By contrast, the American College of Radiology and the Radiological Society of North America, on their website www.radiologyinfo.org, indicate that the cardiac calcium score requires only 2 mSv, while a standard chest CT requires 8 mSv and a routine chest X-ray about 0.1 mSv. Clearly the cardiac CTA is a substantial radiation exposure and the cardiac calcium score is not.
The other major difference is logical. I find it extraordinarily helpful to get the low-radiation cardiac calcium score as a technical check on the adequacy of the standard risk factors (age, gender, blood pressure, cholesterol and smoking) as to whether you are or are not a low-risk person.
Those risk factors do a good job in identifying who is high risk, and who therefore must be treated aggressively with life-style changes and medication. If the numbers say you are high risk, we are encouraged but not dissuaded from aggressive treatment because of a low cardiac calcium score.
But we also know that among the apparently low-risk people lurk occasional folk who are quite high risk and who should also be treated quite aggressively. The cardiac calcium score has proven immensely helpful in identifying such people. (See the earlier article in this blog on the cardiac calcium score in apparently low-risk women.)
Even in our small practice at OHC we have a meaningful list of members who met all the criteria as low-risk for cardiac disease, but whose cardiac calcium score was quite high. In that event, the high cardiac calcium score has been shown to be more accurate and those members are being treated much more actively to minimize all the cardiac risk factors we can.
To summarize, the cardiac calcium score is a useful method to validate or gainsay the standard risk-factor analysis for level of cardiac risk, and is low-cost both in money and radiation. The cardiac CTA is not an appropriate screening test, according to the NY Times evaluation as well as mine, but has a wonderful role to play in many special cases, which I hope will not apply to any of you.
