October 2014

Knowing the Score: Cardiologists Are Taking Advantage of Coronary Artery Calcium Scoring’s Benefits
By Keith Loria
Radiology Today
Vol. 15 No. 10 P. 20

Cardiologists increasingly view coronary artery calcium (CAC) scoring obtained with a noncontrast CT scan of the heart in selected patients as one of the best available tests beyond the usual risk factors to refine cardiac risk assessment.

CAC offers a noninvasive measure of subclinical coronary atherosclerosis and adds incremental absolute risk information to traditional risk factors. It helps physicians further refine risk estimates for heart attacks and coronary heart disease in asymptomatic patients. Patients with higher scores may require more intensive lifestyle therapies as well as drugs such as statins and aspirin.

Amit Khera, MD, director of the preventive cardiology program at the University of Texas (UT) Southwestern Medical Center, says CAC is a screening tool but it is best used for patients who are at intermediate risk based on other risk factors and who are deciding whether to undergo therapy.

“Specifically, if they have some risk factors but are still not sure if they warrant treatment or can tolerate medications, the results of the CAC scan can make a difference in determining if they really need treatment,” Khera says. “There are some patients with very strong family histories of heart disease but few or no risk factors where this test can also be valuable to help more accurately determine their coronary heart disease risk.”

Matthew Budoff, MD, of Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, California, says he uses the CAC scan in preventive cardiology to assess if people have early heart disease so they can decide on statin or aspirin use and/or other lifestyle and medication changes.

“It is widely recommended in the low-intermediate and intermediate risk groups, which means it should be used for persons with probably at least one risk factor for heart disease,” Budoff says. He adds that the test is recommended for determining underlying risks in the prevention guidelines from the American College of Cardiology and American Heart Association, which were published in November 2013 in The Journal of the American College of Cardiology and Circulation.

Daniel Ocazionez-Trujillo, MD, an assistant professor in the department of diagnostic and interventional imaging at UT Health Science Center at Houston Medical School, says CAC scoring helps the referring physician to better understand the relative risk of an asymptomatic patient with intermediate risk factors for coronary artery disease (CAD) having a heart attack in the future.

“The physician can then use that information to decide which strategies should be adopted to reduce the risks,” he says. “This may include changes in diet, exercise, hypertension control, diabetes management, smoking cessation, and blood cholesterol level maintenance. The CAC score is of no benefit to someone who has already had a heart attack, coronary bypass surgery, or a coronary artery stent. These events already indicate the patient is at high risk.”

According to Ocazionez-Trujillo, the extent of CAD is graded according to the CAC score. A score of 0 implies no evidence of CAD. A CAC score of one to 10 implies minimal evidence of CAD, while 11 to 100 is rated as mild, 101 to 400 is moderate, and greater than 400 is extensive evidence of disease.

Risk Factors
According to experts, the chief risk factors that call for a CAC are high cholesterol and a family history of heart disease. Biana Trost, MD, the director of cardiac CT at North Shore University Hospital in Manhasset, New York, part of the 17-hospital North Shore-LIJ Health System, says it is the best test to date to risk stratifying patients for CAD.

“Cardiac risk assessment has traditionally been based on conventional risk factors. The shortcomings of this approach are all too often highlighted by major cardiac events occurring in presumably low-risk people,” Trost says. “Consequently, there has been a focus on markers of subclinical atherosclerosis that may be utilized for risk assessment of individuals, rather than extrapolating from risk factors that reflect trends in large groups of patients in epidemiologic studies. Coronary artery calcium score is the most powerful of these subclinical markers.”

Cardiologist Sheldon Litwin, MD, a cardiac imaging expert at Georgia Regents Medical Center in Augusta, Georgia, says that many patients have plaque present, but it is not severe enough to cause any problems. The CAC score establishes the need for further therapy and helps prevent progression.

“Calcium scoring is used mostly on middle-aged patients with some heart risk factors. Those who have extensive risk factors might likely be treated without testing. It’s the patients with one or two risk factors that are usually screened,” Litwin says. “I am a proponent for screening everyone for atherosclerosis—beginning at age 45 for men and 55 for women. Because atherosclerosis is so common, even without obvious risk factors we frequently see it. It is the most common cause of death in both women and men, and it usually doesn’t cause any symptoms until there is a real problem. So by the time people become symptomatic, they usually have a very serious disease.”

High blood pressure, diabetes, smoking, and high cholesterol are the most significant risk factors. Some of the less severe culprits include obesity, being male, increasing age, family history, and a sedentary lifestyle.

According to the prevention guidelines, “The Work Group notes … the contention that measuring CAC is likely to be the most useful of the current approaches to improving risk assessment among individuals found to be at intermediate risk after formal risk assessment.”

“In health care, physicians screen for lots of other diseases with tests that are imperfect, and in this case we have a test that has almost perfect predictive value,” Litwin says. “The CAC scan is 95% sensitive for picking up disease. Again, it’s cheap, easy, and helps us to determine what course of therapy to take when needed. I would argue that the CAC screening is better than a PSA [prostate-specific antigen], a mammogram, or even a pap smear. In fact, with no false-positives and a very clear picture of the arteries, the calcium score is really one of a kind in screenings.”
Budoff says that while there are still some physicians who like to make headlines by being naysayers, there is no debate about CAC’s importance by people who understand the technology. 

“If you see what they say, it is not based in science but emotion or personal ideas,” Budoff says. “There are many other similar statements, and it is recommended at a IIa level for persons with diabetes [older than age 40] and for patients at intermediate risk, and at a IIb level for low-intermediate risk.”
In its preventive cardiology program, UT Southwestern Medical Center has found it to be a very useful test.

“We have been able to detect patients with strong family histories who are at higher risk as well as reassuring others with such histories,” Khera says. “Some patients who are recommended [to start taking] medications have been able to avoid them where they have had borderline indications or have had side effects, and others have been placed on intensive preventive interventions when high scores were detected.”

Trost says while CAC scanning is effective in predicting risk, to date there is little objective data to indicate that aggressive treatment of patients with subclinical atherosclerosis defined by CAC reduces subsequent cardiac events. “We are in agreement that these patients should be on medical therapy but how aggressive we need to be is still in question,” she says. “We need a randomized trial assessing the effects of CAC scanning and different treatment strategies on patient outcomes.

“Also, while less common, some patients with only noncalcified plaque may develop an acute coronary syndrome, ie, heart attack. Three to 7% of patients who have a calcium score of 0 still have noncalcified plaque, which can only be visualized with a full cardiac CT scan with contrast injection. Contrast cardiac CT scans in the absence of symptoms are still not recommended for screening purposes.”

Improving Equipment
The CT scanning technology is constantly changing, and the number of slices is less important for the CAC scan than it is for coronary CT angiography and many other CT imaging tests. New technologies and protocols that can lower radiation remain important considerations.

The Los Angeles Biomedical Research Institute utilizes a 64-slice CT scanner, which Budoff says was state of the art when it was purchased and still has a lower radiation profile than the newer scanners with more detectors.

“I am not interested in adding detectors and adding radiation to my patients,” he says. “We have excellent diagnostic accuracy with our scanner. As a matter of fact, my [ACCURACY trial] paper [J Am Coll Cardiol. 2008;52(21):1724-1732] is still the best diagnostic accuracy that CT scanners have ever hit, better than the new CORE 320 paper using a Toshiba 320-slice scanner published recently [Eur Heart J. 2014;35(17):1120-1130].”

North Shore University Hospital uses a newer-generation, 640-slice CT scanner, which Trost says has superb resolution and an ultrafast scan time, thus minimizing motion and radiation exposure.

“Some patients who have indications for starting statin therapy are at times hesitant to begin taking medications. If they have a positive CAC, then they will be more likely to start preventative therapy and adhere to the regimen,” Trost says. “Some studies actually showed better statin adherence and more weight loss in those patients who visualized that they have calcium deposits in their arteries.”
At Georgia Regents Medical Center, physicians currently use a 64-slice CT scanner to get reasonable reproducibility and adequate image quality. “The CT is the only way to measure for calcium deposits in the arteries,” Litwin says. “It’s a 10-second test with a single breath hold. It’s fast, simple, and safe.”

Patient Selection
Currently, the American College of Cardiology and American Heart Association recommend a CAC score in asymptomatic individuals who are at intermediate risk of developing CAD. The organizations’ joint guidelines also recommend this test to individuals who are at low risk of developing CAD but who have a family history of premature coronary disease. Lastly, the joint recommendations advise this test for asymptomatic adults with diabetes who are aged 40 and older.

It’s important that patients know CAC is a screening test and is not useful if they already have a stent, bypass, or known CAD, but experts say the test is very useful in determining if someone has heart disease. In patients who are on the fence about treatment, a score of 0 may suggest that drugs are not necessary at that time.

“It is important to ensure that they realize that it is not for everyone,” Khera says.
“There is some radiation involved so patients who are at very low risk or who are already on treatments where the results of the scan would not make a difference should not undergo this test. I also think it is important to review the results with a practitioner who has more experience in interpreting the scan results. I have seen both over- and undertreatment of scan results, and the data are only as good as they are understood and acted upon appropriately.”

Litwin says he’s had several success stories where patients have stopped smoking, lost weight, or made other significant lifestyle improvements after seeing the evidence.

“I’ve also discovered severe blockages that would not have been known about otherwise, and of course, some people have no evidence of calcium,” he says. “Therefore a calcium scan can bring good news that allows the physician to de-escalate treatment. A patient with a low calcium score may be taken off statins or other medications.

“Like most other diseases, early detection means better results,” Litwin adds. “When we find early warning signs of future heart disease, we have more time to implement corrective actions with patients. We can more aggressively and urgently provide pharmacologic treatments and recommend lifestyle improvements in order to hinder the disease progression. And sometimes, showing clear evidence that a problem exists will convince patients to stay faithful in taking their medications.”

Budoff offers a more emphatic view: “If I were a patient, I would demand it. Bill Clinton got a scan after he left the White House, had an astronomical score, and ended up needing bypass surgery within a year. [George W.] Bush [who received the scan while President] had a low score and was put on statin therapy. Only many years later did he require a stent placed, so he deferred his heart disease by over 10 years by knowing the score.”

— Keith Loria is freelance writer based in Oakton, Virginia.