(CNN) -- More than 1 million people in the United States will have a heart attack this year. Most will occur in people with no symptoms.
With better prediction methods for cardiovascular disease, many of those could be prevented.
Two new studies in the Journal of the American Medical Association explore methods for helping doctors identify patients who are at greatest risk for heart problems. They are not definitive, and still point to unanswered questions, but represent a continued fight against the most common killer in the United States.
One new study found that coronary artery calcium was about six times better at predicting cardiovascular risk than a family history of coronary heart disease.
The heart's arteries can develop a substance called plaque in their walls. Cholesterol and other cells compose the plaque. Too much plaque buildup can trigger a heart attack.
A coronary calcium scan assesses whether there are any specks of calcium in the walls of the arteries. These calcifications are an early sign of plaque buildup.
There are about 28 million Americans in the "intermediate risk" group for cardiac events, which means that doctors aren't sure how to treat them or how to tell which of them is most likely to have a heart attack, said Dr. Joseph Yeboah, lead study author and cardiologist at Wake Forest Baptist Medical Center in Winston-Salem, North Carolina.
About 7,000 participants, 1,330 of whom had intermediate risk, were included in the study. Researchers compared six different markers of risk, and found that the calcium was superior to the rest.
The cost for the calcium test varies, but is usually about $200, Yeboah said.
"The cost issue should always be weighed against how much is society prepared to spend for a heart attack," he said.
The cost of treating a person with a heart attack could be more than a thousand times higher than the cost of the calcium test, he said. Additionally, many people die from their first heart attack.
"The current study in JAMA on coronary CT imaging should convince physicians and the public alike that if you are middle-aged, have some risk factors for heart disease, and want to greatly improve your knowledge of what your risk truly is, you should get a calcium score," said Dr. Arthur Agatston, a Miami cardiologist and author of the best-selling South Beach diet books, in an e-mail.
Agatston created the calcium score, first published in the Journal of the American College of Cardiology in 1991. He did not invent the scan to detect it, however, and does not profit from it.
Agatston, who was not involved in this study, praised the test in the 2011 CNN documentary "The Last Heart Attack."
"It is the single best predictor of who is headed for a heart attack and who is not, and is thus the best way to know who needs aggressive lifestyle and pharmacological intervention and who doesn't," he said this week.
Besides costs, one potential issue is the radiation involved in the test, which is about 1 millisievert. That's about one-third the amount of radiation Americans are exposed to from the environment in one year, according to the U.S. Food and Drug Administration. A CT scan to the head is 2 mSv.
Still, it's unclear what effect the radiation from the calcium test would have over time, especially since there has not been a set standard for the radiation involved in the test, Yeboah said. The FDA has not weighed in about this test.
Although many insurance companies do not cover the calcium test, some people pay out of pocket for it anyway, Yeboah said. It is unclear whether the test has helped those people specifically.
Former President Bill Clinton told CNN's Dr. Sanjay Gupta in "The Last Heart Attack" that he'd had one of these scans just months after leaving office, but doctors weren't sure what to do with the results since the technology was so new.
Clinton said he had "some calcium buildup around my heart that put me basically in the top third of risk," but did so well on the stress test that doctors said there wasn't any evidence of blockage.
In 2004, Clinton experienced tightness in his chest, which turned out to be a serious symptom. He underwent quadruple bypass surgery to restore blood flow to his heart. And in 2010, he needed another procedure: two stents to open a vein from his bypass surgery.
More research should be done to further evaluate the costs and benefits of this calcium test, Yeboah said.
A second new study evaluated the benefits of a different kind of screening test: carotid intimal medial thickness. This involves an ultrasound measurement of the thickness of the carotid artery.
The carotid artery is a blood vessel leading to the brain, delivering blood to the brain and face. The thickness of the walls is thought to be a risk factor for cardiac events such as heart attack.
Researchers conducted a meta-analysis of 14 different studies worldwide, encompassing about 46,000 participants. Study authors wrote that their results suggest that the added value of conducting a carotid intimal medial thickness test was small and "unlikely to be of clinical importance."
Their results pertain to a 10-year risk outlook, meaning the study measured the likelihood of a cardiac event within 10 years of the test. But the authors wrote that additional research could find this test may be useful for 20- or 30-year outlooks.
This analysis has limitations, however -- there may be inconsistencies in how cardiac events were determined across the different studies, and there was variation in the use of cholesterol-lowering drugs called statins across the different groups.
A risk assessment based on factors such as age, gender and blood pressure is about as good at predicting cardiovascular disease likelihood as carotid intimal medial thickness, said study co-author Dr. Michiel Bots, of the Julius Center for Health Sciences and Primary Care of the University Medical Center Utrecht in the Netherlands.
While the arterial wall thickness measurement may predict the occurrence of disease, it does not help doctors decide whether a patient should be treated with lipid-lowering or blood-pressure-lowering drugs, Bots said.
But the carotid ultrasound test is inexpensive, and can be easily and safely performed in a doctor's office, Agatston said.
The test can also image atherosclerotic plaques, although this particular study did not separately analyze the presence of plaques. Plaque in the carotid artery is a warning sign for risk of heart attack and stroke.
For prediction and management of cardiac risk in some patients, Agatston believes there is a place for this test.