Many people have had a heart attack and don’t know it. A study of older people in Iceland finds that nearly twice as many had experienced a silent heart attack as had suffered one with all the medical bells and whistles. MRI scans revealed the hidden heart attacks better than standard testing by electrocardiography, or EKG, scientists report in the Sept. 5 Journal of the American Medical Association.
It’s helpful to know who has had a heart attack because for the long term such people are treated more aggressively with medication, says study coauthor Andrew Arai, a cardiologist at the National Heart, Lung, and Blood Institute in Bethesda, Md.
Arai and his U.S. colleagues teamed with Icelandic researchers to test 670 people who were randomly selected from Iceland’s population and 266 others chosen because they had diabetes. The overall median age of the volunteers was 76. Medical records showed that 91 had experienced a previous heart attack. But testing with MRI revealed that 157 others, including 72 who had diabetes, had clear signs of cardiac tissue that was damaged at some point in a silent heart attack. EKG spotted 46 such cases, including 15 patients with diabetes. Some people, but not all, were detected by both diagnostic tests.
“The data are pretty unequivocal,” Arai says. “MRI is much more sensitive.” Those with undiagnosed heart attacks were substantially less likely to be getting drugs such as aspirin to limit blood clotting or statins to lower LDL cholesterol than were people who had a documented history of a heart attack.
Compared with people who hadn’t had a heart attack, those who had — previously diagnosed or silent — had more coronary calcium buildup, an early sign of heart disease, and were more apt to die during six subsequent years of monitoring.
On average, study participants were not overweight and didn’t have dangerous cholesterol numbers. The fact that many experienced a heart attack without knowing it “is not so amazing,” says Renu Virmani, a cardiac pathologist and president of CVPath Institute, a nonprofit research organization in Gaithersburg, Md. For example, people with diabetes often fail to feel pain, she says. “Their nervous system isn’t sensing as much as it should.” Arai notes that some heart attacks happen at night, or are confused with other ailments.
But the study shows the need for testing to head off further heart damage, Virmani says. Some risk factors for heart attack are well-known, such as a smoking history, hypertension, diabetes and high LDL cholesterol. But others get less attention. “People often ignore family history, for example,” she says. “It’s true you can’t change your parents. But if people knew they already had had a heart attack, they would pay much more attention to factors they can change.” A 2011 study showed that 14.4 percent of people showing up at a hospital with a heart attack had none of these five key risk factors.Even so, the National Institutes of Health isn’t advocating cardiac MRIs in seemingly healthy people, Arai says. Radiologists and cardiologists tend to avoid imaging people who don’t have symptoms, he says.