The fear of public speaking might cause some people to do more than just break out in a cold sweat and battle stomach-churning butterflies - it could prove to have consequences for their heart health.

University of Florida cardiologists have identified a group of heart disease patients who appear especially vulnerable to the physical effects of mental stress.

Chronic anxiety, depression or anger are widely recognized as raising the risk of heart attack, hospitalization or sudden death in patients whose hearts suffer dangerous decreases in blood flow during exercise testing. Even something as simple as public speaking, doing mental arithmetic or recounting an argument with a loved one can trigger a problem.

But until now, patients who trod the treadmill without experiencing chest pain or restricted blood flow had never been similarly scrutinized when it came to mental stress. Yet what goes on in their heads could have consequences for their hearts as well, UF researchers write in today’s (March 7) issue of the Journal of the American College of Cardiology. A third of the heart patients they studied developed temporary changes in heart rhythm or restricted blood flow when they were asked to role-play a difficult interpersonal situation, even though their hearts responded normally to exercise.

“Recently our group and some other investigators have started to expand the population of patients that we’re looking at to try to explore what happens when mental stress is applied,” said David S. Sheps, M.D., a professor and associate chairman of cardiovascular medicine at UF’s College of Medicine and the Malcom Randall Veterans Affairs Medical Center. “We believe the phenomenon of mental stress-induced reductions in blood flow to the heart is much more common than has been previously recognized.”

In general, studies have shown that as many as two-thirds of patients with coronary artery disease who experience exercise-related reductions in blood flow to the heart respond similarly to mental stress. These bouts often produce no symptoms of chest pain and are rarely detectable on a standard electrocardiogram. Yet last year UF researchers found that these patients have a threefold greater risk of dying - as large a risk factor as cigarette smoking or High cholesterol. Other studies have linked stress experienced after mass disasters or natural catastrophes with a rise in heart attacks and sudden death.

Psychological stress can leave the heart more prone to developing arrhythmias or electrical instability and the blood more prone to clotting. Stress appears to raise heart rate and rapidly hike blood pressure, increasing the heart’s need for oxygen-rich blood, Sheps said. Yet less oxygen is supplied, in part because coronary arteries constrict, impeding blood flow. Doctors are concerned that this reaction to stress in the laboratory is simply a snapshot of how patients respond to the stress of life day in and day out.

In the current study, funded by the National Institutes of Health and Bristol-Myers Squibb, UF researchers studied 21 men and women with documented heart disease who had no signs of reduced blood flow during exercise on the standard exercise treadmill test or on nuclear perfusion scans of the heart. Participants were given two minutes to prepare to deliver a four-minute speech about a hypothetical stressful situation. Blood pressure and electrocardiographic measurements were taken every minute during the speech and for 10 minutes afterward. About half an hour after the speech, participants underwent heart imaging scans that reflected blood flow to the heart during the stressful situation.

“These are patients who for example might have had a severe lesion or a narrowing of one of the coronary arteries and may have had a stent inserted; they’re tested after that and found to have no decreased blood flow with the standard type of exercise testing,” Sheps said. “However, we found that about 30 percent of them had evidence of decreased blood flow with the mental stressor.”

In general, 20 percent to 30 percent of all patients cardiologists see could respond in a similar fashion, Sheps estimated. Simply warning patients to avoid stress because it’s bad for them is not enough, he added.

“All of us are leading more and more stressful lives, and it’s hard to avoid it,” he said. “We as physicians need to find better ways to treat this phenomenon to avoid having patients develop this type of response to an increased stressor.”

UF researchers are now conducting a related study involving more than 300 patients. They are interested in replicating the findings and determining whether these patients are more likely to suffer a heart attack, be hospitalized or die from cardiac complications, Sheps added.

Why does mental stress restrict blood flow in some patients even when exercise fails to have the same effect? The effects of mental stress could predominantly affect the heart’s smaller vessels, causing them to spasm and temporarily limiting blood flow, he speculated. In contrast, exercise tends to affect the heart’s larger vessels.

The findings suggest patients who experience reductions in blood flow detectable when they are experiencing mental stress but not during standard exercise radionuclide testing may have a worse form of heart disease than expected, cautioned David S. Krantz, Ph.D., chairman and a professor of medical and clinical psychology at the Uniformed Services University in Bethesda, Md.

“This patient group warrants further study since they may have functionally more severe coronary artery disease,” he said.