MR tagging spies early signs of heart failure

June 27, 2006

Research that raises questions about the development of cardiovascular disease may establish a foundation for MR as a means of screening for future heart failure.

Research that raises questions about the development of cardiovascular disease may establish a foundation for MR as a means of screening for future heart failure.

A study conducted at Johns Hopkins University indicates that MR can detect subtle changes in cardiac function that may indicate the beginning of heart failure. These early signs were detected using MRI tagging on middle-aged and elderly subjects who reported feeling healthy but who had early signs of atherosclerosis. The findings may portend an enormous opportunity for MRI in the screening of patients for potentially fatal heart disease.

"The findings suggest that screening by imaging, rather than by blood tests, is the way to detect presence of subclinical atherosclerosis, as well as its effect on heart function," said Dr. Tasneem Z. Naqvi, associate professor of medicine at the University of California, Los Angeles, one of six field centers where the work was done. "A strength of the study is the strong methodology, using recent and more robust techniques for the evaluation of heart function."

The results, published in the June 20 issue of the Journal of the American College of Cardiology, run counter to conventional belief regarding the occurrence of cardiovascular disease.

"We were taught that the way atherosclerosis causes myocardial dysfunction is by causing heart attacks or chest pain or other clinical manifestations of disease. Here we have evidence that subclinical atherosclerosis - atherosclerosis that has not manifested clinically - is influencing left ventricular function, regional myocardial function, before any clinical outcome is detected," said Dr. João A. C. Lima, associate professor of medicine and radiology at Johns Hopkins, another of the field centers. "This is a paradigm shift in the way we understand how myocardial dysfunction is produced."

Naqvi believes the results might explain the etiology of heart failure in patients who are otherwise labeled as having idiopathic cardiomyopathy. These patients demonstrate decreased coronary flow reserve under situations of increased demand, as occurs during exercise or mental stress. A diminished reserve may lead to reduced heart function during stress, and then eventually at rest, he said.

"It would be interesting to find out whether exercise or a mental stress challenge may bring out this abnormality even earlier," Naqvi said.

Researchers studied 500 consecutive MRI studies of participants (209 women and 291 men) in the Multi-Ethnic Study of Atherosclerosis. The MESA trial is a prospective population-based observational cohort study of men and women from four different ethnic groups (Caucasian, African-American, Hispanic, and Chinese), ages 45 to 85 years old, who were free of clinical cardiovascular disease at enrollment.

Using MRI tagging, the researchers were able to detect subtle changes in the movement of the walls of the left ventricles, the main pumping chambers, of the hearts of participants. They compared the results of the MRI heart wall motion studies with ultrasound measurements of the carotid arteries, specifically measuring the intima-media thickness of the carotid artery. (Increased thickness is known to be an early sign of atherosclerosis.)

Even though the participants had no symptoms of cardiovascular disease, increased intima-media thickness was related to reduced heart pumping function.

"Previous studies have looked at the relationship of atherosclerosis and heart failure. We are showing, in a population of people who have never had symptoms, an association between atherosclerosis and fine changes in heart contraction," Lima said. "These results - which were quite unexpected, actually - suggest that we should perhaps implement preventive strategies more vigorously and earlier than we thought."

Possible interventions could include treatment to lower cholesterol levels or use of ultrasound to watch for progression of atherosclerosis.

Among the possible explanations is that early atherosclerosis in major blood vessels could produce blood flow problems that cause heart muscle damage but no symptoms. Such problems could interfere with blood flow in the tiny vessels in the heart muscle. It is also possible that the early atherosclerosis and heart function abnormalities are both connected to some underlying issue that was not identified in this study. Alternatively, the signs of atherosclerosis and reduced heart function may simply occur together.

The Johns Hopkins researchers are now exploring such possibilities and will try to determine whether MR tagging can predict the future health of the participants.