"The novelty of this study is that 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. This is a paradigm shift in the way we understand how myocardial dysfunction is produced. And that speaks to the importance of the report," said João A. C. Lima, M.D., F.A.C.C. from Johns Hopkins University in Baltimore, Maryland.
Researchers at six field centers*, including first author Verônica R. S. Fernandes, M.D., studied 500 consecutive MRI studies of participants (209 women and 291 men) in the Multi-Ethnic Study of Atherosclerosis (MESA). 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 a relatively new and extremely sensitive technique known as 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 of the participants. Specifically, the researchers measured the intima-media thickness of the carotid artery. Increased thickness is known to be an early sign of atherosclerosis.
Even though the participants did not have any 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 the heart contraction," Dr. 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 using ultrasound to watch for progression of atherosclerosis.
Dr. Lima pointed out that this study could show only that signs of atherosclerosis and reduced heart function tend to go together. Further study will be needed to see if the results can predict the future health of the participants.
"That's what we are doing now. We are following this population to see if this really relates to people developing heart failure," Dr. Lima said.
This study was not designed to explain the observed association, but the researchers say other work suggests some leading possibilities. Early atherosclerosis in major blood vessels could be producing blood flow problems and thus causing heart muscle damage, even though the participants don't feel symptoms. Blood vessel problems could be interfering 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.
Tasneem Z. Naqvi, M.D., from the UCLA School of Medicine in Los Angeles, California, who was not connected with this study, said that a "strength of the study is the strong methodology, using recent and more robust techniques for the evaluation of heart function."
"The study findings might explain the etiology of heart failure in several patients who are otherwise labeled as having idiopathic cardiomyopathy. Decreased coronary flow reserve in the face of increased demand such as occurs during exercise or mental stress may lead to reduced heart function during stress and then eventually at rest. It would be interesting to find out whether exercise or mental stress challenge may bring out this abnormality even earlier. 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," Dr. Naqvi said.
* The six field centers participating in this study were Wake Forest University, North Carolina; Columbia University, New York; Johns Hopkins University, Maryland; University of Minnesota, Minnesota; Northwestern University, Illinois, and University of California at Los Angeles, California.
This study was supported by a NHLBI grant and MESA study contracts. Dr. Lima is also supported by the Reynolds Foundation, and Dr. Fernandes was a recipient of a research grant from CAPES, Ministry of Education, Brazil Government.
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