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Lower intramuscular fat for a stronger heart
Researchers observed that fat levels inside patients’ thigh muscles significantly predict cardiovascular health outcomes in heart failure patients.
Even though the inter-reliance of muscle function and cardiovascular health has long been understood, it is primarily limited to aspects of muscle strength on heart capacity. While muscle loss contributes to heart weakness, other factors such as the amount of pericardial fat also bring about coronary health complications. “When the heart’s pumping function is impaired, it leads to heart failure. This results in reduced physical function and shortened life expectancy,” said the lead researcher, Dr. Atsushi Shibata from Osaka City University Graduate School of Medicine. Pericardial fat is an ectopic fat, found outside adipose tissues. When fat accumulates in the pericardium, it impairs heart function. The association of pericardial fat and heart function intrigued the researchers, leading them to hypothesize that measurements of another type of ectopic fat, intramuscular fat, may be useful in predicting outcomes for heart failure patients.
Using computed tomography (CT), the researchers scanned both thighs of 93 heart failure patients, measuring muscle area occupied by fat in images’ cross sections. By taking multiple regularly-spaced images, they measured intramuscular fat through the entire muscle. The patients’ diagnostic criteria, overall fitness levels, and grip strength were also measured. Follow-up interviews were conducted for up to 30 months or until the patients reached another endpoint, be it cardiovascular death or unexpected cardiac rehospitalisation.
The patients were divided into high or low intramuscular fat groups, compared to the median (2.9% of muscle volume). There were no significant differences between the groups based on gender or diagnostic criteria such as hypertension, diabetes mellitus, smoking, or blood pressure. Despite no differences in patients’ thigh extension strength or overall fitness, grip strength was lower in the patients with high intramuscular fat, suggesting that the patients with low intramuscular fat had higher quality muscles, and were less likely to be hospitalized during the course of the study. Only 30 of 46 high intramuscular fat patients finished the study event free, compared to 40 of 47 patients with low intramuscular fat (Figure 1). Single dependent variable regression analysis confirmed a significant relationship between high intramuscular fat and adverse event occurrence; multiple dependent variable regression analysis showed that intramuscular fat can be used as an independent prognostic factor.
When asked about these findings, Dr. Shibata noted, “For some time attention has been paid to skeletal muscle because of the importance of muscle mass and strength. We found that, in addition to muscle mass and strength, muscle quality is also related to the prognosis of heart failure.” The existing discourse on intramuscular fat indicates that high intramuscular fat is associated with decreased activity levels, which can be more harmful to cardiovascular health than age-related muscle loss. “We believe that muscle quality is an important new target for treatments aimed at improving the outcomes for heart failure patients.” Dr. Shibata concluded. The findings extend current understandings of intramuscular fat, and open up promising new approaches for managing cardiovascular illness. The study was published in the American Journal of Cardiology (DOI 10.1016/j.amjcard.2021.12.059) in April 2022.
Dr. Shibata is at Osaka Metropolitan University, a public university formed by a merger of Osaka City University and Osaka Prefecture University in April 2022.
Title: Thigh Intramuscular Fat on Prognosis of Patients With Nonischemic Cardiomyopathy
Journal: American Journal of Cardiology
Grant-in-Aid for Young Scientists from the Japan Society for the Promotion of Science (A.S., 20K17091).
Graduate School of Medicine
Dr. Atsushi Shibata
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