The Heart is not the Only Muscle Involved in Heart Failure
Paul D. Thompson, MD
Skeletal muscle (SM) does more than just move us around. It secretes signaling proteins (myokines) that affect other tissues and has a key role in glucose metabolism since it is the major organ for glucose disposal. The recognition that abnormal glucose metabolism might contribute to heart failure HF) with preserved ejection fraction (HFpEF) begs the question as to how SM might contributes to this problem.
Huynh and colleagues used computerized tomography (CT) in subjects in the Health, Aging and Body Composition study to examine the relationship between intra- and inter- muscle fat and subjects’ first admission for heart failure (HF). They measured thigh intramuscular fat by muscle density with reduced radiologic density indicating more fat. Intermuscular fat was measured as the fat around the muscle, but within the fascia. All subjects were age 70–79 at baseline, so “an older crowd”, and were followed for a median of 12.2 years. Both intra- and inter- muscular fat were associated with more HF, but after adjustment for multiple possible co-founders, intramuscular fat, but not intermuscular fat, was associated with a first HF admission, but only for patients presenting with HF with reduced ejection fraction (HFrEF). This finding is surprising given the putative role of glucose metabolism in HFpEF and the association of fat deposition with diabetes, but of the 455 HF admissions, 154 were HFpEF, 172 HFrEF and 129 were not classified and the unclassified could have obscured any relationship. .
Unfortunately, there is no assessment of physical activity. Almost 20 years ago we documented reduced protein turnover in HF patients and that the reduction in protein turnover was greater in patients with higher insulin levels*. Our findings mimic bedrest so we speculated that they could be due to inactivity. It is not clear how physical activity could have contributed to the findings in the present study, but some measurement of activity should be included in most muscle studies. Nevertheless, these results are intriguing and remind us that cardiac is not the only muscle involved in HF.
