1356577 - Surrogates of Muscle Mass on Cardiac MRI and Its Correlation to Cardiac Functionality During Exercise Stress Testing in Patients with Fontan Circulation

Sarcopenia is an increasingly recognized marker of frailty in cardiac patients, with a deficit in skeletal muscle mass shown to portend a poor prognosis and increased mortality in congestive heart failure and pulmonary hypertension (1, 2). In adult Fontan patients, skeletal muscle wasting on liver MRI surveillance studies has been shown to accompany decreased measures of cardiorespiratory fitness (3).  However, no studies have assessed the utility of thoracic skeletal muscle mass on surveillance cardiac MR (CMR) in Fontan patients. This study aims to evaluate thoracic muscle mass and its correlation with measures of exercise capacity.



Methods:

A retrospective study of patients with Fontan palliation surgery who had CMR was performed. Exercise stress testing data were collected if within six months of the most recent CMR. CMR data were reanalyzed by a single pediatric cardiologist and included routine volumetry and flow data.  The anterior thoracic muscles (pectoralis major and minor) and the paraspinal muscles were contoured as previously described (1). The skeletal muscle area was quantified using offline analysis software (CVi⁴², Circle Cardiovascular Imaging Inc., Calgary, Canada). Values of skeletal muscle area were indexed to body surface area. Pearson correlation and multivariable linear regression were used.



Results:

Sixty-two patients (23 Females, 17.3 ± 8.0 years vs. 39 Males, 19.8 ± 7.6, p=0.8) with Fontan circulation were included, 38 of which had a stress test within six months of CMR. As expected, the indexed skeletal muscle area was smaller in females than in males, a significant result for the anterior muscles (17.93 ± 3.81 cm²/m² vs. 22.38 ± 5.01 cm²/m², p=0.0015), and a lower trend for paraspinal thoracic (5.97 ± 1.46 cm²/m² vs. 6.82 ± 1.96 cm²/m², p=0.0611). There was a significant positive association between paraspinal muscle area index and both peak oxygen consumption (VO_{2 peak}) (r²=0.16, p=0.03), and respiratory exchange ratio (RER) (r²=0.13, p=0.05). There was a negative correlation between the paraspinal muscle mass index and minute ventilation/carbon dioxide production (VE/VCO­₂) (r²= -0.21, p=0.01). No association was seen between these parameters and the anterior thoracic muscles. On multivariable analysis adjusting for sex, the correlations remained the same without differences between men and women.

 

Conclusion:

Increased area of paraspinal muscles on CMR is associated with indices of ventilatory efficiency on exercise stress testing, as evidenced by a positive correlation between peak VO₂ and RER and a negative correlation with VE/VCO_2.  These results are consistent with prior observations in Fontan circulation patients and suggesting paraspinal skeletal muscle index on CMR could potentially be a conveniently obtained biomarker of cardiorespiratory fitness in the Fontan population.