Body Composition in Young Adults Living With a Fontan Circulation: The Myopenic Profile.

Tran D, D’Ambrosio P, Verrall CE, Attard C, Briody J, D’Souza M, Fiatarone Singh M, Ayer J, d’Udekem Y, Twigg S, Davis GM, Celermajer DS, Cordina R.
J Am Heart Assoc. 2020 Apr 21;9(8):e015639. doi: 10.1161/JAHA.119.015639. Epub 2020 Apr 15.
PMID: 32290749 Free Article

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Take Home Points:

• In this relatively healthy group of Fontan patients, low skeletal muscle mass was associated with reduced exercise capacity, ventricular dysfunction, and compensatory erythrocytosis as a marker of cyanosis.
• BMI overestimates skeletal muscle mass and underestimates adiposity in Fontan patients.

Commentary by Dr. Maan Jokhadar (Atlanta), section editor of ACHD Journal Watch: The Fontan circulation is associated with elevated central venous pressure, low cardiac output, and cyanosis. These abnormalities increase the risk of heart failure, arrhythmias, thromboembolic events, hepatic fibrosis, and protein using the neuropathy, to name a few. Prior studies have described role of skeletal muscle as a “muscle pump” that increases venous return and augments pulmonary blood flow, which improves cardiac output and improves exercise capacity in Fontan patients.

Cardiac dysfunction can cause neurohormonal derangement and associated skeletal muscle loss and myopenia. There is also a complicated and often paradoxical interrelationship between obesity and heart failure (obesity paradox) with obese patients more likely to develop heart failure but obese patients with heart failure having improved survival. Data are mixed regarding the presence of the obesity paradox failure in Fontan patients.

Derek Tran and colleagues from Sydney, Australia performed a cross-sectional study of 28 Fontan patients who were prospectively recruited. The mean age was 26 with a near even split between male and female and 57% had a systemic left ventricle. Extracardiac Fontan was present in 50%, lateral tunnel in 39%, and 11% (3 patients) with atriopulmonary Fontan. The median BMI was 22.4 kg/m2. Participants had dual energy x-ray absorptiometry (DXA) to assess Appendicular lean mass index (ALMI) Z score and total percent body fat (%BF). They also underwent cardiopulmonary stress testing, echocardiography, handgrip strength assessment, and biochemical assessments. This was a relatively healthy group with exclusion criteria that included NYHA class III-IV, major intellectual or physical disability, or current pregnancy.

– Fontan associated myopenia ( Z score: -2 or lower) : 11 patients (39%)
– Less pronounced skeletal muscle mass deficit (Z score: between -2 and -1) : 8 patients (29%)
– Normal range muscle mass (Z score: higher than -1) was present in only 9 patients (32%)

All participants with normal range skeletal muscle mass had normal ventricular systolic function. Whereas 80% participants with ventricular dysfunction had skeletal myopenia. Males had lower %BF. High adiposity was present in 32%, moderate adiposity and 14%, 50% had normal range adiposity, and 4% (1) had low adiposity. There were 3 patients who had both Fontan associated myopenia and high adiposity.

Vitamin D deficiency was not associated with myopenia. Above normal range PTH was present in 40%, even though only 7 patients had low vitamin D. Blood leptin was increased and 70% of patients, reflecting elevated adiposity.

ALMI was strongly associated with exercise capacity as measured by peak VO2. Fontan associated myopenia was strongly associated with reduced peak handgrip. There was no difference in spirometry measures between normal and reduced muscle mass groups.

This is the first study to characterize body composition using DXA in Fontan patients. This clinically stable group showed low skeletal muscle mass and adiposity predisposition, which can be unrecognized when looking at BMI alone. BMI may overestimate skeletal muscle mass and underestimate adiposity in Fontan patients. Low skeletal muscle mass was associated with reduced exercise capacity, ventricular dysfunction, and compensatory erythrocytosis as a marker of cyanosis. About two thirds of participant had reduced muscle mass. ALMI was independently associated with absolute peak VO2. Grip strength was positively associated with muscle mass and was lower in patients with Fontan associated myopenia.

Ventricular systolic dysfunction was associated with low muscle mass, which could be due to peripheral “muscle pump” impairment reducing venous return, pulmonary blood flow, and cardiac output. Ventricular dysfunction can also cause myopenia due to myriad physiologic and neurohormonal mechanisms.

Based in DXA analysis of Fontan patients, reduced muscle mass and increased adiposity is common.

Given that reduced muscle mass is associated with ventricular dysfunction and reduced exercise capacity, additional study is needed to determine the therapeutic strategies and potentially substantial benefits of building lean muscle mass in these patients.

Pediatric Cardiac Professionals