Lean mass deficits, vitamin D status and exercise capacity in children and young adults after Fontan palliation

Abstract

Objective: We sought to evaluate body composition in children and young adults with Fontan physiology. Leg lean mass (LM) deficits correlate with diminished exercise capacity in other populations and may contribute to exercise limitations in this cohort.

Methods: This cross-sectional study included whole body dual energy X-ray absorptiometry scans in 50 Fontan participants ≥5 years, and measures of peak oxygen consumption (VO2) in 28. Whole body and leg LM (a measure of skeletal muscle) were converted to sex- and race-specific Z-scores, relative to age and stature, based on 992 healthy reference participants.

Results: Median age was 11.5 (range 5.1-33.5) years at 9.3 (1.1-26.7) years from Fontan. Height Z-scores were lower in Fontan compared with reference participants (-0.47±1.08 vs 0.25±0.93, p<0.0001). Body mass index Z-scores were similar (0.15±0.98 vs 0.35±1.02, p=0.18). LM Z-scores were lower in Fontan compared with reference participants (whole body LM -0.33±0.77 vs 0.00±0.74, p=0.003; leg LM -0.89±0.91 vs 0.00±0.89, p<0.0001). LM Z-scores were not associated with age or Fontan characteristics. Leg LM Z-scores were lower in vitamin D deficient versus sufficient Fontan participants (-1.47±0.63 vs -0.71±0.92, p=0.01). Median per cent predicted peak VO2 was 81% (range 13%-113%) and was associated with leg LM Z-scores (r=0.54, p=0.003).

Conclusions: Following Fontan, children and young adults are shorter than their peers and have significant LM deficits. Skeletal muscle deficits were associated with vitamin D deficiency and reduced exercise capacity. Future studies should examine the progression of these deficits to further understand the contribution of peripheral musculature to Fontan exercise capacity.

Keywords: CONGENITAL HEART DISEASE.

Figure 1

The box plots represent the Z-score distribution for whole body and leg lean mass in Fontan participants. The horizontal line within each box plot represents the median Z-score (50th percentile) for the Fontan participants; the median Z-score value is provided on the plot. The top and bottom of the boxes represent the 75th and 25th percentiles, and the whiskers represent 2 SDs from the mean Z-score. The black horizontal line at Z=0 represents the Z-score of zero in the reference participants; equivalent to the 50th percentile for age. The p values for comparison of Z-scores between Fontan and reference participants are provided below each plot.

Figure 2

Leg lean mass Z-scores were worse in Fontan participants with vitamin D deficiency compared with those with adequate vitamin D levels. The box plots represent the Z-score distribution for leg lean mass in Vitamin D sufficient versus deficient Fontan participants. The horizontal line within each box plot represents the median Z-score (50th percentile) for the group; the median Z-score value is provided on the plot. The top and bottom of the boxes represent the 75th and 25th percentiles, and the whiskers represent 2 SDs from the mean Z-score. The p value for comparison of Z-scores between the two groups is provided on the figure.

Figure 3

In the Fontan participants who completed exercise testing, leg lean mass Z-score was associated with per cent predicted peak VO₂.