Is Cyanosis Exposure Associated with Exercise Capacity or Daily Physical Activity in Children with Complex Congenital Heart Disease: A Cross-Sectional Study

<b>Background/Objectives</b>: Children with complex congenital heart disease (CHD) often exhibit lower levels of physical activity, but whether chronic cyanosis exposure is associated with activity participation is unclear. This cross-sectional study investigated whether the duration of cyanosis prior to surgical correction was associated with submaximal or maximal exercise tolerance or daily habitual physical activity. <b>Methods</b>: Thirty-six children (10-17 years) with transposition of the great arteries (TGA), tetralogy of Fallot (TOF), or Fontan physiology were tested with cardiopulmonary exercise testing (Bruce treadmill protocol) and 7 days of accelerometry. Cyanosis duration from birth to surgery was calculated. <b>Results</b>: Only 17% of participants were meeting daily physical activity recommendations. Age and exercise time were the strongest predictors of activity behavior. Children with <2 months of cyanosis had peak VO₂ comparable with normative data (105% predicted), while those with longer durations of exposure had reduced submaximal and peak capacity (<i>p</i> < 0.001). The direct effect of days exposed to cyanosis on daily physical activity was not statistically significant (<i>p</i> = 0.55) but the indirect effect via submaximal energy consumption was statistically significant (<i>p</i> = 0.05), suggesting that a longer duration of cyanosis exposure negatively impacted physical activity through its detrimental effect on submaximal exercise capacity. <b>Conclusions</b>: These findings suggest that children with prolonged cyanosis exposure are at higher risk for reduced submaximal exercise capacity, which has a negative impact on daily physical activity participation. Age and exercise test duration can accurately estimate daily physical activity behaviors. Interventions to support these patients require investigation due to their increased risk for morbidities associated with inactive lifestyles.