Impact of Adiposity on Cardiopulmonary Fitness in Children and Adolescents with Ventricular Septal Defects: a CPET-Based Comparative Study

<b>Background:</b> Ventricular septal defect (VSD) is the most common congenital heart defect in children. While previously considered benign, recent studies suggest long-term impacts on cardiopulmonary fitness (CPF). Overweight and obesity, increasingly prevalent among children, may further impair CPF in this population. This study aimed to evaluate the relationship between adiposity and CPF in children with VSD using cardiopulmonary exercise testing (CPET). <b>Methods:</b> This retrospective study included 349 children and adolescents with VSD and 349 age-, sex-, and body mass index (BMI)-matched healthy controls. Participants underwent symptom-limited treadmill CPET. Children with VSD were stratified into BMI categories (underweight, normal, overweight, obesity) based on national standards. Multiple CPET parameters were analyzed, including anaerobic threshold metabolic equivalents (AT MET) and peak metabolic equivalents (peak MET). <b>Results:</b> Children with VSD had significantly higher rates of both underweight (15.5% vs. 4.3%) and obesity (14.6% vs. 9.7%) compared to controls (p < 0.001). Within the VSD group, AT MET and peak MET declined progressively with increasing BMI. [AT MET: 7.41 ± 1.57 (underweight), 6.86 ± 1.38 (normal), 6.01 ± 1.23 (overweight), 5.62 ± 1.23 (obese), p < 0.001; Peak MET: 10.37 ± 2.22 (underweight), 9.58 ± 1.94 (normal), 8.56 ± 1.70 (overweight), 7.81 ± 1.60 (obese), p < 0.001]. Compared to controls, children with VSD showed lower AT MET (6.56 ± 1.51 vs. 6.97 ± 1.47, p < 0.001) and peak MET (9.32 ± 2.03 vs. 10.17 ± 1.95, p < 0.001), along with reduced peak heart rate and heart rate at AT. <b>Conclusion:</b> Children with VSD, regardless of surgical status, exhibit diminished CPF compared to healthy peers. Moreover, both undernutrition and excessive adiposity are more prevalent in the VSD group. Obesity was associated with significantly impaired cardiopulmonary fitness, highlighting the need for early identification and lifestyle interventions. Routine CPET and weight management strategies should be incorporated into long-term care for pediatric VSD patients.