Original Research The Relationship Between Heart Rate Deflection and Ventilatory Threshold in Children Following Heart Surgery

This study assessed the relationship between the VO₂ measured at ventilatory threshold (VT) and the VO₂ measured at the point of deflection from linearity of heart rate (HRD). Twelve children (10 boys and 2 girls) with a mean age of 11.3 years (± 4.8) performed a graded exercise test to determine VT and HRD. All children had undergone surgical repair for d-transposition of the great arteries at approximately 13 months of age. Because of failure to demonstrate HRD, the data from 4 patients were excluded from statistical analysis. For the remaining 8 patients there was no significant difference between mean VO₂ (ml/kg/min) at VT and HRD (26.6 ± 6.4 vs. 26.3 ± 6.8; p > 0.25). Linear regression analysis revealed a correlation of r = 0.92 between the VO₂ measured at VT and the VO₂ measured at HRD. Only 8 of the 12 patients (66%) in this study satisfied criteria needed to identify the HRD. Therefore HRD may be an accurate predictor of VT in most but not all children who have had surgery for d-transposition of the great arteries.