Impaired chronotropic response to exercise in children with repaired cyanotic congenital heart disease

Conventionally the heart rate response to exercise has been considered as a useful parameter for the assessment of exercise performance. However, in patients with surgical repair of congenital heart defects sino-atrial dysfunction has been observed after cardiac surgery.The purpose of this study was to assess whether the heart rate response to exercise can be used in the assessment of exercise performance.

Fifty-three patients with surgical repair of congenital heart disease underwent exercise testing.The patients were 19 children with repair of tetralogy of Fallot (TOF), 17 patients with arterial switch operation for transposition of the great arteries and 17 patients with a Fontan circulation for functional univentricular heart. The patients were compared to age-matched control subjects. Exercise capacity was assessed by determination of the maximal oxygen uptake.To account for the effect of age and gender on heart rate response, values in the patients were compared to age-matched control subjects of the same age and gender and were expressed as a Z-score of the normal value.

In the 3 groups of patients a lower than normal heart rate response was observed during submaximal and maximal exercise, varying from -1.7 to -4.6 standard deviation scores.This was not associated with normal values for exercise capacity in patients with TOF or Fontan circulation, as should be expected.

In patients with surgical repair of congenital heart disease, the use of heart rate response in the assessment of cardiovascular exercise performance may be seriously misleading and should be complemented with measurements of gas exchange.