Cardiorespiratory exercise function after the arterial switch operation for transposition of the great arteries

Aims This study compares the functional outcome and cardiorespiratory respo nse to exercise, in patients who have undergone arterial switch for transpo sition of the great arteries, with normal controls and patients who have un dergone atrial switch operation. Methods and Results Fifteen patients who had undergone arterial switch (mea n age 8.5 +/- 2.9 years) were compared to 32 patients who had undergone atr ial switch (9.2 +/- 1.8 years) and 27 normal controls (8-5 +/- 2.1 years). Exercise testing was performed on a treadmill and gas exchange measured bre ath-by-breath. Aerobic capacity, assessed by determination of the ventilato ry anaerobic threshold, averaged 91 +/- 7.8% of normal (95% confidence limi ts: 92-108%) for arterial switch and 75.1 +/- 13.1% for atrial switch (P <0 .001 patients vs normals). Aerobic exercise function was evaluated by calcu lation of the slope of oxygen uptake vs exercise intensity. The mean value for this slope was 2.0 +/- 0.25 for arterial switch, 2.5 +/- 0.46 for norma ls and 1.7 +/- 0.80 for atrial switch (P <0.05, patients vs normals). Effic iency of the pulmonary gas exchange was assessed by calculation of the slop e of ventilation vs carbon dioxide output during exercise. This averaged 38 .7 +/- 14.7 for arterial switch, 48.1 +/- 14.1 for atrial switch and 30.3 /- 7.6 for normals (P <0.001; patients vs normals). Conclusion Cardiorespiratory exercise function is at, or slightly below, th e lower limit of normal in patients with arterial switch, while the lowest values were observed for those who had undergone atrial switch.