Abstract
After the arterial switch operation (ASO) for transposition of the great arteries (TGA), many patients have an impaired exercise tolerance. Exercise tolerance is determined with cardiopulmonary exercise testing by peak oxygen uptake (VO2peak). Unlike VO2peak, the oxygen uptake efficiency slope (OUES) does not require a maximal effort for interpretation. The value of OUES has not been assessed in a large group of patients after ASO. The purpose of this study was to determine OUES and VO2peak, evaluate its interrelationship and assess whether exercise tolerance is related to ventricular function after ASO. A cardiopulmonary exercise testing, assessment of physical activity score and transthoracic echocardiography (fractional shortening and left/right ventricular global longitudinal peak strain) were performed to 48 patients after ASO. Median age at follow-up after ASO was 16.0 (IQR 13.0–18.0) years. Shortening fraction was normal (36 ± 6%). Left and right global longitudinal peak strain were reduced: 15.1 ± 2.4% and 19.5 ± 4.5%. This group of patients showed lower values for all cardiopulmonary exercise testing parameters compared to the reference values: mean VO2peak% 75% (95% CI 72–77) and mean OUES% 82(95% CI 77–87); without significant differences between subtypes of TGA. A strong-to-excellent correlation between the VO2peak and OUES was found (absolute values: R = 0.90, p < 0.001; normalized values: R = 0.79, p < 0.001). No correlation was found between cardiopulmonary exercise testing results and left ventricle function parameters. In conclusion, OUES and VO2peak were lower in patients after ASO compared to reference values but are strongly correlated, making OUES a valuable tool to use in this patient group when maximal effort is not achievable.
Highlights
After correction with the arterial switch operation (ASO), long-term survival and outcome of patients with transposition of the great arteries (TGA) are usually good
TGA patients showed on average lower values for all exercise test parameters compared to reference values from a healthy dataset [13, 16, 20], as reflected by %predicted values: VO2peak% = mean 75%, p < 0.001; and oxygen uptake efficiency slope (OUES)% = mean 82%, p < 0.001. O2pulsemax was decreased with a percentage predicted of 79% (p < 0.001)
No correlation was found between VO2peak or OUES and ventricular function parameters (FS, Left ventricular (LV) and RV global longitudinal strain (GLS)) or the maximal CW Doppler gradient measured in pulmonary arteries
Summary
After correction with the arterial switch operation (ASO), long-term survival and outcome of patients with transposition of the great arteries (TGA) are usually good. Contributing factors to reduced exercise tolerance have been shown to include chronotropic incompetence, narrowing of the main pulmonary artery with or without pulmonary branch obstruction, coronary abnormalities, ventricular dysfunction and longer follow-up time after ASO [5,6,7,8,9,10]. Patients with mental disability or with certain cardiovascular diseases may have reduced capacity to fulfil the required maximum exercise. These considerations make the use of submaximal exercise parameters such as the ventilatory efficiency (VE/VCO2slope) and the oxygen uptake efficiency slope (OUES) potentially valuable [12]. The aim of the present study was to correlate OUES as a submaximal exercise parameter to V O2peak as a maximal exercise parameter in a group of patients after ASO. We studied whether exercise tolerance could be related to ventricular function or right ventricle outflow tract obstruction as assessed by echocardiography
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