Discussion

Assessment of functional capacity has a well-consolidated role in the prognostic stratification of CHD patients. In our cohort of trained patients with CHD, maximum oxygen consumption was well preserved across all categories of anatomies, ranging from 39 (36–44) to 28 (23–32) ml/Kg/min. In a previous large dataset of adult patients with CHD, maximum oxygen consumption ranged from 28.7 ± 10.4 to 11.5 ± 3.6 ml/Kg/min. ^{Reference Diller, Dimopoulos and Okonko1} This significant difference may be explained by a higher level of training, a lower age of our population, and the exclusion of patients with Eisenmenger physiology. However, previous study on a group of children and adolescent with CHD also reported a maximum workload significantly lower than our cohort. ^{Reference Norozi, Gravenhorst, Hobbiebrunken and Wessel5}

A main finding of this paper is that patient practising sport, despite a similar reported NYHA class, displayed a significantly higher objective functional capacity as compared with their counterpart with the same age, anatomy, and body mass index. Interestingly, ventilatory equivalent of CO2 was not significantly different in subjects practising sport. This finding can be the result of the specific characteristics of our cohort which included young patients without pulmonary vascular disease.

Literature data on the effect of exercise training on cardiopulmonary fitness are still conflictual.

It has to be underlined that most of the studies assessing the impact of physical training on functional capacity of patients with CHD are based on heterogenous protocol of limited duration. ^{Reference Duppen, Takken and Hopman3,Reference Amiard, Jullien, Nassif, Bach, Maingourd and Ahmaidi7–Reference Dirks, Kramer and Schleiger12}

Different from previous studies, we included patients that were involved in sports activities as part of their routine lifestyle. We can hypothesise that a training protocol of limited duration might not reproduce the effect of routine training on effort tolerance at long-term follow-up. We observed that functional capacity in terms of maximum oxygen consumption and % predicted maximum oxygen consumption remained stable over the follow-up period while ventilatory equivalent of CO2 slope decreased. It has been demonstrated that a lower level of ventilatory equivalent of CO2 is independently associated with a better prognosis in patients with CHD. ^{Reference Inuzuka, Diller and Borgia13} Efficiency of ventilation-perfusion coupling is a major component of ventilatory equivalent of CO2 slope. In patients with CHD, pulmonary vascular function may be impaired because of global segmental pulmonary hypertension, pulmonary artery branch stenosis, lack of flow pulsatility, contributing to regional ventilation mismatch, and, therefore, impairing ventilation efficiency. This is particularly relevant for specific categories of patients, such as Fontan, that have a passive not pulsatile pulmonary flow. ^{Reference Banks, McCrindle, Russell and Longmuir14} Routine physical training might counteract these pathophysiological mechanisms by optimising NO-mediated pulmonary vascular recruitment. ^{Reference Taylor, Coffman, Summerfield, Issa, Kasak and Johnson15}

Finally, involvement in regular training and surveillance of objective effort tolerance by cardiopulmonary exercise test may increase the detection rate of subclinical but potentially harmful residual defects. (supplementary material).

Larger numbers are needed in order to confirm these trends of exercise parameters in sportive patients with CHD in order to be able to perform sub-analysis in different anatomic categories.