Abstract
Background: Fontan patients have diminished exercise capacity relative to healthy peers. Peak oxygen consumption (pVO2) is a useful marker for maximum exercise capacity, though it may not be achievable in certain patients. We studied clinical validity of submaximal parameters in exercise stress test (EST) in post-Fontan patients. Methods: We retrospectively analyzed EST of post-Fontan patients and age-matched controls by cycle ergometer. We obtained peak values of heart rate (pHR), VO2, oxygen pulse (pOP), respiratory quotient (pRQ), and work rate (pWR). Submaximal parameters included ventilatory anaerobic threshold (VAT), slopes of VO2/HR changes (ΔVO2/ΔHR) and HR/WR changes (ΔHR/ΔWR), and oxygen uptake efficiency slope (OUES). Data are shown as mean ± standard deviation. Results: Twenty four single right ventricle (SRV), 12 single left ventricle (SLV), and 24 controls were studied (Table 1).pHR, pVO2, pOP, and pWR were significantly lower in Fontan patients than in controls, but with no significant difference between SRV and SLV. ΔVO2/ΔHR and OUES were significantly lower in Fontan group than controls, whereas VAT and pRQ were comparable in all three groups. VAT was preserved in Fontan groups. Lower slope of ΔVO2/ΔHR and decreased OUES in the Fontan group suggests an intrinsic exercise limitation or limited stroke volume (SV) increase. This was compensated by a higher HR response up to AT, exhibited by the higher slope of ΔHR/ΔWR despite lower pHR in the Fontan group. Conclusions: Peak exercise parameters were significantly lower in Fontan patients although pRQ and VAT were comparable among the three groups. The lower ΔVO2/ΔHR and pOP in Fontan patients suggest limited SV reserve in response to exercise. A combination of lower ΔVO2/ΔHR and higher ΔHR/ΔWR characterizes Fontan patient. Inclusion of submaximal exercise parameters brings additional value in specifying the physiological responses to exercise.
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