The cardiorespiratory optimal point as a discriminator of lesion severity in adults with congenital heart disease

BACKGROUND: Peak oxygen consumption (VO2peak), which depends on maximal exertion and is reduced in adults with congenital heart disease (ACHD), is associated with lesion severity. The lowest ventilatory equivalent for oxygen (the minimum value of VE/VO2) reflects the cardiorespiratory optimal point (COP) as best possible respiration-circulatory interaction and may discriminate between lesion types without the need for maximal exertion. However, data on COP in ACHD is scarce. METHODS: We retrospectively analyzed stable ACHD with moderate (N.=13) and severe lesions (N.=17) reporting to our outpatient clinic un-dergoing cardiopulmonary exercise testing. The primary outcome of the study was the difference of COP between moderate and severe lesions. Secondary outcomes were between group differences of the submaximal variable exercise oxygen uptake efficiency slope (OUES) and peak O2 pulse (O2pulsemax) as a surrogate for peripheral oxygen extraction and stroke volume increase during exercise. RESULTS: The group of severe lesions displayed higher COP (29.5 & PLUSMN;7.0 vs. 25.2 & PLUSMN;6.2, P=0.028) as well as lower O2pulsemax (13.3 & PLUSMN;8.4 vs. 14.9 & PLUSMN;3.4 mL/beat/kg 102, P=0.038). VO2peak (17.4 & PLUSMN;6.5 vs. 20.8 & PLUSMN;8.5 mL/kg/min, P=0.286) and OUES (1.5 & PLUSMN;0.7 vs. 1.8 & PLUSMN;0.9, P=0.613) showed a trend towards lower values in severe lesions. COP was a better between group discriminator than O2pulsemax (area under the curve 73.8% vs. 72.4%). CONCLUSIONS: As a submaximal variable, COP discriminated between moderate and severe lesions and may prove beneficial in a highly vulnerable population that is often unable to undergo exertional testing.