O2 pulse slope correlates with stroke volume during exercise in patients with a Fontan circulation

BACKGROUND: Peak oxygen pulse (O(2)pulse=oxygen consumption/heart rate) is calculated by the product of stroke volume (SV) and oxygen extraction. It has been shown to be reduced in patients with a Fontan circulation. However, in the Fontan population, it may be a poor marker of SV. We propose that the slope of the O(2) pulse curve may be more reflective of SV during exercise. METHODS: We analysed cardiopulmonary exercise test data in 22 subjects with a Fontan circulation (cohort A) and examined the association between peak SV during exercise (aortic flow measured on exercise cardiac MRI), and O(2) pulse parameters (absolute O(2) pulse and O(2) pulse slopes up to anaerobic threshold (AT) and peak exercise). In a separate Fontan cohort (cohort B, n=131), associations between clinical characteristics and O(2) pulse kinetics were examined. RESULTS: In cohort A, peak aortic flow was moderately and significantly associated with O(2)pulseslope(PEAK) (r=0.47, p=0.02). However, neither absolute O(2)pulse(AT) nor O(2)pulse(PEAK) was significantly associated with peak aortic flow. In cohort B, O(2)pulseslope(PEAK) and O(2)pulseslope(AT) were not significantly associated with clinical parameters, apart from a weak association with forced vital capacity. CONCLUSION: The slope of the O(2) pulse curve to peak exercise may be more reflective of peak SV in the Fontan population than a single peak O(2) pulse value.