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Wang-Giuffre et al. Vessel Plus 2022;6:29 https://dx.doi.org/10.20517/2574-1209.2021.98 Page 3 of 7

are relatively common secondary to previous incisions in the atria creating a substrate for arrhythmias
during exercise.

Peripheral vascular dysfunction
Patients with Fontan physiology have reduced endothelial function and autonomic dysregulation, which is
[10]
deleterious to the aerobic function . The etiology of this is multifactorial. A lifetime of activity restriction
and fear of adverse events from exercise leads to decreased muscle mass and poor conditioning. Low
skeletal muscle mass causes decreased oxygen extraction and poor conditioning leading to poor oxygen
utilization efficiency, thereby further contributing to decreased exercise performance.

Abnormal ventilatory function
Patients with Fontan palliation have abnormal ventilation at both rest and with exercise. The exact cause is
not entirely clear; however, it is more than likely due to several factors. Fontan patients have multiple
median sternotomies, resulting in decreased chest wall compliance secondary to multiple adhesions.
Patients with Fontan circulation also hyperventilate compared to normal two ventricle physiology patients
because of systemic cyanosis and increased dead space to tidal volume ratio [11,12] .

In the presence of a Fontan fenestration, there is increasing right to left shunt with progressive exercise,
thereby exacerbating the Ventilation/Flow (V/Q) mismatch, further compromising the oxygen delivery to
muscle and producing decreased exercise capacity.

CARDIOPULMONARY EXERCISE MEASURES
VO peak
2
VO peak is the rate at which the patient consumes oxygen at peak exercise and represents the efficiency
2
with which the patient utilizes oxygen. It is a measure of aerobic capacity that has been shown to have
prognostic values in adult heart failure patients . Fontan patients have a multitude of reasons for VO peak
[13]
2
to be decreased, such as decreased preload from a lack of a subpulmonary pump, obstruction of the Fontan
circuit, significant AV valve insufficiency, left ventricular outflow obstruction, chronotropic insufficiency,
arrhythmias, decreased peripheral vascular function and abnormal ventilatory function.

Numerous studies in Fontan patients have shown decreased VO peak of ~50%-60% of expected [14-17] . It has
2
also been shown that VO peak declines with age and is also dependent on the morphology of the systemic
2
ventricle, a single right ventricle having decreased VO peak over time compared to a single left
2
[20]
ventricle [18,19] . A recent metaanalysis by Udholm et al. reports that in the seven studies analyzed, there was
universal exercise impairment in Fontan patients with a VO peak range of 21.2-27.1 mL/kg/min; however,
2
it was noted that there was no clear consensus of whether VO peak itself portends greater risk of
2
hospitalization or cardiac adverse event.
Several studies that analyzed the peak VO in Fontan patients as it relates to outcome indicate that
2
decreasing VO peak correlates with cardiac adverse events, i.e., death or cardiac surgery [21-23] . An absolute
2
cut-off value remains elusive, however, decreased peak VO does correlate with cardiac symptoms and
2
worsening functioning class . Egbe et al. noted that a decline in ≥ 3% per year was the only predictor of a
[23]
[24]
5-year risk of death or surgery. VO peak over time can be a helpful measure to survey for possible
2
functional derangements.
Submaximal measures
Aerobic metabolism is the primary source of energy to sustain exercise during the early phase. With
progressive intensity, metabolism shifts from aerobic to anaerobic metabolism. Patients with a Fontan