Page 232 - Read Online

Wang-Giuffre et al. Vessel Plus 2022;6:29 https://dx.doi.org/10.20517/2574-1209.2021.98 Page 5 of 7

[36]
However, Muneuchi et al. found that their patients with EOV were typically smaller, younger and had a
higher VO peak, which they attributed EOV to be a compensatory mechanism to overcome the pulmonary
2
[24]
artery pressure. Nathan et al. found that EOV during a CPET for Fontan was a strong independent
predictor for non-elective hospitalization, death or cardiac transplant. There was no correlation between
VO peak and EOV, mostly likely because patients in this study were larger and older. EOV still is a
2
promising submaximal measure to follow in older Fontan patients, although more studies need to be
performed.

O pulse
2
O pulse is the VO at peak divided by heart rate and is a marker of stroke volume. O pulse in patients with
2
2
2
Fontan’s is lower than biventricular counterparts, largely because of decreased peak VO . Although higher
[25]
2
O pulse at peak exercise was associated with higher peak VO , few studies that have reported O pulse
[37]
2
2
2
and have shown no significant correlation with risk of morbidity or mortality [23,26] . Despite these findings,
patients in both studies were relatively midterm in their course after their Fontan’s; therefore, it would be
difficult to conclude whether changes over a longer period of time would portend a different outcome.
Respiratory efficiency and spirometry
Patients who have undergone staged Fontan have had at least two to three median sternotomies, therefore,
have the presence of adhesions in the chest cavity. These adhesions can decrease chest wall compliance and
restrict excursion of the chest during inspiration. This negatively affects preload given preload is directly
affected by the negative inspiratory pressure and lack of subpulmonary pump. FVC correlates with Fontan
mortality .
[38]
[32]
VE/VCO is a marker of respiratory insufficiency and can be decreased in Fontan patients. Chen et al.
2
showed that a VE/VCO slope ≥ 37 conferred a hazard ratio of 10.77 (p0.023) on univariate analysis for
2
2-year cardiac morbidity. Studies have shown that this is less predictive than FVC for mortality in Fontan.
More than likely, this is secondary to cyanosis that is associated with progressive exercise in Fontan patients.
Heart rate reserve and chronotropic index
Sinus node dysfunction and chronotropic incompetence commonly occur as patients with Fontan
circulation age due to incisions at the SVC/RA junction and progressive fibrosis. The peak heart rates on
[25]
average in a large study in Fontan patients were ~155-165 bpm , which is likely because of other
physiologic factors of the Fontan circulation, rather than chronotropic incompetence. Metabolic acidosis
and cyanosis with progressive exercise in a Fontan patient limit the length and intensity of exercise, thus
keeping the patient from achieving a higher heart rate. There are mixed findings on whether HRR and
Chronotropic index confers poor outcomes and is likely age-dependent.

CONCLUSION
CPET is an important tool in the surveillance of the Fontan circulation to detect trends in the function that
would necessitate intervention. Preload and overcoming pulmonary vascular resistance seem to be the most
important determinant of exercise intolerance in the Fontan population. Metabolic measures including VO
2
peak, VO at anaerobic threshold, oxygen pulse and oxygen uptake efficiency slope and ventilatory
2
efficiency can be followed over time to monitor for subclinical changes and be paired with catheterization,
imaging and clinical data to determine need and timing for intervention.