Case Review Dynamic Assessment of the Fontan Part II: New Horizons in Medical...

Mean capillary filling pressure is a measure of intravascular volume status and venous wall tension and compliance, which is very often abnormal in Fontan circulation patients with reduced compliance.

Fontan patients who respond with rapid venous pressure increases during exercise tend to have diminished exercise capacity, while those with minimal pressure changes tend to exercise longer.

Fontan patients drop their renal near-infrared spectroscopy values very precipitously and early during exercise compared to normal controls, and these values do not return to normal even after 5-6 minutes of recovery.

Cerebral near-infrared spectroscopy shows an early drop in Fontan patients during exercise but returns to normal by the second minute of exercise, in contrast to renal NIRS.

Dynamic assessment of the Fontan patient is essential, and this technique gives good insight to pick up occult abnormal physiology in well-functioning Fontans that would not be appreciated until much later when the patient becomes ill.

With exercise comes central venous hypertension in Fontan patients, which begets liver disease amongst other things.

With any form of exercise, if you take the extremes, the detrimental effects may well outweigh the beneficial effects.

Submaximal exercise protocols already incorporate most of the venous pressure rise seen during maximal testing.

Patients on transplant lists get better with exercise largely because of skeletal muscle function and oxygen extraction improvements, but the hemodynamics may or may not change.

Vessels in Fontan patients change in their histopathology to accommodate higher pressures, with perivenular changes in the liver being quite striking, and vascular adaptive responses seen in the SVC and IVC.

There is virtually no data in any condition suggesting that if you change vascular biology acutely, you change exercise function.

In biventricular patients, supine exercise is limited compared to upright exercise.

In Fontan patients, exercise limitation during supine exercise looks the same as in biventricular patients, with no particular advantage to swimming or other flat exercises in terms of ultimate performance.

This testing increasingly picks up occult problems including obstructions in the Fontan circuit that may not be known about with just echo and clinical assessment.