Systemic ventricular function in Fontan patients at rest and after exercise at altitude

Area of Science:

• Cardiology
• Physiology
• Altitude Medicine

Background:

• Fontan circulation patients face risks with physical activity at high altitudes.
• Systemic ventricular function may be impaired by high-altitude hypoxia.
• Understanding these effects is crucial for patient management and safety.

Purpose of the Study:

• To determine the impact of high-altitude hypoxia on ventricular function in Fontan patients.
• To compare the effects of hypoxia at rest and during exercise (peak and continuous) in Fontan patients versus healthy controls.
• To test the hypothesis that systemic ventricular function deteriorates under hypoxic conditions in Fontan patients.

Main Methods:

• Prospective study involving 21 Fontan patients (NYHA class I-II) and 21 healthy controls.
• Transthoracic echocardiography performed at rest and after peak (PE) and continuous exercise (CE) under normoxia and hypoxia (simulated 2,500m altitude).
• Analysis using linear mixed-effects models to quantify the effect of hypoxia on echocardiographic parameters.

Main Results:

• At rest, Fontan patients showed lower cardiac output (CO) and annular plane systolic excursion (APSE) in hypoxia versus normoxia (APSE: p < 0.001).
• No significant deterioration in systolic function was observed in Fontan patients after exercise under hypoxic conditions compared to normoxia.
• Under hypoxia, Fontan patients exhibited higher CO and workload after CE than PE, unlike controls.

Conclusions:

• Fontan patients tolerated short-term altitude exposure and exercise without consistent deterioration of systolic ventricular function.
• Fontan patients did not exhibit increases in myocardial contractility, heart rate, or cardiac output as seen in controls, potentially due to intrinsic cardiac dysfunction or preload issues.
• Continuous exercise (CE) may be better tolerated than peak exercise (PE) in hypoxic conditions for Fontan patients.