Appropriate heart rate during exercise in Fontan patients

Area of Science:

• Cardiology
• Exercise Physiology
• Pediatric Cardiology

Background:

• The Fontan circulation is a palliative surgical procedure for single-ventricle congenital heart defects, leading to unique physiological challenges during exercise.
• Understanding exercise hemodynamics in Fontan patients is crucial for managing their long-term health and functional capacity.

Purpose of the Study:

• To compare heart rate (HR) responses relative to workload and oxygen consumption (VO2) between Fontan patients and healthy controls during cardiopulmonary exercise testing (CPET).
• To investigate potential limitations in stroke volume and cardiac output during exercise in individuals with Fontan physiology.

Main Methods:

• Cardiopulmonary exercise testing (CPET) was performed on 27 Fontan patients and 25 healthy controls with a linearly increasing workload.
• Heart rate (HR), oxygen uptake (VO2), and heart rate recovery were measured.
• Oxygen pulse (a surrogate for stroke volume) was calculated.

Main Results:

• Fontan patients demonstrated a lower absolute heart rate at midpoint and maximal effort but a higher HR relative to workload compared to controls.
• Heart rate recovery was similar between groups.
• Oxygen pulse was reduced at maximal effort in Fontan patients, indicating impaired stroke volume augmentation.

Conclusions:

• Fontan patients exhibit an elevated heart rate relative to workload, suggesting a compensatory mechanism for reduced stroke volume.
• The inability to further increase stroke volume and cardiac output at higher exercise intensities appears to be a key factor limiting maximal oxygen uptake and physical performance in Fontan survivors.
• These findings highlight the importance of assessing stroke volume dynamics during exercise in Fontan patients.