Abstract 2117: Mechanism of Exercise Limitation in Fontan-Palliated Patients: Results of a Prospective Crossover Trial Using Supine and Upright Exercise
Background: Fontan-palliated patients have reduced exercise capacity, primarily due to limitations in the ability to augment pulmonary blood flow and stroke volume (SV). Using supine exercise, which is associated with an acute increase in venous return, we sought to determine whether exercise performance in the Fontan is predominantly limited by inadequate venous return, excessive pulmonary vascular resistance (PVR), ventricular diastolic dysfunction, or a combination thereof.
Methods and Results: We conducted a single-center prospective crossover trial of supine and upright exercise in 28 Fontan patients (17 male, age 13.4 yrs) and 16 healthy controls (9 male, age 12.7 yrs). All subjects completed the protocol without adverse events. Oxygen consumption (VO2) at ventilatory anaerobic threshold did not differ between Fontan and control patients in either posture (p≥0.09). The duration of exercise, %-predicted peak VO2 and peak work were reduced in the Fontan group, regardless of posture (p≤0.02). The %-predicted oxygen pulse, a surrogate for pulmonary SV, was not increased with supine posture in the Fontan cohort (Upright: 84±16.9% vs. Supine: 84.4±16.7%; p=0.5). In both groups, %-predicted peak VO2 was lower with supine exercise, compared with upright exercise (p≤0.002). Diastolic dysfunction was present in 56% of Fontan patients and associated with a reduction in supine peak work (112±27W vs. 84±20W; p=0.004) and near significant reduction in supine %-predicted peak VO2 (59.9±11.4% vs. 50.5±11.9%; p=0.06). Six Fontan patients who underwent supine exercise with indwelling catheters failed to demonstrate the expected drop in pulmonary vascular resistance (PVR) seen with peak exercise (Rest: 2.8±0.7WU*m2 vs. Peak: 2.8±0.9WU*m2; p=0.9).
Conclusion: In Fontan patients, submaxi-mal exercise is relatively preserved. Supine exercise does not result in an increased VO2 or pulmonary SV, suggesting that inadequate systemic venous return is not the primary limitation of exercise capacity in this population. Diastolic dysfunction and relatively excessive PVR may be more important factors in Fontan exercise limitation.