Systolic Function in the Fontan Circulation is Exercise, but not Preload, Recruitable.

Background: Fontan circulatory failure with impaired systolic function is well documented; however, its mechanisms are not fully understood. We aimed to explore the myocardial functional reserve in adolescent patients with Fontan circulation in response to exercise or acute preload increase.

Methods: Our study comprised 32 patients (median age: 16.7 years, range: 15.4-17.9 years, 12 females) with Fontan circulation. Echocardiographic imaging was performed during exercise using a recumbent cycle ergometer and during heart catheterization with a rapid infusion of 0.9% saline infusion at 5 mL/kg body weight. We measured myocardial peak longitudinal strain (LS) in a 4-chamber view during specific time intervals before, during, and after the exercise (LS_stress) and volume load (LS_cath). During catheterization, central venous pressure (CVP) and ventricular end-diastolic pressures (VEDP) were simultaneously recorded. A control group of 16 healthy individuals participated in the exercise test.

Results: The mean LS_stress was less negative for patients than for controls (P≤0.001 at all stages); however, it significantly improved from -18.4±5.5% at baseline to -22.0±6.5% (P=0.004) at maximal loading. LS_stress at maximal loading did not correlate with changes in heart rate. During catheterization, the mean LS_cath was -19.6±6.0% at baseline and did not improve significantly at 1.00-2.00 min and at 4.00-6.00 min after saline infusion. In more than half of the patients, LS_cath worsened or improved with less than -2% after the saline infusion. Worsening in LS_cath correlated with CVP and VEDP in all conditions (P≤0.017). There was no difference in LS_stress or LS_cath between the morphological right ventricle and the morphological left ventricle.

Conclusion: Patients with Fontan circulation demonstrate systolic myocardial functional reserve that can be recruited with exercise stress but not with an acute increase in preload.