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. The aim of this study was to explore myocardial functional reserve in adolescent patients with Fontan circulation in response to exercise or acute preload increase.

Methods: The study included 32 patients (median age, 16.7 years; range, 15.4-17.9 years; 12 female patients) 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. Myocardial peak longitudinal strain (LS) was measured in a four-chamber view during specific time intervals before, during, and after exercise (LS_stress) and volume load (LS_cath). During catheterization, central venous pressure and ventricular end-diastolic pressure were simultaneously recorded. A control group of 16 healthy individuals participated in the exercise test.

Results: Mean LS_stress was less negative for patients than for control subjects (P ≤ .001 at all stages); however, it significantly improved from -18.4 ± 5.5% at baseline to -22.0 ± 6.5% (P = .004) at maximal loading. LS_stress at maximal loading did not correlate with changes in heart rate. During catheterization, mean LS_cath was -19.6 ± 6.0% at baseline and did not improve significantly at 1.00 to 2.00 minutes and at 4.00 to 6.00 minutes after saline infusion. In more than half of the patients, LS_cath worsened or improved by less than -2% after saline infusion. Worsening of LS_cath correlated with central venous pressure and ventricular end-diastolic pressure in all conditions (P ≤ .017). There was no difference in LS_stress or LS_cath between the morphologic right ventricle and the morphologic left ventricle.

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