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 (LSstress) and volume load (LScath). 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 LSstress 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. LSstress at maximal loading did not correlate with changes in heart rate. During catheterization, the mean LScath 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, LScath worsened or improved with less than -2% after the saline infusion. Worsening in LScath correlated with CVP and VEDP in all conditions (P≤0.017). There was no difference in LSstress or LScath 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.