Feasibility, Reproducibility, and Prognostic Value of Exercise Echocardiography for Cardiac Output Reserve Assessment in Fontan Physiology

BACKGROUND: The purpose of this study was to assess the feasibility and prognostic value of cardiac output (CO) reserve assessment using exercise echocardiography in Fontan patients. We hypothesized that adults with Fontan palliation had lower CO reserve compared with controls, and impaired CO reserve was associated with greater congestion (NT-proBNP [N-terminal pro-B-type natriuretic peptide]) and cardiovascular events (death/transplant/heart failure hospitalization) in Fontan patients. METHODS: Thirty-seven Fontan patients and 61 controls underwent exercise echocardiography using a supine cycle ergometer. Doppler-derived CO and oxygen consumption (VO 2 ) were assessed at rest and every stage of exercise. CO reserve was calculated as ∆CO/Watt (∆CO/W) and ∆CO/∆VO 2 . RESULTS: Assessment of CO reserve was feasible in 95% of the Fontan group with modest reproducibility. Although both groups had similar CO at rest, the Fontan group had lower CO reserve with exercise as evidenced by lower ∆CO/W ratio (46±17 versus 57±19 mL/W; P <0.001) and lower ∆CO/∆VO 2 ratio (4.48±1.02 versus 5.37±2.18 mL/mL; P =0.03). There was a correlation between ∆CO/W ratio and log NT-proBNP (r=0.65; P <0.001), and between ∆CO/∆VO 2 ratio and log NT-proBNP (r=0.53; P =0.009). Impaired CO reserve was associated with congestion and cardiovascular events and provided improved prognostication (higher area under the curve and C statistics) above conventional echocardiographic indices and treadmill peak VO 2 . CONCLUSIONS: Patients with Fontan palliation had lower CO reserve, and impaired CO reserve was associated with congestion and cardiovascular events. Further studies are required to determine whether cardiac interventions can improve CO reserve and whether changes in CO reserve can be used as a surrogate end point for therapeutic response.