Ventricular energetics in Fontan circulation: Evaluation with a theoretical model

Background: Both pulmonary and systemic circulation must be maintained by a single pump in Fontan circulation. This unique property of Fontan circulat ion may be related to decreased exercise tolerance or increased instantaneo us postoperative mortality rate, often observed in patients with this circu lation. To better understand Fontan physiology, the present study theoretic ally investigated cardiac performance of Fontan circulation by using ventri cular-vascular coupling framework analysis. Methods: End-systolic volume elastance (Ees), as a chamber contractile prop erty, and effective arterial elastance (Ea), a lumped measure of ventricula r afterload, were estimated both in normal left ventricular systemic circul ation and in Fontan circulation. Results: End-systolic volume elastance was decreased and Ea was increased i n Fontan circulation. Both ventricular external stroke work (SW) and mechan ical efficiency (EFF) under Fontan circulation were lower compared with tho se under normal circulation. Furthermore, the Ees-Ea relationship in Fontan circulation predicted limited cardiac reserve in terms of SW and EFF. Such cardiac performance in Fontan circulation stemmed from increased impedance due to the additional connection of the pulmonary vascular bed to the syst emic vasculature and from the lack of a compensatory increase in contractil ity for increased afterload. Conclusions: Thus, it was inferred that Fontan circulation had intrinsic di sadvantages and this may explain, in part, abnormal functional status and d ecline in survival following this procedure.