Non-Invasive Quantification of Pressure-Volume Loops in Patients with Fontan Circulation

Background: Pressure-volume (PV) loops provide comprehensive information of cardiac function, but commonly implies an invasive procedure under general anesthesia. A novel technique has made it possible to non-invasively estimate PV loops with cardiac magnetic resonance (CMR) and brachial pressure which would enable good volume estimation of often anatomically complex ventricles without the need of anesthesia in most cases. In this study we aimed to compare how hemodynamic parameters derived from PV loops in patients with Fontan circulation differ to controls. Methods: Patients with Fontan circulation (n=17, median age 12 years, IQR 6-15) and healthy controls (n=17, 14 years, IQR 13-22) were examined with CMR. Short axis balanced steady-state free-precession (bSSFP) cine images covering the entire heart were acquired. PV loops were derived from left ventricular volumes in all timeframes and brachial blood pressure from cuff sphygmomanometry. Results: Patients had lower stroke work, ventricular mechanical efficiency and external power compared to controls. Patients with dominant right ventricle (RV) had higher potential energy indexed to body surface area (BSA) but lower contractility (Ees) compared to controls. Patients had higher arterial elastance (Ea) and Ea/Ees ratio than controls. No difference was seen in energy per ejected volume between patients and controls. Conclusions: This non-invasive PV-loop method could be used in future studies to show the potential prognostic value of these measures and if changes in ventricular function over time can be detected earlier by this method compared to changes in ventricular volumes and ejection fraction (EF). In contrast to patients with acquired heart failure, Fontan patients had similar energy per ejected volume as controls which suggests similar ventricular oxygen consumption to deliver the same volume in Fontan patients as in controls.