Hemodynamic interplay of vorticity, viscous energy loss, and kinetic energy from 4D Flow MRI and link to cardiac function in healthy subjects and Fontan patients

The purpose of this study was to directly assess (patho)physiology of intraventricular hemodynamic interplay between four-dimensional flow cardiovascular magnetic resonance imaging (4D Flow MRI)-derived vorticity with kinetic energy (KE) and viscous energy loss (EL) over the cardiac cycle and their association to ejection fraction (EF) and stroke volume (SV). Fifteen healthy subjects and thirty Fontan patients underwent whole heart 4D Flow MRI. Ventricular vorticity, KE, and EL were computed over systole (vorticity_vol _avg systole, KE _avg systole, and EL _{avg systole}) and diastole (vorticity_vol _avg diastole, KE _avg diastole, and EL _{avg diastole}). The association between vorticity_vol and KE and EL was tested by Spearman correlation. Fontan patients were grouped to normal and impaired EF groups. A significant correlation was found between SV and vorticity in healthy subjects (systolic: r = 0.84, P < 0.001; diastolic: r = 0.81, P < 0.001) and in Fontan patients (systolic: r = 0.61, P < 0.001; diastolic: r = 0.54, P = 0.002). Healthy subjects showed positive correlation between vorticity_vol versus KE (systole: r = 0.96, P < 0.001; diastole: r = 0.90, P < 0.001) and EL (systole: r = 0.85, P < 0.001; diastole: r = 0.84, P < 0.001). Fontan patients showed significantly elevated vorticity_vol compared with healthy subjects (vorticity_vol _{avg systole}: 3.1 [2.3–3.9] vs. 1.7 [1.3–2.4] L/s, P < 0.001; vorticity_vol _{avg diastole}: 3.1 [2.0–3.7] vs. 2.1 [1.6–2.8] L/s, P = 0.002). This elevated vorticity in Fontan patients showed strong association with KE (systole: r = 0.91, P < 0.001; diastole: r = 0.85, P < 0.001) and EL (systole: r = 0.82, P < 0.001; diastole: r = 0.89, P < 0.001). Fontan patients with normal EF showed significantly higher vorticity_vol _{avg systole} and EL _avg systole, but significantly decreased KE _avg diastole, in the presence of normal SV, compared with healthy subjects. Healthy subjects show strong physiological hemodynamic interplay between vorticity with KE and EL. Fontan patients demonstrate a pathophysiological hemodynamic interplay characterized by correlation of elevated vorticity with KE and EL in the presence of maintained normal stroke volume. Altered vorticity and energetic hemodynamics are found in the presence of normal EF in Fontan patients. NEW & NOTEWORTHY Physiologic intraventricular hemodynamic interplay/coupling is present in the healthy left ventricle between vorticity versus viscous energy loss and kinetic energy from four-dimensional flow cardiovascular magnetic resonance imaging (4D Flow MRI). Conversely, Fontan patients present compensatory pathophysiologic hemodynamic coupling by an increase in intraventricular vorticity that positively correlates to viscous energy loss and kinetic energy levels in the presence of maintained normal stroke volume. Altered vorticity and energetics are found in the presence of normal ejection fraction in Fontan patients.