Right ventricular (RV) function is a powerful prognostic indicator in many forms of heart disease, but its assessment remains challenging and inexact. RV dysfunction may alter the normal patterns of RV blood flow, but those patterns have been incompletely characterized. We hypothesized that, based on anatomic differences, the proportions and energetics of RV flow components would differ from those identified in the left ventricle (LV) and that the portion of the RV inflow passing directly to outflow (Direct Flow) would be prepared for effective systolic ejection as a result of preserved kinetic energy (KE) compared with other RV flow components. Three-dimensional, time-resolved phase-contrast velocity, and balanced steady-state freeprecession morphological data were acquired in 10 healthy subjects using MRI. A previously validated method was used to separate the RV and LV end-diastolic volumes into four flow components and measure their volume and KE over the cardiac cycle. The RV Direct Flow: 1) followed a smoothly curving route that did not extend into the apical region of the ventricle; 2) had a larger volume and possessed a larger presystolic KE (0.4 Ϯ 0.3 mJ) than the other flow components (P Ͻ 0.001 and P Ͻ 0.01, respectively); and 3) represented a larger part of the end-diastolic blood volume compared with the LV Direct Flow (P Ͻ 0.01). These findings suggest that diastolic flow patterns distinct to the normal RV create favorable conditions for ensuing systolic ejection of the Direct Flow component. These flowspecific aspects of RV diastolic-systolic coupling provide novel perspectives on RV physiology and may add to the understanding of RV pathophysiology. cardiac disease; interventricular function; kinetic energy; phase-contrast magnetic resonance imaging; pump physiology RIGHT VENTRICULAR (RV) FUNCTION has important prognostic impact on both acquired and congenital cardiac diseases (10). The RV may be affected by primary right-sided pathological conditions, such as pulmonary hypertension, congenital heart disease, or cardiomyopathy, or secondarily involved in states with left ventricular (LV) dysfunction (5, 28).Accurate measurement of RV volume and function is the focus of investigations using many modalities (14,18,(23)(24). The most widely employed clinical technique for RV morphological and functional assessment is two-dimensional echocardiography (14, 23), but its accuracy is limited by the complex crescent shaped geometry of the RV and by its location behind the sternum (14, 18). Magnetic resonance imaging (MRI) offers more detailed, three-dimensional (3-D) anatomy and can improve RV volume assessment (11). The dynamic functional status of the RV, which is significantly impacted by respiratory events and loading conditions, remains challenging and inexact (11).The anatomic structures of the heart and the intracardiac blood flow are highly interdependent, and changes in flow due to altered cardiac shape or function may in turn influence structural remodeling (13,21,29). Three-dimensional, timereso...

Aims4D flow magnetic resonance imaging (MRI) allows quantitative assessment of left ventricular (LV) function according to characteristics of the dynamic flow in the chamber. Marked abnormalities in flow components’ volume and kinetic energy (KE) have previously been demonstrated in moderately dilated and depressed LV’s compared to healthy subjects. We hypothesized that these 4D flow-based measures would detect even subtle LV dysfunction and remodeling.Methods and ResultsWe acquired 4D flow and morphological MRI data from 26 patients with chronic ischemic heart disease with New York Heart Association (NYHA) class I and II and with no to mild LV systolic dysfunction and remodeling, and from 10 healthy controls. A previously validated method was used to separate the LV end-diastolic volume (LVEDV) into functional components: direct flow, which passes directly to ejection, and non-ejecting flow, which remains in the LV for at least 1 cycle. The direct flow and non-ejecting flow proportions of end-diastolic volume and KE were assessed. The proportions of direct flow volume and KE fell with increasing LVEDV-index (LVEDVI) and LVESV-index (LVESVI) (direct flow volume r = -0.64 and r = -0.74, both P<0.001; direct flow KE r = -0.48, P = 0.013, and r = -0.56, P = 0.003). The proportions of non-ejecting flow volume and KE rose with increasing LVEDVI and LVESVI (non-ejecting flow volume: r = 0.67 and r = 0.76, both P<0.001; non-ejecting flow KE: r = 0.53, P = 0.005 and r = 0.52, P = 0.006). The proportion of direct flow volume correlated moderately to LVEF (r = 0.68, P < 0.001) and was higher in a sub-group of patients with LVEDVI >74 ml/m2 compared to patients with LVEDVI <74 ml/m2 and controls (both P<0.05).ConclusionDirect flow volume and KE proportions diminish with increased LV volumes, while non-ejecting flow proportions increase. A decrease in direct flow volume and KE at end-diastole proposes that alterations in these novel 4D flow-specific markers may detect LV dysfunction even in subtle or subclinical LV remodeling.

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1043-1053.

Methods4D flow and morphological 3T MRI data were acquired in 22 patients with mild ischemic heart disease, that were stratified into two groups based on LV end-diastolic volume index (EDVI): lower-LVEDVI and higher-LVEDVI, as well as in 11 healthy controls. The RV volume was segmented at end-diastole (ED) and end-systole (ES).Pathlines were emitted from the ED volume and traced forwards and backwards in time to ES. The blood volume was separated into flow components. The Direct Flow (DF) component was defined as RV inflow passing directly to outflow. The kinetic energy (KE) of the DF component was calculated. Echocardiographic conventional RV indices were also assessed. ResultsThe higher-LVEDVI group had larger LVEDVI and lower LV ejection fraction (98±32 ml/m 2 ; 48±13 %) compared to the healthy (67±12, P=0.002; 64±7, P<0.001) and lower-LVEDI group (62±10; 68±7, both P<0.001). The RV 4D flow specific measures "DF/EDV volume-ratio" and "DF/EDV KE-ratio at ED" were lower in the higher-LVEDVI group (38±5 %; 52±6 %) compared to the healthy (44±6; 65±7, P=0.018 and P<0.001) and lower-LVEDVI groups (44±6; 64±7, P=0.011 and P<0.001). There was no difference in any of the conventional MRI and echocardiographic RV indices between the three groups.4 ConclusionWe found that in primary LV disease, mild impairment of RV function can be detected by 4D flow specific measures, but not by the conventional MRI and echocardiographic indices.