Assessing cardiac mechanics through left ventricular haemodynamic forces

Figures

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  Figure 1. Techniques currently used to assess haemodynamic forces (HDFs). Upper panel: Global haemodynamic forces (HDFs) can be calculated at 4D-flow magnetic resonance imaging (MRI). Left ventricular (LV) endocardial border is manually delineated in cine images. Once the velocity field is known, pressure gradients g in the 4D-data set are computed using the Navier–Stokes equation and integrated over the LV ventricular volume to produce the HDF. The equation uses variables such as ρ for mass density, v for fluid velocity vector field, t for time, and μ for the fluid viscosity. The force vector obtained is decomposed into 3 orthogonal components: basal–apical, lateral–septal, and inferior–anterior. For each component, HDF output, directions, and the transverse/longitudinal ratio are obtained. Lower panel: Thanks to recent advances,1 HDFs can be also computer at cine cardiac magnetic resonance (CMR) and echocardiographic images. First, a four, two, and three-chamber view should be acquired. The global HDF vector F(t) is then calculated thanks to the equation here reported. The fluid velocity vector field v(x, t) is measured at fixed points x at time t, while S(t) represents the closed…

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  Figure 2. Left ventricular (LV) longitudinal HDFs in systole and diastole. The haemodynamic force (HDF, thin arrow) always flows from the area of higher to the lower pressure area. The absence of intraventricular pressure gradient (IVPG) is displayed in grey. The flow direction (wide arrow) goes from the higher to the lower pressure chamber. The start of systole is marked by isovolumic contraction, which occurs between the mitral valve closure (MVC) and the aortic valve opening (AVO), which corresponds to the QRS complex on ECG. During this phase, the longitudinal force shows a positive deflection (A) due to an apex-base IVPG, which causes an acceleration of flow towards the base. When the AV opens, systolic ejection begins. Initially, HDFs exhibit a positive ascending phase, because of the increased IVPG (B). Once the peak is reached, although ventricular contraction continues, LV starts to lose tension; this causes a decrease in the gradient between the apex and the base in a positive descending phase, as a large amount of blood volume has been ejected (C). As systole nears its end, the IVPG reverses (becoming greater at the basal level). At this stage, ventricular flow is decelerating,…

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  Figure 3. LV longitudinal HDF curves. On the left, from top to bottom: I) Time profile of the left ventricular apical-basal and lateral–septal haemodynamic forces; II) haemodynamic power; III) Time profile of the left ventricular apical-basal and lateral–septal volume curves. At the bottom right, the red isosceles triangles within the polar histogram represent the distribution and intensity of the left ventricular haemodynamic force during the entire cardiac cycle. This latter helps defining the main direction of blood flow during the cardiac cycle. As opposed to the physiological longitudinal orientation of blood flow, pronounced transversal HDF components indicate a deviation from the normal synchrony of segmental myocardial deformation, resulting in abnormally oriented pressure gradients.

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  Figure 4. Amplitude intervals commonly used in the calculation of HDFs. Modified with permission from Faganello et al.23

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  Figure 5. Intensity-weighted polar histogram of HDFs orientation. The distribution and intensity of the left ventricular haemodynamic force during the entire cardiac cycle are shown by red isosceles triangles within a polar histogram. A, physiological flow orientation with a mainly longitudinal (apex-base) directed forces; B, pathological flow orientation with a prevalent transversal (septal-lateral or inferior-anterior) directed forces. Reprinted with permission from Vallelonga et al.5

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  Figure 6. HDFs in a patient with left bundle branch block (LBBB) in comparison with a second patient without LBBB. The figure illustrates the HDF plots in a patient with LBBB (left) and in a patient withoutLBBB (right), projected onto a short-axis (SAx) image (top) and long-axis (LAx) image (bottom). The HDF plots are colour-coded according to diastolic phases, E-wave and A-wave. The ‘SAxmax/LAxmax force’ ratio was defined as the ratio between the maximum force along the anteroseptal-to-inferolateral axis in the SAx-view and the maximum force along the apex-to-base axis in the LAx three-chamber view. E-wave, early diastolic filling; A-wave, late diastolic filling; LA, left atrium; LV, left ventricle. Reprinted with permission from Eriksson et al.4

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  Figure 7. Survival analyses in patients on sacubitril/valsartan. Kaplan–Meier survival analysis for the composite endpoint (all-cause death, hospitalization due to worsening heart failure, and new-onset atrial fibrillation) after a median follow-up of 32.5 months. The patients are stratified by angiotensin receptor-neprilysin inhibitor (ARNI) responders and non-responders (A) and according to Δwhole cardiac cycle left ventricular strength (ΔwLVS > 0.5% vs. ΔwLVS > 0.5%) (B). Δ indicates the difference measured between the 6-month ARNI-response protocol and baseline evaluation. Reprinted with permission from Fabiani et al.32

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  Figure 8. Potential applications of HDF analysis.