Cardiac mechanics and reverse remodelling under mechanical support from left ventricular assist devices

Figures

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  Figure 1. Anatomy of a PV loop. (A) Normal PV loop representing the 4 phases of the cardiac cycle, as the heart transitions from diastolic (A) to systolic (B) state and back. (B) Pressure-volume loops at different preloads and contractile states (Ees). All PV loops are bounded by their corresponding linear ESPVR (drawn from the instantaneous end-systolic pressure-volume points) and the EDPVR (drawn from the corresponding end-diastolic pressure-volume points). The slope of ESPVR represents end-systolic elastance (Ees), a measure of intrinsic contractility, and the x-axis intercept is the dead volume (Vd), below which ventricular pressure generation does not occur. Figures are adapted from: (8). ESV, end systolic volume; EDV, end diastolic volume.

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  Figure 2. PV loops in health and disease. ESPVR and EDVPR shifts with decreasing contractility and decreased compliance (depicted by the grey dotted arrows) during pathological remodelling of the heart. Decreased cardiac contractility in HFrEF shifts ESPVR rightwards with a shallower slope (orange dotted line). Progressive ventricular remodelling leads to a rightward shift of the EDPVR (green dotted line), and further downward shifting of the ESPVR, causing LV dilatation and decreased LV contractility. Adapted from: (13).

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  Figure 3. Mechanical circulatory support devices. (A) centrifugal continuous flow durable LVAD (HeartMate 3), (B) continuous axial-flow durable LVAD (HeartWare) and (C) Transvalvular micro-axial flow device (Impella). Images adapted from: (17–19).

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  Figure 4. Mechanical circulatory support unloading and effect on cardiac mechanics. (A) Triangular PV loop with progressive leftwards and downwards shift under mechanical support and (B) LV-aortic pressure uncoupling. LV pressure (LVP—represented by the red theme), and aortic pressure (AoP—represented by the blue theme) progressively uncouple with increased device flow rates. Adapted from: (12, 43).

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  Figure 5. Effects of prolonged mechanical unloading on diastolic function. EDPVR of a healthy vs. HF with reduced ejection fraction (HFrEF) heart and time-dependent LVAD–associated leftward shifts in EDPVR, with shorter (LVAD) and longer duration (LVAD+) of unloading. The effects of immediate mechanical unloading on the point of operation of the heart on the EDPVR are also shown (HFrEF diagonal arrow from orange dot to blue dot). Adapted from: (43).

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  Figure 6. PV area corresponding to myocardial oxygen consumption. The pressure-volume area (PVA) is the sum of the stroke work (SW) and potential energy (PE) and represents the total mechanical work of the ventricle per beat. The PVA is directly correlated to the myocardial oxygen consumption (MVO2). Figure shows PVA before and after implantation of LVAD. Adapted from: (44).

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  Figure 7. Myocardial O2 demand (SPTI) and supply (DPTI) with or without mechanical unloading. Modified Wigger's diagram showing progressive mechanical unloading (represented by grey dotted arrow) and uncoupling of LV pressure (LVP—red themed loops) and aortic pressure (AoP—blue themed loops), correlated with increased DPTI (grey overlay) and decreased SPTI (hashed overlay. Adapted from: (47).

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  Figure 8. Flow and device specific structural remodelling. 3D illustration of RV (red) and LV (orange) endocardial surfaces geometry obtained following implantation of HeartMate 2 or HeartWare LVADs. Figure adapted from (63).

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  Figure 9. Graphical illustration of the cellular and molecular changes seen with LVAD-induced reverse remodelling. Cellular and molecular changes in LVAD-induced reverse remodelling. (Left) Changes in cardiomyocyte size, expression of Ca2+-handling proteins, and cytoskeletal components as a function of mechanical unloading. (Right) Supplementation of cardiac output from mechanical device halts the negative feedback loop [demarcated with (−) here] leading to decreased neurohormonal activation and improved biochemical milieu—these are systemic effects and impact both the RV and LV.