Abstract
Left ventricular (LV) stroke work (SW) is calculated from the pressure-volume (PV) loop. PV loops do not contain information on longitudinal and radial pumping, leaving their contributions to SW unknown. A conceptual framework is proposed to derive the longitudinal and radial contributions to SW, using ventricular force-length loops reflecting longitudinal and radial pumping. The aim of this study was to develop and validate this framework experimentally and to explore these contributions in healthy controls and heart failure patients. Thirteen swine underwent cardiovascular magnetic resonance (CMR) and LV pressure catheterization at baseline (n = 7) or 1 wk after myocardial infarction (n = 6). CMR and noninvasive PV loop quantification were performed on 26 human controls and 14 patients. Longitudinal and radial forces were calculated as LV pressure multiplied by the myocardial surface areas in the respective directions. Length components were defined as the atrioventricular plane and epicardial displacements, respectively. Contributions to SW were calculated as the area within the respective force-length loop. Summation of longitudinal and radial SW had excellent agreement with PV loop-derived SW (ICC = 0.95, R = 0.96, bias ± SD = −4.5 ± 5.4%) in swine. Longitudinal and radial contributions to SW were ~50/50% in swine and human controls, and 44/56% in patients. Longitudinal pumping required less work than radial to deliver stroke volume in swine (6.8 ± 0.8 vs. 8.7 ± 1.2 mJ/mL, P = 0.0002) and in humans (11 ± 2.1 vs. 17 ± 4.7 mJ/mL, P < 0.0001). In conclusion, longitudinal and radial pumping contribute ~50/50% to SW in swine and human controls and 44/56% in heart failure patients. Longitudinal pumping is more energy efficient than radial pumping in delivering stroke volume.NEW & NOTEWORTHY A novel method for quantifying the contributions of longitudinal and radial pumping to stroke work using global left ventricular force-length loops was proposed and validated, which can be quantified noninvasively using cardiovascular magnetic resonance and brachial cuff pressure. We found that longitudinal and radial pumping contributes equally to stroke work in controls and 44/56% in heart failure patients, and that the longitudinal pumping is more energy efficient in delivering stroke volume than radial pumping.
Highlights
Ventricles are a syncytium of branched myocytes with a complex obliquely oriented and helical microstructure that reorients and deforms during contraction [18, 27]
Longitudinal pumping refers to the displacement of the atrioventricular (AV) valve plane in the apicalbasal direction, while radial pumping refers to the inward epicardial displacement [5, 42]
Previous work has shown that the left ventricular (LV) AV-plane displacement, known as mitral annular plane systolic excursion (MAPSE), is a parameter of ventricular function that provides complementary information to ejection fraction [16, 17] and is an independent predictor of major cardiac events and mortality [3, 30, 31, 33, 47]
Summary
Ventricles are a syncytium of branched myocytes with a complex obliquely oriented and helical microstructure that reorients and deforms during contraction [18, 27]. The global deformation and displacement of the myocardial tissue can from a simplified perspective be observed and fractioned into two main comprehensive global modes of pumping: longitudinal and radial pumping [15, 22, 46]. The division into longitudinal and radial components is the result of myocardial shortening in three dimensions and includes helical twisting and sheetlet reorientation. The volume changes can be seen as longitudinal and radial displacements that are the result of the more complex myocardial rearrangement. The division into systolic volume displacements has physiological significance for the systolic atrial filling, which is the result of longitudinal (AV-plane) ventricular pumping. The portion of left ventricular (LV) stroke volume accounted for by longitudinal pumping is ~60%, while the portion accounted for by radial pumping is ~40% [5, 6]. Previous work has shown that the LV AV-plane displacement, known as mitral annular plane systolic excursion (MAPSE), is a parameter of ventricular function that provides complementary information to ejection fraction [16, 17] and is an independent predictor of major cardiac events and mortality [3, 30, 31, 33, 47]
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