Vector flow mapping analysis of left ventricular energetic performance in healthy adult volunteers

Abstract

Background: Vector flow mapping, a novel flow visualization echocardiographic technology, is increasing in popularity. Energy loss reference values for children have been established using vector flow mapping, but those for adults have not yet been provided. We aimed to establish reference values in healthy adults for energy loss, kinetic energy in the left ventricular outflow tract, and the energetic performance index (defined as the ratio of kinetic energy to energy loss over one cardiac cycle).

Methods: Transthoracic echocardiography was performed in fifty healthy volunteers, and the stored images were analyzed to calculate energy loss, kinetic energy, and energetic performance index and obtain ranges of reference values for these.

Results: Mean energy loss over one cardiac cycle ranged from 10.1 to 59.1 mW/m (mean ± SD, 27.53 ± 13.46 mW/m), with a reference range of 10.32 ~ 58.63 mW/m. Mean systolic energy loss ranged from 8.5 to 80.1 (23.52 ± 14.53) mW/m, with a reference range of 8.86 ~ 77.30 mW/m. Mean diastolic energy loss ranged from 7.9 to 86 (30.41 ± 16.93) mW/m, with a reference range of 8.31 ~ 80.36 mW/m. Mean kinetic energy in the left ventricular outflow tract over one cardiac cycle ranged from 200 to 851.6 (449.74 ± 177.51) mW/m with a reference range of 203.16 ~ 833.15 mW/m. The energetic performance index ranged from 5.3 to 37.6 (18.48 ± 7.74), with a reference range of 5.80 ~ 36.67.

Conclusions: Energy loss, kinetic energy, and energetic performance index reference values were defined using vector flow mapping. These reference values enable the assessment of various cardiac conditions in any clinical situation.

Keywords: Energetic performance index; Energy loss; Kinetic energy; Vector flow mapping; Vortex.

Fig. 1

Example of a vector flow mapping image of a healthy volunteer. a The strong clockwise rotating vortex and the weak counterclockwise rotating vortex are shown during early diastole. b The weak counterclockwise rotating vortex diminishes, and the strong clockwise rotating vortex is in the mid-cavity of the left ventricle during mid-diastole. c The clockwise rotating vortex is now in the base cavity of the left ventricle due to the atrial contraction during late diastole. d Vortex momentum facilitates the ejection flow during early systole. e All of the flow from the whole left ventricular cavity is directed to the left ventricular outflow tract

Fig. 2

Example of energy loss images and a graph of a healthy volunteer. The energy loss images are superimposed on apical long-axis echocardiography views. Brightness indicates energy loss. The time phases are, from the left, early systole, mid-systole, isovolumetric relaxation phase, early diastole, mid-diastole, and late diastole. The systolic peak of the graph is due to the flow acceleration from the left ventricular cavity into the left ventricular outflow tract. The velocity vectors are aligned toward the outflow tract, demonstrated on the energy loss image by the bright area around the outflow tract. The diastolic peak of the graph is due to the dissipative transmitral inflow. The inflow forms vortices that minimize the energy loss

Fig. 3

Correlations between energetic performance and other parameters. a Average energy loss over one cycle (ELcycle) and heart rate. b Average energy loss over one cycle (ELcycle) and E wave velocity c Mean systolic energy loss (ELsys) and heart rate (HR). d Mean systolic energy loss (ELsys) and left ventricular functional shortening (LVFS) e Mean diastolic energy loss (ELdia) and E wave velocity. f Average kinetic energy over one cycle (KEcycle) and E wave velocity

Fig. 4

Bland–Altman plots of intra- and inter-observer variability. a Intra-observer variability in the average energy loss over one cycle (ELcycle). b Intra-observer variability in kinetic energy over one cycle (KEcycle). c Inter-observer variability for ELcycle. d inter-observer variability for KEcycle. The mean values of pairs of measurements are plotted against the difference between the measurements. The red continuous line represents the arithmetic mean and the red dotted lines represent 95% limits of agreement

Fig. 5

Trans-catheter aortic valve replacement performance. Graphs of energy loss (a) and kinetic energy (b) over one cardiac cycle before and after trans-catheter aortic valve replacement due to severe aortic valve stenosis. Both energy loss and kinetic energy were low before the procedure because the left ventricular inflow and outflow were stagnated due to the stenotic aortic valve. After the procedure, the left ventricular inflow and outflow became dynamic, and both energy loss and kinetic energy increased. The increase in kinetic energy exceeded the increase in energy loss resulting in an increase in the energy performance index, indicating improvement of the cardiac function