Impact of Age and Diastolic Function on Novel, 4D flow CMR Biomarkers of Left Ventricular Blood Flow Kinetic Energy

Abstract

Two-dimensional (2D) methods of assessing mitral inflow velocities are pre-load dependent, limiting their reliability for evaluating diastolic function. Left ventricular (LV) blood flow kinetic energy (KE) derived from four-dimensional flow cardiovascular magnetic resonance imaging (4D flow CMR) may offer improvements. It remains unclear whether 4D LV blood flow KE parameters are associated with physiological factors, such as age when compared to 2D mitral inflow velocities. Fifty-three healthy volunteers underwent standard CMR, plus 4D flow acquisition. LV blood flow KE parameters demonstrated good reproducibility with mean coefficient of variation of 6 ± 2% and an accuracy of 99% with a precision of 97%. The LV blood flow KEi_EDV E/A ratio demonstrated good association to the 2D mitral inflow E/A ratio (r = 0.77, P < 0.01), with both decreasing progressively with advancing age (P < 0.01). Furthermore, peak E-wave KEi_EDV and A-wave KEi_EDV displayed a stronger association to age than the corresponding 2D metrics, peak E-wave and A-wave velocity (r = -0.51 vs -0.17 and r = 0.65 vs 0.46). Peak E-wave KEi_EDV decreases whilst peak A-wave KEi_EDV increases with advancing age. This study presents values for various LV blood flow KE parameters in health, as well as demonstrating that they show stronger and independent correlations to age than standard diastolic metrics.

Figure 1

Bar chart displaying the reference values for 4D diastolic LV blood flow KE parameters along with myocardial velocities and 2D mitral valve diastolic inflow velocities. Advancing age is denoted on the x-axis, with the study population divided into groups (1–5). Group 1 = 23 ± 2 years old (n = 12), group 2 = 32 ± 3 (n = 9), group 3 = 47 ± 4 (n = 11), group 4 = 54 ± 2 (n = 10), group 5 = 69 ± 6 (n = 11). For the 2D mitral inflow velocities and myocardial velocities, the velocity (in cm/s) is given on the y-axis with errors bars denoting standard deviation (SD), whereas for 4D diastolic blood flow KE parameters, energy in μJ/ml is given, with error bars denoting interquartile range (IQR).

Figure 2

Scatter plot demonstrating the association between 2D mitral valve diastolic inflow assessments versus 4D diastolic blood flow KE parameters. Left upper box shows peak E-wave velocity vs peak E-wave KEi_EDV, Left lower box shows peak A-wave velocity vs peak A-wave KEi_EDV. Right box shows E/A ratio vs KEi_EDV E/A ratio.

Figure 3

Scatter plots demonstrating the correlation between age and (A) log of E/A velocity ratio, (B) log of average E’ velocity, (C) log of KEi_EDV E/A ratio and (D) indexed LA volume.

Figure 4

Line graph showing the various blood flow KE peaks of the cardiac cycle through systole and diastole in healthy volunteers aged 20, 46 and 73 years old. As age increases, systolic peaks decrease. In terms of diastole, early mitral inflow blood flow KE falls whilst the A-wave KEi_EDV sharply increases as a compensatory mechanism to maintain diastolic KE and adequate filling through physiological aging. Time across the cardiac cycle is given on the x-axis, whereas KE is given on the y-axis, in μJ/ml.