Measurement of left ventricular fluid dynamic parameters in healthy Chinese adults based on echocardiographic vector flow mapping

To the Editor: As we concerdered that there was barely any widely representative, recognized, and standardized echocardiographic vector flow mapping (VFM) method has been established for the observation and measurement of the blood flow in cardiac cavities in clinical practice, and there were no commonly accepted normal reference values for Chinese adults have been obtained till now, hindering the further promotion and application of this technology in clinical practice. Establishing normal reference values for echocardiographic VFM that can be widely accepted in clinical practice is of great significance for determining the normal or abnormal fluid dynamic status in the left ventricle (LV) chamber. Echocardiographic VFM-based multicenter, large-sample clinical observation, and quantitative studies are effective methods to test the practicability and reliability of this technology, and they are helpful for establishing a novel, standardized VFM-based echocardiographic observation technique system for the observation, analysis, and quantitative evaluation of cardiac fluid dynamics. On this basis, reliable normal VFM reference values for the fluid dynamics of the LV of healthy Chinese adults can be established.

A total of 728 healthy Chinese adults from 15 medical centers [supplementary table 1, https://links.lww.com/CM9/B501] were included. Among them, there were 336 males, with a mean age of 42.7 ± 17.0 years and there were 392 females, with a mean age of 42.6 ± 15.4 years. For all healthy volunteers, the LV end-diastolic and end-systolic volumes (LVEDV, LVESV), left ventricular ejection fraction (LVEF), cardiac index (CI), and cardiac output (CO) were measured by the biplane Simpson's method. The standard protocols for acquiring spectral Doppler parameters were as follows. Open the pulsed-wave (PW)/tissue Doppler imaging (TDI) mode in standard apical four-chamber (A4C) view, place the PW sampling volume at the mitral orifice during diastole, with a sampling frame size of 5 mm, place the TDI sampling volume on the interventricular septum at the annulus of the mitral leaflet, simultaneously obtain the peak mitral inflow velocity during early diastole (E) and late diastole (A), and the movement velocity (E) of the LV lateral mitral annulus, and calculate E/E′. The real-time color Doppler flow imaging (CDFI) images of the standard A4C, apical three-chamber (A3C), and apical two-chamber (A2C) views of the LV of three complete cardiac cycles were collected from all 728 healthy Chinese adults.

The parameter presettings and image orientation determination principles required for acquiring CDFI images were as follows. A Prosound F75 color Doppler echocardiographic diagnostic system equipped with a UST-52105 probe (Prosound F75, FUJIFILM Healthcare Corporation, Kashiwa-shi, Japan) was used for all examinations, the echocardiographic transmitting frequency for CDFI during the acquisition of CDFI images used for offline VFM analysis was 1 to 5 MHz, and the acquisition conditions were the preset VFM conditions. All CDFI images were acquired with the volunteer at rest and in a state of sinus heart rate. A synchronized body surface electrocardiogram was connected, and the left decubitus position (for the acquisition of cardiac images) was taken.

The acquired dynamic two-dimensional CDFI images (Digital Imaging and Communications in Medicine [DICOM] format) were imported into the dedicated Digital Imaging and Communications in Medicine (DAS-RS1) ultrasound workstation to perform VFM image offline analysis. Based on observing the complete cardiac cycle, the synchronized body surface electrocardiogram and the time-flow curves for the mitral valve orifice and aortic valve orifice were used as the evidence of phase confirmation to determine the four observation phases: early and middle diastole (ED, MD), isovolumic contraction (IC), and rapid ejection (RE). The circulation of vortices and energy loss (EL) in the LV chamber at different phases of the same cardiac cycle were extracted.

Statistical analysis was performed under the guidance of statistical professionals and carried out in strict accordance with the methods and principles of medical statistical processing. All quantitative data included in the analysis were tested for normality and homogeneity of variance. Quantitative data are expressed as $\overline{x}\pm \text{s}$. The bilateral 95% reference range (P2.5, P97.5) obtained by the percentile method was used to calculate the following LV fluid dynamic reference ranges for Chinese adults based on echocardiographic VFM: LV EL and vortex circulation of different apical views at different phases of the same cardiac cycle. Data were analyzed using SPSS version 26.0 (SPSS, Inc., Chicago, IL, USA). The corresponding parametric test or non-parametric test methods were used to compare the same quantitative parameters between the sexes. The cut-off value for the comparison of means was taken as two-tailed, and P < 0.05 was considered statistically significant.

The height, weight, body surface area, and diastolic blood pressure in males were higher (P < 0.05); while age, body mass index, and systolic blood pressure were not significantly different (P > 0.05). There was no significant difference in LVEF and CI between different sex (P > 0.05). The LVEDV, LVESV, and CO were greater in males than in females (P < 0.05). E, A, and E/E′ were lower in males than in that females (P <0.05) [supplementary table 2, https://links.lww.com/CM9/B501].

Normal reference values of echocardiographic VFM observation parameters of LV at different phases were divided according to gender: Table 1 provides the EL and vortex circulation for the A4C, A3C, and A2C views of the LV during ED, MD, IC, and RE.

Table 1 - Measured energy loss and vortex circulation in the LV chamber during different phases of the same cardiac cycle and on different views in males and females.

Parameters			Males		Females
VFM	View	Phase	Lower limit	Upper limit	Lower limit	Upper limit
EL(J·s–1·m–1)	A4C	ED	1.73	63.25	2.87	85.55
		MD	0.03	23.30	0.31	37.12
		IC	0.35	13.51	0.63	20.44
		RE	0.82	13.01	0.96	12.30
	A3C	ED	1.49	66.77	2.77	66.04
		MD	0.06	21.24	0.39	25.49
		IC	0.45	13.90	0.63	17.75
		RE	1.25	19.60	1.18	27.89
	A2C	ED	1.10	70.00	1.73	79.89
		MD	0.01	17.66	0.38	31.10
		IC	0.22	11.91	0.26	17.38
		RE	0.14	15.66	0.52	10.76
CIR (m2/s, ×10–2)	A4C	ED	0.00	4.52	0.00	5.83
		MD	0.00	5.74	0.00	5.64
		IC	0.00	4.96	0.00	5.49
		RE	0.00	2.81	0.00	3.22
	A3C	ED	0.00	4.61	0.00	5.75
		MD	0.00	4.99	0.00	5.00
		IC	0.00	5.79	0.00	4.21
		RE	0.00	2.72	0.00	3.10
	A2C	ED	0.00	3.89	0.00	4.65
		MD	0.00	4.78	0.00	4.81
		IC	0.00	4.52	0.00	4.66
		RE	0.00	2.72	0.00	3.07

Note: 95% reference range, lower limit: 2.5th percentile (P2.5), upper limit: 97.5th percentile (P97.5). A2C: Apical two-chamber view; A3C: Apical three-chamber view; A4C: Apical four-chamber view; CIR: Vortex circulation; ED: Early diastole; EL: Energy loss; IC: Isovolumic contraction; MD: Middle diastole; RE: Rapid ejection; VFM: Vector flow mapping.

Echocardiographic VFM is a non-invasive medical imaging technology that has emerged in recent years to evaluate the fluid dynamic status in a visual manner. At present, there are a large number of reports on the application of VFM in the evaluation of the function of the LV and great vessels.^[1,2] The measurement of fluid dynamics in the LV chamber is an important technique for assessing cardiac diseases. The establishment of normal reference values for echocardiographic VFM that can be widely accepted in clinical practice has important scientific and theoretical significance for future studies of abnormal cardiac fluid dynamics and has significant clinical significance for identifying normal and abnormal fluid dynamic status in the LV chamber. Therefore, carrying out a multicenter, large-sample, quantitative study is an effective method to test the practicability and reliability of the technology, and it is conducive to the establishment of VFM-based, novel, and standardized guidelines for cardiac hydrodynamic function.

Studies have indicated that most of the measured parameters and fluid dynamic parameters of the LV are sex-related.^[3,4] If the same normal reference values are used as the fluid dynamic parameters for the male and female, the results will be biased, and false positives and negatives that could have been avoided will occur. Therefore, in this multicenter study, we observed the VFM parameters in males and females to provide objective, accurate, and representative normal reference values of VFM parameters for Chinese adults.