Correlations among noninvasive right ventricular myocardial work indices and the main parameters of systolic and diastolic functions.

BACKGROUND: Right ventricular (RV) myocardial work (RVMW) is the latest method used to assess RV function. To date, correlations among RVMW indices and RV systolic and diastolic functions have not been studied.
METHODS: A total of 106 healthy volunteers (median age, 34 years; 46% male) were prospectively enrolled. RVMW indices were measured using the RV pressure-strain loop using specific software. The correlations among RVMW indices and other RV functions were analyzed.
RESULTS: During the multivariate analysis, the RV global work index (RVGWI) was significantly correlated with RV global longitudinal strain (RV GLS) (p < .0001), pulmonary systolic artery pressure (PASP) (p < .0001), and tricuspid annular (TA) plane systolic excursion (TAPSE) (p = .036). RV global constructive work (RVGCW) was correlated with RV GLS (p < .0001) and PASP (p < .0001). RV global wasted work (RVGWW) was correlated with RV GLS (p = .008) and TA isovolumetric acceleration (TA IVA) (p = .008). RV global work efficiency (RVGWE) was correlated with RV GLS (p < .0001) and tissue Doppler (TD) RV myocardial performance index (TD RMPI) (p = .043).
CONCLUSION: RVMW indices showed good correlations with RV myocardial systolic function.

INTRODUCTION

Recently, the function of the right ventricle has received increasing attention from researchers and clinicians. Compared with the left ventricle, the right ventricle is more affected by afterload. , The most frequently used methods to analyze right ventricular (RV) function are tricuspid annular (TA) plane systolic excursion (TAPSE), RV fractional area change (RV FAC), and myocardial tissue Doppler (TD) velocities (S′). , , However, these parameters do not consider RV afterload and are unable to accurately evaluate RV function. RV longitudinal strain, as an advanced and superior method of evaluating RV function, remains an afterload‐dependent parameter. ,

RV myocardial work (RVMW) is a novel indicator used to quantitatively analyze RV function. RVMW indices are acquired by integrating the RV global longitudinal strain (RV GLS), pulmonary artery pressures, and tricuspid and pulmonic valvular events. Therefore, RVMW can evaluate RV function more precisely than conventional two‐dimensional (2D) parameters. We aimed to assess the correlations among RVMW indices and other main parameters of RV systolic and diastolic functions.

METHODS

Study population

A group of 143 healthy volunteers were prospectively recruited from May 2021 to July 2021. The inclusion criteria were as follows: age older than 18 years; body mass index < 30 kg/m2; normal physical examination results; normal electrocardiogram results; normal 2D echocardiography results; and absence of any cardiovascular or respiratory diseases. The Organizational Ethics Committee approved the protocol, and all participants provided informed consent before undergoing the examinations.

Echocardiographic acquisition

Transthoracic echocardiography was performed using a Vivid E95 scanner (GE Vingmed Ultrasound, Norway) according to the recommended protocols. , The 2D echocardiography images were acquired using an M5Sc probe, and the four‐dimensional (4D) echocardiography RV images were acquired using a 4Vc probe. All electrocardiogram‐triggered echocardiography images were obtained over three to five consecutive cardiac cycles during breath holding. Datasets were digitally stored and analyzed offline using EchoPAC v204 (GE Vingmed Ultrasound).

Echocardiographic measurements

The RV volume and RV ejection fraction were obtained using a software package (4D Auto RVQ). The TAPSE, RV FAC, and RV index of the myocardial performance according to pulsed‐wave Doppler (PD) and TD imaging (PD RV myocardial performance index [RMPI] and TD RMPI, respectively) and peak systolic velocity of the tricuspid annulus according to pulsed‐wave TD imaging and color TD imaging (TA pulsed‐wave TD S′ and TA color TD S′, respectively) were measured according to the current guidelines. TA isovolumetric acceleration (TA IVA) was measured by color TD imaging. In the RV‐focused apical four‐chamber view, RV GLS was evaluated by tracing the RV free wall and interventricular septum. The tricuspid flow pattern with E and A wave velocities were obtained with the sample volume positioned at the tricuspid leaflet tips. The tricuspid deceleration time was defined as the time from the top point to the end point of the E wave. Isovolumetric relaxation time (IVRT) was measured at the tricuspid lateral annulus using pulsed‐wave TD imaging. TA velocities according to TD imaging included early and late diastolic annular velocities (E′ and A′, respectively).

Pulmonary artery systolic pressure (PASP) was computed as follows: PASP = 4 × [tricuspid regurgitation (TR) velocity]  + mean right atrial (RA) pressure. The mean RA pressure was estimated based on the diameter and collapsibility of the inferior vena cava. The mean RV–RA gradient was estimated by tracing the TR velocity‐time integral (Figure 1A). The pulmonary artery mean pressure equals the mean RV–RA gradient plus the mean RA pressure. According to the theoretical formula, pulmonary artery diastolic pressure (PADP) was assessed as follows: PADP = 1.5 × [pulmonary artery mean pressure − (PASP/3)]. RVMW indices were analyzed using a software package (AFI) designed to assess left ventricular (LV) myocardial work (LVMW). The prognostic validation of LVMW has been performed during several studies. , , The tricuspid and pulmonic valve event timings were derived from direct visualization of the parasternal short‐axis views (Figure 1B). Then, measurements of RV GLS, PASP, and PADP were synchronized by tricuspid and pulmonic valve event timings to produce a noninvasive RV pressure–strain loop (Figure 1A–D).

FIGURE 1

Measurements of right ventricular myocardial work. (A) Calculating the mean gradient between the right ventricle and atrium by tracing the tricuspid regurgitation velocity‐time integral. (B) Visualizing the pulmonic and tricuspid valve events from the parasternal short‐axis views. (C) Evaluating right ventricular global longitudinal strain in a right ventricular focused apical four‐chamber view. (D) Acquiring right ventricular myocardial work by the pressure‐strain loop

The RVMW acquired by the RV pressure–strain loop included the following four parameters:

RV global work index (RVGWI): the area of the RV pressure–strain loop, which presents the total RVMW during tricuspid valve closure and tricuspid valve opening.

RV global constructive work (RVGCW): constructive work during shortening in systole and lengthening during isovolumic relaxation.

RV global wasted work (RVGWW): waste work during lengthening in systole and shortening during isovolumic relaxation.

RV global work efficiency (RVGWE): RVGCW / (RVGCW + RVGWW).

Statistical analysis

The normality of the variables was tested using the Kolmogorov–Smirnov test. Normally distributed variables are expressed as the mean ± SD, and those that were not normally distributed are represented as the median (first quartile, third quartile). Differences between sex groups were analyzed using the two‐tailed independent Student's t‐test and Mann–Whitney U‐test, as appropriate.

Univariate and multivariate linear regression analyzes were performed to examine the independent correlations among the RVMW indices and other RV echocardiographic parameters. Multicollinearity was tested by calculating the variance inflation factors in the multiple linear regression models. The collinear variables included the variables with the highest correlation coefficients.

The intra‐observer and inter‐observer variabilities of the RVMW were estimated for 20 random subjects using the Bland–Altman analysis. One observer analyzed the same echocardiographic images at two different times to evaluate intra‐observer variability. Two independent blinded observers analyzed the echocardiographic images to assess inter‐observer variability.

All data were analyzed using SPSS (version 26.0; SPSS Inc., IBM Corp). When p < .05, the difference between variables was considered significant.

RESULTS

Clinical characteristics

During the study, seven subjects were excluded from enrollment because of poor 2D echocardiography images or RV 4D echocardiography images. A total of 30 subjects were excluded because the TR Doppler envelope could not be obtained or the TR Doppler envelopes were of poor quality. Therefore, the feasibility of the RVMW assessment was 74.1% in the study population. The clinical characteristics of the enrolled patients are summarized in Table 1.

TABLE 1

Characteristics of the study population

Parameters	Total (n = 106)	Men (n = 49)	Women (n = 57)	p value a
Age (years)	34 (28, 44)	33 (29, 42)	34 (27, 47)	.744
BMI (kg/m2)	22.0 (20.0, 23.5)	22.5 (21.7, 24.4)	20.6 (19.1, 22.7)	<.0001
BSA (m2)	1.7 ± 0.2	1.8 ± 0.1	1.6 ± 0.1	<.0001
SBP (mmHg)	125 (115, 131)	130 (118, 132)	119 (106, 129)	.001
DBP (mmHg)	74 ± 10	75 ± 9	73 ± 10	.187
Heart rate (bpm)	68 ± 10	66 ± 10	70 ± 9	.026
PASP (mmHg)	21 (19, 24)	21 (19, 24)	22 (20, 24)	.321
PAMP (mmHg)	16 (14, 18)	15 (14, 18)	17 (15, 18)	.027
PADP (mmHg)	13 (12, 15)	12 (11, 14)	14 (13, 15)	.001
RVEDV	94 (85, 104)	104 (95, 117)	89 (77, 96)	<.0001
RVESV	39 (35, 47)	48 (42, 53)	36 (32, 39)	<.0001

Abbreviations: BMI, body mass index; BSA, body surface area; DBP, diastolic blood pressure; PADP, pulmonary artery diastolic pressure; PAMP, pulmonary artery mean pressure; PASP, systolic pulmonary artery pressure; RVEDV, right ventricular end‐diastolic volume; RVESV, right ventricular end‐systolic volume; SBP, systolic blood pressure.

p value refers to gender differences.

Parameters of RV function

Table 2 summarizes the RVMW and RV systolic and diastolic function parameters of the enrolled population. The RVGWI and RVGCW were lower for men (255 mmHg% [215, 332] vs. 291 mmHg% [263, 341]; p = .018 and 316 mmHg% [268, 387] vs. 357 mmHg% [308, 407]; p = .024, respectively), whereas the RVGWW and RVGWE showed no significant differences between sexes.

TABLE 2

Standard and advanced echocardiographic parameters of the study population

Parameters	Total, mean ± SD or median (IQR)	Men, mean ± SD or median (IQR)	Women, mean ± SD or median (IQR)	p value a
RVMW
RVGWI (mmHg%)	286 (233, 337)	255 (215, 332)	291 (263, 341)	.018
RVGCW (mmHg%)	343 (282, 402)	316 (268, 387)	357 (308, 407)	.024
RVGWW (mmHg%)	20 (11, 31)	20 (12, 31)	20 (11, 32)	.927
RVGWE (%)	93 (89, 96)	93 (90, 96)	93 (89, 96)	.816
RV systolic and diastolic functions
PD RMPI	0.27 ± 0.07	0.27 ± 0.07	0.27 ± 0.07	.999
TD RMPI	0.42 ± 0.06	0.44 ± 0.07	0.41 ± 0.06	.032
RV systolic function
TAPSE (mm)	20 (18, 22)	20 (18, 22)	19 (18, 22)	.456
RV FAC (%)	46 (43, 50)	44 (41, 47)	48 (45, 52)	<.0001
3D RVEF (%)	58 (55, 59)	55 (54, 56)	59 (58, 60)	<.0001
TA PTD S′ (cm/s)	13 (12, 14)	13 (12, 14)	13 (12, 15)	.369
TA CTD S′ (cm/s)	10 (9, 11)	10 (9, 11)	10 (9, 11)	.479
TA IVA (cm/s2)	3.1 (2.6, 4.1)	3.1 (2.4, 4.1)	3.2 (2.7, 4.1)	.347
RV FWLS (%)	−23.4 (−26.0, −21.1)	−23.0 (−26.2, −20.8)	−23.5 (−26.1, −21.4)	.406
RV GLS (%)	−20.0 ± 2.5	−19.8 ± 2.5	−20.2 ± 2.4	.382
RV diastolic function
Tricuspid E wave (cm/s)	55 (48, 63)	52 (48, 64)	56 (49, 63)	.319
Tricuspid A wave (cm/s)	35 (30, 42)	36 (30, 43)	35 (30, 41)	.616
Tricuspid E/A ratio	1.5 (1.3, 1.8)	1.4 (1.3, 1.7)	1.6 (1.3, 1.9)	.075
Tricuspid deceleration time (ms)	167 ± 26	166 ± 26	167 ± 26	.947
Tricuspid IVRT (ms)	51 (44, 58)	51 (44, 58)	51 (46, 59)	.405
TA E′ (cm/s)	14 (12, 17)	14 (11, 16)	14 (13, 18)	.061
TA A′ (cm/s)	13 (11, 15)	12 (11, 15)	13 (11, 16)	.676
TA E′ /A′ ratio	1.1 (0.9, 1.4)	1.1 (0.8, 1.3)	1.2 (0.9, 1.6)	.340
E/ E′ ratio	4.0 ± 1.0	4.1 ± 1.0	3.9 ± 1.0	.290

Abbreviations: 3D, three‐dimensional; A′, tricuspid lateral annular late diastolic velocity; CTD, color tissue Doppler; E′, tricuspid lateral annular early diastolic velocity; FAC, fractional area changes; FWLS, free wall longitudinal strain; GLS, global longitudinal strain; IQR, interquartile range; IVA, isovolumetric acceleration; IVRT, isovolumetric relaxation time; PD, pulsed‐wave Doppler; PTD, pulsed‐wave tissue Doppler; RMPI, right ventricular myocardial performance index; RV, right ventricular; RVEF, RV ejection fraction; RVGCW, RV global constructive work; RVGWE, RV global work efficiency; RVGWI, RV global work index; RVGWW, RV global wasted work; RVMW, RV myocardial work; S′, tricuspid lateral annular peak systolic velocity; SD, standard deviation; TA, tricuspid annulus; TAPSE, tricuspid annular plane systolic excursion; TD, tissue Doppler.

p value differences between genders.

Correlations among RVGWI and other parameters of RV function

The RVGWI showed good correlation with PASP (r = 0.749; p < .0001), moderate correlations with PADP (r = 0.449; p < .0001), TD RMPI (r = −0.220; p = .024), TAPSE (r = 0.294; p = .002), TA pulsed‐wave TD S′ (r = 0.234; p = .016), TA color TD S′ (r = 0.283; p = .003), RV FWLS (r = −0.321; p = .001), RV GLS (r = −0.395; p < .0001), and TA A′ (r = 0.306; p = .001), and weak correlation with TA E′ (Table 3). The multivariate analysis showed that the RVGWI was significantly correlated with PASP (standardized β‐coefficient = 0.691; p < .0001), TAPSE (standardized β‐coefficient = 0.143; p = .036), and RV GLS (standardized β‐coefficient = −0.361; p < .0001) (Table 3 and Figure 2A–C).

TABLE 3

Univariate and multivariate analysis for RVGWI

	Univariate analysis		Multivariate analysis
	Coefficient	p value	Standardized β‐Coefficient	p value
PASP (mmHg)	0.749	<.0001	0.691	<.0001
PADP (mmHg)	0.449	<.0001
RV systolic and diastolic functions
PD RMPI	−0.182	.061
TD RMPI	−0.220	.024
RV systolic function
TAPSE (mm)	0.294	.002	0.143	.036
RV FAC (%)	0.082	.406
3D RVEF (%)	0.101	.302
TA PTD S′ (cm/s)	0.234	.016
TA CTD S′ (cm/s)	0.283	.003
TA IVA (cm/s2)	0.179	.067
RV FWLS (%)	−0.321	.001
RV GLS (%)	−0.395	<.0001	−0.361	<.0001
RV diastolic function
Tricuspid E wave (cm/s)	0.167	.087
Tricuspid A wave (cm/s)	0.100	.305
Tricuspid E/A ratio	0.079	.424
Tricuspid deceleration time (ms)	0.039	.692
Tricuspid IVRT (ms)	−0.037	.705
TA E′ (cm/s)	0.195	.045
TA A′ (cm/s)	0.306	.001
TA E′ /A′ ratio	0.037	.710
E/ E′ ratio	−0.070	.477

Abbreviations: 3D, three‐dimensional; A′, tricuspid lateral annular late diastolic velocity; CTD, color tissue Doppler; E′, tricuspid lateral annular early diastolic velocity; FAC, fractional area change; FWLS, free wall longitudinal strain; GLS, global longitudinal strain; IQR, interquartile range; IVA, isovolumetric acceleration; IVRT, isovolumetric relaxation time; PADP, pulmonary artery diastolic pressure; PASP, pulmonary artery systolic pressure; PD, pulsed‐wave Doppler; PTD, pulsed‐wave tissue Doppler; RMPI, right ventricular index of myocardial performance; RV, right ventricular; RVEF, RV ejection fraction; RVGCW, RV global constructive work; RVGWE, RV global work efficiency; RVGWI, RV global work index; RVGWW, RV global wasted work; RVMW, RV myocardial work; S′, tricuspid lateral annular peak systolic velocity; SD, standard deviation; TA, tricuspid annular; TAPSE, tricuspid annular plane systolic excursion; TD, tissue Doppler.

FIGURE 2

Main correlations between RVMW indices and other parameters of RV function. RV GLS, RV global longitudinal strain; PASP, pulmonary artery systolic pressure; RV, right ventricular; RVGCW, RV global constructive work; RVGWE, RV global work efficiency; RVGWI, RV global work index; RVGWW, RV global wasted work; RVMW, RV myocardial work; TA IVA, tricuspid annular isovolumetric acceleration; TAPSE, tricuspid annular plane systolic excursion; TD RMPI, RV index of myocardial performance by tissue Doppler imaging

Correlations among RVGCW and other parameters of RV function

The RVGCW showed good correlations with PASP (r = 0.810; p < .0001) and PADP (r = 0.541; p < .0001) and moderate correlations with TAPSE (r = 0.275; p = .004), TA pulsed‐wave TD S′ (r = 0.230; p = .018), TA color TD S′ (r = 0.248; p = .010), TA IVA (r = 0.288; p = .003), RV FWLS (r = −0.308; p = .001), RV GLS (r = −0.330; p = .001), and TA A′ (r = 0.349; p < .0001) (Table 4). The multivariate analysis showed that the RVGWI was significantly correlated with PASP (standardized β‐coefficient = 0.716; p < .0001) and RV GLS (standardized β‐coefficient = −0.279; p < .0001) (Table 4 and Figure 2D,E).

TABLE 4

Univariate and multivariate analysis for RVGCW

	Univariate analysis		Multivariate analysis
	Coefficient	p value	Standardized β‐Coefficient	p value
PASP (mmHg)	0.810	<.0001	0.716	<.0001
PADP (mmHg)	0.541	<.0001
RV systolic and diastolic functions
PD RMPI	−0.078	.425
TD RMPI	−0.159	.104
RV systolic function
TAPSE (mm)	0.275	.004
RV FAC (%)	0.158	.105
3D RVEF (%)	0.096	.329
TA PTD S′ (cm/s)	0.230	.018
TA CTD S′ (cm/s)	0.248	.010
TA IVA (cm/s2)	0.288	.003
RV FWLS (%)	−0.308	.001
RV GLS (%)	−0.330	.001	−0.279	<.0001
RV diastolic function
Tricuspid E wave (cm/s)	0.139	.154
Tricuspid A wave (cm/s)	0.084	.390
Tricuspid E/A ratio	0.056	.568
Tricuspid deceleration time (ms)	0.055	.575
Tricuspid IVRT (ms)	−0.003	.977
TA E′ (cm/s)	0.165	.092
TA A′ (cm/s)	0.349	<.0001
TA E′ /A′ ratio	−0.087	.378
E/ E′ ratio	−0.063	.521

Abbreviations: 3D, three‐dimensional; A′, tricuspid lateral annular late diastolic velocity; CTD, color tissue Doppler; E′, tricuspid lateral annular early diastolic velocity; FAC, fractional area change; FWLS, free wall longitudinal strain; GLS, global longitudinal strain; IQR, interquartile range; IVA, isovolumetric acceleration; IVRT, isovolumetric relaxation time; PADP, pulmonary artery diastolic pressure; PASP, pulmonary artery systolic pressure; PD, pulsed‐wave Doppler; PTD, pulsed‐wave tissue Doppler; RMPI, right ventricular index of myocardial performance; RV, right ventricular; RVEF, RV ejection fraction; RVGCW, RV global constructive work; RVGWE, RV global work efficiency; RVGWI, RV global work index; RVGWW, RV global wasted work; RVMW, RV myocardial work; S′, tricuspid lateral annular peak systolic velocity; SD, standard deviation; TA, tricuspid annular; TAPSE, tricuspid annular plane systolic excursion; TD, tissue Doppler.

Correlations among RVGWW and other parameters of RV function

The RVGCW showed moderate correlations with PADP (r = 0.214; p = .028), PD RMPI (r = 0.297; p = .002), TA IVA (r = 0.257; p = .008), and RV GLS (r = 0.247; p = .011; Table 5). The multivariate analysis showed that the RVGWI was significantly correlated with TA IVA (standardized β‐coefficient = 0.279; p = .008) and RV GLS (standardized β‐coefficient = 0.306; p = .008; Table 5 and Figure 2F,G).

TABLE 5

Univariate and multivariate analysis for RVGWW

	Univariate analysis		Multivariate analysis
	Coefficient	p value	Standardized β‐Coefficient	p value
PASP (mmHg)	0.191	.050
PADP (mmHg)	0.214	.028
RV systolic and diastolic functions
PD RMPI	0.297	.002
TD RMPI	0.129	.187
RV systolic function
TAPSE (mm)	0.007	.939
RV FAC (%)	0.167	.087
3D RVEF (%)	0.051	.606
TA PTD S′ (cm/s)	−0.014	.887
TA CTD S′ (cm/s)	−0.044	.655
TA IVA (cm/s2)	0.257	.008	0.279	.008
RV FWLS (%)	0.050	.607
RV GLS (%)	0.247	.011	0.306	.008
RV diastolic function
Tricuspid E wave (cm/s)	−0.016	.868
Tricuspid A wave (cm/s)	−0.007	.943
Tricuspid E/A ratio	−0.038	.700
Tricuspid deceleration time (ms)	0.113	.249
Tricuspid IVRT (ms)	0.161	.099
TA E′ (cm/s)	−0.059	.545
TA A′ (cm/s)	0.165	.090
TA E′ /A' ratio	−0.158	.107
E/ E′ ratio	0.054	.585

Abbreviations: 3D, three‐dimensional; A′, tricuspid lateral annular late diastolic velocity; CTD, color tissue Doppler; E′, tricuspid lateral annular early diastolic velocity; FAC, fractional area change; FWLS, free wall longitudinal strain; GLS, global longitudinal strain; IQR, interquartile range; IVA, isovolumetric acceleration; IVRT, isovolumetric relaxation time; PADP, pulmonary artery diastolic pressure; PASP, pulmonary artery systolic pressure; PD, pulsed‐wave Doppler; PTD, pulsed‐wave tissue Doppler; RMPI, right ventricular index of myocardial performance; RV, right ventricular; RVEF, RV ejection fraction; RVGCW, RV global constructive work; RVGWE, RV global work efficiency; RVGWI, RV global work index; RVGWW, RV global wasted work; RVMW, RV myocardial work; S′, tricuspid lateral annular peak systolic velocity; SD, standard deviation; TA, tricuspid annular; TAPSE, tricuspid annular plane systolic excursion; TD, tissue Doppler.

Correlations among RVGWE and other parameters of RV function

The RVGCW showed moderate correlations with PD RMPI (r = −0.62; p = .007), TD RMPI (r = −0.234; p = .016), RV GLS (r = −0.394; p < .0001), and tricuspid IVRT (r = −0.200; p = .040; Table 6). The multivariate analysis showed that the RVGWI was significantly correlated with TD RMPI (standardized β‐coefficient = −0.232; p = .043) and RV GLS (standardized β‐coefficient = −0.471; p < .0001; Table 6 and Figure 2H).

TABLE 6

Univariate and multivariate analysis for RVGWE

	Univariate analysis		Multivariate analysis
	Coefficient	p value	Standardized β‐Coefficient	p value
PASP (mmHg)	0.099	.314
PADP (mmHg)	0.028	.775
RV systolic and diastolic functions
PD RMPI	−0.262	.007
TD RMPI	−0.234	.016	−0.232	.043
RV systolic function
TAPSE (mm)	0.050	.612
RV FAC (%)	−0.132	.179
3D RVEF (%)	−0.035	.725
TA PTD S′ (cm/s)	0.062	.526
TA CTD S′ (cm/s)	0.137	.162
TA IVA (cm/s2)	−0.054	.581
RV FWLS (%)	−0.127	.193
RV GLS (%)	−0.394	<.0001	−0.471	<.0001
RV diastolic function
Tricuspid E wave (cm/s)	0.015	.875
Tricuspid A wave (cm/s)	−0.004	.970
Tricuspid E/A ratio	0.042	.667
Tricuspid deceleration time (ms)	−0.124	.204
Tricuspid IVRT (ms)	−0.200	.040
TA E′ (cm/s)	0.011	.912
TA A′ (cm/s)	−0.082	.401
TA E′ /A′ ratio	0.079	.419
E/ E′ ratio	−0.014	.889

Abbreviations: 3D, three‐dimensional; A′, tricuspid lateral annular late diastolic velocity; CTD, color tissue Doppler; E′, tricuspid lateral annular early diastolic velocity; FAC, fractional area change; FWLS, free wall longitudinal strain; GLS, global longitudinal strain; IQR, interquartile range; IVA, isovolumetric acceleration; IVRT, isovolumetric relaxation time; PADP, pulmonary artery diastolic pressure; PASP, pulmonary artery systolic pressure; PD, pulsed‐wave Doppler; PTD, pulsed‐wave tissue Doppler; RMPI, right ventricular index of myocardial performance; RV, right ventricular; RVEF, RV ejection fraction; RVGCW, RV global constructive work; RVGWE, RV global work efficiency; RVGWI, RV global work index; RVGWW, RV global wasted work; RVMW, RV myocardial work; S′, tricuspid lateral annular peak systolic velocity; SD, standard deviation; TA, tricuspid annular; TAPSE, tricuspid annular plane systolic excursion; TD, tissue Doppler.

Inter‐observer and Intra‐observer variabilities

The intra‐observer and inter‐observer variabilities of the RVMW parameters are summarized in Table 7, Figures 3 and 4. Good intra‐observer reproducibility and inter‐observer reproducibility were indicated.

TABLE 7

Intra‐ and inter‐observer variabilities of RV myocardial work indices

	Intra‐observer variability			inter‐observer variability
	Bias	95% CI	ICC	Bias	95% CI	ICC
RVGWI (mmHg%)	−6.700	−53.2; 39.9	0.940	−4.500	−50.6; 41.6	0.920
RVGCW (mmHg%)	0.900	−53.8; 55.3	0.960	41.600	−19.9; 103	0.920
RVGWW (mmHg%)	0.400	−8.3; 9.1	0.920	0.700	−12.2; 13.6	0.940
RVGWE (%)	−0.200	−2.9; 2.6	0.860	−0.450	−3.1; 2.2	0.960

Abbreviations: CI, confidence interval; ICC, intraclass correlation coefficient; RV, right ventricular; RVGCW, RV global constructive work; RVGWE, RV global work efficiency; RVGWI, RV global work index; RVGWW, RV global wasted work.

FIGURE 3

The Bland–Altman analysis for examing intra‐observer variability of right ventricular global work index (RVGWI), right ventricular global constructive work (RVGCW), right ventricular global wasted work (RVGWW), and right ventricular global work efficiency (RVGWE)

FIGURE 4

The Bland–Altman analysis for examing interobserver variability of right ventricular global work index (RVGWI), right ventricular global constructive work (RVGCW), right ventricular global wasted work (RVGWW), and right ventricular global work efficiency (RVGWE)

DISCUSSION

The RVMW, derived from the pressure‐strain loop, was first introduced by Butcher et al. as a method to assess RV function. The study showed that RVMW indices were good parameters for comparing the RV function of the healthy control group and patients with reduced LV ejection fraction. All RVMW indices were significantly correlated with the RV GLS. Moreover, RVGCW was moderately correlated with the invasive RV stroke volume. Hence, because of the growing interest in RVMW, we aimed to assess the correlations among RVMW indices and other parameters of RV systolic and diastolic functions.

In our cohort, the RVGWI, RVGCW, RV FAC, and three‐dimensional RV ejection fraction were significantly lower in men than in women. This may be evidence that women have more dynamic RV systolic function than men. The univariate analysis showed that both the RVGWI and RVGCW significantly increased according to the PASP and PADP. However, the multivariate analysis revealed that the RVGWI and RVGCW were not significantly correlated with the PADP. The analysis showed that the RVGWW and RVGWE were not correlated with the PASP. Therefore, we speculated that the PASP only affects the RVGWI and RVGCW, and that the RVGWW and RVGWE do not change according to the PASP in the healthy population.

PD RMPI and TD RMPI are powerful and independent prognostic indicators used to analyze RV global systolic and diastolic functions. , , During our study, the univariate analysis showed that the PD RMPI was significantly associated with the RVGWW and RVGWE, and that the TD RMPI was significantly associated with the RVGWI and RVGWE, thus implying that higher values of PD RMPI and TD RMPI could be translated to lower RVGWI and higher RVGWW, thereby leading to a lower RVGWE. However, only TD RMPI was significantly correlated with RVGWE in the multivariate analysis.

Regarding RV systolic function, both univariate and multivariate analyses revealed that RVMW indices were significantly correlated with RV GLS. As is well known, RV longitudinal strain, derived by speckle tracking echocardiography, is less load‐dependent and angle‐dependent than conventional RV function indices. As a reproducible and sensitive index that is widely used in clinical work and research, , , , , RVMW integrates RV GLS; however, other influences may reflect RV systolic function more sensitively and precisely than RV GLS. In general, the RVGWI and RVGWE could reflect RV positive mechanics and performance, similar to other parameters of RV systolic function. Our study demonstrated that the RVGWI and RVGCW were significantly correlated with RV FWLS, TAPSE, TA pulsed‐wave TD S′, and TA color TD S′ in the univariate analysis. Moreover, the TA IVA is not affected by changes in preload and/or afterload and is a reliable indicator of changes in RV systolic function in clinical trials. During our study, both RVGCW and RVGWW were significantly correlated with the TA IVA in the univariate analysis, possibly implying that a higher TA IVA represents a higher value of the RV contribution and waste work.

Among RV diastolic functions, the univariate analysis showed that the RVMW indices correlated with the TA E′ and A′, the RVGCW correlated with the TA A′, and the RVGWE correlated with the tricuspid IVRT. However, the multivariate analysis showed that RV diastolic function parameters were not significantly associated with RVMW indices. Based on our data, RVMW indices showed weak correlations with RV diastolic function parameters. This result may be because the RVMW is derived from the RV GLS, which mainly reflects RV systolic function. Another possible explanation is that the inclusion of healthy subjects resulted in a limited range of RV diastolic function values.

Our data support RVMW indices as reliable parameters of myocardial systolic performance. Notably, the data showed excellent agreement and repeatability when assessing the RVMW indices. As a noninvasive and convenient technique, the RVMW provides a scientific basis and further information for assessing the RV function. Butcher et al. demonstrated that the RVGWI, RVGCW, and RVGWE of patients with heart failure decreased, and that the RVGWW increased compared to a healthy control group. Additionally, because the RV myocardial work takes into account the pulmonary pressure, it will be an excellent indicator for evaluating the RV systolic function of patients with pulmonary hypertension. Moreover, for patients with arrhythmia, congenital heart disease, and cardiomyopathy (hypertrophic cardiomyopathy, dilated cardiomyopathy, myocardial amyloidosis, and others), the RVMW changes in varying degrees. Therefore, the RVMW can be used for risk stratification of the aforementioned diseases and for the evaluation of treatment effects.

Study limitations

Acquiring and quantifying RVMW datasets using a single‐provider platform may affect the applicability of these reference values to data obtained from other provider platforms. Additionally, the commercial software required to measure the RVMW is specifically designed to measure the LVMW. The RV afterload may have been inaccurate because it was estimated by calculating the pulmonary pressure rather than by performing direct measurements. Therefore, the calculation of the RVMW is not as precise as that of the LVMW because of the complicated and irregular RV anatomy and shape. , The noninvasive RV pressure–strain loop may need to be validated by the invasively derived RV pressure–strain loop in the future. Moreover, for ethical reasons, cardiac magnetic resonance and right heart catheterization were not performed to verify the validity of the RVMW. Additionally, because the TR Doppler envelope may not be acquired, and because imaging of the TR Doppler envelope is obscure in some healthy subjects, selection bias might have occurred. Furthermore, although all subjects were asymptomatic during regular examinations, we cannot rule out the possibility of subclinical cardiovascular or respiratory diseases, especially in the elderly.

CONCLUSIONS

This is the first comprehensive study to use echocardiography to evaluate the relationships among RVMW indices and other RV systolic and diastolic function parameters in a cohort of the healthy individuals. The results of this study show that all RVMW indices have good correlations with RV GLS. The RVMW indices may be reliable parameters of the myocardial systolic performance.

FUNDING INFORMATION

This study was supported by the Xiamen's Key Project of Medical and Health Sciences (No. 3502Z20209147) and the Science and Technology Planning Project of Xiamen (No. 3502Z20214ZD2183 and grant No. 3502Z20214ZD1166).