To our knowledge, this is the first to use echocardiography to quantitatively analyse RVMW in a large cohort of healthy population. RVMW, derived from RVPSL, was first introduced as the latest method to assess RV function by Butcher et al.. In their study, RVMW indices had significant differences between patients with reduced LV ejection fraction and the healthy control group. Meanwhile, all RVMW indices were demonstrated significantly correlated with RV GLS. Moreover, RVGCW revealed a moderate correlation with invasive RV stroke volume. Recently, Russell et al. revealed myocardial glucose metabolism, which was computed by 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET), strongly correlated with noninvasive LVMW. Bokhari et al. have demonstrated that RV myocardial glucose metabolism is associated with pulmonary pressure by 18F- FDG PET. Those discoveries reveal that afterload-enrolled noninvasive RVMW could be more reliable than conventional methods in evaluating RV function.
Our study establishes normal reference values for RVMW indices in healthy Asian adults, and examines the influence of baseline parameters on the reference ranges. Our data suggest that the RVMW index is independent of sex. In our study, RVGWI and RVGCW were lower in men than in women, while no differences were found in RVGWW and RVGWE between genders. Moreover, multivariable analysis for RVGWI and RVGCW were lower in men than in women and the opposite occurred for RVGWW. Specifically, when considering both age and gender, RVGWI and RVGCW were all higher in women than in men in <50 years subgroups. These findings may be due to the RV myocardial systolic function is greater in women than in men. Studies have pointed out that estrogen in women has beneficial effects on the heart, such as regulating inflammation, myocardial hypertrophy, myocardial fibrosis, cardiovascular function and so on.[18, 19] After menopause, estrogen in women is significantly reduced, and the protective effect on the heart is weakened.
There are some differences in RVMW indices according to age. Univariable analysis showed that RVGWI, RVGCW, and RVGWW significantly increased and RVGWE significantly decreased according to age. When gender is considered, only RVGWW increased with age in men and women. Multivariable analysis revealed that only RVGWW significantly increased according to age. RVGWE decreased with age in women along with increasing PASP. RVGCW were higher in men in the ≥50 years subgroup than those in the other age subgroups. RVGCW were lower in women in the <30 years group than those in the 40-50 years, and ≥50 years subgroups. In total, the results above may reflect the physiological processes of aging, such as progressive myocardial fibrosis and cardiomyocyte regulation.
Finally, multivariable analysis showed all RVMW indices did not correlate with BMI, body surface area (BSA), or heart rate, except for RVGWW significantly increased according to BMI. Multivariable analysis revealed RVGWI, RVGCW and RVGWE increased along with increasing PASP, and RVGWW increased according to PADP. This result may be explained that increasing pulmonary artery pressure presents increasing RV afterload, and may boost RVMW to higher levels of energy. Thus, in pulmonary hypertension (PH), RVMW may be at higher energy consumption levels to compensate for increased afterload, which is reflected in higher RVMW indices. Therefore, RVMW could play a vital role in assessing the effectiveness of treatment of patients with PH.
To date, LVMW has been studied in the areas of hypertension, heart failure, cardiac resynchronization therapy, cardiac amyloidosis, nonobstructive hypertrophic Cardiomyopathy, dilated cardiomyopathy, diabetes mellitus, and so on. [22-25] In contrast to LVMW, RVMW is rarely used in clinical and scientific research. As previous studies demonstrated, as the most used measurements of RV function, TAPSE, RV FAC, and S’ are load-dependent.[4, 7] Although, some studies verified RV GLS is less load-dependent.[7, 26, 27] Due to the RV thin walls and low RV elastance, afterload impact of RV GLS still cannot be ignored. Therefore, RVMW, integrating RV GLS, pulmonary pressures, and tricuspid and pulmonic valvular events, could provide a more comprehensive and precise estimation of RV function. In the future, RVMW can also be applied to assessing RV function in a variety of diseases.
As a noninvasive and convenient technique, RVMW derived by echocardiography enable it to provide a scientific theoretical basis and practical significance for assessing RV function. Notably, the data showed excellent agreement and repeatability in assessing RVMW indices, which raises the possibility that these new advanced echocardiographic parameters could be used in clinical practice such as PH, heart failure, RV dyssynchrony, and so on.
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. In addition, commercial software required to measure RVMW is specifically designed to measure LVMW. Therefore, the calculation of RVMW is not as accurate as LVMW due to the complex and irregular shape of the right ventricle.[28, 29] Non-invasive RVPSL may need to be validated with invasively derived RVPSL in the future. Meanwhile, for ethical reasons, cardiac magnetic resonance or right heart catheterization was not used to verify the validity of RVMW. Also, as the TR Doppler envelope may not be acquired or the imaging of the TR Doppler envelope is obscure in some normal population, we might have had selection bias. Furthermore, although all subjects were asymptomatic on regular exams, we cannot rule out the possibility of subclinical cardiovascular or respiratory disease, particularly in the elderly. Finally, it remains unknown whether our results can be generalized to non-Asia subjects.