Assessment of RV function is important to understand the pathophysiology of heart failure; however, it is still challenging to find a simple and comprehensive parameter by echocardiogram. In this study, we demonstrated that RVOT-FS reflects the severity of both left- and right-sided ventricular function. In addition, our data suggested that RVOT-FS might be a useful parameter to predict cardiovascular events in patients with LVSD.
RV originates from a different embryological source to LV . RVOT is defined as a region between the sub-pulmonary infundibulm and pulmonary valve, and is distinct from the rest of RV in origin and anatomy [5, 6, 8]. The measurement of RVOT has not been standardized in healthy subjects; however, the mean diastolic dimension is reported to be 2.8 cm  and RVOT-FS is 0.61  to 0.98 . In this study, patients with LVSD exhibited a relatively enlarged diastolic dimension of RVOT along with its reduced contractility. The pathophysiological and clinical relevance of RVOT-FS measurement was not completely elucidated in this study; however, several potential mechanisms can be suggested. Original study by Lindqvist et al.  showed that RVOT-FS correlated with several RV functional parameters, and our data support that RVOT-FS positively correlated with RVFAC. There are few reports to demonstrate the RVOT-FS with clinical, laboratory and echocardiographic variables, and our data indicate the unique characteristics of this value. Positive correlation with total bilirubin concentration is likely to reflect the increased central venous pressure by the impaired RV hemodynamics , and inverse correlation with serum concentrations of uric acid  and C-reactive protein , in part by indirectly reflecting the chronic systemic inflammation, oxidative stress and diuretic use. It is of note that RVOT-FS was also associated with chamber size of LA and LV, and LVEF. We found that RVOT-FS is associated with LV end-diastolic dimension and BNP independently, suggesting that the magnitude of RVOT-FS reflects the structural and functional capacity of LV as well as RV [17, 18]. The continuity of superficial muscle fibers encircle RV and LV represents the traction of both ventricular free walls, and makes up the anatomic basis for mechanical ventricular-ventricular interaction [19, 20]. LV hemodynamic behavior was reported to be indirectly assessed by the motion of aortic root , and our data implicate that LV overload influences the motion of RVOT. In other point of view, we speculate that the regional contractility of RVOT may affect the LV stroke volume if LV function have failed, because the RVOT segment contributes to up to 15% of total RV stroke volume , but need further investigation. In line with previous reports [14, 22–25], cardiovascular events occurred in patients who were older, with the increased LA size, BNP and total bilirubin concentration, and frequent diuretic use. Interestingly, the prevalence of events was greater in patients with decreased RVOT-FS than LVEF, TR-PG or RVFAC. A number of factors contribute to the outcome in patients with advanced heart failure. In this study, diuretic use, BNP and total bilirubin, LV wall thickness as well as RVOT-FS and NYHA functional class was extracted as the predictors of follow-up patients by Univariate Cox regression analysis. LV overload is initially compensated by the adequate increase of wall thickness, and our data support that the reduced LV wall thickness exhibited poor outcome, and it appears to be a consequence of maladaptive LV remodeling resulting from myocyte cell loss . Multivariate Cox regression analysis demonstrated that RVOT-FS as well as the severity of heart failure was an independent prognostic value, and we showed that RVOT-FS <0.2 exhibited poorer prognosis. However, the specificity of cut-off value chosen by ROC curve was low, and this might have been due to the wide distribution of RVOT-FS in patients with NYHA functional class I or II. In the follow-up echocardiogram, we observed that deterioration of RVOT-FS with a minimal change in LVEF resulted in a poor outcome (data not shown). Drighil et al.  reported that RVOT-FS improved more rapidly than other RV functional parameters such as RVFAC or tricuspid annular plane systolic excursion after mitral valve commissurotomy. Thus, sequential assessment of RVOT-FS by echocardiogram might lead to a more accurate diagnosis and would help to determine the medical approach. Furthermore, it would be interesting whether the intervention of any specific pharmacotherapy and medical device to improve the cardiovascular mortality/morbidity are associated with the contractility of RVOT.
This is a retrospective observation study with a small number of heterogeneous pathologies in patients with LVSD. We did not assess the other RV systolic parameters, such as peak systolic tricuspid annular velocity, integral of the systolic wave, and tricuspid annular plane systolic excursion . In addition, we understand that an oblique section of echocardiographic imaging at the level of RVOT leads to underestimation of the value. Moreover, this study included 23% patients with atrial fibrillation, and single measurement of RVOT-FS potentially hampers the accurate value. We validated the value with cine MRI, but we agree that the reproducibility was sub-optimal , and it is necessary to improve it by newer technologies .