Vascular Disease
Right Ventricular Dyssynchrony Casts New Light on the Risk Stratification and Prediction of Prognosis in Patients With Pulmonary Hypertension
2022 Volume 86 Issue 6 Pages 945-946
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2022 Volume 86 Issue 6 Pages 945-946
Estimating right heart function is essential for predicting the prognosis of patients with pulmonary hypertension (PH). Although right heart function is a broad and ambiguous concept, longitudinal systolic function and dyssynchrony of the right ventricle (RV) are measured using two-dimensional (2D) speckle-tracking echocardiography. Residual issues in this field may be resolved by estimating RV dyssynchrony.
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In terms of its compliance, the RV, which has thinner walls than the left ventricle (LV), demonstrates good tolerance of increasing preload. In contrast, it has heightened sensitivity to elevated afterload (“pulmonary arterial pressure [PAP]”), which leads to the development of pump failure with comparative ease. Although systolic function, diastolic function, and dyssynchrony are all estimated in the RV and LV, accurate estimations are difficult because of the complex anatomy.1 In addition, the RV is mainly composed of 2 types of fibers, forming a 3D network. The superficial layer is formed predominantly by circumferential muscle fibers, and the subendocardial layer is formed by longitudinal muscle fibers, and their shortening is mainly responsible for the RV ejection fraction (EF).
The early stage of RV remodeling is characterized by progressive reduction of longitudinal function with preserved and even increased transverse function via the circumferential fibers of the subepicardial layer. Therefore, longitudinal strain is a sensitive parameter for estimating RV systolic function even when the RVEF and RV fractional area change are within their normal ranges. The RV wall motion related to systolic function is organized by the following movements: shortening of the longitudinal axis; radial movement of the RV free wall, which is often referred to as the bellows effect; bulging of the interventricular septum into the RV during LV contraction; and stretching of the free wall over the septum. Apical traction2 may also influence right systolic motion. These anatomical and contractive complexities of the RV complicate the accurate estimation of RV function.
For these reasons, it is recommended that RV systolic function in patients experiencing high PAP should be measured using volumetric magnetic resonance imaging, which has high reproducibility and accuracy, but frequent use in daily medical practice is limited by problems with cost and medical resources. In patients with PH, right systolic function is a predictive parameter related to prognosis. Many factors in the categorized risk stratification for patients with pulmonary arterial hypertension (PAH) proposed by the European Society of Cardiology are closely related to right systolic function.3 Risk stratification has proven effective when considering not only diagnosis but also follow-up to estimate vital prognosis.4 There are promising technologies that can be used readily in everyday clinical practice to accurately estimate right heart systolic function in a timely fashion.
RV dyssynchrony in patients with PH is a relatively new phenomenon. Right intraventricular dyssynchrony develops in borderline PH,5 and RV dyssynchrony correlates with RV fractional area change and RV global strain, which are parameters reflecting RV systolic function.6 RV dyssynchrony is an independent predictive factor for event-free survival in patients with PH.7 These previous reports suggest that RV dyssynchrony should be estimated simultaneously with the systolic function.5–7 Recently, RV systolic function and dyssynchrony have been measured using 2D speckle tracking on echocardiography.
Myocardial deformation imaging using 2D echocardiography is based on frame-by-frame tracking of small rectangular speckle patterns within the myocardial region of interest on grayscale echocardiographic images. The free wall and septum of the RV are divided into the basal, mid, and apex portions, and are often evaluated in 4 or 6 segments depending on the presence or absence of the apex (Figure). RV global strain is generally evaluated from the RV free wall, whereas RV dyssynchrony can be evaluated by calculating the standard deviation of the time from the QRS to the peak strain of 4 or 6 segments, including the RV free wall and septum.6
One of the methods of measuring right ventricular (RV) dyssynchrony in 2D speckle-tracking echocardiography. RV dyssynchrony is calculated as a standard deviation of the times from QRS to peak strain for the 6 segments in the RV free wall and septum (RV-6SD). (A) Healthy control. The colored dots indicate the negative maximum strain in each segment. As an example, the length of the purple line corresponds to the time from the QRS to the negative peak strain at the apex of the free wall. (B) Connective tissue disease associated PAH. There are dispersions in the time from QRS to peak negative strain among the 6 segments.
PH is a phenotype of many background diseases. In particular, PAH and chronic thromboembolic pulmonary hypertension (CTEPH) have different localizations of impaired arteries due to small vessel disease and thrombi, respectively. Therefore, their effects on the RV may be different. In this issue of the Journal, Yamagata et al8 reveal that CTEPH shows greater dyssynchrony, despite no difference in the hemodynamics between PAH and CTEPH. Furthermore, both afterload and pulmonary artery compliance strongly relate to RV dyssynchrony. In other words, the effect on RV dyssynchrony may differ depending on the background disease. It may also be possible to visualize the effects of background disorders on RV by assessing dyssynchrony. To date, risk stratification of PAH has been performed based on resting hemodynamics, symptoms, exercise tolerance, B-type natriuretic peptide levels, and imaging markers related to RV function. However, with the development of research on RV speckle tracking, not only RV systolic function but also dyssynchrony may become important. RV dyssynchrony has the potential to affect risk stratification, making it a new therapeutic target. Additional balloon pulmonary angioplasty in patients with CTEPH, which normalized their hemodynamics, improved the residual disorder of RV contractility.9 This suggests the importance of aiming to improve RV systolic function beyond the PAP.
Based on these reports, evaluating not only hemodynamics but also RV systolic function and dyssynchrony in patients with PH is important, and 2D speckle tracking is useful for visualizing these RV parameters in everyday medical practice.
The differences in RV dyssynchrony between patients with PH due to pressure overload and volume overload in addition to pressure overload, such as intracardiac shunt and portal hypertension, have not been clarified. Furthermore, verification of the effect of the LV on RV dyssynchrony and pursuing differences in RV dyssynchrony in each background disease causing PH is a future task.
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