Page 67 - Assessing right ventricular function and the pulmonary circulation in pulmonary hypertension Onno Anthonius Spruijt
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treatment [38]. A final emerging technique to describe RV function is the measurement of myocardial deformation or strain. This method allows a global and regional assessment of RV function and can be assessed with 2D Speckle-tracking ECHO and tagged cMRI. Strain measurements were only applied in a few studies in PH [39]. Using 2D speckle tracking ECHO it was shown that in PH, RV free wall longitudinal peak systolic strain is decreased, correlates with RVEF and contains prognostic value [40, 41]. In addition, strain and strain rates can improve after initiation of PH therapy or after pulmonary endarterectomy in chronic thromboembolic pulmonary hypertension [42, 43].
In our opinion, volumetric RV measurements are the most suitable load-dependent parameters to measure RV responses to therapy. Baseline SV and RVEF and the change of SV and RVEF during treatment are strong predictors of mortality and can track RV response to treatment [7, 11].
Load-independent parameters
When load-dependent parameters are used, one cannot distinguish cardiac-specific effects of treatment from indirect effects on RV function. Several methods are available to describe load- independent RV function and the pressure-volume relationship is most commonly used and is readily available. It is well established that combined volume and pressure measurements provide a load-independent assessment of RV function. A load-independent measure of RV contractility is the end-sytolic elastance (Ees) described by the slope of the line connecting multiple end-systolic points, the end systolic pressure volume relation (ESPVR) [44]. In order to derive the ESPVR and to calculate Ees, multiple end-systolic points are required. To obtain multiple pressure-volume loops, it is necessary to briefly change preload conditions, for example by partial occlusion of the caval vein. Because this is considered dangerous in PH patients, attempts have been made to simplify the measurement of the Ees. A sufficient way to obtain a second point, in order to calculate the slope of the ESPVR, is the single beat method. This method uses a RV pressure curve of an ejecting beat to extrapolate the pressure curve of an isovolumic beat in order to obtain the maximum isovolumic pressure (Pmax). Pmax can be used as a second point to measure the ESPVR and subsequently Ees [45]. Since the end-systolic ventricular pressure almost equals the mPAP [46], Ees can be derived from the equation Ees = (mPAP-Pmax) / SV (Figure 1).
Chapter 4
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