Page 65 - Assessing right ventricular function and the pulmonary circulation in pulmonary hypertension Onno Anthonius Spruijt
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while the load itself is not assessed. Despite the prognostic value of baseline imaging, cMRI and ECHO parameters were never used as end-points in the major clinical trials evaluating the effects of PH specific treatment. Imaging-related evaluation of the RV response to therapy has rather been part of descriptive cohort studies [1]. Right ventricular ejection fraction (RVEF) is considered as one of the most important load-dependent measures of RV function. Improvement of the RVEF to PH therapy was described with Ambrisentan treatment [19] and with the combination of Bosentan and Sildenafil [21]. A change in RVEF during treatment predicts long-term outcome in PAH patients [7, 12].
RVEF is calculated as 100% x the difference between end-diastolic volume (EDV) and end-systolic volume (ESV), divided by EDV, or 100% x (EDV-ESV)/EDV. cMRI is considered as the golden standard for assessment of RV volumes, which has led to growing interest in its use in the evaluation of PH patients. With cMRI high resolution 3D images allow accurate assessment of RV volumes despite the complex anatomy of the RV. The most essential drawbacks of cMRI are the relative expensiveness, limited availability, incompatibility with metallic devices like cardiac pacemakers and defibrillators and it is not suitable for bedside analysis. 3D-ECHO is a promising technique for the measurement of cardiac volumes. With 3D-ECHO there is no need to make the mathematical assumptions which are necessary with 2D-ECHO. ECHO is widely available, is relatively inexpensive and can be used for bedside analysis. In a recent meta-analysis, 23 comparative studies on RV volume assessment using 3D-ECHO and cMRI were analyzed and it was concluded that 3D-ECHO underestimates RV volumes. Important for application in PH patients, underestimation of RV volumes and RVEF was greater in dilated RV’s [22-24]. The most important reason for underestimation of RV volumes by ECHO is blurring of the images due to the distance between the transducer and the RV border. The blurred area can become incorporated into the measurement of the RV wall, which leads to an underestimation of RV volumes. Furthermore, suboptimal coverage of the RV outflow tract and a low temporal resolution may contribute to underestimation of the EDV and overestimation of the ESV by 3D-ECHO [22-27]. Inter-observer variability is also higher for 3D-ECHO in comparison to cMRI [25-27]. However, with improvements in temporal and spatial resolution, 3D-ECHO may become an accurate and readily available substitute for cMRI.
The complex anatomy of the RV complicates the assessment of RV volumes and, hence, RVEF. Because automatic contour detection is very difficult, assessing volumes is time-consuming. In an attempt to save analysis time, RV function has been described using one-dimensional measurements. Longitudinal shortening of the RV can be assessed by M-Mode ECHO determining
Chapter 4
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