There are particular challenges and limits in RV echo-assessment. RV volume and ejection fraction (EF) measurements are less reliable, and therefore, 2D echo-derived RV volume and EF calculations are not anymore recommended by the American Society of Echocardiography (ASE) for clinical use [8]. 3D echo is more useful for estimation of RV volumes and EF, but it is technically challenging and not widely available. However, the more reliable RVEF calculation by 3D echo does not change the fact that due to its afterload dependency, RVEF cannot be used as an index of myocardial contractility [8]. Nevertheless, 2D echo is still preferentially used for assessment of RV function because it allows easy measurements of RV fractional area change (FAC_RV) and tricuspid annulus peak systolic excursion (TAPSE), which can provide similar information to RVEF [9]. However, FAC_RV measurements showed high interobserver and intra-observer variability, whereas TAPSE measurements are angle dependent and influenced by both LV function and overall heart motion [9]. Recently only a poor correlation between magnetic resonance imaging (MRI)-derived RVEF and TAPSE (r = 0.45) [10] was also found. It must be also emphasized that, because of their load dependency, RVEF, FAC_RV, and TAPSE can change without changes in myocardial contractility. Thus, they will decrease with increasing PVR even if myocardial contractility remains unaltered. Additionally, TR can induce RVEF, FAC_RV, and TAPSE changes which can be misleading for assessment of RV contractile function and estimation of RV myocardial contractility.

Also Doppler-derived indices of RV function, such as the myocardial performance index (MPI) and the TR-derived rate of RV pressure rise (dp/dt), which are unaffected by RV geometry, are increasingly used for RV echo-assessment. The clinical value of RV dp/dt ratio is limited by the angle and load dependency of measurements [8–10]. RV dp/dt measurements are also less accurate in severe TR [6]. Afterload dependence and unreliability of measurements in patients with elevated RA (including severe TR) limit the diagnostic value of MPI, and the ASE does not recommend MPI as the sole quantitative method for evaluation of RV function [8]. The time interval between onset and cessation of TR flow corrected for heart rate (TRDc), a surrogate for early systolic equalization of RV and RA pressure, appeared also useful for evaluation of RV function. A decreased TRDc in CHF patients before LVAD implantation was identified as a risk factor for postoperative RVF [11].

RV wall motion assessment by TDI-derived velocity measurements is also useful because velocity appeared less load dependent than displacement. A major limitation of TDI is the angle dependency of measurements. Nevertheless, especially the tricuspid lateral annulus peak systolic wall motion velocity (TAPS’), which correlates with TAPSE but is less load dependent, the RV isovolumic contraction peak velocity (IVC_V) and the RV isovolumic acceleration (IVA) appeared suited for evaluation of RV contractile function [12].

Strain imaging is also useful for RV evaluation because myocardial strain (deformation) is not affected by the movement of the entire heart, and deformation analysis (strain and strain rate imaging) allows discrimination between active and passive myocardial tissue movement. Angle-independent speckle-tracking-derived strain imaging parameters like the RV longitudinal peak systolic strain (PSSL) and strain rate (PSSrL) appeared particularly useful for assessment of RV contractile function [13]. Main limitations of speckle-tracking strain imaging are dependency on image quality plus relatively low temporal resolution and segmental reproducibility of measurements (especially for 3D speckle tracking), as well as the influence of RV loading conditions especially on myocardial strain values [13].

Pressure overload-induced RVF in CHF due to primary impaired LV function is finally the result of both systolic and diastolic RV dysfunctions. However, only RV systolic dysfunction was identified as a predictor of mortality in CHF [8]. Echo assessment of RV diastolic function is also challenging because it cannot be described by a single parameter, and the influence of respiration, heart rate, and preload changes on trans-tricuspid velocities can induce misleading diastolic parameter changes [8].

Distinctly load dependency of RV size, geometry, and function indicates the necessity for RV evaluation in relation with its loading conditions, especially in patients with CHF due to primary impaired LV function where RVF is induced by pathological loading conditions, which are potentially reversible during LVAD support. The usefulness of integrative approaches for RV evaluation, using combinations of parameters which include RV afterload, was increasingly investigated during the last years [3–14]. Very promising appeared to be the RV stroke work index (SWI_RV) because its calculation from RHC-derived data (i.e., SWI_RV = { [mean PAP – mean RAP] · SV }/body surface area) appeared more useful than any echo variable used individually for evaluation of RV function in end-stage CHF [15]. However, because echo-estimations of right atrial (RA) and mean PAP are less reliable than their direct measurements during RHC, the poor correlation between echo-derived and RHC-derived SWI_RV calculations is not surprising and therefore echo-derived SWI_RV is rarely used for assessment of RV function. However, recently, two simplified composite echo-derived variables which incorporate either TAPSE and load or SV and load were identified as more easy calculable surrogates for the SWI_RV [16]. One of them is the “simplified RV contraction-pressure index” (sRVCPI), which incorporates TAPSE and load, and is derived as sRVCPI = TAPSE · ΔP _RV–RA, where ΔP _RV–RA is the pressure gradient between RV and RA [17]. sRVCPI showed a close correlation with RHC-derived SWI_RV (r = 0.68; p < 0.001) [15]. The other is the “RV stroke work” (RVSW), which incorporates SV and load RVSW = (pulmonary valve-area · VTI_PV) · (4 · peak TR velocity) [2], where VTI_PV is the velocity-time integral of the systolic trans-pulmonary jet, which also showed a close correlation with the RHC-derived SWI_RV (r = 0.74; p < 0.0001) [16].

Also recently, composite echo variables which incorporate either longitudinal displacement and load (i.e., TAPSE/systolic PAP and TAPSE/PVR) or velocity of myocardial shortening and load (i.e., afterload-corrected peak systolic longitudinal strain rate) were also found suited for assessment of RV contractile function [14, 18, 19]. The TAPSE/systolic PAP ratio is a simplified approach to assess RV contraction by plotting fiber longitudinal shortening versus the force generated for overcoming the imposed load [18]. This allows estimations of RV performance status which in turn might facilitate the decision-making process and prognosis assessments in clinical praxis. The limitations of this index are related to the well-known limitations of TAPSE and systolic PAP echo measurements. Nevertheless, in a larger study, this index appeared as a strong and independent predictor of mortality in patients with HF due to primary impaired LV function [11]. Because PVR is a critical determinant of RV systolic function, its inclusion into echo-derived composite variables can also be beneficial for RV assessment. Echo-derived RV ejection efficiency (RVEe), defined as RVEe = TAPSE/PVR, is such a composite variable which reflects that relationship in a simplified manner [19]. However, there is controversy on the reliability of echo-derived PVR estimations in patients with PVR >6 Wood units [8–19]. Future studies are necessary to determine if echo-derived RVEe is indeed able to predict patient outcome.

The afterload-corrected peak systolic longitudinal strain rate, a reproducibly and easy obtainable combined variable for assessment of RV adaptability to load, defined as PSSrL · ΔP_RV-RA, where PSSrL is the peak global systolic longitudinal strain rate and ΔP _RV-RA the pressure gradient between RV and RA, is based on the relationship between RV myocardial shortening velocity and RV load [16]. Because myocardial shortening velocity is load dependent, RV systolic pressure increase reduces the PSSrL. Nevertheless, as long as RV contractile function remains unchanged, due to the ΔP _RV-RA increase, the RV load-corrected PSSrL will remain relatively stable. However, if RV afterload increase overwhelms RV ability to adapt its contractile function correspondingly, in addition to PSSrL reduction, there will be also a ΔP _RV-RA reduction due to the increase of RA pressure, even before the RV systolic pressure finally also becomes lower due to progressive impairment of RV contractility. The load-corrected PSSrL will be therefore more useful for the evaluation of RV adaptability to loading conditions than the PSSrL alone.

A distinctly different approach for assessment of RV contractile function is provided by the recently introduced “RV load-adaptation index” (LAI_RV). The LAI_RV, a composite echo-derived variable based on the relationship between RV load and RV dilation, also taking the RA pressure into account, is reflected by the ratio between the systolic mean pressure gradient between the RV and RA (ΔP_RV-RA) and RV end-diastolic volume per long-axis length (EDV/L _ED):

Thus, using the TR velocity-time integral (VTI_TR) instead of ΔP _RV-RA and the easily measurable RV end-diastolic area (A _ED) instead of the RV end-diastolic volume (EDV), a dimensionless index of similar value for RV evaluation can be obtained (◘ Fig. 6.1) [3, 6, 14]. Because ΔP _RV-RA is calculated from the mean velocity of the TR jet, the use of VTI_TR instead of ΔP_RV-RA is unrestricted possible and has the advantage to include also the duration of systolic loading. The use of A _ED instead of EDV is justified by the good correlation between the echo-derived RV-A _ED and the MRI-derived RV-EDV [20]. Thus, a small RV area relative to long-axis length (size and geometry unaltered) in a patient with high VTI_TR (i.e., high RV systolic pressure and relatively low RA pressure) yields a high LAI_RV which indicates good adaptation to load (RV ability to increase systolic pressure without relevant RV dilation and without RA pressure increases suggesting good RV contractile function) and the potential of RV to improve its performance after reduction of loading conditions. A large area relative to long-axis length (spherical dilation) despite a relatively low VTI_TR yields a low LAI_RV indicating poor adaptation to load (excessive RV dilation despite low RV pressure-load indicating impaired RV systolic function) suggesting a reduced myocardial contractility. LAI_RV values <15 indicate low RV adaptability to load which is insufficient to prevent RVF even at normal PVR [3–6]. Thus, RV evaluation in relation to its actual loading conditions can be helpful in proper decision making especially before VAD implantation (◘ Fig. 6.2).

Recently, also 3D echo data were used for assessment of the relationship between RV remodeling and afterload. Regression analysis between 3D echo-derived RV end-systolic volume-index and systolic PAP appeared able to distinguish between adapted, adapted-remodeled, and adverse-remodeled RV [21].