Diagnostic and prognostic value of echocardiography in pulmonary arterial hypertension

To the Editor,

1.

We read with great interest the study by Koestenberger et al, which was recently published in Clinical Cardiology, aiming to assess the usefulness of the right ventricle end‐systolic basal‐apical diameter ratio (RVES b/a) for initial diagnosis and follow‐up of pediatric patients with pulmonary arterial hypertension (PAH).1 In that study, the RVES b/a ratio revealed a high ability to distinguish children with PAH from healthy children and might therefore be useful for initial detection of children with previously unknown PAH. As expected, the RVES b/a ratio inversely correlated with both echocardiographic and hemodynamic indicators of increased overload. However, RVES b/a did not correlate with the routinely used echo‐parameters of RV systolic function like tricuspid plane annular systolic excursion (TAPSE) and tricuspid annular peak systolic velocity (S′), which are also altered in PAH.

We consider that this study deserves particular attention. As Koestenberger et al correctly emphasized, echo‐variables for the assessment of RV size, geometry, and function are all load dependent. It is known that TAPSE and S′ will decrease with increasing pulmonary vascular resistance (PVR) even if RV myocardial contractility remains unaltered, and that at the same PVR the magnitude of TAPSE and S′ reduction will depend on the degree of impairment in RV myocardial contractility.2 The lack of correlation between RVES b/a and, either TAPSE or S′, suggest that RV geometry and myocardial longitudinal shortening can be differently affected by the PVR. It would be therefore interesting to know how TAPSE and/or S′ correlated in the study with the PVR and pulmonary arterial pressure (PAP) because, although the correlation between RVES b/a and both PAH and PVR was statistically significant, the correlation coefficient indicated only moderate correlation, especially between RVES b/a and mean PAP (ρ = −0.415).

Despite the observed superiority of echo‐parameters which describe RV morphology (ie, RVES b/a) over certain measures of RV function like TAPSE and S′ in detection of previously unknown PAH or deterioration of an already known PAH, Koestenberger et al correctly pointed out that RVES b/a ratio should however be used together with well‐established measures of RV function. The advantages of multiparameter analysis of myocardial changes under pathological conditions are especially evident in pre‐capillary PH (including PAH) where the particularly high load‐dependency of RV size, geometry and pump function strongly suggests the usefulness of RV evaluation also in relation with its loading conditions. Indeed, more recent integrative approaches using different combinations of parameters, which include also RV afterload, appeared very promising for evaluation of RV function. Thus, the echo‐derived “simplified RV contraction‐pressure index” (sRVCPI), which incorporates TAPSE and load, and is derived as sRVCPI = TAPSE•ΔP _RV‐RA (were ΔP _RV‐RA is the pressure gradient between RV and right atrium) and the “RV stroke work” (RVSW), which incorporates SV and load and is defined as RVSW = 4•(peak TR jet velocity)²•(pulmonary valve‐area •VTI), were TR is the tricuspid regurgitation and VTI is the velocity time integral of the systolic transpulmonary jet, showed close correlation with the catheterization‐derived stroke work index (SWI_RV).3, 4 Composite echo‐variables which incorporate longitudinal displacement and load like TAPSE/systolic PAP and TAPSE/PVR were also proposed for assessment of RV contractile function, but the echo‐estimation of PAP and especially that of PVR has important limitations and weaknesses.2, 5 More reliable appeared to be the afterload corrected peak systolic longitudinal strain rate (PSSrL), a good reproducible and easy obtainable combined variable for assessment of RV contractile function, which is based on the relationship between RV myocardial shortening‐velocity and RV load and is defined as PSSrL • ΔP _RV‐RA. This composite parameter has proved to be particularly useful for the prognostic assessment of potential transplant candidates with PAH.6

A distinctly different approach for RV assessment by echocardiography is provided by the “RV load‐adaptation index” (LAI_RV), a composite variable based on the relationship between RV load and RV dilation, also taking the right atrial (RA) pressure into account.2, 6 This easy obtainable dimensionless index based, in principle, on the ratio between the systolic mean RV‐RA pressure gradient (ΔP _RV‐RA) and RV geometry expressed as the end‐diastolic volume (EDV) per long‐axis length (L _ED). Thus, starting from the ratio ΔP _RV‐RA/(EDV/L _ED) and using TR velocity‐time integral 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:

$${\mathbf{LAI}}_{\mathrm{RV}}=\frac{{\mathbf{VTI}}_{\mathrm{TR}}}{A_{\mathrm{ED}}/L_{\mathrm{ED}}}=\frac{{\mathbf{VTI}}_{\mathrm{TR}}\hspace{0.17em}\left(\mathrm{cm}\right)•L_{\mathrm{ED}}\hspace{0.17em}\left(\mathrm{cm}\right)}{A_{\mathrm{ED}}\hspace{0.17em}\left({\mathrm{cm}}^2\right)}$$

The use of end‐diastolic measurements (eg, volume, area, or diameter) for defining the RV geometry allows more accurate quantification of RV dilation than end‐systolic measurements because the latter can be misleadingly influenced by the RV dilation‐accompanying TR. Thus, a small RV area relative to long‐axis length (size and geometry unaltered) in a patient with high VTI_TR (ie, high RV systolic pressure and relatively low RA pressure) yield a high LAI_RV which indicates good adaptation to load (RV ability to increase systolic pressure without relevant RV dilation and without RA pressure increase suggesting good RV contractile function) and the potential of RV to improve its performance after reduction of afterload. 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) suggesting a reduced myocardial contractility. In potential transplant candidates with PAH, LAI_RV reduction of >20% of the baseline value already before the onset of the first signs for RV failure was found to be a predictor of right heart failure and transplant‐free survival.6 We believe that further efforts in testing the diagnostic value of composite variables which incorporate measures of RV geometry, function and loading will considerably improve the reliability of non‐invasive monitoring of the RV in both patients with PAH and those predisposed to that disease.

Conflict of interest

The authors declare no potential conflict of interests.