Right ventricular strain and strain rate derived from
bidimensional speckle tracking echocardiography (2D STE)
Speckle tracking echocardiography in a non-invasive, innovative
technique that analyses the segmental myocardial deformation along
different planes through the displacement of speckles [15].
Originally designed for the assessment of the LV, it is now also being
applied for the analysis of RV deformation. Strain represents the
percentage change in length of a myocardial segment, while strain rate
represents the rate of deformation over time [40]. Both strain and
strain rate are indices of myocardial contractility [41]. The
measurement of RV longitudinal strain and strain rate is performed in
the apical RV-focused 4-chamber view, using software dedicated for the
LV assessment. The RV free wall and the interventricular septum (IVS)
are each divided into three segments (basal, medial and apical),
providing a six-segment model (Figure 1). Global longitudinal strain of
the RV is calculated as the average of the six segmental values, while
the longitudinal strain of the RV free wall (RVFW) is calculated as the
average of the three segmental values of the free wall [42]. The
latter is considered to be more specific for the RV [15], since the
motion of the IVS contributes to both RV and LV function.
The advantages of bidimensional strain derived from STE are the angle
independence, the relative load-independence, the strong correlation
with RVEF measured by CMR [43] and the ability of detecting subtle
myocardial abnormalities which cannot be determined using conventional
parameters [44, 45]. One study showed that RVFW strain had a good
correlation with the extent of myocardial fibrosis detected on CMR
[46]. However, there is no uniformity in software and no reference
range agreement between vendors. Other drawbacks are that strain
assessment is dependent on good image quality and it neglects the
contribution of the RV outflow tract (RVOT) to the global RV
performance. For the longitudinal strain of the RV free wall, a value
> -20% is considered abnormal [16].
Martin et al. analysed which RV strain parameter was a better predictor
of hospitalizations for HF in patients with left heart disease and found
out that the global longitudinal strain of the RV independently predicts
readmissions, providing additional prognostic information to that
obtained by TAPSE [47]. Similar findings were reported by Motoki et
al., who found global RV strain to be an independent predictor of
long-term adverse outcomes in patients with LVEF<35%, while
RVFW strain was not. In their study, a global RV strain >
-14.8% independently predicted the primary endpoint of death, cardiac
transplantation or hospitalization for HF at 5 year-follow-up [48].
This is contrary to the results of another study, which found that RVFW
strain was a better outcome predictor than global RV strain in HF with
reduced EF, as it independently predicted total mortality and
readmissions for HF even after adjustment for LV dysfunction [49].
Another prospective study showed that a RVFW strain > -21%
in patients with HF is an independent predictor for a composite endpoint
of death, acute HF, emergency transplantation or left ventricular assist
device (LVAD) implantation at 1 year [50].
Carluccio et al. proved the superiority of RV strain over TAPSE, by
following 200 patients with HF and reduced EF but preserved TAPSE
(>16 mm) for a composite endpoint of death and HF
rehospitalization. The authors found that the longitudinal strain of the
RVFW was an independent predictor of adverse outcome, with a cut-off
value for endpoint prediction of -15.3% [51]. In a recent study by
Seo et al., 143 patients with DCM were prospectively followed for
long-term unfavourable events (defined as all-cause death, cardiac
death, aborted sudden cardiac death and HF hospitalization), for a
median period of 40 months. The longitudinal strain of the RVFW was the
only independent predictor of the primary outcome, with an optimal
cut-off value for event prediction of -16.5% [52].
Several studies discovered independent prognostic roles for both global
RV strain and RVFW strain in HF with reduced EF. Cameli et al. found
that in patients with advanced systolic HF referred for cardiac
transplantation, both global and free wall RV strain are independent
predictors of an adverse outcome (defined as cardiac death, heart
transplantation, LVAD placement, intra-aortic balloon pump implantation
or acute HF), with stronger predictive power than other conventional
parameters, including parameters of LV function [53]. Iacoviello et
al. found that both global RV strain and RVFW strain are independent
predictors of all-cause mortality in patients with HF and
LVEF<45% [54]. A recent study by Houard et al. evaluated
the prognostic value of bidimensional RV strain for survival prediction
and compared it with conventional echocardiographic parameters and CMR
in 266 patients with HF and reduced EF. The authors found out that both
global RV strain and RVFW strain were independent predictors for overall
mortality and cardiovascular mortality; moreover, the predictive power
of RV strain was higher than that of FAC, TAPSE, CMR-derived RVEF and
CMR-derived RV strain [55].