JACC: CARDIOVASCULAR IMAGING
VOL. 8, NO. 5, 2015
ª 2015 BY THE AMERICAN COLLEGE OF CARDIOLOGY FOUNDATION
ISSN 1936-878X/$36.00
PUBLISHED BY ELSEVIER INC.
http://dx.doi.org/10.1016/j.jcmg.2015.02.004
EDITORIAL COMMENT
In Pursuit of the Holy Grail* Petros Nihoyannopoulos, MD
I
maging of the right ventricle (RV) has gained popularity.
Terms
such
as
“the
adults (4). These do not include ejection fraction but
forgotten
rather a number of linear parameters, the most pop-
ventricle” or “difficulties in assessing RV func-
ular being the longitudinal motion by M-mode of the
tion attributed to its shape” are frequently used as
tricuspid annular excursion (TAPSE). TAPSE is easily
opening statements in new research. Two things
obtainable and is a measure of RV longitudinal func-
make the RV challenging to assess by any imaging
tion. Although it only measures tricuspid annular
modality: the thin wall and the overall asymmetric
excursion and therefore the RV inflow track alone,
shape in the form of a crescent shell covering part
it has shown good correlation with radionuclide-
of the left ventricle. The RV has also an anatomically
derived RV ejection fraction (5) and is recommended
distinct inflow and outflow that are placed in
by the joint ASE/EAE guidelines for routine use (4).
different planes.
The main disadvantage, however, is that TAPSE as-
What is important in diagnostic imaging is the
sumes that the displacement of a single segment
ability to link patterns or numbers to clinical out-
(tricuspid annulus) represents the overall function of
comes. While “a pretty picture is worth a thousand
a complex structure, and there are no large-scale
words” holds true, the 5 general rules for a diag-
validation studies for this.
nostic test to be clinically useful are: to be feasible
It
is
only
with
the
recent
development
of
for most patients, to be noninvasive (including
3-dimensional (3D) echocardiography that attempts
absence of ionizing radiation), to be consistent
to estimate RV ejection fraction by echocardiography
between and within observers, to be cost-effective,
have re-emerged. As expected, all comparisons have
and to be linked to clinical outcomes. Cardiac mag-
been made against CMR (6–9), and normal reference
netic resonance (CMR) generally fulfills most of those
values have been published (10). The use of 3D
criteria and is probably cost-effective in the assess-
echocardiography for valve disease and also for the
ment of RV function, for this it is widely perceived as
assessment of left and right ventricular function is
the reference method.
rapidly gaining acceptance, and guidelines have
RV ejection fraction provides substantial func-
been reported (11). In expert hands, 3D has become a
tional and prognostic information (1,2). This, until
credible alternative to CMR for assessing RV volumes
recently, could only be determined by CMR or radio-
albeit with some negative bias as indeed for the left
nuclide angiography with some accuracy. Two-
ventricular volumes calculations.
dimensional echocardiography cannot assess RV
But is assessing RV volumes what we should be
ejection fraction and instead, several other surrogate
doing in functional RV assessment? Until now we had
parameters have been advocated (3). Recently, a joint
nothing else. There is no doubt that ejection fraction
effort between the American Society of Echocardiog-
is the best we can do today, and it is linked to out-
raphy (ASE) and the European Association of Echo-
comes. Ventricular volume calculations are notori-
cardiography (EAE) published guidelines for the
ously bad and are load dependent. Reproducibility
echocardiographic assessment of the right heart in
varies among imaging techniques from 10% to 20% (and possibly more). Volume calculations have been used because they are easily derived and there has
*Editorials published in JACC: Cardiovascular Imaging reflect the views of
been little or no alternative. But there is more to
the authors and do not necessarily represent the views of JACC:
phenotyping heart disease, as CMR has shown, that
Cardiovascular Imaging or the American College of Cardiology.
may be prognostically but also therapeutically more
From
exciting, namely, the detection and quantification of
the
Department of
Cardiology, Imperial
College London,
Hammersmith Hospital, London, United Kingdom; and the University of Athens, Ippokrateion Hospital, Athens, Greece. Dr. Nihoyannopoulos has reported that he has no relationships relevant to the contents of this paper to disclose.
myocardial fibrosis (12). Myocardial fibrosis leads to impaired cardiac diastolic and systolic function and is related to adverse
524
Nihoyannopoulos
JACC: CARDIOVASCULAR IMAGING, VOL. 8, NO. 5, 2015 MAY 2015:523–5
Editorial Comment
fibrosis,
cardiovascular events (13,14). Most of the studies,
histology
however, are single-center and suffer from referral
the findings with 2-dimensional strain by speckle
bias. In the recent European Guidelines for Patients
tracking echocardiography. The unique advantage
With Hypertrophic Cardiomyopathy, CMR with late
of this study is that the authors could look at tissue
gadolinium enhancement is a class IIa level B cate-
samples of the RV free wall obtained from explan-
gory for the assessment of cardiac anatomy and
ted hearts. Histology was performed from 3 full-
ventricular
thickness slices of the RV at basal, mid-, and api-
function
and
for
the
detection
of
myocardial fibrosis (15).
RV
free
wall
comparing
cal levels. Fibrosis was calculated as an average of
Myocardial strain calculation is a relatively novel way to assess ventricular function. It provides angleindependent
for
assessment
of
regional
the 3 slices. All patients were studied as part of their trans-
myocardial
plantation work-up including electrocardiography,
deformation and does not rely on geometric as-
cardiopulmonary exercise testing, and NT-pro-BNP
sumptions (16). Longitudinal strain can quantify
assays. A comprehensive echocardiographic assess-
systolic function, allows for the evaluation of regional
ment included a number of standard parameters as
and global deformation properties of the myocar-
recommended by the ASE/EAE guidelines, including
dium, and may be a more sensitive method to identify
TAPSE, RV sphericity, right atrial (RA) function, as
subclinical left ventricular dysfunction (17). An
well as RA longitudinal stain. Seventeen (63%) pa-
important study by Urbano-Moral et al. (18) showed
tients had severe RV myocardial fibrosis defined as
an association between myocardial fibrosis detected
>50% of myocardium. Not surprisingly, all echocar-
by CMR and regional effect on myocardial function.
diographic parameters were also reduced. The major
Myocardial segments with hypertrophy and fibrosis
finding of this study, however, was that RV fibrosis
had the most impaired regional function by all
clearly correlated with free wall longitudinal strain
deformation parameters.
and oxygen consumption (VO 2) max, but poorly
More recently, studies using myocardial strain of
correlated with TAPSE and RA longitudinal strain. RV
the RV have shown that RV systolic strain is a
free wall longitudinal strain was the main determi-
powerful predictor of clinical outcome of patients
nant of myocardial fibrosis and predicted the limited
with known or suspected pulmonary hypertension
exercise tolerance. Because of the nature of the study,
(19,20). This is potentially a breakthrough method
they were unable to ascertain the relationship be-
considering the thin-walled RV, which could be
tween alterations of RV free wall longitudinal strain
challenging to assess with any imaging modality.
and disease progression from subclinical disease to
More recently, we used 3D strain in patients with
severe RV dysfunction.
pulmonary arterial hypertension and found that
The study has also a number of limitations. The
reduced area strain (AS), longitudinal strain, and
etiology of RV dysfunction and fibrosis was sec-
circumferential
with
ondary to left heart disease of variable etiologies
increased mortality risk (21). The new measurement
strain
were
all
associated
(mostly ischemic [59%]), idiopathic cardiomyopathy
of AS had strong associations with RV ejection frac-
(37%), and 1 hypertrophic cardiomyopathy so that
tion, whereas only AS was an independent predictor
most if not all would have had secondary (post-
of death on multivariable analysis, suggesting the
capillary) pulmonary hypertension. These left heart
superiority of 3D–derived AS over other variables.
conditions
Normal values for RV strain have also been published
fibrosis of the left ventricle and therefore relating
(22), thus moving a step closer to establishing strain
with other patients’ clinical data may not be valid.
as a valuable alternative to RV assessment.
The echo analysis was performed by excluding the
SEE PAGE 514
are
also
responsible
for
myocardial
ventricular septum, which is a good thing as its inclusion would have diluted their data because it
In this issue of iJACC, Lisi et al. (23) provide
would contain left heart abnormalities. The authors
new information regarding the correlation between
studied patients with end-stage heart failure with
myocardial strain as assessed by echocardiography
marked RV enlargement. In other words, they
and myocardial fibrosis quantified histologically.
studied the worst of the worst scenarios, and it is
This is a significant study because until now
not possible to extrapolate to patients with less se-
most correlations were made against surrogate
vere heart failure or patients with precapillary pul-
techniques for myocardial fibrosis, such as late
monary hypertension. Finally, they do not provide
gadolinium enhancement using CMR. The authors
any information about cardiac arrhythmias. Studies,
examined 27 patients with end-stage heart failure
particularly in cardiomyopathy patients, have shown
undergoing cardiac transplantation and looked at
an association between fibrosis (assessed by CMR)
Nihoyannopoulos
JACC: CARDIOVASCULAR IMAGING, VOL. 8, NO. 5, 2015 MAY 2015:523–5
Editorial Comment
and arrhythmia. It would have been of interest for
value of advancing fibrosis on RV strain in patients
the authors to show us the extent of fibrosis by
with pulmonary hypertension.
disease, but the number of patients would have REPRINT REQUESTS AND CORRESPONDENCE: Dr.
been limited. So, is assessing RV fibrosis the holy grail of RV
Petros Nihoyannopoulos, Department of Cardiology,
imaging? These data do not provide sufficient sup-
Imperial
port, but it is clearly a step forward to encourage
Hospital, DuCane Road, London W12 0NN, United
College
London,
NHLI,
Hammersmith
further prospective studies looking at the predictive
Kingdom. E-mail:
[email protected].
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KEY WORDS heart failure, myocardial fibrosis, right ventricle
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