Download Tracking the Right Ventricle - JACC: Cardiovascular Imaging

JACC: CARDIOVASCULAR IMAGING
VOL. 4, NO. 2, 2011
© 2011 BY THE AMERICAN COLLEGE OF CARDIOLOGY FOUNDATION
ISSN 1936-878X/$36.00
PUBLISHED BY ELSEVIER INC.
DOI:10.1016/j.jcmg.2010.11.010
EDITORIAL COMMENT
Tracking the Right Ventricle
Work in Progress*
Shyam S. Kothari, MD, DM, Sivasubramanian Ramakrishnan, MD, DM
New Delhi, India
Unraveling the mysteries of cardiac contraction has
been a major preoccupation of the cardiac investigators. More recently, the right ventricle is in focus,
especially the right ventricle in the systemic position. The differences between the right and the left
ventricles in myocardial architecture, blood supply,
metabolism, response to loading conditions, and
embryological origin have been well documented
(1). However, why the right ventricle in systemic
position is compatible with long life only in some
See page 128
patients has not been clearly understood, except
perhaps teleologically. Evaluating the right ventricle
has been difficult due to its complex geometric
shape and position. With advances in imaging
modalities such as tissue Doppler imaging, speckle
tracking imaging (STI), cardiac magnetic resonance
(CMR), and 3-dimensional echocardiography, the
global and regional functions of the right ventricle can be better assessed and could potentially
improve our understanding of the systemic right
ventricular function.
In this issue of iJACC, Khoo et al. (2) report on
the systemic right ventricle function in patients of
hypoplastic left heart syndrome (HLHS). The investigators cleverly used the “unnatural experiment”
of staged correction of HLHS and the available
time window to gain insights into the right ventricle
function and adaptation in this scenario. They
studied 20 patients before and a few months after
*Editorials published in JACC: Cardiovascular Imaging reflect the views of
the authors and do not necessarily represent the views of JACC: Cardiovascular Imaging or the American College of Cardiology.
From the Department of Cardiology, All India Institute of Medical
Sciences, New Delhi, India. The authors have reported that they have no
relationships to disclose.
the Norwood operation and analyzed several echocardiographic parameters using conventional imaging and STI. The patients were studied at the mean
age of 4 days and 150 days, respectively. The conventional indicators of global right ventricular function
such as right ventricular fractional area change and
myocardial performance index did not change, but the
right ventricle had become more spherical. The right
ventricle contractility, as measured by isovolumic acceleration, strain, and strain rate, had decreased. The
longitudinal strain decreased and the circumferential
strain did not change, hence the ratio of longitudinal/
circumferential strain decreased. They also studied
mechanical dyssynchrony by STI and found that
mechanical dyssynchrony was evident at both
stages, and with time, the mechanical dyssynchrony
indexes improved somewhat. The echocardiographic strain parameters correlated with CMRderived right ventricle mass, ejection fraction, and
volumes obtained 0 to 80 days after the echocardiographic studies in 12 patients. Overall, the investigators conclude these findings as evidence of
“left ventricle–like” adaptation of the right ventricle
facing a systemic load. These novel observations
may have important prognostic and therapeutic
implications.
Because STI is a non-Doppler method, it is not
dependent on angle of interrogation and is being
increasingly used to study right ventricular function
(3). However, the need for an excellent 2-dimensional
image and manual tracking of borders, the issue of
appropriate frame rates, the variability in the results
from different algorithms, and other technical issues
remain (4). Normative data of right ventricle function
in children using STI and information on right
ventricle function in other congenital heart disease is
gradually accumulating (3). The study by Khoo et al.
(2) is important in this regard, as it adds to such data.
Low intraobserver and interobserver variability and
JACC: CARDIOVASCULAR IMAGING, VOL. 4, NO. 2, 2011
FEBRUARY 2011:138 – 40
high reproducibility of parameters in this study are
encouraging and may help in the increased use of such
parameters in routine clinical practice with confidence.
A parameter such as isovolumic acceleration is a
validated, load-independent measure of contractility,
but varies with heart rate (5). Whether isovolumic
acceleration measured with STI in circumferential axis
can add in the contractility assessment remains to be
seen, as presently it is measured only in the long axis.
The study showed an increase in post-systolic
strain (PSS) in the systemic right ventricle. PSS
may be a marker of ischemia (6), but it may result
from nonischemic causes as well. PSS has been
shown to have ischemic memory, that is, it remains
abnormal even hours after the ischemia is relieved
(7). Whether myocardial ischemia in patients of
HLHS is indeed the cause for increased postsystolic strain index remains to be established.
Compared with patients with pulmonary atresia,
anatomic coronary abnormalities are less common
in aortic atresia (HLHS). But, HLHS encompasses
a broad range of anatomic variations. Patients with
mitral stenosis in HLHS are considered more likely
to have ischemia than mitral atresia by some workers (8). Detailed anatomic subgroups were not
reported in the present study by Khoo et al. (2), as
the numbers were small. Myocardial ischemia in the
systemic right ventricle may be more common than
realized and may not be the result of coronary
abnormality but may occur due to demand supply
mismatch. Patchy fibrosis, in the adults with systemic right ventricle, has been reported on gadolinium CMR (9). This could possibly result from
ischemia. Thus, the finding of post-systolic strain
index warrants further exploration.
Despite tremendous progress in the operative
management of HLHS, there is a significant mortality in the interstage period (10). As pointed out
by Atallah et al. (10), the established independent
risk factors for interstage mortality in postNorwood palliation include tricuspid valve regurgitation and right ventricular dysfunction. The focus
of the study by Khoo et al. (2) is on the systemic
right ventricle function, but the variations of the left
ventricle in HLHS may also have clinical influence,
albeit less significant (11). The right ventricular
function in patients with systemic right ventricle
after Fontan operation has also been studied with
echocardiographic parameters as in the study by
Chow et al. (12), and RV dysfunction in these
patients remains a clinical concern at follow-up.
Mechanical dyssynchrony in the right ventricle is
complex. The normal right ventricle contracts al-
Kothari and Ramakrishnan
Editorial Comment
most peristaltically like a bellow and the normal
infundibulum is activated 25 to 50 ms later than the
inlet of the ventricle (1). Both the ventricles synchronously deliver the same output into 2 circuits
with vastly different loads. However, when faced
with increased load, this pattern of right ventricle
contraction is altered. The free right ventricle wall
in the patients with idiopathic pulmonary hypertension contracts well into the ventricle diastole,
and mechanical dyssynchrony is the rule (13). The
present study also showed mechanical dyssynchrony
in the basal state as well as later, but it improved
with time despite worsening in some parameters of
longitudinal contractile function. Mechanical dyssynchrony in the right ventricle does not correlate
with QRS duration, and whether it can be favorably
altered by resynchronization therapy is not clear.
One study (14) showed improvement in mechanical
function of right ventricle. But the observed benefits were smaller in another study (15) in the group
with systemic right ventricle or single ventricle.
Further studies are required to identify the potential
benefits of resynchronization therapy in the failing
right ventricle.
Right ventricular mass/volume relationship in
congenital heart disease can now be reliably evaluated with CMR and 3-dimensional echocardiography. Although, right ventricular mass correlated
with basal mechanical dyssynchrony indexes in this
study (2), numerous correlations in a small number
of patients are a potential limitation of the study.
The increase in ventricular mass can be explained by
the changes in myocardial work associated with the
left ventricle–like contractions of the systemic right
ventricle. Indeed, these findings are consistent with
observations of Pettersen et al. (16), who studied 14
patients of transposition of great arteries following
Senning surgery and compared them to healthy
controls using tissue Doppler imaging and tagged
CMR. In patients with transposition of great arteries, the circumferential stain was higher than the
longitudinal strain in the right ventricular free wall,
which is akin to findings in normal left ventricle,
and the opposite was true in the normal right
ventricle. The strain measured at the interventricular septum was not different, and the ventricular
torsion was absent in the systemic right ventricle.
Similarly, increased circumferential contractility of
the right ventricle has also been described in pulmonary artery hypertension (17). Whether it is a
reflection of right ventricle dysfunction or adaptation is not very clear. In the normal right ventricle,
the middle layer circular fibers are not as prominent
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140
Kothari and Ramakrishnan
Editorial Comment
JACC: CARDIOVASCULAR IMAGING, VOL. 4, NO. 2, 2011
FEBRUARY 2011:138 – 40
as in the left ventricle. With hypertrophy, circumferential contraction may have mechanical advantage. Whether the right ventricle hypertrophy actually results from the circular middle layer fibers,
however, remains unclear. Similarly, the role of
right ventricular twisting will require further investigations. Recent CMR-based studies have shown a
dramatic decrease in apical rotation and circumferential strain in the single ventricle of left ventricular
morphology compared with the control group (18).
Yet in a systemic right ventricle, significant twisting
may not be seen (16); the mechanism underlying
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Reprint requests and correspondence: Dr. Shyam S.
Kothari, Department of Cardiology, All India Institute of
Medical Sciences, New Delhi 110029, India. E-mail:
[email protected].
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Key Words: congenital y
echocardiography y heart
defects y myocardial
dyssynchrony y myocardial
mechanics y myocardial strain.