Documento

1. Ultrasound Obstet Gynecol 2010; 35: 4–6
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/uog.7522
Opinion
Role of quantitative assessment in fetal echocardiography
Fetal echocardiography has evolved considerably over the
last two decades. In the past, our focus was to provide
a basic (often structural) cardiac diagnosis, and much
of our counseling consisted of extrapolation to the fetus
from what we understood to be true of postnatal disease.
With technological advances and increasing experience,
detailed anatomical and functional fetal cardiovascular
diagnoses have become the norm1,2
. We have learned
that the fetal circulation, with equalization of pressures
and redistribution of flow between left and right cardiac
chambers and great arteries, results in the absence of
many postnatal hemodynamic findings that would in
the neonate indicate disease severity. Furthermore, we
have come to understand that many fetal cardiovascular
abnormalities have the potential to progress to more
severe disease in utero, including altered growth of cardiac
chambers, great arteries, arches and branch pulmonary
arteries2,3
and the evolution of fetal heart failure3,4
.
Quantification and standardization of measurements
There have been improvements in the evaluation and
serial assessment of fetal heart disease at least in part as a
consequence of the generation of normative dimensional
and Doppler velocity data used to facilitate diagnosis
and track the natural evolution. Our assessment of many
conditions relies on indirect measures of severity, most
commonly altered dimensions of cardiac and vascular
structures. Although comparison of relative left versus
right heart dimensions has assisted our evaluation, it
is far less specific and thus less useful in making a
diagnosis and in defining disease severity. Comparison
of fetal cardiovascular measurements to normative data
aids in identifying where and the extent to which
abnormal growth has occurred, directing the clinician
to a diagnosis. An example is that of left versus right
heart asymmetry, in which the left heart structures
are more diminutive relative to the right ones. Right
ventricular and pulmonary artery dilation with normal
left heart structure dimensions could suggest increased
flow through the right heart as would occur in vein
of Galen aneurysm, in which increased superior vena
caval return is directed into the right ventricle. Small-
for-gestational age left and dilated right heart structures
could be observed when there is a redistribution of blood
from the left towards the right heart, as observed in left
heart obstructive lesions (e.g. aortic coarctation, aortic
stenosis), diastolic pathology of the left ventricle, altered
pulmonary venous return and foramen ovale restriction.
Furthermore, given the risk of progression in fetal heart
disease, observations made against normal growth curves
have provided critical insight into the role of primary
lesions in the evolution of secondary pathology such as
critical aortic and pulmonary outflow obstruction and
the development of left and right heart hypoplasia3,5–8
.
These observations have prompted the development of
fetal cardiac intervention to prevent the evolution of more
severe secondary pathology, which has the potential to
significantly improve the postnatal prognosis of affected
fetuses9,10. Serial evaluation of fetal ventricular and
great artery dimensions following intervention provides
evidence for the impact of intrauterine intervention, with
normalization of growth suggesting success9,10.
Identification of indices that are predictive of prognosis,
particularly in cross-sectional studies, has led to a
need to quantify across different gestational ages the
measurements which change. This has been greatly
facilitated by the generation of z-scores, which quantify
the degree to which a measurement lies above or below
the mean value for a given population. z-scores have
also become invaluable for tracking longitudinal changes
of growth for individual patients and for comparing
changes in growth of cardiac structures for different fetal
populations.
Although to date most quantitative evaluations in
fetal echocardiography have focused on cardiovascular
dimensions, Doppler velocities of intracardiac, arch,
systemic venous and umbilical artery flows are evaluated
most effectively when compared with expected norms
for gestational age. For instance, tracking of ventricular
stroke volumes and outputs relative to gestational
age or fetal biometric indices using normative data
facilitates the evaluation of conditions associated with
high cardiac output states, including twin pregnancies
complicated by twin reversed arterial perfusion or fetal
anemia, both before and after fetal intervention11,12
,
with serial data assisting in determining the timing
and efficacy of intervention. Assessment of fetal cardiac
output compared with normal data can provide insight
into changes in the fetal circulation in compromised
pregnancies, as previously documented for placental
insufficiency13 and Ebstein’s anomaly of the tricuspid
valve, in which evolution of left heart dysfunction and
reduced combined cardiac output ejected from the left
ventricle may contribute to the high rate of fetal hydrops
and spontaneous intrauterine demise14.
Critical to the use of any normative fetal data is
an understanding as to exactly how a measurement is
performed and to what biometric measure it is indexed.
Copyright  2009 ISUOG. Published by John Wiley & Sons, Ltd. OPINION

2. Opinion 5
Measurement of many dimensions may be difficult to
reproduce and thus knowledge of interobserver and
intraobserver variability is important in interpreting
results. Variations in growth from one population to
the next may influence what is considered normal and
thus may result in an inaccurate interpretation of the
normalcy of a measurement in a different population.
Finally, knowledge of how large and normally distributed
the control or normal population truly is remains critical
to any comparison, as suggested by the differences in the
observations of Lee et al.15
, in this issue of the Journal,
and Schneider et al.16
.
Cardiovascular scoring
Cardiovascular scores have been used to estimate the
severity of cardiac dysfunction and predict outcome
in several conditions associated with poor perinatal
outcome. Such scores are particularly useful for fetal
populations in which the cardiovascular pathology is
relatively uniform and follows a usual course. This is
true for twin–twin transfusion syndrome (TTTS), as
demonstrated in this issue of the Journal by the work
of Stirnemann et al.17
, in which they used only a handful
of indices, including the myocardial performance or Tei
index, to define severity of cardiovascular dysfunction.
The myocardial performance index is appropriate in
the scoring of TTTS in that the myocardial disease
of the recipient twin ultimately involves both systolic
and diastolic dysfunction18,19. This index of global
ventricular function, however, does not differentiate
between diastolic and systolic pathology and thus, if
myocardial performance were the only index used,
subtle early abnormalities of diastolic function present
in recipient twins prior to significant changes in central
venous pressure and ductus venosus flow would be missed.
Diastolic pathology has also been shown to be more
important than systolic pathology in the context of fetal
cardiomyopathies, the earliest features of which include
altered ventricular inflow Doppler patterns comparable
to that of the recipient twin20
. Understanding the
individual functional factors that influence the myocardial
performance index is critical in defining the true
pathophysiology and course of this disease, as we have
previously demonstrated in fetal Ebstein anomaly of the
tricuspid valve, in which prolonged isovolumic relaxation
time (an index of diastolic function) correlates strongly
with shorter ejection times with no abnormality of
isovolumic contraction21
. Insight into disease progression
may be further gleaned through the evaluation of many
parameters of function and the timing and order of
resolution of pathology following intervention, as has
been observed in TTTS following laser therapy22
. Still,
creation of a simplified cardiovascular profile score in
the standardization of assessments would potentially
facilitate diagnosis and serial assessment before and after
intervention and the evaluation of treatment strategies in
larger cohorts of affected pregnancies.
Caution, however, must be exercised in the use of a
uniform scoring system for different disease states, as has
been proposed for the cardiovascular score developed
for fetal heart failure23,24
and a recent modification
and application of this score to TTTS recipient and
donor twins25
. Although the cardiovascular score for
heart failure correlates with fetal loss among high-
risk pregnancies, it has been used for both primary
cardiac disease24
, in which myocardial dysfunction leads
to worse outcome, and for placental insufficiency25
, in
which fetal hypoxia is the trigger for late and often
acute onset (secondary) reduced myocardial function.
Doppler indices may reflect different myocardial disease
states and even abnormalities of vascular function,
umbilical venous return and loading conditions of the
fetal heart. Although these scores simplify the evaluation
and prognostication of such conditions, details as to the
mechanisms of dysfunction (i.e. high ventricular filling
versus volume contraction and hypoxia) and the timing
of the evolution of dysfunction, important for staging the
disease and planning intervention, will be missed. Thus,
documentation of the pathogenic mechanisms leading
to cardiovascular compromise and then development
of separate scoring systems appropriate for the disease
state may result in more accurate profiling and a better
understanding of the disease for a given pregnancy.
To conclude, quantitative assessment of fetal cardio-
vascular structure and function is now an integral part of
fetal echocardiography. This approach facilitates diagno-
sis and contributes significantly to our understanding of
the evolution of structural and functional heart disease,
which is critical for improving prenatal and perinatal man-
agement and for the development of timely and effective
intervention. As we venture forward, however, we must
use the tools available to elucidate disease progression,
and yet beware the inherent limitations of the standard-
ization of assessments so as not to miss opportunities to
establish the true pathogenesis and pathophysiology of
fetal cardiovascular disease.
L. K. Hornberger
Fetal & Neonatal Cardiology Program,
Pediatric Cardiology, 4C2 Stollery Children’s Hospital,
Walter C McKenzie Health Sciences Centre,
8440 112th
Street, Edmonton, Alberta, Canada
(e-mail: lisa.hornberger@albertahealthservices.ca)
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