CASE REPORT
Isolated Left Bundle Branch Block Mimicking OutflowVentricular Septal Defect in a Fetus
J. Sharma Æ S. Inglis Æ M. Predanic ÆI. Udom-Rice
Received: 13 March 2009 / Accepted: 15 June 2009 / Published online: 24 July 2009
� Springer Science+Business Media, LLC 2009
Abstract Bundle branch block (BBB) is impossible to
diagnose in a fetus with conventional fetal echocardiogra-
phy. Isolated left BBB is rare in the neonatal period.
Asymmetric left ventricular remodeling in isolated left
BBB is secondary to chronic dyschronous activation and
relaxation, resulting in thinning of the interventricular
septum (IVS). This report describes a case of possible
ventricular septal defect diagnosed at 34 weeks of gestation
due to significant dropout in the outflow portion of the IVS
seen in multiple views secondary to undiagnosed isolated
left BBB in a fetus, with postnatal follow-up evaluation.
Keywords Bundle branch block �Fetal echocardiography � Myocarditis �Ventricular septal defect
Case Report
A 35-year-old primigravida was referred for fetal echo-
cardiography at 34 weeks of gestation due to an abnormal
four-chamber view. Her prenatal serology was negative,
including Ro and La antibodies. She had experienced fever
with viral exanthema 2 weeks earlier.
Fetal echocardiography showed significant dropouts in
the outflow portion of the interventricular septum (IVS) from
multiple views without an evident shunt on the color flow
map (Fig. 1 and video clip 1). The biventricular systolic
function was mildly diminished, and mild dilation of the left
ventricle was noted in the 4-week follow-up evaluation.
The baby was delivered vaginally at full term with good
Apgar scores. She was found to have gallop at physical
examination and baseline labs including an electrolyte
profile were within normal limits. The 12-lead surface
electrocardiogram (ECG) showed normal sinus rhythm, a
normal PR interval with a pattern of left bundle branch
block (BBB), and absent q-wave in the left precordial leads
(Fig. 2). Postnatal transthoracic echocardiography showed
a dilated left ventricle, regional wall motion abnormalities,
and a thinned outflow portion of the IVS with paradoxical
motion (Fig. 3 and video clip 2). Both coronaries showed a
normal origin and a proximal course, and qualitative left
ventricular systolic function was mild to moderately
depressed. In view of maternal viral illness at 32 weeks of
gestation, a workup including serial viral titers as well as
nasopharyngeal and rectal swabs was done but showed
negative results.
The girl was treated with intravenous immunoglobulins
for a possible diagnosis of viral myocarditis due to left
BBB on ECG and a dilated left ventricle with systolic
dysfunction on echocardiogram. There was no change in
her clinical status. Digoxin was administered for inotropic
support. The left BBB disappeared spontaneously in fol-
low-up period after 4 months, with improvement in left
ventricular dimension, function, and appearance of the
outflow portion of the IVS.
Electronic supplementary material The online version of thisarticle (doi:10.1007/s00246-009-9484-4) contains supplementarymaterial, which is available to authorized users.
J. Sharma
Division of Pediatric Cardiology, Jamaica Hospital Medical
Center, 8900, Van Wyck Expressway, Jamaica, NY 11418, USA
S. Inglis � M. Predanic � I. Udom-Rice
Division of Perinatology, Jamaica Hospital Medical Center,
8900, Van Wyck Expressway, Jamaica, NY 11418, USA
J. Sharma (&)
45, Wiltshire road, Scarsdale, NY 10583, USA
e-mail: [email protected]
123
Pediatr Cardiol (2009) 30:1026–1029
DOI 10.1007/s00246-009-9484-4
Discussion
The prevalence of isolated BBB varies from 0.28% to
0.44% in children and adults, with isolated right BBB
much more common than isolated left BBB, and their
prevalence increases with age [5]. The right bundle branch
is a much more discrete structure than the left bundle and
thus more prone to complete interruption of function in
response to disease. Isolated left BBB leads to an abnormal
pattern of ventricular depolarization and can induce or
Fig. 1 a, b Four-chamber and angled left ventricular outflow views of fetal echocardiography show significant dropout in outflow portion of the
interventricular septum (IVS)
Fig. 2 Complete left bundle
branch block with a normal PR
interval
Fig. 3 a, b: Parasternal long-axis and apical four-chamber views of transthoracic echocardiography showing thinned out outflow portion of the
interventricular septum (IVS) with paradoxical motion in the systole
Pediatr Cardiol (2009) 30:1026–1029 1027
123
exacerbate systolic and diastolic left ventricular dysfunc-
tion. It also increases the risk for a high degree of atrio-
ventricular block [5, 6]. Therefore, isolated left BBB is
considered a marker for the presence of clinically occult
cardiac disease.
Left BBB in infants and children is associated with
cardiovascular disease or surgery. Isolated congenital left
BBB with a structurally normal heart and normal electro-
lyte status is rare and not reported to date in the literature.
Left BBB is reported for the premature infant with
hyperkalemia [7].
Left BBB can manifest as progressive disease of the
atrioventricular conduction axis in the infant of an anti-Ro-
positive mother [12]. Left BBB also is reported for children
with noncompaction of the ventricular myocardium, diag-
nosed accurately with echocardiography [4, 8].
The left BBB pattern may occur in Wolf-Parkinson-
White syndrome, with an abnormal conduction pathway
entering into the right ventricle or as a rate-dependent BBB
during supraventricular tachycardia. A cardiac rhabdomy-
oma, based on location, is a rare cause of diffuse conduc-
tion disease from preexcitation to BBB and complete heart
block [2]. Reversible left ventricular dysfunction secondary
to acquired left BBB is reported for adults with fulminant
myocarditis [11]. Viral myocarditis is a possible etiology in
the reported case considering antenatal maternal viral ill-
ness and spontaneous resolution of left BBB with recovery
of left ventricular function during the follow-up period.
The diagnosis of left BBB in the newborn is based on
clinical finding, ECG, and echocardiographic evaluation.
The split-second heart sound secondary to delayed aortic
closure in left BBB is responsible for gallop [14]. Left BBB
is obvious on ECG due to typical QRS configuration and
absent q-wave in left precordial leads. The complicated left
BBB includes an abnormal QRS axis, prolonged QRS
duration, and evidence of additional conduction defects
[13]. The echocardiographic findings of complete left BBB
include asymmetric left ventricular hypertrophy, incoordi-
nate regional wall motion, thinned IVS with or without
paradoxical motion, and dilated left ventricle with both
systolic and diastolic dysfunction.
Ventricular sepal defect is a common cardiac defect
diagnosed in fetal life. The membranous part of the inter-
ventricular septum is a thin translucent structure, seen
under the aortic valve as an apical equivalent of the four-
chamber view. The ultrasound beam is parallel to the IVS
using lateral resolution in the apical equivalent of the four-
chamber view, and it may result in the appearance of
dropout in the septum, leading to a false diagnosis of
ventricular septal defect (VSD) [1]. Therefore, it is
important to evaluate IVS in a different plane with ultra-
sound beam perpendicular to the IVS using axial resolu-
tion. In the reported case, dropout in the outflow portion of
the IVS was consistent in multiple planes although there
was no demonstrable shunt on the color flow map, leading
to the diagnosis of possible VSD.
The pathophysiology of asymmetric left ventricular
hypertrophy in the isolated left BBB is elegantly demon-
strated by Prinzen et al. [3, 10] from animal studies.
Complete left BBB occurs when the electrical impulse
transmission is delayed or interrupted in either the main left
bundle or in both the anterior and posterior fascicles. Thus,
the left ventricle slowly depolarizes by means of cell-to-
cell conduction that spreads from the right ventricle to the
left ventricle. The conduction from the right ventricle
passes first to the IVS, then to the anterior and posterior
portions of the left ventricle and finally to the left lateral
free wall. The early activated interventricular septal region
is consistently thinner than the late activated posterior left
ventricular wall in the isolated left BBB because asyn-
chronous electrical activation causes redistribution of the
mechanical load within the ventricular wall. The fiber
shortening, mechanical work, blood flow, and oxygen
consumption are reduced in the early activated septal
region and increased in the late activated left ventricular
posterior wall [9]. Therefore, asymmetry in wall thickness
of the left ventricle during long-lasting asynchronous
electrical activation is explained by local adaptation of the
myocardial mass to local differences in mechanical load
[10]. Prinzen et al. proved this with dogs by epicardial left
ventricular pacing using the conduction pathway opposite
the left BBB, resulting in asymmetry of the left ventricle
opposite the isolated left BBB. The left ventricular diam-
eter is increased more than the left ventricular mass,
resulting in eccentric hypertrophy and ventricular dys-
function in the left BBB. Therefore, thinning of the outflow
portion of the early activated IVS secondary to undiag-
nosed isolated left BBB in the reported case caused sig-
nificant dropout, as seen in multiple views, and gave the
impression of VSD on fetal echocardiography.
Isolated left BBB is impossible to diagnose with con-
ventional fetal echocardiography and is an unusual cause of
phantom VSD in the fetus.
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