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: jsharma@jhmc.org

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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