B i late ral B undle B r anc h
Block
Jasen L. Gilge, MD*, Benzy J. Padanilam, MD
KEYWORDS
Bilateral bundle branch block Left bundle branch block Right bundle branch block
Bundle branch block Conduction system disorder
KEY POINTS
Bilateral bundle branch block (BBBB) is an uncommon and underrecognized conduction
abnormality.
Electrocardiographic manifestation of BBB includes a right bundle branch block pattern in lead V1
(terminal R wave) and left bundle branch block pattern in leads I and aVL (absence of S wave).
The presence of BBBB, although rare, may confer an increased risk of cardiovascular morbidity and
mortality.
Patients with BBBB may be a new subset of patients that could have a favorable response to car-
diac resynchronization therapy.
INTRODUCTION DEFINITION AND PREVALENCE
When electrocardiographic patterns of right Patients that exhibit the characteristic pattern of
bundle branch block (RBBB) and left bundle BBBB on ECG do not meet classical definitions
branch block (LBBB) occur alternatively, intermit- for either LBBB or RBBB. According to current
tently, or simultaneously in the same patient, a guidelines, they may be categorized as an intra-
diagnosis of bilateral bundle branch block ventricular conduction delay (IVCD).6 Although
(BBBB) is considered.1 Conduction system dis- the professional society guidelines discourage
ease simultaneously affecting the left and right use of terms like BBBB, it is only because of the
bundle branches may manifest a specific electro- paucity of clear anatomic and pathophysiologic
cardiogram (ECG) with an RBBB pattern of termi- basis for it.6 An ECG pattern of complete RBBB
nal R wave in lead V1 and an LBBB pattern in lead (rSR or R) in lead V1 with an apparent LBBB
I and aVL showing no S wave (Figs. 1 and 2). This pattern in lead I and aVL showing no S wave de-
pattern was described as LBBB masquerading as fines BBBB. However, in practice, physicians
RBBB in the 1950s.2 Histologic studies of pa- may label any wide QRS with a terminal R in V1
tients with BBBB have demonstrated extensive as RBBB, and 1 study estimated that 1.5% of
disease in both bundle branches, and electro- ECGs described as having an RBBB actually
physiologic studies have suggested conduction had evidence of BBBB that was not recognized.7
block or delay in both bundle branches.3–5 BBBB is thus underrecognized, and the true
Although the pattern was originally described in prevalence is uncertain. When evaluating the
the 1950s, renewed interest has been generated general population, IVCD, defined as QRS
recently because of its adverse clinical prognosis 110 milliseconds and not meeting LBBB or
and significance in cardiac resynchronization RBBB definitions, has been described to affect
up to 0.6% of the population.8 Although there is
cardiology.theclinics.com
pacing.
This article originally appeared in Cardiac Electrophysiology Clinics, Volume 13 Issue 4, December 2021.
St Vincent Hospital, 8333 Naab Road, Suite 400, Indianapolis, IN 46260, USA
* Corresponding author.
E-mail address: Jasen.gilge@ascension.org
Cardiol Clin 41 (2023) 393–397
https://doi.org/10.1016/j.ccl.2023.03.011
0733-8651/23/Ó 2023 Elsevier Inc. All rights reserved.
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394 Gilge & Padanilam
Fig. 1. BBBB ECG. Twelve-lead ECG
showing BBBB. Features include QRS
duration 120 milliseconds, a termi-
nal R in lead V1 (RBBB pattern), and
no S waves in lead I or aVL (LBBB
pattern).
a paucity of data evaluating BBBB specifically, 1 typical LBBB appearance in lead I. Thus, they
study described the prevalence to be less than believed this ECG finding was truly an LBBB,
0.01% of the general population.9 Pastore and which, as a result of myocardial infarction, was
colleagues10 evaluated 192 consecutive patients masquerading as an RBBB. However, subsequent
undergoing cardiac resynchronization therapy histologic studies in patients with “masquerading
(CRT) and found that 7.8% of patients in this pop- bundle branch block” revealed extensive septal
ulation had BBBB pattern on ECGs. Further pop- fibrosis with near complete destruction of the right
ulation studies are needed to describe the true bundle branch and to a lesser extent in the left
prevalence of BBBB. bundle branch.3,4 These histologic studies pro-
vided substantiation that the ECG manifestation
is truly representative of disease of bilateral bun-
PATHOPHYSIOLOGY
dles and not myocardial infarction related. Further-
In 1954, Richman and Wolff2 introduced the more, BBBB may occur in structurally normal
concept of masquerading bundle branch block hearts.4 In 1955, Rosenbaum and Lepeschkin1 re-
where there is ECG evidence of RBBB in the pre- ported a case series of alternating bundle branch
cordial leads simultaneously with LBBB in the block where patients exhibited ECGs with RBBB
limb leads. Vectorcardiography in these patients and, at other times, LBBB. They postulated that
revealed the initial vector was identical to that of partial and intermittent interruption in both bundle
an LBBB, but the remainder drastically differed. branches produced alternating RBBB and LBBB in
They further postulated that extensive septal and the same patient at varying times. This concept
inferolateral left ventricular infarction drastically was later verified during electrophysiology studies
reduced posteriorly directed forces allowing the of 7 patients by Wu and colleagues11 in 1976
anteriorly directed forces of the right ventricle to revealing an incomplete block in 1 bundle and
produce an R0 in lead V1 while maintaining the intermittent block in the contralateral bundle.
Fig. 2. Comparison of bundle branch
blocks. Each of the 3 different forms
of bundle branch block are depicted
in leads I and V1. Note that BBBB
meets ECG criteria for an RBBB in
lead V1 while simultaneously satis-
fying criteria for an LBBB in lead I.
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Bilateral Bundle Branch Block 395
Fig. 3. Catheter-induced RBBB in a
patient with underlying LBBB. Simul-
taneous His bundle tracing with
limited surface ECG lead recordings
was obtained at the time of acci-
dental catheter-induced RBBB block.
The first 4 beats exhibit an LBBB.
Then, with catheter trauma to the
right bundle branch, there is develop-
ment of RBBB pattern in lead V1 and
an LBBB pattern in lead I. Delay of
conduction in both bundles results
in prolongation of HV interval. (ar-
rows) Timing of catheter-induced
trauma. H, His bundle; HB-D, His
bundle distal; HB-P, His bundle prox-
imal. (From Padanilam BJ, Morris KE, Olson JA, et al. The surface electrocardiogram predicts risk of heart block
during right heart catheterization in patients with preexisting left bundle branch block: implications for the defi-
nition of complete left bundle branch block. J Cardiovasc Electrophysiol. 2010;21(7):781 to 785. doi:10.1111/j.1540
to 8167.2009.01714.x; with permission)
Direct electrophysiologic evidence for the (Fig. 4), providing evidence that BBBB pattern is
mechanism behind BBBB comes from studies specific to BBBB.7 The terminal S wave in lateral
with catheter-induced RBBB. Padanilam and col- leads represents the delayed RV depolarization
leagues12 reported that patients with an ECG in reference to LV depolarization in typical
pattern of LBBB may develop transient complete RBBB. When both right and left bundle branch
heart block or RBBB in response to catheter conduction are delayed with left more than or
trauma to the right bundle branch during right equal to right, the terminal S wave in lateral leads
heart catheterization (Fig. 3). In that series of 27 may be absent.
patients, 9 developed RBBB on top of LBBB, sug- Three-dimensional electroanatomic mapping of
gesting BBBB. In a subsequent study of 50 pa- both ventricles during sinus rhythm has provided
tients by the same group, patterns of catheter- additional insight into the ventricular activation
induced RBBB were evaluated in patients with sequence in patients with conduction disease. In
normal, left fascicular blocks or LBBB at base- the setting of an LBBB, the apical anterolateral
line.7 Among the LBBB population, 7 out of 11 right ventricle is the earliest site to be activated
developed the BBBB pattern with catheter- with delayed transseptal conduction to the left
induced RBBB. The remainder of the LBBB pa- ventricle with the lateral mitral annulus being the
tients, and all patients with baseline normal or latest site of activation.13,14 In RBBB, the left ven-
left fascicular block, developed a typical RBBB tricular septum is the earliest site of ventricular
Fig. 4. Patterns of catheter-induced
RBBB. (A) The baseline ECG exhibits
features of a left anterior fascicular
block. Following the first beat, cath-
eter trauma to the right bundle
branch results in an ECG typical for
RBBB with a prominent S wave in
lead I and aVL as depicted by
the arrows. (B) The baseline ECG ex-
hibits features of an LBBB. Following
the first beat, catheter trauma to
the right bundle results in ECG fea-
tures typical of BBBB with terminal R
wave in V1 and no S wave in lead I
or aVL as depicted by the arrows.
(From Tzogias L, Steinberg LA, Wil-
liams AJ, et al. Electrocardiographic
features and prevalence of bilateral bundle-branch delay. Circ Arrhythm Electrophysiol. 2014;7(4):640 to 644.
doi:10.1161/CIRCEP.113.000999;with permission)
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396 Gilge & Padanilam
activation with delayed transseptal conduction to for cardiac resynchronization.7 The understanding
the right ventricle with the outflow tract being the of the underlying pathophysiology in BBBB with
latest site of activation. In patients with BBBB, delayed LV activation similar to that in patients
the first site of activation is the left ventricular with LBBB pattern could help decisions regarding
septum with slow transeptal conduction to the CRT. When measuring the extent of delayed left
right ventricle, similar to RBBB, but the conduction ventricular activation (Q-LV), BBBB patterns had
velocity to the lateral left ventricle is also dramati- similarly delayed Q-LV when compared with those
cally delayed, as depicted in Fig. 5.5,15 with LBBB.10 Based on studies showing prolonged
Q-LV as an independent predictor of CRT
response, BBBB patients may respond to CRT
CLINICAL IMPLICATIONS AND FUTURE pacing better than patients with RBBB pattern.18,19
PERSPECTIVES Further studies of BBBB could help to further
Chronic bundle branch block of a single bundle clarify the specificity of this ECG pattern, prog-
typically does not progress to complete heart nosis, and response to CRT.
block.16,17 However, the unique ECG manifesta-
tion of BBBB may have increased adverse out- CLINICS CARE POINTS
comes. Tzogias and colleagues7 reported that 8
out of 34 patients (24%) in their cohort required
permanent pacemaker implantation (PPM) or
implantable cardioverter-defibrillator (ICD) implan- The presence of alternating bundle branch
tation. Thirty-eight percent of these patients also blocks is a harbinger of severe conduction
had an ejection fraction less than 40%. Another disease.
report cited 80% of patients with a BBBB had When patients present with syncope and
met a combined end point of death or PPM im- right bundle branch block, carefully inspect
plantation during a 48-month follow-up period. lead I for evidence of bilateral bundle branch
Of the 80%, 41% died, whereas 39% required a block.
PPM.9 Although larger studies are needed to When implanting a cardiac implantable elec-
confirm the poor outcomes associated with tronic device in patients with bilateral bundle
BBBB, it is important to recognize the pattern branch block and systolic congestive heart
and not group it under an IVCD diagnosis. failure, consider cardiac resynchronization
BBBB ECG is often read as RBBB in clinical therapy.
practice, and such patients may not be considered
DISCLOSURES
The authors of this article have no conflicts of inter-
est or financial disclosures.
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personal exclusivamente. No se permiten otros usos sin autorización. Copyright ©2023. Elsevier Inc. Todos los derechos reservados.
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