- Left bundle branch block (LBBB) is caused by conditions that damage the left bundle branch, such as hypertension, dilated cardiomyopathy, and ischemic heart disease. - LBBB is diagnosed based on criteria including a QRS duration of over 120ms and abnormal ST segment and T wave patterns. - The prognosis of LBBB depends on any underlying heart conditions, with LBBB increasing the risk of mortality. LBBB may resolve temporarily following a premature ventricular contraction due to resetting of the conduction system.

1. Left Bundle Branch Block
(LBBB)
Kerolus Shehata, MD

2. Anatomy and Blood supply of LBB
Blood supply of LBB
• LAD Septal branch to anterior LBB.
• LAD (septal) &RCA (terminal)Posterior fascicle of LBB

3. BBB patterns
V1
V6

4. LBBB criteria/Features
• QRS ≥120 msec
• Broad R wave in lateral leads (I, aVL, V5, V6)
• Absence of q waves in lateral leads (I, aVL, V5, V6)
• Dominant S in V1
• R peak time > 60 msec in leads V5 and V 6 but normal in
leads V1, V2 and V 3
• **Discordant ST segment and T waves
• **Poor R wave progression in precordial leads
• **Lt axis deviation

5. Causes of LBBB (Always abnormal)
• Hypertension
• Dilated CMP
• Myocarditis
• Ischemic heart disease
• Degenerative diseases of the conducting
system (Lenegre diseases)
• Rate-dependent LBBB
• Aortic valve lesions (LBB is anatomically
close to the non-coronary cusp of the
aortic valve)
• Digoxin toxicity
• Hyperkalemia

6. • The prevalence of LBBB increases with age: 0.2 : 1.1 %
• LBBB is more commonly a marker of a slowly progressive degenerative
disease of the conduction system.
• Because of the association of LBBB with the subsequent development of
cardiovascular disease, even in otherwise asymptomatic patients, careful
evaluation and follow-up are indicated.
• When LBBB is present, patients should be evaluated for hypertension,
coronary disease, and other disorders that have been associated with
LBBB (e.g., myocarditis, valvular heart disease, cardiomyopathies).
N.B: The diagnosis of left ventricular hypertrophy (LVH) can only be established by echocardiography in the setting
of LBBB since the two disorders produce similar ECG changes:
 LBBB lack of counteracting RV forcesUnmasking of LV forcesincreased QRS voltage in the leads used to
determine the voltage criteria for LVH.
 The ST-T vectors in both LVH and LBBB are directed opposite to the QRS vector.

7. Can we diagnose ischemia in LBBB?

8. Is new onset LBBB is a STEMI equivalent?
• In 2013 ACCF/AHA revised the EKG definitions of ST elevation
myocardial infarction (STEMI) to: “new ST elevation at the J point in at
least 2 contiguous leads of ≥ 2 mm in men (≥ 2.5 mm in men under 40
years old) or ≥ 1.5 mm (0.15 mV) in women in leads V2–V3 and/or of
≥ 1 mm (0.1 mV) in other contiguous chest leads or the limb leads.”
• In the updated guidelines, a presumably new LBBB in isolation is NO
longer considered STEMI equivalent. Moreover, (ACC) emphasized
that AMI is a syndrome, a constellation of clinical findings, including
but not limited to findings on the 12-lead ECG that are concerning for
an acute infarct, but also including the subsequent release of
biomarkers indicative of myocardial necrosis.

9. ACC algorithm for suspected MI and LBBB

10. Prognosis of LBBB
• Related to the type and severity of any concurrent underlying heart
disease and to the possible presence of other conduction disturbances
e.g. patients who also have type II second degree atrioventricular (AV)
block or multi-fascicular block generally have worse prognosis.
• LBBB is an independent predictor of all-cause mortality in CHD
• Individuals with type II DM and LBBB have more severe and extensive
CHD and advanced left ventricular dysfunction as compared with
diabetics without LBBB and in individuals with isolated LBBB.
• LBBB is associated with higher short-term and long-term mortality
following MI.
• Even in the absence of associated structural heart disease, LBBB is
associated with dyssynchronous left ventricular activation, which
reduces the efficiency of left ventricular contraction.

11. Prognosis of LBBB..Cont’d
• CRT is indicated for CHF NYHA III or IV patients with a LBBB and
reduced left ventricular ejection fraction (LVEF) <35%, and it may
prevent progression of heart failure in less symptomatic patients.
Therefore an assessment of LVEF, usually with echocardiography, is
warranted to identify these patients.
• For asymptomatic patients with an isolated LBBB and no other
evidence of cardiac disease, NO specific therapy is required.
• LBBB is an independent risk factor for mortality in patients with heart
failure and is associated with increased all-cause mortality and
sudden death at one year.
• Exercise-induced LBBB is predictive of higher rates of mortality and
cardiac events.

12. Intermittent LBBB
• MCC: Rate-dependent (Acceleration & Deceleration)
• Cardiac blunt trauma
• Exercise-Induced LBBB
• Ischemic heart disease
• Coronary spasm
• Mad Honey poisoning (Grayanotoxin)
• Acute PE
• Acute pancreatitis
• Meds: Lithium, TCAs, Flecainide, propafenone
• Coronary fistulas (With pulmonary arteries)
• GBS
• Hemorrhagic strokes
• ERCP
• ECT
• Post-anesthesia

13. Termination of LBBB following a PVC
• Post-PVC pause allows more time
for the blocked bundle to recover
from its refractoriness
• Linking phenomenon: retrograde
penetration of the LBB by
transeptal concealed conduction
through the the RBBIncrease
LBB refractoriness. The PVC caused
«reset» and interruption of this
phenomenon and, hence, the
subsequent impulses propagated
simultaneously through the both
bundles and their refractory
periods started synchronously

14. THANK YOU