LEFTBUNDLEBRANCHBLOCK(LBBB)
In LBBB, both the left anterior and posterior fascicles are blocked and electrical
conduction to the L ventricle is delayed (after R ventricular conduction) and
slowed.
CAUSES
LBBB does notoccur in a healthy heart. Causes include:
■ Chronic hypertension
■ Valvular disease
■ Ischemia
■ Cardiomyopathy
■ Myocarditis
■ Congenital heart disease
■ Following heart surgery
ECG FINDINGS(SEEFIGURE2.2)
■ Characterized by symmetric slurring through entire QRS complex
■ QRS duration ≥0.12 seconds
■ QS or rS in V 1
■ Monophasic R in V 6
■ Appropriately discordant T waves
LEFTANTERIORFASCICULARBLOCK(LAFB)
LAFB results from failure of conduction of the left anterior fascicle of the left
bundle.
CAUSES
Causes are similar to LBBB.
CARDIOVASCULAR EMERGENCIES
I aVR V1 V4
II aVL V2 V5
III
RHVTHM STRIP: II
25 mm/sec: 1cm/mV
aVF V3 V6
FIGURE 2.2. Left bundle branch block.