FASCICULAR BLOCKS

Question 1

Right Bundle Branch Block:

Answer 1

CRITERIA

Prolonged QRS (>120 ms)

rSR’ (M Shaped) in early precordial leads (V1-V3)

Wide, slurred S in lateral leads (I, aVL, V5-6)

Leads V1-V3 often have ST-segment depression and inverted T Waves (Appropriate discordance)

DDx: ETIOLOGY

Myocarditis
RVH / Cor Pulmonale
Pulmonary Embolus
Ischemic Heart Disease
Cardiomyopathy

Question 2

Incomplete Right Bundle Branch Block

Answer 2

rSR’ in early precordial leads (V1-V3) (M Shaped)

Wide, slurred S in lateral leads (I, aVL, V5-6)

QRS is NOT Prolonged (>120 ms)

Question 3

Left Bundle Branch Block

Answer 3

QRS duration > 120ms

Dominant S wave in V1

Broad monophasic R wave in lateral leads (I, aVL, V5-6) with discordant ST depression and T wave inversion

The ST-segments and the T-waves are directed in an opposite direction to the main QRS vector in all leads (the rule of “appropriatediscordance”

Absence of Q waves in lateral leads

Prolonged R wave peak time > 60ms in leads V5-6

DDx: ETIOLOGY
Ischaemic heart disease
Anterior MI
Aortic stenosis
Hypertension
Dilated cardiomyopathy
Lenègre-Lev disease: primary degenerative disease (fibrosis) of the conducting system

Hyperkalaemia

Digoxin toxicity

Question 4

Left Anterior Fascicular Block (LAFB)

Answer 4

Left Axis Deviation

qR complex in leads I and aVL (small Q waves and tall R waves)

rS in II, III and aVF (small R waves and deep S waves)

Prolong R wave peak time in aVL > 45 ms

NO prolonged QRS

Question 5

Left Posterior Fascicular Block (LPFB)

Answer 5

NO prolonged QRS
Right Axis Deviation
rS complexes in leads I and aVL
qR complexes in leads II, III and aVF

Question 6

BIFASCICULAR BLOCK

Answer 6

RBBB plus either LAD or RAD

RBBB with LAFB: LAD (MC)

RBBB with LPFB: RAD
+/- T wave inversions in the inferior leads
+/- qR in lead IIIn

DDx: ETIOLOGY
Structure Heart Disease (50-80%)
Ischemic Heart Disease (40-60%)
Aortic Stenosis
Anterior MI (New Bifascicular Block + Chest Pain a/w Proximal LAD occlusion)
Lenegre-Lev Disease
Congenital Heart Disease
Hyperkalemia

COMPLICATIONS
Complete Heart Block (1-4% per year symptom free; 17% syncope)

MANAGEMENT
Syncope / Presyncope admission + monitoring