Garcia, Cholson Banjo E.
Conduction disturbance
Originate from:
◦ sinus node
◦ AV node
◦ bundle branch
Sinoatrial Block
Atrioventricular Block
Bundle Branch Block
Fascicular Block
Impaired conduction from the SA node to the
atria
No depolarization of the atria
Absence of PQRST complex
Etiology
◦ Increased vagal tone
◦ Inferior wall MI
◦ Age related degeneration
◦ Drugs (digoxin, beta blockers, ccb, class IA-
antiarrythmic)
◦ Hyperkalemia
◦ myocarditis
RR interval: irregular (creating a pause, atria is
blocked so it never depolarized
PP interval surrounding the pause is commonly
multiple of the previous PP interval
1st degree AV block
2nd degree AV block, Type 1 (Mobitz or
Wenkebach)
2nd degree AV block, Type 2 (Mobitz II)
3rd degree AV block (CHB)
Prolonged conduction between the atria and
the ventricles
Partial block within the AV node
Prolongation of the PR interval and
preservation of the underlying rhythm
• Etiology
– Drugs
– Increased vagal tone
– Hyperkalemia
– MI (inferior wall)
– Myocarditis
– Degeneration of conducting pathways assoc. with
aging
– Idiopathic cause
PR interval: > 0.20 seconds
Length of PR interval is constant
P wave is followed by a QRS complex
Mobitz type I or Wenckebach
Intermittent conduction between the atria and
ventricle
Found with the AV node
• Etiology
– Digitalis
– Escessive vagal tone
– MI (inferior wall)
– Ischemic heart disease
– Myocarditis
– Normal variant
Progressive lengthening of the PR interval
until a QRS complex is dropped; P wave
appears on time, but no QRS follows
RR interval: irregular owing to drop beats
causing the QRS complex to appear clustered
together (narrow)
“Grouped Beating”
PP: constant
Mobitz type II
Intermittent and sudden loss of conduction
between atria and the ventricles
Found below the bundle of his
Can proceed to complete heart block
Ventricular rate tends to be slower and
cardiac output diminishes
• Etiology
– Acute Myocardial Infarction (anterior wall)
– Drugs (digitalis, beta blocker, ccb)
– Degeneration of electrical conduction system
(assoc. with aging)
PR interval: constant or fixed
QRS: wider than normal because of associated
conduction block in ventricles
Conduction ratio varies (1:1, 2:1; 3:1)
PP: regular
RR: irregular
Complete heart block
Complete absence of conduction between
atria and ventricles
• Etiology
– Drug toxicity (digoxin, beta blocker, ccb)
– Excessive vagal tone
– Acute MI
– Age-related Degeneration of electrical conduction
system
– Myocarditis
– Endocarditis
– Cardiac Surgery
– Congenital origin
Atrial and ventricular rates are different
No relationship between P waves and the QRS
complex
P waves appear but no QRS
PP and RR interval: constant
Look for 3 ECG patterns
1. Look for the RR interval. Regular or irregular?
2. Look at the P wave. Is there one or more P wave
for every QRS
3. Look at the PR interval. Stay the same or change?
If REGULAR (1st degree or 3rd degree)
◦ Only 1 P wave for every QRS
◦ PR interval stay the same
1st degree
◦ more than 1 P wave
◦ PR interval changes
3rd degree
IRREGULAR ( 2nd degree)
◦ PR interval change: 2nd degree AV block, TYPE I
◦ PR interval stay the same: 2nd degree AV Block, TYPE
II
Defect in the intraventricular conduction
Supravetricular impulse: from the unblocked
branch depolarizes one ventricle
Blocked branch: impluse spread slowly
through the ventricular muscle resulting in
abnormal depolarization
Hallmark: abnormal wide QRS complex
Conduction Delay in the right bundle branch
• Etiology
– RVH
– Right ventricular strain
– ASD
– Wolf parkinson -white
– Coronary artery disease
– Myocarditis
– Cardiac contusion
– Idiopathic cause
QRS complex: 0.12 or more in width
QRS is wide and positive assumes in lead V1
rSR: leads V1 and V2
Wide or Deep I, avL V5 and V6
Down slopping of ST segment V1 and V2
• Etiology
– LVH
– Cardiomyopathy
– HPN
– Wolf parkinson -white
– Coronary artery disease
– Myocarditis
QRS complex: 0.12 or more in width
QRS is negative V1 and V2
rSR (rabbit ear) in I, avL, V5, V6
Wide or deep S V1 and V2
Down slopping of ST segment I, avL, V5, V6
Right Bundle Branch Block Left Bundle Branch Block
QRS wide and QRS wide and
predominantly positive V1 predominantly negative
V1
rSR in lead V1 rSR in lead V6
Deep S in lead V6 Deep S in lead V1
Late intrinsicoid Late intrinsicoid
deflection in lead V1 deflection in lead V6
Hemiblocks
Disturbed conduction in either the anterior or
posterior division, or fasicle, of the left
bundle branch
Delay in the conduction through the anterior
fascicle of the LBB
Anterior fascicle long thin and has a single
blood supply, making it vulnerable to block
• Etiology
– Coronary artery disease
– MI
– Congenital Heart disease
– Cardiac surgery
– Aging process
– Normal variant
QRS: prolonged (0.08-0.11)
Left axis deviation QRS axis (-45 and -90)
Small q wave and a tall R wave in lead I and
avL
Small r wave and deep S wave in lead II, III
and avF
Delay in the conduction through the posterior
fascicle of the LBB
Posterior: short, thick and has double blood
supply
Appearance implies large amount of
Myocardial injury has occurred
• Etiology
– Coronary artery disease
– MI
– Congenital Heart disease
– Cardiac surgery
QRS: prolonged (0.08-0.11)
Right axis deviation QRS axis (+90 and
+180)
Small q wave and a tall R wave in lead II, III
and avF
Small r wave and deep S wave in lead I and
avL
LAFB LPFB
LAD RAD
qR in lead I qR in lead III
rS in lead III rS in lead I