Download AV Blocks

Chapter 7
Heart Blocks
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Heart Blocks
AV Blocks
Mechanism of Block
 First Degree
 Not a true block
 Delay at the AV node
 Each impulse is eventually
conducted
 Second Degree
 Intermittent block; some beats are
conducted, others are blocked
 Pathology can be within the AV
node or below it in the Bundle of His
 Pathology is often blended with
other types of blocks
 Type I
 Wenckebach
 Type II
 Type II
 2:1 AV block
 High-grade AV
block
 Third Degree
 Atria and ventricles are completely
dissociated
 There is a total block at the AV node
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
First Degree Heart Block
AV node holds each
impulse longer than
normal before
conducting it to the
ventricles. Each
impulse is eventually
conducted.
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
First Degree Heart Block
 Regularity: Depends on underlying
rhythm
 Rate: Depends on underlying rhythm
 P Wave: Upright and uniform; each P
wave followed by QRS complex
 PRI: Greater than .20 seconds;
constant across strip
 QRS: Less than .12 seconds
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
First Degree Heart Block
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Blocked P Waves
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Type II Second Degree Heart Block
AV node selectively
conducts some beats
but blocks others.
Even beats that are
conducted can
encounter delays in
AV node. Conduction
through the ventricles
is normal.
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Conduction Ratios in Type II
Second Degree Heart Block
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Conduction Ratios in Type II
Second Degree Heart Block
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Type II Second Degree Heart
Block with a Prolonged PRI
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Rules for Type II Second Degree
Heart Block
 Regularity: If conduction ratio is consistent, R-R
interval will be constant, and rhythm will be regular.
If conduction ratio varies, R-R will be irregular.
 Rate: Atrial rate is usually normal. Since many atrial
impulses are blocked, ventricular rate is usually
bradycardic (often one-half, one-third, or one-fourth
the atrial rate).
 P Wave: Upright and uniform; always outnumber
QRS complexes.
 PRI: Constant on conducted beats, but possibly
prolonged.
 QRS: Less than .12 seconds.
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Type I Second Degree Heart Block
(Wenckebach)
Sinus impulses
encounter progressive
delays in AV node
until one impulse is
blocked completely
and the cycle starts
over. Conducted
impulses depolarize
ventricles normally.
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Classical Second Degree Heart
Block
 Regularity: Can be regular or irregular,
depending on whether conduction ratio
varies or is constant
 Rate: Usually in bradycardia range; can be
one half to one third the normal rate
 P Wave: Upright and uniform; more than one
P wave for every QRS complex; P-P interval
is regular
 PRI: Constant on conducted beats; can be
greater than .20 seconds
 QRS: Less than .12 seconds
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Conduction Pattern in
Wenckebach
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Wenckebach
 Regularity: Irregular; R-R interval changes
as PR interval gets longer; characteristic
grouped beating
 Rate: Usually slightly slower than normal
 P Wave: Upright and uniform; some P waves
not followed by QRS complexes
 PRI: Progressively lengthens until one P
wave is not conducted
 QRS: Less than .12 seconds
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Wenckebach
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Complete Heart Block
The AV node blocks
all sinus impulses, so
an escape pacemaker
from the AV junction
or ventricles takes
over to pace the
ventricles. Atria and
ventricles are totally
dissociated.
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Complete Heart Block
 Regularity: Regular
 Rate: 40–60 beats per minute if focus is junctional
20–40 beats per minute if focus is ventricular
 P Wave: Upright and uniform; more P waves than
QRS complexes
 PRI: No relationship between P waves and QRS
complexes; P waves occasionally superimposed on
QRS complexes
 QRS: Less than .12 seconds if focus is junctional;
.12 seconds or more if focus is ventricular
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Complete Heart Block
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
The Heart Blocks
P-P
R-R
PRI
Conduction
First Degree
Regular
Usually
Regular
>.20 Seconds,
constant
One P wave
for every QRS
complex
Second
Degree
Wenckebach
Regular
Irregular
Increasingly
longer until one
P wave is
blocked
More P waves
than QRS
complexes
Regular
Usually
Regular
Constant when
conducted
(may be
prolonged)
More P waves
than QRS
complexes
Regular
Regular
No relation
between P
waves and
QRS
complexes
More P waves
than QRS
complexes
Type II
Third Degree
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
Chapter 7 Practice Strips
Gail Walraven, Basic Arrhythmias, Sixth Edition
©2006 by Pearson Education, Inc., Upper Saddle River, NJ
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©2006 by Pearson Education, Inc., Upper Saddle River, NJ
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