Conduction Defects
Atrioventricular
and
Intraventricular
1
Sick Sinus Syndrome
One subset is tachy-brady syndrome
Alternating periods of long pauses/bradycardia with supraventricular tachyarrhythmias
(afib, flutter, SVT)
Causes are multiple; medications used to
control tachyarrhythmias worsen pauses.
Therapy is PPM with meds for rate control
2
A-V conduction
defects
3
First Degree AV block
Fixed, prolonged PR interval (>0.20 sec)
Can be as long as 0.60 sec.
Found in normals with increased vagal tone,
meds (digoxin, Ca Channel blockers, Beta
blockers), and occasional ischemia.
Patients are asymptomatic; no treatment
required. D/C or reduce med if very long.
4
First Degree AV Block
PR = 0.34s
P waves can follow T wave very closely or be hidden
5
Second Degree AV Blocks
Mobitz Type I (Wenckebach)
PR interval lengthens with each successive
beat. This is due to gradually deteriorating
conduction through the AV node until an
impulse is dropped; the AV node then
recovers and the cycle repeats itself.
PR may become very prolonged
Caused by meds, degeneration of AV
node, ischemia-especially inferior MI (RCA
usually supplies AV node)
6
Type I 2nd degree AV
block
Note the progressively longer PR interval until a QRS is
dropped. The rhythm is irregular because of the
dropped QRS. It is often regularly irregular
7
Type I 2nd degree AV
block
Treatment
Usually none; patients are mostly
asymptomatic.
Reduce or D/C meds that may contribute if
QRS is frequently dropped.
If high grade, a pacemaker may be needed.
8
Type II 2nd degree AV
block
Block occurs below the AV node
Random drop of a QRS on ECG
QRS is usually prolonged due to infranodal
conduction system disease.
May progress to 3rd degree AV block
If due to ischemia, usually anterior MI (LAD).
Most often requires a pacemaker, unless
lower grade and heart rate is adequate.
9
Type II 2nd degree AV
block
QRS dropped
High grade
2nd degree AV block
10
Type II 2nd degree AV
block
QRS is dropped after every 2 beats with a
constant PR interval. QRS is somewhat
wide, which is common.
11
High Grade AV Block
Most likely to be type II 2nd degree AV block,
but can be type I where the PR interval
doesn’t have a chance to lengthen before a
QRS is dropped.
12
3rd Degree (Complete)
Heart Block
Lack of conduction between atria and ventricles
P waves should march out and be independent
of QRS complexes. P waves may be hidden, so
look carefully
Escape beats, either junctional (rate 40-60), or
ventricular (20-40) usually appear.
Block may be anywhere in AV node to bundle
branches; this level determines escape rhythm.
13
Escape Rhythm
If block is high in AV node:
junctional escape rhythm
If block is low in AV node:
ventricular escape rhythm
14
3rd Degree (Complete)
Heart Block
Notice wide, slow QRS complexes-ventricular escape rhythm
15
3rd Degree
Heart Block
p
p
p
p
p
p
p
p
16
3rd Degree AV Block
junctional escape rhythm (slower than usual)
17
Intraventricular
Conduction Defects
RBBB
LBBB
Fascicular blocks (part of left bundle branchwe won’t cover these).
18
BBB Changes
Normally the QRS is a composite of depolarization of the
ventricles. In a bundle branch block, the R waves are
separated because the ventricles depolarize separately.
19
Right Bundle Branch Block
Conduction proceeds across septum from
left, thus axis may shift to the right
QRS greater than 0.12 sec
RSR’ in V1 (often V2 and V3)
Wide, slurred S waves in V6
Secondary ST&T wave changes in V1-V3
Often large R’ in V1
20
RBBB
21
RBBB
22
RBBB
Occasionally more extensive ST-T wave changes
23
RBBB
R-R’ are closer together
24
RBBB cont.
Causes:
Occasional normal finding
Almost any right sided heart disease,
pulmonary hypertension, PE, etc.
Usually not ischemic
Imitators: RVH, posterior MI, WPW(Large R in V1)
Treatment: none
25
LBBB
Depolarization proceeds from right to left
Therefore axis may shift left
Septal depolarization is lost (no Q in I, aVL,V5-6)
Broad, deep monophasic QS complex in V1 and
wide, notched R in 1 and V6
Widespread T wave and QRS changes make
diagnosing ischemia/infarct difficult. QRS voltages
can imitate LVH so usual criteria not used.
26
LBBB
27
LBBB
28
LBBB
29
LBBB
30
LBBB
Causes are multiple: degenerative, HTN, acute
MI, valvular anomalies. Not seen in normal
hearts.
BBBs may be intermittent or rate related-as
heart rate speeds up, QRS can widen out.
31
CHAMBER
ENLARGEMENT
32
Atrial Overload
“Overload” is a better term because ECG changes
may be seen with increased volume and pressure,
not exclusively with atrial hypertrophy.
Atrial “enlargement, hypertrophy, or abnormality”
are terms often used.
33
Right Atrial Overload
ECG Features
Tall, peaked p waves in lead II > 2.5 mm high
Biphasic p wave in V1 with a tall, initial deflection.
Causes include pulmonary hypertension, RV
infarct, any right sided valvular abnormality, many
left sided valvular abnormalities
34
RAO
35
Notice the markedly tall and peaked P waves in leads I and II;
the P wave in V1 is also large.
36
Left Atrial Overload
Wide, notched p wave in I or II at least 0.12
seconds long (3 small boxes)
Biphasic p wave in V1 that is at least 1 mm
deep and 0.04 seconds in duration.
Note that a biphasic p in V1 is normal if
each component is no larger than 1mm x
1mm.
Causes: Mitral valve disease, LVH, HTN,
aortic valve disease, cardiomyopathy
37
69 y/o with hypertension and
mitral regurgitation
Large terminal component in V1
AND
Wide and notched P wave in II
Indicate LAO
38
Atrial Overload Patterns
39
Atrial Overload
Only need criteria in lead II or V1 to diagnose
atrial overload. Both are not required
40
Ventricular Hypertrophy
41
Right Ventricular
Hypertrophy
Initially, right axis deviation may be the only
finding-this occurs because the RV mass begins to
overshadow the left.
Classic changes occur when hypertrophy is
advanced
42
ECG changes in RVH:
Reversal of normal
precordial QRS pattern
with a tall R wave in V1
& V2 and deep S waves
in I, aVL, V5, V6.
43
ECG changes in RVH:
Voltage criteria include: (use any one)
R > S in V1
R in V1 at least 7 mm
R in V1 + S in V6 at least 11 mm
44
RVH
Repolarization change
or strain pattern in the
right precordial leads
(V1-V3).
45
Elderly man with
pulmonary HTN
Right Axis Deviation
Large R in V1 with associated
repolarization changes.
46
62 y/o with dyspnea
47
Left Ventricular
Hypertrophy
Several scoring systems have been developed
throughout the years, each with it’s own sensitivity
and specificity.
One of the more commonly used is the RomhiltEstes system.
The Cornell Criteria are also sometimes used.
48
LVH Scoring
49
LVH Criteria:
Voltage (need only one)
R in V5 or V6 at least 30 mm
S in V1 or V2 at least 30 mm
R in aVL > 11 mm (most specific sign)
S in V1(or V2?) + R in V5 or V6 > 35 mm
R in I > 15 mm (some say 20 mm)
50
To Diagnose LVH:
Combine voltage with:
Strain pattern in lateral leads or
Left Atrial Overload or
Left Axis Deviation
51
66 y/o with long hx of HTN
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Voltage*-3 pts
Left Axis Dev.-2 pts
Repolarization-3 pts
LAO-2 pts
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Unknown
54
Voltage Criteria for LVH
but no other criteria
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