Download AV Nodal Blocks - Cardiac and Stroke Networks in Lancashire

AV Nodal Blocks
Lancashire & South Cumbria Cardiac Network
AV Node
AV nodal conduction time is represented
on the ECG as the PR segment.
But - we always measure the PR interval.
AV Nodal Blocks (heart blocks)
Disturbances of the conduction through
the heart, occurring at the AV Node
AV Node – damaged/diseased – delay or
total block of impulses at the AV Node
This conduction defect can be seen on the
ECG
Causes
Increased vagal tone (parasympathetic
nervous system)
IHD (MI)
Endocarditis
Degeneration (age)
Sclerosis (Aortic)
Cardiac surgery trauma
First Degree Heart Block (1º)
SA Node – normal
Normal P wave
AV Node conducts more slowly than
normal
Prolonged PR Interval
Rest of conduction is normal
Normal QRS
First Degree Heart Block (1º)
PR Interval > 0.2 seconds (5 small sq)
Note – the PR Interval is constant
Clinical significance
None
Treatment
None
Note – this can progress to 2º or 3º heart
block
Second Degree Heart Block (2º)
Mobitz Type I (Wenkebach)
Mobitz Type II
2:1
Second Degree Heart Block (2º)
Mobitz Type I
(Wenkebach)
Conduction through the AV Node –
progressively delayed until a drop beat is
seen
Second Degree Heart Block (2º)
Mobitz Type I
(Wenkebach)
PR
PR
PR
DROPPED BEAT
Second Degree Heart Block (2º)
Mobitz Type I
(Wenkebach)
PR Interval prolongs with each beat until a
dropped beat is seen
The PR Interval is NOT constant
After each dropped beat, the PR interval is
normal and the cycle starts again
Clinical Significance
Slight symptoms eg. Lethargy,Confusion
Treatment
Pacemaker if during day &/or symptoms
No treatment if at night
Note – this can progress to 3º Heart Block
Second Degree Heart Block (2º)
Mobitz Type II
Conduction through the AV node is
constant but dropped beats are seen
Second Degree Heart Block (2º)
Mobitz Type II
PR
PR
DROPPED BEAT
PR
Second Degree Heart Block (2º)
Mobitz Type II
PR Interval normal & constant
Occasionally a dropped beat is seen
Clinical significance – this is more
significant disease
Treatment – pacemaker
Note – this can progress to 3º Heart Block
Second Degree Heart Block (2º)
2:1
Unable to strictly classify as Mobitz Type I
or II
Particular type of second degree Heart
Block
Ratio 2 P waves : 1 QRS
Second Degree Heart Block (2º)
2:1
Clinical significance – unable to classify as
Mobitz type I or II
– Will be associated with symptoms, dizziness,
lethargy etc.
Treatment – pacemaker
Note – this can deteriorate to 3º Heart
Block
Third Degree Heart Block (3º)
(Complete)
Complete failure of the AV Node
No impulses from Sinus Node will pass
through to the ventricles
Some part if the conducting system will
take over as pacemaker of the heart (even
a myocardial cell 10-15 bpm)
Third Degree Heart Block (3º)
(Complete)
P wave rate – normal
Ventricular rate – slow
Ventricular complex may be broad
Idioventricular rhythm
Complete dissociation between P waves &
QRS
Third Degree Heart Block (3º)
(Complete)
P
P
QRS
P
P
P
QRS
clinical significance
Symptoms LOC, Confusion, Dizziness, Low
BP
Can lead to standstill, VT or VF (stokes
Adams)
Treatment - pacemaker
Summary
1º - prolongation of PR Interval
2º - Mobitz I – Increasing PR Interval until
dropped beat is seen
Mobitz II – Constant PR Interval with
more P waves to QRS
2 : 1 – Constant PR Interval with more
P waves to QRS
3º - Complete dissociation between P
waves & QRS