Cardiac arrhythmias with atrioventricular block(1)

1. 1. First degree AV block
2. Second degree AV block Mobitz type 1
(Wenckeback phenomenon)
3. Second degree AV block Mobitz type 2
4. Third degree (complete) AV block

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There is a delay in the conduction of impulses to the ventricles usually at the AV node. It is characterised by
a prolonged, but constant PR interval. All the impulses are conducted to the ventricles but delayed.
QRS rate: usually normal
QRS rhythm: usually regular
QRS width: normal width and morphology
P waves: present and constant morphology
PR interval is prolonged (>0.20s/5small squares) . But each P wave is followed by a QRS
complex.

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Not all the P waves are conducted to ventricles. Intermittent failure of transmission of the atrial impulse to
the ventricles. It is characterised by a progressive prolongation of the PR interval until an impulse fails to be
conducted to the ventricles resulting in a dropped beat or QRS complex
QRS rate: usually 85/min
QRS rhythm: Irregular
QRS width: normal
P waves: present and constant morphology
Not every P wave is followed by a QRS, but every QRS complex is preceded by a P wave. PR interval
progressively lengthens until a QRS complex is dropped. In 3:1 AV block every 3rd P wave is not
conducted to the ventricles
Missed beat

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Characterised by intermittent failure of atrial impulse conduction to the ventricles. The block is
usually at the level of the bundle branches, commonly resulting in wide QRS complex. PR interval
remains constant in the conducted beats but some of the P waves are not followed by a QRS complex.
QRS rate: depends on the number of dropped beats; may be normal or bradycardiac.
QRS rhythm: Usually irregular due to dropped beats
QRS width: Usually wide (0.12s/more than 3 small squares) with bundle branch block pattern, may be
normal with and morphology
P waves: present and constant morphology
Not every P wave is followed by a QRS (dropped beat), but every QRS complex is
preceded by a P wave. PR interval is constant but may be prolonged
In high degree AV block, multiple consecutive P waves are not conducted with
uniform PR interval for conducted beats.
no QRS no QRS

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Total failure of conduction between atria and ventricle.
Characterised by AV dissociation; No relation between
P waves and QRS
P P P P P P