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 2. Image: linfeinthefastlane.com 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. 3. Image: www.sw.org 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 4. Image: www.sw.org 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 5. Image: www.Ims.resus.org.uk 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