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Second degree AV block

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Mobitz type I second degree AV block [*]

• Wenckebach phenomenon
1. Progressive lengthening of PR interval
2. Intermittent failure of conduction so P wave occurs without being followed by a QRS
3. Cycle repeats

Mobitz type II second degree AV block [*]

• Constant PR interval
• Intermittent failure of AV conduction
1. P waves are intermittently NOT followed by a QRS
2. Block often at bundle branch level and associated with wide QRS

2:1 AV block

• Cannot determine Mobitz type from rhythm, alone
• Usually due to Wenckebach phenomenon

Non-conducted APC

• May mimic AV block
1. Constant PR interval
2. Apparent dropped beat following non-conducted APC