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Atrioventricular Block (AV Block)
- AV block is when there is a problem conducting the signal from the SA node through the AV node to the ventricles.
First Degree AV Block
- Signals from the SA node are delayed through the AV node
- PR interval is greater than .20 seconds (more than one box on an ECG strip)
- All signals get through.
Second Degree AV Block
- Some signals from the SA node may be delayed through the AV node
- Some signals from the SA node do not reach the ventricles
Second Degree Type 1
- Also known as Mobitz type 1 or Wenckebach
- Longer and longer PR intervals until one is signal is dropped
- May be benign
Second Degree Type 2
- Also known as Mobitz 2
- Intermittent dropped impulse without lengthening PR intervals
- Requires pacing
- 2:1 AV block = Two p waves for every qrs wave
Third Degree (Complete Heart Block)
- No impulses pass through the AV node to the ventricles
- Atria contract and ventricles contract, but they are completely asynchronous
Bundle Branch Block
- Just below the AV node is the bundle of His.
- The conduction system then branches out into the right and left bundle branches
- These continue to branch down into millions of pukinjie fibers which allow the muscle fibers of the ventricles to contract in coordination.
- Damage to this system will cause the the impulse to be propagated through the muscle tissue which is slower and less efficient.
- Extra wide QRS > than 120 ms
- Pace maker may be necessary
