Cardiac Bootcamp ECG Challenge
A 58 yo male presents to the Emergency Department with dizziness. His vitals are: HR 48, BP 87/45, RR 20 and Sats 97% on room air. Here is the ECG. What is the diagnosis?
This is a MOBITZ II 2:1 Block
4 Rules to Diagnose a Mobitz Block
CAUSES OF MOBITZ BLOCKS
There is one particular case where the Mobitz may be missed. This is when the P wave is hidden in the T wave. This may not always be obvious. Remember that the T wave has a smooth and symmetrical shape. If the shape changes from this, then think of a potential P hidden inside a T wave.
The problem with missing the Mobitz II is that it can deteriorate into a complete heart block.
4 Rules to Diagnose a Mobitz Block
- Are there more P waves than QRS's? Then it may be a Mobitz. Remember that there may also be AV Dissociation with more QRS's than P's. However the most common form we see is the first.
- If there are more P's than QRS's , you may also expect the QRS complexes to be clumped.
- In order for this to be a block, the P - P Interval must be constant throughout the ECG. If it is not then the cause may be premature atrial contraction. This is because a P is delivered whilst in the relative refractory period and so a QRS is not generated.
- If the P-P interval is constant, next look for the P - R interval.
- If it is gradually increasing and then a QRS complex is missed, think of Mobitz I, or Wenckebach Block.
- Sometimes the best way to work this out is to simply look at the P-R interval immediately after a QRS being dropped. If this P-R interval is shorter than the previous one, then it is a Mobitz I
- If the P - R Interval is regular and then a QRS is missed, then this is most likely a Mobitz II block.
- If the P - R Interval is irregular, i.e. not consistently increasing or decreasing but random, then it is probably a complete heart block.
- If it is gradually increasing and then a QRS complex is missed, think of Mobitz I, or Wenckebach Block.
CAUSES OF MOBITZ BLOCKS
- AMI
- Hyperkalaemia
- His-Purkinge System Failure below AVN
- Conduction System Fubrosis
- Drug related: Amiodarone, Beta blockers, Calcium Channel Blockers, Digoxin
- Inflammatory/Autoimmune: Myocarditis, Rheumatic Fever, SLE
There is one particular case where the Mobitz may be missed. This is when the P wave is hidden in the T wave. This may not always be obvious. Remember that the T wave has a smooth and symmetrical shape. If the shape changes from this, then think of a potential P hidden inside a T wave.
The problem with missing the Mobitz II is that it can deteriorate into a complete heart block.