Second degree heart block Type 2, which is also called Mobitz II or Hay, is a disease of the electrical conduction system of the heart. Second-degree AV block (Type 2) is almost always a disease of the distal conduction system located in the ventricular portion of the myocardium.
This rhythm can be recognized by the following characteristics:
- non-conducted p-waves (electrical impulse conducts through the AV node but complete conduction through the ventricles is blocked, thus no QRS)
- P-waves are not preceded by PR prolongation as with second-degree AV block (Type 1)
- fixed PR interval
- The QRS complex will likely be wide
Click here to see why.
The QRS on an ECG will most likely be wide because the block occurs in the His bundle or bundle branches and conduction through the ventricles is slowed. This slowing of conduction appears as a wide QRS complex on the ECG.
Second-degree heart block type 2 is usually caused by structural damage to the conduction system of the heart. Causes of the structural damage to the conduction system include the following:
Causes:
- Myocardial infarction that damages the conduction system
- Idiopathic fibrosis
- Cardiac surgery
- Infections and inflammatory conditions
- Hyperkalemia
- Autoimmune diseases affecting the heart
Second-degree AV block (Type 2) should be treated with immediate transcutaneous pacing or transvenous pacing because there is risk that electrical impulses will not be able to reach the ventricles and produce ventricular contraction.
Second-degree AV block (Type 2) is clinically significant because this rhythm can rapidly progress to complete heart block.
Atropine may be attempted if immediate TCP is not available or time is needed to initiate TCP. Atropine should not be relied upon and in the case of myocardial ischemia it should be avoided.
Below is a short video which will help you quickly identify second-degree heart block type 2 on a monitor. Please allow several seconds for the video to load. (2.65 mb)
Click for next Rhythm Review:
Complete Heart Block (3rd Degree Block)
Top Questions Asked On This Page
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Q: The video says “sometimes has wide QRS.” What else would you see with 2nd-degree if the block is occurring in the bundled His? I have seen the portrayed rhythm many times and was not sure what it was.
A: For 2nd-degree block type II you will see:
non-conducted p-waves (electrical impulse conducts through the AV node, but complete conduction through the ventricles is blocked, thus no QRS)
P-waves are not preceded by PR prolongation as with second-degree AV block (Type 1)
fixed PR interval -
Q: Having trouble differentiating between Mobitz II and third-degree block.
A: The main difference is this:
Mobitz II: There will be a P-wave with every QRS. There may not always be a QRS complex with every p-wave. The rate will usually be regular. Also, the PR interval will be regular.
3rd Degree Block: There may not be a p-wave with each QRS, and the PR interval will not be the same with each PQRS.
These videos may help you.
They are kind of hard to hear, but the content is good. -
Q: Your video says pace right away for 2nd degree? TCP should only take place if the patient is symptomatic or showing signs of inadequate perfusion? Correct?
A: Correct. If the patient is unstable which is defined as “showing signs of poor perfusion.”