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 whyThe 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:
- Myocardial infarction that damages the conduction system
- Idiopathic fibrosis
- Cardiac surgery
- Infections and inflammatory conditions
- 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)
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