Talk:Second degree heart block

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Second degree heart block is a disease of the electrical conduction system of the heart.

--- This isn't necessarily true. It is sometimes a manifestation of the Bezold-Jarisch reflex in the early course of inferior wall MI. It doesn't have to be a primary disease of the AV node. Second degree AV block is an arrhythmia, not a disease.

If this term is used without a qualifier, it is usually assumed to be regarding disease of the atrioventricular node (AV node). However it is possible to have a second degree heart block involving the sinoatrial node (SA node) as well.

--- Explain this please. By definition the AV blocks take place in the AV junction.

There are two distinct types of second degree heart block, called type 1 and type 2. The distinction is made between them because type 1 second degree heart block is considered a more benign entity than type 2 second degree heart block.

[edit] Type 1 Second degree heart block Type 1 Second degree heart block, also known as Mobitz I heart block or Wenckebach phenomenon, is a disease of the AV node.

--- Again, the block itself is not a disease, although it may be caused by a disease.

Mobitz I heart block is characterized by progressive prolongation of the PR interval on the electrocardiogram (EKG) on consecutive beats followed by a blocked beat (dropped QRS complex). After the dropped QRS complex, the PR interval resets and the cycle repeats.

--- Often there will be a progressive shortening of the R to R interval until a QRS complex is dropped. You will observe grouping of the QRS complexes, which should alert the clinician to the possibility of Wenckebach.

One of the baseline assumptions when determining if an individual has Mobitz I heart block is that the sinus rhythm has to be regular. If the sinus rhythm is not regular, there could be alternative explanations as to why the P wave wasn't followed by a QRS complex.

--- It would be more appropriate to call this the P to P interval.

[edit] Type 2 Second degree heart block Type 2 Second degree heart block, also known as Mobitz II heart block is a disease of the distal conduction system. This is also known as Infrahisian block because the level of block is below the bundle of His.

--- Again, I would hesitate to call this a disease. It's an arrhythmia with a differential that includes primary ischemia of the AV node.

Mobitz Type II heart block is characterized on a surface ECG by a fixed PR interval, with a series of cycles consisting of one normal P-QRS-T cycle preceded by a series of non-conducted P waves (i.e. P waves not followed by QRS complexes). Each repeating Mobitz series has a consistent P:QRS ratio (2:1, 3:1, 4:1, etc.). Higher conduction ratios (4:1, 5:1, etc.) indicate increased severity of the block, and are known as advanced Mobitz block.

--- There is no need to say "a certain number of P waves." You only need enough blocked P waves to identify the behavior of the AV node. 2:1 conduction is considered Non-typeable Second Degree AV Block.