Talk:Third-degree atrioventricular block

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Third degree heart block, also known as complete heart block, is a disease of the electrical system of the heart, in which the impulse generated in the top half of the heart (typically the SA node in the right atrium) does not propagate to the left or right ventricles.

--- Third degree AV block is an arrhythmia, not a disease. And it is unnecessary to specify "to the right or left ventricles" because obviously with third degree AV block the electrical connection between the atria and ventricles is completely severed. Bringing up the distinction between right and left ventricle here is confusing and belongs in the bundle branch block section, not the complete heart block section.

Due to the blocked rhythm, an accessory pacemaker below the level of the block typically will activate the ventricles. Since this accessory pacemaker activates independently of the impulse generated at the SA node, two independent rhythms can be noted on the electrocardiogram (EKG). One rhythm, generated from the SA node, will activate the atria and create the p wave on the EKG. The second rhythm, generated from the accessory pacemaker, will activate the ventricles and produce the QRS complex on the EKG.

--- Change the words "blocked rhythm" to "blocked impulse." This would be an appropriate place to discuss the difference between a junctional escape rhythm (narrow complexes) and a ventricular escape rhythm (wide complexes).

The hallmark of complete heart block is no apparent relationship between p waves and QRS complexes on the EKG.

--- Which is called "AV Dissociation."

[edit] Etiology Many conditions can cause third degree heart block. Progressive degeneration of the electrical conduction system of the heart can lead to third degree heart block. This may be preceded by second degree heart block, particularly Mobitz II heart block.

An acute myocardial infarction (heart attack), may also lead to third degree heart block. This may be due to damage to the AV node, preventing impulse propagation distal to that portion of the conduction system, or it may be due to damage of the distal conduction system.

--- Damage to the distal conduction system may cause a bundle branch block, but it will not cause an AV block.

An inferior wall myocardial infarction may cause damage to the AV node, causing third degree heart block. In this case, the damage is usually transitory, and the AV node may recover. Studies have shown that third degree heart block in the setting of an inferior wall myocardial infarction typically resolves within 2 weeks.

--- With inferior MI, the AV block may be a manifestation of the Bezold-Jarisch reflex or direct ischemia of the AV node. You will typically see a narrow complex escape rhythm with inferior MI, and yes, the prognosis is good.

An anterior wall myocardial infarction may damage the distal conduction system of the heart, causing third degree heart block. This is typically extensive, permanent damage to the conduction system, necessitating a permanent pacemaker to be placed.

--- Again, the distal conduction system has nothing to do with complete heart block, although it can cause bundle branch blocks. Anterior MI can cause a complete heart block right there at the AV node, as the AV node has a dual blood supply (RCA and LAD). With anterior MI a wide complex escape rhythm is more common, and has a poor prognosis. Various degrees of AV block can also be caused by drugs that slow conduction through the AV node such as beta blockers, calcium channel blockers, and digoxin.— Preceding unsigned comment added by (talkcontribs) 18:53, 4 August 2005‎

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