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Dr.K.G.MoniGandhi

3 degree  av

First-degree AV nodal block - the conduction velocity is slowed so that the P-R interval is increased to greater than 0.2 seconds.  Can be caused by enhanced vagal tone, digitalis, beta-blockers, calcium channel blockers, or ischemic damage.

Second-degree AV nodal block - the conduction velocity is slowed to the point where some impulses from the atria cannot pass through the AV node.  This can result in P waves that are not followed by QRS complexes.  With a Mobitz type I block, the P-R interval gradually increases until a QRS is dropped. Therefore, the atrial rate will be greater than the ventricular rate.  When there is a Mobitz type II block, the P-R interval is usually normal (<0.2 msec), but there may be 2 or 3 P waves before one is followed by a QRS (as shown in the figure). In this type of block, the ventricular rhythm is less than the sinus rhythm.

Third-degree AV nodal block - conduction through the AV node is completely blocked so that no impulses are able to be transmitted from the atria to the ventricles.  QRS complexes will still occur (escape rhythm), but they will originate from within the AV node, bundle of His, or other ventricular regions.  Therefore, QRS complexes will not be preceded by P waves.  Furthermore, there will be complete asynchrony between the P wave and QRS complexes.  Atrial rhythm may be completely normal, but ventricular rhythm will be greatly reduced depending upon the location of the site generating the ventricular impulse.  Ventricular rate typically range from 30 to 40 beats/min.

3 degree av

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