Heart Blocks

Heart Blocks Can occur in the SA node, AV Node, or in larger sections of the ventricular condition system

Types of Heart Blocks:
1.  Sinus Block
2.  AV Blocks
3.  Bundle Branch Blocks
4.  Hemiblocks


Sinus Block-an unhealthy SA node quits pacing activity for at least one compete cycle.  The P waves before and after the block are identical because the same SA node pacemaker is functioning before and after the pause.

AV Blocks-when minimal delays the impulse within the AV node, making a longer than normal pulse before stimulating the ventricles.
-Types of AV Blocks
1.  First Degree AV Block
2.  Second Degree AV Block Type I
3.  Second Degree AV Block Type II
4.  Third Degree AV Block


First Degree AV Block-prolonged PR interval greater than 0.2 seconds.  There is no dropped QRS complex

Second Degree Type I AV Block-the PR interval become lengthened until the P wave does not elicit a responding QRS complex.  The PR interval is greater than 0.2 seconds.  Also called Wenckebach

Second Degree Type II AV Block-also called Mobitz II is when an occasional ventricular  depolarization (QRS complex) is not conducted but dropped.  The P waves are normal and normal PR intervals are present.

Third Degree AV Block-also called complete heart block.  This is when none of the atrial depolarizations conduct to the ventricles.  The P wave rate and the QRS complex rate are independent and will march out with calipers uniformly.

Bundle Branch Blocks-
-Normally the right and left bundles transmit the electrical change to the right and left ventricles at the same time.
-When there is a bundle branch block, there is a delay in the depolarization stimulus that creates the widened QRS complex in the classic rabbit ear pattern (R and R' waves)
-If there is a bundle branch block, look at the chest leads right (V1 and V2) and left (V5 and V6)


Right Bundle Branch Block
-If there is a R,R' waves in V1 or V2 there is a right bundle branch block
-If it is only present in one of the leads it is an incomplete right bundle branch block

Left Bundle Branch Block
-Sometimes the R R' waves will only be seen as notch in the wide QRS complex in V5 and V6
-In a left bundle branch block the left ventricle fires late so the first portion of the QRS complex is right ventricle activity.  We cannot see Q waves originating from the left ventricle because they are buried in the QRS complex

Right Bundle Branch EKG:

Left Bundle Branch EKG:

Wolff Parkinson White:
-There is an accessory pathway for ventricular stimulation causing a delay in ventricle stimulation
-This occurs between the SA node and AV junction
-This produces a delta wave
-These patients are prone to SVT

Delta Wave:

Hemiblocks:
-These are blocks of the anterior and posterior division of the left bundle branch
-These are mostly due to loss of blood supply to the anterior or posterior branches of the left bundle branch