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ECGs Made Easy Ch. 7

Atrioventricular Blocks

QuestionAnswer
What are AV Blocks (AVBs)? A delay or interrup. in impulse conduction from the atria to the vent despite normal conduction of the SA Node, Can be a result of damage to the AV node or transient impairment (ie, ischemia), Changes in the PR interval may be the result of an AV Block
What are 4 variations of AV Blocks? First Degree AV Block, Second Degree: Type 1 AV Block (Mobitz 1, Wenckeback), Second Degree: Type 2 AV Block (Mobitz 2), Third Degree AV Block (Complete Heart Block)
What is First Degree AV Block? Prolonged P-R Interval, Delay in conduction from the SA node to the ventricles. Occurs because of a delay in conduction within the AV node. The delay occurs above the AV Junction, junctional escape may occur.
What causes First Degree AV Block? May be present in hearts with no abnormality in the case of Sinus Bradycardia, Acute MI, CMY, Acute Myocarditis/Endocarditis, Hyperkalemia, Degenerative disease of the conduction system, Medications, Vagal tone.
What does First Degree AV Block look like? Normal P wave, PR Interval is prolonged (>0.20 sec) and constant, QRS complexes are within normal limits and occur after every P wave, P-P Intervals are regular and constant, R-R Intervals are regular and constant.
What is Second Degree Type 1 AV Block (Wenckebach)? One or more (but not all) SA node impulses are blocked, typically due to an AV node lesion (=narrow QRS) but can also be due to an issue within the Purkinje Fibers (=wide QRS) (uncommon), SA node impulses end up earlier and earlier in the AV node refracto
What causes Second Degree Type 1 AV Block (Wenckebach)? Occlusion of RCA (Right coronary artery), Increase in Vagal tone (athletes), Medication, MVP (Mitral valve prolapse), Atrioseptal defect
What does Second Degree Type 1 AV Block (Wenckebach) look like? PR Intervals lengthen until QRS drops. Normal P wave, PR Interval may be prolonged (>0.20 sec) and variable, QRS complexes are within normal limits and do not occur after every P wave, P-P & R-R Intervals are Irregular
What is Second Degree Type 2 AV Block (Mobitz II)? Normal SA node impulses that are occasionally blocked in the His-Purkinje system, If the block occurs in Bundle of His, it will yield narrow QRS (70% of the time), If the block occurs in Purkinje Fibers it will yield wide QRS (30% of the time) Can have pr
What causes Second Degree Type 2 AV Block (Mobitz II)? Disease of LCA, Anterior wall MI, CMY, Fibrosis of conduction system, Myocarditis
What does Second Degree Type 2 AV Block (Mobitz II) look like? Normal P wave, PR Interval may be prolonged (>0.20 sec) and constant, QRS complexes are typically within normal limits and do not occur after every P wave, P-P Intervals are regular, R-R Intervals are irregular
What is 2:1 Atrioventricular Block (AVB)? The occurrence of "blocked" impulses occurring every other beat (or 2 P waves for every 1 QRS complex), Cannot be classified as 2nd Degree Type 1 or 2 (due to lack of PR Intervals to compare)
If 2:1 AVB rhythm shows WIDE QRS? Block is occurring BELOW the AV Junction, usually a Type 2 block
If 2:1 AVB rhythm shows NARROW QRS? Block is occurring ABOVE AV Junction (probably AV node), and is a form of Type 1 (Wenckebach) block
What is Advanced "High Grade" Second Degree AVB? Three or more consecutive non-conducted P waves, Cannot be classified as 2nd Degree Type 1 or 2 (due to lack of PR Intervals to compare), High risk for development of Third Degree AV Block
What is Third Degree AV Block (Complete Heart Block)? Block of the SA node that allows NO impulses through and NO conduction to the ventricles, Most commonly blocked at the His/Branches area, This results in an escape pacemaker from further down in the conduction system in order to stimulate ventricles
What causes Third Degree AV Block (Complete Heart Block)? Acute MI, Myocarditis, Medications, Congenital Disease, Increased parasympathetic tone
What does Third Degree AVB (Complete Heart Block) look like? Normal P wave, PR Interval will be irregular due to P wave (atria)/QRS (ventricular) disassociation, QRS complexes are wide (most commonly) and do NOT occur after every P wave, P-P Intervals are regular, R-R Intervals are regular
First Degree AVB: P wave? Normal
First Degree AVB: PR Interval? Prolonged
First Degree AVB: QRS Complex? Normal
First Degree AVB: P-P Interval? Regular
First Degree AVB: R-R Interval? Regular
Second Degree AVB (Wenckebach): P wave? Normal
Second Degree AVB (Wenckebach): PR Interval? Prolonged, variable
Second Degree AVB (Wenckebach): QRS Complex? Normal
Second Degree AVB (Wenckebach): P-P Interval? Irregular
Second Degree AVB (Wenckebach): R-R Interval? Irregular
Second Degree AVB (Mobitz II): P wave? Normal
Second Degree AVB (Mobitz II): PR Interval? Possibly prolonged, constant
Second Degree AVB (Mobitz II): QRS Complex? Normal or Wide
Second Degree AVB (Mobitz II): P-P Interval? Regular
Second Degree AVB (Mobitz II): R-R Interval? Irregular
Third Degree AVB (Complete Heart Block): P wave? Normal
Third Degree AVB (Complete Heart Block): PR Interval? No association
Third Degree AVB (Complete Heart Block): QRS Complex? Normal or Wide
Third Degree AVB (Complete Heart Block): P-P Interval? Regular
Third Degree AVB (Complete Heart Block): R-R Interval? Regular
How to diagnose Third Degree AV Block? No relationship between P waves and QRS, Cannot establish a pattern of P-R Intervals, Atrial rate faster than ventricular rate, QRS morphology can be normal or have QRS >0.12 depending on the source of the dominating rhythm
How to diagnose Wenckebach? P-R Interval increases progressively from beat to beat, Periodically a P wave is not conducted, The P-R Interval after the blocked P is the shortest
How to diagnose Mobitz II? P-R Interval remains constant, Periodically the SA node signal is blocked so there will be a P wave but no QRS after it
Where is the block in Wenckebach? Block is in the AV node
Where is the block in Mobitz II? Bundle of His, The block is in the distal conduction system (below the AV node)
Which AV Blocks have P waves present? All AV Blocks (First Degree, Wenckebach, Mobitz II, 2:1, Advanced (high grade) and Third)
Created by: kdanie24
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