Atrioventricular Blocks
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| 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
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| 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)
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| 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.
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| 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.
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| 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.
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| 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
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| 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
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| 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
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| 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
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| What causes Second Degree Type 2 AV Block (Mobitz II)? | Disease of LCA, Anterior wall MI, CMY, Fibrosis of conduction system, Myocarditis
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| 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
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| 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)
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| If 2:1 AVB rhythm shows WIDE QRS? | Block is occurring BELOW the AV Junction, usually a Type 2 block
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| 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
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| 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
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| 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
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| What causes Third Degree AV Block (Complete Heart Block)? | Acute MI, Myocarditis, Medications, Congenital Disease, Increased parasympathetic tone
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| 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
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| First Degree AVB: P wave? | Normal
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| First Degree AVB: PR Interval? | Prolonged
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| First Degree AVB: QRS Complex? | Normal
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| First Degree AVB: P-P Interval? | Regular
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| First Degree AVB: R-R Interval? | Regular
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| Second Degree AVB (Wenckebach): P wave? | Normal
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| Second Degree AVB (Wenckebach): PR Interval? | Prolonged, variable
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| Second Degree AVB (Wenckebach): QRS Complex? | Normal
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| Second Degree AVB (Wenckebach): P-P Interval? | Irregular
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| Second Degree AVB (Wenckebach): R-R Interval? | Irregular
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| Second Degree AVB (Mobitz II): P wave? | Normal
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| Second Degree AVB (Mobitz II): PR Interval? | Possibly prolonged, constant
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| Second Degree AVB (Mobitz II): QRS Complex? | Normal or Wide
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| Second Degree AVB (Mobitz II): P-P Interval? | Regular
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| Second Degree AVB (Mobitz II): R-R Interval? | Irregular
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| Third Degree AVB (Complete Heart Block): P wave? | Normal
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| Third Degree AVB (Complete Heart Block): PR Interval? | No association
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| Third Degree AVB (Complete Heart Block): QRS Complex? | Normal or Wide
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| Third Degree AVB (Complete Heart Block): P-P Interval? | Regular
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| Third Degree AVB (Complete Heart Block): R-R Interval? | Regular
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| 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
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| 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
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| 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
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| Where is the block in Wenckebach? | Block is in the AV node
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| Where is the block in Mobitz II? | Bundle of His, The block is in the distal conduction system (below the AV node)
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| Which AV Blocks have P waves present? | All AV Blocks (First Degree, Wenckebach, Mobitz II, 2:1, Advanced (high grade) and Third)
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