Av Nodal Blocks(Hb)

AV Nodal BlocksAV Nodal Blocks

Lancashire & South Cumbria Cardiac Network

AV NodeAV NodeAV nodal conduction time is represented AV nodal conduction time is represented on the ECG as the PR segment. on the ECG as the PR segment.

But But -- we always measure the PR interval. we always measure the PR interval.

AV Nodal Blocks (heart blocks)AV Nodal Blocks (heart blocks)

Disturbances of the conduction through Disturbances of the conduction through the heart, occurring at the AV Nodethe heart, occurring at the AV Node

AV Node AV Node damaged/diseased damaged/diseased delay or delay or total block of impulses at the AV Nodetotal block of impulses at the AV Node

This conduction defect can be seen on the This conduction defect can be seen on the ECGECG

CausesCauses

Increased vagal tone (parasympathetic Increased vagal tone (parasympathetic nervous system)nervous system)IHD (MI)IHD (MI)EndocarditisEndocarditisDegeneration (age)Degeneration (age)Sclerosis (Aortic)Sclerosis (Aortic)Cardiac surgery traumaCardiac surgery trauma

First Degree Heart Block (1First Degree Heart Block (1))

SA Node SA Node normalnormalNormal P waveNormal P wave

AV Node conducts more slowly than AV Node conducts more slowly than normalnormal

Prolonged PR IntervalProlonged PR Interval

Rest of conduction is normalRest of conduction is normalNormal QRSNormal QRS

First Degree Heart Block (1First Degree Heart Block (1))

PR Interval > 0.2 seconds (5 small sq)PR Interval > 0.2 seconds (5 small sq)

Note Note the PR Interval is constant the PR Interval is constant

Clinical significanceClinical significanceNoneNone

TreatmentTreatmentNoneNone

Note Note this can progress to 2this can progress to 2 or 3or 3 heart heart blockblock

Second Degree Heart Block (2Second Degree Heart Block (2))

Mobitz Type I (Mobitz Type I (WenkebachWenkebach))

Mobitz Type IIMobitz Type II

2 : 12 : 1

Second Degree Heart Block (2Second Degree Heart Block (2))Mobitz Type IMobitz Type I((WenkebachWenkebach))

Conduction through the AV Node Conduction through the AV Node progressively delayed until a drop beat is progressively delayed until a drop beat is seenseen


PR PR PR DROPPED BEAT


PR Interval prolongs with each beat until a PR Interval prolongs with each beat until a dropped beat is seendropped beat is seenThe PR Interval is NOT constantThe PR Interval is NOT constantAfter each dropped beat, the PR interval is After each dropped beat, the PR interval is normal and the cycle starts again normal and the cycle starts again

Clinical SignificanceClinical SignificanceSlight symptoms Slight symptoms egeg. Lethargy,Confusion. Lethargy,Confusion

TreatmentTreatmentPacemaker if during day &/or symptomsPacemaker if during day &/or symptomsNo treatment if at nightNo treatment if at night

Note Note this can progress to 3this can progress to 3 Heart BlockHeart Block

Second Degree Heart Block (2Second Degree Heart Block (2))Mobitz Type IIMobitz Type II

Conduction through the AV node is Conduction through the AV node is constant but dropped beats are seenconstant but dropped beats are seen


PR PR DROPPED BEAT PR


PR Interval normal & constantPR Interval normal & constant

Occasionally a dropped beat is seenOccasionally a dropped beat is seen

Clinical significance Clinical significance this is more this is more significant disease significant disease

Treatment Treatment pacemakerpacemaker

Note Note this can progress to 3this can progress to 3 Heart BlockHeart Block

Second Degree Heart Block (2Second Degree Heart Block (2))2 : 12 : 1

Unable to strictly classify as Mobitz Type I Unable to strictly classify as Mobitz Type I or IIor II

Particular type of second degree Heart Particular type of second degree Heart BlockBlock

Ratio 2 P waves : 1 QRS Ratio 2 P waves : 1 QRS

Second Degree Heart Block (2Second Degree Heart Block (2))2 : 12 : 1

Clinical significance Clinical significance unable to classify as unable to classify as Mobitz type I or IIMobitz type I or II Will be associated with symptoms, dizziness, Will be associated with symptoms, dizziness,

lethargy etc.lethargy etc.

Treatment Treatment pacemakerpacemaker

Note Note this can deteriorate to 3this can deteriorate to 3 Heart Heart BlockBlock

Third Degree Heart Block (3Third Degree Heart Block (3))(Complete)(Complete)

Complete failure of the AV NodeComplete failure of the AV Node

No impulses from Sinus Node will pass No impulses from Sinus Node will pass through to the ventriclesthrough to the ventricles

Some part if the conducting system will Some part if the conducting system will take over as pacemaker of the heart (even take over as pacemaker of the heart (even a myocardial cell 10a myocardial cell 10--15 bpm)15 bpm)


P wave rate P wave rate normalnormal

Ventricular rate Ventricular rate slowslow

Ventricular complex may be broadVentricular complex may be broadIdioventricularIdioventricular rhythmrhythm

Complete dissociation between P waves & Complete dissociation between P waves & QRSQRS


P P P P P

QRS QRS

clinical significanceclinical significanceSymptoms LOC, Confusion, Dizziness, Low Symptoms LOC, Confusion, Dizziness, Low BPBPCan lead to standstill, VT or VF (stokes Can lead to standstill, VT or VF (stokes Adams)Adams)

Treatment Treatment -- pacemakerpacemaker

SummarySummary11 -- prolongation of PR Intervalprolongation of PR Interval

22 -- Mobitz I Mobitz I Increasing PR Interval until Increasing PR Interval until dropped beat is seen dropped beat is seen Mobitz II Mobitz II Constant PR Interval with Constant PR Interval with more P more P waves to QRS waves to QRS 2 : 1 2 : 1 Constant PR Interval with more Constant PR Interval with more P waves to QRSP waves to QRS

33 -- Complete dissociation between P Complete dissociation between P waves & QRS waves & QRS

AV Nodal BlocksAV NodeAV Nodal Blocks (heart blocks)CausesFirst Degree Heart Block (1)First Degree Heart Block (1)Second Degree Heart Block (2)Second Degree Heart Block (2)Mobitz Type I(Wenkebach)Second Degree Heart Block (2)Mobitz Type I(Wenkebach)Second Degree Heart Block (2)Mobitz Type I(Wenkebach)Second Degree Heart Block (2)Mobitz Type IISecond Degree Heart Block (2)Mobitz Type IISecond Degree Heart Block (2)Mobitz Type IISecond Degree Heart Block (2)2 : 1Second Degree Heart Block (2)2 : 1Third Degree Heart Block (3)(Complete)Third Degree Heart Block (3)(Complete)Third Degree Heart Block (3)(Complete)Summary

Av Nodal Blocks(Hb)

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