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AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
AV Nodal Blocks
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AV Nodal Blocks

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  • 1. Dr. S. Aswini Kumar. MD Professor of Medicine Medical College Hospital Thiruvananthapuram A V N o d e BLOCK
  • 2. Sino-Atrial Node
    • Anatomy
    • Natural Pacemaker
    • Location
        • Upper Right Atrium
        • Close to SVC, RAA
        • epicardial in location
    • 1.5 cm long 2-3mm wide
    • Neuromyocardial cells
    • Blood supply
      • RCA 60%
      • LCX 40%
    • Physiology
    • IDR - 80 bpm
    • sympathetic & parasympathetic
    • Sympathetic -  HR
    • Parasympathetic  HR
    2007-06-11
  • 3. Atrial Depolarisation
    • Anatomy
    • ? Tracts –
      • Bachman,
      • Thorel
      • Wenkebach
    • Muscular ridges
    • From SA node across myocardial cells
    • Physiology
    • Propagated action potential results in myocardial contraction
    • Represented on the ECG as P wave
    • Passes to AV node in the floor of the RA
    2007-06-11
  • 4. AV Node
    • Anatomy
    • Tadpole shaped
    • 2 X 5 mm
    • Endocardial,
    • IA Septum at the junction of atria and ventricles
    • Blood Supply:
      • RCA - 95 %
      • LCX - 5 %
      • occasionally from both
    • Physiology
    • Spread of depolarisation - from atrial myocardium
    • IDR - 60 bpm
    • Delay 0.15 seconds
      • time atria to expel blood
      • time for ventricular filling
      • protection to ventricles re; atrial arrhythmias
    2007-06-11
  • 5. AV Node
    • Physiology (contd)
    • Autonomic nervous control - not as pronounced as SA Node
    • Sympathetic stimulation -  IDR &  AV nodal conduction time
    • Parasympathetic stimulation - opposite
    • Electrocardiogram
    • AV nodal conduction is represented on the ECG as the PR segment
    2007-06-11
  • 6. The Bundle Of His
    • Anatomy
    • Directly continuous with the AV node
    • 20 mm long
    • Endocardial
    • Within the IV septum
    • Bundle of discreet fibres - crosses AV ring
    • No dedicated blood supply
    • Physiology
    • Only normal pathway Atria  Ventricles
    • IDR - 50 bpm
    • Nervous stimulation - minor effect
    • Depolarisation of the Bundle is not seen on the surface ECG
    2007-06-11
  • 7. The Bundle Branches & Purkinje Fibers
    • Bundle branches
    • Bundle of His separates into 2 main branches,
      • Left bundle
      • Right bundle
    • Left bundle –
      • Antero-Superior division
      • Postero-Inferior division
    • No dedicated blood supply
    • IDR - 40 bpm
    • Purkinje Fibers
    • Bundle Branches divide further
      • Small, dense network conducting tissue
    • Endocardial  Epicardial
    • No dedicated blood supply
    • Entire musculature depolarizes quickly
    • IDR - 20 bpm
    • Nervous stimulation
        • - minor effect only
    2007-06-11
  • 8. Ventricular De & Repolarization
    • Depolarization
    • Bundle Branch & purkinje fibre depolarisation constitutes ventricular depolarisation
    • Represented on the ECG as the QRS
    • Repolarization
    • Repolarisation is smaller in amplitude & slower than depolarisation
    • Atrial repolarisation occurs within the QRS is masked
    • Ventricular repolarisation is represented on the ECG as a T
    2007-06-11
  • 9. The Conducting System - Summary 2007-06-11
  • 10. The AV Nodal Conduction
    • AV nodal conduction time is represented on the ECG as the PR segment.
    • But - we always measure the PR interval.
    PR Segment PR Interval 2007-06-11
  • 11. AV Nodal Blocks (Heart Blocks)
    • Disturbances of the conduction through the heart, occurring at the AV Node
    • AV Node – damaged or diseased
    • Delay or total block of impulses at the AV Node
    • This conduction defect can be seen on the ECG
    2007-06-11
  • 12. Causes
    • Increased vagal tone
    • Highly trained athletes
    • Myocardial Infarction
    • Coronary spasm
    • Digitalis intoxication
    • Beta blockers
    • Viral Myocarditis
    • Degeneration (Age)
    • Sclerosis (Aortic)
    • Cardiac surgery (Trauma)
    2007-06-11
  • 13. Degenerative diseases
    • Lev’s Disease:
        • Calcification and sclerosis of fibrous cardiac cytoskeleton
        • Also involving aortic/mitral valves
    • Lenegre’s Disease
        • Primary sclero-degenerative disease of conducting system
        • No involvement of fibrous skeleton of heart
    2007-06-11
  • 14. First Degree Heart Block (1 º HB)
    • SA Node – normal
        • Normal P wave
    • AV Node conducts more slowly than normal
        • Prolonged PR Interval
    • Rest of conduction is normal
        • Normal QRS
    • PR Interval > 0.2 seconds (>5 small sq) but constant
    2007-06-11
  • 15. First Degree Heart Block (1 º HB) 2007-06-11
  • 16. First Degree Heart Block (1 º HB)
    • More appropriately called as
        • Prolonged AV Conduction
    • PR interval is determined by
        • Atrial, AV nodal and His purkinje activation
    • Site of involvement
        • Could be any of these
        • Narrow QRS – AV nodal origin
    • Clinical significance
        • None, Prognosis good
    • Treatment
        • None
    2007-06-11
  • 17. Second Degree Heart Block (2 º HB) (Intermittent Heart Block)
    • Second degree AV block is said to be present when some atrial impulses fail to conduct to the ventricles
    • Mobitz Type I (Wenkebach)
    • Mobitz Type II
    • 2 : 1 Fixed Heart Block
    Karel Frederik Wenckebach 2007-06-11
  • 18. Second Degree Heart Block (2 ºHB) Mobitz Type I (Wenkebach)
    • Conduction through the AV Node – progressively delayed until a drop beat is seen
    PR PR PR DROPPED BEAT 2007-06-11
  • 19. Second Degree Heart Block (2 ºHB) Mobitz Type I (Wenkebach) 2007-06-11
  • 20. Second Degree Heart Block (2 ºHB) Mobitz Type I (Wenkebach)
    • The PR Interval is NOT constant
    • PR Interval prolongs with each beat until a beat is dropped
    • The pause that follows is less than full compensatory
    • Difference between longest and shortest PR >100msec
    • After each dropped beat, the PR interval becomes normal
    • Clinical Significance
        • Slight symptoms: Lethargy, Confusion
    • Treatment
        • Pacemaker if during day &/or symptoms
        • this can progress to 3 º Heart Block
    2007-06-11
  • 21. Second Degree Heart Block (2 ºHB) Mobitz Type II
    • Conduction through the AV node is constant but dropped beats are seen
    PR PR DROPPED BEAT PR 2007-06-11
  • 22. Second Degree Heart Block (2 ºHB) Mobitz Type II
    • Occasionally a dropped beat is seen
        • Conduction fails suddenly and un expectedly without a preceding change in the PR intervals
    2007-06-11
  • 23. Second Degree Heart Block (2 ºHB) Mobitz Type II
    • It is a regularly irregular grouped rhythm
        • with dropped QRS complexes that shows no variation in the PR interval whatsoever between the dropped beats.
    • PR prolongation
        • is a major diagnostic clue that helps to differentiate between these two types. PR Interval normal & constant
    • Clinical significance –
        • More significant disease due to disease of His Purkinje
    • Treatment
        • Pacemaker
        • This can progress to 3 º Heart Block
    2007-06-11
  • 24. Second Degree Heart Block (2 ºHB) 2 : 1 HB
    • Unable to strictly classify as Mobitz Type I or II
    • Particular type of second degree Heart Block
    • Ratio 2 P waves : 1 QRS
    DROPPED BEAT DROPPED BEAT 2007-06-11
  • 25. Second Degree Heart Block (2 º) 2 : 1 2007-06-11
  • 26. Second Degree Heart Block (2 º) 2 : 1 HB
    • Clinical significance:-
        • Unable to classify as Mobitz type I or II
        • Difficult to diagnose the level of lesion
        • Normal QRS and long PR interval indicate AV nodal
        • Associate BBB suggests level below AV node
        • This can deteriorate to 3 º Heart Block
        • Will be associated with symptoms Dizziness, lethargy etc.
    • Treatment :-
        • Temporary Trans-cutaneous pacing in low risk
        • Temporary Trans-venous pacing
        • Permanent Pacemaker Implantation
        • Withdraw any offending drugs
        • Correction of any electrolyte abnormality
    2007-06-11
  • 27. Third Degree Heart Block (3 º HB) (Complete Heart Block)
    • Pathophysiology:
      • Complete failure of AV Node to conduct impulses from SA Node
      • No impulses from Sinus Node will pass through to the ventricles
      • Some part of conducting system will take over as pacemaker
      • The escape pacemaker can be in the AV node
      • Or it can be in the His bundle or even distal to it
      • Even a myocardial cell have an automaticity at a rate of 10-15 bpm
    • Symptoms:
      • Dizzy spells, near syncope, frank syncope, easy fatiguability
    • Level of block
      • At AV nodal – Junctional rhythm with narrow QRS complex
      • At His-Purkinje level - Ventricular escape rhythm with wide QRS
    2007-06-11
  • 28. Third Degree Heart Block (3 ºHB) (Complete Heart Block)
    • P wave rate – normal
    • Ventricular rate – slow
    • Ventricular complex may be broad
        • Idioventricular rhythm
    • Complete dissociation between P waves & QRS
    P P P P P QRS QRS 2007-06-11
  • 29. Third Degree Heart Block (3 º) (Complete Heart Block) 2007-06-11
  • 30. Differences between CHBs
    • Congenital CHB
    • Present from birth
    • Isolated finding
    • Connective tissue disorders
    • Hereditary form – SCN5A gene
    • QRS occurs at 40-50 bpm
    • QRS duration normal
    • Increases with atropine
    • Site of block is AV node
    • That is a proximal block
    • Pacemaker not mandatory
    • Acquires CHB
    • Occurs later in life
    • Inferior wall infarction - AVB
    • Anterior wall infarction – TFB
    • Leve’s or Lenegre’sdisease
    • QRS occurs at 20-30 bpm
    • QRS duration prolonged
    • Does not  with atropine
    • Site of block distal to AV node
    • That is a distal block
    • Mandates a pacemaker
    2007-06-11
  • 31. Third Degree Heart Block (3 º) (Complete Heart Block)
    • Clinical significance
        • Symptoms LOC, Confusion, Dizziness, Low BP
        • This can deteriorate to Cardiac Asystole
        • This can precipitate VT/VF
    • Treatment – medical
        • Atropine if block at AV nodal level
        • Isoproterenol – IV infusion
        • Caution in Acute MI
    • Treatment - Pacing
        • Temporary trans-cutaneous pacing
        • Temporary Trans-venous pacing
        • Permanent Pacemaker Implantation
    2007-06-11
  • 32. Third Degree Heart Block (3 º HB) (Complete AV Dissociation)
    • P wave rate – normal
    • Ventricular rate – slow
    • Ventricular complex may be broad or normal
    • Occasional Capture Beats
    • Complete dissociation between P waves & QRS
    P P P P P QRS QRS CAPTURED 2007-06-11
  • 33. Two types of AV Dissociation
    • Isorhythmic Dissociation
    • Severe Sinus Bradycardia
    • Junctional Escape Rhythm
    • Sinus rate = Junctional rate
    • They compete against each
    • P waves before in or after QRS
    • Causes
        • Digoxin toxicity
        • Poisonings
    • Treatment
        • Remove cause of bradycardia
        • Discontinue digitalis
        • Stop verapamil or beta blocker
        • Increase sinus nodal rate
    • Interference Dissociation
    • Lower level pacemaker
    • Junctional or ventricular
    • Faster intrinsic rate
    • Compete with sinus node
    • Ventricular Tachycardia
    • Causes
        • Myocardial Ischemia
        • Irritation of cardiac surgery
    • Treatment
        • Antiarrhythmic drugs
        • Correction of ischemia
        • Accelerated ideoventricular rhythm
        • Treatment of metabolic abnormality
    2007-06-11
  • 34. Summary
    • 1 º
        • Prolongation of PR Interval
        • Mobitz I – Increasing PR Interval until dropped beat is seen
        • Mobitz II – Constant PR Interval with more P waves to QRS
        • 2 : 1 – Constant PR Interval with more P waves to QRS
        • Complete pathological block at the AV node
        • Complete dissociation between P waves & QRS
    2007-06-11
  • 35. 2007-06-11

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