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AV Heart Blocks

AV Heart Blocks. Pauline Seydak, Cardiac Physiology Trainer N.I. AV Nodal Blocks (heart blocks). Disturbances of the conduction through the heart, occurring at the AV Node AV Node – damaged/diseased – delay or total block of impulses at the AV Node

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AV Heart Blocks

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  1. AV Heart Blocks Pauline Seydak, Cardiac Physiology Trainer N.I.

  2. AV Nodal Blocks (heart blocks) • Disturbances of the conduction through the heart, occurring at the AV Node • AV Node – damaged/diseased – delay or total block of impulses at the AV Node • This conduction defect can be seen on the ECG

  3. Here’s the key idea - the signal is either getting through: 1-    All the time (but taking a little longer than usual). 2-    Some of the time. 3-    None of the time. All, some, or none of the time. And see, those are the three kinds, or degrees of heart block: first, second, and third degree. All, some, or none.

  4. Causes • Increased vagal tone (parasympathetic nervous system) • IHD (MI) • Endocarditis • Degeneration (age) • Sclerosis (Aortic) • Cardiac surgery trauma

  5. AV Node • AV nodal conduction time is represented on the ECG as the PR segment. • But - we always measure the PR interval.

  6. First Degree Heart Block (1º) • SA Node – normal • Normal P wave • AV Node conducts more slowly than normal • Prolonged PR Interval • Rest of conduction is normal • Normal QRS

  7. First Degree Heart Block (1º) • PR Interval > 0.2 seconds (5 small sq) • Note – the PR Interval is constant

  8. Significance • Clinical significance • None • Treatment • None • Note – this can progress to 2º or 3º heart block

  9. Second Degree Heart Block (2º) • Mobitz Type I (Wenkebach) • Mobitz Type II • 2 : 1

  10. Second Degree Heart Block (2º)Mobitz Type I(Wenkebach) • Conduction through the AV Node – progressively delayed until a drop beat is seen • Karl Wenkebach

  11. Second Degree Heart Block (2º)Mobitz Type I(Wenkebach) • PR Interval prolongs with each beat until a dropped beat is seen • The PR Interval is NOT constant • After each dropped beat, the PR interval is normal and the cycle starts again

  12. Second Degree Heart Block (2º)Mobitz Type I(Wenkebach) PR PR PR DROPPED BEAT

  13. 2nd Degree AV block Mobitz 1

  14. Significance • Clinical Significance • Slight symptoms eg. Lethargy,Confusion • Treatment • Pacemaker if during day &/or symptoms • No treatment if at night • Note – this can progress to 3º Heart Block

  15. Second Degree Heart Block (2º)Mobitz Type II • Conduction through the AV node is constant. • PR interval is normal and constant • Occasionally a dropped beat is seen

  16. Second Degree Heart Block (2º)Mobitz Type II PR PR DROPPED BEAT PR

  17. Significance • Clinical significance – this is more significant disease • Treatment – pacemaker • Note – this can progress to 3º Heart Block

  18. Second Degree Heart Block (2º) 2 : 1 • Unable to strictly classify as Mobitz Type I or II • Particular type of second degree Heart Block • Ratio 2 P waves : 1 QRS

  19. Second Degree Heart Block (2º) 2 : 1

  20. Significance • Clinical significance – unable to classify as Mobitz type I or II • Will be associated with symptoms, dizziness, lethargy etc. • Treatment – pacemaker • Note – this can deteriorate to 3º Heart Block

  21. Third Degree Heart Block (3º)(Complete) • Complete failure of the AV Node • No impulses from Sinus Node will pass through to the ventricles • Some part if the conducting system will take over as pacemaker of the heart (even a myocardial cell 10-15 bpm)

  22. Third Degree Heart Block (3º)(Complete) • P wave rate – normal • Ventricular rate – slow • Ventricular complex may be broad • Idioventricular rhythm • Complete dissociation between P waves & QRS

  23. Third Degree Heart Block (3º)(Complete) P P P P P QRS QRS

  24. 3rd degree AV block

  25. Significance • clinical significance • Symptoms LOC, Confusion, Dizziness, Low BP • Can lead to standstill, VT or VF (stokes Adams) • Treatment - pacemaker

  26. Summary • 1º - prolongation of PR Interval ALL • 2º - Mobitz I – Increasing PR Interval until dropped beat is seen SOME Mobitz II – Constant PR Interval with more P waves to QRS • 2 : 1 – Constant PR Interval with more P waves to QRS • 3º - Complete dissociation between P waves & QRS NONE

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