Av nodal blocks

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AV nodal blocks

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Av nodal blocks

  1. 1. AV Nodal Blocks
  2. 2. Normal AV Node <ul><li>AV nodal conduction time is represented on the ECG as the PR segment. </li></ul><ul><li>But - we always measure the PR interval. </li></ul>
  3. 3. AV Nodal Blocks (heart blocks) <ul><li>Disturbances of the conduction through the heart, occurring at the AV Node </li></ul><ul><li>Due to damage or intrinsic disease of the AV Node </li></ul>
  4. 4. Causes of AV blocks <ul><li>I ncreased vagal tone (inferior MI) </li></ul><ul><li>I schemia: Acute MI </li></ul><ul><li>I atrogenic: Post Cardiac surgery, drugs e.g. digoxin </li></ul><ul><li>I nflammatory: Rheumatic fever, myocarditis </li></ul><ul><li>I nfections: Endocarditis, Chagas’ disease </li></ul><ul><li>I diopathic: Degenerative </li></ul><ul><li>I nfiltrative: Sarcoidosis, Amyloidosis </li></ul>
  5. 5. First Degree Heart Block (1 º) <ul><li>SA Node – normal </li></ul><ul><ul><ul><li>Normal P wave </li></ul></ul></ul><ul><li>AV Node conducts more slowly than normal </li></ul><ul><ul><ul><li>Prolonged PR Interval </li></ul></ul></ul><ul><li>Rest of conduction is normal </li></ul><ul><ul><ul><li>Normal QRS </li></ul></ul></ul><ul><li>All the sinus impulses are conducted to the ventricles </li></ul>
  6. 6. First Degree Heart Block (1 º) <ul><li>PR Interval > 0.2 seconds (5 small sq) </li></ul><ul><li>Note – the PR Interval is constant </li></ul>
  7. 7. Clinical significance <ul><li>Common in the setting of acute MI, digoxin toxicity, rheumatic fever etc </li></ul><ul><li>May progress to higher grade of AV block </li></ul><ul><li>Beta blockers are contraindicated in 1 º AV block </li></ul><ul><li>No specific therapy required </li></ul>
  8. 8. Second Degree Heart Block (2 º) <ul><li>Mobitz Type I (Wenkebach phenomenon) </li></ul><ul><li>Mobitz Type II </li></ul><ul><li>Some of the sinus impulses are not conducted to the ventricles </li></ul>
  9. 9. Second Degree Heart Block (2 º) Mobitz Type I (Wenkebach) PR PR PR DROPPED BEAT
  10. 10. Second Degree Heart Block (2 º) Mobitz Type I (Wenkebach) <ul><li>Conduction through the AV Node is progressively delayed until a beat is dropped </li></ul><ul><li>PR Interval prolongs with each beat until a dropped beat is seen </li></ul><ul><li>The PR Interval is NOT constant </li></ul><ul><li>After the dropped beat, the PR interval is normal and the cycle starts again </li></ul>
  11. 11. Clinical Significance <ul><li>Usually asymptomatic </li></ul><ul><li>Common in acute inferior MI and digoxin toxicity </li></ul><ul><li>May rarely progress to 3 º AV Block </li></ul><ul><li>Treatment </li></ul><ul><ul><ul><li>Pacemaker if during day &/or symptoms </li></ul></ul></ul><ul><ul><ul><li>No specific therapy otherwise </li></ul></ul></ul>
  12. 12. Second Degree Heart Block (2 º) Mobitz Type II <ul><li>Conduction through the AV node is constant but dropped beats are seen </li></ul><ul><li>PR Interval normal & constant </li></ul><ul><li>Occasionally a dropped beat is seen </li></ul>
  13. 13. Second Degree Heart Block (2 º) Mobitz Type II PR PR DROPPED BEAT PR
  14. 14. Clinical significance <ul><li>Indicates more significant conduction system disease (below the His bundle) </li></ul><ul><li>Type II Mobitz block never occurs with digoxin toxicity </li></ul><ul><li>Poor prognosis in anterior MI </li></ul><ul><li>Intermittent complete AV block may cause syncope </li></ul><ul><li>Treatment – Permanent pacemaker </li></ul>
  15. 15. Third Degree Heart Block (3 º) (Complete) <ul><li>Complete failure of the AV Node </li></ul><ul><li>No impulses from Sinus Node will pass through to the ventricles </li></ul><ul><li>Some part if the conducting system will take over as pacemaker of the heart (even a myocardial cell 10-15 bpm) </li></ul>
  16. 16. Third Degree Heart Block (3 º) (Complete) <ul><li>P wave rate – normal </li></ul><ul><li>Ventricular rate – slow and regular </li></ul><ul><li>Ventricular complex may be broad </li></ul><ul><ul><ul><li>Idioventricular rhythm </li></ul></ul></ul><ul><li>Complete dissociation between P waves & QRS </li></ul><ul><li>More P waves than QRS complexes on ECG </li></ul>
  17. 17. Third Degree Heart Block (3 º) (Complete) P P P P P QRS QRS
  18. 18. Clinical significance <ul><li>Usually symptomatic due to bradycardia </li></ul><ul><li>Syncope (Stokes Adams’ episodes) </li></ul><ul><li>May be life-threatening </li></ul><ul><li>Treatment – Permanent pacemaker if symptomatic </li></ul><ul><li>Complete heart block may resolve spontaneously in inferior MI with reperfusion </li></ul>
  19. 19. Summary – AV blocks <ul><li>1 º - prolongation of PR Interval </li></ul><ul><li>2º - Mobitz I – Increasing PR Interval until dropped beat is seen Mobitz II – Constant PR Interval with more P waves to QRS </li></ul><ul><li>3º - Complete dissociation between P waves & QRS </li></ul>

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