Propaedeutics of Internal Diseases · MU Plovdiv

29. Rhythm and conduction disturbances

Inside: 35 sections · 12 labelled pictures · 13 tables · 48 flashcards · 46 min

Topic 29 of 100 in the MU Plovdiv syllabus for Propaedeutics of Internal Diseases (Medicine, Year 3). The free AceMed note covers it in 29 sections, about 5,231 words (46 min of reading), with 48 flashcards.

In this note

  1. Definition and the conduction system
  2. Classification
  3. Etiology
  4. Sinus node dysfunction (sick sinus syndrome)
  5. Atrioventricular block
  6. Bundle branch and fascicular blocks
  7. Long QT (disorder of repolarisation)
  8. Diagnosis
  9. Treatment
  10. Prognosis
  11. Definition
  12. Mechanisms
  13. Haemodynamics
  14. Clinical features
  15. Premature atrial beats
  16. Sinus tachycardia
  17. Focal and multifocal atrial tachycardia
  18. Atrial flutter
  19. Atrial fibrillation
  20. AV nodal re-entrant tachycardia (AVNRT)
  21. AV re-entrant tachycardia (AVRT) and Wolff–Parkinson–White (WPW)
  22. Junctional rhythms
  23. Differential diagnosis
  24. Aetiology
  25. Pathogenesis
  26. ECG recognition
  27. Differential diagnosis: VT or SVT with aberrancy
  28. Complications
  29. Prognosis and risk

Definition and the conduction system

  • Conduction disturbances: slowed or blocked spread of the cardiac impulse at the level of the sinoatrial (SA) node, the atrioventricular (AV) node, the His bundle or the bundle branches and fascicles. They cause bradyarrhythmias (sinus node dysfunction, AV block) or an abnormal QRS complex on the electrocardiogram (ECG) (bundle branch and fascicular blocks).
  • SA node (high right atrium) fires at 60–100/min → atria → AV node (physiological delay; PR interval normally 120–200 ms) → His bundle → right bundle branch (one fascicle) and left bundle branch (left anterior and left posterior fascicles) → Purkinje fibres.
  • Escape rhythms when a higher level fails: AV junction 40–60/min with a narrow QRS; ventricles 20–40/min with a broad QRS (slower and less reliable).
  • Blood supply: the SA node artery comes from the right coronary artery (RCA) in about 60%; the AV node from the RCA (posterior descending artery) in most people — hence AV block in inferior myocardial infarction (MI).

Image: “Electrical conduction system of the heart” by Madhero88, CC BY-SA 3.0, via Wikimedia Commons.

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