Internal Diseases and Therapy · MU Sofia

29. Rhythm abnormalities: supraventricular arrhytmias – classification, hemodinamics,

Covers supraventricular arrhythmias, beginning with definitions and the mechanisms of automaticity, triggered activity and re-entry, then a classification by site of origin and ECG features. It goes on to the haemodynamic consequences of fast rates and loss of atrial kick, clinical features, diagnosis and a table for reading narrow-QRS tachycardias. Separate sections address premature atrial beats, sinus and atrial tachycardias, atrial flutter, atrial fibrillation with its duration classification, AVNRT, AVRT and WPW with a comparison table, junctional rhythms and differential diagnosis.

Inside: 15 sections · 3 labelled pictures · 4 tables · 16 flashcards · 16 min

Topic 29 of 139 in the MU Sofia syllabus for Internal Diseases and Therapy (Medicine, Years 4 and 5). The free AceMed note covers it in 15 sections, about 1,946 words (16 min of reading), with 16 flashcards.

In this note

  1. Definition
  2. Mechanisms
  3. Classification
  4. Haemodynamics
  5. Clinical features
  6. Diagnosis
  7. Premature atrial beats
  8. Sinus tachycardia
  9. Focal and multifocal atrial tachycardia
  10. Atrial flutter
  11. Atrial fibrillation
  12. AV nodal re-entrant tachycardia (AVNRT)
  13. AV re-entrant tachycardia (AVRT) and Wolff–Parkinson–White (WPW)
  14. Junctional rhythms
  15. Differential diagnosis

Definition

  • Arrhythmia: any rhythm other than normal sinus rhythm — abnormal rate, regularity, site of origin or conduction. Grouped into bradyarrhythmias (< 50–60/min), tachyarrhythmias (> 100/min) and premature beats (extrasystoles).
  • Supraventricular arrhythmias arise above the bifurcation of the His bundle — in the sinus node, atrial myocardium or atrioventricular (AV) junction — or use an accessory pathway as part of the circuit.
  • "Supraventricular tachycardia" (SVT) in the narrow sense (European Society of Cardiology, ESC 2019) means the tachycardias other than ventricular tachycardia and atrial fibrillation; in everyday use "paroxysmal SVT" means the regular, sudden-onset re-entrant tachycardias: AV nodal re-entrant tachycardia (AVNRT) and AV re-entrant tachycardia (AVRT).

Mechanisms

  • Abnormal automaticity: a focus outside the sinus node fires spontaneously (focal atrial tachycardia, accelerated junctional rhythm); also enhanced normal automaticity (sinus tachycardia).
  • Triggered activity: afterdepolarisations reach threshold (digoxin toxicity, catecholamines, hypokalaemia).
  • Re-entry — the most common mechanism: two pathways with different conduction speed and refractoriness, a unidirectional block (usually by a premature beat) and slow enough conduction for the tissue ahead to recover. Micro-re-entry: AVNRT; macro-re-entry: AVRT, atrial flutter.

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