Internal Diseases – Part 1 (Rheumatology, Pulmonology, Phthisiatrics, Cardiology, Haematology) · MU Plovdiv

3. Antiarrhythmic drugs.

Inside: 16 sections · 6 labelled pictures · 8 tables · 23 flashcards · 20 min

Topic 30 of 68 in the MU Plovdiv syllabus for Internal Diseases – Part 1 (Rheumatology, Pulmonology, Phthisiatrics, Cardiology, Haematology) (Medicine, Year 4). The free AceMed note covers it in 16 sections, about 1,521 words (20 min of reading), with 23 flashcards.

In this note

  1. Definition and principles
  2. Action potential reminder
  3. Vaughan Williams classification
  4. Class I: sodium-channel blockers
  5. Class II: beta-blockers
  6. Class III: potassium-channel blockers
  7. Class IV: calcium-channel blockers
  8. Other antiarrhythmic drugs
  9. Proarrhythmia and safety
  10. Choice by arrhythmia
  11. Antiarrhythmic Drugs
  12. Classification (Vaughan-Williams Classification System)
  13. Pharmacodynamics (Mechanism of Action)
  14. Pharmacokinetics
  15. Side Effects
  16. Drug Interactions

Definition and principles

  • Antiarrhythmic drugs (AADs): drugs that prevent or terminate arrhythmias by acting on cardiac ion channels, receptors or autonomic tone.
  • They work against the three mechanisms of arrhythmia: they suppress abnormal automaticity and triggered activity, and break re-entry by slowing conduction or by prolonging the refractory period.
  • All of them can cause arrhythmias themselves (proarrhythmia); apart from beta-blockers, none improves survival. Electrical treatment (cardioversion, catheter ablation, an implantable cardioverter-defibrillator, ICD) is often more effective.

Action potential reminder

  • Working myocardium and Purkinje fibres: phase 0 — fast sodium inflow; phase 1 — early repolarisation (transient potassium outflow); phase 2 — plateau (L-type calcium inflow balanced by potassium outflow); phase 3 — repolarisation (delayed rectifier potassium currents IKr and IKs); phase 4 — resting potential (inward rectifier).
  • Sinoatrial (SA) and atrioventricular (AV) nodes: phase 0 depends on calcium channels; phase 4 rises spontaneously (funny current, If), faster with sympathetic and slower with vagal stimulation.
  • On the electrocardiogram (ECG): sodium-channel block widens the QRS, potassium-channel block lengthens the QT, and nodal block (classes II and IV, digoxin) lengthens the PR and slows the rate.

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