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W I L L W E S T N

ANTIARRHYTHMIC DRUGS. W I L L W E S T N. USEFUL TO KNOW…. All of the antiarrhythmic drugs act by altering ion flow within excitable tissues in myocardium. The three ions of primary importance are… … Na+ , Ca2+ and K+.

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W I L L W E S T N

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  1. ANTIARRHYTHMIC DRUGS W I L L W E S T N

  2. USEFUL TO KNOW… • All of the antiarrhythmic drugs act by altering ion flow within excitable tissues in myocardium. • The three ions of primary importance are… • …Na+ , Ca2+ and K+. • Antiarrhythmic drugs can be classified by their ability to directly or indirectly block flow of one or more of these ions across membranes of excitable cardiac muscle cells.

  3. CLASSIFICATION: • Singh-Vaughan Williams Classification (Alternative: Sicilian Gambit Classification) • ADVANTAGES: • Relatively simple and useful as shorthand • Based on mechanism of action • Ability to predict adverse effects

  4. CLASSIFICATION: • DISADVANTAGES: • Drugs within a class not necessarily clinically similar • Almost all of currently available drugs have multiple actions.

  5. CLASS I DRUGS • Act by blocking the Na+ channel (PROLONGING THE QRS INTERVAL) • Subdivided into 3 subgroups, IA, IB, and IC based on their effects on repolarisation and potency towards blocking the Na+ channel

  6. CLASS I DRUGS • Subclass IA: High potency (Prolong QRS), and also usually prolong repolarisation (Prolong QT interval) through blockade of K+ channels • Subclass IB: Low potency (No effect on QRS) in normal tissue, and shorten repolarisation (Decrease QT interval) • Subclass IC: Very High potency (Prolong QRS interval), and have little effect on repolarisation (No effect on QT interval)

  7. CLASS II DRUGS Act indirectly on electrophysiological parameters by blocking beta-adrenergic receptors (Slow Sinus Rhythm, Prolong PR, No Effect On QRS or QT) CLASS III DRUGS Prolong repolarisation (increase refractoriness) by blocking outward K+ conductance (Prolong QT), with typically little effect on rate of depolarization (No Effect On QRS)

  8. CLASS IV DRUGS Are relatively selective AV nodal L-type Ca2+ -channel blockers (Slow Sinus Rhythm, Prolong PR, No Effect On QRS) MISCELLANEOUS In addition to standard classes, IA-C, II, III, and IV… There is also group of drugs that includes digoxin, adenosine, magnesium, alinidine and other compounds whose actions don't fit standard four classes.

  9. IN SUMMARY

  10. PHARMACOLOGY: MOA

  11. PHARMACOLOGY: MOA

  12. PHARMACOLOGY: S/ EFFECTS • Proarrhythmias are drug-induced arrhythmias. • Two recently recognized ventricular proarrhythmias seen with antiarrhythmic drugs: • TORSADES DE POINTES ("twisting of the points") or drug-induced long QT syndrome (DILQTS) • CAST PROARRHYTHMIA

  13. TORSADES DE POINTES • Polymorphic arrhythmia that can rapidly develop into VF • Associated with drugs that have Class III actions • Usually occurs within the first week of Tx • Preexisting prolonged QT intervals may be indicator of susceptibility • Potentiated by bradycardia • Often assoc with concurrent electrolyte disturbances

  14. CAST PROARRHYTHMIA • Monomorphic, sustained ventricular tachycardia first recognized in CAST trials (Cardiac Arrhythmia Suppression Trial) with encainide and flecainide. • Patients with underlying sustained ventricular tachycardia, CHD, and poor LVF are at greater risk to develop this form of proarrhythmia

  15. PHARMACOLOGY: S/ EFFECTS

  16. Tx COMMON ARRHYTHMIAS

  17. Tx COMMON ARRHYTHMIAS

  18. Tx COMMON ARRHYTHMIAS

  19. Tx COMMON ARRHYTHMIAS *Premature ventricular complex

  20. Any Questions

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