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  • SVTagents

    1. 1. Antiarrhythmic Agents in SVT: MOA & ADEs Don Wiest, Pharm.D.
    2. 2. Drugs in Acute Management of SVT
    3. 3. Vaughn-Williams Classification <ul><li>Based on cellular properties of normal His-Purkinje cells </li></ul><ul><li>Classified on drug’s ability to block ionic currents (i.e. Na + , K + , Ca ++ ) and β -adrenergic receptors </li></ul><ul><li>Advantages: </li></ul><ul><ul><li>Physiologically based </li></ul></ul><ul><ul><li>Highlights beneficial/deleterious effects </li></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>All cells not normal </li></ul></ul><ul><ul><li>All cells not His-Purkinje in origin </li></ul></ul>
    4. 5. Antiarrhythmic Agents Vaughn-Williams Classification <ul><li>Class I - Na + - channel blockers </li></ul><ul><ul><li>Direct membrane action </li></ul></ul><ul><ul><li>Slows conduction velocity </li></ul></ul><ul><ul><ul><li>IA- Moderately slow: A, V </li></ul></ul></ul><ul><ul><ul><ul><li>Quinidine, Procainamide , Disopyramide </li></ul></ul></ul></ul><ul><ul><ul><li>IB- Minimally slow: V </li></ul></ul></ul><ul><ul><ul><ul><li>Lidocaine, Mexiletine, Phenytoin, Tocainide </li></ul></ul></ul></ul><ul><ul><ul><li>IC- Markedly slow: A, V </li></ul></ul></ul><ul><ul><ul><ul><li>Flecainide, Propafenone, Moricizine </li></ul></ul></ul></ul>A: atrium; V: ventricle
    5. 6. Antiarrhythmic Agents Vaughn-Williams Classification <ul><li>Class II – Blocks Beta receptors </li></ul><ul><ul><li>Slows sinus rate, AVN conduction, & depress LVF </li></ul></ul><ul><ul><ul><li>Propranolol, atenolol, metoprolol, etc. </li></ul></ul></ul><ul><li>Class III - Blocks K + channels </li></ul><ul><ul><li>Prolongs repolarization ( refractory period) </li></ul></ul><ul><ul><ul><li>Amiodarone, Sotalol, NAPA, Ibutilide, Azimilide </li></ul></ul></ul><ul><li>Class IV- Ca ++ channel blockers </li></ul><ul><ul><li>Affects primarily SA and AV nodes </li></ul></ul><ul><ul><ul><li>Verapamil , Diltiazem, Bepridil </li></ul></ul></ul><ul><li>Purinergic agonists: Adenosine </li></ul><ul><li>Digitalis glycosides </li></ul>AVN: atrioventricular node LVF: left ventricle function;
    6. 7. Purinergic Agonists Adenosine <ul><li>Mode of action </li></ul><ul><ul><li>Endogenous nucleoside </li></ul></ul><ul><ul><li>A1 receptor agonist </li></ul></ul><ul><ul><li>Depresses slow inward Ca ++ current </li></ul></ul><ul><ul><li>Increases K + conductance (hyperpolarizes) </li></ul></ul><ul><li>Kinetics </li></ul><ul><ul><li>Metabolized by RBCs and vascular endothelial cells </li></ul></ul><ul><ul><li>t 1/2 = 5-10 secs </li></ul></ul><ul><li>ECG/EP changes </li></ul><ul><ul><li>Slows sinus rate </li></ul></ul><ul><ul><li>Slows AV node conduction </li></ul></ul>
    7. 8. Purinergic Agonists Adenosine <ul><li>Drug interactions </li></ul><ul><ul><li>Methylxanthines (caffeine/theophylline): </li></ul></ul><ul><ul><ul><li>Decreased effect by blocking receptors </li></ul></ul></ul><ul><ul><li>Dipyridamole: </li></ul></ul><ul><ul><ul><li>Prolonged effects by inhibiting adenosine uptake </li></ul></ul></ul><ul><li>Side effects (10-20%; transient: 2-3 min) </li></ul><ul><ul><li>Flushing/headache/nausea/dyspnea = most common </li></ul></ul><ul><ul><li>A. Fib/ V. tach/ sinus arrest/ sinus bradycardia, bronchospasms = rare </li></ul></ul><ul><li>Caution: heart transplant patients, asthmatics </li></ul><ul><li>Contraindications: wide QRS tachycardia </li></ul>
    8. 9. Class IA - Na+ Channel Blockers Procainamide <ul><li>Mode of action </li></ul><ul><ul><li>Slows conduction and prolong refractoriness </li></ul></ul><ul><ul><ul><li>Atrial, His-Purkinje, ventricular tissue </li></ul></ul></ul><ul><ul><li>Peripheral alpha block </li></ul></ul><ul><ul><li>Vagolytic </li></ul></ul><ul><ul><li>Minimal negative inotropic effect </li></ul></ul><ul><li>Active metabolite: NAPA (Class III activity) </li></ul><ul><li>ECG changes </li></ul><ul><ul><li>Increase PR, QRS </li></ul></ul><ul><ul><li>Toxicity: QTc increases by 30% or QT > 0.5 sec </li></ul></ul>
    9. 10. Class IA - Na+ Channel Blockers Procainamide <ul><li>Side effects: </li></ul><ul><ul><li>Arteriolar vasodilation with IV </li></ul></ul><ul><ul><ul><li>Slow infusion rate </li></ul></ul></ul><ul><ul><li>Negative inotrope (esp. with levels > 12 mcg/ml) </li></ul></ul><ul><ul><li>Pro-arrhythmia: 2-3% </li></ul></ul><ul><li>Drug interactions </li></ul><ul><ul><li>Decrease metabolism of amiodarone </li></ul></ul>
    10. 11. Class III- K + channel Amiodarone <ul><li>Mainly class III- Blocks K + channels </li></ul><ul><ul><li>Has characteristics of all 4 classes </li></ul></ul><ul><li>Acute actions very different from chronic </li></ul><ul><li>Acute Therapy (intravenous) </li></ul><ul><ul><li>Prolongs AV node refractory period </li></ul></ul><ul><ul><li>Lesser effect on the refractory period of the atrium, ventricle or His-Purkinje system </li></ul></ul><ul><ul><li>Minimal effect on contractility </li></ul></ul>
    11. 12. Amiodarone: Acute Therapy <ul><li>Side Effects: </li></ul><ul><ul><li>Acute Treatment (IV) </li></ul></ul><ul><ul><ul><li>Transient hypotension, bradycardia </li></ul></ul></ul><ul><ul><ul><li>Proarrhythmia <2% (e.g., torsade de pointes) </li></ul></ul></ul><ul><ul><ul><li>Hepatocellular necrosis (Polysorbate 80?; rare) </li></ul></ul></ul><ul><ul><ul><li>Benzyl Alcohol (monitor) </li></ul></ul></ul><ul><ul><li>Chronic (PO) </li></ul></ul><ul><ul><ul><li>hyper and hypothyroidism </li></ul></ul></ul><ul><ul><ul><li>Photosensitivity </li></ul></ul></ul><ul><ul><ul><li>Pulmonary fibrosis </li></ul></ul></ul><ul><ul><ul><li>Corneal deposits </li></ul></ul></ul><ul><ul><ul><li>Peripheral neuropathy </li></ul></ul></ul><ul><li>Drug Interactions </li></ul><ul><ul><li>Many </li></ul></ul><ul><ul><li>Digoxin: reduce dose by 50%; monitor Cp </li></ul></ul>
    12. 13. Class IV- Ca ++ channel blocker Verapamil <ul><li>Mode of Action </li></ul><ul><ul><li>Slows conduction velocity of SA and AV nodes </li></ul></ul><ul><ul><li>Lengthens antegrade & retrograde refractory periods of AV node </li></ul></ul><ul><ul><li>Slows sinus rate and increases PR interval on ECG </li></ul></ul><ul><li>Side Effects </li></ul><ul><ul><li>Negative inotrope, hypotension, dizziness, fatigue </li></ul></ul><ul><li>Do not use with other negative inotropes (e.g., beta blocker) </li></ul>
    13. 14. Verapamil <ul><li>Contraindications </li></ul><ul><ul><li>Infants < 1 year of age (apnea, hypotension, bradycardia, CV collapse) </li></ul></ul><ul><ul><li>Heart failure </li></ul></ul><ul><ul><li>Suspected or known WPW </li></ul></ul><ul><ul><li>Wide QRS tachycardia </li></ul></ul><ul><ul><li>Sick Sinus Sydrome </li></ul></ul>
    14. 15. Proarrhythmia <ul><li>Anitarrhythmic drug facilitates emergence of new arrhythmia (e.g., torsade de pointes) </li></ul><ul><li>Increased risk </li></ul><ul><ul><li>Children with structural heart disease </li></ul></ul><ul><ul><li>Class IA: Procainamide 2-3% </li></ul></ul><ul><ul><li>Class IC agents (e.g., Flecainide up to 7.5%) </li></ul></ul><ul><ul><li>Class III: Amiodarone <1%, Sotalol 1-5% </li></ul></ul>
    15. 16. Conclusion <ul><li>Antiarrhythmic drugs act by altering the conduction velocity and refractory periods changing the substrate for reentry. </li></ul><ul><li>Must be used with caution due to proarrhythmic effects </li></ul>

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