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Antiarrhythmic Agents

Antiarrhythmic Agents . Kaylee Fiset, Sarah McKenna & Cassandra Turchet October 17, 2012. PHM142 Fall 2012 Instructor: Dr. Jeffrey Henderson. Overview . What is an arrhythmia? Types and causes of arrhythmias Management of arrhythmias Classes of antiarrhythmic agents

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Antiarrhythmic Agents

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  1. Antiarrhythmic Agents Kaylee Fiset, Sarah McKenna & Cassandra Turchet October 17, 2012 PHM142 Fall 2012 Instructor: Dr. Jeffrey Henderson

  2. Overview • What is an arrhythmia? • Types and causes of arrhythmias • Management of arrhythmias • Classes of antiarrhythmic agents • Drugs used to prevent arrhythmias • Amiodarone • Lidocaine • Summary

  3. What is an Arrhythmia? • An irregular rate or rhythm of the heart beat • Arrhythmias are caused by problems with the heart’s electrical conduction system • Abnormal or extra signals • Electrical signals may be blocked or slowed • Electrical signals may travel in new or different pathways • There are many different types of arrhythmias that range in severity

  4. Types of Arrhythmias • Most common type of arrhythmia • Involves fast and irregularcontraction of the atria • Instead of the heart’s electrical signal originating at the SA node, the signal travels through a disorganized pathway throughout the atria Atrial Fibrillation:

  5. Types of Arrhythmias Atrial Flutter: • Heart beat is very rapid, but regular • Organized circuit around the right atrium causes rapid atrial contraction (250-350 bpm) Ventricular Fibrillation: • An erratic, disorganized firing of impulses from the ventricles • Heart rhythm is irregular • The ventricles are unable to contract or pump blood to the body

  6. Types of Arrhythmias Ventricular Tachycardia: • A rapid, regular heart rhythm that orientates from the ventricles • Electrical impulses circulate in an endless loop • The rapid rate prevents the heart from filling adequately with blood and less blood is pumped through the body • Ventricles can beat up to 120-300 bpm and are no longer coordinated with the atria

  7. Types of Arrhythmias Normal Rhythm Tachycardia Ventricular Fibrillation Principles of Human Physiology. Germann and Stanfield. Benjamin Cummings

  8. Causes of Arrhythmias • Heart attack, heart failure • Abnormal levels of potassium • Alcohol, caffeine, stimulants • Beta-blockers • Cigarette smoking • Drugs that mimic the activity of the nervous system • Medications used for depression

  9. Management of Arrhythmias • Include both non-pharmacologic and pharmacologic therapies • Non-pharmacologic Therapy • Primarily for VF and VT that may cause cardiac arrest (considered “shockable” rhythms) • Defibrillation is the only way to return a heart to its normal rhythm- regulates electrical impulses http://en.wikipedia.org/wiki/File:Defibrillation_Electrode_Position.jpg

  10. Management of Arrhythmias • Pharmacologic Therapies • Sympathomimetics • Epinephrine (Causes vasoconstriction, increases blood flow to brain during cardiac arrest) • Vasopressin • Also known as antidiuretic hormone • Same effects as epinephrine • Thrombolytics • Antiarrhythmic agents • Can help prevent VT and VF that may lead to cardiac arrest • 5 classes according to Vaughn-Williams classification system

  11. Classes of Antiarrhythmic Agents CLASS I: Sodium Channel Blockers • These drugs bind to and block the fast sodium channels that are responsible for the rapid depolarization phase of the cardiac action potentials • Increased duration of the cardiac action potential • Subdivided into 3 sub-classes: • IC>IA>IB • Used to manage atrial fibrillation, atrial flutter, and ventricular tachycardia • Examples: Quinidine, Lidocaine, Propafenone

  12. Classes of Antiarrhythmic Agents CLASS II: Beta Blocking Agents • Blocks sympathetic activity through the beta adrenoceptor • Increases refractory period of atrial and AV tissue to slow contraction • Examples: Propranolol, Metroprolol, Atenolol

  13. Classes of Antiarrhythmic Agents CLASS III: Potassium Channel Blockers • Bind and block K+ channels responsible for repolarization of the cell after an action potential • Prevents re-entrant arrhythmias by lengthening the refractory period • Re-entrant rhythm is less likely to occur with tissue that is still in the refractory phase (suppresses tachyarrhythmias) • Examples: Amiodarone, Ibutilide, Sotalol (also a B-blocker)

  14. CLASS IV: Calcium Channel Blockers (CCBs) • Bind to L-type Ca2+ channels on vascular smooth muscle, cardiac myocytes, nodal tissue to regulate Ca2+ influx • Decrease the firing rate of pacemaker cells in the heart and decrease conduction velocity prolonging repolarization • Help to block re-entry mechanisms at the AV node (preventing supraventricular tachycardia) • Examples: Dihydropyridines, Verapamil, Diltiazem

  15. Classes of Antiarrhythmic Agents CLASS V: Unknown Mechanisms • Suspected mechanism is via direct nodal inhibition • Used to treat supraventricular arrhythmias, especially during heart failure and atrial fibrillation • Examples: Digoxin, Adenosine, Magnesium Sulfate

  16. Amiodarone • Class III antiarrhythmic (K+ channel blocker), with effects from other classes • Indication: Ventricular arrhythmias • Good absorption (lipophilic), long elimination phase • Side effects: pulmonary fibrosis, hepatic/thyroid toxicity http://e-pid.pharmacists.ca

  17. Lidocaine • Class IB antiarrhythmic (Na+ channel blocker) • Indication: Ventricular tachycardia • IV preferred (unpredictable first-pass metabolism when administered orally) • Systemic lidocaine administration- reduces incidence of premature action potentials originating in cardiac muscle • Overdose can lead to drowsiness, seizures, twitching, possible cardiac arrest and death http://static.enotes.com/images/nursing/genh_03_img0251.jpg

  18. Summary • An arrhythmia is an irregular rate or rhythm of the heart beat caused by problems with the hearts electrical conduction system • The four types of arrhythmias are: ventricular defibrillation, ventricular tachycardia, atrial flutter, atrial defibrillation • There are four classes of antiarrhythmic agents: • Class I (A,B,C) – Sodium channel blockers • Class II – Beta blocking agents • Class III – Potassium channel Blockers • Class IV – Calcium channel blockers • Class V – Unknown mechanisms • The two main drugs used to treat arrhythmias are Lidocaine (Class IB) and Amiodarone (Class III)

  19. References Campbell, T. J. & Williams, K. M. (1998). Therapeutic drug monitoring: Antiarryhthmic drugs. Br J ClinPharmacol, 46: 307- 319. Cardiovascular Pharmacology Concepts (2009) Antiarrhythmic Classes. [online] Available at: www.cvpharmacology.com [Accessed: October 2012]. DiPiro, J., Talbert, R. L., Yee, G., Matzke, G., Wells, B., & Posey, L. M. Pharmacotherapy, A Pathophysiologic Approach. 8e. McGraw-Hill Medical, 2011. Print. Goodacre, S. & Irons, R. (2002). ABC of clinical electrocardiography: Atrial arrhythmias. Brit Med J 324: 590-594. Stanfield, C. L, &Germann, W. J. Principles of Human Physiology. 3. London, England: Benjamin Cummings, 2007. Print. Todd, D. W. (2003). A review of the class III antiarrhythmic agents and their uses and implications for patient management. J oral maxilsurg61: 928-931 Tung, R., Boyle, N,G., & Shivkumar, K. (2010). Catheter ablation of ventricular tachycardia. Circulation122: 389-391.

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