Antidysrthythmic Agents

Antidysrhythmic Agents Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics Dysrhythmia • Any deviation from the normal rhythm of the heart Antidysrhythmics • Drugs used for the treatment and prevention of disturbances in cardiac rhythm Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Cardiac Cell • Inside the cardiac cell, there exists a net negative charge relative to the outside of the cell. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Resting Membrane Potential: RMP • This difference in the electronegative charge. • Results from an uneven distribution of ions (sodium, potassium, calcium) across the cell membrane. • An energy-requiring pump is needed to maintain this uneven distribution of ions. • Sodium-potassium ATPase pump Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Instructors may wish to insert: EIC Image # 61: Heart and Conduction System EIC Image # 63: Resting Membrane Potential of a Cardiac Cell Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Action Potential • A change in the distribution of ions causes cardiac cells to become excited. • The movement of ions across the cardiac cell’s membrane results in the propagation of an electrical impulse. • This electrical impulse leads to contraction of the myocardial muscle. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Action Potential Four Phases • The SA node and the Purkinje cells each have separate action potentials. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Instructors may wish to insert: EIC Image # 64: Action Potentials: Phases (SA Node) EIC Image # 65: Action Potentials: Purkinje Fiber EIC Image # 66: Action Potentials: Intervals Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification • System commonly used to classify antidysrhythmic drugs Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification • Class 1 – Class Ia – Class Ib – Class Ic • Class II • Class III • Class IV • Other Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Class I • Membrane-stabilizing agents • Fast sodium channel blockers • Divided into Ia, Ib, and Ic agents, according to effects Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Class I moricizine • General Class I agent • Has characteristics of all three subclasses • Used for symptomatic ventricular and lifethreatening dysrhythmias Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Class Ia quinidine, procainamide, disopyramide • Block sodium channels • Delay repolarization • Increase the APD • Used for atrial fibrillation, premature atrial contractions, premature ventricular contractions, ventricular tachycardia, Wolff-Parkinson-White syndrome Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Class Ib tocainide, mexiletine, phenytoin, lidocaine • Block sodium channels • Accelerate repolarization • Decrease the APD • Used for ventricular dysrhythmias only (premature ventricular contractions, ventricular tachycardia, ventricular fibrillation) Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Class Ic encainide, flecainide, propafenone • Block sodium channels (more pronounced effect) • Little effect on APD or repolarization • Used for severe ventricular dysrhythmias • May be used in atrial fibrillation/flutter Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Class II Beta blockers: atenolol, esmolol, petaprolol, propranolol • Reduce or block sympathetic nervous system stimulation, thus reducing transmission of impulses in the heart’s conduction system • Depress phase 4 depolarization • General myocardial depressants for both supraventricular and ventricular dysrhythmias Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Class III amiodarone, bretylium, sotalol, ibutilide • Increase APD • Prolong repolarization in phase 3 • Used for dysrhythmias that are difficult to treat • Life-threatening ventricular tachycardia or fibrillation, atrial fibrillation or flutter—resistant to other drugs • Sustained ventricular tachycardia Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Class IV verapamil, diltiazem • Calcium channel blockers • Depress phase 4 depolarization • Used for paroxysmal supraventricular tachycardia; rate control for atrial fibrillation and flutter Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Vaughan Williams Classification Other Antidysrhythmics digoxin, adenosine • Have properties of several classes and are not placed into one particular class Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics Digoxin • Cardiac glycoside • Inhibits the sodium-potassium ATPase pump • Positive inotrope—improves the strength of cardiac contraction • Allows more calcium to be available for contraction • Used for CHF and atrial dysrhythmias • Monitor potassium levels, drug levels, and for toxicity Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics adenosine (Adenocard) • Slows conduction through the AV node • Used to convert paroxysmal supraventricular tachycardia to sinus rhythm • Very short half-life • Only administered as fast IV push • May cause asystole for a few seconds • Other side effects minimal Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics: Side Effects ALL antidysrhythmics can cause dysrhythmias!! • Hypersensitivity reactions – Nausea – Vomiting – Diarrhea – Dizziness – Blurred vision – Headache Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics: Nursing Implications • Obtain a thorough drug and medical history. • Measure baseline BP, P, I & O, and cardiac rhythm. • Measure serum potassium levels before initiating therapy. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics: Nursing Implications • Assess for conditions that may be contraindications for use of specific agents. • Assess for potential drug interactions. • Instruct patients regarding dosing schedules and side effects to report to physician. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics: Nursing Implications • During therapy, monitor cardiac rhythm, heart rate, BP, general well-being, skin color, temperature, heart and breath sounds. • Assess plasma drug levels as indicated. • Monitor for toxic effects. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics: Nursing Implications • Instruct patients to take medications as scheduled and not to skip doses or double up for missed doses. • Patients who miss a dose should contact their physician for instructions if a dose is missed. • Instruct patients not to crush or chew any oral sustained-release preparations. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics: Nursing Implications • For class I agents, monitor ECG for QT intervals prolonged more than 50%. • IV infusions should be administered with an IV pump. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics: Nursing Implications • Patients taking propranolol, digoxin, and other agents should be taught how to take their own radial pulse for 1 full minute, and to notify their physician if the pulse is less than 60 beats/minute before taking the next dose of medication. Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved. Antidysrhythmics: Nursing Implications • Monitor for therapeutic response: – Decreased BP in hypertensive patients – Decreased edema – Regular pulse rate or – Pulse rate without major irregularities, or – Improved regularity of rhythm Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved.