Antidysrhythmic Drugs Chapter 25 Antidysrhythmic Drugs Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Antidysrhythmics Dysrhythmia Any deviation from the normal rhythm of the heart Antidysrhythmics Used for the treatment and prevention of disturbances in cardiac rhythm Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Cardiac Cell Inside the resting cardiac cell there is a net negative charge relative to the outside of the cell This difference in electronegative charge results from an uneven distribution of ions (sodium, potassium, calcium) across the cell membrane Resting membrane potential (RMP) Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Resting Membrane Potential (RMP) An energy-requiring pump is needed to maintain this uneven distribution of ions Sodium-potassium ATPase pump Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 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 an electrical impulse spreading across the cardiac cells This electrical impulse leads to contraction of the myocardial muscle Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Action Potential (cont’d) Four phases The SA node and the Purkinje cells each have separate action potentials Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

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Action Potential Duration Absolute or effective refractory period Relative refractory period Threshold potential Automaticity or pacemaker activity Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

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Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Electrocardiography ECG or EKG P wave PR interval QRS complex ST segment T wave Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

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Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Common Dysrhythmias Supraventricular dysrhythmias Ventricular dysrhythmias Ectopic foci Conduction blocks Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Vaughan Williams Classification System commonly used to classify antidysrhythmic drugs Based on the electrophysiologic effect of particular drugs on the action potential Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Vaughan Williams Classification (cont’d) Class Ia Class Ib Class Ic Class II Class III Class IV Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Vaughan Williams Classification: Mechanism of Action Membrane-stabilizing drugs Fast sodium channel blockers Divided into Ia, Ib, and Ic drugs, according to effects Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Vaughan Williams Classification: Mechanism of Action and Indications Class Ia: quinidine, procainamide, disopyramide Block sodium (fast) channels Delay repolarization Increase APD Used for atrial fibrillation, premature atrial contractions, premature ventricular contractions, ventricular tachycardia, Wolff-Parkinson-White syndrome Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Vaughan Williams Classification: Mechanism of Action and Indications (cont’d) Class Ib: phenytoin, lidocaine Block sodium channels Accelerate repolarization Increase or decrease APD Lidocaine is used for ventricular dysrhythmias only Phenytoin is used for atrial and ventricular tachydysrhythmias caused by digitalis toxicity, long QT syndrome Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Vaughan Williams Classification: Mechanism of Action and Indications (cont’d) Class Ic: 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, Wolff-Parkinson-White syndrome, supraventricular tachycardia dysrhythmias Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Vaughan Williams Classification: Mechanism of Action and Indications (cont’d) Class II: beta blockers: atenolol, esmolol, metaprolol 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 Also used as antianginal and antihypertensive drugs Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Vaughan Williams Classification: Mechanism of Action and Indications (cont’d) Class III: amiodarone, dronedarone, dofetilide, 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 that is resistant to other drugs *Sotalol also exhibits Class II properties Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Vaughan Williams Classification: Mechanism of Action and Indications (cont’d) Class IV: verapamil, diltiazem Calcium channel blockers Inhibit slow-channel (calcium-dependent) pathways Depress phase 4 depolarization Reduce AV node conduction Used for paroxysmal supraventricular tachycardia; rate control for atrial fibrillation and flutter Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Unclassified Antidysrhythmic adenosine (Adenocard) Slows conduction through the AV node Used to convert paroxysmal supraventricular tachycardia to sinus rhythm Very short half-life—less than 10 seconds Only administered as fast IV push May cause asystole for a few seconds Other adverse effects minimal Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Classroom Response Question A patient has received an IV dose of adenosine, and almost immediately the heart monitor shows asystole. What should the nurse do next? Check the patient’s pulse. Prepare to administer CPR. Set up for defibrillation. Continue to monitor the patient. Correct answer: D Rationale: The half-life of adenosine is very fast—only 10 seconds, and the asystole only lasts for a few seconds. The nurse should continue to monitor the patient for therapeutic and adverse effects of the medication. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Elsevier items and derived items © 2009, 2005, 2001 by Saunders, an imprint of Elsevier Inc.

Antidysrhythmics: Adverse Effects ALL antidysrhythmics can cause dysrhythmias! Hypersensitivity reactions Nausea Vomiting Diarrhea Dizziness Blurred vision Headache Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 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 © 2014 by Mosby, an imprint of Elsevier Inc.

Nursing Implications (cont’d) Assess for conditions that may be contraindications for use of specific drugs Assess for potential drug interactions Instruct patients to report dosing schedules and adverse effects to physician Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Nursing Implications (cont’d) During therapy, monitor cardiac rhythm, heart rate, BP, general well-being, skin color, temperature, heart and lung sounds Assess plasma drug levels as indicated Monitor for toxic effects Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Classroom Response Question A patient is in the emergency department with an unspecified supraventricular dysrhythmia. The physician orders a dose of diltiazem (Cardizem) IV push. While the nurse administers the medication through the IV lock, the patient states she feels something wet spilling on her arm. Her heart rate was unchanged. What will the nurse do next? Assess the patient for diaphoresis. Check the IV lock to see if it is functioning properly. Repeat the dose of diltiazem (Cardizem) Restart the IV in another location. Correct answer: B Rationale: Since the heart rate was unchanged and the patient felt fluid on her arm, the IV lock is probably not working properly. Before anything else is done, the IV lock should be checked for proper functioning. Another dose would be wasted if the IV lock is not working. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Elsevier items and derived items © 2009, 2005, 2001 by Saunders, an imprint of Elsevier Inc.

Nursing Implications (cont’d) Instruct patients to take medications as scheduled and not to skip doses or double up for missed doses Instruct patients to contact their physician for instructions if a dose is missed Instruct patients not to crush or chew oral sustained-release preparations Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Classroom Response Question A patient is receiving oral quinidine. Which assessment finding is of most concern? Nausea Prolonged QT interval Diarrhea Occasional palpitations Correct answer: B Rationale: Patients on quinidine need to be monitored for prolonged QRS or QT intervals, which may be a precursor to more serious dysrhythmia problems. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. Elsevier items and derived items © 2009, 2005, 2001 by Saunders, an imprint of Elsevier Inc.

Nursing Implications (cont’d) Monitor ECG for prolonged QT interval with use of antidysrhythmics, including amiodarone, procainamide, quinidine, dofetilide, bepridil, sotalol, flecainide Administer IV infusions with an IV pump Solutions of lidocaine that contain epinephrine should not be given IV—they are to be used ONLY as local anesthetics Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Nursing Implications (cont’d) Ensure that the patient knows to notify health care provider of any worsening of dysrhythmia or toxic effects Shortness of breath Edema Dizziness Syncope Chest pain GI distress Blurred vision Edema Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Nursing Implications (cont’d) Teach patients taking beta blockers, digoxin, and other drugs 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 Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

Nursing Implications (cont’d) Monitor for therapeutic response Decreased BP in hypertensive patients Decreased edema Decreased fatigue Regular pulse rate Pulse rate without major irregularities Improved regularity of rhythm Improved cardiac output Copyright © 2014 by Mosby, an imprint of Elsevier Inc.