Antidysrhythmic Drugs Antidysrhythmics Dysrhythmia Any deviation from the normal rhythm of the heart Antidysrhythmics Used for the treatment and prevention of disturbances in cardiac rhythm 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 o Resting membrane potential RMP Resting Membrane Potential RMP An energy requiring pump is needed to maintain this uneven distribution of ions o Sodium potassium ATPase pump 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 Four phases The SA node and the Purkinje cells each have separate action potentials Action Potential Duration Absolute or effective refractory period Relative refractory period Threshold potential Automaticity dependent on the distribution of ions or pacemaker activity Electrocardiography ECG or EKG P wave PR interval QRS complex ST segment and T wave Common Dysrhythmias Supraventricular dysrhythmias Ventricular dysrhythmias Ectopic foci pacemaker is coming from somewhere else in the heart muscle Conduction blocks results in an abnormal rhythm or abnormal pulse Vaughan Williams Classification System commonly used to classify antidysrhythmic drugs Based on the electrophysiologic effect of particular drugs on the action potential Normal digoxin level 0 5 2 ng mL Normal K 3 5 5 mg dL Class I Class Ia Class Ib and Class Ic Class II Class III and Class IV Mechanism of Action Class I o Membrane stabilizing drugs o Fast sodium channel blockers o Divided into Ia Ib and Ic drugs according to effects Class Ia quinidine procainamide pronestol disopyramide o Block sodium fast channels Using this to slow down the heart o Delay repolarization o Increase APD o Used for atrial fibrillation premature atrial contractions premature ventricular contractions ventricular tachycardia Wolff Parkinson White syndrome o Diarreha Class Ib phenytoin antiseizure lidocaine o Block sodium channels Can further liver damage Can become toxic o Accelerate repolarization o Increase or decrease APD o Lidocaine is used for ventricular dysrhythmias only o Phenytoin is used for atrial and ventricular tachydysrhythmias caused by digitalis toxicity long QT syndrome o Too much lidocaine leads to toxicity then convulsions Class II beta blockers atenolol esmolol metaprolol o Reduce or block sympathetic nervous system stimulation thus reducing transmission of impulses in the heart s conduction system o Depress phase 4 depolarization o General myocardial depressants for both supraventricular and ventricular dysrhythmias o Also used as antianginal and antihypertensive drugs Class III amiodarone Last drug of choice dronedarone dofetilide sotalol most potent only used here ibutilide o Increase APD action potential duration o Prolong repolarization in phase 3 o Used for dysrhythmias that are difficult to treat Life threatening ventricular tachycardia or fibrillation atrial fibrillation or flutter that is resistant to other drug o Amiodarone can cause skin to slough off cause dysrhythmia very hard medicine Class IV verapamil diltiazem o Antidysrhythmics reduce AV node conduction tachycardia o Calcium channel blockers Inhibit slow channel calcium dependent pathways o Depress phase 4 depolarization o Reduce AV node conduction o Used for paroxysmal supraventricular tachycardia rate control for atrial fibrillation and flutter 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 Used instead of dyfibrilator to cure Antidysrhythmics Adverse Effects ALL antidysrhythmics can cause dysrhythmias o Hypersensitivity reactions o Nausea o Vomiting o Diarrhea Increase fiber unless on digoxin then it is contraindicated o Dizziness o Blurred vision o Headache 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 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 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 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 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 Ensure that the patient knows to notify health care provider of any worsening of dysrhythmia or toxic effects o Shortness of breath Edema Dizziness Syncope Chest pain GI distress Blurred vision 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 Monitor for therapeutic response o Decreased BP in hypertensive patients o o o o o o Decreased edema Decreased fatigue Regular pulse rate Pulse rate without major irregularities Improved regularity of rhythm Improved cardiac output Questions 1 A patient has received an IV dose of adenosine and almost immediately the heart monitor shows asystole What should the nurse do next A Check the patient s pulse B Prepare to administer CPR C Set up for defibrillation D Continue to monitor the patient 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