Antidysrhythmic Agents Chapter 22

Antidysrhythmics Dysrhythmia Antidysrhythmics Any deviation from the normal rhythm of the heart Antidysrhythmics Drugs used for the treatment and prevention of disturbances in cardiac rhythm

Cardiac Cell Inside the cardiac cell, there exists a net negative charge relative to the outside of the cell.

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

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.

Action Potential Four Phases The SA node and the Purkinje cells each have separate action potentials.

Vaughan Williams Classification System commonly used to classify antidysrhythmic drugs

Vaughan Williams Classification Class Ia Class Ib Class Ic Class II Class III Class IV Other

Vaughan Williams Classification Membrane-stabilizing agents Fast sodium channel blockers Divided into Ia, Ib, and Ic agents, according to effects

Vaughan Williams Classification moricizine General Class I agent Has characteristics of all three subclasses Used for symptomatic ventricular and life-threatening dysrhythmias

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

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)

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

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

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

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

Vaughan Williams Classification Other Antidysrhythmics digoxin, adenosine Have properties of several classes and are not placed into one particular class

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

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

Antidysrhythmics: Side Effects ALL antidysrhythmics can cause dysrhythmias!! Hypersensitivity reactions Nausea Vomiting Diarrhea Dizziness Blurred vision Headache

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.

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.

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.

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.

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.

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.

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

What would you do????