ANTIDYSRHYTHMIC DRUGS
Dysrhythmia
•Any deviation from the normal rhythm of the heart
Antidysrhythmics
•Drugs used for the treatment and prevention of disturbances in cardiac rhythm
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.
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
•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.
Four Phases
•The SA node and the Purkinje cells each have separate action potentials.
•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.
Four Phases
•The SA node and the Purkinje cells each have separate action potentials.
Vaughan Williams Classification
•System commonly used to classify antidysrhythmic drugs
Classification
•Class 1
–Class Ia
–Class Ib
–Class Ic
•Class II
•Class III
•Class IV
•Other
::Class I::
•Membrane-stabilizing agents
•Fast sodium channel blockers Divided into Ia, Ib, and Ic agents, according to effects
moricizine
•General Class I agent
•Has characteristics of all three subclasses Used for symptomatic ventricular and life-threatening dysrhythmias
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
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)
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
::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
::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
::Class IV::
-verapamil, diltiazem
•Calcium channel blockers
•Depress phase 4 depolarization Used for paroxysmal supraventricular tachycardia; rate control for atrial fibrillation and flutter
***Other Antidysrhythmics
-digoxin, adenosine
•Have properties of several classes and are not placed into one particular class
Classification
•Class 1
–Class Ia
–Class Ib
–Class Ic
•Class II
•Class III
•Class IV
•Other
::Class I::
•Membrane-stabilizing agents
•Fast sodium channel blockers Divided into Ia, Ib, and Ic agents, according to effects
moricizine
•General Class I agent
•Has characteristics of all three subclasses Used for symptomatic ventricular and life-threatening dysrhythmias
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
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)
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
::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
::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
::Class IV::
-verapamil, diltiazem
•Calcium channel blockers
•Depress phase 4 depolarization Used for paroxysmal supraventricular tachycardia; rate control for atrial fibrillation and flutter
***Other Antidysrhythmics
-digoxin, adenosine
•Have properties of several classes and are not placed into one particular class
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
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
: Side Effects
ALL antidysrhythmics can cause dysrhythmias!!
•Hypersensitivity reactions
–Nausea
–Vomiting
–Diarrhea
–Dizziness
–Blurred vision
–Headache
•Hypersensitivity reactions
–Nausea
–Vomiting
–Diarrhea
–Dizziness
–Blurred vision
–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 agents.
•Assess for potential drug interactions.
•Instruct patients regarding dosing schedules and side effects to report to physician.
•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.
•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.
•For class I agents, monitor ECG for QT intervals prolonged more than 50%.
•IV infusions should be administered with an IV pump.
•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.
•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
•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 agents.
•Assess for potential drug interactions.
•Instruct patients regarding dosing schedules and side effects to report to physician.
•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.
•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.
•For class I agents, monitor ECG for QT intervals prolonged more than 50%.
•IV infusions should be administered with an IV pump.
•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.
•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