Antidysrhythmic Drugs & Cardiac Rhythms

• Antidysrhythmic drugs are used for the treatment and prevention of disturbances in cardiac rhythm.
• Dysrhythmia is any heart deviation from the normal rhythm.

Action Potential

• A change in the distribution of ions causes cardiac cells to become excited
• Movement of ions across the cardiac cell's membrane results in an electrical impulse, this spreads across the cardiac cells.
• The electrical impulse leads to contraction of the myocardial muscle.
• The three states are: resting, depolarization, and repolarization

Cardiac Cell

• Inside a resting cardiac cell there is a net negative charge relative to the outside of the cell.
• Resting Membrane Potential is the difference in electronegative charge as a result of uneven distribution of ions (sodium, potassium, calcium) across the cell membrane.
• The Sodium-Potassium ATPase pump maintains this difference.

Electrical Activity of the Heart

• The Sinoatrial (SA) node is the natural pacemaker.
• The Inherent Rate of the SA node is 60-100 BPM
• The Inherent Rate of the AV node is 40-60 BPM
• The Inherent Rate of the Bundle of His is 40-60 BPM
• The Inherent Rate of the Left and Right Bundle Branches are 20-40 BPM
• The Inherent Rate of the Purkinje Fibers are 20-40 BPM

Electrocardiography

• ECG or EKG shows the electrical activity of the heart.

• P wave shows electricity to the atria

• QRS complex shows contraction and electricity to the ventricles

• In Atrial Depolarization, the P wave shows that the atria are contracting

• In Ventricular Repolarization, the T wave shows that the ventricles are relaxing

• In Ventricular Depolarization, the QRS Complex shows that the ventricles are contracting

• Supraventricular Tachycardia includes a PR interval thats too small to ineligible

• Atrial Fibrillation includes no p-waves

• Atrial Flutter includes a predictable pattern

Ventricular Dysrhythmias

• Ventricular Tachycardia
• Ventricular Fibrillation

Antidysrhythmic Drugs

• Mechanisms of Action for Antidysrhythmic Drugs include: prolong the AV node, increase or reduce conduction speed, alter ectopic pacemakers and SA node, reduce myocardial excitability, and simulate autonomic nervous system
• Multiple different classes of medications are used
  • Sodium Channel Blockers
  • Beta-Adrenergics
  • Potassium Channel Blockers
  • Calcium Channel Blockers
  • Additional Classes
• Inotropic means force of contraction
• Chronotropic means rate of contractions
• Dromotropic means electrical current

Vaughan Williams Classification

• A System commonly used to classify antidysrhythmic drugs
• Based on the electrophysiologic effect of particular drugs on the action potential
• The classifications are:
  • Class I: Sodium Channel Blocker
    • Class Ia
    • Class Ib
    • Class Ic
  • Class II: Beta Blocker
  • Class III: Potassium Channel Blocker
  • Class IV: Calcium Channel Blocker
  • Other:
    • Digoxin
    • Adenosine

Drugs Affecting the Cardiac Action Potential

• Class 1 contains Na+ channel blockers
  • Quinidine and Procainamide are moderate
  • Lidocaine and Phenytoin are weak
  • Flecainide and Propafenone are strong
• Class 2 contains beta-blockers
  • Propranolol
  • Metoprolol
• Class 3 contains K+ channel blockers
  • Amiodarone
  • Sotalol
• Class 4 contains Ca2+ channel blockers
  • Verapamil
  • Diltiazem

Vaughan Williams Class Ia: Sodium Channel Blocker

• Procainamide (Proneystl), Quinidine gluconate, and disopyramide (Norpace) are Class Ia drugs.
• These drugs work by blocking sodium (fast) channels and delays repolarization
• Used for Atrial fibrillation, Atrial flutter, Ventricular Tachycardia, Supraventricular Tachycardia, Wolff-Parkinson-White Syndrome
• Adverse Effects of procainamide: Systemic Lupus Syndrome, Neutropenia/Thrombocytopenia, Cardiotoxicity, and Hypotension
• Contraindications/Precautions include: Pregnancy Risk Category C and Liver or renal disorders
• Medication/Food Interactions include: Antidysrhythmics and Antihypertensives
• When administering, do not crush or chew sustained-released medications

Vaughan Williams Class Ib: Sodium Channel Blocker

• Class Ib drugs include lidocaine (Xylocaine), mexiletine (Mexitil), and tocainide (Tonocard)
• Decrease electrical conduction and Increase rate of repolarization.
• Class IB drugs are used for Ventricular Dysrhythmias
• Class Ib drugs can cause the Adverse Effect of CNS: twitching, convulsions, and respiratory depression.
• Contraindications: Liver and renal dysfunction
• Beta Blockers and Phenytoin increase serum levels of lidocaine
• Nursing Administration involves IV administration usually started with a weight based dose and then a maintenance dose
• Should not be used for no more than 24 hours

Vaughan Williams Class Ic: Sodium Channel Blocker

• Class Ic drugs include propafenone (Rhythmol), flecainide (Tambocor)
• Mechanism of Action includes: Decease electrical conduction, Decrease excitability, Increase rate of repolarization
• Class Ic is used for Supraventricular Tachycardia
• Adverse Effects include: Bradycardia, Heart failure, Dizziness, Weakness
• Contraindications for use include: Severe heart failure, Severe hypotension
• Medication interactions include: Digoxin, oral anticoagulants, beta blockers
• Monitor ECG during treatment, and for bradycardia and hypotension.
• Take medication with food, do not crush

Vaughan Williams Class II: Beta Blocker

• Propranolol hydrochloride (Inderal), esmolol hydrochloride (Brevibloc), metoprolol (Lopressor) are Class II drugs
• Mechanism of Action:
  • Prevent sympathetic nervous system stimulation of the heart
  • Decrease heart rate, slow rate of conduction through the SA node
• Used for Atrial fibrillation, Atrial flutter, SVT
• Adverse Effects: Bradycardia, hypotension, impotence
• Contraindications: Severe, heart failure, asthma
• Medication Interactions include: Verapamil and Diltiazem, can mask the hypoglycemic effect of insulin
• Nursing Administration includes: Take apical pulse daily. Administer IV form slowly.

Vaughan Williams Class III: Potassium Channel Blockers

• Class III drugs include: amiodarone (Cordarone, Pacerone), sotalol (Betapace), dofetilide (Tikosyn)

• Mechanism of Action includes: Prolong the action potential and refractory period of the cardiac cycle, decrease rate of repolarization, decrease electrical conduction, decrease contractility

• Used for: Atrial Fibrillation by oral route, recurrent ventricular fibrillation, ventricular tachycardia

• Contraindications for Class III includes: AV block, and bradycardia, liver, thyroid or respiratory dysfunction

• Medication/Food Interactions includes: Diltiazem, digoxin, and warfarin, and grapefruit juice

• Nursing Administration includes: Amiodarone is highly toxic. Adverse effects may continue until medication is discontinued. Provide patients with information regarding toxicities.

Vaughan Williams Class IV: Calcium Channel Blockers

• Class IV drugs include verapamil (Calan), diltiazem (Cardizem)
• Mechanism of Action: Depress depolarization and decrease myocardial oxygen demand, decrease force of contraction, decrease heart rate, and slow rate of conduction through SA and AV Node
• Used for atrial fibrillation, Atrial flutter, and SVT
• Adverse Effects include: Bradycardia, hypotension, constipation
• Contraindications: SA/AV dysfunction and Heart blocks
• Nursing Administration includes: May cause orthostatic hypotension, change positions slowly, notify the provider for peripheral edema, or shortness of breath

Vaughan Williams Classification: Other Antidysrhythmics

• These have properties of several classes and are not placed into one particular class
• These include Digoxin and Adenosine

Unclassified Antidysrhythmics

• Digoxin (Lanoxin) is used for advanced heart failure

• It slows conduction between the SA & AV node

• Used to slow the rate in atrial fibrillation/flutter

• Can be administered PO or IV

• Long half life and duration of action

• High risk for toxicity: can lead to renal impairment

• Follow Digoxin levels to determine dose

• Adverse Effects: Cardiac arrhythmias and Yellow halos

• Antidote: Digoxin Immune Fab (Digibind)

• Adenosine (Adenocard) corrects only AU node problems

• It 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 (6mg)

• May cause asystole for a few seconds

• Other adverse effects minimal

Nursing Implications for administering Antidysrhythmics Drugs

• Obtain a thorough drug and medical history
• Measure baseline BP/P, I & O, and cardiac rhythm
• Measure serum potassium levels before initiating therapy, due to renal function
• 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 side 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
• Administer IV infusions with an IV pump
• 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
• Ensure that the patient knows to notify health care provider of any worsening of dysrhythmia or toxic effects – this is due to changes in cardiac output, shortness of breath, Edema, Dizziness, Syncope, Chest pain, Gl distress, Blurred Vision, and Edema

Expected Outcomes of Antidysrhythmic Drugs

• Decreased BP in hypertensive patients
• Decreased edema
• Decreased fatigue
• Regular pulse rate
• Pulse rate without major irregularities
• Improved regularity of rhythm
• Improved cardiac output
• Goals should include target: HR and BP

SDOH

• Older adults with HTN, heart failure, diabetes and thyroid disease are more at risk of developing dysrhythmias
• Lidocaine - $5 for 20 doses
• Propranolol – 30 day supply $30-$80
• Digoxin - $50 for 100 tablets