Antidysrhythmic Drugs and Cardiac Function

• Antidysrhythmic drugs treat and prevent cardiac rhythm disturbances.

Dysrhythmia

• Dysrhythmia refers to any deviation from the heart's normal rhythm.

Action Potential

• A change in ion distribution excites cardiac cells.
• Ion movement across the cardiac cell membrane generates an electrical impulse that spreads and leads to myocardial muscle contraction.

Cardiac Cell

• A net negative charge exists inside the resting cardiac cell relative to the outside.
• Uneven ion distribution (sodium, potassium, calcium) across the cell membrane causes this charge difference.
• The Sodium-Potassium ATPase pump maintains this difference.

Electrical Activity of the Heart

• The sinoatrial (SA) node functions as the natural pacemaker.
• The SA node has an inherent rate of 60-100 BPM.
• The AV node has an inherent rate of 40-60 BPM.
• The Bundle of His has an inherent rate of 40-60 BPM.
• The left and right bundle branches have an inherent rate of 20-40 BPM.
• The Purkinje Fibers have an inherent rate of 20-40 BPM.

Electrocardiography

• ECG or EKG are used to measure electricity to atria and ventricular contraction.
• The P wave represents atrial depolarization, where atria are contracting.
• The QRS complex represents ventricular depolarization, where ventricles are contracting.
• The T wave represents ventricular repolarization, where ventricles are relaxing.

Common Atrial Dysrhythmias

• Supraventricular Tachycardia features too small of a PR interval.
• Atrial Fibrillation lacks p-waves.
• Atrial Flutter has a predictable pattern.

Ventricular Dysrhythmias

• Ventricular Tachycardia occurs when ventricles beat too fast.
• Ventricular Fibrillation occurs during uncoordinated contraction of the ventricles.

Antidysrhythmic Drugs: Mechanisms of Action

• Prolong the AV node
• Increase or reduce conduction speed
• Alter ectopic pacemakers and the SA node.
• Reduce myocardial excitability
• Simulate the autonomic nervous system.
• Different medication classes include sodium channel blockers, beta-adrenergics, potassium channel blockers and calcium channel blockers with additional classes available.
• Inotropic drugs affect the force of contraction.
• Chronotropic drugs affect the rate of contractions.
• Dromotropic drugs affect electrical current.

Vaughan Williams Classification

• It classifies antidysrhythmic drugs based on their electrophysiologic effect on the action potential.
• Class I drugs are sodium channel blockers: Class Ia, Class Ib, and Class Ic.
• Examples of Class II drugs are Beta Blockers.
• Class III drugs are potassium channel blockers.
• Class IV drugs are calcium channel blockers.
• Other drugs include Digoxin and Adenosine.

Drugs Affecting the Cardiac Action Potential

• Class 1: Na+ channel blockers
  • 1a (moderate): Quinidine, Procainamide
  • 1b (weak): Lidocaine, Phenytoin
  • 1c (strong): Flecainide, Propafenone
• Class 2: β-blockers: Propranolol, Metoprolol
• Class 3: K+ channel blockers: Amiodarone, Sotalol
• Class 4: Ca2+ channel blockers: Verapamil, Diltiazem

Vaughan Williams Class Ia: Sodium Channel Blocker

• Drugs in Class Ia include procainamide (Pronestyl), quinidine gluconate, and disopyramide (Norpace).
• Class 1a blocks sodium (fast) channels and delays repolarization.
• They are used for atrial fibrillation, atrial flutter, ventricular tachycardia, supraventricular tachycardia, and Wolff-Parkinson-White Syndrome.
• Adverse effects of procainamide: include systemic lupus syndrome, neutropenia/thrombocytopenia, cardiotoxicity, and hypotension.
• Contraindications/Precautions: use during pregnancy risk category C, or with liver/renal disorders.
• Medication/Food Interactions: Avoid use with antidysrhythmics and Antihypertensives.
• Do not crush or chew sustained-release medications during Nursing Administration.

Vaughan Williams Class Ib: Sodium Channel Blocker

• Class Ib: includes lidocaine (Xylocaine), mexiletine (Mexitil), and tocainide (Tonocard).
• Decreases electrical conduction and increases the rate of repolarization.
• Used for ventricular dysrhythmias.
• CNS effects are twitching, convulsions, and respiratory depression.
• Contraindications include liver and renal dysfunction.
• Beta Blockers and Phenytoin increases serum levels of lidocaine.
• IV administration is usually started with a weight based dose and then a maintenance dose for no more than 24 hours.

Vaughan Williams Class Ic: Sodium Channel Blocker

• Class Ic: drugs include propafenone (Rhythmol) and flecainide (Tambocor).
• Mechanism of action: decreases electrical conduction and excitability and increase the rate of repolarization.
• Used for Supraventricular Tachycardia.
• Adverse effects: Bradycardia, Heart failure, Dizziness, and Weakness
• Contraindications include severe heart failure and severe hypotension
• Digoxin, oral anticoagulants, and beta blockers interact with medication and food.
• The medication should be taken with food and not crushed.
• Monitor ECG during treatment and check for bradycardia and hypotension.

Vaughan Williams Class II: Beta Blocker

• Includes propranolol hydrochloride (Inderal), esmolol hydrochloride (Brevibloc), and metoprolol (Lopressor).
• Prevents sympathetic nervous system stimulation of the heart, decrease heart rate, and slows rate of conduction through the SA node.
• Used for: Atrial fibrillation, Atrial flutter, and SVT.
• Adverse Effects include bradycardia, hypotension, and impotence,
• Contraindications include severe heart failure and asthma.
• Interacts with Verapamil and Diltiazem and can mask the hypoglycemic effect of insulin.
• Nursing Administration: Take apical pulse daily and Administer IV form slowly

Vaughan Williams Class III: Potassium Channel Blockers

• Amiodarone (Cordarone, Pacerone), sotalol (Betapace), and dofetilide (Tikosyn) drug examples.
• Prolongs the action potential and refractory period of the cardiac cycle.
• Decreases the rate of repolarization, electrical conduction, and contractility.
• Treats atrial fibrillation given orally, and recurrent ventricular fibrillation/tachycardia
• Contraindications include AV block, bradycardia, and liver, thyroid, or respiratory dysfunction.
• Interacts with Diltiazem, digoxin, and warfarin. Do not consume Grapefruit juice.
• Amiodarone is highly toxic with adverse effects continuing until discontinued. Offer the patient information regarding toxicities. High chance of pulmonary toxicity and fibrosis. Sinus bradycardia and visual disturbances are potential effects.

Vaughan Williams Class IV: Calcium Channel Blockers

• Includes verapamil (Calan) and diltiazem (Cardizem).
• Depresses depolarization, decreases myocardial oxygen demand/force of contraction, decreases heart rate, and slows conduction through SA and AV Nodes.
• Treats atrial fibrillation, Aflutter and SVT.
• Has adverse effets like bradycardia, hypotension, and constipation.
• Contraindications include SA/AV dysfunction and heart blocks.
• Interacts with Beta-blockers and Digoxin.
• May cause orthostatic hypotension and change positions slowly to increase venous return to the heart. Contact the provider for peripheral edema or shortness of breath.

Vaughan Williams Classification: Other Antidysrhythmics

• These have properties across several classes.
• Digoxin is one example.
• Adenosine is an emergent medication for extreme tachycardia

Unclassified Antidysrhythmic Drugs

• Digoxin (Lanoxin) is used with advanced heart failure.
• Digoxin slows conduction between the SA & AV node.
• Can be administered PO or IV for atrial fibrillation/flutter.
• Toxicity is a high risk that can lead to renal impairment.
• Follow Digoxin levels to determine the dose to administer.
• Cardiac arrhythmias and yellow halos are effects.
• An antidote is Digoxin Immune Fab (Digibind).
• Inotropic increases the force of contraction, Chronotropic increases the rate of contractions and Dromotropic increases electrical current.

Unclassified Antidysrhythmic: Adenosine (Adenocard)

• Adenosine slows conduction through the AV node and corrects AV node problems only.
• Used to convert paroxysmal supraventricular tachycardia to sinus rhythm.
• Very short half-life of less than 10 seconds.
• Administered as a fast IV push (6mg).
• May cause asystole for a few seconds, otherwise has minimal adverse effects.

Nursing Implications

• Obtain a thorough drug and medical history.
• Check baseline BP/P, I & O, and cardiac rhythm.
• Check Serum potassium levels before initiating therapy due to potential renal dysfunction. Monitor heart rate, cardiac rhythm, BP, general well-being, skin color, temperature, heart and lung sounds during therapy.
• Assess plasma drug levels as indicated.
• Monitor for side effects.
• Patients should take medications as scheduled and avoid skipping doses or doubling up for missed doses.
• Contact the medical professional if a scheduled dose is missed.
• Do not crush or chew sustained-release oral medications.
• Administer IV infusions through an IV pump.
• With beta-blockers, digoxin, and other drugs, instruct patients to check their radial pulse for one minute and reach out to the medical professional with pulses lower than 60 bpm.
• Inform the patient to contact the health care provider if worsening dysrhythmia or toxic effects such as shortness of breath, edema, dizziness, syncope, chest pain, GI distress or vision occur.

Expected Outcomes

• Target decreased blood pressure in hypertensive patients.
• Decreased irregularities in pulse rate.
• Improved regularity of rhythm and cardiac output.
• Reduced edema and fatigue and improved pulse rate.
• Goals should include target HR and BP.

SDOH

• Disease populations at risk include older adults with HTN, heart failure, diabetes, and thyroid disease who are all at increased risk or dysrhythmias.
• Costs for medications include: Lidocaine - $5 for 20 doses, Propranolol – 30 day supply $30-$80 and Digoxin - $50 for 100 tablets.