Antidysrhythmics and Electrocardiography

• Dysrhythmia is any heart deviation from the normal rhythm.
• Antidysrhythmics are used for the treatment and prevention of disturbances in cardiac rhythm.
• A change in the distribution of ions causes cardiac cells to become excited.
• Movement of ions across the cell's membrane results in an electrical impulse spreading across the cardiac cells.
• This electrical impulse leads to contraction of the myocardial muscle.
• Resting cardiac cells have a net negative charge relative to the outside of the cell.
• A difference in electronegative charge results from an uneven distribution of ions across the cell membrane, which is maintained by the Sodium-Potassium ATPase pump
• The sinoatrial (SA) node is the natural pacemaker of the heart and has an inherent rate of 60-100 BPM

Electrocardiography

• ECG or EKG
• P wave represents electricity to atria
• PR interval represents electricity to atria
• QRS complex represents contraction and electricity to ventricles
• ST segment
• T wave

Common Atrial Dysrhythmias

• Supraventricular Tachycardia. The PR interval is too small / ineligible to see
• Atrial Fibrillation has no P waves
• Atrial Flutter shows a predictable pattern

Ventricular Dysrhythmias

• Ventricular Tachycardia
• Ventricular Fibrillation

Antidysrhythmic Drugs Mechanisms of Action

• Prolong the AV node
• Increase or reduce conduction speed
• Alter ectopic pacemakers and SA node
• Reduces myocardial excitability
• Stimulates the autonomic nervous system

Pharmacodynamics

• Inotropic: force of contraction (increase or decrease)
• Chronotropic: rate of contractions
• Dromotropic: electrical current

Vaughan Williams Classification of Antidysrhythmic Drugs

• Class I: Sodium Channel Blocker (Ia, Ib, Ic)
• Class II: Beta Blocker
• Class III: Potassium Channel Blocker
• Class IV: Calcium Channel Blocker
• Other antidysrhythmics include digoxin and adenosine

Drugs Affecting the Cardiac Action Potential

• Class 1 agents block Na+ channels
• Class 2 agents are B-blockers
• Class 3 agents block K+ channels
• Class 4 agents block Ca2+ channels

Class Ia Sodium Channel Blockers:

• Procainamide (Proneystl), Quinidine gluconate, disopyramide (Norpace)
• They block sodium (fast) channels and delay repolarization
• Used for atrial fibrillation, flutter, ventricular of ventricular tachycardia, supraventricular tachycardia and Wolff-Parkinson-White Syndrome
• Adverse effects include Systemic Lupus Syndrome, cardiotoxicity and hypotension
• are contraindicated for liver or renal disorders, and pregnancy risk category C medications
• Food interactions include with antidysrhythmics and antihypertensives
• Do not crush or chew sustained-release medications

Class Ib Sodium Channel Blockers:

• Lidocaine(Xylocaine), mexiletine (Mexitil), tocainide (Tonocard)
• They decrease electrical conduction and increase the rate of repolarization
• Used for Ventricular Dysrhythmias
• Adverse effects are CNS-related, (twitching, convulsions, respiratory depression)
• Liver and renal dysfunction may be a contraindication
• IV administration is weight-based and then a maintenance dose

Class Ic Sodium Channel Blockers:

• Propafenone (Rhythmol), flecainide (Tambocor)
• Decrease electrical conduction and excitability but increase the rate of repolarization
• Used for Supraventricular Tachycardia
• Contraindications: Severe heart failure and Severe hypotension
• Monitor patient's ECG, for bradycardia and hypotension
• Take medication with food and do not crush

Class II Beta Blockers:

• Propranolol hydrochloride (Inderal), esmolol hydrochloride (Brevibloc), metoprolol (Lopressor)
• Action: Prevents sympathetic nervous system stimulation of the heart, decreasing heart rate, and slows rate of conduction through the SA node
• Used for Atrial fibrillation, Atrial flutter, SVT
• Adverse Effects: Bradycardia, hypotension, impotence
• Contraindications: Severe asthma/ heart failure (Short-acting inhaler does not have receptor sites)
• Mask the hypoglycemic effect of insulin
• Nursing Administration: Take apical pulse daily and administer IV form slowly

Class III Potassium Channel Blockers:

• Amiodarone (Cordarone, Pacerone), sotalol (Betapace), dofetilide (Tikosyn)
• Prolong the action potential and refractory period of the cardiac cycle by decreasing the rate of repolarization, electrical conduction, and contractility
• Used for Atrial Fibrillation, recurrent ventricular fibrillation, ventricular tachycardia
• Contraindications: AV block, bradycardia, liver, thyroid or respiratory dysfunction
• Caution with Diltiazem, digoxin, and warfarin
• Amiodarone is highly toxic and can cause pulmonary fibrosis

Class IV Calcium Channel Blockers:

• Verapamil (Calan), diltiazem (Cardizem)
• Decreases myocardial oxygen demand, force of contraction, heart rate and rate of conduction through SA and AV nodes and also decreases depolarization of muscles
• Used for Atrial Fibrillation /Flutter and SVT
• Adverse Effects include bradycardia, hypotension, constipation
• Contraindications: SA/AV dysfunction and Heart blocks
• May cause orthostatic hypotension so change positions slowly and notify health provider if peripheral edema or shortness of breath

Other Antidysrhythmics

Digoxin (Lanoxin)

• For Advanced heart failure
• Slows conduction between the SA & AV node an so is used to slow the rate in atrial fibrillation and flutter
• Administer PO or IV
• Follow Digoxin levels due to high risk for toxicity and/or potential for renal impairment
• Cardiac arrhythmias and yellow halos are adverse effects

Adenosine (Adenocard)

• Corrects only AV node problems
• Slows condition through the AV node
• Used to convert paroxysmal supraventricular tachycardia to sinus rhythm
• Very short half-life so must administer as a fast IV push
• May cause asystole for a few seconds

Nursing Implications Regarding Antidysrhythmics

• Obtain a thorough drug and medical history
• Measure baseline BP/P, I & O, and cardiac rhythm
• Measure serum potassium levels before initiating therapy
• 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 the patient knows to notify health care provider of any worsening of dysrhythmia or toxic effects.
• Shortness of breath
• Edema
• Dizziness
• Syncope
• Chest pain
• Gl distress
• Blurred Vision
• Changes in cardiac output

Expected outcomes from Antidysrhythmic treatment

• Decreased BP in hypertensive patients
• Decreased edema
• Decreased fatigue
• Regular pulse rate with no major irregularities
• Improved regularity of rhythm
• Improved cardiac output

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