Pharmacology Test 2: Cardiac Arrhythmias

Front 1

Cardiac Arrhythmia

Back 1

A variation in either the site or rate of cardiac impulse formation or a variation in the sequence of cardiac impulse propagation

Problem with formation and conduction that causes change in rhythm

Cardiac drugs change impulse formation or impulse conduction—change cardiac arrhythmias by creating cardia arrhythmias; main side effects proarrythmia and cardia arrythmia

Front 2

Class 1 Sodium Channel Blockers

Back 2

PROCAINAMIDE, QUINIDONE, disopyramide, moricizine

LIDOCAINE(major drug), tocainide, mexiletine, phenytoin

FLECAINIDE, propafenone

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Class 1 Agents

Back 3

Local Anesthetics

Front 4

Quinidine

Back 4

Absorption: Oral

Elimination: Renal

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Procainamide

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Absorption: Oral

Elimination: Renal and Hepatic

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Class 1-A Effects of Cardiac Activity

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Depress phase 0 of the action potential (Na+)

Lengthen refractory period (K+)

QUINIDINE has anticholinergic (atropine like action) to increase AV conduction used with digitalis, beta blocker or calcium channel blocker

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Class 1-A Uses

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Wide spectrum: useful for atrial, junctional and ventricular tachycardias

PROBLEM: blocks muscarinic receptors (muscarinic antagonist); speeds up conduction in the AV node

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Class 1-A Side Effects

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Hypotension, reduced cardiac output

Proarrhythmia (generation of a new arrhythmia) eg. Torsades de Points (QT interval)—ventricular tachycardia due to nothing but pacemakers in the ventricle—all QRS waves on the ECG; produced by any drug that increases the QT interval; Treatment is IV magnesium

Dizziness, confusion, insomnia, seizure (high dose)

Gastrointestinal effects (common)

Lupus-like syndrome (esp. procainamide)

Front 9

Class 1-B Agents

Back 9

LIDOCAINE (major drug) tocainide
mexiletine
phenytoin

Front 10

Lidocaine

Back 10

Absorption: IV ONLY, hepatic metabolism; great ER drug

Front 11

Tocainide and Mexiletine

Back 11

oral forms of Lidocaine; hepatic metabolism

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Class 1-B: Effects on Cardiac Activity

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No change in phase 0 in normal tissue

In fast beating heart or ischemic tissue, large decrease in phase 0 (Na+)

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Class 1-B: Uses

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Only used for VENTRICULAR TACHYCARDIA and fibrillation, esp. during ischemia

Not used in atrial arrhythmias or supraventricular arrhythmias

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Class 1-B: Side Effects

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Less proarrhythmic than Class 1-A (less QT effect)

CNS Effects: dizziness, drowsiness, confusion

Front 15

Class 1-C Agents

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FLECAINIDE

PROPAFENONE--newest of the local anesthetics; very potent and big effects on phase 0

Front 16

FLECAINIDE

Back 16

Absorption: oral

Elimination: renal

Front 17

PROPAFENONE

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Absorption: oral

Elimination: hepatic

Front 18

Class 1-C: Effects on Cardiac Activity

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Substantially decrease phase 0 (Na+)

Decrease automoticity

Increase refractory period esp. in atrial tissue

Effects are greater in ischemic tissue

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Class 1-C: Uses

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Wide spectrum

Used for ATRIAL and AV JUNCTIONAL ARRHYTHMIAS (fibrillation and flutter)--greatest effect in the atria--used to treat supraventricular cardiac arrhythmias

Convert/fix atrial fibrillation and flutter

Developed to prevent premature ventricular contractions (PVC)--an extra beat every now and then

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Class 1-C: Side Effects

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Proarrhythmia and sudden death esp. with chronic use (CAST Study)

CNS and GI effects like other local anesthetics

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Class 2 Agents

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PROPRANOLOL
ESMOLOL

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PROPRANOLOL

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Absorption: oral

Elimination: hepatic

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ESMOLOL

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Absorption: IV only; very short-acting beta blocker with a T1/2 of 9 minutes

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Class 2: Cardiac Effects

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Slow AV conduction

Decrease heart rate (catecholamine dependent)

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Class 2: Uses

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Treating SINUS TACHYCARDIA and CATECHOLAMINE DEPENDENT ARRHYTHMIAS

Prevent arrhythmia in post MI pts.--decreases oxygen consumption and slows the metabolism of the heart

Protecting the ventricles from high atrial rates (slow AV conduction)

Treat supraventricular tachycardia--only beta blockers are used for this

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Class 2: Side Effects

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Bronchospasm

Hypotension

Dont use in partial AV block or ventricular failure

Be careful in pts. who have asthma

Front 27

Class 3 Agents

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AMIODARONE
SOTALOL
ibutalide
dofetalide

Front 28

AMIODARONE Absorption and Elimination

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Absorption: oral

Elimination: hepatic metabolism (T 1/2 about 3 months)

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AMIODARONE: Cardiac Effects

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Increase refractory period (K+)

Decrease phase 0 (Na+)

Decrease phase 4 (beta block and Ca2+ block)

Decrease AV conduction

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AMIODARONE: Uses

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Very wide spectrum: effective for most arrhythmias; first choice for VT (ventricular tachycardia) and VF (ventricular fibrillation)

This drug takes care of everything

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AMIODARONE: Side Effects (many are serious that increase with time)

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Proarrhythmia

Pulmonary Toxicity

Hepatic Injury

Increase LDL Cholesterol

Thyroid Disease

PROBLEM: highly lipophilic and has a 3 month 1/2 life

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SOTALOL: Absorption and Elimination

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Absorption: oral

Elimination: renal

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SOTALOL: Cardiac Effects

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Increase refractory period

Slow phase 4 (beta blocker)

Slow AV conduction

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SOTALOL: Uses

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Wide spectrum

Approved for use in ventricular tachycardia and atrial arrhythmias

K channel blocker and beta blocker

Big this is to SLOW AV CONDUCTION

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SOTALOL: Side Effects

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Proarrhythmia

Fatigue

Insomnia

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Ibutalide and Dofetalide

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Brand new drugs

Almost pure K+ channel antagonists--but these channels only exist in the heart

Primary use is atrial flutter--supraventricular arrhythmias

They are restricted use though, so need special permission/training to use them

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Class 4 Agents

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VERAPAMIL
DILTIAZEM

*Ca2+ channel blockers (primarily L-type)

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VERAPAMIL

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Absorption: oral or IV

Elimination: hepatic

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DILTIAZEM

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Absorption: oral

Elimination: hepatic

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Class 4: Cardiac Effects

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Decrease conduction through the AV node (Ca2+)

Protects the ventricle

Front 41

Class 4: Uses

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Supraventricular tachycardia esp. involving AV node

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Class 4: Side Effects

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Caution when partial AV block is present. Can also get systole if beta blocker is on board

Caution when hypotension, decreased CO or sick sinus

Some GI problems

Decrease BP and have reflex increase in HR--this is bad

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Additional Antiarrhythmic Agents

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ADENOSINE
DIGITALIS
ATROPINE
MAGNESIUM

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ADENOSINE

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Given IV (short T 1/2 of about 7 seconds)

Mechanism of Action: binds A1 receptors in AV and SA node; slows AV conduction for supraventricular

Uses: Atrial Fibrillation and Flutter

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DIGITALIS (cardiac glycosides)

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Mechanism of Action: Slows AV conduction

Uses: Treat Atrial Fibrillation and Flutter

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ATROPINE

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Used to treat a slow heart rate, because it will increase heart rate

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MAGNESIUM

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Used to treat Torsades de Pointes

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Mechanical Devices

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Implantable defibrillator--for sudden death has been shown to be more effective than pharmacological therapy for increasing longevity