Drugs for Dysrhythmias

19

Learning Outcomes

1. Explain how rhythm abnormalities can affect cardiac function.

2. Illustrate the flow of electrical impulses through the normal heart.

3. Classify dysrhythmias based on their location and type of conduction abnormality.

Learning Outcomes

4. Explain the importance of ion channels to cardiac function and the pharmacotherapy of dysrhythmias.

5. Identify the importance of nonpharmacologic therapies in the treatment of dysrhythmias.

6. Identify basic mechanisms by which antidysrhythmic drugs act.

Learning Outcomes

7. For each of the classes in the Drug Snapshot, identify representative drugs, explain their mechanisms of action, primary actions, and important adverse effects:

8. Categorize antidysrhythmic drugs based on their classifications and mechanisms of action.

Core Concept 19.1

Some types of dysrhythmias produce no patient symptoms,

whereas others may be life threatening.

Symptoms

Dizziness Weakness Decreased exercise tolerance Shortness of breath Fainting. Palpitations

Core Concept 19.2

Dysrhythmias are classified by their location and type of rhythm abnormality produced.

Types of Dysrrhythmias

Types of Dysrrythmias

Atrial fibrillations

Diseases Commonly Associated With Dysrhythmias:

Hypertension (HTN) Cardiac valve disease, such as mitral

stenosis Coronary artery disease Medications such as digoxin Low potassium levels in the blood Myocardial infarction

Diseases Commonly Associated With Dysrhythmias:

Adverse effect from antidysrhythmic medication

Stroke Diabetes mellitus Congestive heart failure

Core Concept 19.3

The electrical conduction pathway in the myocardium keeps the heart beating in a

synchronized manner.

Common Factor

A defect in the formation or conduction of electrical impulses across the myocardium

Normal ECG tracing

Core Concept 19.4

Most antidysrhythmic drugs act by blocking ion channels in myocardial cells.

The flow of ions through ion channels in myocardial cells

Core Concept 19.5

Antidysrhythmic drugs are classified by their mechanisms of

action.

Categories of Antidysrhythmics

Sodium channel blockers (Class I) Beta-adrenergic blockers (Class II) Potassium channel blockers (Class III) Calcium channel blockers (Class IV) Miscellaneous antidysrhythmic drugs

Core Concept 19.6

Sodium channel blockers slow the rate of impulse conduction through the

heart.

Sodium Channel Blockers

Largest group of antidysrhythmics Three subgroups

IA, IB, and IC Based on subtle differences in their

mechanisms of action

Sodium Channel Blockers

Because progression of the action potential depends on the opening of sodium ion channels, a blockade of these channels will slow the spread of impulse conduction across the myocardium

Core Concept 19.7

Beta-adrenergic blockers reduce automaticity and slow

conduction velocity in the heart.

Beta Blockers

Ability to slow the heart rate and conduction velocity can suppress several types of dysrhythmias.

Slow the heart rate Decrease conduction velocity

through the AV node.

Beta Blockers

Myocardial automaticity is reduced

Many types of dysrhythmias are stabilized

Main value is to treat atrial dysrhythmias associated with heart failure.

Core Concept 19.8

Potassium channel blockers prolong the refractory period of the heart.

Potassium Channel Blockers

Blocks potassium ion channels in myocardial cells

Prolong the duration of the action potential by lengthening the refractory period (resting stage)

Stabilizes dysrhythmias.

amiodarone (Pacerone, Cordarone)

Core Concept 19.9

Calcium channel blockers are available to treat supraventricular dysrhythmias.

Calcium Channel Blockers

Slowconduction velocity Stabilize certain dysrhythmias Effects include

Reduced automaticity in the SA node Slowed impulse conduction through the

AV node Prolongs the refractory period Stabilizes many types of dysrhythmias

Calcium Channel Blockers

Only effective against supraventricular dysrhythmias.

Core Concept 19.10

Digoxin and adenosine are used for specific dysrhythmias, but do not act by

blocking ion channels.

Adenosine (Adenocard, Adenoscan)

Given as a 1- to 2-second bolus IV injection

Actions Terminates serious atrial

tachycardia Slows conduction through the AV

node decreases automaticity of the SA node

Adenosine (Adenocard, Adenoscan)

Primary indication Paroxysmal supraventricular

tachycardia (PSVT), for which it is a drug of choice

10-second half-life, adverse effects are generally self-limiting.

Digoxin (Lanoxin, others)

Primarily used to treat heart failure

Prescribed for certain types of atrial dysrhythmia

Decreases automaticity of the SA node

Slows conduction through the AV node