Group 2 DPT– 5 th

Course: Pharmacology-I
Course Instructor: Dr. Aliza Hamayun

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Group members
Muneeb ur Rehman

Iqra Ali

Hassan Mansoor

Ramia Jabeen

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 Cardiac arrhythmias

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 Lecture outline
Introduction to Cardiac arrhythmias
Types of arrhythmias
Mechanism of arrhythmias
Symptoms
Causes
Phases of action potential of cardiac cells
Classification of anti-arrhythmias drugs
Summary

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Introduction
An arrhythmia is a heart rhythm that isn’t normal. Your heart may be
beating too fast when you’re at rest or just not beating in a regular
pattern.

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Definition

Arrhythmias, also known as cardiac arrhythmias,

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Mechanism of arrhythmias
• Disturbance in impulse generation may be due to
o Abnormal automaticity
o Delayed after depolarizations
• Disturbance of impulse conduction
o The impulse may recirculate in heart causing repeated activation (re-
entry)
o Conduction blocks.

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Re-entry phenomenon

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Types of Arrhythmias
Supraventricular arrhythmias: These begin in your atria (your heart’s
upper chambers). “Supraventricular” means above your ventricles or
lower chambers of your heart.
Ventricular arrhythmias: These begin in your heart’s ventricles or
lower chambers.
Bradyarrhythmias and junctional rhythms: These can happen
because of issues in your heart’s conduction system, such as the
sinoatrial (SA) node, atrioventricular (AV) node or His-Purkinje
network.

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Symptoms
• Heart palpitations.
• Dizziness or lightheadedness.
• Fainting episodes.
• Shortness of breath.
• Chest discomfort.
• Weakness or fatigue.

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Causes
• Coronary artery disease.
• Irritable tissue in your heart (due to genetic or acquired causes).
• High blood pressure.
• Changes in your heart muscle (cardiomyopathy).
• Valve disorders.
• Electrolyte imbalances in your blood.
• Injury from a heart attack.
• The healing process after heart surgery.

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Phases of action potential of cardiac cells

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Classification of Antiarrhythmias drugs
Class I : sodium channel blockers
Class II : β- Adrenergic blockers
---Propranolol , acebutolol , esmolol
Class III : potassium channel blockers
---Amiodarone , bretylium , satalol
Class IV : calcium channel blockers
---verapamil , diltiazem

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Class I : sodium channel blockers
IA : Prolong repolarization
---Quinidine , procainamide , disopyramide
IB : Shorten repolarization
--- Lignocaine , phenytonin
IC : Little effect on repolarization
--- Encainide , propafenone

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Class IA

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Quinidine
Mechanism of action : blocks sodium channels.
• ↓Automaticity , conduction velocity and prolongs replorization
• ↓ Phase 0 depolarization , ↑action potential duration (APD) and
↑ effective refractory period(ERP)
Adverse effects :
Hypotension , QT prolongation , hepatitis , high doses causes
cinchonism

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Procainamide :
Adverse effect : nausea , vomiting hypersensitivity reactions,
Higher doses can cause hypotension , heart block and QT prolongation.

Disopyramide :
Adverse effect : dry mouth , blurred vision , constipation

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Class IB drugs

Blocks the sodium channels and

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Lignocaine
• Raises threshold for action potential , ↓ automaticity
• Suppress electrical activity of arrhythmogenic tissue , normal tissue less
effected
• Uses : ventricular arrhythmias
• Adverse effects :
• Drowsiness, hypotension , blurred vision , confusion and convulsions
Phenytonin :
• Antiepileptic also useful in ventricular arrhythmias.
Mexiletine :
• Adverse affects : nausea , tremors blurred vision
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Class IC Drugs

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Class II drugs
• Supress adrenergic mediated ectopic activity
• Antiarrhythmic action due to of β blockade
• Depress myocardial contractility , automaticity and conduction
velocity .
Propranolol :
• treatment and prevention of supraventricular arrhythmias especially
associated with exercise , emotion.
Esmolol :
• IV short acting can be used to treat arrhythmias during surgery .
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Class III Drugs
↑ APD and ↑ RP by blocking the
K+ channels

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Amiodarone
Mechanism of action :
• Prolongs action potential duration by blocking K+ channels
• Block inactivated sodium channels
• β blocking action ,blocks Ca2+ channels
• ↓ Conduction , ↓ ectopic automaticity
Uses
• Can be used for both supraventricular and ventricular tachycardia

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Adverse effect :
• Heart block , QT prolongation , bradycardia , cardiac failure ,
hypotension
• Pulmonary fibrosis
• Bluish discoloration of skin .
• GIT distribution
• Hyperthyroidism or hypothyroidism

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Class IV (calcium channel blocker)

• Inhibit the inward movement of

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Summary (clinically classification)

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 ANY QUESTION ?

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 THANK YOU
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