pharmacology of anti-arrhythmics
DESCRIPTION
PHARMACOLOGY OF ANTI-ARRHYTHMICS. Arrhythmia (a-rhythm) means no rhythm,whereas dysrhythmia (dys-rhythm) means an abnormal heart rhythm. In practice,both terms are used interchangeably to mean an abnormal of irregular heart beat. Arrhythmia. Cardiac arrhythmias. 25% with digitalis. - PowerPoint PPT PresentationTRANSCRIPT
PHARMACOLOGY OF ANTI-ARRHYTHMICS
Arrhythmia (a-rhythm) means no rhythm,whereas dysrhythmia (dys-rhythm) means an abnormal heart rhythm. In practice,both terms are used interchangeably to mean an abnormal of irregular heart beat.
ArrhythmiaArrhythmia
Cardiac arrhythmias
25%
with digitalis
50% Aneathetized patients
over 80% with acute myocardial
infarction
Genesis of Normal
Heart Rhythm
Genesis of Tachyarrhythmia
Antiarrhythmic Drugs
ManagingTachyarrhythmias
Heart Rhythm
Genesis of Normal Heart Rhythm: The Myocardial Action Potential
(1) pacemaker activity
(2) absence of fast Na+ current in SA and AV nodes, where slow inward Ca2+ current initiates action potentials.
(3) long action potential ('plateau') and refractory period
(4) influx of Ca2+ during the plateau.
Electrophysiological Features
Phase-4 Depolarization results in automaticity of the cardiac action potential, in normal SA nodal cells.
The Effective Refractory The Effective Refractory Period(ERP)Period(ERP)
Genesis of Normal Heart Rhythm : Ion Channel
Genesis of Tachyarrhythmia
11 Classification of ArrhythmiasClassification of Arrhythmias
22 Enhanced AutomaticityEnhanced Automaticity
44 AfterpotentialsAfterpotentials
33 ReentryReentry
Classification of ArrhythmiasClassification of Arrhythmias
Bradyarrhythmias
Tachyarrhythmias
Unidirectional Block and Reentry
Late After DepolarizationLate After Depolarization
Sufficient Preparation
Depress resting membrane potential
Prolong Effective Refractory Period
Suppress enhanced automaticity
Slow conduction in tissue
Managing Tachyarrhythmias:
Strategies
Class IClass I Na+ Channel Blockers
Class IIClass II β-adrenergic Blockers
Class IIIClass III Prolong ERPClass IVClass IV Ca2+ Channel Blockers
Adenosine
Digoxin
Classification of Antiarrhythmic Classification of Antiarrhythmic Drugs (Vaughan-Williams)Drugs (Vaughan-Williams)
Classification of antiarrhythmic drugs
Class I:
Na+ Channel Blockers
Class I: Na+ Channel Blockers
Guinidine
Class II Antiarrhythmic Drugs:β1-adrenoceptor blockers
How Sympathetic Stimulation Increases Heart Rate and Accelerates Conduction:
Non-pacemaker Tissue:Sympathetic activity→Accelerated Conduction
Pacemaker:β- adrenoceptor stimulation:→ ↑ automaticity
Class II: β-adrenergic Blockers: Oppose effects of sympathetic tone
• Reduce automaticity (including physiological)
• Slow conduction• Mainly active in atrial & atrioventricu
lar tissue• Reduce risk of sudden death after he
art attack
Class II: Examples
• Propranolol• Metoprolol• many other -olol’s• Other aspects of pharmacology: loo
k up autonomic pharmacology notes
Class III:
Drugs that Prolong Action Potential Duration & ERP
Class III: Examples
• Amiodarone 胺碘酮• Sotalol 索他洛尔 (also β-block
er)
Class IV
Calcium Channel Blockers (also active in angina and
hypertension)
Adenosine
• Adenosine receptors on atrial myocardium and atrioventricular conducting tissue
• K+ channels are adenosine receptor-linked
Adenosine: Pharmacology
• Very rapid hydrolysis in blood – only IV use – rapid IV bolus
• For supraventricular tachycardias (may help diagnosis)
Effects of antidysrhythmic drugs on the dEffects of antidysrhythmic drugs on the different phases of the cardiac action poteifferent phases of the cardiac action potentialntial
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