吉林大学：《药理学》课程PPT教学课件（七年制）Antiarrhythmic drugs

Antiarrhythmic drugs

Antiarrhythmic drugs

OVERVIEW the heart contains specialized cells that exhibit automaticity,that is,they can intrinsically generate rhythmic action potentials in the absence of external stimuli

OVERVIEW ◼ the heart contains specialized cells that exhibit automaticity, that is, they can intrinsically generate rhythmic action potentials in the absence of external stimuli

INTRODUCTION TO THE ARRHYTHMIAS cardiac arrhythmias may cause the heart ■ (1)to beat too slowly (sinus bradycardia); (2)to beat too rapidly (sinus or ventricular tachycardia,atrial or ventricular premature depolarization,atrial flutter); (3)to respond to impulses originating from sites other than the SA node; (4)to respond to impulses traveling along accessory (extra)pathways that lead to deviant depolarizations (A-V reentry)

INTRODUCTION TO THE ARRHYTHMIAS ◼ cardiac arrhythmias may cause the heart ◼ (1) to beat too slowly (sinus bradycardia); ◼ (2) to beat too rapidly (sinus or ventricular tachycardia, atrial or ventricular premature depolarization, atrial flutter); ◼ (3) to respond to impulses originating from sites other than the SA node; ◼ (4) to respond to impulses traveling along accessory (extra) pathways that lead to deviant depolarizations (A-V reentry)

Causes of arrhythmias Abnormal automaticity:The SA node shows the fastest rate of Phase 4 depolarization if cardiac sites other than the SA node show enhanced automaticity,they may generate competing stimuli

Causes of arrhythmias ◼ Abnormal automaticity: The SA node shows the fastest rate of Phase 4 depolarization ◼ if cardiac sites other than the SA node show enhanced automaticity, they may generate competing stimuli

Effect of drugs on automaticity Most of the antiarrhythmic agents suppress automaticity (1)by decreasing the slope of Phase 4 (diastolic)depolarization (2)by raising the threshold of discharge to a less negative voltage

Effect of drugs on automaticity ◼ Most of the antiarrhythmic agents suppress automaticity ◼ (1) by decreasing the slope of Phase 4 (diastolic) depolarization ◼ (2) by raising the threshold of discharge to a less negative voltage

Abnormalities in impulse conduction Impulses from higher pacemaker centers are normally conducted down pathways that bifurcate to activate the entire ventricular surface .A phenomenon called reentry can occur if a unidirectional block caused by myocardial injury or a prolonged refractory period results in an abnormal conduction pathway

Abnormalities in impulse conduction ◼ Impulses from higher pacemaker centers are normally conducted down pathways that bifurcate to activate the entire ventricular surface .A phenomenon called reentry can occur if a unidirectional block caused by myocardial injury or a prolonged refractory period results in an abnormal conduction pathway

Effects of drugs on conduction abnormalities Antiarrhythmic agents prevent reentry by slowing conduction and/or increasing the refractory period required to convert a unidirectional block into a bidirectional block

Effects of drugs on conduction abnormalities ◼ Antiarrhythmic agents prevent reentry by slowing conduction and/or increasing the refractory period required to convert a unidirectional block into a bidirectional block

Antiarrhythmic drugs the antiarrhythmic drugs can modify impulse generation and conduction

Antiarrhythmic drugs ◼ the antiarrhythmic drugs can modify impulse generation and conduction

Classification Mechanism of Action Comment of Drug A Na channel blocker Slows Phase 0 depoiarizatlon B Nachannel blocker Shortens Phase 3 repoiarization IC Natchannei biocker Markediy siows Phase 0 depoiarization B Adrenoreceptor biocker Suppresses Phase 4 depoiarization K*channei blocker Prolongs Phase 3 repolarization IV Ca+channei blocker Shortens action potential

CLASS I ANTIARRHYTHMIC DRUGS Class I antiarrhythmic drugs act by blocking voltage-sensitive sodium channels Class I antiarrhythmic drugs therefore generally cause a decrease in excitability and conduction velocity

CLASS I ANTIARRHYTHMIC DRUGS ◼ Class I antiarrhythmic drugs act by blocking voltage-sensitive sodium channels ◼ Class I antiarrhythmic drugs therefore generally cause a decrease in excitability and conduction velocity