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