Lecture 10 - Cardiac Electrophysiology

Lecture 10 - Cardiac Electrophysiology - Lecture 10 -...

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Lecture 10 - Cardiac Electrophysiology Lecture Outline I. Introduction ( 1-2 ) A. Normal sequence of electrical activation B. Electrophysiological categories of cardiac cells II. Cardiac action potentials (APs) ( 3-9 , 16 ) A. APs in fast fibers: fast response APs B. APs in slow fibers: slow response APs C. Refractoriness III. Conduction velocity (10-11 , 16 ) A. Major determinants of conduction velocity B. Interventions that change the conduction velocity C. Fast fibers vs. slow fibers IV. Automaticity ( 12-16 ) A. Mechanisms for automaticity B. Automaticity vs. firing rate C. Interventions that change the firing rate V. Bridge to electrocardiography ( 17-18 ) Normal Sequence of Electrical Activation The electrical current is conducting SA nove – Atria – AV Node (slowly so that it creates a lag so that atria systole can finish contraction and finish the ventricular filling before the ventricle contract) – his purkinje system (rapidly conduct impact throughout the ventricule) – the left and right bundle branch run along the endocardium surfaces on the septum and LV wall ; the purkeinje fiber penetrate from the endocardium to the enthealcardium - These cells are not nerve cells BUT myoctes Electrophysiological Categories of Cardiac Cells Fast fibers o Atrial and ventricular myocytes o His-Purkinje system (Purkinje cells) The specialized cells in this system Slow fibers o SA node AV node Very similar to RMP in nerve Can be attributed to two characteristics of resting cell o Concentration gradients across cell membrane o Selective permeability of cell membrane Cardiac Action Potentials (APs) - Fast Response APs APD = Action potential duration - Resting potential -90 - Threshold potential -60/-65 (start of AP) - Spike up to +20 - Depolarization back to membrane potential - Spike 0 - (the amplitude of the height of the spike is >100mV) - Gradual 1,2,3 - (long APD is the main different between a nerve AP and the heart AP --- short AP in nerve but in her it is much longer skeletal is only 2-3 msec) - Resting 4 Phases of Fast Response AP These AP different from the slow fibers Changes in TMP produced by ion currents Ion currents result from activation of specific ion channels Major Ion Currents and Ion Channels o K + currents o Na + currents o Ca 2+ currents Phases of Fast Response AP-- Phase 4 (RMP) - Resting potential is the same like other cells - Can be contributed to two factors: 1. Concentration gradients across cell membrane 1. Most importantly the K+ 2. Selective permeability of cell membrane
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P K >> P Na (At rest the permeability is higher for K+ then Na+ b/c of the special population of K+ channels – K IR channels) Inwardly rectifying K + channels (K ir or K 1 channels) account for high P K - If cell were permeable only to K + , RMP ≈ E K E K = 61.5 log { [K + ] o / [K + ] i } mV E K = 61.5 log { 4/140 } mV E K = -94 mV (this is less negative than the K+
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Lecture 10 - Cardiac Electrophysiology - Lecture 10 -...

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