ALS Lecture 13 - The Pharmacology of Rhythm Control DONE Flashcards
2 types of heart cells
pacemaker, myocyte
Type 1 heart cells, pacemaker (4)
depolarise without stimulation, SA node, AV node, conduction tissue
Type 2 heart cells, myocytes (3)
fire when stimulated, atria, ventricles
muscle cells in diastole (phase 4) remain at
resting membrane potential of -90mv till stimulated
3 properties of cardiac cells
automaticity, excitability, refractoriness
automaticity
spontaneous depolarisation till threshold potential reached when cell fires (phase 0)
spread of excitation sequence (8 steps)
- SA node
- atria
- AV node
- bundle of His
- bundle branches
- Purkinje fibres
- endocardium to epicardium
- apex to base
label the diagram of the phases of excitation (A)
done
phase 0 of cardiac action potential
rapid depolarisation, fast Na+ inflow
phase 1 of cardiac action potential
initial rapid repolarisation due to Na+ closure, Cl- influx, outflow of K+
phase 2 of cardiac action potential
plateau, delayed repolarisation by slow inward Ca+ and outflow of K+
phase 3 of cardiac action potential
2nd period of repolarisation, continual K+ outflow and Ca2+ inflow
what class is digoxin?
5
what effect does digoxin do? (5)
slow HR, reduced AV conduction, increased contraction force, rhythm disturbance, increased ectopic pacemaker
digoxin MOA (4 steps)
- inhibits Na+K+ATPase pump
- increased Na+, decreased K+
- Na+/Ca2+ transported gets rid of Na+, bringing in Ca2+
- strengthens ventricular contraction so more blood each beat
Vaughan Williams classification, Class 1 agents interfere with
sodium channel
Vaughan Williams classification, Class 1a agents
lengthen action potential
Vaughan Williams classification, Class 1b agents
shorten action potential