59-291 section 3 lecture 3 antiarrhythmic drugsmutuslab.cs.uwindsor.ca › mutus › 59-291 ›...
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59-291 Section 3 Lecture 3
Antiarrhythmic Drugs
• Heart beats (HB) originate fromAV node
• Normal 70 beats/min at rest• Arrhythmia (dysrhythmia):
Abnormal origin, rhythm, or rate• Supraventricular arrhythmia:
arise in the atria or AV node• Ventricular arrhythmia: arise in
the ventricles• Tachyarrhythmia: HB too rapid• Bradyarrhythmia: HB too slow
Some arrhythmias are benign anddo not require treatment othersinterfere with cardiac output or BPor can cause more severe or lethalrhythm disturbances.
2Resting membrane potential of a cardiac cell
Resting membrane potential (RMP): A net negative charge relative to the outside of acardiac cell
Action potential: Change in the distribution of ions across the cell membrane andpropagation of an electrical impulse and the subsequent contraction of myocardialcells. AP consist of 4 phases
Spontaneous depolarization is referred to automaticity or pacemaker activity
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P-wave:atrialdepolarization
PR: Time it takes for theaction potential toconduct through the atriaand the AV node
QRS wave: Ventricular depolarization
T wave: Ventricular repolarization
ECG –is a summation of theaction potentials generated bythe heartQT: time between
ventriculardepolarization andrepolarization
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Pacemaker cells
3 distinct phases:
0- rapid depolarization
3- repolarization
4- resting potential (unstable)
Non pacemaker cells5 distinct phases:
0- rapid depolarization
1-initial repolarization
2- action potential plateau
3- repolarization
4- resting potential (stable)
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+1400.0001 mM2 mMCa2+
-90150 mM4 mMK+
+5010 mM145 mMNa+
EquilibriumPotentialmV
InsideCell
Outside Cell
ion
Threshold potential (TP)
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P-wave:atrialdepolarization
PR: Time it takes for theaction potential toconduct through the atriaand the AV node
QRS wave: Ventricular depolarization
T wave: Ventricular repolarization
ECG –is a summation of theaction potentials generated bythe heartQT: time between
ventriculardepolarization andrepolarization
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Pathophysiology of Arrhythmias
• Coronary ischemia and hypoxia• Electrolyte imbalance• Overstimulation of sympathetic NS• General anesthetics• Other conditions that perturb cardiac
conduction
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Abnormal impulse formation• Increased automaticity
• Decreased the required time for depolarization from themaximal diastolic potential (MDP) to the threshold potential
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• Afterdepolarizations• Abnormal calcium influx into cardiac cells during or immediately after phase 3
of ventricular action potential