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59-291 Section 3 Lecture 3
Antiarrhythmic Drugs
• Heart beats (HB) originate from
AV 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 and
do not require treatment others
interfere with cardiac output or BP
or can cause more severe or lethal
rhythm disturbances.
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Resting membrane potential (RMP): A net negative charge relative to the outside of a
cardiac cell
Action potential: Change in the distribution of ions across the cell membrane and
propagation of an electrical impulse and the subsequent contraction of myocardial
cells. AP consist of 4 phases
Spontaneous depolarization is referred to automaticity or pacemaker activity
Resting membrane potential of a cardiac cell
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QRS wave: Ventricular depolarization
T wave: Ventricular repolarization
P-wave: atrial depolarization
PR: Time it takes for the
action potential to
conduct through the atria
and the AV node
QT: time between
ventricular
depolarization and
repolarization
ECG –is a summation of the
action potentials generated by
the heart
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Pacemaker cells
3 distinct phases:
0- rapid depolarization
3- repolarization
4- resting potential (unstable)
Non pacemaker cells
5 distinct phases:
0- rapid depolarization
1-initial repolarization
2- action potential plateau
3- repolarization
4- resting potential (stable)
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ion
Outside
Cell
Inside
Cell
Equilibrium
Potential
mV
Na+
145 mM
10 mM
+50
K+
4 mM
150 mM
-90
Ca2+
2 mM
0.0001 mM +140
Threshold potential (TP)
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QRS wave: Ventricular depolarization
T wave: Ventricular repolarization
P-wave: atrial depolarization
PR: Time it takes for the
action potential to
conduct through the atria
and the AV node
QT: time between
ventricular
depolarization and
repolarization
ECG –is a summation of the
action potentials generated by
the heart
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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 the
maximal 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
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