Brief description of drugs which are used to alter cardiac action potential in arrythmic patients. It focuses on understanding of action potentials in short descriptions as possible.

1. Drugs and Their Effects on
Cardiac Action Potential in
Arrythmic Patients
Presented by
Sabarni Sarker
Student, M. Pharm.
Rajshahi University
28 May 2014

2. What is Action Potential?
• Action potential is a short-lasting
event in which the
electrical membrane potential of
a cell rapidly rises and falls
• Action potentials are generated by
special types of voltage-gated ion
channels embedded in a cell's plasma
membrane.

3. How Action Potential Proceeds

4. Action Potential in Heart Muscle

5. Terminology
• Cardiac arrhythmia or irregular heartbeat is any
of a group of conditions in which the electrical
activity of the heart is irregular or is faster or
slower than normal.
• A heartbeat that is too fast is called tachycardia,
a heartbeat that is too slow is called bradycardia.
• After an action potential initiates, the cardiac cell
is unable to initiate another action potential for
some duration of time (which is slightly shorter
than the "true" action potential duration). This
period of time is referred to as the refractory
period.

6. Class of Drugs Affecting Cardiac Action
Potential

7. Class IA
These drugs binds to
open and inactivated
sodium channels and
prevents sodium influx,
thus slowing the rapid
upstroke during Phase 0.
It also decreases the
slope of Phase 4
spontaneous
depolarization.
Examples: 1) Quinidine – 1st
antiarrhythmic used, treat
both atrial and ventricular
arrhythmias, increases
refractory period
2)Procainamide
3)Disopyramide

8. Class IB
The IB agents rapidly
associate and
dissociate from
sodium channels. Thus
the actions of Class IB
agents are manifested
when the cardiac cell
is depolarized or firing
rapidly. Class IB drugs
are parlicularly useful
in treating ventricular
arrhythmias.
Examples: Lidocaine,
Mexiletine, Tocainide

9. Class IC
These drugs slowly dissociate from
resting sodium channels and show
prominent effects, even at normal
heart rates. These drugs are
approved only for refractory
ventricular arrhythmias. However,
recent data have cast serious
doubts on the safety of the Class IC
drugs.
Propafenone slows conduction,
weak β – blocker, also some Ca2+
channel blockade
Flecainide (initially developed as a
local anesthetic) Also inhibits
abnormal automaticity

10. Class II
• The Class II agents include the ß-adrenergic
antagonists.
• These drugs diminish Phase 4 depolarization, thus
depressing automaticity, prolonging AV conduction,
and decreasing heart rate andb contractility.
• Includes
Propranolol
Metoprolol
Nadolol
Pindolol
Sotalol
Timolol
Esmolol

11. Class III
Class Ill agents block
potassium channels and
thus diminish the outward
potassium current during
repolarization of cardiac
cells. These agents prolong
the duration of the action
potential without altering
Phase 0 of depolarization or
the resting membrane
potential. Instead, they
prolong the effective
refractory period. All Class III
drugs have the potential to
induce arrhythmias.
It includes Sotalol, bretylim
and amiodarone.

12. Class IV
Class IV drugs are calcium-
channel blockers. They
decrease the inward current
carried by calcium, resulting
in a decreased rate of Phase 4
spontaneous depolarization.
They also slow conduction in
tissues that are dependent on
calcium currents, such as the
AV node. Although voltage
sensitive calcium channels
occur in many different
tissues, the major effect of
calcium-channel blockers is on
vascular smooth muscle and
the heart.
Example: Verapamil,
Diltiazem, Nifedipine

13. Other Drugs
• Digoxin shortens the refractory period in atrial and
ventricular myocardial cells while prolonging the effective
refractory period and diminishing conduction velocity in the
AV node.
• Adenosine is a naturally occurring nucleoside, but at high
doses, the drug decreases conduction velocity, prolongs the
refractory period, and decreases automaticity in the AV
node.
• Implantable cardioverter-defibrillator (ICD) is a
small battery powered electrical impulse generator that is
implanted in patients who are at risk of sudden cardiac
death due to ventricular fibrillation and ventricular
tachycardia.

14. Thank you
for your patience