Antiarrhythmics screening models

1. Preclinical screening models for
Antiarrhythmics
Presented To : Presented by:
Dr . M Rupesh Kumar Sharanappa
Head of Department Reg no: 22MPY113
Department of Pharmacology I semester M Pharm
SACCP, B. G. Nagara Pharmacology Department
SACCP, B. G. Nagara

2. contents
 Introduction
Pathophysiology
Antihypertensive drugs
Screening models
References
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3. Cardiac Arrhythmia:
DEFINITION :
• Arrhythmias are deviations from normal heartbeat pattern. They
include abnormalities of impulse formation, such as heart rate, rhythm,
or site of impulse origin and conduction disturbances, which disrupt
the normal sequence of atrial and ventricular activation.
• Failure of impulse initiation, in the sinus node, may result in slow
heart rates (bradyarrhythmia's)
• Abnormally rapid heart rhythms (tachyarrhythmia’s)
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4. 4
Electrical pathway through the heart:
The sinoatrial (sinus) node (1) initiates an
electrical impulse that flows through the right
and left atria (2), making them contract. When
the electrical impulse reaches the
atrioventricular node (3), it is delayed slightly.
The impulse then travels down the bundle of
His (4), which divides into the right bundle
branch for the right ventricle (5) and the left
bundle branch for the left ventricle (5). The
impulse then spreads through the ventricles,
making them contract.
Figure 1:

5. Pathophysiology:
Inadequate acceleration of sinus rate
Failure of sinus impulse formation MI, HT, Coronary spasm
Abrupt sinus prolonged pulse Aortic & mitral valve stenosis
SA node dysfunction Degeneration or Damage of conduction system
AV conduction block Ventricular dysfunction
Arterial dysfunction
CARDIAC ARRHYTHMIA
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6. Pharmacological classification of antiarrhythmics:
CLASS ACTIONS DRUGS
IA Na- channel blockers Quinidine, procainamide, Disopyramide
IB Na- channel blockers Lidocaine, Mexiletine
IC Na- channel blockers Flecainide, Propafenone
II Beta- blockers Propranolol, esmolol
III K- channel blockers Amidarone, dofetilide
IV Ca- channel block Verapamil, diltiazem
V Unknown moa Digoxin, adenosine
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Table 1 ; classification of drugs

7. a. In vivo models:
In vivo models used to screen anti-arrhythmic drugs can be divided into
five groups:-
I. Chemically induced arrhythmia
II. Electrically induced arrhythmia
III. Exercise induced ventricular fibrillation
IV. Mechanically induced arrhythmia
V. Genetically induced arrhythmia
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8. b. In vitro models
In vitro models used to screen anti-arrhythmic drugs can be divided into
five groups:-
I. Isolated guinea pig papillary muscle.
II. Action potential & refractory period in isolated guinea pig papillary
muscle.
III. Lagendorff technique.
IV. Acetylcholine & potassium induced arrhythmia.
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9. Chemically Induced Arrhythmia:
Aconitine antagonism in rats:
Rationale:
▪ Aconitine, a plant alkaloid from aconitine root, acts persistently on
sodium channels and activates it resulting in ventricular arrhythmias.
▪ Drugs considered to have anti-arrhythmic properties can be tested in
aconitine intoxicated rats.
▪ Administered by infusion to anesthetized rats it can produce
ventricular arrythmias of varying intensity depending on the dose.
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10. Procedure :
▪ Males Ivanova rats (300-400 g) are anesthetized intraperitoneally with
urethane (1.25g/ kg).
▪ Aconitine (5 µg/kg) is dissolved in 0.1 N HNO , and continuously
infused into the rat's saphenous vein at a rate of 0.1 ml/min. Lead II
ECG is recorded every 30 sec.
▪ Test compound is injected orally or intravenously 5 min before the
aconitine infusion.
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11. Evaluation :
▪ A higher dose of aconitine in the test group compared to untreated
group gives an index of antiarrhythmic activity.
▪ The antiarrhythmic effect of test compound is measured by the amount
of aconitine /100 g animal (infusion duration) and includes ventricular
extrasystoles tachycardia, fibrillation and death.
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12. Lagendorff technique:
Rationale:
▪ The basic principle involved is that heart is perfused in a retrograde
direction from the aorta either at constant pressure or constant flow
with oxygenated saline solutions.
▪ Retrograde perfusion closes the aortic valves, just as in the in-situ
heart during diastole.
▪ The perfusate is displaced through the coronary arteries flowing off
the coronary sinus and the opened right atrium.
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13. Procedure
▪ Guinea pigs of either sex weighing 300-500 g are anesthetized and
sacrificed.
▪ The heart is removed as quickly as possible and placed in a dish
containing Ringer's solution at 37°C. Associated pericardial and lung
tissues are removed.
▪ The aorta is located and cut below the point of division. A cannula is
inserted into the aorta and tied and the heart is perfused with
oxygenated Ringer's solution.
▪ The heart is transferred to a double wall plexi glass perfusion
apparatus maintained at 37°C.
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14. ▪ Oxygenated Ringer's solution is perfused at a constant pressure of 40
mm Hg at a temperature of 37°C from a reservoir.
▪ Ligature is placed around the LAD coronary artery and occlusion is
maintained for 10 min followed by reperfusion.
▪ Test compound is administered through perfusion medium either
before or after occlusion.
▪ An epicardial ECG electrode is used for pulsatile stimulation and
induction of arrhythmias (rectangular pulses of 0.75 msec duration,
usually of 10 V; frequency 400-1800 shocks per min).
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Figure 2:

16. Figure 2: Experimental setup.
• (A) Diagram of the isolated heart perfusion system; arrows denote the
direction of flow.
• (B) A cannulated heart is shown with electrode placement. RA = right
atria, RV = right ventricle, LV = left ventricle, ECG = lead II
electrocardiogram.
• (C) The imaging platform in close proximity to the heart tissue.
• (D) Emission of each complementary probe (voltage, calcium) is
separated by wavelength using an image splitting device with
appropriate emission filters and dichroic mirror.
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17. Evaluation :
▪ Contractile force is measured isometrically by a force transducer and
recorded on a polygraph.
▪ Heart rate is measured through a chronometer coupled to the
polygraph.
▪ Drugs are injected into the perfusion medium.
▪ Incidence and duration of ventricular fibrillation or ventricular
tachycardia is recorded in the control as well as test group.
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18. References
▪ S K Gupta, Dug Screening Methods; third edition, Page no: 266-304.
▪ N S Parmar, Shiv Prakash, Screening Methods in Pharmacology; Page no: 161-
193.
▪ Avanapu Srinivasa Rao, Namburi Bhagya Lakshmi, Pharmacological Screening
Methods and Toxicology; Page no:196-207.
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19. THANK YOU