Antiarrhythmic drugs by Dr. Md. Saiduzzaman

1. Anti-arrhythmic Drugs
and updates

2. Speaker:
Dr. Md. Saiduzzaman
MD Resident (Neurology),
Mymensingh Medical College Hospital.

3. What is an Arrhythmia?
• The arrhythmias are altered cardiac rhythm
caused by abnormalities in-
– impulse formation (abnormal automaticity)
– conduction in the myocardium (reentry),
– or combination of both.
However, in the cardiology ward, arrhythmias
present as a complex family of disorders that
show a variety of symptoms.

4. Why should we treat arrhythmia?
Arrhythmias can cause serious
complications like-
1. Heart failure.
2. Sudden cardiac death
3. Syncope.
4. Stroke.

5. Factors that precipitate arrhythmia:
− Cardiac ischemia,
– Structural heart disease,
– Hypoxia,
– Acidosis, alkalosis
– Electrolyte disturbances
– Excessive catecholamine exposure
– Exposure to toxic substances
– Unknown etiology

6. The heart cavity from which the arrhythmia originates
gives the name to the arrhythmia
1. Supraventricular
• Ectopic (atrial or AV nodal)
• Multifocal Atrial Tachycardia(MAT)
• Atrial fibrillation and flutter
2. Ventricular
• Ectopic (Extrasystole or PVC)
• Tachycardia
• Ventricular fibrillation

7. ARRHYTHMIAS
Sinus arrythmia
Atrial arrhythmia
Nodal arrhythmia
(junctional)
Ventricular arrhytmia
SVT

8. +30 mV
0 mV
-80 mV
-90 mV
OUTSIDE
MEMBRANE
INSIDE
Na+
0
4
3
2
1
K+
Ca++ K+
Atp
K+
Na+
K+
Ca++
Na+
K+
Na+
Resting
open
Inactivated
Phase zero
depolarization
Early
repolarization
Plateau phase
Rapid
Repolarization
phase
Phase 4
depolarization

9. Antiarrhythmic drugs

10. Vaughn william Classification:

13. Class I – blocker’s of fast Na+ channels
– Subclass IA
• Cause moderate Phase 0 depression
• Prolong repolarization
• Increased duration of action potential
• Includes
– Quinidine – 1st antiarrhythmic used, treat both atrial
and ventricular arrhythmias, increases refractory
period
– Procainamide - increases refractory period but side
effects
– Disopyramide – extended duration of action, used
only for treating ventricular arrhythmias

14. Quinidine-indications and MOA
• Indication: both VA and SVA
• Blocks activated Na+ channel: ↓slope of phase 0 and 4
• Inhibit K+ current:↑phase 3
• Both above effects ↑ Action potential ↑ QT
interval
• α-blocking  vasodilation reflex tachycardia
• Antimuscarinic effect

15. Quinidine-adverse effects
Cardiac Adverse effects:
• torsade depoints (↑QT interval) twisting of peak in ECG
• Proarrhythmogenic effects, AV block or asystole (toxic
dose)
Extracardiac Adverse effects:
• GIT: Diarrhoea,Nausea,Vomiting
• Cinchonism: headache, dizziness, confusion, tinnitus,
deafness, blurring of vision
• Quinidine syncope because of VA (↑QT);
light headedness and fainting

16. • Shortens depolarization.
• Decreased action potential duration
–Lidocaine (also acts as local anesthetic) – blocks
Na+ channels mostly in ventricular cells, also
good for digitalis-associated arrhythmias.
–Mexiletine - oral lidocaine derivative, similar
activity.
–Phenytoin – anticonvulsant that also works as
antiarrhythmic similar to lidocaine.
Subclass IB: Lidocaine, mexiletine, tocainide, phenytoin

17. Class IB-Lidocaine
• t1/2 1-1.5 hr given by I.V loading dose followed by I.V
infusion
• Block both activated & inactivated Na+ channel
• ↓The slope of phase 0 & 4
Main uses:
• Ventricular Arrhythmia following MI.

18. Dose :
IV 75-200 mg flushing, then 2-4 mg/min for 24-
30 hrs.
Flushing dose is given to saturate hepatic
enzymes.
Dose reduction by half is required in conditions
where hepatic blood flow is reduced.
(shock,beta-blocker,hepatic cirrhosis, severe
heart failure)

19. Lidocaine adverse effects
CNS:
drowsiness,
numbness,
parathesia,
slurred speeches,
difficulty of swallowing,
convulsions,
nystagmus,
tremor,
Diplopia
Heart:
• AV block
• ↓contractility

20. • Strong Phase 0 depression
• No effect of depolarization
• No effect on action potential duration
– Flecainide (initially developed as a local anesthetic)
» Potent blocker of Na+ shorten AP
» Potent blocker of K+ prolong AP
» Net result no change
» Slows conduction in all parts of heart,
» Also inhibits abnormal automaticity
Proarrhytmogenic : reserved for life threatening
SVA & VA in pts without myocardial structural
abnormalities
Subclass IC: flecainide, propafenone, moricizine

21. Class IC- Flecainide, Propafenone & Moricizine
– Propafenone
» Has some structural similarities to propranolol
» Weak β – blocker
» Also some Ca2+ channel blockade
» Also slows conduction
» VA & SVA: its spectrum of action similar to that
flecainide
» AE: metallic taste & constipation
– Moricizine
» Derivative of phenothiazine
» Mechanism of action similar to flecainide-VA
» Proarrhythmogenic

22. Class II – β–adrenergic blockers
– Based on two major actions
1) blockade of myocardial β–adrenergic
receptors↓cAMP  ↓ both Na+ & Ca+ current
2) Direct membrane-stabilizing effects related to Na+
channel blockade
↓both automaticity & HR and suppression of abnormal
pacemaker activity
• The AV node is particularly sensitive to β-blockers
• The PR interval is usually prolonged by β-blockers

23. Class II- β–adrenergic blockers
• Propranolol
– Slows SA node and ectopic pacemaker
– Can block arrhythmias induced by exercise or
apprehension
– Other β–adrenergic blockers have similar
therapeutic effect
• Metoprolol ,Nadolol, Atenolol, Acebutolol, Pindolol,
Sotalol, Timolol; prophylactic in MI
• Esmolol (very short acting; I.V exclusively for acute
surgical arrhythmia)

24. Class III – K+ channel blockers
– Cause delay in repolarization and prolonged refractory
period
– Includes:
• Amiodarone – markedly prolongs action potential by
delaying K+ efflux.
• Ibutilide – slows inward movement of Na+ in addition to
delaying K + influx.
• Bretylium – is an older drug that combines general
sympathoplegic actions & a K+ channel blocking effects
in ischemic tissues.
• Dofetilide - is a newer K+ channel blocker prolongs
action potential by delaying K+ efflux.

25. Class III-Amiodarone
• Structurally related to thyroid hormone.
• Effective in most types of arrhythmias & is most
efficacious of all antiarrhythmic, because of toxicities,
mainly used in arrhythmias that are resistant to other
drugs.
• Blocks Na+, Ca+2 & K+ channels and α-& β-receptors
• Marked prolongs the QT interval & QRS duration, it
increases Atrial, AV and Ventricular refractory period.

26. Amiodarone: main clinical use
• It’s a unique wide spectrum anti-arrhythmic drug.
• Pts with AF where rapid rhythm control is needed.
• Recurrent ventricular fibrillation.
• Recurrent haemodynamically unstable ventricular
tachycardia.

27. Dose:
Oral loading dose 600-1200mg; maintenance
dose 200-400mg.
IV 150 mg over 10 mins; then 350 mg over 6 hrs;
then 540 mg over 24 hrs.
Hepatic metabolism; lipid soluble with extensive
distribution in body.

28. Amiodarone: contraindications
• Cardiogenic shock
• Severe sinus node dysfunction
• 2nd or 3rd degree AV block.
• Bradycardia associated with syncope.

29. Amiodarone-adverse effects
• Toxicity due to accumulation
• Hepatic, cardiac, pulmonary fibrosis.
• Thyroid hypo- or hyperthyroidism
• Skin discoloration
• Peripheral neuropathy
• Corneal deposits
• ↑Digoxin level
• Development of new arrhythmia.

31. Class IV – Ca2+ channel blockers
Verapamil & Diltiazem
• slows AV-conduction rate in patients with atrial
fibrillation.
• ↑PR interval
• Verapamil – blocks Na+ channels in addition to Ca2+; also
slows SA node in tachycardia
Suppression of SA node; bradycardia
Slowing of AV node: abolish AV reentry
• Diltiazem
Class IV: Drug of choice for SVA: flutter and fibrillation ?

32. Miscellaneous
• Adenosine I.V bolus (6-12 mg), short t1/2 15 secs
• Markedly slows or completely blocks conduction in
AV node.
• Acts by hyperpolarizing AV node through ↑K+ (Ach-
sensitive K+ channel in SA & AV node) and ↓Ca+2
currents.
• Adverse Effects : flushing, hypotension, dyspnea,
chest pain, bronchospasm.

33. Drugs of choices
S.
No
Arrhythmia Drug
1 Sinus tachycardia Propranolol
2 Atrial extrasystole Propranolol,
3 AF/Flutter Esmolol, verapamil ,digoxin
4 PSVT Adenosine ,esmolol,
amiodarone
5 Ventricular Tachycardia Lignocaine , procainamide ,
Amiodarone
6 Ventricular fibrillation Lignocaine, amiodarone
7 A-V block Atropine , isoprenaline