Antiarrythmic drugs part IIDr Mirunalini R Asst. ProfessorDept. of Pharmacology

A N TIARRHYTHMICS

ELECTROPHYSIOLOGY OF CARDIAC RHYTHM

-90mV

-80mV

0 mV

+30mV

Out Side

In Side

Na+K+

ATPase

PHASE 4Diastolic Depolarization

Ca++

Na+

Exchan

K

Ca Na

A N TIARRHYTHMICS

ELECTROPHYSIOLOGY OF CARDIAC RHYTHM

Capable Of generating Their own Impulse

1. Abnormal Impulse Generation2. After depolarization3. Abnormal impulse conduction

Reentry

Class I: Na+ channel Blockers1a: Quinidine, Procainamide, Disopyramide1b: Lidocaine, Phenytoin, Mexiletine Tocainide1c: Propafenone, Flecainide, Encainide

Class I: Na+ channel Blockers1a: Quinidine, Procainamide, Disopyramide1b: Lidocaine, Phenytoin, Mexiletine Tocainide1c: Propafenon, Flecainide, Encainide, moricizine

Class II: Beta BlockersPropanolol, Esmolol, metoprolol, acebutolol

Class III: Potassium Channel BlockersAmiodarone, Dofetilide,ibutilide, bretylium, sotalol

CLASSIFICATION

ANTIARRHYTHMICS

Vaughan William & Singh

Class IV: Calcium Channel BlockersVerapamil, diltiazem

Class V: MiscellaneousAdenosine, potasssium, magnesium, Amrinone, Milrinone

CLASSIFICATION

ANTIARRHYTHMICS

Vaughan William & Singh

Block the adrenergic stimulation of cardiac B receptors

Decreases slope of Phase 4 depolarization and Automaticity in SA Node.

Prolongs ERP & AP by decreasing conduction. Decrease heart rate

Propranolol, acebutalol, metoprolol, esmolol

DRUGS

ANTIARRHYTHMICS

Class II

MOA

Prolong the duration of AP & ERP by affecting phase 0

Also blocks Na+ channels, beta blocking & Ca2+ channel blocking action also

DRUGS

ANTIARRHYTHMICS

Class III AMIODARONE

MOA

ALL ACTION

supraventricular arrhythmias. VT and VF are most important indications. 300 to 600 mg/day 150 mg iv for 10 min Heart block Pulmonary toxicity, hepatitis, photo dermatitis,

corneal deposits, hypo & hyperthyoidism

DRUGS

ANTIARRHYTHMICS

AMIODARONE

USE & AE

Fall in BP, Bradycardia and Myocardial depression. Nausea, GI upset. Photosensitization and skin pigmentation . Corneal micro deposits: On long term Use. Pulmonary alveolitis and fibrosis. Peripheral neuropathy Interferes with thyroid function.

DRUGS

ANTIARRHYTHMICS

AMIODARONE

ADVERSE EFFECTS

Dronedarone• Noniodinated congener ;less toxic• No interference with thyroid• No hypothyroidism, pul fibrosis& peri neuropathy• SVT/ maintain sinus rhythm• Adr : GI,cardiac & skin reactions• CI:- CHF , AV block

Bretylium – adrenergic blocker. For life threatening resistant VT. Only in ICU. Parotid swelling

Sotalol – both class II & III action

Ibutilide & dofetilide – only class IIIconvert AF /AFI to sinus rhythm

DRUGS

ANTIARRHYTHMICS

Class III

Other drugs

Calcium Channel Blocker Blocks L type Ca2+ Channels Phase 4 Depolarisation of SA node & prolong ERP.Diltiazem & verapamil Used in supra ventricular & PSVT Ankle edema,constipation & lassitude

DRUGS

ANTIARRHYTHMICS

Class IV

MOA, USES & AE

First drug of choice in PSVT. Administration by rapid i.v inj ; terminates attack

within 30 sec.(3mg) Activates K+ channels by acting through A1 type of

Adenosine receptor on SA node.; prolongation of ERP in AV node; shortening of AP in atrium.

Facial flushing, bronchospasm, dyspnea, chest pain…

DRUGS

ANTIARRHYTHMICS

MISC - ADENOSINE

MECHANISM OF ACTION

Advantage Efficacy equivalent or better than verapamil. Action lasts for 30 sec to 1 min. No haemodynamic deterioration. Safe in wide QRS tachycardia. Effective in patients not responding to verapamil. Other uses: brief coronary vasodilation,controlled

hypotention during surgery

DRUGS

ANTIARRHYTHMICS

ADENOSINE

Drugs for AV block• Mainstay of treatment is pacemaker• For acute & transient cases drugs are used• Atropine• Sympathomimetics: Isoprenaline, Adr

Summary • Asymptomatic • Chronic prophylaxix- propranolol amiodarone• Arrythmia is life threatening, hypotention, asso with palpitation,

activity limitation- need vigorous therapy• Choice- ECG, Mech, pK profile,, hemodynamic effect• Aim- to restore sinus rhythm