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Pharmacology

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Cardiovascular Systems

Question
73 out of 84
 

Which of the following is false regarding anti-arrhythmic? (AIIMS May 2010)



A Amiodarone belongs to class III and acts by prolonging APD

B Verapamil belongs to class II and acts by blocking fast Na+ channel

C Mexiletine belongs to class Ib and acts by decreasing refractory period

D Quinidine belongs to class Ic and acts by prolonging APD

Ans. B Verapamil Belongs To Class Ii And Acts By Blocking Fast Na+ Channel

The major electrophysiological effects resulting from 'block' of cardiac calcium ion channels are in slow-response tissues, the sinus, and AV nodes. Only verapamil, diltiazem, and bepridil blocks calcium ion channels in cardiac cells at clinically used doses. With these drugs heart rate is generally reduced, although hypotension, if marked, can cause reflex sympathetic activation and tachycardia.

AV nodal conduction velocity decreases increasing the PR interval. AV nodal block occurs as a result of decremental conduction as well as increased AV nodal refractoriness.

These later effects form the basis of the antiarrhythmic actions of the calcium channel blockers in re-entrant arrhythmias whose circuit involves the A V node, such as A V re-entrant tachycardia.

Classification of antiarrhythmic drugs

Class I

Sodium ion channel blockers

Class II

Beta blockers

Class III

Action potential prolongation agents (usually by potassium ion-channel blockage)

Class IV

Calcium channel blockers

Cardiovascular Systems Flashcard List

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