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MCQ on antiarrhythmic agents: Page-4

Which of the following drugs can produce torsade de pointes

(A) Q and S

(B) P and R

(C) S only

(D) R only

Sotalol is class II agent which may increase QT interval and can precipitate Torsade De Pointes. Verapamil is class IV, Lidocaine in class Ib and flecainide is class Ic all have no role on potassium channels. Class Ia drugs like quinidine, disopyramide and procainamide also block potassium channels in addition to their sodium channel block and can precipitate Torsade De Pointes.

The drugs which have fast association and fast dissociation kinetics towards sodium channels are

(A) Class Ia

(B) Class Ib

(C) Class Ic

(D) Class III

Class Ib has fast association and dissociation , class Ic has slow association and dissociation whereas class Ia drugs have intermediate rate of association and dissociation from sodium channels. Class Ib drugs also shorten phase III repolarisation therefore shorten the action potential duration. Class Ia drugs have additional class III activity by blocking potassium channels which delays repolarisation. Hence these drugs increase action potential duration. Class Ic drugs have no additional action and show little effect on action potential duration.

Pain produced in cardiac ischaemia can be due to the release of

(A) 5-HT

(B) Adenosine

(C) Histamine

(D) Dopamine

Pain in cardiac ischemia is a sign of inadequate blood supply to the myocardium. In this condition adenosine is released which is a potent nociceptor that can induce pain.

Which of the following drug decreases action potential duration

(A) Class Ia

(B) Class Ib

(C) Class Ic

(D) Class III

Class Ib decrease, class Ia and class IIII increase action potential duration.

Adenosine receptors are coupled with

(A) IP 3/DAG

(B) Increase in cAMP

(C) Decrease in cAMP

(D) opening of K + channels

Adenosine acts on A1 receptors which are coupled with opening of potassium channels resulting in decrease in the rate of contraction of the heart. It also decreases AV conduction. Hence adenosine is a drug of choice in supraventricular tachycardia.