MCQ on antiarrhythmic agents: Page-4

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.

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 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.

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

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.