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.
Verapamil is class IV, propranolol in class II, Sotalol is class III and encainide is class Ic.
Lidocaine has high extraction by liver and used to estimate hepatic blood flow.
(A) Ectopic pacemaker activity
(C) Delayed after depolarization
(D) Heart failure
It is the heart block but not heart failure. Heart block because of a decreased conduction at AV node may lead to ventricular arrhythmias.
Phenytoin is both class Ib antiarrhythmic agent as well as anticonvulsant. Nowadays its use is mainly confined to convulsions.