Adenosine is a vasodilator that is used to treat supra ventricular tachycardia (SVT). It doesn’t act on any ion channel but simply restores the sinus rhythm very rapidly. It is generally considered as class V antiarrhythmic agent.
(A) Class Ia
(B) Class Ib
(C) Class Ic
(D) None of the above
Class Ia drugs also block potassium channels in addition to their sodium channel block. Hence they act both on phase 0 and phase III. Because of their phase III action, they may increase QT interval in ECG and can precipitate Torsade De Pointes.
(C) Magnesium sulfate
Nifedipine is a calcium channel blocker that directly acts on smooth muscle but it has no action on cardiac muscle. On the other hand, verapamil and diltiazem belonging to same category still act on cardiac muscle and used in arrhythmias. Other drugs listed here again used in arrhythmias in few special conditions.
(A) Dilatation of afferent arterioles
(B) Dilatation of efferent arterioles
(C) Constriction of afferent arterioles
(D) Release aldosterone
Glomerular filtration is increased by dilatation of afferent arterioles and constriction of efferent arterioles. Natriuretic peptides are released in heart failure as a compensatory mechanism and cause dilatation of afferent arterioles leading to increase in dieresis.