What is the action of adenosine in tachycardia?

Introduction: Adenosine is an endogenous nucleoside used as a first-line pharmacological intervention for Supraventricular Tachycardia (SVT). It acts on A1 receptors coupled to Gi proteins, leading to the activation of acetylcholine-sensitive inward rectifying potassium channels and the inhibition of adenylyl cyclase within the specialized cardiac conduction tissues. A. Adenosine acts primarily by DECREASING AV NODE conduction. By slowing the conduction time through the ATRIOVENTRICULAR NODE, it can effectively interrupt re-entry pathways that sustain SVT. This action often results in a brief period of asystole, which allows the sinoatrial node to regain control as the dominant pacemaker. B. While adenosine has some indirect effects on calcium currents by antagonizing cyclic AMP, it is not classified as a calcium channel blocker. Medications like diltiazem or verapamil are the primary agents that inhibit L-type calcium channels to slow the heart rate, whereas adenosine's mechanism is distinct and much shorter-acting. C. Adenosine does not increase cardiac contractility; in fact, its effect on the atria is negatively inotropic. Increasing contractility (positive inotropy) is a characteristic of catecholamines or phosphodiesterase inhibitors like milrinone. Adenosine's therapeutic utility is strictly related to its potent, albeit transient, dromotropic effect on the conduction system. D. Prolonging the QT interval is a characteristic of Class IA and Class III antiarrhythmics, such as amiodarone or sotalol. Adenosine has an extremely short half-life of less than 10 seconds and does not cause significant prolongation of the QT interval. Its focus is the rapid termination of nodal re-entrant tachycardias.