PSVT

Paroxysmal supraventricular tachyarrthymias (PSVT) may be managed, depending upon clinical presentation, by increasing the vagal tone at the AV node

• Valsalva maneuver

• Alpha-adrenergic receptor agonist administration

• digoxin administration

• by administration of drugs that reduce AV transmission:

  • Adenosine , verapamil , diltiazem , esmolol or DC cardioversion.

    • Adenosine (Adenocard)

      • Effects mediated through G protein-coupled adenosine receptor.

      • Activates acetylcholine-sensitive K+ current in the atrium and sinus and A-V node.

      • Decreases action potential duration, reduces automaticity

      • Increases A-V nodal refractoriness

      • Rapidly terminates re-entrant supraventricular arrhythmias (I.V)

    • Verapamil (Isoptin, Calan) & Diltiazem (Cardiazem)

      • Blocks cardiac calcium channels in slow response tissues, such as the sinus and AV nodes.

      • Useful in treating AV reentrant tachyarrhythmias and in management of high ventricular rates secondary to atrial flutter or fibrillation.

      • Major adverse effect (i.v. administration) is hypotension. Heart block or sinus bradycardia can also occur.

    • Esmolol (Brevibloc)

      • Esmolol is a very short acting, cardioselective beta-adrenergic receptor antagonist.

      • i.v. administration is used for rapid beta-receptor blockade in treatment of atrial fibrillation with high ventricular following rates.

      • Antiarrhythmic effects are due mainly to beta-adrenergic receptor blockade. Normally, sympathetic drive results in increased in Ca²⁺ ,K⁺and Cl^- currents.

      • Increased sympathetic tone also increases phase 4 depolarization (heart rate goes up), and increases DAD (delayed afterdepolarizations) and EAD (early afterdepolarization) mediated arrhythmias. These effects are blocked by beta-adrenergic receptor blockers.

      • Beta-adrenergic receptor blockers

        • increase AV conduction time

        • increase AV nodal refractoriness, thereby helping to terminate nodal reentrant arrhythmias

Category: Pharmacology Notes