Introduction:

Supraventricular tachycardia (SVT) is a common cardiac arrhythmia characterized by rapid heart rates originating above the ventricles. Adenosine, a potent pharmacological agent, is frequently employed in the acute management of SVT. This article elucidates the mechanism of action, efficacy, dosing considerations, and clinical implications of adenosine administration for SVT.

Mechanism of Action:

Adenosine acts primarily by activating adenosine A1 receptors in the atrioventricular (AV) node, thereby inhibiting calcium influx and slowing conduction through the AV node. This transient AV nodal block interrupts reentrant tachycardias, such as AV nodal reentrant tachycardia (AVNRT) or AV reentrant tachycardia (AVRT), terminating the arrhythmia.

Efficacy in SVT:

Adenosine is highly effective in terminating SVT, with success rates exceeding 90% in most cases. It rapidly converts narrow-complex SVT to sinus rhythm within seconds of administration, making it a first-line agent for acute SVT management in emergency settings.

Dosing Considerations:

The standard dosing regimen for adenosine in SVT is an initial intravenous bolus of 6 mg administered rapidly followed by a saline flush to ensure delivery to the central circulation. If there is no response within 1-2 minutes, a second bolus dose of 12 mg can be administered in a similar manner. Higher doses may be required in some cases, particularly in patients with refractory SVT or delayed response to initial therapy.

Clinical Considerations:

Several clinical factors should be considered when using adenosine for SVT:

• Electrocardiographic Monitoring: Continuous electrocardiographic monitoring is essential during adenosine administration to detect rhythm changes, including transient AV block, bradycardia, or asystole.
• Patient Positioning: Patients should be positioned supine or semi-recumbent during adenosine administration to minimize the risk of hypotension or syncope.
• Vagal Maneuvers: Vagal maneuvers, such as carotid sinus massage or Valsalva maneuver, can be attempted before adenosine administration to enhance its efficacy in terminating SVT.
• Alternative Routes of Administration: In cases where intravenous access is challenging, alternative routes of adenosine administration, such as intraosseous or intramuscular routes, may be considered.

Adverse Effects:

Adenosine administration may be associated with transient adverse effects, including:

• Bradycardia: Due to its effect on AV nodal conduction, adenosine can induce transient bradycardia or AV block, typically lasting a few seconds to minutes.
• Transient Flushing or Dyspnea: Patients may experience transient flushing, shortness of breath, or a metallic taste in the mouth following adenosine administration, which resolves spontaneously.

Conclusion:

Adenosine is a highly effective and rapidly acting pharmacological agent for terminating SVT by interrupting reentrant tachycardias involving the AV node. With proper dosing, careful patient monitoring, and attention to clinical considerations, adenosine administration is safe and can restore sinus rhythm promptly in patients with SVT.

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