Overview of Adenosine in SVT Management

A Table to recap the key information about Adenosine in the management of Supraventricular Tachycardia (SVT) and other relevant aspects:

Category	Details
Drug Name	Adenosine
Mechanism of Action	Slows conduction through the AV node, interrupts reentrant pathways.
Indications	- Paroxysmal Supraventricular Tachycardia (SVT)
	- Diagnostic utility in tachycardia to uncover underlying atrial activity.
Dosage	- Initial Dose: 0.1 mg/kg IV bolus
	- If ineffective, double the dose to a maximum of 0.2 mg/kg.
Administration Technique	Double Syringe Technique
	1. Rapidly administer adenosine using a syringe.
	2. Immediately follow with a rapid saline flush using a second syringe.
ECG Interpretation	SVT Characteristics
	- Narrow QRS complex (<120 ms).
	- Regular rhythm, heart rate between 150-250 bpm.
	- P waves may be absent, retrograde, or buried.
	Monomorphic VT Characteristics
	- Wide QRS complex (>120 ms) with uniform morphology.
Contraindications	- Second or third-degree AV block without a pacemaker.
	- Sick sinus syndrome without a pacemaker.
	- Bronchospastic diseases (e.g., asthma).
	- Known hypersensitivity to adenosine.
Complications/Side Effects	- Flushing
	- Chest discomfort
	- Dyspnea
	- Light-headedness
	- Brief period of asystole or bradycardia.
Use in Monomorphic VT	- Use with caution. Ensure no structural heart disease or ischemia.
Post-Administration ECG	- Restoration of normal sinus rhythm if effective.
	- Continuous ECG monitoring is necessary to evaluate efficacy and guide further treatment.
Conclusion	Adenosine is vital for SVT management with rapid action. Proper understanding of indications, contraindications, and interpretation of ECG is crucial. The double syringe technique optimizes efficacy.

Additional Notes:

1. Clinical Implications: Adenosine is effective and safe when used correctly but requires rapid administration due to its short half-life.

2. Double Syringe Technique: This technique ensures rapid delivery to the central circulation, crucial due to adenosine's extremely short half-life (~10 seconds). It maximizes the drug's potential to terminate SVT effectively.

3. Important Considerations: Always assess patient history for contraindications and monitor the patient closely for any adverse reactions or complications post-administration.
   

Key Points to Remember:

• Initial Dose: 0.1 mg/kg IV; if needed, increase to 0.2 mg/kg.

• Use: Primarily for SVT but cautiously for monomorphic VT.

• ECG: Essential for confirming the diagnosis and monitoring post-administration.

This table provides a concise and comprehensive overview of adenosine use in clinical practice, focusing on its application in SVT management.

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Introduction to Adenosine Adenosine is an endogenous nucleoside with multiple physiological roles, including the modulation of myocardial oxygen consumption and coronary blood flow. Clinically, adenosine is primarily used for the acute management of specific supraventricular tachycardias (SVTs).

Mechanism of Action Adenosine works by slowing conduction through the atrioventricular (AV) node and interrupting reentrant pathways, which are often the underlying mechanisms of SVTs. This action can result in the temporary cessation of the heart's electrical activity, leading to a "reset" that can restore normal rhythm.

Indications for Use Adenosine is indicated for:

• Paroxysmal SVT: Adenosine is the drug of choice for the acute termination of paroxysmal SVTs, including those associated with accessory bypass tracts (e.g., Wolff-Parkinson-White syndrome).

• Diagnostic Utility: It can help diagnose the type of tachycardia by revealing the underlying atrial activity during a slow AV nodal conduction.
  

Dosage and Administration The recommended initial dose of adenosine for SVT is 0.1 mg/kg administered rapidly IV, followed by a saline flush. If the initial dose is ineffective, it can be doubled to a maximum dose of 0.2 mg/kg.

Double Syringe Technique The double syringe technique is employed to ensure the rapid administration of adenosine and immediate follow-up with a saline flush. This technique involves two syringes: one containing adenosine and the other saline. The adenosine is administered first, immediately followed by the saline flush. This method ensures the medication reaches the heart quickly and maximizes its efficacy.

Electrocardiogram (ECG) Interpretation in SVT

• SVT Characteristics: SVT typically presents on an ECG with a narrow QRS complex (<120 ms), regular rhythm, and a heart rate typically between 150-250 bpm.

• Identification: P waves may be absent, buried in the preceding T wave, or seen as retrograde P waves (if AV nodal reentrant tachycardia is present).
  

Use in Monomorphic Ventricular Tachycardia (VT) While adenosine is primarily used for SVT, it can occasionally be employed in certain cases of monomorphic VT. However, its use in VT is more controversial and should be approached with caution.

• Monomorphic VT Characteristics: This presents with a wide QRS complex (>120 ms) and uniform QRS morphology on the ECG.

• Considerations: Before administration, it is critical to ensure that the tachycardia is not due to underlying structural heart disease or ischemia, as adenosine may precipitate adverse effects in such scenarios.
  

Contraindications Adenosine is contraindicated in:

• Patients with second or third-degree AV block without a functioning pacemaker.

• Sick sinus syndrome without a pacemaker.

• Bronchospastic diseases (e.g., asthma).

• Known hypersensitivity to adenosine.
  

Complications and Side Effects Common side effects include:

• Flushing

• Chest discomfort

• Dyspnea

• Light-headedness

• A brief period of asystole or bradycardia
  

Post-Adenosine Administration ECG Interpretation Following adenosine administration, the ECG should be closely monitored. Effective termination of SVT will result in the restoration of normal sinus rhythm. Failure to convert may necessitate additional doses or alternative therapies.

Conclusion Adenosine is a crucial agent in the acute management of SVT due to its rapid onset and efficacy. Understanding its indications, correct dosage, contraindications, and interpretation of the post-administration ECG is vital for effective patient care. The double syringe technique enhances the delivery and effectiveness of adenosine, ensuring prompt therapeutic action.

By adhering to these guidelines and accurately interpreting ECGs, healthcare providers can ensure appropriate use of adenosine and optimize outcomes for patients experiencing SVT and, in specific scenarios, monomorphic VT.