What is the role of adenosine in diagnosing and treating undifferentiated regular stable wide-complex tachycardia?

Role of Adenosine in Undifferentiated Regular Stable Wide-Complex Tachycardia

Adenosine is relatively safe for both diagnosis and treatment of undifferentiated regular stable monomorphic wide-complex tachycardia when the etiology cannot be determined (Class IIb, LOE B). 1

Diagnostic Value

Adenosine helps differentiate the origin of wide-complex tachycardia through its effects:

• Terminates SVT involving the AV node (revealing the underlying mechanism)
• Produces transient AV block that can unmask atrial arrhythmias
• Has minimal effect on ventricular tachycardia (VT), helping confirm VT diagnosis
• May reveal retrograde atrial activation patterns by producing ventriculoatrial dissociation

The diagnostic accuracy of adenosine in wide-complex tachycardias has been reported at approximately 92%, making it a valuable diagnostic tool when the ECG diagnosis is uncertain. 2

Treatment Value

• May terminate the tachycardia if it is supraventricular in origin with aberrancy
• Can convert AV nodal reentrant tachycardias and accessory pathway-mediated tachycardias
• Extremely short half-life (<10 seconds) allows for rapid recovery if ineffective

Contraindications and Precautions

Adenosine should NOT be used in:

• Unstable patients (immediate cardioversion is indicated) 1
• Irregular or polymorphic wide-complex tachycardias 1
• Patients with known Wolff-Parkinson-White syndrome with pre-excited atrial fibrillation
• Patients with severe asthma (due to risk of bronchospasm) 3

Administration Protocol

1. Ensure patient is on continuous cardiac monitoring with resuscitation equipment available
2. Start with 6 mg rapid IV bolus followed by saline flush
3. If ineffective after 1-2 minutes, administer 12 mg IV bolus
4. Maximum of two 12 mg doses if needed

Potential Adverse Effects

• Transient side effects (lasting <1 minute): flushing, dyspnea, chest pain 4
• Ventricular pauses >2 seconds (reported in 16% of patients) 2
• Potential to induce ventricular fibrillation in patients with coronary artery disease 5
• Early recurrence of arrhythmia (reported in 35% of patients with junctional tachycardias) 2

Algorithm for Wide-Complex Tachycardia Management

1. Assess hemodynamic stability

   • If unstable: Immediate synchronized cardioversion (Class I, LOE B) 1
   • If stable: Proceed with diagnostic evaluation

2. For stable regular monomorphic wide-complex tachycardia:

   • Consider adenosine for both diagnosis and potential treatment (Class IIb, LOE B) 1
   • If adenosine fails or is contraindicated, consider:
     • Procainamide (Class IIa, LOE B) 1, 6
     • Amiodarone (Class IIb, LOE B) - preferred in patients with heart failure 1, 6
     • Sotalol (Class IIb, LOE B) 1

3. If antiarrhythmic therapy is unsuccessful:

   • Proceed to synchronized cardioversion (Class IIa, LOE C) 1
   • Consider expert consultation 1

Important Caveats

• Verapamil is absolutely contraindicated for wide-complex tachycardias unless known to be supraventricular in origin (Class III, LOE B) 1, 6
• Procainamide and sotalol should be avoided in patients with prolonged QT interval 1
• Multiple antiarrhythmic agents should not be given without expert consultation 1
• While adenosine is generally safe, be aware that it can occasionally induce ventricular fibrillation in patients with ventricular tachycardia 5

By following this approach, adenosine can serve as both a diagnostic and potentially therapeutic agent in the management of undifferentiated regular stable wide-complex tachycardia, while minimizing risks through appropriate patient selection and monitoring.