What is the recommended use of adenosine for treating supraventricular tachycardia (SVT) in patients with stable blood pressure, considering their medical history, including conditions like asthma or chronic obstructive pulmonary disease (COPD)?

Adenosine for Supraventricular Tachycardia

Adenosine is the recommended first-line pharmacologic agent for acute treatment of regular SVT in hemodynamically stable patients, administered as 6 mg rapid IV push followed by 12 mg doses if needed, but is absolutely contraindicated in patients with asthma due to risk of severe bronchospasm. 1, 2

Administration Protocol

For patients with stable blood pressure and regular SVT:

• Administer adenosine 6 mg as a rapid IV bolus through a large proximal vein, followed immediately by a 20 mL saline flush 2
• If no conversion within 1-2 minutes, give 12 mg IV push 2
• May repeat 12 mg dose once more if necessary 2
• Success rate is 90-95% for AVNRT and 78-96% for AVRT 1, 2

Critical Contraindication: Asthma and COPD

Adenosine should NOT be given to patients with asthma due to risk of severe, potentially life-threatening bronchospasm 2, 3. The FDA labels this as an absolute contraindication for "bronchoconstriction or bronchospasm (e.g., asthma)" 3.

• Severe bronchospasm can occur even in patients without known pulmonary disease 4
• Use with extreme caution in COPD patients with obstructive lung disease not associated with active bronchospasm (e.g., emphysema, bronchitis) 3
• Discontinue immediately if severe respiratory difficulties develop 3
• Have aminophylline available for reversal if bronchospasm occurs 4

Dose Modifications for Special Populations

Reduce initial dose to 3 mg in:

• Patients taking dipyridamole or carbamazepine 2
• Heart transplant recipients 2
• Administration via central venous access 2

Increase dose requirements for:

• Patients with significant theophylline, caffeine, or theobromine levels 2, 3

Safety Considerations

• Have a defibrillator immediately available, especially if Wolff-Parkinson-White syndrome is a consideration, as adenosine may precipitate atrial fibrillation with rapid ventricular rates 2
• Monitor continuously during and after administration 2
• Common transient side effects include flushing, dyspnea, and chest discomfort lasting <60 seconds 2, 5
• Adenosine is safe and effective during pregnancy 2

Post-Conversion Management

• Watch for immediate recurrence, which commonly occurs within seconds to minutes 2
• If recurrence develops, consider longer-acting AV nodal blocking agents (diltiazem, verapamil, or beta-blockers) rather than repeat adenosine 2
• Premature complexes post-conversion are triggers for recurrence and may warrant prophylactic AV nodal blockade 2

Alternative Agents When Adenosine is Contraindicated

For asthma/COPD patients with stable SVT:

• IV diltiazem 15-20 mg over 2 minutes (64-98% conversion rate) 1, 6
• IV verapamil 2.5-5 mg over 2 minutes 1, 6
• IV beta-blockers (though use cautiously in severe COPD) 1

Critical pitfall: Never use calcium channel blockers if wide-complex tachycardia cannot be definitively distinguished from ventricular tachycardia, as this may cause hemodynamic collapse 7, 6.

Hemodynamically Unstable Patients

• Proceed directly to synchronized cardioversion if patient shows hypotension, altered mental status, signs of shock, chest pain, or acute heart failure 1
• Adenosine may still be considered first if tachycardia is regular with narrow QRS complex 1