What is the first drug of choice and its dosage for Paroxysmal Supraventricular Tachycardia (PSVT) in an emergency?

First-Line Drug Treatment for PSVT in Emergency

Adenosine is the first drug of choice for treating paroxysmal supraventricular tachycardia (PSVT) in an emergency setting, with an initial dose of 6 mg given as a rapid IV bolus followed by a 20 mL saline flush. 1

Treatment Algorithm for PSVT

Initial Assessment and Stabilization

• For hemodynamically unstable patients with PSVT, synchronized cardioversion is recommended 1
• For hemodynamically stable patients, proceed with pharmacological management 1

First-Line Pharmacological Treatment

• Step 1: Attempt vagal maneuvers (Valsalva maneuver or carotid sinus massage) 1, 2
• Step 2: If vagal maneuvers fail, administer adenosine:
  • Initial dose: 6 mg IV as a rapid bolus through a large vein (e.g., antecubital) followed by a 20 mL saline flush 1
  • If no response within 1-2 minutes: Give 12 mg IV as a rapid bolus followed by a 20 mL saline flush 1
  • If still no response: May repeat 12 mg dose once more 1, 3

Administration Technique for Adenosine

• Use the largest accessible vein, preferably antecubital 1
• Administer as a rapid IV push followed immediately by saline flush 1, 4
• Continuous ECG monitoring is required during administration 1

Second-Line Treatment Options

If adenosine fails or is contraindicated:

• Calcium channel blockers: Diltiazem or verapamil 1
  • Diltiazem: 15-20 mg (0.25 mg/kg) IV over 2 minutes; may repeat with 20-25 mg in 15 minutes if needed 1
  • Verapamil: 2.5-5 mg IV over 2 minutes; may repeat with 5-10 mg every 15-30 minutes to total dose of 20-30 mg 1, 2
• Beta-blockers: Esmolol, metoprolol 1

Important Considerations and Precautions

Adenosine Contraindications

• Second or third-degree AV block (unless patient has functioning pacemaker) 5
• Sick sinus syndrome or symptomatic bradycardia 5
• Bronchoconstrictive or bronchospastic lung disease (e.g., asthma) 1, 5
• Known hypersensitivity to adenosine 5

Dosage Adjustments

• Reduce initial dose to 3 mg in patients:
  • Taking dipyridamole or carbamazepine
  • With transplanted hearts
  • When administered via central venous access 1
• Larger doses may be required for patients with significant blood levels of theophylline, caffeine, or theobromine 1

Common Side Effects

• Side effects are common but transient and include flushing, dyspnea, and chest discomfort 1, 6
• A defibrillator should be immediately available during administration 1
• Adenosine may induce atrial fibrillation with rapid ventricular rates in patients with Wolff-Parkinson-White syndrome 1

Efficacy

• Adenosine successfully converts 80-90% of PSVT cases 6, 3
• Approximately 70% of patients convert with the initial 6 mg dose 3, 7
• If adenosine fails, calcium channel blockers have conversion success rates of 64-98% 1

Special Situations

• In patients with impaired venous return to the right heart (e.g., pulmonary hypertension), higher doses of adenosine may be required for effective termination of PSVT 8
• For pediatric patients, the initial dose is 0.1 mg/kg with a maximum first dose of 6 mg 1