What is the role of Verapamil (Calaptin) in the management of supraventricular tachycardia (SVT)?

Role of Verapamil (Calaptin) in SVT Management

Verapamil is effective for acute conversion of paroxysmal supraventricular tachycardia (SVT) but should be used as a second-line agent after adenosine and beta blockers due to its risk of hypotension. 1, 2

Mechanism of Action

• Verapamil inhibits calcium ion influx through slow channels into myocardial cells, affecting the SA and AV nodes 2
• By inhibiting calcium influx, verapamil slows AV conduction and prolongs the effective refractory period within the AV node 2
• This mechanism interrupts reentry at the AV node, restoring normal sinus rhythm in patients with paroxysmal SVT 2

Acute Management of SVT

• First-line treatments for acute SVT are vagal maneuvers and adenosine (Class I recommendation) 3
• Intravenous verapamil is recommended as a second-line option (Class IIa recommendation) for hemodynamically stable patients 1
• Conversion rates with IV verapamil range from 60-80% of patients with SVT returning to normal sinus rhythm within 10 minutes 2
• For patients with atrial flutter/fibrillation, verapamil decreases ventricular rate by at least 20% in about 70% of cases 2
• Synchronized cardioversion is recommended for hemodynamically unstable SVT when pharmacological therapy is ineffective 4

Specific Considerations

• Verapamil should be avoided in patients with:
  • Suspected ventricular tachycardia (can cause severe hypotension or cardiac arrest) 5
  • Pre-excited atrial fibrillation (can accelerate ventricular response) 2
  • Systolic heart failure (negative inotropic effects) 1
  • Severe hypotension 2
  • Second or third-degree AV block without pacemaker 2
• In pregnant patients, IV verapamil may be reasonable for acute treatment when adenosine and beta blockers are ineffective or contraindicated (Class IIb recommendation) 4
• Risk of maternal hypotension is higher with verapamil than with adenosine in pregnant patients 4

Dosing and Administration

• Standard IV dose is 5-10 mg 2
• Slow infusion (up to 20 minutes) may reduce the risk of hypotension 1
• Peak therapeutic effects occur within 3-5 minutes after bolus injection 2
• Pre-treatment with calcium has been reported to potentially mitigate verapamil-induced hypotension 6

Long-term Management

• Oral verapamil is a Class I recommendation for ongoing management of symptomatic SVT in patients without ventricular pre-excitation 1, 3
• Long-term prophylaxis with oral verapamil has shown good control of SVT symptoms in follow-up studies 7, 8
• Electrophysiological study with catheter ablation is considered definitive treatment for SVT and should be considered for patients with frequent or poorly tolerated episodes 3

Efficacy Based on SVT Type

• Verapamil appears more effective in SVT due to AV nodal re-entry than in SVT due to concealed accessory pathway 7
• For Wolff-Parkinson-White syndrome, verapamil has shown variable efficacy and should be used with caution 9

Safety Considerations

• A small fraction (<1%) of patients may experience life-threatening adverse responses including:
  • Rapid ventricular rate in atrial flutter/fibrillation with accessory bypass tract
  • Marked hypotension
  • Extreme bradycardia/asystole 2
• Initial use should be in a treatment setting with monitoring and resuscitation facilities 2