What is the management of Supraventricular Tachycardia (SVT) refractory to adenosine?

From the Guidelines

For SVT refractory to adenosine, consider alternative pharmacological agents such as beta-blockers (esmolol 500 mcg/kg IV bolus followed by infusion, or metoprolol 5 mg IV) as the first-line treatment, as recommended by the latest guidelines 1.

Rationale

The latest European Society of Cardiology (ESC) guidelines for the management of patients with supraventricular tachycardia, published in 2020, recommend beta-blockers as the first-line treatment for acute management of narrow-QRS tachycardias and atrioventricular re-entrant tachycardia (AVRT) 1.

Key Points to Consider

• Adenosine remains the drug of choice for the acute therapy of SVT when vagal maneuvers fail, but its effectiveness may be limited in certain cases 1.
• If pharmacological management fails, synchronized electrical cardioversion starting at 50-100 joules should be performed, especially if the patient is hemodynamically unstable.
• For long-term management, catheter ablation is highly effective and should be considered.
• Adenosine resistance may occur due to high catecholamine states, methylxanthine use (caffeine, theophylline), or certain SVT mechanisms like atrial tachycardia or atrial flutter.
• When adenosine fails, it's essential to reassess the rhythm diagnosis, as what appears to be SVT might actually be atrial flutter with rapid ventricular response or ventricular tachycardia, which would require different management approaches.

Monitoring and Follow-up

Always ensure the patient is on continuous cardiac monitoring during treatment attempts. Some key points to keep in mind when managing SVT refractory to adenosine include:

• The importance of prompt recognition and treatment of hemodynamically unstable patients
• The need for careful consideration of the underlying rhythm mechanism and potential causes of adenosine resistance
• The role of alternative pharmacological agents, such as beta-blockers, in the management of SVT
• The potential benefits and risks of synchronized electrical cardioversion and catheter ablation in the treatment of SVT.

From the FDA Drug Label

Apart from studies in patients with VT or VF, described below, there are two other studies of amiodarone showing an antiarrhythmic effect before significant levels of DEA could have accumulated A placebo-controlled study of intravenous amiodarone (300 mg over 2 hours followed by 1200 mg/day) in post-coronary artery bypass graft patients with supraventricular and 2- to 3-consecutive-beat ventricular arrhythmias showed a reduction in arrhythmias from 12 hours on

• SVT refractory to adenosine may be treated with amiodarone, as it has shown an antiarrhythmic effect in patients with supraventricular arrhythmias.
• The recommended dose is not explicitly stated for SVT, but the drug label recommends a starting dose of about 1000 mg over the first 24 hours of therapy for life-threatening arrhythmias, delivered by a specific infusion regimen 2.
• It is essential to note that the effectiveness of amiodarone for SVT refractory to adenosine is not directly addressed in the provided drug labels, and the information is based on studies of patients with VT or VF and other supraventricular arrhythmias.
• Close monitoring with adjustment of dose is essential, as amiodarone shows considerable interindividual variation in response 2.

From the Research

SVT Refractory to Adenosine

• SVT (Supraventricular Tachycardia) is an abnormal rapid cardiac rhythm that involves atrial or atrioventricular node tissue from the His bundle or above 3
• The condition is caused by reentry phenomena or automaticity at or above the atrioventricular node, and includes atrioventricular nodal reentrant tachycardia, atrioventricular reciprocating tachycardia, and atrial tachycardia 4
• Adenosine is effective in the acute setting for terminating SVT, but in some cases, it may be refractory to standard doses 5, 6
• High-dose adenosine may be required in refractory supraventricular tachycardia, with doses up to 24 mg or 36 mg being administered in some cases 5, 6
• Calcium channel blockers (diltiazem or verapamil) or beta blockers (metoprolol) can be used acutely or as long-term therapy for SVT, and catheter ablation has a success rate of 95% and recurrence rate of less than 5% 3, 4
• In patients who are hemodynamically unstable, synchronized cardioversion is first-line management, while in those who are hemodynamically stable, vagal maneuvers are first-line management, followed by stepwise medication management if ineffective 3

Management of Refractory SVT

• Refractory SVT may require collaboration with an expert in cardiac electrophysiology and deviation from standard dosing recommendations for adenosine 6
• High-dose adenosine may be effective in terminating refractory SVT, but its use should be carefully considered and monitored due to potential side effects 5, 6
• Alternative treatments, such as calcium channel blockers or beta blockers, may be considered in patients who are refractory to adenosine 3, 4
• Catheter ablation may be a viable option for long-term management of refractory SVT, particularly in patients with recurrent, symptomatic episodes 3, 4