Can beta blockers be given in Supraventricular Tachycardia (SVT) due to an accessory pathway?

Beta Blockers in SVT Due to Accessory Pathways

Beta blockers should NOT be given in SVT with pre-excitation (manifest accessory pathway) but CAN be safely used in SVT with concealed accessory pathways (no pre-excitation on ECG).

Critical Distinction: Manifest vs. Concealed Pathways

The safety of beta blockers depends entirely on whether pre-excitation is visible on the resting ECG:

Manifest Accessory Pathways (Pre-excitation Present)

Beta blockers are contraindicated in patients with pre-excitation on their resting ECG 1. This includes:

• Intravenous beta blockers should NEVER be given in pre-excited atrial fibrillation or any arrhythmia with visible delta waves 1
• Oral beta blockers are also contraindicated in patients with manifest pathways 1

Why this is dangerous:

• Beta blockers can enhance conduction over the accessory pathway by slowing AV nodal conduction, which removes competitive concealed retrograde conduction into the pathway 1
• Drug-induced hypotension from beta blockers increases catecholamines, which may further accelerate accessory pathway conduction 1
• If atrial fibrillation develops, enhanced accessory pathway conduction can lead to extremely rapid ventricular rates and degenerate into ventricular fibrillation and sudden cardiac death 1, 2

Concealed Accessory Pathways (No Pre-excitation)

Beta blockers are safe and recommended for orthodromic AVRT in patients WITHOUT pre-excitation on their resting ECG 1.

• Oral beta blockers are Class I recommended for ongoing management of orthodromic AVRT when the accessory pathway conducts only retrogradely (concealed pathway) 1
• These patients have no delta wave on baseline ECG because the pathway cannot conduct anterogradely 1
• Beta blockers work by slowing AV nodal conduction, which is part of the reentrant circuit in orthodromic AVRT 3
• Approximately 50% of patients with concealed pathways respond to beta blocker therapy 1

Clinical Algorithm for Decision-Making

Step 1: Examine the resting 12-lead ECG

• Look for delta waves (slurred upstroke of QRS complex) indicating pre-excitation 1
• If delta waves present → manifest pathway → beta blockers contraindicated
• If no delta waves → concealed pathway → beta blockers safe

Step 2: During acute SVT episode

• For orthodromic AVRT (narrow complex): Vagal maneuvers first, then adenosine 1
• Beta blockers can be used acutely ONLY if no pre-excitation on baseline ECG 1
• If wide complex or pre-excited rhythm → avoid beta blockers entirely 1

Step 3: For ongoing management

• Concealed pathway (no pre-excitation): Oral beta blockers are appropriate first-line therapy 1
• Manifest pathway (pre-excitation present): Use flecainide or propafenone in patients without structural heart disease, or refer for catheter ablation 1

Common Pitfalls to Avoid

• Never assume a narrow complex SVT is safe for beta blockers without reviewing the baseline ECG for pre-excitation 1, 2
• Orthodromic AVRT can spontaneously degenerate into atrial fibrillation during an episode, even in patients without prior AF history 2
• Do not use beta blockers in any patient with known Wolff-Parkinson-White syndrome unless you have confirmed the pathway is concealed 4, 2
• Other medications to avoid in pre-excitation include digoxin, diltiazem, verapamil, and IV amiodarone for the same mechanistic reasons 1, 2

Definitive Treatment Consideration

Catheter ablation is the Class I recommended definitive therapy for all patients with accessory pathway-mediated arrhythmias, with 93-95% success rates and 3% major complication risk 1. This eliminates the need for chronic medication therapy and removes the risk of sudden cardiac death in patients with manifest pathways 1.