Why are beta blockers (beta-adrenergic blocking agents) and ACE inhibitors (angiotensin-converting enzyme inhibitors) not indicated for atrial ventricular tachycardia (AVT)?

Beta Blockers and ACE Inhibitors Are Not Indicated for AVT

Beta blockers and ACE inhibitors are contraindicated for atrial ventricular tachycardia (AVT) because they can enhance conduction over accessory pathways, increase ventricular rate, and potentially precipitate life-threatening ventricular arrhythmias. 1

Mechanisms and Risks

Beta blockers and ACE inhibitors present several specific risks in AVT:

1. Enhanced accessory pathway conduction:

   • Beta blockers slow conduction through the AV node, which can paradoxically enhance conduction over accessory pathways 1
   • This creates preferential conduction through the accessory pathway rather than the normal AV nodal route

2. Increased ventricular rates:

   • Beta blockers and ACE inhibitors may cause hypotension, leading to increased catecholamine release 1
   • The resulting sympathetic surge can accelerate conduction through accessory pathways
   • This can convert a stable tachycardia into a rapid, potentially unstable rhythm

3. Risk of proarrhythmia:

   • When AVT converts to pre-excited atrial fibrillation, these medications can be particularly dangerous
   • By blocking the normal AV nodal pathway, they force conduction through the accessory pathway, potentially leading to ventricular fibrillation 1

Preferred Management Approaches for AVT

Acute Management

1. First-line options:

   • Synchronized cardioversion for hemodynamically unstable patients 1
   • Ibutilide or intravenous procainamide for hemodynamically stable patients with pre-excited AF 1

2. Pharmacological alternatives:

   • Class IC antiarrhythmics (flecainide, propafenone) in patients without structural heart disease 1
   • Amiodarone in select cases, though with caution 1

Long-term Management

1. Definitive treatment:

   • Catheter ablation of the accessory pathway (success rate 93-95%) 1
   • This is considered first-line therapy for symptomatic AVT

2. When ablation is not feasible:

   • Oral flecainide or propafenone (for patients without structural heart disease) 1
   • Oral dofetilide or sotalol as second-line options 1
   • Oral amiodarone as a third-line option when other medications are ineffective or contraindicated 1

Medications Explicitly Contraindicated

The 2015 ACC/AHA/HRS guidelines specifically state: "Intravenous digoxin, intravenous amiodarone, intravenous or oral beta blockers, diltiazem, and verapamil are potentially harmful for acute treatment in patients with pre-excited AF." 1

Special Considerations

• Heart failure patients: While beta blockers and ACE inhibitors are cornerstone therapies for heart failure in general, they remain contraindicated in AVT with heart failure. For these patients, amiodarone or dofetilide are recommended for rhythm control 1

• Diagnostic importance: The contraindication of beta blockers in AVT highlights the critical importance of correctly diagnosing the specific type of arrhythmia before initiating treatment

• Risk stratification: Patients with known accessory pathways should be evaluated for the risk of sudden cardiac death, as the management approach may differ based on pathway characteristics

By avoiding beta blockers and ACE inhibitors in AVT, clinicians can prevent potentially dangerous proarrhythmic effects and focus on more appropriate and effective treatment strategies that target the specific mechanisms of this arrhythmia.