What is the initial treatment for a patient with stable wide QRS (Quadrature Amplitude Modulation R-wave, S-wave) tachycardia?

Treatment Algorithm for Stable Wide QRS Tachycardia

For patients with stable wide QRS tachycardia, IV procainamide (1.5 mg/kg over 5 minutes) is the recommended first-line pharmacological treatment, followed by amiodarone as an alternative, while treating all undiagnosed wide QRS tachycardias initially as ventricular tachycardia. 1

Initial Assessment and Diagnosis

When encountering a patient with stable wide QRS tachycardia:

1. Assume it is ventricular tachycardia (VT) until proven otherwise

   • This is the safest approach as inappropriate treatment of VT can be fatal
   • Wide QRS tachycardia is most commonly VT 2

2. Assess for diagnostic features suggesting VT:

   • RS interval >100 ms in any precordial lead
   • Negative concordance in precordial leads
   • Presence of fusion or capture beats
   • QR complexes (present in ~40% of post-MI VT)
   • AV dissociation 1

Treatment Algorithm for Stable Wide QRS Tachycardia

First-Line Treatment:

• IV Procainamide: 1.5 mg/kg over 5 minutes (Class IIa, LOE B) 1
  • Most effective for hemodynamically stable monomorphic VT
  • Contraindicated in patients with severe CHF or acute MI 3

Alternative Treatment:

• IV Amiodarone: 150 mg over 10 minutes (Class IIa, LOE C) 1
  • Preferred for patients with impaired LV function or heart failure
  • Can be used in patients with or without CHF or AMI 3

Other Options:

• IV Sotalol may be considered for hemodynamically stable sustained monomorphic VT, including patients with AMI 3

Diagnostic Aid:

• IV Adenosine may be considered for both diagnosis and treatment of undifferentiated regular stable wide-complex tachycardia 3, 1
  • Can help convert the rhythm to sinus or help diagnose the underlying rhythm
  • Use with caution as it may precipitate ventricular fibrillation in patients with coronary artery disease 1

Special Considerations

For Specific Types of Wide QRS Tachycardia:

1. Polymorphic VT associated with long QT syndrome:

   • Familial long QT: IV magnesium, pacing, and β-blockers (avoid isoproterenol) 3
   • Acquired long QT: IV magnesium (consider pacing or isoproterenol if bradycardia is present) 3

2. Polymorphic VT without long QT syndrome:

   • Consider IV β-blockers for ischemic or catecholaminergic VT
   • Consider isoproterenol in other cases 3

3. VT associated with acute myocardial ischemia:

   • IV Lidocaine may be considered (Class IIb, LOE C) 1

Critical Cautions

• NEVER use calcium channel blockers (verapamil, diltiazem) for wide QRS tachycardia of unknown origin (Class III, LOE C) 1

  • These can cause catastrophic hemodynamic collapse in VT

• Use extreme care with concomitant use of IV calcium-channel blockers and beta blockers due to potential hypotensive and bradycardic effects 3

• Continuously monitor for deterioration in hemodynamic status and be prepared to immediately perform synchronized cardioversion if the patient becomes unstable 1

If Tachycardia Persists

• Consider electrical cardioversion if pharmacological therapy fails
• After successful termination, refer the patient to an arrhythmia specialist for further evaluation 3
• Consider long-term management options including catheter ablation or chronic drug therapy

This algorithm prioritizes patient safety by treating all wide QRS tachycardias as VT initially while providing specific guidance for different clinical scenarios, ensuring the best outcomes in terms of morbidity and mortality.