Is ventricular tachycardia (VT) always regular?

Is Ventricular Tachycardia Always Regular?

No, ventricular tachycardia (VT) is not always regular, though it typically presents with regular R-R intervals in most cases. According to the European Society of Cardiology guidelines, VT may show "slight variation over several beats" in the R-R interval 1.

Characteristics of Ventricular Tachycardia

Regular vs. Irregular VT

• Typical presentation: Most VTs present as regular rhythms with consistent R-R intervals, particularly monomorphic VT
• Irregular variants: Some VTs can show variations in the R-R interval, particularly:
  • During the initial 10-20 beats before stabilizing
  • In specific subtypes of VT (polymorphic VT, torsades de pointes)
  • In some rare cases of focal VT

ECG Findings in VT

• QRS morphology: Different from sinus rhythm, usually wide (≥0.12 seconds)
• Rate: 200-500 beats per minute in infants 1, typically 100-250 beats per minute in adults
• P waves: May show AV dissociation with sinus P waves continuing unrelated to VT, retrograde P waves, or no visible P waves 1
• R-R interval: Usually regular after initial stabilization, but may show "slight variation over several beats" 1

Types of VT with Irregular Patterns

1. Polymorphic VT/Torsades de Pointes:

   • Characterized by continuously changing QRS morphology and irregular R-R intervals
   • Associated with QT prolongation, electrolyte abnormalities, or structural heart disease

2. Irregular Monomorphic VT:

   • Rare but documented phenomenon 2, 3
   • May show "regularly irregular" patterns (bigeminal or trigeminal patterns) 2
   • Possible mechanisms include:
     • Longitudinal dissociation within the reentry circuit
     • Two alternative circuits sharing the same exit pathway
     • Focal origin with variable conduction properties

3. VT with Variable Block:

   • Variable conduction ratios can create irregular ventricular responses

Clinical Implications of Regular vs. Irregular VT

The regularity of VT has important clinical implications:

• Response to therapy: Regular VT responds better to anti-tachycardia pacing (ATP) than irregular VT 4
• Spontaneous termination: Irregular VT is more likely to terminate spontaneously than regular VT 4
• Misdiagnosis risk: Irregular VT may be misdiagnosed as atrial fibrillation with aberrancy 3
• Prognosis: Both regular ("stable") and irregular VT carry significant mortality risk 5

Diagnostic Approach

When evaluating a wide-complex tachycardia:

1. Assess hemodynamic stability: Unstable patients should be presumed to have VT and receive immediate cardioversion 1

2. Obtain 12-lead ECG to evaluate:

   • QRS width (≥0.12 seconds suggests VT)
   • Presence of AV dissociation (strongly diagnostic of VT)
   • QRS morphology (different from sinus rhythm suggests VT)
   • Regularity of the rhythm

3. Key diagnostic features of VT:

   • AV dissociation with ventricular rate faster than atrial rate
   • Fusion complexes
   • QRS concordance in precordial leads
   • R-S interval >100 ms in any precordial lead
   • Initial R wave in aVR

Treatment Considerations

Treatment should be guided by hemodynamic stability:

• Unstable patient: Immediate synchronized cardioversion
• Stable patient with regular VT: Consider anti-tachycardia pacing if ICD present, or pharmacological therapy
• Stable patient with irregular VT: May require direct cardioversion or antiarrhythmic medications as ATP is less effective 4

Remember that even "stable" VT is not benign and is associated with high mortality rates, potentially indicating a substrate capable of producing more malignant arrhythmias 5.