Is Ventricular Tachycardia Always Regular?
No, ventricular tachycardia is not always regular—monomorphic VT is typically regular, but polymorphic VT is irregular by definition.
Monomorphic VT: Regular Rhythm
- Monomorphic VT presents as a regular rhythm with a stable, single QRS morphology and consistent cycle length 1
- The regularity is characterized by cycle length variability of 30 ms or less 1
- When evaluating a wide-complex tachycardia, a regular rhythm with monomorphic QRS complexes suggests either VT or SVT with aberrancy 1
Polymorphic VT: Irregular Rhythm
- Polymorphic VT is characterized by a changing or multiform QRS morphology, making it an irregular rhythm 1
- The QRS configuration is not stable when viewed in a single ECG lead, with episodic changing of the QRS-complex electrical axis, amplitude, or both 2
- Polymorphic VT occurs at cycle lengths between 600 and 180 ms 1
Clinical Distinction Matters for Management
- The distinction between regular (monomorphic) and irregular (polymorphic) VT is critical because treatment approaches differ significantly 1
- Regular monomorphic VT in stable patients can be treated with antiarrhythmic medications like procainamide, amiodarone, or sotalol 1
- Irregular polymorphic VT requires immediate defibrillation using the same strategy as ventricular fibrillation 1
Special Forms of VT
- Torsades de pointes is a specific type of polymorphic VT associated with long QT interval, characterized by twisting of the QRS complexes around the isoelectric line 1
- Bidirectional VT shows beat-to-beat alternans in the QRS frontal plane axis, often associated with digitalis toxicity 1
- Ventricular flutter is a regular ventricular arrhythmia at approximately 300 bpm with monomorphic appearance 1
Common Pitfall
- Do not assume all wide-complex tachycardias are regular—always assess rhythm regularity on the ECG before determining treatment strategy 1
- An irregular wide-complex tachycardia may represent polymorphic VT, atrial fibrillation with aberrancy, or pre-excited atrial fibrillation 1
- The presence of irregularity in a wide-complex tachycardia should prompt immediate consideration of polymorphic VT requiring defibrillation rather than antiarrhythmic drug therapy 1