Monomorphic VT vs Polymorphic VT
How to tell Monomorphic VT and Polymorphic VT apart when a board question makes them look alike.
Step 2 CK pairs are in open beta while clinical review finishes. Spot an issue? Tell us.
Uniform QRS shape means monomorphic VT, while continuously changing QRS shape means polymorphic VT.
Side by side
Wide-complex tachycardia with a uniform QRS morphology beat-to-beat suggests monomorphic VT.
Beat-to-beat changing QRS axis and amplitude indicates polymorphic VT, including torsades when QT is prolonged.
A stable reentry circuit in scarred myocardium produces repeated identical ventricular depolarization.
Multiple shifting ventricular foci or reentry pathways create changing vector morphology, often from repolarization instability.
Telemetry shows regular wide-complex tachycardia above 120/min with constant QRS shape; if unstable, synchronized cardioversion starts at 100 J biphasic.
ECG shows polymorphic wide-complex tachycardia with twisting axis; QTc above 500 ms supports torsades and requires IV magnesium sulfate 2 g over 10 to 15 minutes.
The trap
Learners give amiodarone first to every wide-complex rhythm. Unstable polymorphic VT cannot be synchronized reliably and needs immediate unsynchronized defibrillation, while torsades specifically needs magnesium even if potassium is normal.
The repair move
Next best step: if pulseless or unstable polymorphic VT, defibrillate immediately. If unstable monomorphic VT with a pulse, perform synchronized cardioversion at 100 J and escalate energy as needed. For torsades, give IV magnesium sulfate 2 g, correct potassium to above 4.0 mEq/L, and stop QT-prolonging drugs.
Try a free question
CoreA 70-year-old patient with ischemic cardiomyopathy develops regular wide-complex tachycardia at 170/min with identical QRS morphology. He is confused with BP 78/46 mm Hg. What is the next best step in management?
Show answer and explanation
Answer: A. Immediate synchronized cardioversion. Unstable monomorphic VT with a pulse requires immediate synchronized cardioversion.
Why the other choices are tempting
- B. Wrong. Adenosine is not first-line for unstable ventricular tachycardia.
- C. Wrong. Oral rate control is unsafe in unstable VT.
- D. Wrong. Magnesium is specific for torsades or polymorphic QT-related VT, not isolated monomorphic VT shock state.
- E. Wrong. Imaging does not precede rhythm stabilization in unstable VT.
Flashcards
Tap a card to flip it.
What morphology clue identifies monomorphic VT in seconds?
A fixed, uniform wide QRS shape across beats.
Which rhythm feature points to polymorphic VT rather than monomorphic VT?
QRS complexes vary in axis and amplitude beat-to-beat.
Quick answers
What is the fastest way to tell Monomorphic VT from Polymorphic VT?
Uniform QRS shape means monomorphic VT, while continuously changing QRS shape means polymorphic VT.
What is the key clue for Monomorphic VT?
Wide-complex tachycardia with a uniform QRS morphology beat-to-beat suggests monomorphic VT.
What is the key clue for Polymorphic VT?
Beat-to-beat changing QRS axis and amplitude indicates polymorphic VT, including torsades when QT is prolonged.
What is the common trap with Monomorphic VT vs Polymorphic VT?
Learners give amiodarone first to every wide-complex rhythm. Unstable polymorphic VT cannot be synchronized reliably and needs immediate unsynchronized defibrillation, while torsades specifically needs magnesium even if potassium is normal.