How the ECG Tells You Where VT Is Coming From
1️⃣ When a rhythm comes from the ventricles, it travels slowly across muscle instead of racing through the Purkinje system. That’s why VT is wide, fast, and regular.
2️⃣ Next trick: look at the bundle-branch pattern.
- VT that looks like LBBB usually started in the right ventricle.
- VT that looks like RBBB usually started in the left ventricle.
Impulse travels away from its origin as if the opposite bundle is blocked.
3️⃣ VT comes from the RVOT =most common idiopathic VT
It has LBBB shape with a strong inferior axis (big positive in II, III, aVF).
These patients often feel palpitations during exercise or stress.
4️⃣ If the QRS looks RBBB with an inferior axis, think LVOT i.e near the aortic valve or left ventricular outflow.
5️⃣ There’s a special one called fascicular VT.
Young patient, no structural disease, heart suddenly takes off at 150–180 bpm.
ECG: RBBB pattern + left axis deviation.
And here’s the magic: it usually stops with Verapamil.
6️⃣ In patients with an old MI or cardiomyopathy, the ventricles have scar tissue.
That scar becomes a little electrical maze.
The circuit keeps spinning in the same path--) monomorphic VT with a stable QRS every beat.
7️⃣ Torsades de Pointes is a different beast.
The QRS keeps changing direction it literally "twists."
You’ll almost always find a long QT before the episode.
8️⃣ When the QRS is polymorphic but the QT is normal, think acute ischemia, especially if there are ST changes.
9️⃣ There’s even a VT that forms its own race track inside the bundle branches: bundle-branch reentry VT.
Very wide QRS, looks like a classic BBB, but going way too fast
🔟 So here’s a quick summary clinicians rely on:
◾Monomorphic VT: usually scar or idiopathic outflow/fascicular origin
◾Polymorphic VT: usually ischemia, long QT,..
The ECG won’t pinpoint the exact millimeter, but it gets you surprisingly close to the neighborhood.
References:
Braunwald’s Heart Disease, 12th edition
Zipes & Jalife: Cardiac Electrophysiology
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