VT Localizer

Stepwise EKG localization of VT origin

Bundle Morphology

What is the bundle pattern?

Use the predominant QRS morphology in V1. LBBB is predominantly negative in V1. RBBB is predominantly positive in V1.

Frontal Plane Axis

Choose whether the QRS is predominantly positive or negative in each limb lead.

Lead I

aVF

Lead II

Lead III

Select Lead I and aVF to determine the axis quadrant.

Precordial Transition

Where is the R-wave transition?

The transition is where the R wave becomes larger than the S wave, meaning the QRS becomes predominantly positive.

V1 Morphology

What does the QRS look like in V1?

Choose the pattern that most closely resembles the ventricular QRS.

How to read these patterns

QS
Entire QRS is negative with no initial R wave.

rS
Small initial R followed by a larger negative S wave.

Monophasic R
One dominant positive R wave without a major S wave.

qR
Small initial negative q wave followed by a dominant R wave.

rsR′ / RSR′
Positive-negative-positive pattern with a terminal R′.

Additional Limb-Lead Clues

aVR morphology

Note the predominant polarity and whether an initial R wave is present.

aVL morphology

Record the predominant QRS polarity or a clear initial q wave.

Structural Heart Disease

Select any known substrate. These findings change how strongly an apparently idiopathic EKG pattern should be interpreted.

Prior MI or ischemic scar

Cardiomyopathy / reduced EF

CMR scar or LGE

ARVC / RV cardiomyopathy

Prior cardiac surgery

No known structural disease

Most likely localization

Complete the EKG pattern

Start with bundle morphology, axis, and precordial transition.

Chamber of origin will appear here.

Likely Site of Origin

The view and highlighted region update automatically from the selected EKG pattern.

Anterior / outflow view

Left ventricular endocardial view

Complete the EKG pattern to highlight the most likely region.

Primary Alternate Broader chamber

Schematic localization only. Highlighting represents the likely EKG exit region, not a precise ablation target.

Selected EKG clues

No findings selected

Quick Localization Cheat Sheet

Finding	What it suggests
LBBB morphology	Favors a right ventricular or septal site of origin.
RBBB morphology	Favors a left ventricular site of origin.
Inferior axis	Activation is directed inferiorly, suggesting a superior origin such as the ventricular outflow tracts.
LBBB + inferior axis	Classic morphology of RVOT ventricular arrhythmia.
Early precordial transition	In an outflow-tract pattern, favors a more leftward source such as LVOT or aortic cusp origin.
Late precordial transition	In an outflow-tract pattern, favors RVOT origin.
RBBB + superior axis	Consider LV inferoseptal origin or posterior fascicular VT, particularly without structural heart disease.
Known myocardial scar	Raises concern for scar-related VT even when the surface morphology resembles an idiopathic focus.