ECG Anatomy - The Heart, the Leads and the Tracing

The ECG is taught as a pattern on paper long before anyone explains what the paper is a picture of. This puts the heart, the electrodes and the tracing in the same model, so the leads stop being abstract names and become what they are: views of a real organ from measured positions.

Rotate the heart and the lead axes move with it. Change the cell type and the action potential changes shape. Build a lead from its electrode pair and watch the deflection follow.

Using it in a teaching session

The lead construction slides are the core. Einthoven, then Goldberger, then Wilson, in that order, with the law checked live against the tracing at each step. Trainees who have only met these as definitions usually realise for the first time that aVR is not an arbitrary convention.

The action potential module is worth pairing with the strip. Running the cursor through the cycle while watching which ions are moving connects cellular electrophysiology to the surface tracing in a way that two separate lectures never manage.

Infarct staging works well at the end, since by then the class has the vector machinery to predict what a wall that stops depolarising will do to the tracing.

Sources

Anatomy slides summarise Mori S and Shivkumar K, Atlas of Cardiac Anatomy (Cardiotext, 2022), in the authors own words. Anatomical orientation and nomenclature also follow McAlpine WA, Heart and Coronary Arteries (Springer-Verlag, 1975).

What the model simplifies

The torso is treated as a uniform volume conductor and the tracings are computed rather than recorded. It shows the geometry and the logic behind the twelve leads, not the variability of a real recording.