Introducing EP Diagram

The ECG ladder diagram app EP Diagram is at long last finished, after nearly 2 years of development. The 2 year time span reflects more on me than on the app itself. There were programming techniques I had to learn in the course of developing the app that I didn’t know when I started its development. I’ll discuss this process in another blog post aimed at developers who like to read about the trials and tribulations of creating an app from start to finish. For this post I’ll talk more about the motivation behind the app, and what the app actually does.

Ladder diagrams have been around almost as long as electrocardiography. They were popularized by, though not invented by, the omnipresent Sir Thomas Lewis. For example, here is a ladder diagram published by him in 1920:

Ladder diagram published by Lewis in 1920

Although the ECG tracing includes an incredible amount of electrical noise, this diagram is not too different from those of today. The electrocardiogram is on the top, the ladder on the bottom. The ladder consists of horizontal lines, with labels on the left. A and V regions are labeled, though for some reason he leaves out the label for the AV region. It appears that impulse origin in the AV region is marked by a tiny dot, and conduction is indicated by lines draw in the AV region. Unlike most modern ladder diagrams, Lewis draws atrial and ventricular depolarization (and apparently repolarization as well) as solid blocks of black in the A and V regions. He also omits any symbol for conduction block such as a short line capping the blocked impulse. But despite its crudity by today’s standards, this representation clearly demonstrates what is going on in the tracing, namely a junctional rhythm with intermittent retrograde block to the atria.

A more recent ladder diagram is this one from 1950.

Complex AV nodal reentry, published in 1950

Here we see the same layout as in Lewis’s ladder, with A, AV, and V regions labelled on the left. Atrial and ventricular depolarizations are indicated by vertical lines, and diagonal lines are drawn in the AV nodal region of slow conduction. The ladder illustrates complex reentry due to dual AV nodal pathways. Again tiny dots are used to indicate impulse formation, and now block is indicated by a short line capping the blocked conduction path. In addition conduction times in milliseconds are added to this diagram.

These two illustrations come from a review article entitled The Ladder Diagram (A 100+ Year History). This and another more recent review are about it as far as the published literature on the technique of ladder diagramming goes, though I imagine ladder diagrams might be still discussed in ECG textbooks such as Marriott’s. But the sad truth is that ladder diagrams have fallen out of favor these days. The reasons for this may be multiple. Partly this falling out may be just another manifestation of the fact that “electrophysiology” has morphed into “electotherpeutics” in training programs. “Burn first, and ask questions later” is often the guiding principle today. But it may be more than that. Ladder diagrams might be another victim of the digital age. Sure you can quickly sketch out a ladder on a blackboard or whiteboard, or even on a napkin. But for publication, there are no tools other than hiring an artist or having a go with Photoshop to produce a high quality diagram. Measurements are often done with physical calipers and thus not as precise as we’d like. The results are often esthetically displeasing.

This is a shame, for a good ladder diagram with accurate measurements is a great teaching tool for demonstrating that, for example, despite the PR interval getting longer in Mobitz I AV block, the QRS complexes get closer together. Or that, in the same example, the 2nd beat after the blocked beat has the longest increment of the PR interval. Ladders are also great for demonstrating concealed extrasystoles and concealed conduction, or complex conduction patterns in atrial flutter due to multiple levels of block. But no digital tool to create ladder diagrams existed, and nature abhors a vacuum, hence…my motivation for developing EP Diagram.

EP Diagram on a Mac

As you can see, the app follows closely the pattern of ladder diagrams in the literature. The ECG is loaded into a view at the top of the screen, and the ladder is at the bottom. The ladder labels are on the left side. Marks are created by tapping, clicking, or dragging on the ladder. When you create or tap on a mark a cursor appears, extending up into the ECG and the position of the mark can be adjusted by sliding the cursor left and right. Marks drawn close together automatically snap together and afterwards stay linked when one of them is moved. You can also connect marks by tapping the Connect button and then tapping pairs of marks. You can add measurements by calibrating the diagram, and these measurements are updated on the fly when you add, delete, or move the marks. Symbols for impulse origin and block are added automatically, though you can override these symbols, or place them wherever you’d like. Diagrams are automatically saved to files, and almost all actions are undo/redo-able. These basic functions are documented in a YouTube video.

The Edit button allows extensive editing of the diagram, important for creating a publication quality image. You can change marks from solid to dashed to dotted. You can regularize rhythms, copy and paste marks and mark patterns, and regularize the slant and termination points of groups of marks. You can even add rhythms such as atrial fibrillation with random conduction and impulse formation.

You are not limited to the standard A-AV-V ladder. You can add and delete ladder regions, re-label regions, and change their relative size. There is also a ladder editor that allows you to create your own ladder templates.

In short, there is a lot of functionality, hence a fair amount of complexity. This is all detailed in the Help for the app, but I intend to upload another YouTube video that demonstrates how to do the more advanced functions of the app.

The next version of the app will include pacemaker sense/pace markers, refractory periods, and more labelling options.

My hope is that the app will be useful for those interested in teaching electrocardiography, as well as those interested in learning it. As always, I am open to suggestions for improvements–just email me.

By mannd

I am a retired cardiac electrophysiologist who has worked both in private practice in Louisville, Kentucky and as a Professor of Medicine at the University of Colorado in Denver. I am interested not only in medicine, but also in computer programming, music, science fiction, fantasy, 30s pulp literature, and a whole lot more.

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