The EP Study, Made Simple - Reading the Electrogram, Pacing and the Manoeuvres

An EP study is a timing study: four catheters in the heart, three letters, A, H and V, and a stopwatch. Nearly every question asked in the lab is a question about time: what fired first, how long the wave took to get there, and what changed when one more beat was added. Learn to read those times and the manoeuvres stop being a list to memorise.

Every recording in the course is computed as the wave runs, on a model of the heart’s conduction. Nothing is drawn by hand. The manoeuvres play out on a four-chamber section traced from a CT, with the electrograms computed at each catheter’s electrodes, so dragging a catheter changes what it records and where it paces. A line on every figure says what is happening at that moment and why, and every beat can be stepped through, slowed to a quarter of its speed or measured with calipers.

Using it in a teaching session

The course has two tracks. Basic, twenty-four modules, covers the catheters, the AH and the HV, the coronary sinus, pacing, the three tachycardias every fellow meets, the manoeuvres that tell them apart and entrainment on a simple circuit, with fewer controls in each module. Advanced, all forty-nine, adds the physics of the recording, the rules of the tissue, every manoeuvre and resetting and entrainment in depth. A class can switch tracks at any time without losing its place.

Step through a figure before playing it: the line under each one moves on a beat at a time. Take a prediction before each step, such as which A comes first or whether the His moves. The wrong answers are the useful ones.

Para-Hisian pacing shows the route of the paced wave rather than asking the class to infer it. Drag the His catheter’s tip off the His and back, and the close-up shows what it captures while the electrograms change beneath it.

Entrainment from the right ventricle runs in two halves: count the fully paced beats it takes to capture the atrium once pacing starts, then read the return once it stops. Junctional or AVNRT? does the same with a single PAC, given late and given early.

The EP lab is one tab away: a recording system, a stimulator and cases whose diagnosis the learner has to find. It makes a good closing exercise. Progress is remembered in the browser, and every module has its own address, such as /sims/ep-study/index.html#m32 for para-Hisian pacing, to send a class straight to it.

What the model simplifies

The recordings of the study and the EP lab run on one network of a few hundred points: the atria, the two pathways into the AV node, the His bundle, the bundle branches and Purkinje network, the ventricles and, in some cases, an accessory pathway or an atrial focus. Each has a conduction time and a refractory period that follows the rate before it. Intervals are accurate to a few milliseconds; QRS widths and shapes are approximate.

Refractory periods are single numbers that do not drift during a study, the catheters never lose contact or cause ectopy, and isoprenaline, adenosine and vagal tone act through a few parameters. The circuits of the entrainment section, from Mines’s ring to flutter and scar VT, are drawn sheets of muscle with computed timing. The last module lists every simplification. The values are the model’s calibration, not reference ranges.

Sources

The manoeuvres follow Josephson’s Clinical Cardiac Electrophysiology (6th ed., Wolters Kluwer). The count of fully paced beats to entrain from the right ventricle follows Dandamudi et al. (Heart Rhythm 2010;7:1326-9); the late and the early PAC, Padanilam et al. (J Am Coll Cardiol 2008) and Gilge et al. (Europace 2021); the classification of atrial tachycardias, Saoudi et al. (Eur Heart J 2001;22:1162-82).