Conduction and Arrhythmia, Start to Finish - Block, Re-entry and Ventricular Tachycardia

Arrhythmias are usually taught as a gallery of tracings to recognise. Underneath the gallery is a much shorter list: how fast each structure conducts, how long it stays refractory and how it recovers. Learn how those behave and most rhythms stop needing to be memorised.

One conduction engine drives all fifty-six modules, and every rhythm is a set of parameters on it. No ratio is scripted. Wenckebach, the blocked PAC, fusion beats, and the induction and termination of re-entry all follow from refractoriness and recovery, so one slider can start a tachycardia, change its rate or break it, with the activation drawn in the heart and the ECG computed beside it.

Using it in a teaching session

Each module gives the class something to try before it shows what should have happened. Take a prediction before anyone moves a slider: the wrong answers are the useful ones.

Decremental conduction is the idea the rest of the course leans on. Shorten the coupling interval and the node’s recovery curve plots itself, beat by beat. Wenckebach, the jump of dual AV-nodal pathways and the protection the node gives the ventricles in fibrillation all hang on that curve.

The bundle branch block modules end with the criteria from the AHA/ACCF/HRS recommendations, so each tracing can be checked against the definitions.

Eight modules are marked EP level. They go into catheter-laboratory detail, such as the Jackman pathways, Nogami’s P1 and P2 and entrainment of scar VT, and can be left for a second pass.

Name the rhythm, near the end, shows ten random tracings with the heart hidden until the learner commits to an answer. It makes a good closing exercise for a group. Progress is remembered in the browser, so a trainee can work through the course over several sittings.

What the model simplifies

The heart is a set of connected structures, not a sheet of tissue. Conduction is computed between them, each with its own refractory period and recovery curve, and the wavefronts in the heart view are drawn from those timings. A few triggers are set because they are the thing being taught, such as the premature beat that induces a tachycardia; what they start is not.

The fibrillating and fluttering atrium is a source rather than a circuit, nothing in the model knows whether a rhythm produces a pulse, and only verapamil and adenosine have a time course. Part of each waveform’s shape is a template fitted to published criteria, while widths, intervals and the QT are computed. The last module lists every simplification. The preset values are calibration, not patient data.

Sources

Criteria for bundle branch and fascicular block follow the AHA/ACCF/HRS recommendations (Surawicz B et al., J Am Coll Cardiol 2009;53:976-81). Locating an atrial focus follows the P-wave algorithm of Kistler PM et al. (J Am Coll Cardiol 2006;48:1010-17).