The Biophysics of Ablation, Made Simple - RF, Cryo and Pulsed Field

Ablation is usually taught energy by energy, as a list of settings to remember. Underneath the list is a single job: push a volume of myocardium past an injury threshold, through the whole wall, and stop short of what lies beyond. DC shock, radiofrequency, cryo and pulsed field differ only in what they deliver and in what holds them back.

One engine sits under every lab: a slice through the catheter, the blood and the wall, solved live in the browser. Set the power, the contact, the flow or the freeze and the lesion forms in front of you, with temperature, impedance and current computed as it grows. No lesion in the course is a recorded animation.

Using it in a teaching session

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

Which RF catheter is a good place to start a discussion. Turn the flow down and a 4 mm tip in temperature control reaches its target on a few watts and makes a small lesion, while an irrigated tip keeps its power and goes deeper.

What lies behind the wall changes with the site, and the labs draw it: lung behind a free wall, the other chamber’s blood behind the septum, the oesophagus behind the posterior left atrium. The same application can be safe in one place and not in another.

Where cryo helps puts the five septal targets on a real heart rebuilt from CT, with the right atrium opened and the ablation catheter at each site, from the para-Hisian region to the non-coronary cusp. Usual settings collects the starting values most laboratories use, with the signs that mean stop.

There are two tracks. Basic has thirty-five modules; Advanced adds eleven marked EP detail, which can be left for a second pass. Four practice challenges near the end each set a target and a limit: a transmural posterior-wall lesion that spares the oesophagus, a thick septum reached without a steam pop, a deeper cryolesion, and a deep pulsed-field lesion that stays cool. Progress is remembered in the browser, so a trainee can work through the course over several sittings.

What the model simplifies

Every lab solves the same axisymmetric slice. The catheter stands perpendicular to a flat, still wall, with no beating, sliding, anisotropy, oedema or tissue shrinkage, and the flow is steady. An RF lesion is tissue that reached 50 °C, treated as instant; cryo uses a cold-dose rule; the pulsed-field threshold ignores the number of pulses. The cryoballoon is a separate one-dimensional model through the contact ring. The last module lists every simplification and how the engine was checked. Its numbers are calibration, not device data, and not a guide to settings.

Sources

The engine was checked against irrigated and temperature-controlled RF lesions (Nakagawa H et al., Circulation 1995;91:2264-73), the porcine 4 mm cryolesions in the FDA’s summary of safety and effectiveness for Freezor Xtra (P020045/S073), cryoballoon and junction temperatures (Takami M et al., Circ Arrhythm Electrophysiol 2015;8:836-45) and the 4-7 mm depth of current pulsed-field lesions. Tissue properties follow the IT’IS Foundation database and Gabriel S et al. (Phys Med Biol 1996;41:2251-93). The heart in Where cryo helps is the one in The EP study, made simple, rebuilt from a contrast-enhanced coronary CT.