Fibrillation Persists When the Wavelength Fits

01The evidence

• Spectral analysis of the termination of atrial fibrillation by flecainide gives mechanistic insight into how the drug changes the organisation of the fibrillatory waves rather than simply reducing excitability.Europace
• Electrophysiologic studies of human atrial fibrillation describe the fibrillatory process in terms of wavelength and rotor dynamics, which is the framework a geometric threshold requires.Electrophysiologic aspects of AF

02The tension

Antiarrhythmic drugs are classified by their effect on excitability and refractoriness, and the classification predicts success poorly. Two drugs that lengthen the refractory period similarly can differ in efficacy, and efficacy depends on atrial size in ways the classification does not represent.

03The theory

A reentrant circuit can only close if its wavelength, the distance the wave travels during the refractory period, fits inside the tissue. If the wavelength exceeds the chamber, the wave runs out of recovered tissue and dies.

Fibrillation is a collection of rotors, each of which must fit. The number that fit decreases as the wavelength grows, and below a critical number the fibrillatory pattern cannot sustain itself. That makes termination a geometric transition rather than a gradual suppression.

The prediction is that efficacy should depend on the ratio of wavelength to chamber size, not on the drug's class. A drug that lengthens the wavelength moderately will terminate in small atria and fail in large ones, which is exactly the clinical pattern of size-dependent response.

This also explains why the same drug works when given early and fails when given late: the atria have remodelled and enlarged, so the wavelength must be lengthened further to cross the same geometric threshold.

04What this is not

05Predictions

• P1Termination should depend on the wavelength-to-chamber-size ratio rather than on drug class.
• P2A drug should terminate in small atria and fail in large ones at the same concentration.
• P3Early treatment should succeed more often than late treatment because the geometry has not yet changed.

06What would refute it

Efficacy tracking refractoriness regardless of atrial size would leave the geometric account without a threshold.

07What it would change

It would make atrial size a dosing variable, and shift drug development toward wavelength targets.