Figure 1. Summary of wavelength calculations from primary electrophysiological data and their relationship to the concept of wavebreak re-entry.

A, typical monophasic action potential obtained from the Scn5a^+/− RV epicardium upon which is superimposed indications of BCL, APD90, latency and DI of both the current (n^th) and its preceding ((n–1)^th) action potential. These form the basis for computations of the wavelength parameters representing λ′ and λ′₀ (B). These sum together to give the BCD′ which is primarily determined by the pacing rate and conduction velocity of the tissue. C, long wavelength AP encountering a heterogeneity which may cause a unidirectional conduction block. This may be functional; due to wavelength differences, discordant alternans leading to nodal line formation or refractoriness, or anatomical due to anisotropy or damage. As the long wavelength AP passes over the heterogeneity, retrograde propagation is blocked by the back of the propagating wave, causing it to be extinguished, leaving only the orthograde excitation wave to continue. D, short wavelength AP encountering the same-sized heterogeneity. In this case the waveback has passed the heterogeneity before the retrograde excitation has passed through the unidirectional block. Therefore a new propagating retrograde wave is set up which may in turn back-excite the orthograde direction setting up a sustained re-entrant circuit.