Allessie et al induced and mapped electrically induced tachycardia in isolated rabbit atria and documented the circular movement reentry in that model.209 Using a limited number of electrodes, the authors detected an activation sequence that suggested centripetal direction of wavelet propagation. The authors proposed that these centripetal wavelets activated tissue at the center of the circuit, resulting in double responses (double potentials) of subnormal amplitude. Because the centripetal wavelets were unable to propagate beyond the center, they prevented the impulse from shortcutting the circuit, resulting in the maintenance of reentry. This mechanism of reentry was named leading circle reentry by Allessie et al.209 Building on ideas put forward initially by Mines and later quantified by Wiener and Rosenblueth, Allessie et al suggested that functional reentry naturally establishes itself in the shortest circuit that can maintain reentry, defined by the distance a cardiac impulse travels during the RP.210,211,212 This distance determines the length of the shortest reentrant cardiac excitation wave (wavelength, WL) and is equal to the product of conduction velocity (CV) and RP (e.g., WL = CV × RP). If AF is maintained by multiple simultaneous reentrant waves, the likelihood of spontaneous termination is greatest when the atria are only large enough to maintain one reentrant wave; if the wavelength is shortened so that multiple waves can be maintained simultaneously, the chances of spontaneous termination will be greatly reduced and AF is likely to be sustained. Evidence to support this notion was obtained in a dog model by varying autonomic tone and administering antiarrhythmic drugs (AADs).211 However, some clinical observations were incompatible with the leading circle mechanism, notably the effectiveness of Na+ channel blockers in AF. According to the leading circle notion, Na+ channel blockers should decrease the wavelength by reducing CV and thereby promote, rather than terminate, AF. Furthermore, for many years, multiple numerical studies and high-density mapping studies in cardiac tissues have failed to confirm the idea of the leading circle or the presence of centripetal wavelets in the maintenance of reentrant excitation.