In the current issue of the Anatolian Journal of Cardiology, the study by Erdem et al. (1) aims at determining the area of slow conduction in typical (counterclockwise) and reverse typical (clockwise) atrial flutter (AF). For this, they cleverly used the isochronal maps as retrieved from the electro-anatomical system to investigate the conduction velocities and the conducting areasi.e. surface of the areas activated at the same time-all around the tricuspid annulus. They conclude that conduction is slowing at the lower septal right atrium, while conducting areas are larger in the upper right atrium (in other words the conduction is faster in these areas) for both typical and reverse typical AF.As mentioned by the authors in the discussion, the slow conducting area-what is usually called the "isthmus" of a reentry circuit, even if this term originally refers to a protected path of the circuit rather than to conduction velocities-has been located at the cavo-tricuspid isthmus (CTI) or at the low septum during AF in most previous studies. This is easily explained by the complex muscular arrangement of the CTI and areas covering the coronary sinus ostium, with interlacing trabeculae stemming from the right atrial pectinate muscles, prominent Eustachian ridge or sub-Eustachian recesses or pouches, all this leading to non-uniform anisotropic conduction (2-4). Conversely, conduction is faster at the other parts of the tricuspid annulus, possibly due to the continuous subepicardial circumferential layer (which is less developed in the septal region) and due to the discontinuous subendocardial perpendicular myofibers (which are lacking in the anterior region) (5).The authors claims that the technique used in this study is probably more reliable for determining conduction velocities, being less dependent on lead orientation and allowing averaging of otherwise heterogeneous local activation times. Even if probably true, maybe explaining the differences in absolute conduction velocities with previous works, this did not lead to a dramatical change in the location of the areas of slow conduction, since their findings do not contradict most of the previous reached conclusions.In which aspects the present findings are original? Most if not all of the referenced works cited by the authors conclude that the area of slowest conduction during AF was more or less located at the CTI. In that aspect, no new data was given by this work, except maybe that the septal side of the CTI is more slowly conducting than the lateral one, although this had already been reported before [see discussion and references in the current paper (1).A more original result is the comparison the authors made between the areas of slow conduction during typical and reverse typical AF. They do not find any difference between both AF, septal CTI being the slowest area shared by both reentry circuits. However, left to right conduction through the CTI has been said to be slower than conduction over the reverse direction (6), possibly due to the non-uniform anisot...