Clinical translation
Operators are nowadays more familiar with 3D colour-coded gradient maps than with preexcitation patterns in ECG. A tool that supports AP localization in a familiar fashion, with color-coded gradient map that covers the mitral and tricuspid rings, may be a more descriptive and predictive method to enhance utility of standard 12-lead ECG for the assessment and treatment of WPW cases. Moreover, the WPW24.com app has a substantial educational potential by illustrating the relationship between changing morphology of QRS and the related changes in AP distribution along the tricuspid and mitral annuli (Figures 6 and Supplementary Figure 1 ).
Algorithms are often complex, introduce subjectivity with binary categorizations, and are difficult to memorize. The polarity of the initial 20 ms of the delta wave, used in several algorithms, is often difficult to discern and has significant inter-observer variability. In our experience, algorithms are rarely followed in real life practice, but physicians rather use simple set of rules, similar to these on which the current method was based. The WPW24.com addresses these limitations by being readily available to any smartphone or tablet user without the need to memorize anything. And, by being based on the QRS polarity (net vector) - a feature so easy to ascertain, especially with the provided inside app examples of different QRS configurations that are compatible with a particular category (Figure 2 ), makes the preexcited ECG analysis straightforward.
Use of an algorithm, that indicates one particular AP location, can fix the operator on undue pursuit of ablation in that region even when multiple energy applications were not successful. A gradient map by being more honest with regard to the possible AP locations, while directing to the most probable area as well, gives also clues what other locations should be explored in the next steps. For example, even quite typical ECG pattern for RPS site (QRS transition to positive at V2, negative II) is sometimes seen with AP at RMS, RP, LMS, LPS, and EPI locations.
WPW24.com can be seen as a tool for memory enhancement and sharing of experience. A small-volume AP ablationist might have never experienced or likely does remember a patient ablated several years ago, that had a rare preexcited ECG pattern that was identical to the ECG of the patient currently on the table. Yet that pattern could be an excellent clue to the localization of the AP that is undergoing ablation. Illustration of such scenario that occurred during the current study is presented inFigure 1 and Supplementary Video 1 . In the future, WPW24.com database can be expanded by adding datasets of consecutive APs from other centers, getting as close as possible to making precise diagnosis of AP type/location via full 12-lead QRS pattern recognition.