Quantitative assessment of the fast pathway in atrioventricular nodal reentrant tachycardia

Background: Mathematical modelling has allowed calculation of the length of the slow and fast pathways in typical atrioventricular nodal reentrant tachycardia (AVNRT). The length of the slow pathway has been correlated with the measured length of the right inferior extension in human histologic specimens, but no histology data exist about the fast pathway. Methods: In preparations of cadaveric human hearts, the AV node was identified, and the site of the fast pathway was projected according to both existing evidence and results of our electroanatomic mapping. This permitted measurement of the length of the fast pathway as a limb of the tachycardia circuit. Results: Measurements of the length of the projected area of the fast pathway on histology specimens were performed in 8 hearts. The estimated length of the fast pathway was 39.6 ± 5.8 mm (range: 30.4–45.9 mm). These numbers are comparable to those produced by mathematical calculations of the length of the fast pathway. Conclusions: Typical AVNRT uses a circuit from the AV node to the septal isthmus of an average size of 5–6 cm, confined within the pyramid of Koch.