[Nodofascicular fibers (Mahaim) as a part of the reentry circuit in patients with supraventricular tachycardia].

A history of paroxysmal tachycardia with broad QRS complexes resembling left bundle branch block led to electrophysiologic studies in a 20-year-old female. The results were diagnostic of a nodofascicular Mahaim fiber. Delayed retrograde conduction following transient proximal right bundle branch block as well as an infranodal termination mode were noted and are considered to be proof of participation of the nodofascicular fibers in the re-entry loop. Marked differences of atrioventricular conduction were noted on comparing refractory period determinations from the right atrium and from the coronary sinus. These observations are consistent with partial supranodal bypass of the N zone of the AV node and preferential depolarisation of the Mahaim fiber via the superficial (anterior) nodal approaches. The report provides an example of a nodofascicular fiber being the only connection of an alternative nodal pathway to the ventricles, thus providing a basis for junctional re-entry. Furthermore our data allow an analysis of the different characteristics of intranodal conduction to the His bundle versus to the nodofascicular fibers.