title: Mahaim fiber: an atriofascicular or a long atrioventricular pathway?
abstract: There is debate concerning the distal insertion of Mahaim fibers. Some findings favor an atriofascicular fiber connected with the distal right bundle branch. Other findings favor a long atrioventricular (AV) structure inserting into the myocardium. A patient having a decrementally conducting accessory pathway is reported. Proximal and distal Mahaim potentials were recorded during sinus rhythm, atrial pacing, and antidromic tachycardia. Both proximal and distal M potentials always preceded the QRS complex during sinus rhythm and antidromic tachycardia earlier than the right bundle branch potential. During tachycardia, the distal M potential was recorded 6 ms before the retrograde right bundle potential. Other arguments consistent with an AV connection were a change in the QRS configuration during tachycardia after the first radiofrequency pulse at the site of the distal M potential and absence of right bundle branch block after successful ablation. Conduction through the proximal part of the Mahaim fiber was unaltered after ablation, as assessed by recording the proximal M potential. Electrophysiologic evidence is presented suggesting a long AV accessory pathway inserting close to the distal right bundle branch rather than an atriofascicular connection in this patient with a Mahaim fiber.
authors.affiliation: Biocor Instituto, Nova Lima, Brazil. eduardosternick@aol.com
authors.forename: Eduardo Back
authors.initials: EB
authors.lastname: Sternick
authors.forename: Carl
authors.initials: C
authors.lastname: Timmermans
authors.forename: Luz Maria
authors.initials: LM
authors.lastname: Rodriguez
authors.forename: Hein J J
authors.initials: HJ
authors.lastname: Wellens
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D002037:Bundle-Branch Block / Q000503:physiopathology / Q000601:surgery; D002304:Cardiac Pacing, Artificial; D017115:Catheter Ablation; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D011227:Pre-Excitation, Mahaim-Type / Q000503:physiopathology* / Q000601:surgery; D013610:Tachycardia / Q000503:physiopathology / Q000601:surgery