title: Automaticity in Mahaim fibers.
abstract: BACKGROUND
  Automatic rhythms associated with Mahaim fibers usually occur during radiofrequency catheter ablation. The incidence and significance of spontaneous automaticity in Mahaim fibers are unknown.
  
  
  RESULTS
  Spontaneous automatic rhythms were observed in 5 (12.5%) of 40 patients with Mahaim fibers referred for nonpharmacologic therapy because of recurrent episodes of symptomatic tachyarrhythmias, usually antidromic circus movement tachycardia (33/40 patients). Three were female and two were male. Their mean age was 15 +/- 7 years compared to 26 +/- 13 years of the patients without automaticity (P = 0.09). Three patients had both antidromic tachycardia and asymptomatic spontaneous automatic rhythms recorded during ambulatory ECG (1 patient) or electrophysiologic study (2 patients). In 2 patients, the automatic rhythm triggered antidromic tachycardia. Two other patients had nonsustained repetitive episodes of wide QRS tachycardia due to automaticity arising in the Mahaim fiber, without antidromic tachycardia. All automatic rhythms were abolished by successful catheter ablation of the Mahaim fibers.
  
  
  CONCLUSIONS
  Spontaneous automaticity occurred in 12.5% of our Mahaim patients and may trigger antidromic tachycardia. Spontaneous automaticity, which is not seen in rapidly conducting accessory pathways, is another argument for the presence of an AV nodal-like structure in Mahaim fibers.
authors.affiliation: Biocor Instituto, Belo Horizonte, Brazil. eduardosternick@aol.com
authors.forename: Eduardo Back
authors.initials: EB
authors.lastname: Sternick
authors.forename: Eduardo A
authors.initials: EA
authors.lastname: Sosa
authors.forename: Carl
authors.initials: C
authors.lastname: Timmermans
authors.forename: Fernando E
authors.initials: FE
authors.lastname: Cruz Filho
authors.forename: Luz-Maria
authors.initials: LM
authors.lastname: Rodriguez
authors.forename: Luiz M
authors.initials: LM
authors.lastname: Gerken
authors.forename: Mauricio I
authors.initials: MI
authors.lastname: Scanavacca
authors.forename: Marcio L
authors.initials: ML
authors.lastname: Fagundes
authors.forename: Savia C
authors.initials: SC
authors.lastname: Bueno
authors.forename: Mario O
authors.initials: MO
authors.lastname: Vrandecic
authors.forename: Hein J J
authors.initials: HJ
authors.lastname: Wellens
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001283:Atrioventricular Node / Q000503:physiopathology; D017115:Catheter Ablation; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011227:Pre-Excitation, Mahaim-Type / Q000503:physiopathology* / Q000601:surgery