title: Paroxysmal atrial fibrillation in seven dogs with presumed neurally-mediated syncope.
abstract: OBJECTIVE
  To document the electrocardiographic findings of vagally-induced paroxysmal atrial fibrillation following a presumed reflex syncopal episode in the dog.
  
  
  METHODS
  Seven dogs with a syncopal episode followed by a paroxysm of atrial fibrillation recorded on a 24-hour Holter.
  
  
  METHODS
  Twenty-four hour Holter monitors were retrospectively reviewed, analysing the cardiac rhythm associated with syncopal events. Each recording was analysed from 10 min before the syncopal episode to until 10 min after a normal sinus rhythm had returned.
  
  
  RESULTS
  Nine episodes were recorded in seven dogs, with one patient experiencing three events during one Holter recording. Five of the seven dogs presented with underlying structural heart disease. In two the syncopal episodes occurred following exercise, two associated with coughing and three were during a period of rest. All dogs had documented on the Holter recording a rhythm abnormality during syncope. The most common finding leading up to the syncopal event was development of a progressive sinus bradycardia, followed by sinus arrest interrupted by a ventricular escape rhythm and then ventricular arrest. This was then followed by an atrial fibrillation. The atrial fibrillation was paroxysmal in seven recordings and persistent in two. In two dogs, the atrial fibrillation reorganised into self-limiting runs of atypical atrial flutter.
  
  
  CONCLUSIONS
  This combination of electrocardiographic arrhythmias are probably caused by an inappropriate parasympathetic stimulation initiating a reflex or neurally-mediated syncope, with abnormal automaticity of the sinus node and of the subsidiary pacemaker cells and changes in the electrophysiological properties of the atrial muscle, which promoted the paroxysmal atrial fibrillation.
authors.affiliation: Clinica Veterinaria Malpensa, Viale Marconi 27, 21017, Samarate, Varese, Italy.
authors.forename: D M
authors.initials: DM
authors.lastname: Porteiro Vázquez
authors.affiliation: Clinica Veterinaria Malpensa, Viale Marconi 27, 21017, Samarate, Varese, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Perego
authors.affiliation: Federal University of São Paulo, São Paulo, Brazil.
authors.forename: L
authors.initials: L
authors.lastname: Santos
authors.affiliation: Clinica Veterinaria Malpensa, Viale Marconi 27, 21017, Samarate, Varese, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Gerou-Ferriani
authors.affiliation: The Veterinary Cardiorespiratory Centre, Thera House, Kenilworth, Warwickshire, UK.
authors.forename: M W S
authors.initials: MW
authors.lastname: Martin
authors.affiliation: Clinica Veterinaria Malpensa, Viale Marconi 27, 21017, Samarate, Varese, Italy. Electronic address: rasantil@alice.it.
authors.forename: R A
authors.initials: RA
authors.lastname: Santilli
mesh_terms: D000818:Animals; D001146:Arrhythmia, Sinus / Q000662:veterinary; D001281:Atrial Fibrillation / Q000503:physiopathology / Q000662:veterinary*; D004283:Dog Diseases / Q000503:physiopathology*; D004285:Dogs; D004562:Electrocardiography / Q000662:veterinary; D005260:Female; D008297:Male; D012189:Retrospective Studies; D013575:Syncope / Q000503:physiopathology / Q000662:veterinary*
keywords: Arrhythmias; Atrial flutter; Dog; Transient loss of consciousness