title: Electrophysiological and antiarrhythmic effects of the atrial selective 5-HT(4) receptor antagonist RS-100302 in experimental atrial flutter and fibrillation.
abstract: BACKGROUND
  Stimulation of 5-HT(4) receptors increases atrial chronotropic and inotropic responses. Whether other electrophysiological effects are produced is unknown. In humans and swine, 5-HT(4) receptors are present only in atrium. Therefore, the effects of a novel 5-HT(4) receptor antagonist, RS-100302, and the partial agonist cisapride on atrial flutter and fibrillation induced in swine were studied to delineate the role of the 5-HT(4) receptor in modulating atrial electrophysiological properties and the antiarrhythmic potential of RS-100302.
  
  
  RESULTS
  In 17 anesthetized, open-chest, juvenile pigs, atrial flutter or fibrillation was induced by rapid right atrial pacing with or without a right atrial free wall crush injury, respectively. Atrial effective refractory period (ERP), conduction velocity, wavelength, and dispersion of refractoriness were determined during programmed stimulation via a 56-electrode mapping plaque sutured to the right atrial free wall. Ventricular electrophysiological parameters were also measured. All electrophysiological parameters were measured at baseline and after infusion of RS-100302 and cisapride. In the atrium, RS-100302 prolonged mean ERP (115+/-8 versus 146+/-7 ms, P<0.01) and wavelength (8.3+/-0.9 versus 9.9+/-0.8 cm, P<0.01), reduced dispersion of ERP (15+/-5 versus 8+/-1 ms, P<0.01), and minimally slowed conduction velocity (72+/-4 versus 67+/-5 cm/s, P<0.01). These effects were all partially reversed by cisapride. RS-100302 produced no ventricular electrophysiological effects. RS-100302 terminated atrial flutter in 6 of 8 animals and atrial fibrillation in 8 of 9 animals and prevented reinduction of sustained tachycardia in all animals.
  
  
  CONCLUSIONS
  The electrophysiological profile of RS-100302 suggests that it may have atrial antiarrhythmic potential without producing ventricular proarrhythmic effects.
authors.affiliation: Cardiac Electrophysiology Program, Division of Cardiology, Department of Medicine, University of California, San Diego, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Rahme
authors.forename: B
authors.initials: B
authors.lastname: Cotter
authors.forename: E
authors.initials: E
authors.lastname: Leistad
authors.forename: M K
authors.initials: MK
authors.lastname: Wadhwa
authors.forename: R
authors.initials: R
authors.lastname: Mohabir
authors.forename: A P
authors.initials: AP
authors.lastname: Ford
authors.forename: R M
authors.initials: RM
authors.lastname: Eglen
authors.forename: G K
authors.initials: GK
authors.lastname: Feld
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000188:drug therapy*; D001282:Atrial Flutter / Q000188:drug therapy*; D020117:Cisapride / Q000494:pharmacology*; D004562:Electrocardiography / Q000187:drug effects; D011985:Receptors, Serotonin / Q000187:drug effects*; D044422:Receptors, Serotonin, 5-HT4; D012032:Refractory Period, Electrophysiological / Q000187:drug effects; D012702:Serotonin Antagonists / Q000494:pharmacology*; D013552:Swine
chemical_list: D000889:Anti-Arrhythmia Agents; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D044422:Receptors, Serotonin, 5-HT4; D020117:Cisapride