title: Does cardiac pacing reproduce the mechanism of focal impulse initiation?
abstract: Stimulation of myocardium by either a native pacemaker or an artificial stimulus requires the initiation of a self-propagating wave of depolarization originating from the site of initial activation. In the present study we perform artificial stimulation at a site of focal discharge with the aim to compare the two mechanisms of impulse formation. High resolution epicardial mapping in senescent rat hearts provided examples of focal discharge during sinus rhythm at a single epicardial breakthrough (BKT) point emerging from an isolated Purkinje-ventricular muscle junction (PMJ) site. Stimulation was also performed at the same BKT point and potential distributions recorded during spontaneous and artificial stimulation were compared. During excitation latency, the negative potential pattern was elongated perpendicularly to fiber direction at both pacing and BKT point, in agreement with virtual cathode membrane polarization predicted by the bidomain model during point stimulation. During impulse initiation, activation wave fronts were initially circular around pacing site or BKT point and then elongated along local fiber direction. The similarity between impulse initiation during focal discharge and point stimulation in cardiac muscle suggests that high resolution pace mapping studies can help to elucidate the mechanism of abnormal impulse formation.
authors.affiliation: Dipartimento di Biologia Evolutiva e Funzionale, Sezione Fisiologia, Italy. macchi@biol.unipr.it
authors.forename: Emilio
authors.initials: E
authors.lastname: Macchi
authors.forename: Silvana
authors.initials: S
authors.lastname: Baruffi
authors.forename: Stefano
authors.initials: S
authors.lastname: Rossi
authors.forename: Michele
authors.initials: M
authors.lastname: Miragoli
authors.forename: Andrea
authors.initials: A
authors.lastname: Bertuzzi
authors.forename: Ezio
authors.initials: E
authors.lastname: Musso
authors.forename: Domenico
authors.initials: D
authors.lastname: Corradi
authors.forename: Franco
authors.initials: F
authors.lastname: Di Gregorio
mesh_terms: D000818:Animals; D018780:Body Surface Potential Mapping; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D006329:Heart Conduction System / Q000033:anatomy & histology / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D010496:Pericardium / Q000502:physiology; D011690:Purkinje Fibers / Q000502:physiology; D051381:Rats; D016276:Ventricular Function; D018879:Ventricular Premature Complexes / Q000503:physiopathology