title: The N + 1 difference: a new measure for entrainment mapping.
abstract: OBJECTIVE
  The purpose of this study was to develop and test a new entrainment mapping measurement, the N + 1 difference.
  
  
  BACKGROUND
  Entrainment mapping is useful for identifying re-entry circuit sites but is often limited by difficulty in assessing: 1) changes in QRS complexes or P-waves that indicate fusion, and 2) the postpacing interval (PPI) recorded directly from the stimulation site.
  
  
  METHODS
  In computer simulations of re-entry circuits, the interval from a stimulus that reset tachycardia to a timing reference during the second beat after the stimulus was compared with the timing of local activation at the site during tachycardia to define an interval designated the N + 1 difference. The N + 1 difference was compared with the PPI-tachycardia cycle length (TCL) difference in simulations and at 65 sites in 10 consecutive patients with ventricular tachycardia (VT) after myocardial infarction and at 45 sites in 10 consecutive patients with atrial flutter.
  
  
  RESULTS
  In simulations, the N + 1 difference was equal to the PPI-TCL difference. During mapping of VT and atrial flutter, the N + 1 difference correlated well with the PPI-TCL difference (r > or = 0.91, p < 0.0001), identifying re-entry circuit sites with sensitivity of > or = 86% and specificity of > or = 90%. Accuracy was similar using either the surface electrocardiogram or an intracardiac electrogram (Eg) as the timing reference.
  
  
  CONCLUSIONS
  The N + 1 difference allows entrainment mapping to be used to identify re-entry circuit sites when it is difficult to evaluate Egs at the mapping site or fusion in the surface electrocardiogram.
authors: Department of Internal Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors: K
authors: K
authors: Soejima
authors: W G
authors: WG
authors: Stevenson
authors: W H
authors: WH
authors: Maisel
authors: E
authors: E
authors: Delacretaz
authors: C B
authors: CB
authors: Brunckhorst
authors: K E
authors: KE
authors: Ellison
authors: P L
authors: PL
authors: Friedman
mesh_terms: D000368:Aged; D001282:Atrial Flutter / Q000175:diagnosis / Q000503:physiopathology; D018780:Body Surface Potential Mapping; D002304:Cardiac Pacing, Artificial; D003198:Computer Simulation; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000175:diagnosis* / Q000503:physiopathology; D013615:Tachycardia, Sinoatrial Nodal Reentry / Q000175:diagnosis* / Q000503:physiopathology