title: Cycle length dynamics at the onset of postinfarction ventricular tachycardias induced in canines: dependence on interval-dependent excitation properties of the reentrant substrate.
abstract: BACKGROUND
  Postinfarction monomorphic ventricular tachycardias induced by programmed stimulation may display initial cycle length (CL) variations before stabilizing.
  
  
  RESULTS
  To show that tachycardia onset dynamics depend on rate-dependent electrical properties of the reentrant substrate, we extracted activation times and maximum negative slopes of local activation complexes (-dV/dt(max)) from 191 unipolar electrograms recorded in the anterior left ventricular wall of anesthetized, 3-day-old infarct canine preparations. Measurements were made of the responses to programmed stimulation, as well as in early and later beats of tachycardias, which displayed either a constant trend in CL (group A, n = 5 preparations) or one in which CL prolongation occurred according to an exponential course before stabilizing (group B, n = 9). Stimulation protocols inducing the tachycardias were more aggressive and their CL was significantly shorter (CL = 159 +/- 24 msec) in group A than in group B (stabilized CL = 206 +/- 34 msec). Reentrant activity occurred in subepicardial areas in which the absolute value of -dV/dt(max) (absolute value(-dV/dtmax)) was heterogeneously depressed (<2 mV/msec). Absolute value(-dV/dtmax) was reduced and activation delay increased in the successive responses to extrastimuli. Further reductions in absolute value(-dV/dtmax) (10% to 23%) were shown to occur between early and later beats in 5 of the 9 tachycardias in group B (no change in the 4 others), and they were associated with localized prolongation of conduction times in reentrant pathways. In contrast, absolute value(-dV/dtmax) improved in all group A tachycardias (7% to 25%).
  
  
  CONCLUSIONS
  This study provides evidence that the onset dynamics of postinfarction ventricular tachycardias are determined by interval-dependent electrical changes occurring in the reentrant substrate.
authors.affiliation: Hôpital du Sacré-Coeur de Montréal, the Department of Pharmacology and the Institut de Génie Biomédical, Faculty of Medicine, Université de Montréal, Québec, Canada.
authors.forename: F
authors.initials: F
authors.lastname: Hélie
authors.forename: A
authors.initials: A
authors.lastname: Vinet
authors.forename: R
authors.initials: R
authors.lastname: Cardinal
mesh_terms: D000818:Animals; D018780:Body Surface Potential Mapping; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects; D004285:Dogs; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology*; D008297:Male; D009203:Myocardial Infarction / Q000150:complications* / Q000503:physiopathology; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000209:etiology / Q000503:physiopathology*