Cycle length variability and tachycardia sites of origin in a canine model

The purpose of this study was to examine the spontaneous changes in cycle length during episodes of sustained monomorphc (MVT) and polymorphic (PVT) ventricular tachycardas and to relate these changes with the sites of earliest epicardial activation. Isochronal activation maps were obtained from 127 unipolar electrograms recorded from the surface of both ventricles with a sock electrode array in open chest anesthetized dogs. Cycle length (431 ± 80 msec) in MVT (7 dogs) had beat to beat variations of 15 ± 17 msec corresponding with small shfts in sites of epicardial breakthrough clustered along the border of the ischemic myocardium. In PVT (5 dogs), the cycle length (352 ± 90 msec) had a variability of 61 ± 23 msec, corresponding to wide changes on the sites of epicardial breakthrough. Mean cycle length and variability were significantly different (≪0.01) between MVT and PVT. Linear regression analysis showed a strong and significant correlation between cycle length variability and the number of electrodes detecting the earliest activation (r=0.77, p≪0.000l).