Purkinje and ventricular contributions to endocardial activation sequence in perfused rabbit right ventricle

Interactions between peripheral conduction system and myocardial wave front s control the ventricular endocardial activation sequence. To assess those interactions during sinus and paced ventricular beats, we recorded unipolar electrograms from 528 electrodes spaced 0.5 mm apart and placed over most of the perfused rabbit right ventricular free wall endocardium. Left ventri cular contributions to electrograms were eliminated by cryoablating that ti ssue. Electrograms were systematically processed to identify fast (P) defle ctions separated by >2 ms from slow (V) deflections to measure P-V latencie s. By using this criterion during sinus mapping (n = 5), we found P deflect ions in 22% of electrograms. They preceded V deflections at 91% of sites. P eripheral conduction system wave fronts preceded myocardial wave fronts by an overall P-V latency magnitude that measured 6.7 +/- 3.9 ms. During endoc ardial pacing (n = 8) at 500 ms cycle length, P deflections were identified on 15% of electrodes and preceded V deflections at only 38% of sites, and wave fronts were separated by a P-V latency magnitude of 5.6 +/- 2.3 ms. Th e findings were independent of apical, basal, or septal drive site. Modest changes in P-V latency accompanied cycle length accommodation to 125-ms pac ing (6.8 +/- 2.6 ms), although more pronounced separation between wave fron ts followed premature stimulation (11.7 +/- 10.4 ms). These results suggest ed peripheral conduction system and myocardial wave fronts became functiona lly more dissociated after premature stimulation. Furthermore, our analysis of the first ectopic beats that followed 12 of 24 premature stimuli reveal ed comparable separation between wave fronts (10.7 +/- 5.5 ms), suggesting the dissociation observed during the premature cycles persisted during the initiating cycles of the resulting arrhythmias.