ACTIVATION TIME DETERMINATION BY HIGH-RESOLUTION UNIPOLAR AND BIPOLAREXTRACELLULAR ELECTROGRAMS IN THE CANINE HEART

Introduction: To identify the optimal criteria for activation time (AT ) determination of bipolar electrograms from normal hearts, a high-res olution cross electrode array comprising 128 unipolar electrodes of 50 0-mu m spacing was used to record extracellular potentials from the le ft ventricular epicardium of 12 dog hearts. Methods and Results: Recor dings were made during broad wavefront propagation (B wave) and local elliptical wavefront propagation (E wave). Characteristics of 863 bipo lar electrograms (1-mm spacing) were constructed from unipolar data st andardized for differences in polarity, then classified morphologicall y. Features for bipolar AT determination were compared to the time of the negative peak of the first temporal derivative of a unipolar elect rogram situated mid-way between the bipoles. During B wave, three dist inct morphologies were observed: uniphasic (61%), biphasic (23%), and triphasic (16%). Peak voltage of uniphasic and triphasic signals was t he best predictor of AT (error: 0.6 +/- 0.6 msec and 0.6 +/- 0.8 msec, respectively). During E wave, parallel orientation of the bipoles wit h respect to the direction of impulse propagation wavefront resulted i n uniphasic signals (> 99%), while for perpendicular orientation of th e bipoles, electrogram morphology was variable. For parallel orientati on of the bipoles, peak negative voltage was the best predictor off AT for both longitudinal and transverse propagation, while for perpendic ular bipole orientation, peak negative voltage was a less reliable pre dictor for propagation along both fiber axes. Increasing interpolar di stance resulted in a degradation in AT accuracy for B wave (from 0.6 /- 0.6 msec at 1 mm to 1.1 +/- 1.2 msec at 7 mm) and for E wave (from 0.4 +/- 0.3 msec at 1 mm to 3.1 +/- 2.9 msec at 7 mm). Conclusions: (1 ) The accuracy of bipoIar electrograms is sensitive to wavefront direc tion, bipole orientation, and interpolar distance; (2) peak negative v oltage of uniphasic and triphasic signals is a reliable predictor of A T, but only for B wave; (3) a maximum interpolar distance of 2 mm and bipole orientation parallel to the direction of the impulse wavefront are minimally required for accurate determination of AT during impulse propagation initiated near the recording electrodes; and (4) for impu lses initiated near the recording site in normal tissue, a biphasic or triphasic morphology almost certainly indicates that the bipolar elec trode is oriented perpendicular to the wavefront direction, irrespecti ve of fiber orientation.