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A total of 39 New Zealand white rabbits weighing 4-5
kg were utilized in the various phases of this investigation. The animals were
anesthetized with intravenous pentobarbital and heparin. The hearts were then rapidly
excised, and retrograde perfusion carried out with a Langendorff apparatus.
A plaque array of multiple bipolar recording electrodes (0.7 mm inter-electrode
distance, and 3 mm between pairs) was sutured to the left ventricle. Separate stimulating
electrodes, bipolar plunge electrodes, an indifferent electrode, a floating fine tip
micro-electrode with tip resistance > 10 ohms, and a fluid filled balloon catheter were
placed. Once pacing thresholds were determined, a computer program was adjusted to
generate the required trains of test pulses and record the data automatically.
In addition, preliminary data on contractility and hemodynamics were obtained in dogs
using gated-MRI 6 techniques.
The time differences between the activation wavefronts reaching successive bipoles was
used to compute the conduction velocity between successive electrodes, the maximum
derivative of the upstroke was calculated from the intracellular recordings, and the
hemodynamic parameters measured by hand from the pressure waveforms.
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