To study the spread of excitation in ventricular heart preparations we have designed a fast, high-resolution recording and mapping system. Papillary muscles were dissected from the isolated guinea pig hearts. The preparation was fixed in a tissue bath and superfused with Tyrode solution. Linear and two-dimensional arrays of Ag/AgCl electrodes were made on glass with a thin-film technique. The transparent sensors with up to 24 electrodes (spaced 50, 90, or 180 microns apart) were positioned close to the surface of the preparation with a custom-designed three-dimensional micromanipulator. Extracellular signals were simultaneously recorded by a 24-channel data acquisition system with a 200 kHz per channel sample rate, with 12-bit amplitude resolution and a maximum data length of up to 3 MB. Digitized video images of the electrode array and the underlaying preparation were used to identify the locations of the recording sites. A UNIX-based computer system with a custom-designed data acquisition and database program was used to control the instruments and to manage the experimental data. This technique gave signals with excellent signal-to-noise ratios (up to 65 dB) and permitted accurate evaluation of the time and the site of the local activation with high resolution (to within 5 microseconds, 50 microns). We describe the spread of excitation within the area of a few cells and found a substantial dispersion of conduction velocities. Beat-to-beat comparison of activation patterns showed relatively small variations in the spread of excitation (a few microseconds).

In recent years there has been a remarkable progress in the knowledge of the microstructure of the cardiac tissue and its influence on the conduction of the cardiac impulse. The tissue domain can be thought as a discrete network of cells coupled electrically at stochastically distributed sites. During in-vitro experiments the tissue is surrounded by a conducting superfusate which represents a continuous domain. With electrode arrays, electrograms can be recorded simultaneously at many sites in this volume conductor and the spatio-temporal distribution of potentials can be obtained. In this paper we show, that despite the fact that the sensors were placed in a continuous medium, we were able to detect microscopic discontinuities of propagation with appropriate techniques.

No abstract

No abstract