Baseline impedance maps for tissue proximity indications

Apparatus, comprising:

• an electrical interface;
• and
• a processor, configured:
• to ascertain, for each volume of a plurality of different volumes within a heart of a subject, one or more impedances between a catheter electrode, which is in the volume, and an external electrode that is externally coupled to the subject, based on a signal received via the electrical interface,
• to construct a baseline impedance model (BIM) that models a portion of the heart as a collection of three-dimensional cells, each of which corresponds to a respective one of the volumes, by:
• for each cell of a first subset of the cells, calculating a respective representative impedance, based on the one or more impedances ascertained for the volume to which the cell corresponds, and
• designating a second subset of the cells, which is a subset of the first subset of the cells, as baseline-impedance cells, each cell of which has, as a respective baseline impedance, the representative impedance of the cell,
• to ascertain, subsequently to constructing the BIM, that the catheter electrode is within a threshold distance of tissue of the heart, based on the baseline impedance of one of the baseline-impedance cells, and
• to update a map of the tissue, in response to ascertaining that the catheter electrode is within the threshold distance.

A method, comprising:

• constructing a baseline impedance model (BIM) that models a portion of a heart of a subject as a collection of three-dimensional cells, each of which corresponds to a respective volume within the heart,
• at least some of the cells being designated as baseline-impedance cells, for each of which the BIM specifies a respective baseline impedance;
• ascertaining, by a processor, an impedance between a catheter electrode, which is within the heart, and an external electrode that is externally coupled to the subject;
• identifying one of the baseline-impedance cells as a reference cell;
• ascertaining that the catheter electrode is within a threshold distance of tissue of the heart, by comparing the ascertained impedance to the baseline impedance that is specified for the reference cell;
• and
• in response to ascertaining that the catheter electrode is within the threshold distance of the tissue, updating a map of the tissue.

A method, comprising:

• for each volume of a plurality of different volumes within a heart of a subject, ascertaining, by a processor, one or more impedances between a catheter electrode, which is in the volume, and an external electrode that is externally coupled to the subject;
• constructing a baseline impedance model (BIM) that models a portion of the heart as a collection of three-dimensional cells, each of which corresponds to a respective one of the volumes, by:
• for each cell of a first subset of the cells, calculating a respective representative impedance, based on the one or more impedances ascertained for the volume to which the cell corresponds, and
• designating a second subset of the cells, which is a subset of the first subset of the cells, as baseline-impedance cells, each cell of which has, as a respective baseline impedance, the representative impedance of the cell;
• subsequently to constructing the BIM, ascertaining that the catheter electrode is within a threshold distance of tissue of the heart, based on the baseline impedance of one of the baseline-impedance cells;
• and
• in response to ascertaining that the catheter electrode is within the threshold distance, updating a map of the tissue.