Note: The following information pertains to equipment used in animal-based cardiac research. If your interest is in clinical devices used on human patients, please click here for more information.

The conductance catheter (CC) is a device designed to measure the luminal volume of the chambers of the heart, most often the left ventricle. It resembles catheters used by cardiologists in cath-labs during clinical EP (electro-physiological) procedures. The single common feature of all conductance catheters is that they have an arrangement of ring-electrodes which are usually equally spaced at the distal end of the catheter.

The theory of operation of the CC is that the conductance of the volume of blood between adjacent electrodes is measured and, through the use of complex formulas, results in a calculation of the volume of the chamber being measured. The chamber is therefor represented as a stack of cylindrical segments the thickness of which is defined by the spacing of the electrodes. Since blood is a conductive medium, the more blood that surrounds two adjacent electrodes, the greater the conductivity will be between those electrodes. This effect exists not only near the electrodes but, to a lesser and more complicated extent, to the blood further away as well.

If the researcher wants accurate or absolute (not relative) volume measurements, then it is necessary to measure the resistivity of a representative blood sample. During an experiment, changes in the electrical properties of the blood can occur (because of continuous IV saline administration, for example) and it may be necessary to periodically re-calibrate the resistivity changes.

In actual use, the tip of the CC is placed at the vertex of the left ventricle and from there it runs up and out of the LV through the aortic or mitral valve. To aid in placement at the vertex, most CC's have a curl at tip. This curl, however, must be straightened when introduced into the femoral or corotid artery, and the tendency for it to "re-curl" can provide some level of frustration on the part of the operator to successfully introduce the catheter all the way down into the LV. If X-ray fluoroscopy is not available to aid in the placement of the CC, then the operator must rely on a visual assessment of the volume signal to appraise the correctness of the placement. As the heart beats, the catheter can move within the chamber (both towards and away from the apex and away from the center line of the LV, bringing it closer to the endocardial wall). This motion can lead to erroneous artifacts in the volume signal.

The use of a CC to measure chamber volume is almost always limited to the left ventricle because of the need to keep all electrodes from directly contacting the endocardial wall and because the volume formulas assume a reasonably uniform spatial distribution of the mass of blood around the catheter. Both of these factors limit, if not prevent, the use of CC's to accurately measure right ventricular volume.

Because the CC must be introduced into the blood stream, it can be a major source for pathogens and infectious agents that can lead to septic reactions in some research animals (pigs, for example). For acute experiments that last for 4 hours or more, either the CC must be sterilized or the researcher may have to resort to a canine model because of their superior immune system.