In-vivo characterization of left-ventricle pressure-volume telemetry system in swine model

We present in-vivo study related to the use of our implantable RF telemetry system for pressure-volume (PV) cardiac monitoring in a animal subject. We implant a commercial MEMS PV sensor into the subject's heart left-ventricle (LV), while the telemetry system is implanted outside of the heart and connected to the sensor with a 7-microwires tether. The RF telemetry system is suitable for commercial application in medium sized subjects, its total volume of 2.475cm(3) and a weight of 4.0g. Our designed system is 58 % smaller in volume, 44 % in weight and has a 55 % reduction in sampling power over the last reported research in PV telemetry. In-vivo data was captured in both an acute and a freely moving setting over a 24 hour period. We experimentally demonstrated viability of the methodology that includes the surgical procedure and real-time monitoring of the in-vivo data in a freely moving subject. Further improvements in catheter design will improve the data quality and safety of the subject. This real-time implantable technology allows for researchers to quantify cardiac pathologies by extracting real-time pressure-volume loops, wirelessly from within freely moving subjects.

Murine heart volume: numerical comparison and calibration of conductance catheter models

A full set of finite-element method (FEM) studies of the catheter within a cylindrical cuvette and within an elliptical cuvette are presented along with novel insight on the fundamental electromagnetic properties of the catheter. An in vitro experiment with modified small mouse pressure-volume catheters was conducted and the results are presented as a validation of the FEM models. In addition, sensitivity analysis on the electrode size and position is conducted and the results allow for a novel calibration factor based on catheter geometry to be presented. This calibration factor is used in conjunction with Wei's conductance volume equations to reduce the average measured error in cuvette volume measurements from 26.5% to 5%.

Advancements in pressure-volume catheter technology - stress remodelling after infarction

Microconductance catheters have been successfully applied to measure left ventricular (LV) function in the mouse to assess cardiac or pharmacological interventions for a number of years. New complex admittance methods produce an estimate of the parallel admittance of cardiac muscle that can be used to correct the measurement in real time. This contrasts with existing conductance technologies that require in vivo calibration using a bolus of hypertonic saline. Here, we report the application of this emerging technology in the context of myocardial infarction and LV remodelling. Using a combination of high-resolution ultrasound and LV conductance catheters, we compared measures of LV function using an admittance system and a traditional conductance-derived pressure-volume (PV) system. We subjected C57BL/6 mice to focal myocardial ischaemia-reperfusion by transient ligation of the left anterior descending coronary artery and assessed cardiac function with different systems to determine the reliability and accuracy of these methods to distinguish between normal and dysfunctional ventricle. We demonstrate that the admittance PV system, in our hands, provides a straightforward solution for assessing LV function in mice. Using this technique in combination with other established methods, we measured LV dysfunction following coronary artery occlusion and reperfusion, which can be ameliorated using a known preconditioning agent (CORM-3), and found that functional read-outs are representative of other methods. We have found that, especially in diseased tissue, LV pressure-volume loops derived from complex admittance provide a reproducible and reliable method of determining LV function without the need for technically challenging calibration. Our data suggest that admittance records accurate/physiological LV cavity volumes when compared with other invasive methods in the same animal. This emerging technology is both effective and reproducible for measuring LV function and dysfunction in the mouse, without the need for complicated interventions to calibrate the measurements or training in a new technology. This may mark the way towards a fast and accurate assessment of murine cardiac function in normal animals and disease models.