Left ventricular pressure measurement in conscious rats via telemetry

Abstract

The development of a new telemetry device with a solid state micro-tip 2 Fr sensor has opened up the possibility of recording left ventricular pressure (LVP) chronically in the conscious rat. With particular relevance to LVP measurement is the possibility that high frequency sampling at 2000 Hz permits accurate determination of dP/dT. In the present study, we have explored the surgical placement and long-term stability of the sensor for LVP measurement. We implanted the body of the TRM54P transmitter in the abdomen of rats and used a transdiaphragmatic approach to implant the tip of the catheter through the apex of the left ventricle. The rats were then monitored for 4 to 6 weeks after surgery. To assess the effect of chronic catheter placement, echocardiography was used both before and three weeks after implantation to determine fractional shortening. Our ability to measure changes in dP/dT was assessed using subcutaneous injections of verapamil, isoproterenol and propranolol. Maximum dP/dT values in conscious rats were between 9,000 mmHg/s and 14,000 mmHg/s on the third day after surgery (average 11,000 mmHg/s) and were subsequently stable for at least 4 weeks. The results of this study show that we can accurately measure LVP over long periods in the conscious rat without inducing significant impairment of cardiac function.