In vivo measurements of the heat convection coefficient on the endocardial surface

This work describes the fundamentals, calibration procedure and in vivo results of an instrument for the measurement of the heat convection coefficient between the endocardium and the circulating blood flow. The heat transfer parameters will assist calculating the proper dose for radio-frequency ablation. The probe is a thermistor mounted in a Swan-Ganz catheter, and it is driven by a constant temperature anemometer circuit. A 1-D thermal model of the sensor behavior in a convective medium, the calibration procedure, and the apparatus are explained in detail. A performance analysis of the instrument in the range tested showed that the average absolute error of full scale was 7.4 %, and its time-constant was 0.05 s. This instrument was used to measure the heat transfer on the right atrial and ventricular endocardial surfaces of two pigs in vivo. The average heat convection coefficients found were between 510 and 4800 Wm−2K−1 . It was found that the average heat convection coefficient varied significantly both spatially and temporally on the endocardium.