In vitro and in vivo studies on thermistor-based intracoronary temperature measurements: effect of pressure and flow.

ABSTRACT

BACKGROUND: Intracoronary thermography has been proposed to detect vulnerable plaques. We hypothesized that changes in coronary pressure and flow in the coronary tree may interfere with the temperature measurements obtained with thermistors. METHODS AND RESULTS: First, a very close correlation was found in vitro between the temperature measured by a thermocouple and by a thermistor-based temperature measuring guide wire (PressureWire, PW) over a large temperature range. Second, the PW was tested in a vitro low pressure model of "hot plaque". The sensor of the PW could detect changes in temperature of the wall of 0.5 degrees C as long as the distance from the wall was less than 0.5 mm and the flow less than 60 mL/min. Third, in 18 patients with an acute myocardial infarction, intracoronary pressure and temperature variations were assessed. Although crossing the occlusion, the temperature rose by 0.059 +/- 0.02 degrees C and this increase was correlated with the distal coronary pressure (r = 0.72, P < 0.001). Fourth, a balloon coronary occlusion (BCO) with the sensor distally in the distal part of the vessel (low flow/low pressure conditions) systematically induced an increase in temperature (0.14 +/- 0.07 degrees C) while with the sensor proximally to the balloon occlusion (low flow/normal pressure conditions), no change occurred. CONCLUSION: Taken together these observations suggest that thermistor-based sensors are not suited for assessing thermal heterogeneity in the vascular wall and that the data obtained so far in patients with acute coronary syndromes might have been flawed by pressure (and flow) artifacts.