Interpretation of Transpulmonary Thermodilution Curves

To the Editor:

Michard1 recently reported a possible artifact that appeared to mimic the biphasic thermodilution display of temperature vs time of an intracardiac right-to-left shunt after injection of cold indicator via a femoral vein catheter and temperature measurement using a thermistor placed via the femoral artery. It was thus stated to be similar to transpulmonary thermodilution curves observed with this technique in the presence of right-to-left intracardiac shunts with early temperature change from rapid transit of indicator through the shunt followed later by temperature change from transpulmonary transit of indicator. Although the author did not provide a time scale on the Figure displayed, the time interval between the peaks of the thermodilution curves appears to be much too short to be explained by the transit of indicator through the pulmonary circulation. This fact alone would preclude consideration of an intracardiac shunt to explain the...