Affiliations: Holy Name Hospital, Teaneck, NJ,
University of Paris XI, le Plessis Robinson, France
Correspondence to: Randolph P. Cole, MD, Holy Name Hospital, 718 Teaneck Rd, Teaneck, NJ 07666; e-mail: firstname.lastname@example.org
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 tracings displayed.
I thank Dr. Cole for focusing on a figure I recently published in CHEST (August 2004).1 However, I totally disagree with his comments. Dr. Cole claims that the time interval between the two peaks of the so-called camel transpulmonary thermodilution curve (with two humps) that was presented in my article is “much too short” to mimic a right-to-left intracardiac shunt.
When the camel curve is due to a right-to-left intracardiac shunt, the time interval between the two peaks represents the blood transit time between the right and left atrium through the pulmonary circulation.2 When the camel curve is due to a cross-talk phenomenon, the time interval between the two peaks is necessarily longer (and not shorter!), since it represents the blood transit time between the femoral vein (cold indicator injection) and the femoral artery (a longer distance means a longer time interval).
Moreover and more importantly, in both cases the time interval between the two peaks is highly dependent on cardiac output and, for instance, will be three times shorter in a patient with a cardiac output of 9 L/min than if the cardiac output is only 3 L/min. Therefore, I still believe that the “eyeball” inspection of a transpulmonary thermodilution curve does not allow the discrimination between a cross-talk phenomenon and a right-to-left intracardiac shunt. The camel curve represented in my article is now depicted in Figure 1
with a different time scale and really looks like a camel curve due to a right-to-left intracardiac shunt.2
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