Novel method for measurement of medium size arterial lumen area with an impedance catheter: in vivo validation

Abstract

Gregersen. Novel method for measurement of medium size arterial lumen area with an impedance catheter: in vivo validation. Am J Physiol Heart Circ Physiol 288: H2014 -H2020, 2005; doi:10.1152/ ajpheart.00508.2004.-There is no doubt that the transformation of a cardiac catheter into a conductance catheter that allows reliable and accurate assessment of lumen cross-sectional area (CSA) will provide a powerful diagnostic and treatment tool for the invasive cardiologist. The objective of this study was to develop a method based on the impedance catheter that allows accurate and reproducible measurements of CSA for medium size vessels (e.g., coronary, femoral, and carotid arteries). Two solutions of NaCl (0.5% and 1.5%) with known conductivities were injected directly into the lumen of the artery in eight swine. We showed that the CSA can be determined analytically from two Ohm's law-type algebraic equations that account for the parallel conductance of the current into the surrounding tissue. Excellent agreement was found between the conductance catheter with the proposed two-injection method and B-mode ultrasound (US). The root mean square error for the impedance measurements was 4.8% of the mean US diameter. The repeatability of the technique was assessed with duplicate measurements. The mean of the difference between the two measurements was nearly zero, and the repeatability coefficient was within 2.4% of the mean of the two measurements. The validated method was used to assess the degree of acute vasodilatation of the vessel in response to flow overload. carotid artery; femoral artery; coronary artery; conductance catheter; cylindrical model THE CONDUCTANCE CATHETER METHOD, which has been used previously to measure ventricular volume (4 -5, 7, 14 -16, 29, 30, 33), has recently been adapted to determine the crosssectional area (CSA) of the aorta (11-13). The conductance catheter technique is based on a cylindrical model by measuring the electrical impedance of the blood with two outer electrodes for excitation and two inner electrodes for detection to yield the CSA of the chamber of interest. Two major difficulties have hampered the routine use of the conductance catheter for measurement of absolute CSA or volume of the aorta or ventricle, respectively: 1) nonhomogeneity of the electric field and 2) leakage of current into the organ wall and surrounding tissue (parallel conductance). These two factors violate the assumptions that underlie the cylindrical model for the conductance method. The current approach to the problem is to include a slope correction term in the cylindrical model to account for the nonhomogeneity of the electric field and an offset error term to correct for the current "leakage" through the vessel wall and surrounding tissue.The nonuniformity in electric field is known to be very significant in the aorta under in vivo conditions (13), primarily because of the complex electrical properties of blood cells under dynamic flow conditions (6, 21-28, 31-32). The error due to parallel conductance i...

New method to measure coronary velocity and coronary flow reserve

“…The measurement can be made in real time with adenosine in the saline solution (IC) to measure hyperemic flow. The same injection can produce measurements of lumen CSA as previously reported (8,12,14).…”

“…The same 2.7-Fr catheter was previously shown to accurately and reproducibly measure lumen CSA (12,14). Currently, there is no combination device that measures both CFR and CSA simultaneously.…”

“…The LR catheter has been validated for vessel lumen area or diameter measurements by our group (8,(12)(13)(14). The LR is a multilumen impedance catheter [2.7-Fr similar to standard intravascular ultrasound (IVUS)] with four platinum electrodes (1 mm width) at the catheter tip with customized spacing for diameter range of interest as shown in a previous publication (13).…”

“…Neither method allows for a real-time assessment in the catheterization laboratory. Hence, there is a need for an accurate, reproducible, and real-time assessment of coronary flow along with lumen sizing capability on the same interventional device.We have previously developed an intravascular conductance catheter [LumenRecon (LR) catheter, FlowCo, Indianapolis, IN] used to measure cross-sectional lumen area in both coronary and peripheral vessels (12)(13)(14). The catheter has been demonstrated to be accurate and easy to use in vivo in patients (8).…”

“…We have previously developed an intravascular conductance catheter [LumenRecon (LR) catheter, FlowCo, Indianapolis, IN] used to measure cross-sectional lumen area in both coronary and peripheral vessels (12)(13)(14). The catheter has been demonstrated to be accurate and easy to use in vivo in patients (8).…”