Measurement of Coronary Lumen Area Using an Impedance Catheter: Finite Element Model and in Vitro Validation

Sensorized Endovascular Technologies: Additional Data to Enhance Decision-Making

BACKGROUND

Current endovascular procedures rely mostly on anatomic information, guided by fluoroscopy, to perform interventions (i.e. angioplasty, stent placement, coils). However, the structural parameters provided by these imaging technologies do not provide any physiological data on either the disease state or efficacy of intervention. Additional endovascular tools are needed to collect physiologic and other both anatomic and nonanatomic data to further individualize endovascular interventions with the ultimate goal of improving patient outcomes. This review details the current state of the art for these sensorized endovascular technologies and details systems under development with the aim of identifying gaps and new directions. The objective of this review was to survey the Vascular Surgery literature, engineering literature, and commercially available products to determine what exists in terms of sensor-enabled endovascular devices and where gaps and opportunities exist for further sensor integration.

METHODS

Search terms were entered into search engines such as Google and Google Scholar to identify endovascular devices containing sensors. A variety of terms were used including directly search for items such as "sensor-enabled endovascular devices" and then also completing more refined searches bases on areas of interest (i.e. fractional flow reserve, navigation, retrograde endovascular balloon occlusion of the aorta, etc.). For the most part, systems were included where the sensor was mounted directly onto the catheter and implantable sensors such as those that have been investigated for use with stents have been excluded.

RESULTS

The authors were able to identify a body of literature in the area of endovascular devices that contain sensors to measure physiologic information. However, areas where additional sensing capabilities may be useful were identified.

CONCLUSIONS

Several different types of sensors and sensing systems were identified that have been integrated with endovascular catheters. Although a great deal of work has been done in this field, there are additional useful data that could be obtained from additional novel sensing technologies. Furthermore, significant effort needs to be allocated to carefully studying how these new technologies can be employed to actually improve patient outcomes.

Novel venous balloon for compliance measurement and stent sizing in a post-thrombotic swine model

Objective: Real-time accurate venous lesion characterization is needed during endovenous interventions for stent deployment. The goal of this study is to validate a novel device for venoplasty sizing and compliance measurements. Methods: A compliance measuring sizing balloon (CMSB) uses real-time electrical conductance measurements based on Ohm's Law to measure the venous size and compliance in conjunction with pressure measurement. The sizing accuracy and repeatability of the CMSB system were performed with phantoms on the bench and in a swine model with an induced post thrombotic (PT) stenosis in the common femoral vein of swine. Results: The accuracy and repeatability of the CMSB system were validated with phantom bench studies of known dimensions in the range of venous diameters. In 9 swine (6 experimental and 3 control animals), the luminal cross-sectional areas (CSA) increased heterogeneously along the PT stenosis when the CMSB system was inflated by stepwise pressures. The PT stenosis showed lower compliance compared to the non-PT vein segments (5 mm2 vs. 10 mm2 and 13 mm2 at a pressure change of 40 cm H2O). Compliance had no statistical difference between venous hypertension (VHT) and Control. Compliance at PT stenosis, however, was significantly smaller than that at Control and VHT (p < 0.05, ANOVA). Conclusion: The CMSB system provides accurate, repeatable, real-time measurements of CSA and compliance for assessment of venous lesions to guide interventions. These findings provide the impetus for future first-in-human studies.

Novel gel bolus to improve impedance-based measurements of esophageal cross-sectional area during primary peristalsis

INTRODUCTION

Intraluminal esophageal impedance (ILEE) has the potential to measure esophageal luminal distension during swallow-induced peristalsis in the esophagus. A potential cause of inaccuracy in the ILEE measurement is the swallow-induced air in the bolus.

AIM

Compare a novel gel bolus to the current alternatives for the measurement of impedance-based luminal distension (cross-sectional area, CSA) during primary peristalsis.

METHODS

12 healthy subjects were studied using high-resolution impedance manometry (HRMZ) and concurrently performed intraluminal ultrasound (US) imaging of the esophagus. Three test bolus materials were used: 1) novel gel, 2) 0.5 N saline, and 3) commercially available Diversatek EFTV viscous. Testing was performed in the supine and Trendelenburg (-15°) positions. US imaging assessed air in the bolus and luminal CSA. The Nadir impedance values were correlated to the US measured CSA. A custom Matlab software was used to assess the bolus travel times and impedance-based luminal CSA.

RESULTS

The novel gel bolus had the least amount of air in the bolus during its passage through the esophagus, as assessed by US image analysis. The novel gel bolus in the supine and Trendelenburg positions had the best linear fit between the US measured CSA and nadir impedance value (R²  = 0.88 & R²  = 0.90). The impedance-based calculation of the CSA correlated best with the US measured CSA with the use of the novel gel bolus.

CONCLUSION

We suggest the use of novel gel to assess distension along with contraction during routine clinical HRM testing.

Biologically Inspired Catheter for Endovascular Sensing and Navigation

Minimally invasive treatment of vascular disease demands dynamic navigation through complex blood vessel pathways and accurate placement of an interventional device, which has resulted in increased reliance on fluoroscopic guidance and commensurate radiation exposure to the patient and staff. Here we introduce a guidance system inspired by electric fish that incorporates measurements from a newly designed electrogenic sensory catheter with preoperative imaging to provide continuous feedback to guide vascular procedures without additional contrast injection, radiation, image registration, or external tracking. Electrodes near the catheter tip simultaneously create a weak electric field and measure the impedance, which changes with the internal geometry of the vessel as the catheter advances through the vasculature. The impedance time series is then mapped to a preoperative vessel model to determine the relative position of the catheter within the vessel tree. We present navigation in a synthetic vessel tree based on our mapping technique. Experiments in a porcine model demonstrated the sensor's ability to detect cross-sectional area variation in vivo. These initial results demonstrate the capability and potential of this novel bioimpedance-based navigation technology as a non-fluoroscopic technique to augment existing imaging methods.

Injection-Less Conductance Method for Vascular Sizing

Lumen vessel sizing is important for optimization of interventional outcomes for treatment of vascular disease. The objective of this study is to develop an injection-less method to determine the lumen diameter, using multiple frequencies that eliminates the need for saline injections. We utilize the same electrical conductance devices developed for the two-injection method. A mathematical electrical model was devised to estimate the lumen area and diameter of the arteries. In vitro experiments were used to validate the method for various lumen diameters with both 5-5-5 (peripheral) and 2-2-2 (coronary) spacing conductance guidewires. The majority of 11 vessel data fall within one standard deviation and all the data fall within two standard deviations. The results indicate that the two-frequency model can reasonably predict the lumen diameter in an in-vitro test set-up. Our findings show that this approach can potentially translate to in vivo which would enable pull-back to reconstruct the lumen area profile of the vessel.

LumenRECON Guidewire: Pilot Study of a Novel, Nonimaging Technology for Accurate Vessel Sizing and Delivery of Therapy in Femoropopliteal Disease

BACKGROUND

Proper vessel sizing during endovascular interventions is crucial to avoid adverse procedural and clinical outcomes. LumenRECON (LR) is a novel, nonimaging, 0.035-inch wire-based technology that uses the physics-based principle of Ohm's law to provide a simple, real-time luminal size while also providing a platform for therapy delivery. This study evaluated the accuracy, reliability, and safety of the LR system in patients presenting for a femoropopliteal artery intervention.

METHODS AND RESULTS

This multicenter, prospective pilot study of 24 patients presenting for peripheral intervention compared LR measurements of femoropopliteal artery size to angiographic visual estimation, duplex ultrasound, quantitative angiography, and intravascular ultrasound. The primary effectiveness and safety end point was comparison against core laboratory adjudicated intravascular ultrasound values and major adverse events, respectively. Additional preclinical studies were also performed in vitro and in vivo in swine to determine the accuracy of the LR guidewire system. No intra- or postprocedure device-related adverse events occurred. A balloon or stent was successfully delivered in 12 patients (50%) over the LR wire. Differences in repeatability between successive LR measurements was 2.5±0.40% (R²=0.96) with no significant bias. Differences in measurements of LR to other modalities were 0.5±1.7%, 5.0±1.8%, -1.5±2.0%, and 6.8±3.4% for intravascular ultrasound core laboratory, quantitative angiography, angiographic, and duplex ultrasound, respectively.

CONCLUSIONS

This study demonstrates that through a physics-based principle, LR provides a real-time, safe, reproducible, and accurate vessel size of the femoropopliteal artery during intervention and can additionally serve as a conduit for therapy delivery over its wire-based platform.

Optimization of Peripheral Vascular Sizing with Conductance Guidewire: Theory and Experiment

Although the clinical range of interventions for coronary arteries is about 2 to 5 mm, the range of diameters of peripheral vasculature is significantly larger (about 10 mm for human iliac artery). When the vessel diameter is increased, the spacing between excitation electrodes on a conductance sizing device must also increase to accommodate the greater range of vessel diameters. The increase in the excitation electrodes distance, however, causes higher parallel conductance or current losses outside of artery lumen. We have previously shown that the conductance catheter/guidewire excitation electrode distances affects the measurement accuracy for the peripheral artery lumen sizing. Here, we propose a simple solution that varies the detection electrode distances to compensate for parallel conductance losses. Computational models were constructed to simulate the conductance guidewire with various electrodes spacing combinations over a range of peripheral artery lumen diameters and surrounding tissue electrical conductivities. The results demonstrate that the measurement accuracy may be significantly improved by increased detection spacing. Specifically, an optimally configured detection/excitation spacing (i.e., 5-5-5 or an equidistant electrode interval with a detection-to-excitation spacing ratio of 0.3) was shown to accurately predict the lumen diameter (i.e., -10% < error < 10%) over a broad range of peripheral artery dimensions (4 mm < diameter < 10 mm). The computational results were substantiated with both ex-vivo and in-vivo measurements of peripheral arteries. The present results support the accuracy of the conductance technique for measurement of peripheral reference vessel diameter.

Measurement of peak esophageal luminal cross-sectional area utilizing nadir intraluminal impedance

BACKGROUND

Multichannel intraluminal impedance (MII) is currently used to monitor gastroesophageal reflux and esophageal bolus clearance. We describe a novel methodology to measure maximal luminal cross-sectional area (CSA) during bolus transport from MII measurements.

METHODS

Studies were conducted in-vitro (test tubes) and in-vivo (healthy subjects). Concurrent MII, high resolution manometry, and intraluminal ultrasound (US) images were recorded 7-cm above the lower esophageal sphincter. Swallows with two concentrations of saline, 0.1 and 0.5 N, of bolus volumes 5, 10, and 15 cc were performed. The CSA was estimated by solving two algebraic Ohm's law equations, resulting from the two saline solutions. The CSA calculated from impedance method was compared with the CSA measured from the intraluminal US images.

KEY RESULTS

The CSA measured in duplicate from B-mode US images showed a mean difference between the two manual delineations to be near zero, and the repeatability coefficient was within 7.7% of the mean of the two CSA measurements. The calculated CSA from the impedance measurements strongly correlated with the US measured CSA (R(2) ≅ 0.98). A detailed statistical analysis of the impedance and US measured CSA data indicated that the 95% limits of agreement between the two methods ranged from -9.1 to 13 mm(2) . The root mean square error of the two measurements was 4.8% of the mean US-measured CSA.

CONCLUSIONS & INFERENCES

We describe a novel methodology to measure peak esophageal luminal CSA from the nadir impedance during peristalsis. Further studies are needed to determine if it is possible to measure patterns of luminal distension during peristalsis across the entire length of the esophagus from the MII recordings.

Two-in-one aortic valve sizing and valvuloplasty conductance balloon catheter

BACKGROUND

Inaccurate aortic valve sizing and selection is linked to paravalvular leakage in transcatheter aortic valve replacement (TAVR). Here, a novel sizing valvuloplasty conductance balloon (SVCB) catheter is shown to be accurate, reproducible, unbiased, and provides real-time tool for aortic valve sizing that fits within the standard valvuloplasty procedure.

METHODS AND RESULTS

The SVCB catheter is a valvuloplasty device that uses real-time electrical conductance measurements based on Ohm's Law to size the balloon opposed against the aortic valve at any given inflation pressure. Accuracy and repeatability of the SVCB catheter was performed on the bench in phantoms of known dimension and ex vivo in three domestic swine aortic annuli with comparison to computed tomography (CT) and dilator measurements. Procedural workflow and safety was demonstrated in vivo in three additional domestic swine. SVCB catheter measurements had negligible bias or error for bench accuracy considered as the gold standard (Bias: -0.11 ± 0.26 mm; Error: 1.2%), but greater disagreement in ex vivo versus dilators (Bias: -0.3 ± 1.1 mm; Error: 4.5%), and ex vivo versus CT (Bias: -1.0 ± 1.6 mm; Error: 8.7%). The dilator versus CT accuracy showed similar agreement (Bias: -0.9 ± 1.5 mm; Error: 7.3%). Repeatability was excellent on the bench (Bias: 0.02 ± 0.12 mm; Error: 0.5%) and ex vivo (Bias: -0.4 ± 0.9 mm; Error: 4.6%). In animal studies, the device fit well within the procedural workflow with no adverse events or complications.

CONCLUSIONS

Due to the clinical relevance of this accurate, repeatable, unbiased, and real-time sizing measurement, the SVCB catheter may provide a useful tool prior to TAVR. These findings merit a future human study.

A lumen sizing workhorse guidewire for peripheral vasculature: two functions in one device

OBJECTIVES

Ideally, guidewires used during peripheral vasculature (PV) interventions could serve both as a therapy delivery platform and a diagnostic tool for real-time vessel sizing (2-in-1 function).

BACKGROUND

Vascular imaging modalities, like intravascular ultrasound (IVUS), used during lower PV interventions, can improve outcomes versus angiographic assessment alone, but are rarely used due to added time, cost, and required clinical training/interpretation.

METHODS

A 0.035″ bodied 0.035″ conductance guidewire (CGW) is described here as a vascular navigation and diagnostic real-time PV sizing tool. When attached to a console, the CGW creates a safe, electric field to determine vascular size through simultaneous voltage measurements.

RESULTS

The CGW showed functionality as a workhorse guidewire on the bench (torqueability and trackability equivalent to a Wholey guidewire) and in vivo (over-the-wire stent deployment in domestic swine and first-in-man study with no major adverse events). Validation of CGW sizing versus the true diameter and IVUS was completed in 4-10 mm diameter phantoms on the bench and in swine and showed virtually no bias with excellent repeatability and accuracy (i.e., CGW repeatability: swine phantom bias = 0.03 ± 0.09 mm (1.3% error). CGW vs. true diameter: in vivo bias = 0.14 ± 0.15 mm (2.7% error). IVUS vs. true diameter: swine phantom bias = 0.01 ± 0.36 mm (4.7% error). CCW vs. IVUS: swine phantom bias = 0.13 ± 0.26 mm (3.8% error)).

CONCLUSIONS

Real-time, accurate, and safe PV dimension assessment and therapy-delivery (2-in-1 function) is possible using a novel workhorse 0.035″ bodied CGW.

Effect of saline injection mixing on accuracy of conductance lumen sizing of peripheral vessels

Transient displacement of blood in vessel lumen with saline injection is necessary in the conductance method for measurement of arterial cross-sectional area (CSA). The displacement of blood is dictated by the interactions between arterial flow hemodynamics and saline injection dynamics. The objective of the present study is to understand how the accuracy of conductance measurements is affected by the saline injection. Computational simulations were performed to assess the error in predictions of arterial CSA using conductance measurements over a range of peripheral artery diameters (i.e., 4, 7, and 10 mm) with an introducing catheter (6 Fr.) for various blood flow and saline injection rates. The simulation results were validated using the conductance measurements of the phantoms with known diameters (i.e., 7 and 10 mm). The results demonstrated that a minimum ratio of saline injection rate to blood flow rate of 3 is needed to fully displace the blood and result in accurate measurement of CSA for the peripheral artery sizes considered. Furthermore, the error was shown to be minimized as the detection electrodes are positioned between the distal to the mixing zone induced by saline injection and far downstream (4–8 cm from the injection catheter tip). The present study shows that even for the large peripheral arteries (7–10 mm) where mixing can occur, an appropriate injection rate and detection position can produce accurate measurement of lumen size.

Conductance sizing balloon for measurement of peripheral artery minimal stent area

BACKGROUND

Because stent underdeployment occurs frequently, accurate minimal stent area (MSA) measurement during postdilatation is necessary. This study investigated the accuracy and repeatability for MSA determination using a novel conductance balloon (CB) catheter for peripheral vessels.

METHODS

The CB catheter is a standard balloon catheter that measures electrical conductance (ratio of current/voltage drop) in real-time during inflation, which directly relates to the balloon cross-sectional area through Ohm's law. CB measurements were made in 4- to 10-mm phantoms on the bench, ex vivo in stents fully deployed in diseased human peripheral arteries, and in vivo in stents fully deployed in peripheral vessels in six swine. CB measurement accuracy and repeatability were calculated and compared with the known dimension (bench phantoms) or with intravascular ultrasound (IVUS) measurement after stent deployment (ex vivo and in vivo).

RESULTS

CB measurements were highly accurate (error: 1.8% bench, 5% ex vivo, and 5% in vivo) and repeatable (error: 0.9% bench, 1.8% ex vivo, and 1.3% in vivo), with virtually no bias (average difference in measurements: -0.05 mm bench CB vs known phantom diameters, -0.06 mm ex vivo CB vs IVUS, and -0.11 mm in vivo CB vs IVUS).

CONCLUSIONS

The CB sizing capability can be integrated within a standard balloon catheter (two-in-one function) to provide accurate, real-time assessment of MSA to ensure full stent apposition rather than the use of pressure as a surrogate for size.

Accurate nonfluoroscopic guidance and tip location of peripherally inserted central catheters using a conductance guidewire system

BACKGROUND

Bedside placement of peripherally inserted central catheters (PICCs) may result in navigation to undesirable locations, such as the contralateral innominate or jugular vein, instead of the superior vena cava or right atrium. Although some guidance and tip location tools exist, they have inherent limitations because of reliance on physiological measures (eg, chest landmarks, electrocardiogram, etc), instead of anatomical assessment (ie, geometric changes in the vasculature). In this study, an accurate, anatomically based, non-X-ray guidance tool placed on a novel 0.035" conductance guidewire (CGW) is validated for PICC navigation and tip location.

METHODS

The CGW system uses electrical conductance recordings to assess changes in vessel cross-sectional area to guide navigation of the PICC tip. Conductance rises and oscillates when going in the correct direction to the superior vena cava/right atrium, but drops when going in the incorrect direction away from the heart. Bench and in vivo studies in six swine were used to confirm the accuracy and repeatability of the PICC placement at various anatomical locations. The PICC tip location was confirmed by direct visualization vs the desired location.

RESULTS

CGW PICC guidance was highly accurate and repeatable with virtually no difference between actual and desired catheter tip location. The difference between the CGW PICC location vs the desired target was -0.07 ± 0.07 cm (6.6% error) on the bench and 0.04 ± 0.10 cm (5% error) in vivo. No complications or adverse events occurred during CGW usage.

CONCLUSIONS

The CGW provides an anatomically based, reproducible, and clinically significant method for PICC navigation and tip location that can improve accuracy, decrease the wait time prior to therapy delivery, decrease cost, and minimize the need for X-ray. These findings warrant clinical evaluation of this navigation tool for PICC line placement.

Implications of complex anatomical junctions on conductance catheter measurements of coronary arteries

In vivo, the position of the conductance catheter to measure vessel lumen cross-sectional area may vary depending on where the conductance catheter is deployed in the complex anatomical geometry of arteries, including branches, bifurcations, or curvatures. The objective here is to determine how such geometric variations affect the cross-sectional area (CSA) estimates obtained using the cylindrical model. Computer simulations and in vitro and in vivo experiments were used to assess how the electric field and associated CSA measurement accuracy are affected by three typical in vivo conditions: 1) a vessel with abrupt change in lumen diameter (e.g., transition from aorta to coronary ostia); 2) a vessel with a T-bifurcation or a Y-bifurcation; and 3) a vessel curvature, such as in the right coronary artery, aorta, or pulmonary artery. The error in diameter from simulation results was shown to be relatively small (<7%), unless the detection electrodes were placed near the junction between two different lumen diameters or at a bifurcation junction. Furthermore, the present findings show that the effect of misaligned catheter-vessel geometrical configuration and vessel curvature on measurement accuracy is negligible. Collectively, the findings support the accuracy of the conductance method for sizing blood vessels, despite the geometric complexities of the cardiovascular system, as long as the detection electrodes are not placed at a large discontinuity in diameter or at bifurcation junctions.

Impact of surrounding tissue on conductance measurement of coronary and peripheral lumen area

Parallel conductance (electric current flow through surrounding tissue) is an important determinant of accurate measurements of arterial lumen diameter, using the conductance method. The present study is focused on the role of non-uniform geometrical/electrical configurations of surrounding tissue, which are a primary source of electric current leakage. Computational models were constructed to simulate the conductance catheter measurement with two different excitation electrodes spacings (i.e. 12 and 20 mm for coronary and peripheral sizing, respectively) for different vessel-tissue configurations: (i) blood vessel fully embedded in muscle tissue, (ii) blood vessel superficially embedded in muscle tissue, and (iii) blood vessel superficially embedded in muscle tissue with fat covering half of the arterial vessel (anterior portion). The simulations suggest that the parallel conductance and accuracy of measurement is dependent on the inhomogeneous/anisotropic configuration of surrounding tissue, including the asymmetric dimension and anisotropy in electrical conductivity of surrounding tissue. Specifically, the measurement was shown to be accurate as long as the vessel was superficial, regardless of the considerable total surrounding tissue dimension for coronary or peripheral arteries. Moreover, it was shown that the unfavourable impact of parallel conductance on the accuracy of conductance catheter measurement is decreased by the combination of a lower transverse electrical conductivity of surrounding muscle tissue, a smaller electrode spacing and a larger lumen diameter. The present findings confirm that the conductance catheter technique provides an accurate platform for sizing of clinically relevant (i.e. superficial and diseased) arteries.

Conductance catheter measurements of lumen area of stenotic coronary arteries: theory and experiment

An injection of saline solution is required for the measurement of vessel lumen area using a conductance catheter. The injection of room temperature saline to displace blood in a vessel inevitably involves mass and heat transport and electric field conductance. The objective of the present study is to understand the accuracy of conductance method based on the phenomena associated with the saline injection into a stenotic blood vessel. Computational fluid dynamics were performed to simulate flow and its relation to transport and electric field in a stenotic artery for two different sized conductance catheters (0.9 and 0.35 mm diameter) over a range of occlusions [56–84% cross-sectional area (CSA) stenosis]. The results suggest that the performance of conductance catheter is dependent on catheter size and severity of stenosis more significantly for 0.9 mm than for 0.35 mm catheter. Specifically, the time of detection of 95% of injected saline solution at the detection electrodes was shown to range from 0.67 to 3.7 s and 0.82 to 0.94 s for 0.9 mm and 0.35 mm catheter, respectively. The results also suggest that the detection electrodes of conductance catheter should be placed outside of flow recirculation region distal to the stenosis to minimize the detection time. Finally, the simulations show that the accuracy in distal CSA measurements, however, is not significantly altered by whether the position of detection electrodes is inside or outside of recirculation zone (error was within 12% regardless of detection electrodes position). The results were experimentally validated for one lesion geometry and the simulation results are within 8% of actual measurements. The simulation of conductance catheter injection method may lead to further optimization of device and method for accurate sizing of diseased coronary arteries, which has clinical relevance to percutaneous intervention.

New method to measure coronary velocity and coronary flow reserve

Coronary flow reserve (CFR) is an important index of coronary microcirculatory function. The objective of this study was to validate the reproducibility and accuracy of intravascular conductance catheter-based method for measurements of baseline and hyperemic coronary flow velocity (and hence CFR). The absolute coronary blood velocity was determined by measuring the time of transit of a saline injection between two pairs of electrodes (known distance) on a conductance catheter during a routine saline injection without the need for reference flow. In vitro validation was made in the velocity range of 5 to 70 cm/s in reference to the volume collection method. In 10 swine, velocity measurements were compared with those from a flow probe in coronary arteries at different CFR attained by microsphere embolization. In vitro, the mean difference between the proposed method and volume collection was 0.7 ± 1.34 cm/s for steady flow and −0.77 ± 2.22 cm/s for pulsatile flow. The mean difference between duplicate measurements was 0 ± 1.4 cm/s. In in vivo experiments, the flow (product of velocity and lumen cross-sectional area that is also measured by the conductance catheter) was determined in both normal and stenotic vessels and the mean difference between the proposed method and flow probe was −1 ± 12 ml/min (flow ranged from 10 to 130 ml/min). For CFR, the mean difference between the two methods was 0.06 ± 0.28 (range of 1 to 3). Our results demonstrate the reproducibility and accuracy of velocity and CFR measurements with a conductance catheter by use of a standard saline injection. The ability of the combined measurement of coronary lumen area (as previously validated) and current velocity and CFR measurements provides an integrative diagnostic tool for interventional cardiology.

A novel system for the reconstruction of a coronary artery lumen profile in real time: a preclinical validation

Accurate sizing of vessel diameter is important for understanding the physiology of blood vessels as well as the treatment of coronary and peripheral artery disease. The objective of this study was to validate a novel catheter-based system [the LumenRECON (LR) system] for the real-time reconstruction of lumen cross-sectional area (CSA) along the length of a vessel segment. A total of 22 swine (20 Yorkshire and 2 atherosclerotic Ossabaw swine) were used to evaluate the accuracy, reproducibility, and safety of the system compared with intravascular ultrasound (IVUS). The CSA of the right coronary artery, left anterior descending coronary artery, and left circumflex artery were determined by IVUS and the LR system over a 3- to 4-cm segment in 12 Yorkshire and 2 atherosclerotic Ossabaw swine and 2 postmortem atherosclerotic human hearts. In eight chronic animals, the effect of the LR catheter on the vessel wall was evaluated at 1 day and 2 wk (4 animals each) after the intervention. A Bland-Altman plot of the LR and IVUS data showed a mean difference between the two measurements of 0.055 mm in diameter, which was not statistically significant from zero, indicating a lack of bias in the comparison of the LR system with IVUS. The root mean square error of the two measurements was 10.2% of the mean IVUS diameter. The repeatability of the LR system was assessed using duplicate measurements. The mean of the difference between the two measurements was nearly zero, and the repeatability coefficient was within 4.5% of the mean of the two measurements. No injury or intimal hyperplasia was found acutely or chronically after the use of the LR system. This study establishes the accuracy, reproducibility, and safety of a nonimaging 2.7-Fr catheter for lumen sizing of coronary arteries. The system provides a continuous quantitative axial profile of the mean vessel lumen in real time and may have significant utility in vascular research and clinically in the catheterization laboratory.

Finite element modelling and simulations in cardiovascular mechanics and cardiology: A bibliography 1993–2004

The paper gives a bibliographical review of the finite element modelling and simulations in cardiovascular mechanics and cardiology from the theoretical as well as practical points of views. The bibliography lists references to papers, conference proceedings and theses/dissertations that were published between 1993 and 2004. At the end of this paper, more than 890 references are given dealing with subjects as: Cardiovascular soft tissue modelling; material properties; mechanisms of cardiovascular components; blood flow; artificial components; cardiac diseases examination; surgery; and other topics.

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

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.