The transponder system: a new method of precise catheter placement in the right atrium under echocardiographic guidance

A Real-time Color Doppler Marker for Echocardiographic Guidance of an Acoustically Active Extracorporeal Membrane Oxygenation Cannula

B-mode ultrasound imaging guidance of cannulas can be compromised by noise, artifacts, and echogenicity that is not distinctive from that of surrounding anatomy. We have modified a venovenous extracorporeal membrane oxygenation cannula by embedding piezoelectric crystals into each of its 3 blood flow ports. Each vibrating crystal acoustically interacts with a Doppler imaging signal and produces an instantaneous color marker. The aim of this study was to compare identification of the extracorporeal membrane oxygenation cannula ports by B-mode imaging versus the color Doppler marker. Unlike B-mode imaging, the color Doppler marker identified the corresponding port even in highly challenging closed-chest scans in anesthetized pigs. The method could improve guidance accuracy of cannulas by ultrasound scans.

Real-Time Visualization of an Acoustically Active Injection Catheter With Ultrasound Imaging: Algorithm and In Vivo Validation in a Swine Model

OBJECTIVE

To independently visualize a catheter and needle during minimally invasive surgery in order to aid in precisely guiding them to their intended location.

METHODS

Symmetric frequency detection allows for the visualization of the acoustically active catheter tip as a unique color in live imaging. This study extends the algorithm to identify two different crystals by unique colors, validating the algorithm with in vivo pig experiments while simulating the human condition using different attenuation pads.

RESULTS

The catheter and needle tip were identified with unique colors, differentiable from common Doppler colors, with a frame rate varying between 8 and 10 Hz. Both were visible at graded levels of attenuation induced by interposed polymer pads. Reducing ensemble length increased the frame rate and decreased the signal-to-noise ratio (SNR), though not significantly. At the highest in-path attenuation of 12 dB at 5 MHz, the catheter spot marker was visible whereas the needle was not. The SNR of the catheter signal varied between 12.50 and 18.24 dB and the size of the spot marker varied between 149 and 1015 mm². The SNR of the needle signal varied between 6.37 and 16.3 dB and the size of the spot marker between 59 and 169 mm². A reliability index greater than 50% was achieved for all cases except for the needle crystal at the highest attenuation setting.

CONCLUSION

Modified symmetric frequency detection algorithm can uniquely visualize both catheter and needle in real time with in-path attenuation.

SIGNIFICANCE

Unambiguous and distinct visualization of separate locations on the catheter facilitates real-time tracking of minimally invasive procedures.

Unambiguous Identification and Visualization of an Acoustically Active Catheter by Ultrasound Imaging in Real Time: Theory, Algorithm, and Phantom Experiments

OBJECTIVE

Ultrasound-guided biopsies and minimally invasive procedures have been used in numerous medical applications, including catheter guidance. The biggest challenge for catheter guidance by ultrasound lies in distinguishing the catheter from neighboring tissue, as well as the ability to differentiate the catheter body from its tip.

METHODS

In our previous work, we introduced a functional prototype of an acoustically active catheter, in which a miniature piezoelectric crystal allowed accurate localization of the catheter tip by pulsed wave (PW) Doppler imaging and Doppler spectrogram. In this paper, the theory behind the symmetric Doppler shift due to the interaction of ultrasound wave with a vibrating piezoelectric crystal is explained. The theory is validated in an experimental continuous flow phantom setup. A novel algorithm, symmetric frequency detection algorithm, is presented for identification and visualization of the catheter tip in real time along with B-mode and PW Doppler.

RESULTS

The catheter tip is identified with a distinct color differentiable from common Doppler colors with a frame rate varying from 22 to 50 Hz. The catheter tip can be visualized in a small region of 2.4 mm in the elevational direction.

CONCLUSION

The algorithm can be implemented in most clinical ultrasound machines with minor additions to the PW Doppler processing algorithm. The algorithm is optimized to be robust for a variety of blood flow velocities and is shown to perform well when the signal from the blood is on par in amplitude with the catheter signal.

SIGNIFICANCE

Unambiguous and distinct visualization of catheter tip facilitates real-time tracking of the catheter and aids minimally invasive procedures.

Acoustically Active Catheter for Intracardiac Navigation by Color Doppler Ultrasonography

Navigation of intracardiac catheters by echocardiography is challenging because of the fundamental limitations of B-mode ultrasonography. We describe a catheter fitted with a piezoelectric crystal, which vibrates and produces an instantaneous marker in color flow Doppler scans. The navigation learning curve was explored first in six pigs. Accuracy and precision of targeting with the navigation marker "off" (i.e., B-mode imaging) and "on" were assessed in another six pigs. Paired comparisons confirmed significantly (p = 0.04) shorter mean distances achieved in each pig with the color Doppler marker. Pooled (mean ± standard deviation) distance of the catheter tip from the target crystal was 5.27 ± 1.62 mm by B-mode guidance and 3.66 ± 1.45 mm by color Doppler marker navigation. Dye injection targeted into the ischemic border zone was successful in 8 of 10 pigs. Intracardiac catheter navigation with color Doppler ultrasonography is more accurate compared with conventional guidance by B-mode imaging.

Acoustically active injection catheter guided by ultrasound: navigation tests in acutely ischemic porcine hearts

Catheters are increasingly used therapeutically and investigatively. With complex usage comes a need for more accurate intracardiac localization than traditional guidance can provide. An injection catheter navigated by ultrasound was designed and then tested in an open-chest model of acute ischemia in eight pigs. The catheter is made "acoustically active" by a piezo-electric crystal near its tip, electronically controlled, vibrating in the audio frequency range and uniquely identifiable using pulsed-wave Doppler. Another "target" crystal was sutured to the epicardium within the ischemic region. Sonomicrometry was used to measure distances between the two crystals and then compared with measurements from 2-D echocardiographic images. Complete data were obtained from seven pigs, and the correlation between sonomicrometry and ultrasound measurements was excellent (p < 0.0001, ρ = 0.9820), as was the intraclass correlation coefficient (0.96) between two observers. These initial experimental results suggest high accuracy of ultrasound navigation of the acoustically active catheter prototype located inside the beating left ventricle.

Accurate guidance of a catheter by ultrasound imaging and identification of a catheter tip by pulsed-wave Doppler

BACKGROUND

With the advent of numerous minimally invasive medical procedures, accurate catheter guidance has become imperative. We introduce and test an approach for catheter guidance by ultrasound imaging and pulsed-wave (PW) Doppler.

METHODS

A steerable catheter is fitted with a small piezoelectric crystal at its tip that actively transmits signals driven by a function generator. We call this an active-tip (AT) catheter. In a water tank, we immersed a "target" crystal and a rectangular matrix of four "reference" crystals. Two-dimensional (2D) ultrasound imaging was used for initial guidance and visualization of the catheter shaft, and then PW Doppler mode was used to identify the AT catheter tip and guide it to the simulated target that was also visible in the 2D ultrasound image. Ten guiding trials were performed from random initial positions of the AT catheter, each starting at approximately 8 cm from the target.

RESULTS

After the ten navigational trials, the average final distance of the catheter tip from the target was 2.4 ± 1.2 mm, and the range of distances from the trials was from a minimum of 1.0 mm to a maximum of 4.5 mm.

CONCLUSIONS

Although early in the development process, these quantitative in vitro results show promise for catheter guidance with ultrasound imaging and tip identification by PW Doppler.

Echocardiographic imaging of a basket catheter for mapping and ablation of ventricular tachycardia in pigs

Our objective was to assess the feasibility and efficacy of the recently described left ventricular simultaneous deployment of a new multi-electrode mapping catheter and a standard radio-frequency ablation catheter in pigs, with echocardiography monitoring and fluoroscopy guidance. Introduction and deployment of both catheters in five healthy anesthetized pigs were guided on-line by fluoroscopy and monitored with transthoracic echocardiography. Heart rate and femoral blood pressure were also continuously monitored. Both catheters were deployed for up to 5 hours. Three animals underwent three to five radio-frequency energy applications. Left ventricular dimensions obtained from long axis two-dimensional echocardiography imaging before and after basket-catheter deployment in the left ventricular cavity, were 3.9 +/- 0.3 versus 3.7 +/- 0.6 cm at end-diastole and 2.8 +/- 1.1 versus 2.6 +/- 0.8 cm at end-systole, respectively (mean +/- standard error of the mean, p > 0.05). Shortening fraction measured from long axis two-dimensional echocardiography images before and after catheter deployment was 28% +/- 10% versus 25% +/- 5%, respectively (mean +/- standard error of the mean, p > 0.05). Additional findings included the following: (1) good conformation of the multi-electrode mapping catheter to the left ventricular dimensions during diastole; (2) absence of catheter-induced aortic and/or mitral insufficiency, as well as left ventricular outflow tract obstruction; (3) absence of damage to mitral and aortic valves or to the left ventricular wall. Postmortem examination and hemodynamic measurements confirmed these findings and showed only minor subendocardial hemorrhages; (4) radio-frequency energy application produced intracavitary bubbles, which were demonstrable echocardiographically, enabling identification of the gross anatomic location of ablation sites. Echocardiography during simultaneous deployment of multi-electrode mapping catheter and radio-frequency ablation catheters enables estimation of mechanical interaction with the left ventricle and detects interaction with myocardial/valvular function. During radio-frequency energy application, bubble production may identify gross anatomic location of ablation.

A system for ultrasonic beacon-guidance of catheters and other minimally-invasive medical devices

Catheters and other interventional medical devices are presently guided by X-ray imaging, despite the advantages of ultrasound imaging over X-ray imaging in cost, safety, and availability. X-ray imaging is used because ultrasound reflects specularly from catheters and similar devices; their visibility is highly angle-dependent. With an omni-directional receiver mounted on a device, the receiver's location in the ultrasound image can be deduced from knowing which acoustic ray struck the receiver and the time from transmission of the imaging pulse to its reception by the receiver. This information is independent of specular reflection. The location of the device can then be indicated in the ultrasound image by an arrow pointing to the sensor, making possible ultrasound guidance of these devices. This paper describes the technical and practical considerations in the design and construction of the device-mounted receiver and associated electronics, and describes some clinical uses.

A system for ultrasonic beacon-guidance of catheters and other minimally-invasive medical devices

Catheters and other interventional medical devices are presently guided by X-ray imaging, despite the advantages of ultrasound imaging over X-ray imaging in cost, safety, and availability. X-ray imaging is used because ultrasound reflects specularly from catheters and similar devices; their visibility is highly angle-dependent. With an omni-directional receiver mounted on a device, the receiver's location in the ultrasound image can be deduced from knowing which acoustic ray struck the receiver and the time from transmission of the imaging pulse to its reception by the receiver. This information is independent of specular reflection. The location of the device can then be indicated in the ultrasound image by an arrow pointing to the sensor, making possible ultrasound guidance of these devices. This paper describes the technical and practical considerations in the design and construction of the device-mounted receiver and associated electronics, and describes some clinical uses.

The value of perioperative echocardiography in percutaneous balloon mitral valvuloplasty

In order to investigate the value of perioperative echocardiography in percutaneous balloon mitral valvuloplasty (PBMV), two-dimensional echocardiography (2-DE), Doppler echocardiography and color Doppler flow imaging (CDFI) were employed prior to PBMV in 52 patients and during or after PBMV in 15 patients. The results showed that TTE and TEE were helpful in the selection of candidates for 2-DE transseptal and balloon dilation procedures. Continuous monitoring of 2-DE, Doppler echocardiography and CDFI during PBMV could make this procedure safer and more effective, reduce X-ray exposure and avoid complications. Echocardiography was useful in fluoroscopy and could be used for evaluation of the effects of operation.

Intracardiac echocardiography during radiofrequency catheter ablation of cardiac arrhythmias in humans

OBJECTIVES

The purpose of this study was to describe our preliminary experience using catheter-based intracardiac echocardiography as an adjunct to biplane fluoroscopy for guiding radiofrequency catheter ablation of atrial arrhythmias in the right side of the heart.

BACKGROUND

Catheter ablation requires precise positioning and stable ablation electrode-endocardial contact. This procedure is currently guided by an analysis of intracardiac electrograms and fluoroscopy. However, the use of fluoroscopy does not allow the endocardium and certain anatomic landmarks to be identified and is associated with the hazards of radiation exposure.

METHODS

Seventeen symptomatic patients were studied. A 10F 10-MHz intracardiac imaging catheter was used to visualize specific anatomic landmarks in the right atrium for directing the ablation electrode in 15 patients undergoing radiofrequency ablation of 19 arrhythmias and to assist with interatrial septal puncture in 3 patients.

RESULTS

Continuous intracardiac imaging was performed for a mean +/- SD of 63.6 +/- 39.2 min and demonstrated distal electrode-endocardial tissue contact in 81 (60%) of 134 radiofrequency applications. Movement of the catheter was demonstrated during 36 (44%), microcavitations during 39 (48%) and thrombus during 15 (19%) of the 81 imaged applications. In 7 of 10 procedures for atrial flutter, successful ablation was directed at anatomic corridors in the right atrium visualized with intracardiac echocardiography. During ablation of atrial tachycardia, imaging identified abnormal atrial anatomy related to previous surgery and guided successful ablation of a reentrant tachycardia circulating around these anatomic obstacles. In two procedures for slow pathway modification of atrioventricular node reentrant tachycardia, intracardiac echocardiography confirmed catheter stability at the tricuspid annulus anterior to the coronary sinus.

CONCLUSIONS

During catheter ablation, intracardiac echocardiography augments fluoroscopy by visualizing anatomic landmarks, ensuring stable endocardial contact and assisting in transseptal puncture. Ablation of typical atrial flutter can be successfully directed at anatomic corridors identified using intracardiac imaging.

Doppler catheter tip localization using color enhancement

The objective of this research was to determine if the ultrasound emissions of the Doppler catheter can be used to locate its position in 3 dimensions by conventional echocardiography. A Doppler catheter has previously been shown to permit nonfluoroscopic retrograde catheterization of the aortic root and left ventricular chamber by using velocity waveform polarity for directional guidance. A significant difficulty in providing ultrasound catheter guidance, however, has been the inability to recognize the Doppler catheter tip, because each point at which a flexible catheter crosses the image plane can be misinterpreted as the catheter tip. Initial in vitro water bath trials were performed using the Doppler catheter attached to a standard velocimeter. Using a 5 MHz imaging transducer and color Doppler methods, the presence or absence of a banded color pattern which could demarcate the Doppler catheter tip was recorded at various angles in and out of the scanning plane. Using Doppler retrograde guidance and transesophageal echocardiography, color Doppler banded patterns, which could identify the Doppler catheter tip, were investigated in the dog aorta. In order to understand the physical mechanisms involved, a series of water bath trials were then conducted using the Doppler catheter attached to a velocimeter which was synchronized to the echo machine. Initial nonsynchronized water bath trials revealed distinct banded color patterns demarcating the Doppler catheter tip when it pointed in any direction within the beam width, except for a 40 degrees blind cone directly away from the imaging transducer.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiofrequency catheter ablation guided by intracardiac echocardiography

BACKGROUND

Radiofrequency catheter ablation requires precise positioning of the ablation electrode. Fluoroscopically guided catheter manipulation has limitations, and there are risks of radiation exposure. The purpose of this study was to examine the feasibility of guiding catheter ablation within the right atrium with catheter-based intracardiac echocardiography.

METHODS AND RESULTS

A 10F, 10-MHz intracardiac imaging catheter was used to direct an ablation electrode at four or five anatomic landmarks in the right atrium. Thirty-eight radiofrequency energy applications were performed in nine anesthetized dogs, and 38 lesions were identified on pathological examination. Lesions were created a mean of 1.9 +/- 2.1 mm from the ultrasound-guided site. Twenty-six of 38 lesions (68%) were less than 2.2 mm from the imaged site. Intracardiac echocardiography also was used to confirm stable electrode-endocardial contact in 37 energy applications (97%) and identified catheter movement in 9 energy applications (24%). Discrete lesions, microcavitations, and thrombi were observed in 13 (34%), 23 (61%), and 19 (50%) of 38 energy applications, respectively. Microcavitations predicted the appearance of thrombus. Fluoroscopy time required to create four or five lesions decreased from 23 minutes in the first study to less than 2 minutes in the last five studies.

CONCLUSIONS

Catheter-based intracardiac echocardiography can accurately guide catheter ablation directed at anatomic landmarks and potentially reduced ionizing radiation exposure. Intracardiac imaging can be used to confirm endocardial contact, identify electrode movement, and directly visualize lesions. Intracardiac echocardiography also can be used to identify microcavitations, which predict thrombus formation during radiofrequency energy applications.

Transesophageal echocardiography to improve positioning of radiofrequency ablation catheters in left-sided Wolff-Parkinson-White syndrome

Two patients with the Wolff-Parkinson-White syndrome who underwent successful radiofrequency catheter ablation of their left-sided bypass tracts are described. Transesophageal echocardiography, a relatively new echocardiographic technique, was utilized in both patients and provided excellent visualization of intracardiac anatomy as well as the catheter tip. Transesophageal echocardiography was also synergistic with fluoroscopy and the intracardiac electrogram in providing more precise catheter placement. In addition, the use of transesophageal echocardiography may reduce fluoroscopic exposure and shorten the procedure time.

Properties of ultrasonically marked leads

We have developed an ultrasonic marking system for pacing leads and the electrophysiological study of catheters. The aim of this study was to evaluate the accuracy of our system, its usability in the measurement of performance of implanted leads, and to investigate the potential of electrical shock and ultrasonic hazard. The measurements have shown that different applications require specific electronic design, involving some compromise between accuracy and sensitivity. A higher sensitivity at the beginning of the ultrasonically guided cardiac lead implantation yields poorer accuracy. Quantitative measurements show that accuracy can be subsequently improved by reduction of sensitivity of the marking system. The transponder marking circuit is better suited for general use and the passive electronic circuit is better suited for multiple electrode electrophysiological studies. Experiments concerning electrical safety show that in the worst failure case, the energy of the marking system released within the heart is less than 10(-9) J per pulse within the pacing frequency spectrum and the current was below 50 microamperes. Ultrasound intensities were within the safety limits set by international and national organizations. The experiments using the marking system for detection of the pacing lead failure showed that the system can yield an early warning of the lead malfunction. The system can significantly reduce the exposure of the medical staff and the patients to x rays as well as improve patient follow-up accuracy.