Feasibility study: transesophageal echocardiography with a 10F (3.2-mm), multifrequency (5.5- to 10-MHz) ultrasound catheter in a small rabbit model

Prospective evaluation of complications associated with transesophageal echocardiography in dogs with congenital heart disease

Background

Transesophageal echocardiography (TEE) is useful in the assessment and procedural monitoring of congenital heart disease (CHD) with a relatively low complication rate in humans.

Objectives

To evaluate the safety of TEE and report complications in dogs.

Animals

Forty client‐owned dogs with CHD.

Methods

Prospective observational study including gastroesophagoscopy before and after TEE imaging. TEE was planned with a GE 6VT‐D adult probe in dogs weighing ≥4 kg and a GE 10T‐D microprobe alternating with an intracardiac echocardiography probe placed in the esophagus in dogs <4 kg. Difficulties with probe placement, probe interference and TEE probe imaging times were recorded. Dogs were monitored in the recovery period after TEE using an established nausea scoring system.

Results

New gastroesophageal abnormalities were identified after TEE in 4 dogs including 4 areas of mucosal damage involving <25% of the lower esophageal sphincter (n = 4) and 1 lesion at the heart base (n = 1) and were not attributed to longer imaging times or a specific probe. Lesions identified before TEE in 4 dogs remained unchanged after TEE. The 6VT‐D probe could not be placed in 1 dog with enlarged tonsils, and it obstructed fluoroscopic views in 3 dogs. The probes did not compress any structures in dogs in which fluoroscopy was performed (n = 20). Four dogs had evidence to suggest nausea after the procedure.

Conclusions and Clinical Importance

While major complications remain possible, complications in this study were mild and few in number. Dog size and probe characteristics are factors to consider when performing TEE.

Shape analysis of the prostate: establishing imaging specifications for the design of a transurethral imaging device for prostate brachytherapy guidance

PURPOSE

To examine specific prostate and urethra dimensions and prostate shape to facilitate the design of a transurethral ultrasonographic imaging device.

METHODS AND MATERIALS

Computed tomographic (CT) data sets were retrospectively evaluated from 191 patients who underwent permanent prostate brachytherapy at our institution. The prostate, rectum, urethra, and bladder were each segmented with imaging software. Collected data and calculations included prostate volume at specific distances from the urethra and rectum, distances from seeds to urethra (SU), distances from seeds to rectum (SR), prostate length, and curvilinear prostatic urethra length.

RESULTS

The CT-based, postimplant mean prostate volume was 49cm(3) (range, 22-106cm(3)). Mean prostate length was 4.5cm (range, 3.1-6.0cm). The mean curvilinear length of the prostatic urethra was 4.5cm. The mean (standard deviation) prostatic urethra bend was 29.0° (12.2°). The mean surface distance from the prostate to the urethra was 2.9cm and from the prostate to the rectum w as 4.6cm (p<0.001, paired t test). The mean SU distance was 1.6cm, and the mean SR distance was 2.3cm (p<0.001). In the largest prostate, the mean SU distance was 3.9cm and the mean SR distance was 6.0cm.

CONCLUSIONS

A urethral imaging device for prostate brachytherapy and other minimally invasive prostate therapies should ideally have a 6-cm imaging field of view to image all the prostates in this series in a single image. The mean distance from the SU in permanent prostate brachytherapy is less than 70% of the mean SR distance.

Cardiac impairment evaluated by transesophageal echocardiography and invasive measurements in rats undergoing sinoaortic denervation

Background

Sympathetic hyperactivity may be related to left ventricular (LV) dysfunction and baro- and chemoreflex impairment in hypertension. However, cardiac function, regarding the association of hypertension and baroreflex dysfunction, has not been previously evaluated by transesophageal echocardiography (TEE) using intracardiac echocardiographic catheter.

Methods and Results

We evaluated exercise tests, baroreflex sensitivity and cardiovascular autonomic control, cardiac function, and biventricular invasive pressures in rats 10 weeks after sinoaortic denervation (SAD). The rats (n = 32) were divided into 4 groups: 16 Wistar (W) with (n = 8) or without SAD (n = 8) and 16 spontaneously hypertensive rats (SHR) with (n = 8) or without SAD (SHRSAD) (n = 8). Blood pressure (BP) and heart rate (HR) did not change between the groups with or without SAD; however, compared to W, SHR groups had higher BP levels and BP variability was increased. Exercise testing showed that SHR had better functional capacity compared to SAD and SHRSAD. Echocardiography showed left ventricular (LV) concentric hypertrophy; segmental systolic and diastolic biventricular dysfunction; indirect signals of pulmonary arterial hypertension, mostly evident in SHRSAD. The end-diastolic right ventricular (RV) pressure increased in all groups compared to W, and the end-diastolic LV pressure increased in SHR and SHRSAD groups compared to W, and in SHRSAD compared to SAD.

Conclusions

Our results suggest that baroreflex dysfunction impairs cardiac function, and increases pulmonary artery pressure, supporting a role for baroreflex dysfunction in the pathogenesis of hypertensive cardiac disease. Moreover, TEE is a useful and feasible noninvasive technique that allows the assessment of cardiac function, particularly RV indices in this model of cardiac disease.

Transesophageal echocardiography in critically ill acute postoperative infants: comparison of AcuNav intracardiac echocardiographic and microTEE miniaturized transducers

BACKGROUND

Multiple barriers to transthoracic echocardiography are present in critically ill infants immediately after surgery. Transesophageal echocardiography (TEE) is sometimes needed to obtain specific important information that transthoracic echocardiography fails to demonstrate. Formerly, the investigators used the AcuNav intracardiac echocardiographic (ICE) intravascular ultrasound transducer (8 Fr, 2.5 mm, 64-element crystal array, multifrequency [5.5-10 MHz], single longitudinal plane, linear phased array [Siemens Medical Solutions USA, Inc., Mountain View, CA]). Recently, the investigators have also used the microTEE transducer (8-mm transducer tip, 5.2-mm shaft, multifrequency [3-8 MHz], multiplane phased array, 32-element probe [Philips Medical Systems, Andover, MA]). Both transducers have two-dimensional, M-mode, color Doppler, and pulsed-wave and continuous-wave Doppler capabilities. The aim of this study was to compare the efficacy, safety, ease of insertion, capabilities, utilization, and cost of the AcuNav ICE transducer versus those of the microTEE transducer.

METHODS

A retrospective review of all 50 postoperative critically ill infants who underwent TEE using the AcuNav and microTEE in the past 5 years was conducted. TEE was performed as ordered by the attending physician to answer a specific question not answered by transthoracic echocardiography.

RESULTS

In all cases, the clinical information sought was obtained. The AcuNav ICE transducer was safe, easy to insert through the transnasal route, and did not require paralysis; however, it had a limited number of echocardiographic views and had greater sterilization cost. The microTEE transducer had greater echocardiographic capabilities and lower sterilization cost; however, it was slightly more difficult to insert, had a few manageable complications, and required more sedation and paralysis.

CONCLUSIONS

TEE in this setting has increased because of demonstrated efficacy and safety. Both the AcuNav ICE and microTEE transducers are useful and effective in this critical clinical scenario.

Ventricular actuation improves systolic and diastolic myocardial function in the small failing heart

BACKGROUND

Direct mechanical ventricular actuation (DMVA) provides non-blood contacting augmentation of ventricular function. The device has promise for supporting the pediatric heart. The purpose of this study was to assess DMVA's effect in a small animal model of heart failure.

METHODS

Anesthetized rabbits (n = 6) underwent sternotomy and were instrumented for hemodynamic monitoring. A 10-MHz ultrasound probe was used for transesophageal echocardiography imaging. Heart failure (cardiac output <50% baseline) was induced with esmolol. Phenylephrine was titrated to maintain baseline mean arterial pressure. Transesophageal echocardiography imaging was acquired at baseline, heart failure, and subsequent DMVA support for 2 hours. Image analysis was used to derive ejection fraction, cardiac output, and stroke work as measures of left ventricular function. Speckle tracking software was used to derive myocardial strain rates as load-independent measures of left ventricular myocardial function.

RESULTS

Mean ejection fraction was significantly increased during DMVA support (0.585 +/- 0.035) versus failure (0.215 +/- 0.014; p < 0.001). Peak global left ventricular systolic and diastolic strain rates (1/second) were significantly increased during DMVA (-2.85 +/- 0.33 and 2.92 +/- 0.37) versus failure (-1.69 +/- 0.11 and 1.99 +/- 0.14; p < 0.001 and 0.004, respectively). Peak strain rates during DMVA in the failing heart were similar to baseline.

CONCLUSIONS

Direct mechanical ventricular actuation augments both systolic and diastolic left ventricular pump function. Diastolic augmentation distinguishes the device from other direct cardiac compression methods. This study demonstrated that DMVA in the small-sized, failing heart improves both systolic and diastolic myocardial function, which has favorable implications for left ventricular recovery. Direct mechanical ventricular actuation's salutary effects can be provided to the failing pediatric heart without complications of blood contact.

Intracardiac echocardiography in congenital heart disease

The use of intracardiac echocardiography (ICE) in congenital heart disease has become well established over the past 7 years since its introduction into clinical imaging. The greatest experience has been to guide percutaneous device closures of secundum atrial septal defects and patent foramen ovale, with excellent safety and clinical results. However, ICE has also been used for the evaluation and management of many other congenital heart defects given its unique blood/transducer interface and close proximity to relevant cardiac anatomy. Clinical application of ICE is expanding, with the current ICE catheters being used as micro-transesophageal echo probes, and three-dimensional prototypes already developed and tested in animal models. It is expected that ICE will further increase in use with refinements in technology and greater operator experience, aiding the management of complex congenital heart disease.

Echocardiographic characterization of the cardiovascular phenotype in rodent models

Echocardiographic techniques are commonly utilized to describe the rodent cardiovascular phenotype. These approaches are contrasted with other in vivo methods and are positioned in the assay selection process by a review of studies from our laboratory and others. Although not conventionally considered a biomarker, the technique has the potential to be exploited as a marker of intentional or unanticipated toxic biological effects in the preclinical development of drugs and chemicals.

An initial application of transesophageal Doppler echocardiography in experimental small animal models

This study examined whether an intracardiac echocardiography catheter could be used for transesophageal echocardiography (TEE) examinations in normal rats, and intraoperative TEE in small animal models of disease. The study used 30 Sprague-Dawley normal rats, 10 rats undergoing coronary artery ligation, and 10 rats with experimentally induced mitral regurgitation. The rats were anesthetized with isoflurane and intubated. An intracardiac echocardiographic catheter was inserted into the esophagus. M-mode, 2-dimensional, and Doppler studies were performed in multiple views. TEE probe insertions were successful in all animals. Intraoperative TEE was safely performed in the rat models of myocardial infarction or mitral regurgitation. Mitral regurgitation was well assessed using color Doppler and pulmonary venous flow. This study demonstrates that TEE (including intraoperative TEE) can be safely performed in rats using an intracardiac echocardiographic catheter. It provides a new approach to the assessment of cardiac function and valvular regurgitation in small animals.

3D visualization, analysis, and treatment of the prostate using trans-urethral ultrasound

In the year 2000, it is estimated that over 20,000 men underwent transperineal interstitial permanent prostate brachytherapy (TIPPB) for treatment of prostate cancer. Trans-urethral ultrasound (TUUS) is a new interactive, real-time 3D imaging method that may be effective in therapy-guidance during and after TIPPB. TUUS provides higher resolution than trans-rectal ultrasound (TRUS). TUUS can be used to accurately localize radioactive seeds and therefore contribute to more accurate determination of radiation dose distribution throughout the tissue after the completion of the procedure, similar to information currently provided by expensive and offline CT scans. A TUUS catheter can be used to acquire 2D section images or 3D volume images for detailed analyses of the prostate and associated tissue. Initial development of TUUS imaging was carried out on an ultrasound-equivalent prostate phantom with cylindrical dummy radiation sources. This was followed by preliminary studies in animals and then in patients. Both CT and TRUS data were acquired in these studies for comparative purposes. Segmentation of the prostate capsule and radioactive seeds was carried out using several semi-automated 3D algorithms and image processing techniques. Presentation of the data to the clinician is provided by a variety of complementary 2D and 3D display methods. In comparison with the CT data, TUUS data provided both greater spatial resolution and better soft tissue differentiation. In comparison to the TRUS data, TUUS data provided greater resolution and better seed localization. Combining these advantages suggests the possibility of TUUS becoming the exclusive imaging method in prostate cancer brachytherapy.

Feasibility of transesophageal echocardiography with a ten-French monoplane probe

OBJECTIVES

We examined the feasibility of transesophageal echocardiography (TEE) using a 10F monoplane probe developed for intracardiac ultrasound (AcuNav, Acuson/Siemens, Mountain View, Calif).

BACKGROUND

Traditional TEE uses a 10- to 12-mm-diameter probe, and conscious sedation is customary to minimize patient discomfort. Because of its small size (3.2-mm diameter), the 10F monoplane probe can be inserted into the esophagus using only topical anesthesia. This provides the potential for a more easily tolerated examination.

METHODS

A total of 20 patients underwent a comprehensive TEE using an adult multiplane probe. Immediately afterward, the 10F monoplane probe was inserted into the esophagus and a targeted examination completed. The 10F monoplane studies were blindly reviewed by 3 observers for the study indication and for 16 diagnostic elements. These were graded against an expert's review of standard TEE.

RESULTS

The 10F monoplane probe was well tolerated in all patients. Observers A, B, and C answered the clinical question in 80%, 85%, and 100%, respectively, with the 10F probe. The percentage of clinical elements deemed evaluable was 71%, 78%, and 80%, respectively. Limitations included incomplete visualization of the mitral valve and a systematic underestimation of the severity of valve regurgitation.

CONCLUSIONS

The 10F monoplane probe is safe, well-tolerated, and capable of evaluating many clinical questions. Because of its small size, conscious sedation may not be necessary. It may be useful for targeted evaluations, for monitoring invasive procedures, or for intermediate or long-term monitoring in an intensive care department.

Use of a phased vector array US catheter for EUS

BACKGROUND

Existing EUS catheter probes have limited depth of penetration and lack color flow and Doppler capabilities. This study prospectively assessed the feasibility and safety of using a phased vector array US catheter in the human GI tract.

METHODS

Eleven patients underwent EUS with a steerable 9F phased vector array catheter. Images obtained with the catheter were compared with standard EUS images.

RESULTS

The GI wall layers were equally well imaged with the catheter compared with standard echoendoscopes in 90% of the cases. Images of the liver, spleen, pancreatic parenchyma, and pancreatic duct were of equal quality and resolution with both techniques in the majority of patients. Some deeper structures and blood vessels were better visualized with the catheter. No complications were encountered.

CONCLUSION

The steerable phased vector array US catheter is a safe device when used in the GI tract and offers images comparable with those obtained with a dedicated echoendoscope. Further studies are needed to determine the accuracy of tumor staging and clinical utility of this device.

Miniaturized transesophageal echocardiography in newborn infants

BACKGROUND AND METHODS

A miniaturized 5.5 to 10 MHz, phased-array, single longitudinal plane transducer mounted on a 3.3-mm diameter catheter (miniaturized transesophageal echocardiography [TEE]) may overcome mechanical limitations of standard pediatric transesophageal probes. We evaluated whether the miniaturized TEE probe could define clinically relevant anatomy in 17 infants who weighed less than 6 kg.

RESULTS

Twenty-two studies were performed in 17 infants without complication, weighing 2.1 to 5.6 kg. Twenty of twenty-two studies were diagnostic. Pediatric biplane TEE was not possible in 13 studies. Lack of horizontal plane imaging with miniaturized TEE made evaluation difficult in patients with atrioventricular septal defect.

CONCLUSION

Miniaturized TEE provided diagnostic intraoperative TEE in the majority of infants studied and may allow broader and safer application of TEE to neonates and small infants.

Ultrasound imaging: principles and applications in rodent research

Ultrasound imaging utilizes the interaction of sound waves with living tissue to produce an image of the tissue or, in Doppler-based modes, determine the velocity of a moving tissue, primarily blood. These dynamic, real time images can be analyzed to obtain quantitative structural and functional information from the target organ. This versatile, noninvasive diagnostic tool is widely used and accepted in human and veterinary medicine. Until recently its application as a research tool was limited primarily to larger, nonrodent species. Due to advances in ultrasound imaging technology, commercially available ultrasound systems now have the spatial and temporal resolution to obtain accurate images of rat and mouse hearts, kidneys, and other target tissues including tumor masses. As a result, ultrasound imaging is being used more frequently as a research tool to image rats and mice, and particularly to evaluate cardiac structure and function. The developing technology of ultrasound biomicroscopy has even greater spatial resolution and has been used to evaluate developing mouse embryos and guide site-specific injections into mouse embryos. Additional ultrasound imaging technologies, including contrast-enhanced imaging and intravascular ultrasound transducers adapted for transesophageal use, have been utilized in rats and mice. This paper provides an overview of basic ultrasound principles, equipment, and research applications. The use of noninvasive ultrasound imaging in research represents both a significant refinement as a potential replacement for more invasive techniques and a significant advancement in research techniques to study rats and mice.

Initial experience with a steerable, phased vector array ultrasound catheter in the GI tract

BACKGROUND

EUS requires a significant capital outlay. The ability to perform high-resolution phased array scanning and Doppler interrogation by using a catheter that interfaces with a standard US console could increase the accessibility of EUS. Recently, an electronic phased-array US catheter was developed for intracardiac use. To date, this technology has not been applied to the GI tract. The aim of this study is to determine the feasibility and imaging characteristics of a new phased array scanning US catheter in the GI tract.

METHODS

Swine were placed under general anesthesia. This study used a 100 cm, 10F, torquable catheter with 4-way tip deflection to greater than 90 degrees. The catheter tip houses a phased vector array transducer with variable frequency (5.5-10 MHz) and variable focal distance. It has pulsed/color and power Doppler capability. The probe was passed through a therapeutic flexible sigmoidoscope into the upper GI tract. Acoustic coupling was achieved via a condom filled with water or by gastric water infusion. Needle visualization experiments were performed with a second endoscope (also passed per oral) with a standard EUS-guided fine needle aspiration needle.

RESULTS

Acoustic coupling was easily achieved. Resolution of the GI wall into characteristic layers (esophagus 5, stomach 7) was demonstrated. At 5.5 MHz, tissue resolution and Doppler imaging were excellent to greater than 10 cm from the transducer. A 22-gauge EUS-guided fine needle aspiration needle was easily visualized at depth greater than 4 cm. Flow in gastric, hepatic, and pancreatic parenchymal vessels approximately 1 mm diameter was visualized by using power and color Doppler.

CONCLUSIONS

This 10F array US catheter is capable of high-resolution two-dimensional imaging of the gut wall as well as high-quality Doppler imaging. The Doppler capabilities of this equipment may have new GI applications.