Intracardiac echocardiography in humans using a small-sized (6F), low frequency (12.5 MHz) ultrasound catheter. Methods, imaging planes and clinical experience

Baseline intracardiac echocardiography predicts haemodynamic changes and Doppler velocity patterns during follow-up after percutaneous pulmonary valve implantation

BACKGROUND

Intracardiac echocardiography Doppler-derived gradients have previously been shown to correlate with post-procedure echocardiographic evaluations when compared with invasive gradients measured during percutaneous pulmonary valve implantation, suggesting that intracardiac echocardiography could offer an accurate and predictable starting point to estimate valve function after percutaneous pulmonary valve implantation.

METHODS

We performed a retrospective chart review of 51 patients who underwent percutaneous pulmonary valve implantation between September 2018 and December 2019 in whom intracardiac echocardiography was performed immediately after valve implantation. We evaluated the correlation between intracardiac echocardiography gradients and post-procedural Doppler-derived gradients. Among the parameters assessed, those which demonstrated the strongest correlation were used to create a predictive model of expected echo-derived gradients after percutaneous pulmonary valve implantation. The equation was validated on the same sample data along with a subsequent cohort of 25 consecutive patients collected between January 2020 and July 2020.

RESULTS

All the assessed correlation models between intracardiac echocardiography evaluation and post-procedure transthoracic echocardiographic assessments were statistically significant, presenting moderate to strong correlations. The strongest relationship was found between intracardiac echocardiography mean gradients and post-procedural transthoracic echocardiographic mean gradients. Therefore, an equation was created based on the intracardiac echocardiography-derived mean gradient, to allow prediction of the post-procedural and follow-up transthoracic echocardiographic-derived mean gradients within a range of ±5 mmHg from the observed value in more than 80% of cases.

CONCLUSIONS

There is a strong correlation between intracardiac echocardiography and post-procedure transthoracic echocardiographic. This allowed us to derive a predictive equation that defines the expected transthoracic echocardiographic Doppler-derived gradient following the procedure and at out-patient follow-up after percutaneous pulmonary valve implantation.

The use of intracardiac echocardiography during percutaneous pulmonary valve replacement

High-quality live imaging assessment of cardiac valves and cardiac anatomy is crucial for the success of catheter-based procedures. We present our experience using Intracardiac echocardiography (ICE) during transcatheter Percutaneous Pulmonary Valve replacement (tPVR).This is a retrospective study that included 35 patients who underwent tPVR between April 2008 and June 2012. Thirty-one of these patients had the procedure performed under continuous ICE guidance. Pre-procedure transthoracic echocardiography (TTE) was obtained in all patients. ICE was performed at baseline, during the procedure, and at the conclusion of the procedure. Comparisons between the pre-procedure TTE and baseline ICE data and between post-procedure ICE data and the following day TTE were performed. Total of 35 patients had tPVR during the above-mentioned time period. Twenty-one patients received the Edwards Sapien valve and 14 patients had the Melody valve. Thirty-one patients had the procedure performed under continuous ICE guidance. The mean Pre-TTE peak gradient (PG) and Pre-ICE-PG were 45.5 ± 20 vs 33 ± 13 mmHg (p < 0.001) and the mean Pre-TTE mean gradient (MG) and Pre-ICE-MG were 27.7 ± 13 vs 21 ± 18 mmHg (p < 0.001). The mean Post-TTE- PG and Post-ICE-PG were 24.3 ± 11 vs 15.3 ± 7 mmHg (p < 0.001) and the mean of the Post-TTE-MG and Post-ICE-MG were 14.2 ± 7 vs 8.4 ± 4 mmHg (p < 0.001). There was a good correlation between peak ICE and TTE gradient at baseline and after valve placement. For the degree of pulmonary regurgitation, there was no significant difference between TTE and ICE. ICE is an important modality to guide tPVR in patients with dysfunctional homograft valve between the right ventricle and pulmonary artery and should be used to assess valve function before, during and immediately after the procedure.

Intracardiac transvenous echocardiography is superior to both precordial Doppler and transesophageal echocardiography techniques for detecting venous air embolism and catheter-guided air aspiration

BACKGROUND

Venous air embolism (VAE) is a potentially fatal complication during surgical procedures with patients in the sitting position. Since methods for detection of persistent low-volume VAE and targeted air aspiration are limited, we tested the hypotheses that transvenous intracardiac echocardiography (ICE) 1) improves detection of small air emboli in comparison to transesophageal echocardiography (TEE) and precordial Doppler monitoring (PCD) techniques, and that 2) image-guided multiorifice central venous catheter manipulation improves air recovery in moderate and large VAE, when compared with aspiration with the multiorifice central venous catheter in a static position.

METHODS AND RESULTS

Adult swine (73 +/- 4.6 kg, n = 7) were premedicated, anesthetized with propofol and fentanyl, endotracheally intubated, mechanically ventilated, and placed in a 45 degrees head-up position. First, nine different small volumes of air emboli (0.05-1 mL) were randomly injected via an ear vein, and VAE detection methods were applied in random order. For 378 small volume air injections, ICE had a much higher sensitivity (82.5%, P < 0.0001) on the analysis of VAE detection than TEE (52.8%) or PCD (46.8%), with no difference (P = 0.571) between TEE and PCD. An injected air volume as small as 0.15 mL was detected by ICE in 90% of injections performed, whereas PCD and TEE detected only half of the boluses of 0.25-0.30 mL of air, and required boluses of 0.4-1.0 mL to achieve 100% detection. Air recovery was assessed in a second series of moderate VAE (2, 5, 10 mL); image-guided aspiration-catheter manipulation recovered significantly more (34.1% vs 17.2%, P < 0.0001) intracardiac air than without catheter manipulation. In a third series of injections of large air volumes (25, 50, and 100 mL), air recovery was not significantly different with ultrasound-guided aspiration (41.3% vs 31.8%, P = 0.11).

CONCLUSION

Small air emboli are detected by ICE with much greater sensitivity compared with both PCD and TEE techniques. Furthermore, recovery of embolized air is enhanced by image-guided manipulation of a multiorifice central venous catheter. Clinical studies are required to assess this technique during surgery with patients in the sitting position.

Intracardiac echocardiography in patients with pacing and defibrillating leads: a feasibility study

BACKGROUND

Lead extraction, an important and necessary component of treatment for many common device and lead-related complications, is a procedure that can provoke much anxiety in even the most experienced operators given the potentially serious complications. The principal impediment to lead extraction is the body's response to an intravascular foreign body with matrix intravascular neoformation, which causes the lead to adhere to the endocardium or vascular structure, increasing the risk of vascular or myocardial damage with lead removal. Fluoroscopic visualization, the commonly visualization used tool, has several limits in terms of anatomical structures visualization. The aim of this study was to assess the safety and feasibility of intracardiac echocardiography (ICE) in patients undergoing pacing and defibrillating leads before and during a transvenous device removal, and its potential role in detecting intracardiac leads and areas of fibrous adherence.

METHODS

ICE interrogation was performed in 25 consecutive patients with pacing and defibrillating implantable cardioverter defibrillators (ICD) leads before and during device removal.

RESULTS

A programmed ICE analysis was completed in 23 out of 25 patients with excellent resolution, providing a "qualitative-quantitative" information on anatomical structures, cardiac leads, and related areas of fibrous adherence. No ICE-related complications occurred.

CONCLUSIONS

ICE evaluation is safe and feasible in patients with pacing and defibrillating leads before and during transvenous lead removal, offering an excellent visualization of cardiac leads and related areas of adherence. ICE can assist pacing and ICD lead removal and could improve procedure efficacy and safety.

Echocardiography in the critically ill: current and potential roles

BACKGROUND

The use of echocardiography in the critically ill presents specific challenges. However, information of direct relevance to clinical management can be obtained relating to abnormalities of structure and function and can be used to estimate pulmonary arterial and venous pressures.

DISCUSSION

Investigation of the consequences of myocardial ischaemia, valvular dysfunction and pericardial disease can be facilitated, and changes characteristic of specific conditions (e.g. sepsis, pulmonary thromboembolism) detected. Echocardiography can also be used to monitor the effects of therapeutic interventions.

CONCLUSIONS

The applications of echocardiography in the critical care setting (excluding standard peri-operative echocardiography for cardiac surgery) are reviewed, with particular emphasis on the assessment of cardiac physiology.

History of the evolution of echocardiography

Echocardiography provides information regarding cardiac morphology, function and hemodynamics non-invasively. It is the most frequently performed cardiovascular examination after electrocardiography and chest X-ray. In less than half a century, this technique has evolved to a mainstay of cardiovascular medicine. The historical evolution of echocardiography is succinctly described including that of M-mode, two-dimensional, Doppler, stress, transesophageal, intraoperative, contrast, digital, three-dimensional and intracardiac echocardiography.

Electroanatomic mapping of the right atrium with a right atrial basket catheter and three-dimensional intracardiac echocardiography

The ablation of arrhythmias progresses towards an approach based upon application of linear lesions between nonconducting anatomic/electrical areas. Hence the identification of detailed anatomy together with electrical behavior becomes increasingly important. This study aims to achieve true electroanatomic mapping by the use of three-dimensional intracardiac imaging of the right atrium combined with use of a right atrial basket to obtain detailed electrical information. We studied nine patients, seven requiring atrial flutter ablation. A 9 Fr, 9 MHZ intracardiac echo catheter was pulled back from SVC to IVC using respiratory and ECG gating. The images, recorded on a Clearview ultrasound machine, were reconstructed using commercially available software. The intracardiac basket was placed into the atrium using the markers and fluoroscopy to allow orientation. Isochronal maps were obtained from the basket in sinus rhythm, pacing from different sites within the atrium and in atrial flutter. Isochronal maps were constructed and superimposed on the ICE image. The maps with pacing were consistent with that which was expected, confirming the validity of this approach. We were able to visualize changes in activation sequence following the placement of bidirectional isthmus block. True electroanatomic mapping is possible by the use of three-dimensional ICE reconstruction of the right atrium with electrical activation obtained from an intracardiac basket. This has significance for anatomically based arrhythmia ablations such as the ablation of atrial flutter, atrial fibrillation, with transcatheter MAZE procedures and pulmonary vein isolation. Further developments in software will allow such maps to be produced simultaneously with greater rapidity.

On-line intracardiac echocardiography alone for Amplatzer Septal Occluder selection and device deployment in adult patients with atrial septal defect

BACKGROUND

During the last few years, several different devices have been proposed for atrial septal defect (ASD) percutaneous closure. For the Amplatzer Septal Occluder (ASO) device, accurate balloon sizing is considered of paramount importance because the prosthesis waist has to be exactly adjusted to the defect diameter (+/-1 mm). In this study, we aimed to demonstrate the possibility of marked misinterpreting of the actual defect size using the balloon technique in patients with secundum ASD and to evaluate the accuracy of intracardiac echocardiography (ICE) measurements as a new method for selecting the size of ASO device.

METHODS

Between February 1999 and December 2000, 166 consecutive adult patients underwent percutaneous transvenous secundum ASD occlusion using the ASO device. In 124 patients (control group), ASD were closed by conventional methods. In 13 patients (pilot group), balloon pulling technique was used in size selection, whereas ICE was used on-line to monitor device placement and off-line to assess its possibilities for accurate quantitative measurements and qualitative evaluation. In 31 patients (study group), ICE was used as the sole imaging tool both for guiding device selection and monitoring the procedure. All patients underwent complete transthoracic echocardiographic study before discharge and during follow-up visits at 3 and 12 months.

RESULTS

Successful device implantation was accomplished in 163 of the 166 patients (98.2%). Short-term follow-up results were available in all eligible patients at least 3 months. Complete occlusion was demonstrated in 91.4% and 92.2% of patients in the control and pilot groups, respectively, increasing to 97.3% in the study group (p<0.01 vs. both control and pilot groups). There were no significant differences in mean ASO diameters in the control and pilot groups (20+/-7.7 and 22+/-5.4 mm, respectively), whereas the mean size of the devices used in the study group was significantly larger (27.4+/-6.2 mm, p<0.01 vs. both control and pilot groups). In the pilot group, the underestimation effect of the balloon strategy was evident, with a mean 12.3% larger diameter required on ICE measurements. Moreover, a misalignment between the ASO and the atrial septum was seen on ICE in 9 of 13 patients of the pilot group, whereas good apposition of the ASO on the septum secundum was seen in all patients of the study group.

CONCLUSION

ICE is a safe and effective method for selecting ASO size and continuous monitoring of the procedure. In contrast to the previously reported implantation procedure (device-to-defect ratio 1:1), a device 10-20% larger than invasively measured stretched defect diameter should be chosen and implanted on the basis of the ICE data.

Role of intracardiac ultrasound in interventional electrophysiology

PURPOSE OF REVIEW

Interventional procedures in the electrophysiology and catheterization laboratory are rapidly advancing. Critical to the advancement of these procedures is accurate identification of critical anatomic landmarks and catheter position. Fluoroscopy remains the mainstay for general identification of anatomic landmarks but is inadequate for the precise imaging needed for complex procedures. Precise imaging of anatomic landmarks and catheter position is now possible during the procedure with the use of intracardiac echocardiography (ICE). This paper reviews the rapid development and utilization of ICE in interventional electrophysiology.

RECENT FINDINGS

Several recent studies show ICE as a major contribution to providing a safer, more reliable, and more cost-effective means of accomplishing the tasks performed by existing techniques. In the electrophysiology laboratory, the dependence on this new technology has been due to the rapid development of catheter-based radiofrequency ablation of the pulmonary veins for treatment of atrial fibrillation. Since the initial use of ICE in facilitating ablation of atrial fibrillation, other uses for ICE are continuously being identified.

SUMMARY

A comprehensive look is provided at the history and development of this new technology along with the most recent applications of ICE in interventional electrophysiology.

Use of Intracardiac Echocardiography to Guide Catheter Closure of Atrial Communications

Intracardiac echocardiography (ICE) is slowly replacing transesophageal echocardiography as the preferred imaging tool to guide device closure of atrial septal defects and patent foramen ovale. This article is a brief review of the literature related to ICE, the technical aspects ICE imaging, techniques for obtaining the standard views, and the future directions of this methodology.

Real time quantification of low temperature radiofrequency ablation lesion size using phased array intracardiac echocardiography in the canine model: comparison of two dimensional images with pathological lesion characteristics

OBJECTIVE

To evaluate the feasibility of quantifying low temperature radiofrequency catheter ablation (RFCA) lesions using a phased array intracardiac echocardiography (ICE) catheter--with better tissue penetration and in a deflectable device-in the canine model.

INTERVENTION

Low temperature radiofrequency (RF) energy (50-60 degrees C at up to 40 W) was delivered to the left ventricle in 11 beagles for 60 seconds, using an 8 French catheter with a deflectable tip and a 4 mm distal electrode.

MAIN OUTCOME MEASURES

Comparison of the width and depth of RFCA lesions measured by ICE with pathological findings.

RESULTS

33 RF energies were delivered in 11 dogs. 31 lesions (94%) were confirmed at necropsy. 27 of 31 ablation lesions (87%) were detected by ICE. The mean (SD) width and depth of the ICE detected lesions were 10.4 (2.6) mm and 5.7 (1.9) mm, respectively. Pathological findings showed that RFCA lesions consisted of inner and outer layers. Macroscopically, the mean (SD) width and depth of the inner layers were 7.6 (2.3) mm and 3.6 (1.2) mm and those for the whole layers were 10.0 (2.8) mm and 5.3 (1.5) mm, respectively. Microscopically, the inner and outer layers corresponded to necrotic and oedematous areas, respectively. The ICE detected lesion size had better correlation with the pathological measurements of the whole layers in width (r = 0.911) and in depth (r = 0.756).

CONCLUSION

The real time evaluation of RFCA lesion size using the phased array ICE is feasible, even with a low temperature RF application. However, ICE slightly overestimates RFCA lesion size compared with pathological necrotic lesion size.

Invasive echocardiography: the use of catheter imaging by the interventional cardiologist

Ultrasound imaging is frequently used for diagnostic purposes or guidance during procedures in the pediatric and congenital cardiac catheterization laboratory. As new imaging modalities emerged, many interventional cardiologists rather than noninvasive specialists are now performing the ultrasound imaging as part of the catheterization. The focus of this discussion will be to detail the technique and application of echocardiography by the interventional cardiologist.

Intracardiac echocardiography using the AcuNav ultrasound catheter during percutaneous balloon mitral valvuloplasty

During the past 10 years, there has been a trend toward and an interest in the use of catheter-based interventions to perform procedures that were once only approached surgically. The problem with the catheter-based approach has been procedure-related complications. Improved imaging of cardiac structures while undertaking interventional procedures may help to prevent or allow for early identification of these complications. Transesophageal echocardiography has been used during catheter-based procedures as a guide, and has both advantages and disadvantages. Intracardiac echocardiography is a relatively new imaging technique that also provides an enhanced view of cardiac structures and may also allow for the safe and efficient performance of catheter-based procedures. We report the first case of successful percutaneous balloon mitral valvuloplasty done under ultrasound guidance using an intracardiac echocardiography catheter (10F, 5-10 MHz) (Acunav). The strengths and weaknesses of this approach are described and compared with transesophageal echocardiography and older intracardiac echocardiography devices.

Anatomic and hemodynamic imaging using a new vector phased-array intracardiac catheter

BACKGROUND

We used a new vector, phased-array intracardiac catheter (AcuNav) with complete 2-dimensional imaging and Doppler capabilities to describe a systematic approach for a detailed anatomic and hemodynamic cardiac assessment.

METHODS

In 14 dogs, the intracardiac echocardiographic catheter was inserted through an 11F venous access and placed in the right side of the heart to perform a comprehensive ultrasound examination of the heart.

RESULTS

Imaging was successful in all dogs. All 4 cardiac chambers and valves were imaged clearly in multiple orientations. Additional structures seen included the vena cavae, coronary sinus, right and left appendages, interarterial septum, coronary arteries, and all 4 pulmonary veins. Intra-abdominal structures, such as the aorta, liver, and hepatic veins were also visualized. A complete Doppler examination of intracardiac and paracardiac flows was also possible.

CONCLUSION

AcuNav is a unique intracardiac imaging device, which allows comprehensive structural and functional cardiac assessment.

Intracardiac phased-array imaging: methods and initial clinical experience with high resolution, under blood visualization: initial experience with intracardiac phased-array ultrasound

OBJECTIVES

This study was designed to test the feasibility of high-resolution phased-array intracardiac imaging.

BACKGROUND

Intracardiac echocardiographic imaging of the heart during interventional electrophysiologic (EP) procedures has been limited by inadequate ultrasound penetration and absence of Doppler hemodynamic and flow information produced by rotating mechanical ultrasound elements.

METHODS

A 10F (3.2 mm) phased-array, variable 5.5 to 10 MHz frequency imaging catheter with a four-way deflectable tip was applied in 24 patients undergoing EP studies. Sixteen prespecified cardiac targets were imaged from a right heart venue.

RESULTS

Fifteen patients had no underlying organic heart disease; nine had ischemic, cardiomyopathic, valvular or congenital heart disorders. Longitudinal and short-axis imaging readily disclosed each cardiac valve, support structures and chamber, as well as the pericardium, right and left atrial appendages, the junction of the right atrium and superior vena cava, crista terminalis, tricuspid valve isthmus, coronary sinus orifice, membranous fossa ovalis and pulmonary veins. The average target depth was 8.8+/-1.5 cm (range 0.5 to 15 cm), with adequate penetration at a 7.5 MHz imaging frequency. Color flow and Doppler utilities clearly characterized transaortic and pulmonic valve and pulmonary vein blood flow, including during low output states.

CONCLUSIONS

These first human studies with this technology demonstrate the methods, feasibility and utility of intracardiac phased-array vector and Doppler imaging for long-axis, apex-to-base global cardiac imaging. High resolution of endocardial structures and catheters suggests additional utility for visualizing interventional procedures from the right heart.

Balloon atrial septostomy in end-stage pulmonary hypertension guided by a novel intracardiac echocardiographic transducer

Blade and balloon atrial septostomy has been used to reduce cardiopulmonary symptoms and as a bridge to lung or heart lung transplant in primary pulmonary hypertension. Due to severe right atrial dilatation and resultant loss of anatomical landmarks, the procedure is technically difficult, and the reported postprocedure mortality rate varies between 5% and 50%. Among others, marked systemic desaturation and systemic hypotension presumably secondary to an excessively large atrial septal defect have been reported as causes of postprocedure death. We report a case where a novel intracardiac catheter-based phased-array 5.5--10 MHz transducer with spectral and color-flow Doppler capabilities was used to assist a balloon atrial septostomy and to obtain hemodynamic data in a patient with end-stage pulmonary hypertension.

Intracardiac echocardiography (9 MHz) in humans: methods, imaging views and clinical utility

A new low-frequency (9 MHz, 9 Fr) catheter-based ultrasound (US) transducer has been designed that allows greater depth of cardiac imaging. To demonstrate the imaging capability and clinical utility, intracardiac echocardiography (ICE) using this lower frequency catheter was performed in 56 patients undergoing invasive electrophysiological procedures. Cardiac imaging and monitoring were performed with the catheter transducer placed in the superior vena cava (SVC), right atrium (RA) and/or right ventricle (RV). In all patients, ICE identified distinct endocardial structures with excellent resolution and detail, including the crista terminalis, RA appendage, caval and coronary sinus orifices, fossa ovalis, pulmonary vein orifices, ascending aorta and its root, pulmonary artery, RV and all cardiac valves. The left atrium and ventricle were imaged with the transducer at the limbus fossa ovalis of the interatrial septum and in the RV, respectively. ICE was important in identifying known or unanticipated aberrant anatomy in 11 patients (variant Eustachian valve, atrial septal aneurysm and defect, lipomatous hypertrophy, Ebstein's anomaly, ventricular septal defect, tetralogy of Fallot, transposition of the great arteries, disrupted chordae tendinae and pericardial effusion) or in detecting procedure-related abnormalities (narrowing of SVC-RA junction orifice or pulmonary venous lumen, atrial thrombus, interatrial communication). In patients with inappropriate sinus tachycardia, ICE was the primary ablation catheter-guidance technique for sinus node modification. With ICE monitoring, the evolution of lesion morphology with the three imaging features including swelling, dimpling and crater formation was observed. In all patients, ICE was contributory to the mapping and ablation process by guiding catheters to anatomically distinct sites and/or assessing stability of the electrode-endocardial contact. ICE was also used to successfully guide atrial septal puncture (n = 9) or RA basket catheter placement (n = 4). Thus, ICE with a new 9-MHz catheter-based transducer has better imaging capability with a greater depth. Normal and abnormal cardiac anatomy can be readily identified. ICE proved useful during electrophysiological mapping and ablation procedures for guiding interatrial septal puncture, assessing placement and contact of mapping and ablation catheters, monitoring ablation lesion morphological changes, and instantly diagnosing cardiac complications.

Intracardiac echocardiography via the transvenous approach with use of 8F 10-MHz ultrasound catheters

OBJECTIVE

To study the safety and feasibility of intracardiac imaging using a novel 8F 10-MHz non-over-the-wire ultrasound catheter system.

SUBJECTS AND METHOD

Intracardiac imaging using a transfemoral venous approach was performed in 33 adults, 14 men and 19 women, aged 25 to 66 years (mean, 46 years). Six were normal subjects, 12 had congenital heart diseases (5 atrial septal defects, 3 ventricular septal defects, 1 tetralogy of Fallot, 2 patent ductus arteriosus, and 1 Ebstein anomaly), 14 had valvular heart diseases (12 mitral stenoses and 2 calcific aortic stenoses), and 1 had acute pulmonary embolism.

RESULTS

Ultrasound images were obtained, without any complications, from the right side of the heart in all subjects. The atria and ventricles could be recognized by anatomic relationships to the cardiac chambers and the valves by their characteristic motion during each cardiac cycle. The vessels were verified by their connections to the cardiac chamber and by contrast echocardiography if indicated.

CONCLUSION

Intracardiac imaging using the 8F 10-MHz non-over-the-wire ultrasound catheter system via a transfemoral venous approach is feasible and safe. Intracardiac echocardiography is potentially useful for assessing a variety of cardiac anomalies and in guiding and monitoring certain intervention procedures.

Low-power radiofrequency application and intracardiac echocardiography for creation of continuous left atrial linear lesions

INTRODUCTION

Continuity of radiofrequency (RF) lesions for a catheter-based cure of atrial fibrillation is essential in order to avoid reentrant tachycardias. In the present study, we assessed the value of intracardiac echocardiography and preablation electrode-tissue interface parameters for creation of left atrial linear lesions.

METHODS AND RESULTS

In six healthy dogs, two left atrial linear lesions (lesion 1, along the inferior posterior left atrium; lesion 2, from the appendage to the left atrial roof) were attempted via a transseptal approach using a deflectable catheter with six 7-mm coil electrodes. In a randomized fashion, one lesion was performed under echocardiographic guidance and one with blinded echocardiographic monitoring. The following preablation parameters were assessed for every coil electrode: (1) mean atrial electrogram amplitude of six consecutive sinus beats; (2) diastolic pacing threshold; and (3) temperature response to application of 5 W for 10 seconds. After ablation (target temperature 70 degrees C, maximum power 50 W, duration 60 sec), the excised left atrium was examined macroscopically and histologically for lesion length, continuity, and presence or absence of lesions associated with each coil. Out of 12 attempted RF lesions, 7 were continuous (length, 47+/-5 mm, lesion 2, n = 6) and 5 were discontinuous (lesion 1, n = 5). Fifty-two of 70 coil electrodes (74%) had pathologic evidence of lesion creation. Intracardiac echocardiography was superior to fluoroscopy with respect to the actual number of coil electrodes creating lesions, and lesion continuity was correctly predicted in 9 of 12 lesions. Intracardiac echocardiography was 85% sensitive and 54% specific in predicting lesions created by individual coils. The correlation between the mean 60-second ablation temperature and the preablation parameters was 0.45 for the electrogram amplitude, -0.67 for the pacing threshold, and 0.81 for the temperature response to low-power application. Sensitivity and specificity for prediction of lesions created by individual coils, respectively, were 84% and 48% for the electrogram amplitude, 90% and 68% for the pacing threshold, and 96% and 76% for the low-power RF application.

CONCLUSION

Long linear lesions can be safely and effectively performed in the canine left atrium, using a tip-deflectable multielectrode catheter. Intracardiac echocardiography may be helpful for positioning the ablation catheter in some parts of the left atrium, and preablation parameters, especially a nontraumatic low-power RF application, are able to predict ultimate lesion creation with high accuracy.

Narrowing of the superior vena cava-right atrium junction during radiofrequency catheter ablation for inappropriate sinus tachycardia: analysis with intracardiac echocardiography

OBJECTIVES

The study explored the potential for tissue swelling and venous occlusion during radiofrequency (RF) catheter ablation procedures using intracardiac echocardiography (ICE).

BACKGROUND

Transient superior vena cava occlusion has been reported following catheter ablation procedures for inappropriate sinus tachycardia (IST). Presumably, venous occlusion could occur owing to thrombus formation or tissue swelling with resultant narrowing of the superior vena cava-right atrial (SVC-RA) junction.

METHODS

Intracardiac echocardiography (9 MHz) was used to guide ablation catheter position and for continuous monitoring during RF application in 13 ablation procedures in 10 patients with IST. The SVC-RA junction was measured prior to and following ablation. Successful ablation was marked by abrupt reduction in the sinus rate and a change to a superiorly directed p-wave axis.

RESULTS

Eleven of 13 procedures were successful, requiring 29 +/- 20 RF lesions. Prior to the delivery of RF lesions, the SVC-RA junction measured 16.4 +/- 2.9 mm. With RF delivery, local and circumferential swelling was observed, causing progressive reduction in the diameter of the SVC-RA junction to 12.6 +/- 3.3 mm (24% reduction, p = 0.0001). A reduction in SVC-RA orifice diameter of > or = 30% compared to baseline was observed in five patients.

CONCLUSIONS

The delivery of multiple RF ablation lesions, often necessary for cure of IST, can cause considerable atrial swelling and resultant narrowing of the SVC-RA junction. Smaller venous structures, such as the coronary sinus and the pulmonary veins, would also be expected to be vulnerable to this complication. Thus, ICE imaging may be helpful in preventing excessive tissue swelling leading to venous occlusion during catheter ablation procedures.

Potential applications of intracardiac echocardiography in the assessment of the aortic valve from the right ventricular outflow tract

Intracardiac echocardiography (ICE) is a developing technology and a promising method for visualizing intracardiac structures. However, its applications are currently limited to guidance during mitral valvuloplasty, catheter ablation, or electrophysiologic examination. The goal of this study was to observe the aortic valve, measure the annular diameter of the valve by ICE through a right-sided approach, and compare the results by ICE with those by transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE). We studied 18 patients (9 men, 9 women, aged 19 to 72 years) with various heart diseases, including 15 patients with mitral or aortic valvular disease. An imaging catheter was advanced through a long sheath into the outflow tract of the right ventricle. We obtained good longitudinal views of the aortic valve in all patients. Two of the 18 patients had poor image quality by TTE. The annular diameter by ICE correlated more closely with TEE than with TTE. In conclusion, right-sided ICE is a safe, simple, and useful procedure for observing the aortic valve during cardiac catheterization without additional discomfort in the patients. Right-sided ICE is superior to TTE in observing the aortic valve and measuring the annular diameter of the valve. The annular diameter can be measured by ICE as precisely as by TEE.

Intracardiac echocardiographic guidance during microwave catheter ablation

The purpose of this study was to explore the potential of intracardiac echocardiography in monitoring lesion formation and assisting with the assessment of ablative lesions using microwave energy. Microwave energy is a promising modality for catheter ablation. Because microwave lesions may have considerable variability in dimension, the ability to assess them may be particularly useful. One hundred twenty-five microwave lesions were created in vitro in ovine left ventricles. Correct assessment of catheter-endocardial contact was possible in virtually all cases. Intracardiac imaging always identified correctly whether or not an ablation was performed. During ablation, gas formation was observed in all instances. Sensitivity, specificity, and predictive values for identification of ablation lesions were 88% to 92%. Although the correlations with pathology for lesion dimensions were relatively poor, intracardiac imaging had a predictive accuracy of 80% to 85% to discriminate small from large lesions. Intracardiac guidance for microwave ablation is useful for verifying tissue-electrode contact, monitoring lesion formation, and localizing lesions. It is also a useful tool for the assessment of lesion size. These attributes, combined with the ability to facilitate transseptal catheterization and to identify complications such as hemopericardium, make intracardiac echocardiography a potentially useful method for guiding microwave ablation of arrhythmic foci.

Imaging technique and clinical utility for electrophysiologic procedures of lower frequency (9 MHz) intracardiac echocardiography

Intracardiac echocardiography using a new 9-MHz ultrasound catheter was performed in 30 patients undergoing percutaneous catheter mapping and radiofrequency ablation of a tachyarrhythmia, because the imaging capabilities with this intracardiac echocardiographic catheter permit detailed identification of normal and abnormal cardiac anatomy with improved imaging depth. Intracardiac echocardiography is of significant clinical utility during ablation for guiding interatrial septal puncture, assessing placement and contact of mapping/ablation catheters, monitoring ablation lesion morphologic changes, and diagnosing procedure-related complications.

Automated tracking of left ventricular wall thickening with intracardiac echocardiography

OBJECTIVE

We developed and evaluated a new method to automatically measure regional left ventricular wall thickening by analyzing the radiofrequency backscatter signal from an intracardiac echocardiographic catheter.

METHODS

We inserted 10-MHz echocardiographic catheters in 11 dogs. Wall thickness was perturbed by altering loading conditions and inotropic state. The backscatter signal from a single selected radial scan line was digitized. An automated algorithm identified the digitized endocardial and epicardial signals, tracked them throughout the cardiac cycle, and plotted the spatial difference over time. Pressure-thickness loops were generated.

RESULTS

End-systolic and end-diastolic thickness and percent wall thickening from the unedited, unsmoothed signals compared favorably with independent manual analysis of transthoracic echocardiographic images of the same region: r = 0.89 for wall thickness and 0.81 for systolic thickening.

CONCLUSION

The backscatter signal from an intracardiac echocardiographic device can be analyzed automatically to continuously assess regional left ventricular wall thickening and generate pressure-thickness loops.

Intracardiac Echocardiographic Imaging in Guiding and Monitoring Radiofrequency Catheter Ablation at the Tricuspid Annulus

Intracardiac echocardiography (ICE) with lower frequency is a new imaging modality. We present the case of a patient with dilated cardiomyopathy and recurrent supraventricular tachycardia due to a right posterolateral accessory pathway. ICE imaging was performed using a 9-MHz (9-Fr) catheter positioned in the right atrium and guided precise catheter localization at the lateral tricuspid annulus where the bypass tract was located, which facilitated successful radiofrequency ablation. In addition, ICE imaging detected anatomic abnormalities, including localized pericardial effusion and torn tricuspid chordae tendineae, which were all identified at the onset of the procedure. The effusions remained stable during imaging monitoring throughout the procedure, which helped reassure us that these abnormalities were not procedure related. In summary, ICE imaging may significantly improve procedural efficacy in selected catheter ablation procedure and help detect anatomic abnormalities, procedural complications, or both.

Intracardiac echocardiographic imaging of the left ventricle from the right ventricle: quantitative experimental evaluation

PURPOSE

Our purpose was to demonstrate that intracardiac ultrasound imaging from a transducer placed in the right ventricle can be used to quantitatively image the left ventricle in a swine model.

BACKGROUND

The left ventricles and right ventricles of dogs and human beings have been studied with intracardiac echocardiography. Usually intracardiac echocardiography has been performed with the ultrasound catheter in the chamber being studied because of limited depth of field. Thus left ventricular imaging required that the ultrasound catheter be placed intra-arterially and manipulated into the left ventricle. The availability of lower frequency ultrasound catheters may allow left ventricular imaging from the right ventricle--a more clinically attractive approach.

METHODS

In 10 closed chest swine, a 10F, 10-MHz ultrasound catheter was placed into the right ventricle through an introducer sheath placed in the right internal jugular vein. Two-dimensional transthoracic echo images were obtained for comparison. Two protocols were used to image global left ventricular function and regional wall motion during pharmacologic challenge. In protocol 1 (n = 4) we evaluated global left ventricular performance in response to interventions: dobutamine, halothane (a myocardial depressant), nitroprusside, and volume loading. In protocol 2 (n = 6) we evaluated regional contraction abnormalities induced by coronary arterial balloon inflation and deflation (reperfusion) and dobutamine. At baseline and after each intervention, global function of the right ventricle and left ventricle was measured as cross-sectional end-diastolic area and end-systolic area, and regional contraction was evaluated as the percentage of left ventricular circumference with a wall motion abnormality. Intracardiac pressures and cardiac output were also measured for comparison. Left ventricular cross-sectional area ejection fractions (area EF) were calculated for both intracardiac and transthoracic echo images as (end-diastolic cross-sectional area - end-systolic cross-sectional area)/end-diastolic cross-sectional area.

RESULTS

The 10F, 10-MHz intracardiac ultrasound catheter successfully imaged the left ventricle from the right ventricle in all 10 swine. In protocol 1, dobutamine increased area EF from a baseline of 0.60 +/- 0.03 to 0.87 +/- 0.04 (P < .05). When dobutamine was added to the myocardial depressant halothane, left ventricular area EF increased from a baseline of 0.55 +/- 0.03 to 0.68 +/- 0.04. In protocol 2, coronary occlusion resulted in a detectable regional wall motion abnormality (circumferential percentage) of 23% +/- 3%. After reperfusion and during dobutamine stimulation, the wall abnormality decreased to 12% +/- 4%. Transthoracic echocardiography correlated well with these intracardiac findings.

CONCLUSIONS

The left ventricle can be quantitatively imaged from the right ventricle with the use of a 10F, 10-MHz intracardiac catheter in swine. This system can detect changes in global and regional left ventricular systolic function. This technique warrants evaluation in clinical applications.

Nonfluoroscopic transseptal catheterization: safety and efficacy of intracardiac echocardiographic guidance

INTRODUCTION

Recently, there has been a revival in the use of transseptal catheterization due to the development of balloon mitral valvuloplasty and radiofrequency catheter ablation. Complications of transseptal puncture, although rare, can be serious and life-threatening. In the present study, we evaluated the use of intracardiac echocardiography (ICE) as the sole imaging modality to guide transseptal puncture and catheterization.

METHODS AND RESULTS

In each animal, 10 transseptal punctures were performed guided solely by ICE. The standard approach to transseptal catheterization using a Brockenbrough needle and long vascular sheath was used except for the use of ICE instead of fluoroscopy. A 6.2-French/12.5-MHz and 9-French/9-MHz ICE catheter was used for imaging. At the end of each study, pathologic evaluation was performed. Transseptal puncture was performed safely, guided solely by ICE, in each of 100 attempts (five attempts guided by each ICE catheter in 10 dogs). While the fossa ovalis was easily visualized with both ICE catheters, the 9-French/9-MHz catheter offered an enhanced field of view. On pathologic evaluation, there was no evidence of perforation of either the right or left atrium outside of the fossa ovalis.

CONCLUSION

Both ICE catheters used in this trial allowed for excellent visualization of the fossa ovalis and safe transseptal puncture. Intracardiac echocardiography may be a better imaging modality than fluoroscopy for guiding transseptal catheterization, especially in less experienced hands.

Application of tissue Doppler imaging technique in evaluating early ventricular contraction associated with accessory atrioventricular pathways in Wolff-Parkinson-White syndrome

To examine the feasibility of a tissue Doppler imaging (TDI) technique for evaluating the early contraction sites in Wolff-Parkinson-White (WPW) syndrome, we analyzed the time-sequential changes in ventricular wall motion in WPW syndrome by TDI. Fifty patients with WPW syndrome were examined by the TDI system in which the high-speed scanning technique allowed for a frame rate up to 38 frames/sec. Among 42 patients in whom the acceptable images were obtained by TDI, the early contraction, which was represented by a red or blue spot appearing on the subendocardial side at the time of the delta wave in the electrocardiogram, was demonstrated in 25 of 29 patients with left-sided accessory pathways. However, in 13 patients with right-sided pathways, the early contraction sites could be identified in only five patients. The TDI-determined early contraction sites were well coincided with the sites of the accessory pathways determined by the electrophysiologic examination (p < 0.01). After the successful radiofrequency catheter ablation, early contraction sites were found to disappear by TDI in all patients. These results demonstrate the feasibility of the TDI technique to evaluate the early ventricular contraction associated with the atrioventricular accessory pathways. We suggest that the TDI system is helpful to localize the accessory pathways and to evaluate the results after radiofrequency ablation, although further studies are necessary to demonstrate the advantage of TDI over conventional echocardiography and electrophysiologic study in the evaluation of the accessory pathways in WPW syndrome.

Adjunctive intracardiac echocardiography to guide slow pathway ablation in human atrioventricular nodal reentrant tachycardia: anatomic insights

BACKGROUND

Because of the inability of fluoroscopy to image intracardiac structures, the precise anatomic location of successful slow pathway (SP) ablation is controversial. We hypothesized that adjunctive intracardiac echocardiography (ICE) in concert with conventional fluoroscopy and electrogram guidance could identify the anatomic site of successful SP ablation.

METHODS AND RESULTS

In 25 patients, radiofrequency ablation was performed in the triangle of Koch directed by biplane fluoroscopy and a 6.2F, 12.5-MHz ICE catheter positioned adjacent to the triangle of Koch. Persistent SP conduction, number of radiofrequency applications, presence of junctional tachycardia, and fluoroscopy times were evaluated. As demonstrated by ICE, anterograde SP ablation was achieved between 2 and 7 mm from the tricuspid valve in imaging planes containing the AV muscular septum in all cases. Radiofrequency energy applications applied at other sites within the triangle of Koch failed to interrupt SP conduction. A mean of three radiofrequency energy applications (3+/-2; range, 1 to 12) successfully ablated all evidence of anterograde SP conduction in all patients studied. Junctional tachycardia was seen in 96% (71/74) of the radiofrequency energy applications.

CONCLUSIONS

Radiofrequency ablation at the tricuspid valve's insertion into the AV muscular septum as identified by ICE reliably terminates anterograde SP conduction, supporting the hypothesis that the SP consistently traverses this anatomic location.

Anatomy of atrioventricular nodal reentry investigated by intracardiac echocardiography

Intracardiac echocardiography was used to evaluate posteroseptal space anatomy in patients with atrioventricular nodal reentrant tachycardia compared with patients with other mechanisms of tachycardia. The posteroseptal space was found to be significantly wider in patients with atrioventricular nodal reentry, suggesting an anatomic basis for dual atrioventricular nodal physiology.

Intracardiac ultrasound detection of right ventricular infarction in a canine model

Our objective was to demonstrate that right ventricular (RV) infarction could be demonstrated by intracardiac ultrasonography in a canine model. RV infarction is a common and important clinical condition in patients with myocardial infarction. Traditional methods for diagnosing RV infarction have limitations. Intracardiac echocardiography, in which an ultrasonic transducer on the tip of a catheter is placed intravenously into the RV chamber, should allow detection of RV infarction. Nine closed-chest dogs were studied. The animals were instrumented with a 10 MHz ultrasound catheter placed into the right ventricle. The right coronary artery was occluded with a balloon angioplasty catheter for 20 minutes and subsequently embolized with elemental mercury. Intracardiac ultrasound images were obtained at baseline, during balloon occlusion, and during embolization. RV cross-sectional end-diastolic and end-systolic areas were calculated and fractional area changes were calculated; RV wall motion abnormalities were also evaluated. The interventricular septal thickening was also calculated. The 10 MHz intracardiac ultrasound catheter allowed visualization of much of the RV chamber and interventricular septum. The RV cross-sectional area increased with mercury embolization, which was also associated with regional wall motion abnormalities. RV end-systolic area was 1.6 cm2 and end-diastolic area 3.9 cm2 at baseline; these increased to 4.8 cm2 and 6.5 cm2 after embolization (p < 0.05). Interventricular septal thickening remained unchanged. The echocardiographic features of RV infarction, which include RV dilation and RV regional wall motion abnormalities, could be demonstrated in a canine infarct model with a 10 MHz intracardiac ultrasound catheter.

Multiplane Transesophageal and Intracardiac Echocardiography in Large Swine: Imaging Technique, Normal Values, and Research Applications

Transthoracic echocardiographic imaging has been difficult to attain in the swine model. This study: (1) compares multiplane transesophageal echocardiography (TEE) with single plane TEE and intracardiac catheter echocardiography (ICE) for imaging of the swine cardiovascular system; and (2) defines normal values using these techniques in a closed chest large swine model (n = 24, body weight 50-114 kg). Multiplane TEE increased success rate over the single plane (the variable plane array only at 0 degrees ) TEE (P < 0.01) for imaging the left ventricular (LV) long-axis view (100% vs 50%), LV outflow tract (100% vs 33%), right atrium and its appendage (79% vs 33%), ascending aorta (100% vs 58%), and aortic arch (100% vs 17%). TEE-derived normal values at end-diastole (ED) and end-systole (ES) were: LV internal diameter (ID) = 49 +/- 3 mm (ED) and 33 +/- 4 mm (ES); LV wall thickness = 7 +/- 1 mm (ED); right ventricular (RV) ID = 24 +/- 4 mm (ED); RV wall thickness = 4 +/- 2 mm (ED); left atrial ID = 48 +/- 6 mm (ES); aortic root ID = 26 +/- 3 mm (ES); LV volume = 157 +/- 49 ml (ED) and 57 +/- 22 ml (ES). Baseline LV ejection fraction (64% +/- 6%), Doppler-derived stroke volume (86 +/- 14 ml), and cardiac index (107 ml/min per kg) were determined. Basal normal values, except for an elevated cardiac index in swine, are comparable to those reported for human adults. Multiplane TEE provided better overall cardiac imaging than did single plane TEE. ICE provided higher resolution imaging of individual cardiac chambers and structures when the ultrasound catheter was introduced into the right or left heart, but whole heart imaging was limited by ultrasound penetration at 12.5 MHz. Normal indices of chamber size and function provide a reference for the physiological significance of induced pathological states in this relevant animal model.

Lower frequency (5 MHZ) intracardiac echocardiography in a large swine model: imaging views and research applications

Our previous investigation indicated that, in the 50-114-kg weight range, the swine model provides transeosophageal echocardiographic normal values for cardiac structures comparable to those found in human adults. Intracardiac echocardiographic imaging using a 12.5-MHz ultrasound catheter is limited, due to ultrasonic attenuation. Transesophageal echocardiographic imaging of the right heart is also limited with its anterior anatomic location. To further study the utility of intracardiac imaging, we placed a 5-MHz (30 Fr) multiplane transducer at the junction of the superior vena cava and right atrium, in the right atrium and right ventricle in 8 closed-chest swine (weight 129 +/- 61 kg). In each animal, complete whole heart imaging was obtained, with tomographic views including the cardiac 4-chamber, right atrium, right ventricle and outflow, left atrium and ventricle, and basal great vessels. Major intracardiac anatomic landmarks (i.e., crista terminalis, right atrial appendage, coronary sinus orifice, interatrial septum, tricuspid valve, right ventricular outflow, pulmonary veins, mitral valve and left ventricular papillary muscles) were visualized in every swine. Thus, this 5-MHz multiplane transducer, as a prototype for a steerable low-frequency intracardiac ultrasound catheter, improved both whole heart and individual cardiac structure imaging from a single intracardiac location. Further technological development and refinement is needed for routine use in research and clinical imaging practice.

Volume-rendered, three-dimensional echocardiographic determination of the size, shape, and position of atrial septal defects: validation in an in vitro model

Accurate evaluation of atrial septal defect (ASD) size and shape is very important for the selection of patients for transcatheter occlusion. The ability of volume-rendered, three-dimensional echocardiography (3DE) in displaying ASDs in a dynamic mode has been demonstrated; however, its accuracy in sizing ASDs is unknown. To assess this, we performed 3DE of 10 explanted pig hearts in which ASDs of various locations, sizes, and shapes had been experimentally created. From en face 3DE views of the atrial septum containing the defects, major and minor diameters of the defect were measured by a blinded observer, and these data were compared to direct anatomic measurements. The correlations between 3DE and anatomy for the major and minor ASD diameters were y = 0.83x + 3.4 (r = 0.97, p < 0.0001) and y = 0.92x + 1.3 (r = 0.92, p < 0.0001) respectively. The correlation between the measures for major and minor axis ratio was y = 1.06 x - 0.052, r = 0.91, p < 0.0002. Good agreement between both methods of measurements was demonstrated for all measurements. In addition, 3DE portrayed the location and shape of the defects accurately. Thus 3DE provides excellent visualization of ASD and is able to accurately define the size of the defects. These qualitative and quantitative capabilities enhance the clinical potential of this technique in the appraisal of ASDs for decisions regarding application of closure devices.

Ultrasound cardioscopy: embarking on a new journey

OBJECTIVE

To present the results of investigation of a new application of invasive ultrasonography-ultrasound cardioscopy, a procedure in which a self-contained ultrasound device is capable not only of producing an under-blood field of view but also of delivering diagnostic and therapeutic tools.

DESIGN

Twenty adult mongrel dogs were studied with the ultrasound cardioscopy device during experimental catheter ablation procedures.

MATERIAL AND METHODS

A rigid prototype probe, 34 cm long and 8 mm in diameter with a 7-MHz side-viewing transducer at the tip and an 8-F diameter tool delivery port, was introduced through the right external jugular vein into the right heart chambers. Remote and device-directed ablation procedures were monitored. Subsequently, the canine hearts were excised and examined.

RESULTS

The self-contained cardioscopy device with a contained ablation catheter could both direct and visualize a specified ablation injury. Under-blood observation of the details of the ablation procedure was possible. Although a learning curve existed for appropriate manipulation of the device, inspection of the excised hearts showed that the size of the injury was accurately predicted with use of ultrasound cardioscopy.

CONCLUSION

Ultrasound cardioscopy is a promising means of performing precise under-blood diagnostic and therapeutic maneuvers.

Quantitative assessment of stenotic aortic valve area by using intracardiac echocardiography: in vitro validation and initial in vivo illustration

Quantitative assessment of aortic stenosis (AS) is subject to the limitations of all current noninvasive and invasive methods. The ability to obtain a direct measure of aortic valve area with high resolution by intracardiac echocardiography (ICE) could be of great benefit to catheterized patients. To provide a fixed AS area as an ideal standard for comparison, we performed ICE in 12 sheep hearts with experimentally created AS and five human AS hearts from autopsies. ICE catheters were passed retrograde across the aortic valve, and the minimal orifice area on pullback was planimetered and compared with calibrated video imaging. The entire orifice circumference could be successfully recorded in 16 (94%) hearts. Orifice area from ICE correlated well with actual values (r=0.98; standard error of the estimate [SEE] = 0.06 cm2). To illustrate the applicability in vivo, two canine models and 10 patients with AS were studied. The limiting orifice could be imaged in both animals and in 8 of 10 patients, in whom values agreed well with invasive data (r= 0.95; SEE = 0.04 cm2). ICE can therefore accurately measure AS orifice area in vitro; it can be applied in vivo as well. These validation studies laid the foundation for subsequent clinical studies and applications.

Determination of aortic valve area in valvular aortic stenosis by direct measurement using intracardiac echocardiography: a comparison with the Gorlin and continuity equations

OBJECTIVES

This study sought to 1) show that intracardiac echocardiography can allow direct measurement of the aortic valve area, and 2) compare the directly measured aortic valve area from intracardiac echocardiography with the calculated aortic valve area from the Gorlin and continuity equations.

BACKGROUND

Intracardiac echocardiography has been used in the descriptive evaluation of the aortic valve; however, direct measurement of the aortic valve area using this technique in a clinical setting has not been documented. Despite their theoretical and practical limitations, the Gorlin and continuity equations remain the current standard methods for determining the aortic valve orifice area.

METHODS

Seventeen patients underwent intracardiac echocardiography for direct measurement of the aortic valve area, including four patients studied both before and after valvuloplasty, for a total of 21 studies. Immediately after intracardiac echocardiography, hemodynamic data were obtained from transthoracic echocardiography and cardiac catheterization.

RESULTS

Adequate intracardiac echocardiographic images were obtained in 17 (81%) of 21 studies. The average aortic valve area (mean +/- SD) determined by intracardiac echocardiography for the 13 studies in the Gorlin analysis group was 0.59 +/- 0.18 cm2 (range 0.37 to 1.01), and the average aortic valve area determined by the Gorlin equation was 0.62 +/- 0.18 cm2 (range 0.31 to 0.88). The average aortic valve area determined by intracardiac echocardiography for the 17 studies in the continuity analysis group was 0.66 +/- 0.23 cm2 (range 0.37 to 1.01), and that for the continuity equation was 0.62 +/- 0.22 cm2 (range 0.34 to 1.06). There was a significant correlation between the aortic valve area determined by intracardiac echocardiography and the aortic valve area calculated by the Gorlin (r = 0.78, p = 0.002) and continuity equations (r = 0.82, p < 0.0001).

CONCLUSIONS

In the clinical setting, intracardiac echocardiography can directly measure the aortic valve area with an accuracy similar to the invasive and noninvasive methods currently used. This study demonstrates a new, quantitative use for intracardiac echocardiographic imaging with many potential clinical applications.

Intracardiac echocardiography-guided biopsy of intracardiac masses

A 69-year-old man diagnosed with lung cancer had a transesophageal echocardiogram performed because of suspicion of intramyocardial tumor. The transesophageal echocardiogram confirmed the presence of both a right and left atrial mass. The lung cancer was believed to be potentially resectable if this mass did not represent tumor; therefore, biopsy of the intracardiac mass was requested. Intracardiac ultrasound was used to guide the biopsy procedure. Using intracardiac ultrasound guidance, a successful biopsy was performed that revealed the presence of tumor cells.

Intracardiac ultrasonographic assessment of atrial septal defect area: in vitro validation and technical considerations

Assessment of atrial septal defect (ASD) size and shape is important for planning and guiding its transcatheter occlusion and can potentially be achieved by intracardiac ultrasonography (ICUS). ICUS accuracy, however, must first be established against stable standards and technical imaging requirements defined. We therefore used 10, 20, and 30 MHz ICUS catheters to examine 17 ASDs that were 0.16 to 6.7 cm2 in area and were surgically created in excised ovine hearts with 10, 20, and 30 MHz ICUS catheters. ASD shape and area by ICUS were compared with direct video images of the actual ASD. In all instances minimal area by ICUS pullback agreed well with actual values (y = 1.04x + 0.2, SEE = 0.23 cm2, r = 0.99) and corresponded well with defect shapes. The maximum angle between ultrasonography beam and septal plane allowing for complete ASD visualization was 20 degrees. The angle depended on transducer frequency and septal thickness. This new technique has potential value for the accurate assessment of ASD shape and size and may be especially useful in the setting of transcatheter occlusion.

Intracardiac ultrasound imaging during transseptal catheterization

STUDY OBJECTIVE

The purpose of this study was to assess the feasibility of using small 12.5- or 20-MHz intracardiac ultrasound catheters to image the fossa ovalis and guide transseptal catheterization.

DESIGN

The study was performed in three phases. First, in vitro imaging of human autopsy hearts was performed to define the intracardiac ultrasound appearance of the fossa ovalis and transseptal apparatus. Subsequently, the optimum approach for imaging the fossa ovalis in vivo was established in 30 patients. Finally, intracardiac ultrasound imaging was performed during transseptal catheterization of 10 patients undergoing percutaneous mitral commissurotomy.

INTERVENTIONS

Intracardiac ultrasound imaging was performed with a 12.5- or 20-MHz single-element mechanical device in which a central imaging core is rotated within a 6F polyethylene sheath.

MEASUREMENTS AND RESULTS

In both in vitro and in vivo studies, the fossa ovalis was easily identifiable as a thin membranous region surrounded by the thicker muscular portion of the interatrial septum. Initial in vivo studies established venous access by the femoral route to be superior to the internal jugular approach for catheter introduction. Studies performed during transseptal catheterization established the utility of using the fluoroscopic image of the catheter adjacent to the fossa ovalis to generate a guiding shot for positioning the transseptal apparatus. In addition, distention of the fossa prior to needle perforation could be demonstrated. However, since it was often difficult to track the tip of the needle, actual puncture of the fossa was rarely demonstrated.

CONCLUSIONS

Intravascular ultrasound imaging can precisely locate the fossa ovalis in virtually all subjects. It therefore may assist transseptal catheterization.

Intracardiac echocardiography with a steerable low-frequency linear-array probe for left-sided heart imaging from the right side: experimental studies

Despite a need for intracardiac echocardiographic guidance during interventional procedures, an optimal catheter device is not available. The depth of field of catheters bearing 10 to 20 MHz transducers does not allow easy or complete visualization of the left side of the heart from the right side of the heart. Lower frequency transducers would be required to increase the depth of view of such rotational devices. These low-frequency transducers would require an expanded aperture and thus a larger catheter size. Other transducer modalities that could exploit the length of the imaging device rather than the circumference could potentially solve the problem of aperture size. To examine whether a linear-array transducer could provide adequate images of the left side of the heart from the venous side, we employed a prototype 7 MHz linear-array probe with a steerable tip inside eight animal hearts. Atrial and ventricular septal defects were created experimentally. The device was introduced into the right side of the heart through the inferior and superior vena cavae. Intracardiac imaging with this probe allowed visualization of the left side of the heart and major arteries from the right side with excellent image quality. By advancing the probe in various locations in the right side of the heart and using the steerability of this device, we were able to identify useful imaging planes for different cardiac structures. Atrial and ventricular septal defects were also detected easily and delineated clearly. The concept of a low-frequency (< 8 mHz) linear-array probe for intracardiac echocardiography may represent another step toward "whole-heart imaging" from the venous side.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracardiac echocardiography without fluoroscopy: potential of a balloon-tipped, flow-directed ultrasound catheter

Intracardiac echocardiography is a technique that uses catheter-based ultrasound transducers placed within the heart to image cardiac structures. One disadvantage to this technique is that it requires fluoroscopy for catheter placement. This study was performed to evaluate a prototype balloon-tipped, flow-directed catheter for use during intracardiac echocardiography in seven dogs. With the balloon deflated, the catheter could not be successfully advanced without fluoroscopy. Even with fluoroscopic imaging, catheter advancement was often difficult. With the balloon inflated, it could easily be passed into the pulmonary artery without fluoroscopy in 12 of 14 attempts. Images of the cardiac chambers, valves, and pulmonary artery could be obtained. In conclusion, use of a balloon-tipped, flow-directed catheter for intracardiac echocardiography and pulmonary artery imaging can be performed without the use of fluoroscopy. With continued refinements, such as enhancement of the visual field, intracardiac echocardiography could possibly be performed at the bedside to assess cardiac function or assist with interventional procedures.

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.

Intracardiac ultrasound measurement of volumes and ejection fraction in normal, infarcted, and aneurysmal left ventricles using a 10-MHz ultrasound catheter

BACKGROUND

Our objective was to examine the accuracy of intracardiac ultrasound (ICUS) measurement of left ventricular (LV) volumes and ejection fraction (EF) using a 10-MHz ultrasound catheter. ICUS can image the LV in cross sections at all levels along the long axis with a transducer mounted on the tip of a catheter. Sequential serial LV cross-sectional images can be obtained during cardiac catheterization and used to calculate LV volumes by Simpson's rule. This technique may be an alternative to contrast LV angiography.

METHODS AND RESULTS

A beating-heart in vivo model was created to measure LV volume directly and continuously with an intracavity high-compliance latex balloon connected to a calibrated extracardiac reservoir in eight dogs in 35 experimental stages. A 10F ICUS catheter with a 10-MHz single-element transducer was introduced retrogradely via the aortic valve to the apex. Series of sequential LV cross-sectional images were recorded from the apex to the base during a calibrated pullback of the catheter. At each 5-mm interval, the LV cross section was traced at end diastole and end systole. LV volume was calculated by Simpson's rule by integrating all segmental areas multiplied by segmental height. The effect on accuracy of selecting 5-, 10-, or 15-mm heights or a single section at the midventricular level for measurement was assessed. The influence of distorted ventricular shape on the accuracy of ICUS measurements of LV volume was evaluated. This method was applied in 19 experimental stages in 10 intact dogs and pigs catheterized via the femoral artery. In the in vivo canine model, LV end-diastolic volume, end-systolic volume, and EF determined by ICUS using 5-, 10-, or 15-mm segments were not different from the actual measurements. But correlation and agreement between ICUS end-diastolic volume and direct measurements for 5- and 10-mm segments were significantly better than for 15-mm segments or a single section. Similar excellent correlations and agreement were observed for actual and ICUS-derived end-systolic volumes using 5-, 10-, or 15-mm segments. The ICUS-derived EF correlated very well with actual EF with a small measurement error of 3.91 +/- 2.59% for 5-mm or 4.13 +/- 2.79% for 10-mm segments but a significantly greater measurement error for 15-mm segments (5.35 +/- 3.76%) or single sections (14.8 +/- 12.2%). The presence of LV infarction or aneurysm did not significantly influence the accuracy of ICUS calculations for segmental heights < or = 10 mm. Application in intact animals demonstrated a good correlation between stroke volume measured by ICUS and by thermodilution or flowmeter. ICUS-derived LV volumes correlated well with biplane angiographic volumes, with a tendency toward underestimation. There was no significant difference between ICUS-determined LV EF and EF determined by angiography.

CONCLUSIONS

Intracardiac echocardiography accurately measures LV volumes and global systolic function in both regularly shaped and distorted left ventricles. This technique directly and continuously visualizes circumferential LV endocardium and wall thickness without contrast agents or geometric assumptions for calculation of LV volume. Thus, it should be particularly useful in patients at high risk for contrast-related complications or distorted LV shapes in which geometric assumptions may not be valid.