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

Echocardiography-guided interventions

A major advantage of echocardiography over other advanced imaging modalities (magnetic resonance imaging, computed tomographic angiography) is that echocardiography is mobile and real time. Echocardiograms can be recorded at the bedside, in the cardiac catheterization laboratory, in the cardiovascular intensive care unit, in the emergency room-indeed, any place that can accommodate a wheeled cart. This tremendous advantage allows for the performance of imaging immediately before, during, and after various procedures involving interventions. The purpose of this report is to review the use of echocardiography to guide interventions. We provide information on the selection of patients for interventions, monitoring during the performance of interventions, and assessing the effects of interventions after their completion. In this document, we address the use of echocardiography in commonly performed procedures: transatrial septal catheterization, pericardiocentesis, myocardial biopsy, percutaneous transvenous balloon valvuloplasty, catheter closure of atrial septal defects (ASDs) and patent foramen ovale (PFO), alcohol septal ablation for hypertrophic cardiomyopathy, and cardiac electrophysiology. A concluding section addresses interventions that are presently investigational but are likely to enter the realm of practice in the very near future: complex mitral valve repairs, left atrial appendage (LAA) occlusion devices, 3-dimensional (3D) echocardiographic guidance, and percutaneous aortic valve replacement. The use of echocardiography to select and guide cardiac resynchronization therapy has recently been addressed in a separate document published by the American Society of Echocardiography and is not further discussed in this document. The use of imaging techniques to guide even well-established procedures enhances the efficiency and safety of these procedures.

Using Transthoracic Two-Dimensional Echocardiography to Guide the Placement of Coronary Sinus Catheters: A Randomized Study

OBJECTIVE

To assess the value of transthoracic echocardiography (TTE) as an image guide in placing a coronary sinus catheter into the coronary sinus.

METHODS

Sixty consecutive patients undergoing electrophysiologic study were randomized to TTE (30 patients, "TTE group") or x-ray fluoroscopy (30 patients, "x-ray group") as an image guide to assist in the placement of a coronary sinus catheter.

RESULTS

The success rate of placing the coronary sinus catheter was 96.7% in TTE group and 100% in x-ray group (P > 0.05). The procedure duration was 5.8 +/- 5.7 minutes in TTE group and 5.9 +/- 3.3 minutes in x-ray group (P > 0.05), The x-ray exposure time was 0.15 +/- 0 minute in TTE group and 4.2 +/- 2.8 minutes in x-ray group (P < 0.0001).

CONCLUSION

Using TTE as an image guide, coronary sinus cannulation is feasible and as rapid as standard x-ray fluoroscopy, without the radiation risk.

Real-time cardiac catheter navigation on three-dimensional CT images

INTRODUCTION

Targets for ablation of atrial fibrillation, atrial flutter, and non-idiopathic ventricular tachycardia are increasingly being selected based on anatomic considerations. Because fluoroscopy provides only limited information about the relationship between catheter positions and cardiac structures, and is associated with radiation risk, other approaches to mapping may be beneficial.

METHODS

The spatial and temporal information of an electromagnetic catheter tip position sensing system (Magellan, Biosense Inc.) was superimposed on a three-dimensional (3D) CT of the chest in swine using fiducial markers for image registration. Position and orientation of a 6 French catheter with an electromagnetic sensor was displayed in real-time on a corresponding 3D-CT. Catheter navigation within the heart and the great vessels was guided by detailed knowledge about catheter location in relation to cardiac anatomy.

RESULTS

Anatomic structures including the atrial septum, pulmonary veins, and valvular apparatus were easily identified and used to direct catheter navigation. During the right heart examination, the catheter was navigated through the superior and inferior vena cava to predetermined anatomic locations in right atrium, right ventricle and pulmonary artery. The ablation catheter was also navigated successfully from the aorta through the aortic valve in the left ventricle. No complication was encountered during the experiments. The accuracy and precision of this novel approach to mapping was 4.69 +/- 1.70 mm and 2.22 +/- 0.69 mm, respectively.

CONCLUSIONS

Real-time display of catheter position and orientation on 3D-CT scans allows accurate and precise catheter navigation in the heart. The detailed anatomic information may improve anatomically based procedures like pulmonary vein ablation and has the potential to decrease radiation times.

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.

Echocardiographic transponder-guided catheter ablation feasibility and accuracy

BACKGROUND

The utility of echocardiography for catheter guidance during percutaneous endocardial ablation is increasingly apparent. However, the technique is currently imperfect due to limitations in discerning the ablation electrode from other parts of the catheter shaft.

PURPOSE

To examine the feasibility and accuracy of echocardiography-guided ablation using commercial ablation catheters fitted with a transponder to improve localization of the ablation electrode.

METHODS

Fifteen healthy pigs and five pigs with chronic anterior myocardial infarction were studied. In healthy animals, echocardiographically distinct endocardial sites in right and left cardiac chambers were targeted for ablation. In infarcted animals, the left ventricular infarction border zone was targeted. Both intracardiac (ICE; 12.5 megahertz and 5 megahertz) and transesophageal echocardiographic (TEE) techniques were utilized.

RESULTS

In healthy animals, transponder-guided ablation was feasible with each of the echocardiographic techniques. Accuracy was 82 % (45 of 55 lesions) with ICE-12.5 MHz, 87 % (27 of 31 lesions) with ICE-5 MHz, and 81 % (22 of 27 lesions) with TEE. In infarcted animals, the accuracy was 38 % (3 of 8 lesions) for ICE-5 MHz and 38 % (3 of 8 lesions) for TEE. Errant lesions in healthy animals were observed in earlier experiments, due to operator misinterpretation of the plane of imaging. Errant lesions in infarcted animals were observed throughout the experimental series, and may have been due to a variable relationship between echocardiographic and histologic infarction border zones.

CONCLUSIONS

Echocardiographic transponder-guided catheter ablation is feasible. Accuracy for normal endocardial targets was excellent, less so for chronic infarction border.

Visualization and temporal/spatial characterization of cardiac radiofrequency ablation lesions using magnetic resonance imaging

BACKGROUND

The purpose of this study was to describe a system and method for creating, visualizing, and monitoring cardiac radiofrequency ablation (RFA) therapy during magnetic resonance imaging (MRI).

METHODS AND RESULTS

RFA was performed in the right ventricular apex of 6 healthy mongrel dogs with a custom 7F nonmagnetic ablation catheter (4-mm electrode) in a newly developed real-time interactive cardiac MRI system. Catheters were positioned to intracardiac targets by use of an MRI fluoroscopy sequence, and ablated tissue was imaged with T2-weighted fast spin-echo and contrast-enhanced T1-weighted gradient-echo sequences. Lesion size by MRI was determined and compared with measurements at gross and histopathological examination. Ablated areas of myocardium appeared as hyperintense regions directly adjacent to the catheter tip and could be detected 2 minutes after RF delivery. Lesions reached maximum size approximately 5 minutes after ablation, whereas lesion signal intensity increased linearly with time but then reached a plateau at 12.2+/-2.1 minutes. Lesion size by MR correlated well with actual postmortem lesion size and histological necrosis area (55.4+/-7.2 versus 49.7+/-5.9 mm(2), r=0.958, P<0.05).

CONCLUSIONS

RFA can be performed in vivo in a new real-time interactive cardiac MRI system. The spatial and temporal extent of cardiac lesions can be visualized and monitored by T2- and T1-weighted imaging, and MRI lesion size agrees well with actual postmortem lesion size. MRI-guided RFA may be a useful approach to help facilitate anatomic lesion placement and to provide insight into the biophysical effects of new ablation techniques and technologies.

The Role of Transesophageal Echocardiography During Port-Access Minimally Invasive Cardiac Surgery: A New Challenge for the Echocardiographer

The recent development of endovascular catheters that are placed via the femoral artery and vein has enabled patients to be placed on cardiopulmonary bypass without the need for direct visualization of the heart or great vessels via sternotomy. This has allowed cardiac surgery to be performed through smaller, thoracotomy incisions. Placement of these catheters initially was performed under fluoroscopic guidance, which has major imaging limitations. Now, transesophageal echocardiography (TEE) has replaced fluoroscopy as the primary imaging technique to assist in the placement of endovascular catheters during minimally invasive, port-access cardiac surgery. In our institution, 449 port-access procedures have been performed from May 1996 through July 1998. We found that TEE is able to adequately visualize the cardiac structures and assist in the placement of the endovascular catheters in all patients. Fluoroscopy is helpful only as an aid to the use of TEE for placement of the coronary sinus catheter.

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.

Transcatheter closure of ventricular septal defects using the Rashkind device: initial experience

We report our initial experience with transcatheter closure of ventricular septal defects (VSD) using the Rashkind device. Transcatheter closure of 25 VSDs was attempted in 16 patients with a median age of 2 (range 0.1-4) years and a median weight of 11 (range 4.1-19) kg. The location of the VSDs was apical in 14, midmuscular in 8, and anterior muscular in 3. Five patients had complex heart lesions, 10 patients had associated defects, including perimembranous VSD, atrial septal defect, patent ductus arteriosus, and coarctation of aorta. The remaining patient had isolated multiple muscular VSDs. The surgical repair of VSDs was a high-risk option in all the patients. Of the 25 attempted closures, 22 devices were placed successfully. Nine patients had a single device, four patients had two devices each and one patient had a total of five devices placed. In two patients attempts to close three VSDs were associated with major problems/death. Fourteen patients have been followed up for at least 1 year and all are doing well. Five patients, who otherwise remain asymptomatic, have a trace residual shunt. The fluoroscopy time ranged from 51 to 205 min (median 110) and the procedure time 120 to 300 min (median 200). The transcatheter closure of VSDs acts as a palliation as well as a definitive therapeutic modality in some patients with surgically inaccessible VSDs. Deployment of multiple devices in a patient is feasible. Increased experience may diminish the initial rate of complications.

Utility of transesophageal echocardiography during port-access minimally invasive cardiac surgery

In this study, we sought to determine the use of transesophageal echocardiography (TEE) as the primary imaging technique to assist in the placement of endovascular catheters during minimally invasive, port-access cardiac surgery. The recent development of endovascular catheters that are placed via the femoral artery and vein has enabled patients to be placed on cardiopulmonary bypass without the need for direct visualization of the heart or great vessels via sternotomy. This has allowed cardiac surgery to be performed through smaller thoracotomy incisions. Placement of these catheters has previously been performed with fluoroscopic guidance, which has major imaging limitations. Thirty-six patients underwent port-access cardiac surgery at our institution during the study period. All patients underwent intraoperative TEE. We used TEE to visualize the coronary sinus os, right atrium and superior vena cava, and thoracic aorta to assist with placement of the coronary sinus catheter, venous cannula, and endoaortic clamp. Twenty patients underwent mitral valve surgery, 14 patients coronary artery bypass grafting, 1 patient aortic valve replacement, and 1 patient repair of an atrial septal defect by the port-access approach. TEE was able to adequately visualize the cardiac structures and assist in the placement of the endovascular catheters in all patients. Fluoroscopy was only helpful as an aid to TEE for placement of the coronary sinus catheter. TEE is an excellent imaging modality for the proper placement of these new endovascular catheters, obviating the need for fluoroscopy, except to be on standby and for placement of the coronary sinus catheter.

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

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

Use of miniature biplane transesophageal echocardiography during pediatric atrial catheter interventional procedures

We reported the use of a new miniature biplane TEE probe during pediatric cardiac interventional catheterization procedures. Use of this imaging modality provided significant advantages during dilation of obstructed venous pathways and closure of interatrial defects. Procedural characteristics and specific congenital heart lesion-related advantages were discussed.

Doppler Echocardiography During Pregnancy: Physiological and Abnormal Findings

Despite continuous improvements in diagnostic cardiology techniques, echocardiography remains the cornerstone for noninvasive cardiovascular assessment of the pregnant woman with heart disease or suspected cardiac abnormality. Reversible physiological cardiac remodeling of pregnancy associated with changes in valve patency or transvalvular flow pattern can be suitably assessed by the complementary use of quantitative pulsed- and continuous Doppler and qualitative color Doppler technology. These techniques are also useful for a better understanding of the pathophysiology of the hemodynamic consequences of fixed valve stenosis during pregnancy with respect to the labile nature of gradients resulting from variable loading conditions as occurs during pregnancy. Recent and specific areas of clinical use including cardiac output estimation, contrast echocardiography minimizing radioscopy during cardiac catheterization, and transesophageal echocardiography for selection of patients with mitral stenosis suitable for percutaneous catheter valvotomy illustrate the large spectrum of capabilities of this versatile method during pregnancy. (ECHOCARDIOGRAPHY, Volume 13, March 1996)

Use of adenosine to identify patients at risk for recurrence of accessory pathway conduction after initially successful radiofrequency catheter ablation

OBJECTIVE

The use of adenosine after radiofrequency catheter ablation of accessory pathways was prospectively studied to determine its utility for identifying patients at risk for recurrence of accessory pathway conduction and to guide therapy that might reduce late recurrence in this group.

BACKGROUND

Accessory pathway conduction recurs in 5%-12% of patients following initially "successful" radiofrequency catheter ablation. Adenosine may facilitate conduction over accessory pathways that have been modified by radiofrequency delivery, thus identifying patients at risk for recurrence.

METHODS

Radiofrequency catheter ablation was performed in 109 patients. Prior to ablation, 12-18 mg of adenosine was administered. After ablation, when all evidence of accessory pathway conduction remained absent for at least 30 minutes, adenosine 12-18 mg was again administered.

RESULTS

Adenosine given prior to radiofrequency catheter ablation did not block accessory pathway conduction in any patient. Adenosine given after elimination of accessory pathway conduction induced complete atrioventricular and ventriculoatrial block in 95 patients; 11 (11.6%) subsequently had recurrence of accessory pathway function. Accessory pathway conduction was unmasked by adenosine in 12 patients (11.2%). After further deliveries of radiofrequency energy, 7 of these 12 patients subsequently demonstrated adenosine induced atrioventricular and ventriculoatrial block; 1 of these 7 patients experienced recurrence of accessory pathway conduction. The remaining 5 patients demonstrated persistent accessory pathway conduction only with adenosine; all experienced clinical recurrence of accessory pathway function.

CONCLUSION

The use of adenosine after presumed successful radiofrequency catheter ablation may reveal persistent accessory pathway conduction. Elimination of this latent accessory pathway conduction reduces the risk for recurrence.

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.

Transesophageal echocardiographic guidance of transcatheter ventricular septal defect closure

OBJECTIVES

This report describes transesophageal echocardiographic guidance of transcatheter closure of ventricular septal defects and its value as an adjunct to fluoroscopy and angiography in this procedure.

BACKGROUND

Experience with transcatheter closure of ventricular septal defects has identified a diverse group of patients in whom it may be the procedure of choice. Although facilitating other interventional procedures, such as transcatheter closure of atrial septal defects, the value of transesophageal echocardiographic guidance for transcatheter ventricular septal defect closure has not been documented.

METHODS

All patients who underwent ventricular septal defect closure with transesophageal echocardiographic guidance before November 1992 were included. Angiograms and echocardiograms were reviewed to evaluate device position and relation to valve tissue during placement and to assess residual flow after device implantation. The ability of transesophageal echocardiography to assess these variables was compared with fluoroscopy and angiography.

RESULTS

Transesophageal echocardiographic guidance was used in 31 of the 83 catheterizations involving transcatheter ventricular septal defect closure performed between February 1990 and November 1992. Under transesophageal echocardiographic guidance, 45 devices were implanted: 23 in muscular ventricular septal defects, 17 in residual postoperative patch margin defects and 5 in other ventricular septal defects. Transesophageal echocardiographic guidance enhanced assessment of device position and proximity to valve structures and markedly improved assessment of residual flow. Assessment of residual flow with transesophageal echocardiography eliminated the need for multiple angiograms in some patients. Combining transesophageal echocardiography with fluoroscopy and angiography provided the most information.

CONCLUSIONS

Transesophageal echocardiography facilitates transcatheter closure of ventricular septal defects by improving assessment of device position and effectiveness of closure. It is indicated when device placement is likely to be difficult or may interfere with valve structures or when multiple interventional procedures are anticipated.

Potential of intracardiac ultrasonography as an adjunct for mapping and ablation

Radio frequency catheter ablation of cardiac tissues has evolved rapidly as the standard therapy for various arrhythmias. Current mapping techniques include fluoroscopy and endocardial ECG recordings. These techniques are time-consuming and give only limited information with regard to cardiac anatomy and pathology. Moreover, fluoroscopy leads to significant radiation exposure to the patient and the operator. Intracardiac ultrasonography is a promising new technique that may improve intracardiac anatomic orientation, reduce radiation exposure, allow better control of lesion formation during radio frequency current application, and identify possible complications such as thrombus formation or perforation. Intracardiac ultrasonography systems that are presently available are limited by insufficient penetration depth and image resolution. Technical refinements are discussed that may improve the applicability of intracardiac echocardiography for electrophysiologic mapping procedures.

Echocardiographically guided electrophysiologic testing in pregnancy

Electrophysiologic testing is usually performed with fluoroscopy to guide catheter positioning. This method of visualizing catheter placement may not be ideal for patients who are pregnant. We report four cases of echocardiographically guided placement of catheters for electrophysiologic testing because of the consideration of pregnancy. Adequate visualization of catheters was possible, allowing for proper catheter positioning and complete electrophysiologic testing, including the recording of atrial, His-bundle, and ventricular potentials, as well as cardiac stimulation and induction of tachycardia. This method holds promise for patients in whom fluoroscopy may be relatively contraindicated, such as pregnant patients, as well as patients in whom it is desirable to avoid x-ray exposure such as women of childbearing age and young children.

Radiofrequency catheter ablation guided by intracardiac echocardiography

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Transesophageal echocardiography during radiofrequency catheter ablation of ventricular tachycardia

Radiofrequency lesion formation requires stable catheter tip/endocardial contact. Energy delivery is limited when temperatures are > 100 degrees C due to coagulum formation at the catheter tip. Transesophageal echocardiographic imaging may be useful for monitoring catheter position and detecting boiling. Transesophageal echocardiographic images were recorded during production of 22 radiofrequency lesions in bovine myocardium in a saline bath. Lesion size, tissue temperature and appearance of echo contrast (bubbles) were assessed. In 11 patients, transesophageal echocardiography was used to guide catheter movement and detect boiling during radiofrequency ablation for ventricular tachycardia. In the tissue bath, the appearance of echo bubbles was associated with visual bubbling at the catheter tip, tissue temperatures > 60 degrees C and larger lesions (284 +/- 165 vs 30 +/- 54 mm3; p < 0.001). In humans, transesophageal images easily identified the catheter tip in either ventricle and enabled continuous observation of electrode-tissue contact during radiofrequency application. Transesophageal echocardiographic bubbles appeared in 59 of 217 radiofrequency applications (27%). Continued radiofrequency application after appearance of bubbles was followed by an increase in impedance. Prolonged placement of the probe in heavily sedated patients resulted in a mild sore throat, but no other complications. Transesophageal echocardiographic imaging enables continuous monitoring of catheter position during radiofrequency energy application. The abrupt appearance of echo bubbles indicates boiling and impending coagulum formation at the catheter tip.