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

Intracardiac Echocardiography-Applications in the Electrophysiology and the Cardiac Catheterization Labs

Background. Intracardiac echocardiography (ICE) is routinely used in cardiac electrophysiology and catheterization labs. It plays a vital role in understanding cardiac anatomy, procedural planning, and early identification of complications. In this review, we describe the utility of ICE for procedures in the electrophysiology lab, including atrial fibrillation ablation, left atrial appendage occlusion device implantation, and cardiac implantable electronic device (CIED) extraction. Intracardiac echocardiography also helps in the identification of complications such as pericardial effusion, pulmonary vein stenosis, and left atrial appendage thrombus. Compared with traditional echocardiographic modalities such as transesophageal echocardiogram (TEE), ICE has equivalent image quality, requires less sedation, and possesses no risk of esophageal injury. The disadvantages of ICE include a learning curve and necessity for central vascular access.

UltraSOUND-based characterization of ventricular tachycardia SCAR and arrhythmogenic substrate: The SOUNDSCAR study

BACKGROUND

Intracardiac echocardiography (ICE) represents a valuable image integration technique, with the unique advantage of dynamic real-time scar characterization.

OBJECTIVES

The goals of this study were to assess the correlation between ICE-defined and electroanatomic mapping (EAM)-defined scar in patients with ischemic cardiomyopathy and to define the outcomes of ICE-guided ventricular tachycardia (VT) ablation.

METHODS

Thirty-eight patients with ischemic cardiomyopathy (SOUNDSCAR cohort) underwent full left ventricular (LV) ICE imaging and EAM. ICE-defined scar parameters (end-diastolic and end-systolic wall diameter [EDWD and ESWD], end-systolic wall thickening [percentage difference between EDWD and ESWD with respect to EDWD], slope [end-diastole to end-systole wall thickening], and American Heart Association wall motion scoring) were correlated with EAM-defined scar (voltage <1.5 mV). In a separate cohort (n = 21), outcomes of an ICE-guided VT ablation approach (EAM focused to ICE-defined scar regions) were compared with those of conventional ablation (full left ventricular mapping with EAM only; n = 21).

RESULTS

In the 38 SOUNDSCAR patients (mean age 67 ± 11 years; 35 male [92%]; left ventricular ejection fraction 31% ± 10%; 2474 ICE segments; 524 ICE sectors), all ICE-defined parameters strongly predicted EAM-defined scar (area under the curve: American Heart Association score 0.873; ESWD 0.880; EDWD 0.827; slope 0.855; percentage difference between EDWD and ESWD with respect to EDWD, 0.851). All ICE-defined parameters had large effect sizes for predicting EAM-defined scar (logistic regression, P < .001). A detailed topographical comparison of ICE-defined (slope) and EAM-defined scar was possible in 25 patients and demonstrated 88% ± 10% overlap. Compared with conventional VT ablation, ICE-guided ablation was associated with shorter procedure times and comparable VT-free survival (ICE-guided vs conventional: procedure time 240 ± 20 minutes vs 298 ± 39 minutes; P < .001; VT recurrence 3 [14%] vs 7 [31%]; P = .19).

CONCLUSION

ICE-defined scar demonstrates a strong correlation with EAM-defined scar. ICE-guided VT ablation is associated with enhanced procedural efficiency.

Three-dimensional acoustic radiation force of a eukaryotic cell arbitrarily positioned in a Gaussian beam

Expressions are derived for calculating the three-dimensional acoustic radiation force (ARF) on a multilayer microsphere positioned arbitrarily in a Gaussian beam. A theoretical model of a three-layer microsphere with a cell membrane, cytoplasm, and nucleus is established to study how particle geometry and position affect the three-dimensional ARF, and its results agree well with finite-element numerical results. The microsphere can be moved relative to the beam axis by changing its structure and position in the beam, and the axial ARF increases with increasing outer-shell thickness and core size. This study offers a theoretical foundation for selecting suitable parameters for manipulating a three-layer microsphere in a Gaussian beam.

Left atrial thickness and acute thermal injury in patients undergoing ablation for atrial fibrillation: Laser versus radiofrequency energies

INTRODUCTION

Thermally induced cardiac lesions result in necrosis, edema, and inflammation. This tissue change may be seen with ultrasound. In this study, we sought to use intracardiac echocardiography (ICE) to evaluate pulmonary vein tissue morphology and assess the acute tissue changes that occur following radiofrequency (RF) or laser ablation for atrial fibrillation (AF).

METHODS AND RESULTS

Patients with AF underwent pulmonary vein isolation (PVI) using irrigated RF or laser balloon. Pre- and post-ablation ICE imaging was performed from within each pulmonary vein (PV). At least 10 transverse imaging planes per PV were evaluated and each plane was divided into eight segments. The PV/atrial wall thickness and the luminal area were measured at each segment. Twenty-seven patients underwent PVI (15 with laser, 12 with RF). Ninety-eight pulmonary veins were analyzed (58 PVs laser; 40 PVs RF). At baseline, there were no regional differences in PV wall thickness in the right-sided veins. The anterior regions of left superior pulmonary vein (LSPV) and left inferior pulmonary vein (LIPV) were significantly thicker compared with the posterior and inferior regions (p < .01). Post-ablation, PV wall thickness in RF group increased 24.1% interquartile range (IQR) (17.2%-36.7%) compared with 1.2% IQR (0.4%-8.9%) in laser group, p = .004. In all PVs, RF ablation resulted in significantly greater percent increase in wall thickness compared with laser. Additionally, RF resulted in more variable changes in regional PV wall thickness; with more increases in wall thickness in anterior versus posterior LSPV (75.4 ± 58.5% vs. 46.8 ± 55.6%, p < .01), anterior versus posterior right superior pulmonary vein (RSPV) (62.9 ± 63.9% vs. 44.6 ± 51.7%, p < .05), and superior versus inferior RSPV (69.1 ± 45.4% vs. 35.9 ± 45%, p < .05). There were no significant regional differences in PV wall thickness changes for the laser group.

CONCLUSIONS

Rotational ICE can be used to measure acute tissue changes with ablation. Regional variability in baseline wall thickness was nonuniformly present in PVs. Acute tissue changes occurred immediately post-ablation. Compared with laser balloon, RF shows markedly more thickening post-ablation with significant regional variations.

Acoustic radiation forces on three-layered drug particles in focused Gaussian beams

Drug delivery by acoustic waves is a crucial technology for targeted therapy. Recently, a three-layered drug micro-particle was proposed and fabricated, the second shell of which greatly improves both the encapsulation of the drug and the flexibility in its release rate. In this work, the acoustic radiation force (ARF) of an acoustic focused Gaussian beam on a three-layered particle comprising an inner drug core (D), a middle layer of poly(lactide-co-glycolide) (PLGA), and an outer chitosan shell (CS) is investigated. A three-layered elastic shell (TES) mimics the D-PLGA-CS structure, and the acoustic scattering from and ARF of the D-PLGA-CS are studied using Mie theory. This paper focuses on how the geometry and acoustic parameters of the outer shell influence the ARF, finding that the Poisson's ratio of the outer shell affects the ARF more than does the density or Young's modulus. In addition, this paper finds that the choice of the inner drug has little effect on the ARF acting on the D-PLGA-CS particle. The present work may benefit the acoustic manipulation of both TESs and three-layered drugs.

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.

First experience with microprobe transoesophageal echocardiography in non-sedated adults undergoing atrial fibrillation ablation: feasibility study and comparison with intracardiac echocardiography

AIMS

Imaging of the left atrium (LA) is mandatory during catheter ablation of atrial fibrillation (AF) and may be achieved by echocardiography. The aim of the present study was to assess the feasibility of using a recently released transoesophageal echocardiography (TEE) microprobe (micro-TEE) in non-sedated adult patients undergoing AF ablation and to directly compare this new technique with intracardiac echocardiography (ICE).

METHODS AND RESULTS

The study group consisted of 12 consecutive patients (8 males, mean age 49 ± 14 years) who underwent first radiofrequency AF ablation. All patients underwent standard TEE, computed tomography, intraprocedural micro-TEE, and ICE. The easiness of introducing the microprobe in the supine position in non-sedated patients in the electrophysiology laboratory, its tolerability, and quality of obtained images were assessed using a five-point scale. There were no problems with microprobe introduction and obtaining images for a mean of 54 ± 17 min. The microprobe was significantly better tolerated than the standard TEE probe (4.3 ± 0.5 vs. 3.4 ± 0.6 points, P < 0.01). The micro-TEE was scored as significantly better than ICE in the assessment of the LA and LA appendage (LAA) anatomy and function. Both techniques were very useful in guiding transseptal puncture, although micro-TEE images were ranked higher by an echocardiographer than by an electrophysiologist (tenting 4.8 ± 0.6 vs. 4.0 ± 0.6 points, P < 0.01), whereas ICE images were ranked equally excellent by both observers.

CONCLUSION

In non-sedated patients undergoing AF ablation, the micro-TEE can be used for the assessment of the LA, LAA, and pulmonary veins anatomy as well as the guidance of transseptal puncture.

Full-motion two- and three-dimensional pulmonary vein imaging by intracardiac echocardiography after pulmonary vein isolation

BACKGROUND

The pulmonary veins (PVs) are topographically complex and motile, so angiographic visualization of the PVs anatomy is limited. An imaging technique that accurately portrays the pulmonary vein (PV) anatomy would be valuable during and after catheter ablation procedures.

PURPOSE

We investigated whether three-dimensional (3D) intracardiac echocardiography (ICE) can visualize radiofrequency (RF)-induced tissue changes after PV isolation.

METHODS

We performed 3D ICE studies with a 9F, 9-MHz ICE catheter after segmental or extended PV isolation. The ICE catheter was placed 3-4 cm inside the PV ostium and mounted onto a pullback device. Sequential two-dimensional (2D) images of the full length of the vein were obtained in 0.3 mm steps with cardiac and respiratory cycle gating. Each image was fed into a computer, and the aggregate data set was reconstructed into a 3D, full-motion image. RF lesion location and lesion size were studied on 67 pullback images from 29 patients.

RESULTS

The 2D and 3D reconstruction was possible for 27 left superior PVs, 13 left inferior PVs, 26 right superior PVs, and one right inferior PV. The ablation site was identified 3-7 mm inside the PV ostium, and a 1/2 - 4/5 circumferential area was ablated with no clinically relevant stenosis. No significant differences were found on the ablated area or ablation site between segmental and extensive PV isolation.

CONCLUSION

The 2D and 3D ICE of the PVs provides detailed anatomical information of the proximal PVs, and RF-induced tissue changes in the PV wall can be visualized by ICE.

Intracardiac echocardiography in monitoring atrial septal defect percutaneous closure: initial experience in an adult laboratory

Two cases of percutaneous closure of atrial septal defect and patent foramen ovale with intracardiac echo monitoring are described. Intracardiac echocardiography was compared to contemporary TOE with full data concordance. The inherent implications and limitations of this new method are discussed.

Utilization of Intracardiac Echocardiography to Access the Coronary Sinus for Left Ventricular Lead Placement

This is a presentation of a case series of 10 consecutive patients undergoing implantation of cardiac resynchronization therapy defibrillator (CRT-D). Intracardiac echocardiography (ICE) is utilized to gain access to the coronary sinus. The method used is detailed with a brief discussion of observations gained from this early experience.

Acoustic radiation force impulse imaging of myocardial radiofrequency ablation: initial in vivo results

Acoustic radiation force impulse (ARFI) imaging techniques were used to monitor radiofrequency (RF) ablation of ovine cardiac tissue in vivo. Additionally, ARFI M-mode imaging methods were used to interrogate both healthy and ablated regions of myocardial tissue. Although induced cardiac lesions were not visualized well in conventional B-mode images, ARFI images of ablation procedures allowed determination of lesion location, shape, and relative size through time. The ARFI M-mode images were capable of distinguishing differences in behavior through the cardiac cycle between healthy and damaged tissue regions. As conventional sonography is often used to guide ablation catheters, ARFI imaging, which requires no additional equipment, may be a convenient modality for monitoring lesion formation in vivo.

Impact of catheter ablation on pulmonary vein morphology and mechanical function

INTRODUCTION

Previous reports have documented that radiofrequency catheter ablation of pulmonary veins induces a significant increase in the peak velocity of transvenous blood flow. Although the magnitude of the increase infers a state of pulmonary vein stenosis, there have been no reports of direct visualization of the ablation zone.

METHODS AND RESULTS

In each of 23 subjects, the myocardium investing one or more pulmonary veins (total of 42 veins) was electrically isolated by applying a confluent circumferential ablation lesion to the atrial side of the venoatrial junction. Doppler measurements of transvenous flow velocity were made before and after ablation using phased-array intracardiac echocardiography. Direct visualization of the ablation zone was performed using rotating intracardiac echocardiography, permitting assessment of shape, cross-sectional area, phasic variation in cross-sectional area, and wall thickness. In a subset of 5 subjects, a more detailed assessment of the ablation and contiguous regions was performed using three-dimensional echocardiography (rotating transducer). Prior to ablation, venoatrial junctions demonstrated noncircular shape and marked phasic variation in cross-sectional area. There was a trivial transvenous pressure gradient. After ablation, there was a significant increase in both anterograde and retrograde flow velocities and pressure gradient, the magnitudes of which were inversely proportional to the preablation and postablation areas. Direct visualization of the ablation zone revealed circumferential wall swelling, reduced cross-sectional area, and diminishment in phasic variation in cross-sectional area. Similar observations were made at contiguous nonablated sites, diminishing in magnitude as a function of distance.

CONCLUSION

Pulmonary vein ablation induces significant acute changes in morphology and mechanical function that extend beyond the ablation zone.

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.

Comparison of intracardiac echocardiography versus transesophageal echocardiography guidance for percutaneous transcatheter closure of atrial septal defect

Transcatheter closure of interatrial septal defects is guided by transesophageal echocardiography (TEE), which requires general anesthesia in most cases. Using a new intracardiac echocardiographic (ICE) catheter may avoid endotracheal and esophageal intubation while using only local anesthesia. Forty-two patients underwent transcatheter interatrial septal defect closure; half of them underwent TEE guidance with general anesthesia and the other half underwent ICE guidance with local anesthesia. Device deployment success rate, adequate 2-dimensional and Doppler visualization of the defect and deployment steps, interatrial communication closure at 24 hours, and at 3 and 6 months, procedure time length, complications, fluoroscopic time, and length of hospitalization were compared between both methods. All interventions were completed successfully with no complications, except for 1 patient in the TEE group who had a minor oral trauma. Echocardiographic visualization of the septal defect and deployment was adequate by both methods. Catheterization laboratory time (92 +/- 18 vs 50 +/- 12 minutes, p <0.001) and interventional procedure length (47 +/- 8 vs 35 +/- 6 minutes, p <0.001) were shortened using ICE. There was no difference in the rate of closure after 6-month follow-up by either method. ICE guidance offers equivalent echocardiographic views compared with TEE and similar rates of closure. ICE is associated with decreased procedure length while eliminating the risks of endotracheal or esophageal intubation and general anesthesia.

Catheter ablation to suppress atrial fibrillation: evolution of technique at a single center

BACKGROUND

Catheter ablation of atrial fibrillation is a rapidly evolving art. There is currently no consensus as to optimal methodology. We report a sequential experience, during which three distinct ablation techniques were utilized.

METHODS

A cohort of 112 patients in whom atrial fibrillation onset was precipitated by ectopy arising solely from myocardium investing the pulmonary veins underwent catheter ablation using one of three techniques: focal (Group A); individual vein encircling (Group B); vestibule encircling (Group C). In each group, non-fluoroscopic guidance of the mapping and ablation process was provided by the tandem use of CARTO and intracardiac echocardiography.

RESULTS

In all groups, endocardial topography was complex, and ablation electrode-endocardial contact was often unstable. Maximal electrode temperatures were low, despite frequent echocardiographic evidence of myocardial boiling. A significant progression in the number of radiofrequency energy applications between groups A and C was observed. Although acute suppression of atrial fibrillation inducibility was observed uniformly, chronic suppression rates were significantly different: Group A = 47%; Group B; 69%; Group C = 87%.

CONCLUSIONS

In this non-concurrent cohort, the rate of chronic suppression of atrial fibrillation correlated with the amount of myocardium ablated or electrically isolated. Prospective data will be required to further evaluate whether "more is better."

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.

Phased-array intracardiac echocardiography for defining cavotricuspid isthmus anatomy during radiofrequency ablation of typical atrial flutter

INTRODUCTION

Cavotricuspid isthmus (CTI) topography includes ridges, pouches, recesses, and trabeculations. These features may limit the success of radiofrequency ablation (RFA) of typical atrial flutter (AFL). The aim of this study was to assess the utility of phased-array intracardiac echocardiography (ICE) for imaging the CTI and monitoring RFA of AFL.

METHODS AND RESULTS

Fifteen patients (mean age 64 +/- 9 years) underwent ICE assessment (imaging frequency 7.5-10 MHz) before and after RFA of AFL. The ICE catheter was positioned at the inferior vena cava-right atrial junction and the following parameters were measured: (1) CTI length from the tricuspid valve to the eustachian ridge; (2) extent of CTI pouching; and (3) thickness pre/post RFA of the anterior, mid, and posterior CTI. CTI length was 35 +/- 6 mm at end-ventricular systole but shorter (30 +/- 6 mm) and more pouched at end-ventricular diastole (P = 0.02). A pouch or recess was seen in 11 of 15 patients (mean depth 6 +/- 2 mm). The septal CTI was more pouched than the lateral CTI, but the latter had more prominent trabeculations. Trabeculations were seen in 10 of 15 patients, and at these locations the CTI was 4.6 +/- 1 mm thick. Anterior, mid, and posterior CTI thickness pre-RFA was 4.1 +/- 0.8, 3.3 +/- 0.5, and 2.7 +/- 0.9 mm, respectively (P < 0.001 by analysis of variance). ICE guided RFA away from unfavorable CTI features (recesses/thick trabeculations). RFA applications created discrete CTI lesions that coalesced, forming diffuse CTI swelling. Post-RFA thickness was as follows: anterior 4.8 +/- 0.8 mm (P = NS vs pre); mid 3.8 +/- 0.8 mm (P = 0.05 vs pre); and posterior 3.8 +/- 0.8 mm (P = 0.02 vs pre).

CONCLUSION

Phased-array ICE permits novel real-time CTI imaging with excellent endocardial resolution and may facilitate RFA of AFL.

Characterization of left atrium and distal pulmonary vein morphology using multidimensional computed tomography

OBJECTIVES

This study was designed to examine the dimensions and morphology of left atrial (LA) and distal pulmonary veins (PVs) using multidetector helical computed tomography (MDCT).

BACKGROUND

Detailed knowledge of LA and PV anatomy will assist in the development of techniques for ablative intervention. Multidetector helical computed tomography is a method for multidimensional imaging of cardiac anatomy.

METHODS

Multidetector helical computed tomography was used to image the LA and PVs in 70 subjects with and 47 subjects without atrial fibrillation (AF). Accuracy of the MDCT data was confirmed by correlation with echocardiography and endocardial electrogram recordings.

RESULTS

Left atrial and PV dimensions were significantly larger in AF versus non-AF subjects, men versus women, and subjects with persistent versus paroxysmal AF. There were no differences between groups in morphologic detail.

CONCLUSIONS

Multidetector helical computed tomography images of the LA and PVs are accurate and provide detailed anatomic information. Significant differences in dimensions but not morphologic detail were apparent between groups.

IVUS guidance of thoracic and complex abdominal aortic aneurysm stent-graft repairs using an intracardiac echocardiography probe: preliminary report

PURPOSE

To report our learning experience using an intracardiac echocardiography (ICE) probe to guide endovascular aortic procedures.

METHODS

Between November 1999 and July 2001, 17 patients (12 men; mean age 73.1+/-2.3 years) underwent endovascular repair of 9 thoracic, 6 complex abdominal, and 2 thoracoabdominal aortic aneurysms. The most suitable dimensions and configuration of the stent-graft were based on preoperative computed tomographic (CTA) or magnetic resonance (MRA) angiography. Intraoperative intravascular ultrasound (IVUS) imaging was obtained using a 9-F, 9-MHz ICE probe, 110 cm in length, inserted through a 10-F, 55 degrees precurved long polyethylene sheath.

RESULTS

The endografts were deployed as planned by CTA or MRA. Before stent-graft deployment, interrogation with the ICE probe visualized the aortic arch and descending thoracoabdominal aorta without position-related artefacts and identified the sites of stent-graft fixation. After stent-graft deployment, visualization with the ICE probe detected the need for additional procedures in 8 patients, including 2 incompletely expanded thoracic grafts, which were treated with adjunctive balloon angioplasty. In 1 patient, ICE probe interrogation determined that the lesion was inappropriate for endovascular exclusion.

CONCLUSIONS

ICE probe interrogation provides accurate information on the anatomy of thoracic and abdominal aortic aneurysms and allows rapid identification of attachment sites and stent-graft characteristics. It might be considered as a valid imaging modality for monitoring all phases of endovascular procedures.

Site-selective atrial septal puncture

Atrial transseptal puncture is a technique that provides pervenous access to the left heart. The aim of this technique is to provide catheter access to the left atrium and ventricle for mapping, as well as stable electrode-endocardial contact for ablation energy application. In the present report, "site-selective" atrial septal puncture is described and illustrated using case reports.

Usefulness of phased-array intracardiac echocardiography for the assessment of left atrial mechanical "stunning" in atrial flutter and comparison with multiplane transesophageal echocardiography(*)

We compared transesophageal and phased-array intracardiac echocardiography (TEE/ICE) for the 2-dimensional and spectral Doppler assessment of left atrial (LA) mechanical function. TEE is commonly used to assess LA body and LA appendage mechanical function in patients who are undergoing radiofrequency ablation of typical atrial flutter. Fifteen patients underwent TEE and ICE imaging before and after ablation of typical atrial flutter. The following parameters were measured: (1) LA appendage emptying velocity and fractional area change, (2) severity of LA spontaneous echo contrast (graded 0 to 4), (3) maximal inflow velocity of the left and right upper pulmonary veins, and (5) maximal mitral valve E- and A-wave inflow velocities in sinus rhythm. Diagnostic quality imaging was achieved in all patients with TEE and ICE. Comparing TEE and ICE, the following absolute values and linear correlation coefficient (R) were obtained: preablation LA appendage emptying velocity: 0.45 +/- 0.21 versus 0.44 +/- 0.21 m/s (r = 0.95, p = <0.001); postablation LA appendage velocity: 0.33 +/- 0.24 versus 0.34 +/- 0.24 m/s (r = 0.97, p <0.001); LA appendage fractional area change: 35.3 +/- 13.7 versus 35.9 +/- 17.1% (r = 0.81, p <0.001); left upper/right upper pulmonary vein inflow velocity: 0.50 +/- 0.17/0.49 +/- 0.18 versus 0.51 +/- 0.17/0.47 +/- 0.20 m/s (r = 0.93/0.90, p <0.001); mitral valve E/A wave: 0.66 +/- 0.14/0.31 +/- 0.14 versus 0.69 +/- 0.17/0.35 +/- 0.23 (r = 0.84/0.97, p <0.002); LA spontaneous echo contrast (pre- and postablation): 1.1 +/- 1.2/1.3 +/- 1.2 versus 1.2 +/- 1.3/1.4 +/- 1.3 (r = 0.92/0.90, p <0.001). No patients were identified with LA appendage thrombus. Thus, TEE and phased-array ICE provided equivalent imaging data with high statistical correlation. ICE may be an imaging alternative to TEE in the evaluation of a "stunned" left atrium.

Intracardiac and intraluminal echocardiography: indications and standard approaches

In particular clinical scenarios, transthoracic and transoesophageal echocardiography (TEE) have limitations. This study sought to test if intracardiac and intraluminal echocardiography (ICLE), including 2-D, M-mode and Doppler analysis with a miniaturised, multiple-frequency transducer-tipped catheter, is suitable for assessing distinct cardiac and vascular disorders. ICLE was employed in 10 animals using 6 standard approaches. In 12 patients undergoing device closure of patent foramina ovalia (PFO) (n = 6) or atrial septal defects (ASD) (n = 3), or aortic stent implantation (n = 3), interventional procedures were guided by ICLE and, for comparison, also by TEE. ICLE provided enhanced diagnostic information on the aorta, cardiac valves, main pulmonary vessels and both atria and, therefore, added to the diagnostic spectrum of TEE. Especially for guiding interventional procedures (e.g., device closure of atrial septal defects and patent foramina ovalia), ICLE was shown to be helpful. Compared with the conventional approach, the technique reduced fluoroscopy time for device closure procedures: 6.5 min vs. 8.9 min, p < 0.0011. With the patient in a supine position, ICLE was better tolerated than TEE. Complications did not occur, either with ICLE or with TEE. In conclusion, ICLE adds to conventional echocardiography and promises to become a clinical alternative for guiding interventional procedures.

Intracardiac echocardiography-guided, anatomically based radiofrequency ablation of focal atrial fibrillation originating from pulmonary veins

OBJECTIVES

In patients with a pulmonary vein (PV) source for atrial fibrillation (AF), we sought the use of intracardiac echocardiography (ICE) to evaluate PV anatomy, guide radiofrequency (RF) ablation and monitor for acute stenosis during ablation.

BACKGROUND

A focal source for AF may be found in the proximal component of the PVs and can be effectively treated by ablative techniques. However, the procedure may be challenging due to the complex anatomy of the left atrium and PVs, uncertain catheter positioning within the PVs and difficulties in mapping atrial extrasystoles, which may be rare or repeatedly induce AF and require cardioversion.

METHODS

Sixty-four patients were referred for RF ablation of a focal source of AF, and 56 were identified as having AF triggers in > or =1 PV. Using ICE guidance, RF lesions were applied around the circumference of the vein near the os until there was electrical isolation.

RESULTS

Lesions were placed in 82 veins (36 right superior PV, 33 left superior PV, 9 left inferior PV, 4 right inferior PV); 24 +/- 12 lesions per vein were necessary to create electrical isolation with a fluoroscopic time of 11 +/- 4 min and a mean of 22% reduction in luminal area. After a follow-up of 13 +/- 7 months, 66% of patients remained free of AF, and another 13% responded better to medications.

CONCLUSIONS

We describe an anatomic approach to PV electrical isolation in which ICE is used to define the anatomy, guide RF ablation and monitor for acute PV changes.

Value of intracardiac ultrasound in the diagnosis of arrhythmogenic right ventricular dysplasia-cardiomyopathy

The value of imaging techniques such as transthoracic echocardiography, angiography and magnetic resonance imaging in the diagnosis of arrhythmogenic right ventricular dysplasia-cardiomyopathy (ARVD) is limited. First experiences with intracardiac ultrasound have been made during electrophysiological interventions. The ability of using intracardiac ultrasound in ARVD should be tested. In 25 patients with IFSC/ESC criteria of ARVD (nine males, 16 females) with a mean age of 54 (29-78) years suffering from sustained ventricular tachycardia in three cases, positive family history in four cases and syncopes in six cases intracardiac ultrasound was done using 6 French (Fr) 12.5 MHz catheters and the CLEAR VIEW ULTRA Intravascular System (Boston Scientific). Images were taken from the right ventricular apex, outflow tract and infundibulum. Results were compared to selective right ventricular angiography. Right ventricular (RV) angiography revealed bulges and a partial or complete loss of trabecular structure in 22 cases at the apex, in 13 cases at the infundibulum and in 14 cases at the right ventricular outflow tract. Intracardiac echocardiography was able to demonstrate sacculations in all patients at the apex, in 20 cases at the infundibulum and in 16 patients at the right ventricular outflow tract. Sacculations in all segments of the right ventricle were based on a partial or complete loss of trabecular structure. A whole of 36 segments presented with wall thinning (<3 mm) and 15 segments with normal wall structure and wall thickening of surrounding myocardium (>4 mm). In 26 segments the structure of right ventricular wall was inhomogeneous. In comparison to angiography as the 'gold standard' intracardiac ultrasound presented with additional details in 12 cases and the demonstration of angiographic misinterpretation in one case. Intracardiac ultrasound in ARVD is feasible in all cases with 6 Fr 12.5 MHz catheters and provides additional information to the angiographic phenomenon of bulges and to the aspect of tissue characterisation.

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.

Attenuation of interatrial conduction using right atrial septal catheter ablation

OBJECTIVES

We sought to characterize a method of attenuating interatrial conduction using radiofrequency ablated lesions applied to the right atrial septum.

BACKGROUND

Interatrial conduction occurs in specific zones. Recent data suggest that interatrial conduction can be important in triggering and sustaining atrial fibrillation. Therefore, a method for attenuating interatrial conduction may have therapeutic value.

METHODS

In 13 healthy pigs, interatrial conduction was evaluated before and after sequential ablation of the right atrial septum, targeting interatrial conduction zones. In six animals, zone 1 (crista terminalis and limbus) was ablated first, followed by ablation of zone 2 (fossa ovalis and coronary sinus ostium). In the other seven animals, the order of ablation was reversed. Electrophysiologic and pathologic findings were correlated.

RESULTS

After ablation of zone 1, interatrial conduction was slowed, but there was no block. After ablation of zone 2, conduction was unchanged. After ablation of both zones, complete block was observed in four animals, and there was left atrial quiescence. In the remaining nine animals, incomplete block was observed, with marked conduction slowing or block during sinus rhythm and pacing. Ablation did not adversely affect atrioventricular node conduction, nor did it facilitate sustenance of an atrial arrhythmia. Pathologic analysis revealed that complete interatrial conduction block was associated with confluent ablation of both targeted zones.

CONCLUSIONS

Catheter ablation of the right atrial septum attenuated interatrial conduction without disturbing atrioventricular conduction.

Electrogram-guided radiofrequency catheter ablation of atrial tissue comparison with thermometry-guide ablation: comparison with thermometry-guide ablation

OBJECTIVES

To characterize a new method for radiofrequency energy titration during ablation of atrial tissue based on reduction in electrogram amplitude. To compare this method with energy titration using electrode thermometry.

BACKGROUND

Complications associated with "anatomy-based" atrial endocardial radiofrequency ablation for suppression of atrial fibrillation may be due to flawed methods of energy titration.

METHODS

The effect of radiofrequency ablation on electrogram amplitude was characterized in a porcine model. A method for energy titration guided by electrogram amplitude reduction ("electrogram-guided") was developed and validated prospectively. Focal (smooth and trabeculated endocardial areas) and linear (smooth endocardial areas) ablation was performed comparing energy titration guided by amplitude reduction with electrode thermometry.

RESULTS

Amplitude reduction during radiofrequency application was not necessarily equal among unipolar and bipolar electrograms in the ablation region; specific patterns of reduction could be discerned, based on factors such as catheter-endocardial orientation. A criterion of >90 % reduction of unipolar and/or bipolar amplitude best predicted pathologic lesion success. Electrogram-guided focal and linear lesions in smooth areas were free of lesion complications such as endocardial charring, barotrauma, or damage to contiguous extraatrial structures. However, there was a significant incidence of insufficient lesion size, principally non-transmurality, probably due to undertitration of energy. Thermometry-guided focal and linear lesions in smooth areas were uniformly transmural but frequently evidenced complications, due to overtitration of energy. Electrogram-guided focal lesions in trabeculated areas could usually not be achieved, probably due to insufficient contact of the ablation electrode with adjacent pectinate muscles. Thermometry-guided focal lesions in trabeculated areas were smaller than electrogram-guided lesions and did not evidence complications.

CONCLUSIONS

Electrogram-guided lesions in smooth endocardial areas were uncomplicated but had a significant incidence of non-transmurality. Thermometry-guided lesions were uniformly transmural but were frequently complicated.

Coronary risk area measurement by intracardiac echocardiography and ultrasound contrast

The perfusion bed of an occluded coronary artery-the coronary risk area-determines infarct size. Our objective was to evaluate the combined techniques of intracardiac echocardiography (ICE) and ultrasound contrast echocardiography for real-time estimation of the coronary risk area in an experimental model. We studied 13 pigs and 2 dogs. The left anterior descending coronary was occluded by inflating coronary balloons. An ultrasound contrast agent was injected either through the dilation catheter (distal to the inflated balloon) directly into the occluded artery to opacify the "positive" risk area or into the aortic root during coronary balloon inflation to determine the nonopacified "negative" risk area. Evans blue dye was injected into the occluded artery to stain the risk area, allowing an independent measurement. The mean left anterior descending negative risk area was 26% +/- 10% of the left ventricular myocardial area, the mean positive risk area was 24% +/- 10%, and the Evans blue-stained risk area was 25% +/- 9%. By Bland-Altman analysis, the positive Optison-Evans blue mean +/- SD difference was 1.42% +/- 6.42%; the negative Optison-Evans blue mean +/- SD difference was 1.02% +/- 7.56%. Coronary risk area can be determined with intracardiac echocardiography and ultrasound contrast.

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.

Cardiac swelling associated with linear radiofrequency ablation in the atrium

OBJECTIVES

To characterize myocardial swelling in response to application of endocardial radio-frequency ablation lesions.

BACKGROUND

In individual patients, we have observed that ablation in the posterior right atrium was associated with echocardiographic evidence of atrial and contiguous right pulmonary vein wall swelling.

METHODS

1. Human Subjects: "linear" ablation was performed in the posterior right atrium in 10 subjects; a portion of the ablation lesion was contiguous to the right pulmonary vein; this area was defined as the "contiguity zone". In the contiguity zone, right atrial wall thickness and pulmonary vein lumen diameter were measured utilizing intracardiac echocardiography. Measurements were made just prior to (baseline) and immediately after ablation.2. Porcine Subjects: linear ablation was performed in the posterior right atrium of 14 pigs. In the contiguity zone, atrial wall thickness, interstitial space thickness, right pulmonary vein wall thickness and lumen diameter were measured using intracardiac echocardiography. Measurements were made at baseline, immediately after ablation, and at 1, 4, 8 or 12 weeks after ablation (followup). Post-mortem pathologic evaluation of the contiguity zone was performed.

RESULTS

1. Human Subjects: Immediately after ablation, relative to baseline right atrial wall thickness was significantly increased (9.4+/-3.1mm versus 5.4+/-1.5 mm) and right pulmonary vein lumen diameter was significantly decreased (6.2+/-2.9 mm versus 8.1+/-2.9 mm).2. Porcine Subjects: Immediately after ablation, right atrial wall thickness (4.1+/-1.2 mm), interstitial space thickness (1.9+/-1.1mm), and right pulmonary vein wall thickness (1.2+/-0.4 mm) were each significantly increased relative to baseline (1.0+/-0.3 mm, 0+/-0 mm, and 0.7+/-0.2 mm, respectively) and pulmonary vein lumen diameter was significantly decreased (5.0+/-1.4 mm versus 6.9+/-2.2 mm). Similar findings were made at the 1 week followup interval. At 4, 8 and 12 week followup intervals, thicknesses and lumen diameter were not significantly different from baseline. At post-mortem examination, direct measurements of wall thickness were significantly correlated with echocardiographic measurements. Histologic analysis demonstrated edema to be the cause of the early wall thickness and lumen diameter changes. Ablation lesions were transmural in the right atria of all animals; in some animals, lesion formation was also observed in the pulmonary vein wall.

CONCLUSIONS

Cardiac edema resulting from right atrial linear ablation results in swelling of atrial and contiguous right pulmonary vein walls, as well as the interposed extracardiac interstitial space. These changes are associated with a decrease in pulmonary vein lumen diameter. Swelling evolves rapidly and resolves within 4 weeks.

Linear ablation using an irrigated electrode electrophysiologic and histologic lesion evolution comparison with ablation utilizing a non-irrigated electrode

OBJECTIVES

To characterize the electrophysiologic and histologic sequelae of linear atrial ablation utilizing an irrigated electrode. To compare "irrigated" lesions with lesions deployed using the same electrode in a non-irrigated mode.

BACKGROUND

Previous reports of radiofrequency catheter ablation using an irrigated electrode have emphasized its favorable effect on lesion depth. We hypothesized that electrode irrigation would also benefit linear ablation of smooth atrial myocardium, a relatively superficial target.

METHODS

In healthy pigs, lesions were deployed in the right and left atria. Acutely, lesions resulting from ablation using an irrigated electrode, with radiofrequency energy titration guided by electrogram amplitude reduction, were compared to lesions using the same electrode without irrigation, with energy titration guided by electrode thermometry. Irrigated lesions were also assessed serially.

RESULTS

Acutely, irrigated lesions formed complete conduction barriers and were uncomplicated. In contrast, non-irrigated lesions formed complete conduction barriers but were frequently complicated, exhibiting endocardial charring, barotrauma, and pericardial damage. The rate and pattern of histologic evolution of irrigated lesions were uniform throughout each lesion; right and left atrial lesions healed similarly. During healing, 90 % of lesions remained complete conduction barriers and 10 % manifested single discrete conduction gaps where viable appearing myocytes bridged the lesion.

CONCLUSIONS

Complete, uncomplicated linear lesions could be reliably deployed in either atrium with an irrigated electrode. Not all lesions remained complete barriers to conduction during their histologic evolution. Lesions deployed with the same electrode in a non-irrigated mode were complete but frequently complicated.

Transcatheter closure of atrial septal defects and patent foramen ovale under intracardiac echocardiographic guidance: feasibility and comparison with transesophageal echocardiography

Transesophageal echocardiography (TEE) has been employed successfully for guiding transcatheter device closure of secundum atrial septal defect (ASD) and patent foramen ovale (PFO). However, the use of TEE for device closure requires general anesthesia. Intracardiac echocardiography (ICE) can provide similar anatomical views that might replace the use of TEE for device closure. Eleven patients (eight female/three male) with secundum ASD and PFO associated with strokes underwent attempts at transcatheter closure of their defects under sequential TEE and ICE guidance (six patients) and under ICE alone (five patients). The ages of the patients ranged from 6.6 to 74.7 yr, and their weights ranged from 23 to 124.5 kg. The sizes of the defects, as measured by TEE (six patients), ranged from 3 to 27 mm and, as measured by ICE (11 patients), from 3 to 27 mm. The balloon-stretched diameter of the ASD, as measured by TEE (six patients), ranged from 16 to 38 mm and, as measured by ICE (11 patients), from 16 to 35 mm. Both techniques correlated well for the measured two-dimensional diameter and for the balloon-stretched diameter (r = 0.97 and 0.98, respectively). Both TEE and ICE provided similar views of the defects and the various stages of device deployment. Owing to the proximity of the left atrium to the esophagus, however, the images obtained by ICE were more helpful and informative than those obtained by TEE. All patients experienced successful device placement (six patients under both TEE and ICE; five patients under ICE guidance alone); complete closure of the defects was effected in nine patients, whereas two patients had small residual shunts. There were no complications. We conclude that ICE provides unique images of the atrial communications and measurements similar to those obtained by TEE. ICE potentially could replace TEE as a guiding imaging tool for ASD and PFO device closure, thus eliminating the need for general anesthesia.

Intracardiac echocardiography: newest technology

Intracardiac echocardiography, defined as ultra-sonographic navigation and visualization within large blood-filled cavities or vessels of the cardio-vascular system, has recently undergone refinement as a clinical tool through technologic advances in transducer miniaturization. Intra-cardiac ultra-sound catheters image at lower frequencies than current conventional intravascular ultrasound catheters used for intracoronary imaging. The lower imaging frequency enables greater tissue penetration, permitting whole-heart evaluation from a right-sided catheter position. Newer devices are steerable, have variable imaging frequency (5.5 to 10 MHz), and full Doppler capability (pulsed, continuous wave, and tissue Doppler). These advances have made intracardiac high-resolution imaging as well as hemodynamic assessment possible. A historical perspective, current capabilities and limitations, and potential clinical and research applications of this new imaging technique are discussed.

Accuracy of fluoroscopic localization of the Crista terminalis documented by intracardiac echocardiography

The crista terminalis is an important anatomic target for ablation of atrial arrhythmias. We determined the accuracy of catheter placement guided by fluoroscopy alone when directed to 24 sites along the crista terminalis in 6 patients. The sites selected included the most medial superior, most lateral superior, mid lateral, and most inferolateral sites along the crista terminalis in each patient. These sites were selected because of their recognized importance in sinus node and/or atrial tachycardia ablation and the importance of avoiding caval structures when targeting the most superior and/or inferior right atrium. The position of the catheter tip was documented using a catheter based ultrasound transducer in the right atrium or vena cava. The operator was blinded to the intracardiac echocardiographic (ICE) results until reviewing the images after the procedure in each patient. The catheter tip, guided by fluoroscopy alone, was identified by ICE to be within the right atrium and within 1cm of the crista terminalis at only 10 of the 24 sites (42%). Importantly, when targeting the most superior and inferior sites along the crista terminalis, the catheter tip, guided by fluoroscopy, was noted to be adjacent to the venous junction with the right atrium but actually located in the superior or inferior vena cava at 5 of the 18 such sites. The catheter was positioned appropriately (within 1 cm of the crista and within the right atrium) guided by fluoroscopy alone when targeting 1 of the 12 sites in the first 3 patients versus 9 of 12 sites in the last 3 patients, p<0.05. In conclusion, it appears that using fluoroscopic guidance alone: 1) localization of the crista terminalis is frequently inaccurate and 2) catheter positioning in the superior/inferior vena cava is commonly noted when targeting very superior and inferior sites along the crista terminalis. A learning curve, assisted by review of ICE recordings after each procedure, appears to improve the accuracy of catheter placement by fluoroscopy alone but still does not result in uniform success. ICE appears to facilitate and ensure accurate targeting of specific anatomic sites along the crista terminalis and thus may serve as an important adjunctive imaging technique in electrophysiology.

Electroanatomic left ventricular mapping in the porcine model of healed anterior myocardial infarction. Correlation with intracardiac echocardiography and pathological analysis

BACKGROUND

Catheter ablation for ventricular tachycardia in healed infarction is limited to patients with inducible, tolerated arrhythmias. Strategies that would allow mapping during sinus rhythm might obviate this limitation.

METHODS AND RESULTS

Two sets of experiments were performed in adult pigs to refine a new technique for left ventricular mapping. First, detailed endocardial maps were done in 5 normal pigs and 7 pigs 6 to 10 weeks after left anterior descending coronary artery infarction to characterize electrograms in normal and infarcted tissue by electroanatomic mapping (CARTO, Biosense). Electrogram recording sites were verified by intracardiac echo (ICE, 9 MHz) and grouped by location: infarct (area of akinesis by ICE), border (0.5-cm perimeter of akinetic area), and remote. Compared with remote sites, electrograms from infarct sites had smaller amplitudes (1.2+/-0.5 versus 5.1+/-2.1 mV, P<0.001), longer durations (74.2+/-26.3 versus 36.3+/-6.4 ms, P<0.001), and more frequent notched or late components. Border zone electrograms were intermediate in amplitude and duration. Second, infarct characterization by electroanatomic mapping was compared with pathological (exclusion of triphenyltetrazolium chloride staining) and ICE measurements. Infarct size by pathology correlated with the area defined by contiguous electrograms with amplitude </=1 mV (r=0.98, P=0.0001). Infarct size by ICE imaging correlated with the area defined by contiguous electrograms with amplitude </=2 mV (r=0.95, P=0.0016).

CONCLUSIONS

Electroanatomic mapping during sinus rhythm allows accurate 3D characterization of infarct architecture and defines the relationship of electrophysiological and anatomic abnormalities. This technique may prove useful in devising anatomically based strategies for ablation of ventricular tachycardia.

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.

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.