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Kulhanek, Jan; Sorrell, Vincent Leigh
East Carolina University, Greenville, NC, USA
Background: The significance of functional or fixed barriers in the genesis and treatment of atrial tachyarrhythmias has been recognized both in animal models and in humans.
Objectives: We tested the ability of three-dimensional echocardiography (3DE) to visualize key intracardiac structures important for mapping and catheter ablation of supraventricular tachyarrhytmias.
Methods: Transesophageal echocardiography was used in conjunction with the computerized setup to control rotation of the multiplane probe in three-degree increments from 0 to 180 degrees. Off-line image post-processing was then used to generate shaded-gray three-dimensional images.
Results: The following intracardiac structures were clearly visualized: pulmonary vein ostium (pv) and section, tricuspid annulus (TA), triangle of Koch (TK), crista terminals (CT) and ostia of both caval veins (SVC, IVC), see (LA - left atrium, VS - interventricular septum, TV - tricuspid valve, TT - tendon of Todaro, AR - aortic root, HV - Hepatic vein, RAW - right atrial wall)
currently used views of two-dimensional intracardiac echocardiography can be
dramatically improved with three-dimensional technology. Three-dimensional reconstruction
may reduce catheter artifact, making imaging potentially clearer in the setting
of multiple intracardiac catheters. The improved visualization of crista terminals
may help in attempts to modify or ablate the sinus node and map automatic atrial
tachycardias. Better views of the atrial floor could help assure the continuity
of linear ablation of atrial flutter isthmus.
Conclusion: Three-dimensional echocardiography image reconstruction, using transesophageal echocardiography, provides clear anatomic views of structures inside the human atria, useful for guiding catheter ablation of supraventricular arrhythmia, including crista terminals, triangle of Koch and ostia of the pulmonary veins.
The significance of functional or fixed barriers in the genesis and treatment of atrial tachyarrhythmias has been recognized both in animal models  and in humans . Activation and entrainment mapping techniques are used to localize regions of myocardium critical to the maintenance of reentrant circuits . However, because current imaging modalities, such as fluoroscopy, that are used to guide catheter placement do not allow direct visualization of anatomic structures, such mapping techniques are unable to directly relate functional properties of the circuit to specific anatomic features in the intact human heart. Other imaging methods are needed to improve orientation of the operator within the cardiac cavity.
We tested the ability of three-dimensional echocardiography to visualize key intracardiac structures important for mapping and catheter ablation of supraventricular tachyarrhytmias. We hypothesized that three-dimensional echocardiography (3DE) will provide clear views of the superior and inferior venae cavae, crista terminalis and its caval juncture, fossa ovalis, coronary sinus, tricuspid annulus, tendon of Todaro and triangle of Koch.
Three-dimensional echocardiography (TEE). Multiplane TEE was used in the standard manner using a Hewlett-Packard (Andover, MA, USA) Sonos 5500 ultrasound machine and a 7.5-MHz probe. For 3-D reconstruction, the multiplane probe was manipulated to bring the area of interest as close to the middle of the sector scan as possible to ensure that the structures to be examined did not disappear from view as the ultrasonic beam was rotated from 0 degrees to 180 degrees. A computerized setup (TomTec Echo-Scan [Chicago, Ill]) was used to control the rotation of the multiplane probe, which was set in 3-degree increments. Based on the patient's heart rate, a gating
window of 120 msec or less was set using the RR intervals of the ECG. Sixty cardiac cycles were acquired and stored in the computer as the probe was rotated in a controlled manner by the computer from 0 to 180 degrees. The time taken for a complete acquisition varied from 1 to 3 minutes depending upon heart rate and rhythm. The dataset was then processed off-line into a three-dimensional image.
The attempted two-dimensional (2D) acquisitions were successfully achieved and subsequent 3DE reconstructions were performed without technical difficulties. All of the target intracardiac structures were reliably visualized in a shaded-gray color display system. The anatomic structures were seen in multiple custom defined view angles, with clear 3D prospective to other anatomy. The following intracardiac structures were visualized: tricuspid annulus, triangle of Koch, crista terminalis and ostia of both caval veins pulmonary vein ostium and section.
|Figure 1: Demonstrates antero-posterior view of the right atrial floor and the base of postero-lateral wall. The view provides localization of most of the structures of interest for electrophysiologists, including tricuspid annulus, eustachian ridge and triangle of Koch. This patient had an elevated right atrial pressure and a dilated hepatic vein is well seen. CT - crista terminalis, HV - hepatic vein, IVC - inferior vena cava, LA - left atrium, TA- tricuspid valve annulus, TK - triangle of Koch, VS - ventricular septum|
|Figure 2: Shows a view of the inferior vena cava ostium and the adjacent floor of the right atrium. This particular angle visualizes the entire length of the area where the line of block is created during ablation of the typical atrial flutter. Visible is triangle Koch, delineated by tricuspid annulus, and tendon of Todaro. IAS - intraatrial septum, IVC - inferior vena cava, TA - tricuspid annulus.|
|Figure 3: Infero-superior view into the ostium of superior venae cavae, demonstrating the superior aspect of crista terminalis. Radiofrequency ablation in this are is performed resulting in modification of the sinus node function. AR - aortic root, CT - crista terminalis, RAW - right atrial free wall, SVC - superior vena cava.|
Figure 4: Antero-lateral wall of right atrium. Crista terminalis is visible near the ostium of the superior vena cava. CT - crista terminalis, HV - hepatic vein.
|Figure 5: Enface view of the left upper pulmonary vein ostium into the left atrial cavity and it's relation to the left atrial appendage. This view is particularly useful for electrophysiologist performing a circumferential ablation line around the ostium the pulmonary vein for treatment of atrial fibrillation. LAA - Left atrial appendage. Pv - ostium of the left upper pulmonary vein|
|Figure 6: View of the intraatrial septum demonstrating
ostium of the coronary sinus (CS), fossa ovalis (FO) and tricuspid valve
annulus (TVA). Clear visualization of intraatrial septum is useful during
transseptal catheterization of the left atrium and also during mapping
and ablation of arrhythmia originating from and around the coronary sinus.
The 2D data post-processing into a three-dimensional image required approximately additional five minutes after image acquisition.
Crista terminalis has been previously implicated as a barrier in animal models of atrial flutter.  Olgin et al. found that crista terminalis was the posterolateral boundary in human flutter as well.  Intracardiac echocardiography (ICE) appears to facilitate and ensure accurate targeting of specific anatomic sites along the crista terminalis [6,7,8].
Three-dimensional echocardiography re-construction has been used to perform volumetric measurements of left and right ventricular cavity for ejection fraction and myocardial mass evaluation in stress testing, better definition of valvular disease, atrial septal defect. Cavity volume assessment by three-dimensional system mounted on a transesophageal echocardiographic probe was found to be comparable to magnetic resonance imaging. 
This study demonstrated clear detailed views of intraatrial anatomy and visualized key intracardiac structures used by electro-physiologist to guide catheter mapping and ablation of supraventricular arrhythmias. The currently used views of two-dimensional intracardiac echocardiography can be dramatically improved with three-dimensional technology.  Three-dimensional re-construction may reduce catheter artifact, making imaging potentially clearer in the setting of multiple intracardiac catheters. The improved visualization of crista terminalis may help in attempts to modify or ablate the sinus node and map automatic atrial tachycardias. Better views of the atrial floor could help assure the continuity of linear ablation of atrial flutter isthmus.
The limitation of this technique is the fact that the process requires up to 10 minutes from the beginning of image acquisition to final reconstruction display. Most of the additional time is consumed by off-line post-processing on another terminal. The possible advantage is the fact that there is no need for an additional catheter placed in right atrium.
Despite the limitations we have demonstrated that this technique is capable of unique rapid imaging of important atrial structures.
Future systems, currently under development will provide real-time 3D image postprocessing while image acquisition will be available from all three modalities (transthoracic, transesophageal and intracardiac).
We have demonstrated the ability of the three-dimensional echocardiographic image reconstruction, using transesophageal echo-cardiography, to provide clear anatomic views of important structures inside the left and right atrium, including crista terminalis, eustachian ridge, tricuspid annulus, triangle of Koch and ostium of a pulmonary vein.
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