Intracardiac Echocardiography
Introduction
Intracardiac echocardiography (ICE) provides an invaluable tool during invasive electrophysiologic procedures by providing an important link between anatomy and electrophysiology, particularly when integrated with an electro-anatomic map. It serves several functions including 1) identifying critical structures involved in arrhythmogenesis, 2) visualizing the fossa ovalis for transeptal access, and 3) monitoring radiofrequency lesions and ablation complications (e.g., pericardial effusion, thrombus formation).
The purpose of this chapter is to:
Provide an understanding of different ICE views relative to transducer position and beam orientation within the heart.
Provide techniques to image important structures involved in arrhythmogenesis.
TYPES OF ICE CATHETERS
Two basic types of ICE catheters are 1) radial ICE and 2) phased-array ICE.1,2,3,4,5 Radial ICE (9-12 MHz) uses a single, rotating (1800 rpm) crystal element mounted to the end of a nonsteerable catheter providing a 360-degree field of view perpendicular to the long axis of the shaft. It lacks Doppler capabilities and far-field resolution (penetration depth of <5 cm), limiting visualization of left heart structures from the right atrium (RA). Phased-array ICE (5.5-10 MHz) uses a 64-element transducer mounted longitudinally to a steerable (4-way articulation) catheter, providing a 90-degree ultrasound (US) sector parallel to the long axis of the shaft. It possesses Doppler capabilities and, because of its lower frequency, has greater tissue penetration (12 cm), allowing visualization of the left heart from the RA. Because of its greater capabilities for complex left heart ablations, this discussion primarily involves use of phased-array ICE with standard imaging from the right heart (RA/right ventricle [RV]), although imaging from the left atrium (LA), coronary sinus (CS), and pericardial space has also been described.2,3
ICE VIEWS
HOME VIEW
The characteristic neutral or home view provides a starting reference plane for orientation (Fig. 3-1). The ICE catheter is positioned in the mid-RA parallel to the spine with the US beam directed anteriorly toward the tricuspid valve (TV). The home view images the anterior RA, septal TV, longitudinal RV and outflow tract, aortic valve (noncoronary cusp [NCC] and right coronary cusp [RCC]), and proximal aortic root. The catheter tip during ablation of the posteroseptum (e.g., slow pathway), midseptum (e.g., accessory pathway [AP]), anteroseptum (e.g., His bundle), and cusp tachycardias (e.g., NCC atrial tachycardia [AT]) can be visualized in this view (see Figs. 8-2, 8-3, 13-6, 13-7 and 13-8, and 16-5). A posterior location of the ICE transducer in the RA with slight clockwise torque from the home view intersects the aortic valve (NCC and left coronary cusp [LCC]) and left ventricle (LV) longitudinally. Because of the apical displacement of the TV relative to the mitral valve (MV), the location where the RA and LV intersect (“atrio-ventricular [AV] septum”) can be seen (Fig. 3-2).
LEFT ATRIUM
Further clockwise torque of the ICE catheter from the home view images the structures of the LA in the following order: 1) MV/left atrial appendage (LAA)/proximal CS, 2) leftsided pulmonary veins (longitudinal view), 3) posterior LA/esophagus, and 4) right-sided pulmonary veins (cross-sectional view) (Figs. 3-3, 3-4, 3-5 and 3-6).6,7,8 The catheter for ablation of mitral annular-related tachycardias (e.g., AP) can be imaged in the MV view (see Figs. 12-2, 12-3 and 12-4 and 12-11, 12-12, 12-13, 12-14, 12-15 and 12-16). This view also images the anterior portion of the fossa ovalis for more
anterior transeptal puncture sites (e.g., cryoablation).9 Withdrawal of the ICE catheter inferiorly visualizes the CS in cross section and the catheter during ablation of CS-related tachycardias (e.g., AP, AT) (Fig. 3-7; see also Fig. 13-10).
anterior transeptal puncture sites (e.g., cryoablation).9 Withdrawal of the ICE catheter inferiorly visualizes the CS in cross section and the catheter during ablation of CS-related tachycardias (e.g., AP, AT) (Fig. 3-7; see also Fig. 13-10).
 FIGURE 3-1 Home view. The US transducer is in the mid-RA with an anterior beam rotation. |
Additional views of the LAA can be obtained from the 1) RA (posterior tilt)/anterobasal RV (level with short axis view of the aortic valve), 2) RV beneath the pulmonic valve (anterior tilt; given the close proximity between the pulmonary artery [PA] and LAA), 3) from the LA (via a transeptal sheath), and 4) from within the CS (Figs. 3-8 and 3-9).3,6 With the short axis view of the aortic valve, the Coumadin ridge between the LAA and left superior pulmonary vein (LSPV) (an important structure during LSPV isolation) is seen.
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