Applications of Intracardiac Echocardiography
- Thomas Bartel, MD
- Silvana Müller, MD
- Angelo Biviano, MD
- Rebecca T. Hahn, MD
- Silvana Müller, MD
Current percutaneous catheter–based procedures used to treat structural heart disease and cardiac arrhythmias require peri-interventional echocardiographic monitoring and guidance to be safe, expedient, and well tolerated by patients. During the last two decades, transesophageal echocardiography (TEE), including real-time three-dimensional (3D) imaging, has been complemented and in part replaced by two-dimensional (2D) and recently by 3D intracardiac echocardiography (ICE) as the standard approach to guide noncoronary cardiac interventions. ICE takes full advantage of the capabilities of echocardiography for guiding device closure of interatrial communications (IACs) and electrophysiologic ablation procedures. It represents an alternative guiding tool for other interventional procedures and can also be recommended in pediatric patients. ICE is exclusively indicated for procedural guidance. In contrast to TEE, ICE does not require general anesthesia but is highly compatible with monitored anesthesia care and even with local anesthesia alone. ICE does not interfere with fluoroscopic viewing and provides high image resolution. It represents a valuable alternative to 2D and 3D TEE in transcatheter aortic valve replacement (TAVR), rare left-to-right shunt closure procedures, and intra-aortic interventions. In MitraClip implantation, left atrial appendage (LAA) occlusion, and closure of paravalvular leaks, ICE remains an investigational imaging tool.
Device closure of interatrial communications
IACs are defined as patent foramen ovale (PFO), atrial septal defect (ASD), or multiply fenestrated interatrial septum. A PFO is a remnant of the fetal foramen ovale and represents a flap valve mechanism intermittently opening a small channel between the atria. It is typically associated with an intermittent right-to-left shunt but only exceptionally with a permanent left-to-right shunt; it is highly treatable with device closure. In contrast, ASDs are permanent openings characterized by left-to-right shunting shortly interrupted by right-to-left shunting, depending on the breathing cycle. Different types of ASDs are distinguished by whether they involve particular structures, which are the septum primum (ostium primum ASD), the septum secundum (ostium secundum ASD), the sinus venosus (sinus venosus ASD), or the coronary sinus (coronary sinus ASD). The ostium secundum ASD is the most common type and is the only one that can be treated with transcatheter device closure.
ICE provides adequate imaging of the IAC and the surrounding structures, particularly the inferior rim of ASDs. The method’s efficacy has been repeatedly shown, and ICE is considered superior to 2D TEE. Two transatrial standard views, the longitudinal view complemented by the perpendicular short-axis view, are recommended ( Fig. 15.1 ). These permit unlimited echocardiographic viewing in fully conscious patients. Thereby ICE is used to confirm adequate wire position, assist with balloon sizing, place a long sheath for device delivery, release the left-sided disc in the left atrium (LA), and release the right-sided disc in the right atrium (RA). The “wiggle maneuver ” should be monitored in both standard views. In the short-axis view, compression of the aortic bulb by the occluder device can be ruled out. Disconnection of the device from the delivery cable should be monitored by ICE as well. When released, the device will fully line up with the interatrial septum, reaching its definitive orientation. The final position of the device should again be visualized in both standard views to ascertain that the discs enclose the septal rims completely ( Fig. 15.2 ).
ICE provides uninterrupted monitoring and is therefore expected to increase safety, particularly in device closure of complex PFO and ASD, where significant complications are known to occur. This approach seems to be beneficial in transcatheter closure of ASDs in patients with impaired left ventricular (LV) function and in closure of multiple defects requiring either simultaneous or staged deployment of closure devices. Compared with TEE, ICE is associated with much less procedural stress to the patient, and fluoroscopic and procedural times can be shortened. Since many patients with IAC are of reproductive age or younger, reduction of radiation exposure represents an important advantage. Closure of ASD and complex IAC may especially be facilitated by 3D ICE. Tracking thin wires, catheters, and devices is generally easier with 3D than with 2D ICE.
Electrophysiologic ablation procedures
ICE has become established to meet the growing need for real-time monitoring of patient anatomy and catheter location, and surveillance of intraprocedural complications, such as pericardial effusion or thrombus formation. ICE catheters are usually placed in the right side of the heart and use rotating circumferential transducers or phased array transducers. The latter allow for more detailed imaging of left-sided cardiac structures. ICE images can be collected from multiple planes and then overlaid onto existing electroanatomic maps (which may include regions where real-time data were not or could not be collected). ICE images can also be overlaid onto existing computed tomography or magnetic resonance scans. Thus, ICE can be used concomitantly with other imaging modalities to enhance the spatial depiction of cardiac anatomy and catheter positions.
Imaging requirements are procedure specific. For ablation of atrial fibrillation, imaging is used to confirm catheter placement, to perform transseptal puncture from the RA to the LA, and to assess for complications when navigating catheters ( Fig. 15.3 ). Relevant reference structures include the RA, fossa ovalis, LA, aorta, pulmonary veins, LAA, esophagus, and pericardial space. Structures important for the ablation of ventricular tachycardia include the mitral and aortic valves, left ventricular papillary muscles, ventricular scars and aneurysms, sinus of Valsalva, coronary ostia, and pericardial space. For patients with congenital heart disease, ICE can help assess enlarged chambers, intracardiac baffles and shunts, and areas of scarring or severe hypertrophy.
Transcatheter aortic valve replacement
Transcatheter aortic valve replacement (TAVR) is considered an alternative to surgery for high-risk or inoperable patients with severe, symptomatic aortic stenosis. TEE has been established as an important supplement to fluoroscopic imaging for positioning, and as the primary imaging tool for the comprehensive assessment of complications following valve implantation. Because intraprocedural TEE is frequently performed with general anesthesia, it is not always an ideal tool for TAVR in this patient population. Some centers have advocated a minimalist approach to this procedure, with no echocardiographic guidance. However, current guidelines do not address this approach but continue to advocate echocardiographic support for interventional procedures. ICE may thus be a more acceptable alternative during procedures in which TEE is not performed. The main advantage of ICE imaging is its suitability for monitoring with ultralow doses of contrast agent, an approach helpful for preserving renal function and for lowering the occurrence of acute kidney injury.
Longitudinal views from the cavoatrial junction are the primary ICE views ( Fig. 15.4 ), continuously displaying the ascending aorta, native aortic valve, and aortic valve prosthesis. After valve deployment, short-axis views are obtained to rule out annulus rupture and to check for paravalvular leaks. The severity of any regurgitation can be easily graded by a multiparametric approach. ICE can be consistently used to (1) assist with guide wire passage through the native valve, (2) position the balloon for predilatation and observe balloon inflation, (3) position the catheter system that is carrying the valve, (4) observe valve deployment and verify adequate prosthetic valve function, (5) rule out pericardial hemorrhage, and (6) ultimately check LV function from the transventricular view ( Fig. 15.5 ). The ICE guiding strategy for TAVR is safe, effective, and compatible with monitored anesthesia care. The first clinical impressions on using 3D ICE for TAVR guidance are promising. In particular, this technique appears to facilitate precisefinal positioning of the valve-carrying balloon immediately before deployment of the valve prosthesis (see Fig. 15.5 ). Initial experience suggests that 3D capabilities can augment the advantages of ICE in TAVR ( Fig. 15.6 ).
Rare and investigational applications
Successful use of ICE guidance for device closure of ventricular septal defects (VSDs) has been described. Complemented by a transatrial short-axis view, a modified home view provides the best visualization of the perimembranous portion of the interventricular septum. All procedural steps should be simultaneously monitored by fluoroscopy and ICE ( Fig. 15.7 ), which is more appropriately called intraluminal phased-array imaging (IPAI), if used from inside a vessel. Guidance of the interventional closure of a patent ductus arteriosus (PDA) represents another beneficial application. The ICE catheter is positioned in the descending aorta and the probe aimed at the infundibulum of the PDA, depicting continuous shunt flow. This probe position also permits unobstructed monitoring of all procedural steps ( Fig. 15.8 ). The advantages of ICE demonstrated for device closure of IACs, including lower radiation exposure and shorter fluoroscopy times, can be potentially transferred to device closure of perimembranous VSDs and PDA.
