PART II - INTRACARDIAC ECHOCARDIOGRAPHY
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Updated on June 22, 2020
PART II

Intracardiac echocardiography

Anna E. Bortnick, Rim Halaby, Frank E. Silvestry, Howard C. Herrmann

Summary

Intracardiac echocardiography (ICE) is used to guide many advanced interventions on structural heart disease, with the goal of decreasing lengthy procedure times, minimising radiation exposure, increasing safety, and facilitating procedural success. Mechanical (rotational or radial) and phased array transducers are the two available imaging systems, and the latter generates images that are similar to transoesophageal echocardiography (TOE). A series of standardised views helps the operator to assess the target anatomy and surrounding cardiac structures, rule out important contraindications to the percutaneous approach not appreciated in prior studies, and deliver therapeutic devices. Closure of interatrial and interventricular septal defects, transseptal puncture, rhythm ablation, and balloon mitral valvuloplasty are some of the more common ICE-guided procedures which are reviewed in this chapter.

Introduction

Percutaneous interventional repair of structural heart disease in the cardiac catheterisation laboratory is becoming more widespread as an alternative to open heart surgery. Proper anatomic assessment is crucial during procedures to confirm the eligibility of the patient for an interventional procedure, guide catheter and device placement, and quickly diagnose any complications. ICE and TOE are two imaging modalities used in the catheterisation laboratory to perform these objectives [1]. Some of the advantages of ICE over TOE include: the ability to perform imaging without sedation, anaesthesia or intubating the oesophagus, increased patient comfort, direct visualisation of structures that are not well seen on TOE, decreased fluoroscopy time, plus potential cost savings as less personnel are needed and probes can be re-sterilised for multiple uses [2, 3, 4, 5]. The interventionist can independently perform ICE if the practitioner is familiar with the technology, while TOE necessitates an echocardiographer be present at the bedside. In the electrophysiology laboratory, ICE is a main imaging modality for transseptal puncture, pulmonary vein isolation for atrial fibrillation [6], and other rhythm ablation [7, 8, 9, 10, 11]. ICE results in decreased complications [12, 13, 14] and possibly less radiation exposure for complex cases [15]. It will continue to be an attractive imaging modality to the invasive cardiologist with the advent of three-dimensional (3D) ICE imaging. This chapter reviews the fundamentals of ICE, key anatomic views, and specific applications of ICE imaging for interventions on the interatrial and interventricular septae, transseptal puncture, and for valvular heart disease.

Intracardiac echocardiography systems

Two types of intracardiac ultrasound catheters are currently in use, the mechanical (rotational or radial) transducer and the phased array system [16]. Catheters come wrapped in sterile for individual, once only use and connect to portable or built-in imaging systems. Mechanical transducers are generally less expensive than the phased array transducers. Mechanical transducers image perpendicular to the distal tip of the ultrasound catheter, generating cross-sectional views similar to those generated by intravascular ultrasound (IVUS) catheters, with the radiopaque catheter tip in the center of a 360° field of view. The Ultra ICE™ Catheter (Boston Scientific, Natick, MA, USA) [17] is a 9 French (Fr), 110 centimetre (cm) mechanical transducer, which consists of a rotational drive shaft powering a 9 megahertz (MHz) transducer ( Figure 1 ). The transducer is housed in a 1 cm long sheath and sterile water is introduced into the catheter to optimise imaging. The piezoelectric crystal rotates through the sector at a high sweep speed to generate the image. The catheter is inserted over-the-wire through precurved Convoy™ introducer sheaths (Boston Scientific, Natick, MA, USA) that are bent at 15° to 140° curves. One sheath may be exchanged for another if a different view is needed. The catheter can be used with a freestanding, portable display cart or the fully integrated iLab™ Ultrasound Imaging System (Boston Scientific, Natick, MA, USA), which displays images on a screen above the table. Mechanical transducers have high resolution in the near-field, are good for basic views, and are conveniently compatible with equipment used for IVUS, but do not offer spectral or colour Doppler imaging, have a limited imaging depth, and are stiffer due to the rotational core.

Phased array systems have broader capabilities than mechanical transducers, generating the familiar, two-dimensional (2D) wedge-shaped, longitudinal axis image seen on transthoracic or TOE [16]. The imaging sector is 90° to the tip of the transducer. They function at a low or high frequency (5 to 10 MHz). At lower frequencies, they achieve a greater depth of penetration to image far-field structures. At higher frequencies, they enhance spatial resolution of near-field structures. Phased array catheters can be steered with one hand. The system is a miniaturised form of the traditional, hand-held ultrasound probe. A set of 64 piezoelectric crystals is electrically stimulated in a sequential manner to produce multiple ultrasound scan lines. The waves reflect off intracardiac structures, are received by the transducer, and then are transformed electronically into an imaging sector. The phased array systems perform M-mode, pulse wave, continuous wave, and colour Doppler, especially useful in assessing the closure of intracardiac shunts. The Acuson AcuNav™ Diagnostic Ultrasound Catheter (Siemens, Mountain View, CA, USA) [18] comes in 8 Fr, 110 cm and 10 Fr, 90 cm sizes ( Figure 2 ). They attach to various consoles via the reusable SwiftLink™ connector (Siemens, Mountain View, CA, USA). The AcuNav™ (Siemens, Mountain View, CA, USA) can be connected to the Acuson Sequoia™ (Siemens, Mountain View, CA, US), a traditional 2D echocardiography system for use with a transthoracic or transoesophageal probe, economical for multipurpose use. The AcuNav™ also connects to the Aspen™ console, CV70™ system, and the smaller, portable Cypress™ ultrasound machine (all Siemens, Mountain View, CA, USA). The ViewFlex™ PLUS [19] and ViewFlex™ Xtra ICE Catheters [20] (EP Medsystems, St. Jude Medical, St. Paul, MN, USA) are 9 Fr catheter designed for use with the ViewMate™ II and ViewMate™ Z (EP Medsytems, St. Jude Medical, St. Paul, MN, USA) imaging consoles ( Figure 3 ). Both AcuNav™ and ViewFlex™ catheters can be axially rotated and the tips deflected anteriorly/ posteriorly, up to 120° for the ViewFlex™ and 160° for the AcuNav™. The ViewFlex™ PLUS lacks rightward and leftward steering which the AcuNav™ and ViewFlex™ Xtra afford.

3D ICE has been undergoing major technological advancements, and its role to guide structural heart interventions and electrophysiology procedures has been expanding. 3D ICE was initially introduced through the integration of 2D ICE imaging with electroanatomic mapping in electrophysiology laboratories. The Biosense Webster Soundstar™ ultrasound catheter (Biosense Webster, Johnson & Johnson, Diamond Bar, CA, USA) is used in conjunction with Carto systems to create a 3D cartoon map for ablation [21]. Newer catheters have been tested ex vivo and some have been used in limited animal experiments. The HockeyStick is a 9 Fr, 7 to 12 MHz side looking catheter (similar to the AcuNav™), that connects to the NavX electroanatomical navigation system to pick up electrocardiogram signals and monitor catheter position in 3D. The MicroLinear catheter is 9 Fr, 14 MHz and is forward-looking, producing an imaging sector directly in front of the catheter tip. It has a metal radiofrequency ablation tip built into the ICE catheter, with simultaneous diagnostic and therapeutic capabilities. Capacitive micromachined ultrasonic transducer (cMUT) devices have an additional 5 Fr lumen large enough to pass ablation devices through them [22, 23].

The AcuNavTM V ultrasound catheter (Siemens, Mountain View, CA, USA) is the first ICE probe with 3D imaging functionality [24] . The utility of 3D AcuNavTM V catheter was investigated in atrial fibrillation ablation [25], percutaneous mitral valve repair [26], and transaortic valve replacement [27]; however, these experiences are limited to case reports and small single-center studies. More recently, Siemens introduced the AcuNav™ Volume ICE catheter (Siemens, Mountain View, CA, USA) [28], which allows 4-dimensional (4D) imaging with a larger field of view of 90°x50° in comparison to 90°x24° for AcuNavTM V. 4D imaging consists of real-time volume 3D with fast volume rates, “time” being the fourth dimension. The AcuNav™ Volume catheter has a diameter of 12.5 Fr (10F for AcuNavTM V) and a usable length of 90 cm (same as AcuNav™ V). AcuNav™ Volume ICE is attached via a SwiftlinkTM cable to the ACUSON SC2000TM ultrasound imaging platform. Both AcuNav TM V and AcuNav TM Volume ICE are FDA approved. Nuvera Medical launched the 4D NuveraTM ICE Catheter (Nuvera Medical Inc., Silicon Valley, CA, USA), a 10 F catheter with an even wider field of view of 90°x90° [29]. The hope is that these newer 3D and 4D catheters will decrease lengthy procedure times, minimise radiation exposure, and facilitate transcatheter delivery of therapy or devices. The high unit cost of current non-reusable ICE devices has limited the uptake of this technology. Certified resterilisation and re-use lower the cost but are only offered in some countries.

FOCUS BOX 1Comparison of the two types of intracardiac ultrasound systems

Standard views

Anatomic assessment with ICE is important for planning the interventional approach and may reveal anomalies not appreciated by TOE, for example, multiple fenestrations of an atrial septal defect, deficient rim for secure deployment of a closure device, or anomalous pulmonary veins. Standard views for mechanical and phased array transducers will be reviewed briefly. Interventional procedures in this text will be described based on imaging with the AcuNav™ catheter, as this transducer is easily steerable, performs linear and Doppler measurements, plus colour Doppler flow.

The starting views for mechanical transducers, such as the Ultra ICE™ catheter, consist of four transverse (cross-sectional) images and one longitudinal (or “four-chamber”) section, for basic imaging from the right atrium [30, 31]. The images are displayed with the same right-left and anterior-posterior orientation as computed tomography (CT) or magnetic resonance imaging (MRI) slices, with left-sided structures oriented on the right side of the image. To begin, a 55° Convoy™ sheath is introduced over a guide wire. The catheter is advanced through the sheath into the superior vena cava (SVC) and the sheath is then slowly pulled back into the right atrium and then into the inferior vena cava (IVC). As the catheter is pulled back through the right atrium, one is able to obtain the four transverse views; 1) transverse great vessels view, 2) SVC- right atrium junction view, 3) aortic valve view, 4) IVC- right atrium junction (cavotricuspid isthmus) view. A four-chamber view is created by repositioning the catheter through the curved sheath in the mid-right atrium, rotating it posteriorly and to the left to bring the interatrial septum into view. Further clockwise rotation yields a five-chamber view.

The starting or “home” view for the phased array system, with standard femoral venous access, begins at the level of the mid-right atrium ( Figure 4 ). The catheter is inserted in a neutral position through a sheath in the right or left femoral vein. It is advanced into the IVC and positioned in the mid-right atrium. From neutral, it is rotated clockwise in 15° increments to image more posterior structures. At 15° to 30° (the “home view”) it is possible to visualise the mid-right atrium, tricuspid valve, right ventricle, and short-axis view of the aortic valve. In this view, the non-coronary cusp of the aortic valve is the closest to the transducer. Atrial septal aneurysms may bow into the right atrium and be seen on this image. This view allows parallel, colour Doppler interrogation of the tricuspid valve.

Clockwise rotation to 30° to 40° (“right ventricular outflow tract (RVOT) view”) brings the RVOT and pulmonic valve into view ( Figure 5 ). Continued clockwise rotation to 45° (“left ventricular outflow tract (LVOT) view”), brings the left ventricle into view in the oblique long axis ( Figure 6 ). The anterior and inferior walls of the left ventricle are seen, in addition to the LVOT, and long-axis view of the aortic valve. This view is best for Doppler interrogation of the aortic valve. Advancing the catheter higher into the right atrium and clockwise rotating to 60° to 70° (“left atrial appendage (LAA) view” or “lower interatrial septal view”) allows the catheter to look down on the left atrium ( Figure 7 ). This view is best for imaging the lower interatrial septum, left atrium, left atrial appendage, and mitral valve. Colour Doppler interrogation of the mitral valve is best in this view because the beam is parallel to flow, and thrombus or smoke in the left atrium can be evaluated. A four-chamber view can be obtained from this position by tilting the catheter to the right.

Clockwise rotation to 70° to 80° optimises the view of the left atrial appendage (“left atrial appendage view”) and lower rim of the interatrial septum. Slowly advancing the catheter brings the fossa ovalis into view ( Figure 8 ). Clockwise rotation to 90° to 100° (“left pulmonary veins view”) reveals a long-axis view of the left inferior and left superior pulmonary veins which appear as branches (like ‘’trouser legs’’) off the left atrium ( Figure 9 ). The interatrial septum is seen at the top of the image. This view is classically used for pulmonary vein isolation in the treatment of atrial fibrillation. Posterior and rightward deflection from this position constitutes the “interatrial septal long-axis view” ( Figure 10 ). The septum secundum and fossa ovalis are well seen in this position, which is ideal for atrial septal defect (ASD) and patent foramen ovale (PFO) closure. A small amount of clockwise rotation results in the “aortic” or “septal short-axis view”, imaging the aortic valve in short axis and the upper septum, comparable to the short-axis view of the septum and aortic valve seen on TOE ( Figure 11 ). Continued clockwise rotation to 150° to 180° (“right pulmonary veins view”), reveals a short-axis view of the right inferior and right superior pulmonary veins and right pulmonary artery ( Figure 13 ). The right atrial appendage, crista terminalis, and a portion of the right atrium are seen with slight clockwise rotation, an important view for atrial flutter ablation. The SVC is well seen by removing the posterior deflection and resetting the catheter to neutral, then clockwise rotating to 210° to 240° (“superior vena cava view”). This view is analogous to the bicaval view on TOE ( Figure 12 ). The SVC-right atrial junction is best imaged by slightly advancing the catheter. The interatrial septum is also well seen in its entirety. Advancing the catheter into the superior vena cava reveals the aortic arch, plus the bifurcation of the brachiocephalic, left common carotid, and left subclavian arteries, a view that is unobtainable with TOE.

Additional views of the left atrium, left atrial appendage, and pulmonary veins can be obtained by crossing interatrial septal defects into the left atrium (under systemic anticoagulation), or by entering the right ventricle and advancing into the pulmonary artery. Non-traditional views from the RVOT and the pulmonary arteries allow better evaluation of the left atrial appendage and can be useful to guide left atrial appendage closure procedures. The ultrasound catheter may even be introduced arterially to guide abdominal aortic stent graft procedures. These non-standard views confer additional risks, namely, access site bleeding, thrombotic embolism and perforation.

Applications of intracardiac echocardiography

ATRIAL SEPTAL DEFECT AND PATENT FORAMEN OVALE CLOSURE

Percutaneous closure of ASD or PFO is a common indication for ICE. There are four general types of ASD, but only the ostium secundum ASD is amenable to percutaneous closure [32]. PFO present in 20% of the population, is a tunnel-like defect in which non-fused septum primum and secundum alternatingly open and close due to changes in atrial pressures. The presence of PFO is associated with a higher risk for stroke [33] , and several clinical trials demonstrated that PFO closure in selected patients with cryptogenic stroke reduced recurrent ischemic stroke [34, 35, 36]. PFO have been also implicated in migraine headache, although this association has been called into question [37, 38, 39, 40, 41] and there are no clear European or ACC/AHA guidelines on PFO closure for the management of migraine.

The Amplatzer™ PFO Occluder (AGA Medical Corp., Plymouth MN, USA now merged with St. Jude, St. Paul, MN) and Gore™ Cardioform Septal Occluder (W.L. Gore & Associates, Newark, DE, USA) are FDA approved for PFO closure. Gore ™ Helex (W.L. Gore & Associates, Newark, DE, USA), CardioSEAL™ and STARFlex™ umbrella closure devices (NMT Medical Inc., Boston, MA, USA), as well as a bioabsorbable version of the STARFlex™ device, the Biostar™, were implanted for PFO closure but are no longer manufactured.

The technical aspects of ASD and PFO closure are similar. The interventional approach is well tolerated with few complications and has been used since the 1970’s when the technique was first described in a 17 year-old girl [42]. ASD closure devices have gone through several generations of design; currently, the Amplatzer™ Septal Occluder (AGA Medical Corp., Plymouth, MN, USA) and the Gore™ Cardioform ASD Occluder (W.L. Gore & Associates, Newark, DE, USA) are FDA approved for ASD closure. Additional devices are available in Europe. The Gore™ Helex device (W.L. Gore & Associates, Newark, DE, USA), the CardioSEAL™ double umbrella device and the STARFlex™ (NMT Medical Inc., Boston, MA, USA) are no longer being manufactured. Amplatzer™ and Gore ™ Cardioform deployment will be reviewed here.

The Amplatzer ™ Septal Occluder consists of two Nitinol self-expanding discs with polyester insert to promote endothelialisation connected by a central waist. The device is housed in a catheter, which is placed across the atrial septal defect. The left atrial disc is deployed with a pushing motion, and then pulled up against the septum. The right atrium disc is deployed in a similar fashion and lastly, the catheter is unscrewed from the occluder. The Gore ™ Cardioform device is made of an expanded polytetrafluoroethylene (ePTFE ) membrane stretched in a Nitinol wire frame. The device is deployed in a “push, pull manner” in which the operator forms the left atrial, then right atrial discs, and then a “lock loop” pins the discs together. Both the Amplatzer™ and Gore ™ Cardioform devices are retrievable post-placement.

ICE imaging for ASD closure involves standard views to evaluate the presence of one or multiple fenestrations, rule out anomalous pulmonary veins, quantify the amount of septal rim for proper device gripping, balloon size the defect, and assess colour Doppler flow. With PFO closure, injection of agitated saline via a femoral or peripheral vein is used to determine the extent of shunting. ICE imaging may exclude a patient from a percutaneous approach if the ASD anatomy is unfavourable or if there are associated defects that need surgical repair. The septal rim must be assessed in all 6 quadrants: superior, anterosuperior, anteroinferior, inferior, posteroinferior, and posterosuperior. Five millimetres of septal tissue in all quadrants is considered adequate. The Gore ™ Cardioform device may be more conducive to ASD closure where there is deficient septal tissue bordering the aorta, as the ePTFE membrane conforms in contact with the vessel. In theory, this may be advantageous over an Amplatzer™ device because there is less Nitinol in contact with the aorta [43], but this aspect of the Gore ™ Cardioform device has not been formally studied.

ICE imaging begins in the home view at the level of the mid-right atrium with the tip of the catheter rotated clockwise to 15° to see the right atrium, tricuspid valve, right ventricle. The tip is then flexed posteriorly and locked into place. The interatrial septal long-axis view is obtained by clockwise rotating to 90° to 100° and aiming posteriorly. From this position, it is rotated clockwise to obtain the septal short-axis view. This is an ideal working view for closure. Colour Doppler or agitated saline injection should be performed in this view. Next, the catheter is advanced into the SVC to show the superior portion of the septum, then withdrawn into the IVC to show the inferior portion. Once the defect is deemed acceptable for percutaneous closure, the ICE catheter should be positioned in the septal short-axis view for passage of wires and deployment of the device ( Figure 14 ). It may be necessary to visualise more of the left atrium during the procedure by going back to the lower interatrial septal/left atrial appendage view at 60° to 70°. Lastly, colour Doppler or reinjection of agitated saline should be performed in the septal short-axis view to confirm adequate sealing.

Some operators perform ASD and PFO closure without the use of TOE or ICE, relying on fluoroscopy alone, arguing that echocardiographic imaging increases procedure time, cost, and poses risk to the patient with additional vascular access in the case of ICE or need for deeper sedation with TOE [44]. Using fluoroscopy alone, complete closure was achieved in 88% to 91% of patients at 6 months in one study, with a minimal, moderate or large residual shunts persisting in 6% to 7%, 2% to 3%, and 1% to 2% of patients, respectively [45]. Others argue that procedural success is improved with echocardiographic guidance by allowing additional device placement or repositioning at the time of the study and avoiding repeat procedures [46].

VENTRICULAR SEPTAL DEFECT CLOSURE

Like defects of the atrial septum, some defects of the ventricular septum (VSD) are amenable to percutaneous closure. There are four types of VSD; supracristal, inlet, perimembranous, and muscular [47, 48]. Supracristal defects are rare, located just under the pulmonic valve and result in lack of support for the right coronary cusp of the aortic valve, leading to concomitant aortic insufficiency. Inlet or atrioventricular (AV) canal defects are also rare, occurring at the AV annulus due to incomplete fusion of the endocardial cushions. They are often associated with mitral or tricuspid valve abnormalities (complete AV canal defect). Perimembranous defects are the most common congenital VSD, but percutaneous closure bears the risk of complete AV block. A phase I clinical trial of percutaneous closure of perimembranous VSD showed that Amplatzer™ device closure was feasible, although 3 out of 32 patients (8.6%) had serious adverse outcomes including complete AV block, tricuspid valve injury, and perihepatic bleeding [49]. Muscular defects are more common in adults and can be acquired post myocardial infarction, trauma, and post aortic valve surgery. These are most amenable to percutaneous closure. The Amplatzer™ VSD Occluder (AGA Medical, Plymouth, MN, USA) is FDA approved for VSD closure. The Post-Myocardial Infarction Amplatzer™ VSD Occluder device has a thicker connecting waist to seal larger defects and is deployed like the ASD occluder, as previously described.

ICE imaging for percutaneous VSD closure begins in the home view, as previously described, with the tip parallel to the spine and facing the tricuspid valve [49]. The short-axis view is obtained by clockwise rotating to around 100° and aiming posteriorly such that the transducer tip is laying about the tricuspid valve “looking” upwards at the LVOT. Perimembranous VSDs can be seen in home and short-axis views. Muscular VSDs are best seen in the four and five chamber views. A four chamber view is obtained by positioning the tip of the catheter in the mid-right atrium, clockwise rotating to 60° to 70°, then tilting the catheter to the right to look down on the four chambers. The left atrium, left ventricle, and interventricular septum are well seen in this view.

The next series of views are obtained from the right ventricle, exercising caution not to induce ventricular ectopy or puncture the right ventricular free wall. The catheter is advanced across the tricuspid valve in the neutral position, and then flexed rightward ( Figure 16 ). An oblique long-axis view of the left atrium, mitral valve, and left ventricle are seen with the interventricular septum at the top of the image. Flexing leftward gives a short-axis view of the left ventricle and interventricular septum ( Figure 17 ). Advancing into the right ventricular outflow tract brings the membranous septum into view ( Figure 15 ).

If there is an ASD, the ICE catheter can be guided across into the left atrium. A long-axis view of the left atrium, mitral valve, left ventricle, and aortic valve is obtained by 90° of anterior flexion such that the beam is aimed posteriorly. A short-axis view is obtained by flexing to 45°. A four-chamber view is obtained by flexing the tip to 90° such that the beam points towards the apex and the five-chamber view is obtained by pointing the tip anteriorly.

TRANSSEPTAL PUNCTURE

Transseptal puncture allows direct access into the left atrium, traditionally performed for direct left atrial haemodynamic assessment in instances where the pulmonary capillary wedge is a poor surrogate or the aortic valve cannot be crossed for simultaneous left ventricular/aortic or left ventricular/wedge pressure measurements. Today, transseptal puncture has an expanding role in the delivery of devices into the left heart for percutaneous valve repair, closure of ASDs or PFOs (in which a sheath does not easily traverse the defect), and ablation procedures. The proper position for crossing the septum is at the mid-portion of the right atrium on the anteroposterior projection and posterior/inferior to the aortic valve (marked by a pigtail catheter) in the lateral projection. Biplane fluoroscopy best defines the proper position of the needle. Accomplishing safe transseptal puncture with biplane fluoroscopy alone is challenging, especially if the septal anatomy is distorted by bulging, atrial septal aneurysms, kyphosis of the spine, or aortic root dilatation, which is why many operators have turned to TOE or ICE to guide even routine transseptal puncture [49].

There are few direct comparisons of TOE versus ICE-guided transseptal puncture, but there may be clinical scenarios in which one is favoured over the other. One small study indicated comparable results of both techniques for interatrial septal and left atrial imaging pre-cardioversion for atrial fibrillation, but ICE was slightly less sensitive than TOE for imaging the left atrial appendage [51]. This could have implications for transseptal puncture in the placement of LAA occluder devices and more studies are needed to understand the role of ICE for this application. Another clinical scenario in which TOE may be preferred is transseptal puncture for percutaneous edge-to-edge clip repair of the mitral valve. This procedure is frequently done under 2D and 3D TOE guidance in order to puncture the septum with enough height to position the clip over the mitral leaflets. Since there is a prolonged procedure time relative to other structural heart disease interventions, general anaesthesia is used and TOE can be easily performed. Real-time 3D TOE offers several advantages over 2D ICE, as it allows structures to be examined “en face” and the tip of catheters to be fully seen, in motion [52]. Further studies are needed to evaluate the role of 3D ICE to guide transcatheter therapies of the mitral valve. ICE is an adjunctive imaging modality for aligning the needle and septum in most transseptal puncture procedures. It provides additional assessment of procedure success and quick diagnosis of complications.

ICE imaging for transseptal puncture can be performed from the left femoral vein, which frees the right femoral vein for device transit. Imaging begins by obtaining the interatrial septal long-axis view (clockwise rotating to 90° to 100° and aiming posteriorly), then rotating clockwise into the septal short-axis view [30]. This is the same working view for ASD or PFO closure and is the ideal position for monitoring transseptal puncture for mitral valvuloplasty, ventricular tachycardia ablation, and left atrial appendage closure. A more posterior plane containing the left pulmonary veins is optimal for atrial fibrillation ablation with pulmonary vein isolation. An anterior plane containing the aorta should be avoided given risk of aortic puncture. Aortic puncture is also possible if the needle is aimed superiorly. Once the optimal imaging plane is identified, the Mullin sheath is brought into the right atrium and the Brockenbrough needle is advanced to the mid-septum until tenting is seen. The needle should not be passed through the septum until the operator is satisfied that the entry point is squarely in the mid-septum.

BALLOON MITRAL VALVULOPLASTY

For balloon mitral valvuloplasty, once through the septum in the home view, a wire is advanced into the left atrium. Then, the sheath and dilator are introduced into the left atrium, the dilator is separated from the sheath and the sheath advanced. At this point, the view is changed to concentrate on the mitral valve and left ventricle ( Figure 8 ). A wire is placed across the mitral valve and the Inoue balloon is positioned, inflated, and withdrawn ( Figure 18 ). Repeat spectral Doppler analysis allows measurement of the slope and calculation of the mitral valve area by the pressure half time method, plus assessment of mitral regurgitation by continuous wave and colour Doppler. Once the equipment is removed, colour Doppler should be performed in the septal short-axis view to evaluate the small atrial septal defect created by the transseptal puncture. Some prefer 3D TOE to assess mitral regurgitation post-mitral balloon valvuloplasty because it visualises split commissures and leaflet tears that are not well-seen on 2D echocardiogram [53].

TRANSCATHETER AORTIC VALVE REPLACEMENT

Intracardiac echocardiography of transcatheter aortic valve replacement (TAVR) is a newer frontier. TAVR is usually accomplished under TOE guidance, but there are disadvantages in using TOE to position and deploy a transcatheter valve. The TOE probe is positioned in the esophagus, directly behind the ascending aorta and aortic valve, obstructing the operator’s view of the valve plane on fluoroscopy. The TOE probe is withdrawn during aortography so that the operator can find the best alignment of the transcatheter valve within the annulus and during deployment of the valve. These limitations of TOE are overcome by ICE when high-quality images of the left ventricular outflow tract ( Figure 6 ) and aortic valve ( Figure 11 ) can be obtained from a stable position in the right atrium [54]. The use of 2D ICE and 3D ICE [27, 55] in TAVR was evaluated in small studies and needs further investigation.

LEFT ATRIAL APPENDAGE CLOSURE

Intraprocedural imaging plays a crucial role in guiding percutaneous left atrial appendage (LAA) closure. Adequate imaging is needed to confirm absence of LAA thrombus, identify the LAA dimensions for sizing of the closure device, guide the transseptal puncture, and ensure accurate device positioning. While TOE is the gold standard for guidance of LAA closure, ICE has emerged as a potential alternative imaging modality [56]. One disadvantage of 2D ICE is the inability to well visualise the LAA from the catheter’s location in the right atrium due to sub-optimal far-field resolution. The visualisation of the LAA can be improved by imaging the LAA from the left atrium, which could be achieved by advancing the ICE catheter into the left atrium alongside the transseptal sheath through a single transseptal puncture and positioning the ICE catheter at the entrance of the left upper pulmonary vein [57, 58]. Alternatively, non-standard ICE views from the RVOT and pulmonary arteries can improve visualisation of the LAA [59]. 3D ICE may provide a better comprehensive anatomic assessment than 2D and could be useful to guide LAA closure [60, 61, 62]. Additional data is needed to assess the appropriate application of this technology and its potential benefits in LAA closure, particularly with 3D ICE and non-standard ICE views.

Imaging of complications

One important advantage of ICE-guided procedures is the ability to quickly diagnose complications and facilitate treatment [16]. Actual complications caused by the ICE catheter itself potentially include cardiac perforation and atrial arrhythmia from catheter stimulation, but it is more likely that ICE will help a judicious operator prevent complications, such as thrombus formation on wires or devices, perforation of cardiac, arterial or venous structures, and pericardial effusion. Layering of a pericardial effusion can be seen by entering the right ventricle and angling rightward to image the inferior wall of the left ventricle ( Figure 15 ). While the aim of ICE is to minimise these possibilities, swift diagnosis and treatment of a complication could impact outcomes.

Conclusions

ICE has become a widely used alternative to TOE in the catheterisation laboratory. Understanding the key anatomical views and specific imaging protocols for interventions on the interatrial and interventricular septae, transseptal puncture and valvular disease assists the operator to make the intervention efficient and safe, or to expose unfavourable anatomy. Mechanical (rotational or radial) and phased array transducers are the two technologies currently available. Phased array systems generate images that are similar to those seen on transthoracic or transoesophageal echocardiogram which makes them easily interpretable. The advancement of real time 3D ICE will likely expand the use of this imaging modality in complex transcatheter interventions. Mastering the basics of ICE is worthwhile for the interventionist who treats structural heart disease.

Personal perspective – Howard C. Herrmann

Echocardiography is an important tool for interventionists who treat structural heart disease, not only for pre-planning, but for intraprocedural guidance. Intracardiac echocardiography systems are becoming more powerful and emerging 3D ICE transducers may obviate the preference for 3D transoesophageal echocardiography in the future. If so, ICE may become the predominant imaging mode for newer interventional techniques, such as mitral and tricuspid valve repair with clipping of regurgitant leaflets, transcatheter aortic valve replacement, and left atrial appendage occlusion, thereby expanding the capabilities of the interventionist in the treatment of structural heart disease.

Online data supplement

Moving image 1
Standard views for intracardiac echocardiography rotating clockwise

Moving image 2
15° to 30° (“home view”)

Moving image 3
30° to 40° (“right ventricular outflow tract [RVOT] view”)

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45° (“left ventricular outflow tract [LVOT] view”)

Moving image 5
60° to 70° (“left atrial appendage view” or “lower interatrial septal view”)

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70° to 80° (“left atrial appendage view” or “lower interatrial septal view”)

Moving image 7 & Moving image 8
90° to 100° (“left pulmonary veins view”)

Moving image 9
90° to 100° (“interatrial septal long-axis view”)

Moving image 10
100° to 150° (“aortic” or “septal short-axis view”)

Moving image 11
150° to 180° (“right pulmonary veins view”)

Moving image 12
Guidewire across an atrial septal defect

Moving image 13
Balloon sizing of the defect

Moving image 14
Amplatzer™ device across an atrial septal defect with deployment of the left atrial disc

Moving image 15
Amplatzer™ device across an atrial septal defect with deployment of the right atrial disc

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Final position of the Amplatzer™ device before deployment across an atrial septal defect

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Fully deployed Amplatzer™ device across an atrial septal defect

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Tricuspid valve visualised on 4D ICE using AcuNav™ Volume ICE catheter

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Amplatzer™ device delivery sheath across an atrial septal defect (4D ICE)

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Amplatzer™ device across an atrial septal defect with deployment of the left and right atrial discs (4D ICE)

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