Equipment and Handling Procedures

Current devices (Acuson, Mountain View, Calif.) are multimodal, phased-array transducer-tipped intracardiac echocardiographic catheters. Nowadays, the 8 F AcuNav catheter has become the tool of choice for ICE. Other devices have been introduced⁵ but have gained only limited acceptance (Table 6-1).

TABLE 6-1 Presently Available Intracardiac Echocardiographic Devices

Just like conventional echocardiography, the miniaturized AcuNav transducer provides a 90°-sector image. The ICE probe can be connected to standard ultrasound units (Siemens and General Electric) through the SwiftLink Catheter Connector, which attaches to the ultrasound unit like any probe. After the SwiftLink Catheter Connector is covered with a sterile jacket, it is placed into the sterile field at the catheter table, where it is connected to the sterile intracardiac echocardiographic probe. The catheter steering mechanism and the function of the transducer should be checked in a water bath before insertion.

In comparison to the 10-Fr version, the 8-Fr AcuNav catheter has facilitated ICE and increased patient comfort and probably safety as well. After its introduction in pediatric cardiology,² the 8-Fr ICE catheter now is also used in adult interventional cardiology. The catheter possesses the unlimited echocardiographic capabilities of its predecessor but is available with more insertable length and in a shorter version. Besides two-dimensional (2D) and M-mode imaging, the ICE catheter also permits functional analysis. It possesses complete Doppler capabilities, including pulsed wave, continuous wave, color flow, and tissue Doppler modalities (Table 6-2).

TABLE 6-2 Doppler Imaging Modes and Frequencies of the Intracardiac Echocardiographic Catheter Family

PW, Pulsed wave.

An access sheath is required for introducing the ultrasound catheter into the femoral vessels or the right jugular vein. The disposable ICE catheter can be navigated through the inferior vena cava (femoral venous access) or the superior vena cava (SVC) (jugular venous access) into the right atrium (RA). This may present a potential risk, although most patients undergo ICE as part of an interventional procedure, so the additional risk remains minimal. Special caution is needed when navigating the ICE catheter through the pelvic veins. Although the risk of venous injury or perforation is very low, isolated pelvic vein perforation and inferior vena cava dissection have been described. Adequate handling of the catheter device includes use of a long access sheath and fluoroscopy, two recommended precautions that enhance patient safety. The long access sheath in particular spares the examiner problems associated with pelvic vein navigation, thereby increasing patient safety. In addition, it is recommended to infuse saline solution before ICE. This increases venous pressure and dilates the central veins, facilitating venous puncture and insertion of access sheaths and the ICE catheter. Even intracardiac navigation becomes easier if the heart is well filled. The intracardiac probe does not accommodate a guidewire and is therefore fundamentally different from IVUS catheters. These require guidewires and are therefore relatively safe to manipulate. Obtaining arbitrary views may be difficult, however, especially in the near field. Particularly in the vicinity of the RA, the guidewire can restrict full visualization of lumen and wall, and it will frequently not allow adequate views of structures of interest, such as the transition into other chambers or vessel orifices.

To permit adequate imaging of the interatrial septum and its neighboring structures, two standardized views are used: (1) a transatrial longitudinal view showing the extent of the atrial septum from cranial to its distal margins—this view is seen with the catheter retroflexed inside the RA; and (2) a perpendicular transatrial short-axis view for visualizing the anterior part of the atrial septum and the transition to the aortic valve and the ascending aorta (Fig. 6-1).

Figure 6-1 Standard transatrial views for intracardiac imaging are obtained with the catheter tip in the RA.

Two image planes are shown in blue—a short-axis view of the aortic valve and interatrial septum atrium, and a longitudinal view through the interatrial septum.

The aortic valve is visualized by turning the catheter toward the aorta. One may need to straighten or even slightly anteflect the catheter. The tricuspid valve and the right ventricle (RV) are best displayed in a longitudinal view by anteflexing the probe after positioning the tip in the high RA. The left and right pulmonary veins as well as the left atrial appendage (LAA) are each visualized in a modified transatrial longitudinal view. For depicting the left pulmonary veins and the LAA, the catheter is angulated inferiorly; to visualize the right pulmonary veins, it is turned clockwise and advanced superiorly.

Clockwise rotation of the straightened ICE catheter permits visualization of the smallest anatomic details in the near field as well as to a depth of up to 12 cm. In order to enter the right ventricle, the tip of the probe is positioned in the mid to upper RA with the piezoelectric crystal facing the free wall of the RA, before the probe is gradually deflected anteriorly. From the right ventricle, the transventricular long-axis view of the left ventricle (LV) is obtained, which shows the interventricular septum proximally, the LV outflow tract, and the mitral valve apparatus. When the catheter tip is tilted to the right, the transventricular short-axis view of the LV comes into view (Figs. 6-2 and 6-3).

Figure 6-2 Transventricular long-axis view of the LV and the LA in patient with pericardial effusion. PE, Pericardial effusion.

Figure 6-3 Transventricular short-axis view of the LV. IVS, Interventricular septum.

Interpretation of LV wall motion from transventricular views requires care because the catheter is moving inside the RV. By tilting the catheter tip away from the transventricular long-axis view, the RV outflow tract and pulmonary valve can be visualized as well (Fig. 6-4).

Figure 6-4 Catheter positioned in the RV provides a view of the right ventricular outflow tract (RVOT) and the pulmonic valve (PV). PA, Pulmonary artery.

To avoid ventricular arrhythmias, the catheter has to be carefully navigated inside the RV cavity. The catheter should not be advanced beyond the pulmonary valve. When using the SVC approach, inadvertent catheter passage into the coronary sinus has to be avoided by all means. A certain expertise in intracardiac catheter manipulation is essential to safely advance the catheter into the right heart, to orient oneself inside the heart, to obtain standardized views, and to adequately visualize the cardiac anatomy⁶ (Table 6-3; also see Fig. 6-1).

TABLE 6-3 Standardized Views

IAS, Interatrial septum; IVC, inferior vena cava; IVS, interventricular septum; LAA, left atrial appendage; LVOT, left ventricular outflow tract; TV, tricuspid valve.

Although the diagnostic potential and limitations of this imaging modality have not been fully evaluated, ICE may find an adequate place in operating rooms and catheterization laboratories for online monitoring of complex intracardiac interventions. Nonsurgical cardiac procedures require real-time, high-quality, and near-field views for optimal results. Moreover, continuous progress in the field of percutaneous interventions warrants more effective imaging guidance without compromise to patient comfort and safety. ICE has been proven an important diagnostic tool for depicting expected or unanticipated aberrant anatomy in patients with congenital heart disease. Tissue motion, intracardiac devices, and their relation to the surrounding structures can be very clearly delineated.

Guiding Device Closure of Interatrial Communications

Device closure of interatrial communications is performed for treatment of severe left-to-right shunts associated with atrial septal defects (ASDs) (see Chapter 44) and for prevention of recurrent paradoxical embolism in patients with a patent foramen ovale (see Chapter 41). Some complications with closure of interatrial communications are due to suboptimal device performance.⁷ Others, however, may be related to discontinuous echocardiographic monitoring, because supine patients do not tolerate continuous monitoring with TEE well unless they are sedated or under general anesthesia. More than 10 years of experience make us believe that some specific complications of transcatheter closure can potentially be avoided with improved echocardiographic monitoring. In that respect, ICE can be recommended as the method of choice for guiding percutaneous device closure, especially of ASDs.

Before passing instrumentation through the interatrial communication, the ICE catheter is advanced through the inferior vena cava into the RA. The transducer is aimed at the left atrium (LA) to obtain the transatrial longitudinal view. As a first step, adequate position of a long guidewire in the left superior pulmonary vein is demonstrated. The left superior pulmonary veins are depicted by angulating the probe from the longitudinal view inferiorly. The stretched size of ASDs can be adequately measured by ICE; however, sizing balloons must still be used—a mandatory step for estimating the size of the communication before ASD device closure.⁸

Next, the long access sheath required for occluder device application is inserted over the guidewire. Fluoroscopic imaging during that part of the procedure can be reduced to very short intermittent checks because placement of the tip of the sheath into the LA can be primarily guided and documented by ICE. Simultaneous echocardiographic and fluoroscopic viewing is recommended during deployment of the closure device.

Practical Tips

• ICE displays release of the left-sided counteroccluder opening in the LA.

• The whole system including the long access sheath with the delivery cable inside and the opened left-sided counteroccluder is slightly pulled back until the open counteroccluder applies some traction on the atrial septum. ICE depicts the moment when the left-sided counteroccluder is closely aligned with the atrial septum.

• With the delivery cable still under traction, the long access sheath is further withdrawn to release the right-sided counteroccluder. ICE demonstrates release of the right-sided counteroccluder inside the RA and the left-sided counteroccluder remaining on the left side of the septum.

• While monitoring the opening of the right-sided counteroccluder, the delivery cable is carefully pushed forward until the counteroccluder also fits tightly into the atrial septum, but from the right side. Viewing two perpendicular cut planes (transatrial longitudinal and short-axis views) is mandatory to confirm the result and to rule out jamming of one of the counteroccluders in the interatrial communication (Fig. 6-5).

Figure 6-5 Device closure of an atrial septal defect (ASD) guided by intracardiac echocardiography. A, ASD. ASD II, Secundum atrial septal defect. B, Significant left-to-right shunt. C, Long access sheath with indwelling wire. 1, Long sheath crossing the septum; 2, tip of long sheath; 3, wire. D, Unfolded left-sided counteroccluder. 1, Sheath with folded right-sided counteroccluder inside; 2, unfolded left-sided counteroccluder. E, Unfolded counteroccluders with the device being pulled. 1, Unfolded right-sided counteroccluder; 2, left-sided counteroccluder. F, Final device position. 1, Device after release from the delivery cable; 2, aorta (Ao) is shown to be unaffected.

With the occluder device positioned but still connected to the delivery cable, the “wriggle maneuver” is monitored. Aiming to ensure that the counteroccluder cannot tilt or slip to the contralateral side, the occluder device is pushed and pulled before release. This will guarantee that the atrial septum is optimally engaged. Details of this maneuver, which is considered the best technique to avoid unsatisfactory device orientation or embolization, can be nicely shown by ICE. The wriggle maneuver should be visualized in the transatrial longitudinal view and again in the transatrial short-axis view. In the short-axis view, any compression of the aortic bulb by the occluder device can be ruled out. It is sensible to also use ICE for monitoring device disconnection from the delivery cable.

Once it is released, the device lines up with the atrial septum, reaching its definitive orientation. The final position of the device should be visualized to ensure that the counteroccluder completely encloses the rims of the interatrial communication. After device deployment, color flow imaging can depict any residual shunt. During deployment of the occluder device, the device and the intracardiac echocardiographic catheter do not interfere with each other. As a precaution, the intracardiac echocardiographic catheter should be kept at least 1 cm from the occluder device. A closer position would impair optimal imaging of the occluder device. As elucidated, continuous ICE imaging during each stage of the procedure allows optimal device positioning, a prerequisite for safe percutaneous closure of interatrial communications. Real-time 3D ICE imaging will be available soon.

Several investigators demonstrated that ICE can safely guide interventional therapy in interatrial communications and that ICE monitoring is superior to conventional TEE.^9–12 TEE requires general anesthesia with or without endotracheal intubation, whereas ICE permits unlimited echocardiographic viewing in fully conscious and compliant patients. This is of utmost importance, because malposition and migration of the device into the systemic or pulmonary circulation or perforation of the cardiac wall and rapid thrombus formation on the device are known to happen on occasion.^7,13,14 ICE provides better image resolution than TEE and therefore facilitates the procedure, particularly when long continuous or repeated echocardiographic viewing is required or when complications begin to develop. ICE results in much less procedural stress to the patient, and fluoroscopic and procedural times can be shortened.^9,12 Because many patients with interatrial communications are of reproductive age or younger, reduction of radiation exposure has to be considered a major advantage of ICE. In that respect, patients who undergo ASD closure benefit more from ICE than patients undergoing closure of a patent foramen ovale, because ASD closure is more complex and more time consuming. Employing ICE in the pediatric population is also recommended. Several years’ experience show that ICE is a practical and straightforward approach for guiding device closure in children and adolescents.^2,11 The overall risk related to ICE appears to be low. Moreover, it is likely that ICE improves the safety of interventional device closure in interatrial communications. From an economic point of view, savings from shorter procedural time and from avoiding general anesthesia need to be weighed against the cost of the ICE catheter. After a brief learning curve, interventional cardiologists who are familiar with echocardiography can fully benefit from the advantages of ICE.

Monitoring of Percutaneous Left Atrial Appendage Closure

ICE guidance for LAA device closure has only been described in a few cases.^15,16 It is an option in patients with atrial fibrillation in whom oral anticoagulation is contraindicated. Anatomical variation of the LAA, exclusion of thrombi, and the diameter of the ostium are usually assessed by TEE, which is also used for intraprocedural monitoring. As in any other percutaneous transseptal catheter interventions, one needs to establish access to the atrial appendage by septal puncture before LAA closure. This is best done under ICE guidance. Before atrial septal puncture, anatomic anomalies should be ruled out. When tenting of the fossa ovalis identifies contact with the transseptal needle, the pressure on the needle can be slightly increased until the needle perforates the atrial septum. For device closure, using novel placement of an intracardiac echo probe via a Mullins sheath in the RV outflow tract and pulmonary artery¹⁶ seems to be advantageous over viewing from the LA. This allows near-field visualization of device deployment in the LAA. This technique may increase the spectrum of patients who benefit from the procedure by decreasing procedure time, fluoroscopy, and procedure-related morbidity (Fig. 6-6).

Figure 6-6 Intracardiac echocardiographic imaging depict “tenting” of the fossa ovalis (arrow) while a Brockenbrough needle is advanced from the RA.

Transseptal crossover and advancement of the dilator and sheath are adequately imaged and the ostium of the LAA is easily delineated and measured by ICE. Device positioning, release, potential periprosthetic leaks, and especially the spatial relation of the device to the surrounding structures can be continuously monitored in the transatrial longitudinal view. In some patients, the transventricular long-axis view can represent an alternative (see Table 6-3).

Guiding Radiofrequency Pulmonary Vein Ablation

The rapidly evolving field of interventional electrophysiology creates a demand for guidance by imaging. This is particularly true in view of the fact that currently available techniques, such as fluoroscopy and endocardial ECG, may be helpful but have certain limitations. In many cases, angiographic guidance of circular mapping catheters is not sufficiently accurate. After initial puncture of the interatrial septum, high-quality images provided by ICE are capable of guiding transseptal pulmonary vein ablation, a treatment option in atrial fibrillation. Delineation of the endocardium and direct visualization of the pulmonary venous ostium facilitate mapping and radiofrequency ablation by depicting the target area, ensuring electrode-tissue contact, and helping with energy titration (Fig. 6-7).

Figure 6-7 Transatrial longitudinal view.

Left atrial appendage (LAA) and transmitral flow into the LV.

Angiography-guided placement can result in poor contact between the ablation catheter and the endocardial surface. Inadequate contact reduces heat transfer to the tissue and allows convective heat loss into the circulating blood.

In the transatrial longitudinal view, the left pulmonary veins can be imaged by advancing the probe without tension or steering forces. Clockwise rotation of the catheter and insertion into the SVC allows the right pulmonary veins to be visualized in a cross-sectional view. Left or right steering permits longitudinal views of the right pulmonary veins. Thus, accurate anatomical positioning of the ablation catheter tip in relation to adjacent endocardial structures is supported¹⁷ (Fig. 6-8).

Figure 6-8 Modified transatrial longitudinal view.

Flow from left-sided pulmonary veins into the LA. LIPV, Left inferior pulmonary vein; LSPV, left superior pulmonary vein.

Doppler measurements of pulmonary vein flow velocities before and after ablation are recommended. During the procedure, the ablation zone can be directly visualized, including the evolving tissue injury. Visualization permits assessment of shape, cross-sectional area, wall thickness, and lesion formation¹⁸ and depicts lesion size and continuity.¹⁹ ICE is also useful for monitoring bubble formation during the phase of radiofrequency energy delivery, allowing radiofrequency dose titration to prevent overheating of the catheter tip. After effective ablation, transvenous flow velocities should be interrogated using continuous-wave Doppler in order to identify the potential presence of a gradient,²⁰ which can occur as a complication. This illustrates that ICE contributes to the safety of the ablation procedure and to prevention or early detection of potential complications associated with electrophysiologic interventions, that is, thrombus formation²¹ and development of pulmonary vein stenosis.²⁰ Periinterventional monitoring depicts each step of the ablation process, improves efficacy, and also reduces early and late complications.²² As demonstrated for device closure of interatrial communications, ICE can lower fluoroscopy time and shorten the ablation procedure.

Monitoring Transcatheter Aortic Valve Implantation

Generally, potential alternative sound windows are available for ICE-based intrainterventional assessment in TAVI. These include the transaortic window for viewing from inside the ascending aorta²³ and the transventricular window for transseptal viewing from the right ventricle.²⁴ Views from inside the aorta are inconvenient because the ICE catheter is prone to interfere with procedural catheters. In many individuals, it is also challenging to keep the ICE catheter stabilized in the RV (transventricular approach) throughout the procedure. However, longitudinal views from the lower SVC and the upper RA supplemented by RA short-axis views seem to be most suitable for continuous guidance, because the catheter position remains stable and the catheter does not interfere with the TAVI procedure^24a (Figs. 6-9 and 6-10).

Figure 6-9 Longitudinal transcaval/transatrial (A) and short-axis transatrial (B) standard intracardiac echocardiographic views for transcatheter aortic valve implantation. Ao, Ascending aorta; AC, AcuNav catheter; AVP, aortic valve prosthesis; DA, descending aorta; IVC, inferior vena cava; SVC, superior vena cava.

(From Bartel T, Bonaros N, Müller L, et al: Intracardiac echocardiography: a new guiding tool for transcathter aortic valve replacement. J Am Soc Echocardiogr 24:966-57, 2011).

Figure 6-10 Longitudinal transcaval (A) and short-axis (B) intracardiac echocardiographic views of aortic valve prosthesis after deployment and at end-diastole. 1, Minimal paravalvular leak; Ao, aorta; AVP, aortic valve prosthesis; RCA, right coronary artery.

(From Bartel T, Bonaros N, Müller L, et al: Intracardiac echocardiography: a new guiding tool for transcathter aortic valve replacement. J Am Soc Echocardiogr 24:966-57, 2011).

Even in asymptomatic patients, aortic stenosis is known to be associated with a poor prognosis.²⁵ An increasing number of patients cannot undergo surgical aortic valve replacement owing to high perioperative risk due to comorbidities and advanced age.²⁶ The periinterventional risk of TAVI must be weighed against these facts.²⁷ Especially in extremely high-risk patients, each step of the procedure can cause life-threatening complications.²⁸ Although periprocedural echocardiography is regarded as an important means of lowering the rate of complications, and although TEE monitoring is frequently used in those patients exposed to extreme risks to assist with the interventional steps and to detect complications, current guidelines for TAVI do not include any detailed methodologic suggestions for intraprocedural use of echocardiography.²⁹

Echocardiography also qualifies as a tool for guiding TAVI with the purpose of increasing its benefit-to-risk ratio.³⁰ Intraprocedural TEE has become an established method,²⁹ although it is not necessarily an ideal guiding tool, one reason being the difficulty of aligning the Doppler beam with transvalvular flow in the deep transgastric view. Transgastric measurement of aortic valve blood flow cannot be considered a routine approach and is known to require a significant learning curve. It also may not depict the maximum transvalvular or transprosthetic gradient because the TEE approach results in a non-parallel Doppler angle. In contrast, the Doppler beam can be nicely aligned with transvalvular flow in the transcaval/transatrial longitudinal ICE view, and determination of transvalvular pressure gradients is therefore much easier than with TEE. The gradient not only gives an estimate of the effectiveness of predilatation, but helps to avoid unnecessary additional dilatations. This is meaningful for risk management because each balloon dilatation is associated with the risk of annulus dissection and significant aortic regurgitation.

When positioned at the level of the aortic valve, the TEE probe impedes posterior-to-anterior fluoroscopic viewing, which is mandatory for angiography, balloon dilatation, final adjustment of the prosthesis, and its subsequent implantation. This is another drawback of TEE. The only workaround is repeated TEE probe withdrawal at crucial points of TAVI work flow, subsequent repositioning of the probe, and new alignment to obtain appropriate TEE views. Consequently, TEE provides only episodic monitoring on the one hand. On the other hand, repeated repositioning of the TEE probe may cause several interruptions of TAVI work flow. Although real-time 3D TEE represents a feasible guiding tool and may improve spatial orientation, it nevertheless remains a variant of TEE with all disadvantages inherent in this technique when applied to TAVI.

In contrast to TEE, the ICE catheter can be left in place with the probe aimed at the aortic valve during the entire TAVI procedure. Slight readjustments of the catheter may be occasionally required. Simultaneous and uninterrupted echocardiographic guidance by ICE is an ideal method for assisting predilatation, final adjustment, and deployment of the valve prosthesis; for ruling out potential complications as early as possible; for confirming proper prosthetic valve function without a need for repeated angiography; and for checking LV function immediately after implantation. Decreased use of contrast agents is meaningful, because renal failure has been reported to be the commonest short-term complication after TAVI.³¹ In comparison to TEE, ICE provides a more coaxial view of the ascending aorta and may therefore help to improve coaxiality between the valve-balloon system and the ascending aorta. ICE also assists wire crossing of the native valve in the majority of patients and better depicts the coronary ostia than TEE, which helps to rapidly exclude any obstruction by displaced debris from the calcified native valve (Fig. 6-11).

Figure 6-11 Longitudinal intracardiac echocardiographic view demonstrates both coronary arteries branching off above the opened aortic valve prosthesis. Ao, Aorta; LCA, left coronary artery, RCA, right coronary artery.

(From Bartel T, Bonaros N, Müller L, et al: Intracardiac echocardiography: a new guiding tool for transcathter aortic valve replacement. J Am Soc Echocardiogr 24:966-57, 2011).

Both ICE and TEE approaches can be considered equivalent with respect to determining annulus size and LV function. Measuring annulus size is particularly critical and essential for selecting the correct size valve prosthesis. The ICE catheter is maneuverable by the interventional operator, who can adjust the transducer as needed and independently from a noninvasive cardiologist or anesthetist, while the ultrasound unit is operated by an ultrasonographic technician. Operated by an interventional cardiologist also experienced in echocardiography and especially in ICE application, this tool has some potential in minimizing procedural risks by avoiding and, whenever possible, detecting TAVI complications³² at the earliest possible time.

TAVI can also be completed under local anesthesia and moderate sedation,^33,34 provided patients are selected accordingly. However, prolonged TEE imaging requires deeper sedation. The availability of ICE as an adjunct for TAVI lets the operator decide whether to use local anesthesia plus sedation or general anesthesia independently of the need for echocardiographic guidance.

Perioperative and Periinterventional Imaging of the Ascending Aorta

When a high transesophageal image plane—also known as “banana view”—is used, TEE depicts the caudal part of the ascending aorta anteriorly to the right pulmonary artery. Unfortunately, ascending aortic flow is not aligned with the Doppler beam in this plane. For that reason, perioperative functional assessment of the aortic valve and the ascending aorta by TEE is limited to regurgitant flow detection. Perioperative IPAI and ICE from the RA and the SVC may become alternative approaches for complete morphologic assessment of the ascending aorta and functional evaluation of the aortic valve. In order to display the proximal ascending aorta, the ICE catheter is used as described for TAVI. Alternatively, it can be inserted via a jugular venous access and advanced through the SVC into the upper RA. In contrast to transfemoral access, no fluoroscopic guidance is needed with the jugular venous approach because the access sheath guides the catheter sufficiently, making direct catheter navigation superfluous. From the superior RA, the aortic bulb and aortic valve can be displayed in the long-axis view and, after tilting the tip of the catheter, also in a short-axis view. After the catheter is pulled back into the SVC, a longitudinal cut plane of the whole ascending aorta reaching up to the innominate artery can be obtained. In contrast to TEE, systolic flow is mostly aligned with the Doppler beam of the catheter, permitting color flow and pressure gradient recordings of highest image quality. Therefore, ICE might be of clinical interest immediately after aortic valve surgery or surgery of the ascending aorta (Fig. 6-12).

Figure 6-12 Aortic valve and ascending aorta seen from the superior vena cava:

measurement of pressure gradients (PG) before transcatheter aortic valve replacement (A), after predilatation (B), and after valve deployment (C). This approach allows full intraoperative hemodynamic assessment as well.

Intraoperative cannulation of the ascending aorta with surgical devices can also be monitored with IPAI views from the SVC. Further development of right-heart assist devices could create another potential application. Nevertheless, clinical experience with the transjugular approach is limited.

Periinterventional Imaging of the Descending Thoracic Aorta

TEE adds incremental information, improving the safety of stent-graft placement in type B aortic dissection. In addition, IVUS is considered helpful in patients with complex dissection including abdominal extension.³⁵ With respect to aortic diseases, the main limitation of IVUS is attributable to its inability to perform Doppler analysis. Flow detection by TEE is also limited if the flow is not aligned with the Doppler beam. In consequence, detecting flow from true to false lumen and vice versa by TEE depends on the alignment of the dissection flap. Therefore, TEE has a low sensitivity for detecting small entries and reentries (Fig. 6-13).

Figure 6-13 Intraluminal phased-array imaging from the true lumen (TL) to the false lumen (FL): thrombus formation in type B aortic dissection. E, Entry.

On the other hand, sonographic approaches may help lower the current complication rate of percutaneous stent-graft implantation,³⁶ thus opening up new opportunities for monitoring interventional therapy in aortic diseases using IPAI. In that respect, IPAI not only combines advantages of TEE and IVUS, but adds capabilities.

The descending thoracic aorta cannot be viewed from any venous approach. Periinterventional sonographic diagnostic methods need to clarify which lumen supplies the side branches, a difficult feat with TEE and even with IVUS images. Thus, the need to navigate the aorta with the echocardiographic catheter turns from a disadvantage into an advantage, because the Doppler beam can be aligned with any flow between true and false lumen and with blood flow into small branches. Thus, intraaortic monitoring by IPAI has great potential to become a tool for the effective guidance of aortic stent-graft implantation, in such a manner that all entries are closed. First case reports also suggest that IPAI is capable of safely guiding other diagnostic intraaortic procedures in aortic diseases.³⁷

Since the approval of the 8-Fr ICE catheter, its intraaortic use has added to the diagnostic spectrum in aortic disease.³⁷ For intraaortic employment of the echocardiographic catheter, a very long access sheath is definitely recommended so that only the tip of the catheter with the transducer sticks out of the sheath. Sheath and indwelling catheter are then jointly pulled back while imaging is performed. The catheter can be rotated intermittently and aimed at the region of interest by tilting its tip.

In type B aortic dissection, the echocardiographic catheter is placed into the true lumen and IPAI performed carefully. IPAI provides scans of the dissection flap when the device is rotated and withdrawn. Detection and precise localization of tears in the dissection membrane must be considered important for therapeutic decision making. In most cases, there are obviously more entries than are demonstrable by angiography, IVUS, or TEE. The fact that such data form the basis for optimal stent-graft placement, which aims to close all entries to the false lumen, mandates a detailed analysis of the sensitivity of conventional diagnostic approaches. If overlooked or not properly closed by interventional treatment, even small tears can lead to significant flow into and inside the false lumen, impairing the desired thrombus formation in the false lumen and thereby impeding healing of the dissection. IPAI depicts more entries than one would expect from conventional diagnostics and demonstrates which abdominal vessels originate from the true and the false lumen. Thrombus formation in the false lumen, a result of effective pressure separation between true and false lumen, can be also displayed.

IPAI can also be used to safely guide percutaneous biopsies of intraaortic masses suspected to be tumors. To accomplish that, the transducer is aimed at the mass and the radial-jaw biopsy forceps (Fig. 6-14).

Figure 6-14 Intraluminal phased-array imaging of an intraaortic mass (M). 1, Flow around the mass; AW, aortic wall.

Under continuous ultrasonographic imaging, targeted biopsies are taken from the depth of the mass. Opening, pushing, and closure of the biopsy forceps can be precisely guided and documented.³⁷ With careful handling, interference between the echocardiographic catheter and the lesion can be avoided. Nevertheless, there is some risk of peripheral embolization during the procedure.

Percutaneous device closure of patent ductus arteriosus is another interventional approach nicely guidable by use of IPAI. It may help to reduce procedural time, limit radiation exposure, and lower the amount of contrast agent administered. It is conceivable that IPAI can contribute to the safety and success of this nonroutine procedure³⁸ (Fig. 6-15).

Figure 6-15 Intraaortic viewing: device closure of patent ductus arteriosus (PDA). Ao, Aorta; PA, pulmonary artery; PDA-O, patent ductus arteriosus occluder.

Periinterventional Imaging of the Mitral Valve

Percutaneous transseptal balloon mitral valvotomy (BMV) (see Chapter 21) can be performed in concentric stenosis when the commissures are fused because of rheumatic heart disease without significant calcification and mitral regurgitation. Suitability of mitral stenosis for BMV can be assessed using the Wilkins score and a commissural score. As described for interventional left atrial appendage closure, atrial septal puncture is guided by the ICE transatrial longitudinal view. In that view, tool positioning in the LA can also be monitored. After introduction of a special guidewire into the LA, the transventricular long-axis view of the LV is obtained. Mitral ring diameter and intercommissural distance are measured, and the fused commissures are visualized. A balloon of appropriate size is selected. The same view is also useful for guiding a balloon through the stenotic mitral valve into the LV. Adhering to the double balloon technique, the distal balloon is inflated. Inflation should be monitored with ICE and fluoroscopy simultaneously. The next steps must be completed quickly to avoid prolonged LV inflow occlusion. Simultaneous echocardiographic and fluoroscopic viewing and documentation are recommended to accomplish this goal. The distal balloon is first inflated, and then pulled back toward the stenotic valve. Not until this step is completed is the proximal balloon inflated and valvotomy performed. At this time, ICE demonstrates that the balloon fits tightly into the stenotic valve orifice. The newer single-balloon technique³⁹ may require even closer echocardiographic guidance to precisely position the cylindrical balloon into the stenosis.

After balloon deflation and withdrawal, immediate two-dimensional and Doppler analyses are recommended to show the split commissures and to exclude any injury of the commissures or the mitral valve apparatus. In addition, the degree of mitral regurgitation is reassessed. Intraprocedural ICE viewing may be considered an optional imaging modality, especially if the transthoracic acoustic window is very poor. It allows analysis of the valvular anatomy and is ideal when enhanced views are required.⁴⁰ ICE is capable of providing excellent imaging and guidance, which results in low radiation exposure and minimizes the need for contrast angiography.¹⁵

One would expect the more sophisticated interventional procedures to derive more benefits from ICE. Thus, there is great potential for ICE in percutaneous valve implantation techniques and other catheter-based “valvular repair” procedures currently under development. Another future application may arise from the increasing importance of minimally invasive and reconstructive mitral valve surgery.

Limitations

Adequate handling of the ICE catheter requires a learning curve, even for an interventionalist familiar with left and right heart catheterization and IVUS. Additionally, the relatively large probe may limit its use in infants. In addition, the multifrequency probe does not provide harmonic imaging capability. ICE does, however, eliminate the need for general anesthesia and intubation, thereby lowering costs and increasing patient comfort. On the other hand, the high price for one AcuNav catheter remains an important shortcoming. Today, the catheter is no longer a disposable device. The lumenless catheter can be resterilized with gas. Vanguard AG Medical Services for Europe (Berlin, Germany) is an approved CE-certified company licensed to resterilize ICE catheters. Technical and medical safety and compliance with appropriate legal regulations governing health care products are guaranteed. After more than 2 years of experience, we can recommend resterilization as a safe procedure that permits each catheter to be reused approximately three times. Although the image quality may slightly deteriorate from resterilization, each catheter can eventually be used four times, markedly lowering the costs for each use, even when the cost of resterilization is accounted for.

Finally, the relation between advantages and disadvantages of using ICE and IPAI depends mainly on the expenditure and the risk of the specific interventional procedures. Increasing familiarity of interventional cardiologists with this technique may also affect its use in clinical practice (Table 6-4).

TABLE 6-4 Usefulness and Effectiveness of Intracardiac and Intravascular Imaging

PTSMA, Percutaneous transluminal septal myocardial ablation.