The complexity of structural heart disease interventions necessitates procedural imaging guidance. Echocardiography has many advantages in the hybrid catheterization laboratory, including the ability to image structures two-dimensionally and three-dimensionally (3D) in real-time with good temporal and spatial resolution.¹ Transesophageal echocardiography (TEE) has been the mainstay to guide structural heart interventions; however, intracardiac echocardiography (ICE) is an alternative. Both TEE and ICE have inherent strengths and weakness that should be evaluated by the heart team when deciding the optimal modality for a given procedure. TEE and ICE can reduce fluoroscopy times and lead to reduced radiation exposure and procedural duration and enhanced technical success.

Intracardiac Echocardiography

ICE has been widely adopted in the electrophysiology laboratory to guide transseptal punctures due to its ability to define atrial septal anatomy and provide visualization of transseptal catheter position in relation to other structures within the heart. It is now being applied in structural heart cases such as closure of atrial septal defects (ASD) and patent foramen ovale (PFO).²

ICE generates images from within the heart; therefore, it can image at short distances with high spatial resolution. ICE is performed through a venous or, less frequently, arterial sheath, so it negates the need for general anesthesia and the associated risks of esophageal intubation such as trauma to the gastrointestinal tract and aspiration.³ This can be particularly appealing in the elderly or clinically tenuous patient.

There are disadvantages to ICE, including the high upfront cost of the single-use catheters. 3D ICE is limited to a small volume (22 x 90 degrees) compared with TEE.³ ICE has a shorter field of view, making imaging far-field structures from the right atrium, such as the pulmonary veins and left atrial appendage, difficult. This can be overcome by positioning the ICE catheter in the right ventricular outflow tract or pulmonary artery.⁴ Finally, the catheter may interfere with a temporary pacemaker, making it less advantageous for transcatheter aortic valve replacement (TAVR).

Transesophageal Echocardiography

TEE has a well-established role in guiding interventional procedures due to its ability to provide real-time 3D imaging with superior resolution to transthoracic echocardiography. It has the advantage of being a familiar technique to cardiologists. Like ICE, it can aide transseptal puncture, particularly in cases in which specific anatomic positing of crossing catheters is necessary for the success of the procedure, such as in left atrial appendage occlusion device implant and percutaneous mitral interventions such as MitraClip (Abbott Vascular; Santa Clara, CA) (Figure 1) or balloon valvuloplasty.^5-7 For TAVR, TEE is associated with frustrations such as image quality and probe interference with fluoroscopy. Compared with ICE, TEE has the advantage of lower upfront cost.³ It does not require a venous or arterial access (ICE procedures usually require an 8-10 F catheter), thereby possibly limiting vascular access-site complications.

Figure 1

The major drawback of TEE is the requirement for sedation or general anesthesia to allow esophageal intubation for an extended period.⁸ Due to its posterior position in the esophagus, imaging far-field structures in the anterior heart and chest may be limited. Additionally, the TEE probe may interfere with visualization of structures on fluoroscopy. Procedural TEE has fallen out of favor for TAVR in many centers where operators are comfortable deploying valves under fluoroscopy alone, and there is a strong desire to avoid general anesthesia in patients with elevated risk.⁹

Both TEE and ICE are useful and can be complementary for ASD/PFO closure. TEE can be used for initial evaluation and planning for ASD closure, and procedural ICE can provide additional guidance for device size selection and positioning. ICE is better able to image the posterior-inferior interatrial septum, and TEE provides better visualization of the anterior-superior rim.¹⁰

The entire structural heart team, including interventionalists and imagers, work in concert to perform safe and effective procedures. Knowing the strengths and limitations of ICE and TEE is crucial in choosing the best imaging modality to assist with structural interventions (Table 1). Future advances in crystal technology may lead to more widespread use of ICE in the interventional laboratory, especially if we see that technology improve 3D visualization significantly.

Table 1: Comparison of ICE Versus TEE for Procedural Imaging

ICE	TEE
Image structures near the right atrium Limited 3D evaluation Limited temporal resolution Minimal sedation required Can be performed by interventionalist Risk of vascular access complications High upfront cost	More comprehensive examination Full 3D evaluation Improved temporal resolution Sedation or anesthesia required Requires imaging echocardiographer Risk of trauma to gastrointestinal tract May result in increased length of stay

References

1. Khalique OK, Hahn RT. Role of Echocardiography in Transcatheter Valvular Heart Disease Interventions. Curr Cardiol Rep 2017;19:128.
2. Alqahtani F, Bhirud A, Aljohani S, et al. Intracardiac versus transesophageal echocardiography to guide transcatheter closure of interatrial communications: Nationwide trend and comparative analysis. J Interv Cardiol 2017;30:234-41.
3. Basman C, Parmar Y, Kronzon I. Intracardiac Echocardiography for Structural Heart and Electrophysiological Interventions. Curr Cardiol Rep 2017;19:102.
4. Frangieh AH, Alibegovic J, Templin C, et al. Intracardiac versus transesophageal echocardiography for left atrial appendage occlusion with watchman. Catheter Cardiovasc Interv 2017;90:331-8.
5. Saw J, Lempereur M. Percutaneous left atrial appendage closure: procedural techniques and outcomes. JACC Cardiovasc Interv 2014;7:1205-20.
6. Silvestry F, Rodriguez LL, Herrmann HC, et al. Echocardiographic Guidance and Assessment of Percutaneous Repair for Mitral Regurgitation With the Evalve MitraClip: Lessons Learned From EVEREST I. J Am Soc Echocardiogr 2007;20:1131-40.
7. Park SH, Kim MA, Hyon MS. The advantages of On-line transesophageal echocardiography guide during percutaneous balloon mitral valvuloplasty. J Am Soc Echocardiogr 2000;13:26-34.
8. Lee AP, Lam YY, Yip GW, Lang RM, Zhang Q, Yu CM. Role of real time three-dimensional transesophageal echocardiography in guidance of interventional procedures in cardiology. Heart 2010;96:1485-93.
9. Hyman MC, Vemulapalli S, Szeto WY, et al. Conscious Sedation Versus General Anesthesia for Transcatheter Aortic Valve Replacement: Insights from the National Cardiovascular Data Registry Society of Thoracic Surgeons/American College of Cardiology Transcatheter Valve Therapy Registry. Circulation 2017;136:2132-40.
10. Assaidi A, Sumian M, Mauri L, et al. Transcatheter closure of complex atrial septal defects is efficient under intracardiac echocardiographic guidance. Arch Cardiovasc Dis 2014;107:646-53.

Clinical Topics: Arrhythmias and Clinical EP, Cardiac Surgery, Congenital Heart Disease and Pediatric Cardiology, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Cardiac Surgery and Arrhythmias, Cardiac Surgery and CHD and Pediatrics, Congenital Heart Disease, CHD and Pediatrics and Arrhythmias, CHD and Pediatrics and Imaging, CHD and Pediatrics and Interventions, Interventions and Imaging, Interventions and Structural Heart Disease, Echocardiography/Ultrasound, Nuclear Imaging

Keywords: Foramen Ovale, Patent, Echocardiography, Transesophageal, Transcatheter Aortic Valve Replacement, Imaging, Three-Dimensional, Balloon Valvuloplasty, Pulmonary Veins, Pulmonary Artery, Atrial Appendage, Echocardiography, Atrial Septum, Fluoroscopy, Esophagus, Gastrointestinal Tract, Anesthesia, General, Pacemaker, Artificial, Electrophysiology, Diagnostic Imaging

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