Mini 3D transesophageal probe: technical advances and clinical applications

Abstract

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With the growing complexity of structural heart disease procedures, the need for advanced intraprocedural imaging has become increasingly critical. Transesophageal echocardiography remains the gold standard for procedural guidance but is associated with risks such as upper gastrointestinal tract injury and the need for general anesthesia for patient comfort and safety. Miniaturized three-dimensional transesophageal echocardiography (miniTEE) probes offer a promising solution by providing high-resolution imaging which could be performed under conscious sedation. Studies evaluating the miniTEE probe for safety, image quality, and ability to guide specific structural and non-structural heart disease procedures will be reviewed. The limitations and future developments will be discussed.

Graphical abstract: smaller transesophageal echocardiography probes have a number of advantages and limitations. As the technology improves, the utilization of these probes will likely increase

Introduction

As structural heart disease (SHD) procedures continue to grow in complexity, intraprocedural imaging demands also increase [1,2,3]. Although the risk for upper gastrointestinal tract injury is well known, as SHD procedures have increased in both volume and complexity, the frequency of these injuries may also have also increased [4,5,6,7]. Risk factors for these injuries include patient related factors such as age, prior history of dysphagia or esophageal disease, pre-existing bleeding risk (i.e., liver disease or oral anticoagulation) or acuity of medical condition. A recent retrospective cohort study using an electronic health record database found that among 12,043 adult patients undergoing transesophageal echocardiography (TEE) for transcatheter SHD interventions, 429 (3.6%) patients had a major complication (composite of bleeding and esophageal and upper respiratory tract injury) [4]. The relative frequency of a major complication differed by procedure: 1.8% for transcatheter aortic valve implantation (TAVI), 8.6% for left atrial appendage occlusion (LAAO) procedure, and 2.5% for transcatheter mitral valve repair/replacement (TMVR). These findings were confirmed by a single site retrospective [7] as well as prospective study [8]. Independent factors associated with an increased risk of complex lesions were a longer procedural time under TEE manipulation (for each 10-min increment in imaging time, odds ratio: 1.27; 95% confidence interval: 1.01 to 1.59) and poor or suboptimal imaging quality (odds ratio: 4.93; 95% confidence interval: 1.10 to 22.02).

The need for an alternative imaging modality to guide SHD procedures arises not only from the risk of injury from the standard TEE probe, but also from the progression from use of general anesthesia to conscious sedation or monitored anesthetic care for some of the more common procedures. Intracardiac echocardiography has been proposed as an alternative, but its use is limited by cost, the need for additional vascular access, a significant learning curve and a limited field of view. Miniaturized three-dimensional (3D) transesophageal echocardiography probes (miniTEE) offer a promising solution by providing high-resolution imaging with a small probe that could be tolerated with conscious sedation, reducing the need for general anesthesia, and minimizing procedural complexity.

Three-dimensional Mini-Transesophageal echocardiography

Although intracardiac echocardiography (ICE) has been proposed as an alternative or adjunct to some SHD procedures which could obviate the need for general anesthesia [9, 10], a smaller three-dimensional (3D) phased array TEE probe could mitigate the risk of injury to the esophagus while providing a larger field of view and depth of imaging. Other disadvantages of ICE only procedures include a significant operator learning curve, the need for a second vascular access, and increased costs of a single-use catheter. A miniaturized TEE (miniTEE) probe could also be tolerated by sedated patients and has additional utility for adults with esophageal pathologies (i.e., strictures), being tested initially in the pediatric population [11]. A list of these smaller TEE probes is shown in Table 1

Table 1 Standard adult TEE and contemporary minitee probe characteristics

Table 2 summarizes the Key studies on TEE-related complications and minitee use in SHD. Briefly, a number of investigators have reported the use of these new imaging tools in a limited number of SHD procedures [12,13,14,15]. In a study of 202 patients undergoing atrial septal defect (ASD) or patent foramen ovale (PFO) closure, micro-TEE guidance without general anesthesia showed to be safe as TEE, without a significant difference in the residual shunt rate after closure [16]. In a study of 49 patients, Nienhuis et al. [12] explored the utility of a first generation 32-element phased array TEE transducer referred to as a microTEE probe (S8-3t micro-TEE, Philips Healthcare), compared to either standard TEE for the evaluation of left atrial appendage anatomy, or intracardiac echocardiography (ICE) for transseptal puncture. General anesthesia was used in 55% of cases. In cases where conscious sedation was used, the microTEE was not related to significant discomfort. Image quality obtained with the microTEE probe was however lower than with standard TEE (p = 0.04) and LAA dimensions were consistently smaller (p ≤ 0.2 for all measurements except depth). MicroTEE images were comparable to ICE images for interatrial septal anatomy (p = 0.13) but had a wider field of view.

The largest study of both the microTEE (32 elements) and miniTEE (48 elements) included 546 consecutive LAAO procedures that were performed in 5 European centers [13]. The probes used for this study included: S8-3t micro-TEE (Philips Healthcare), the 10T-D micro-TEE (GE Healthcare), and the S7-3t mini-TEE (Philips Healthcare); 368 (67.0%). LAAO procedures were attempted with micro-TEE guidance, and 178 (33.0%) patients were attempted with the mini-TEE probe. Technical success was achieved in 534 (98.0%) patients. Sixteen major periprocedural complications occurred in 15 (2.9%) patients yielding a procedural success rate of 97.0%. Conversion to general anesthesia was needed in 4 (0.7%) patients. When using TEE as imaging follow-up, the presence of peri-device leaks was detected in 64 (23.7%) of 270 patients: mild (> 0 and < 3 mm) in 32 (11.8%) patients, moderate (≥ 3 and ≤ 5 mm) in 30 (11.2%) patients, and severe (> 5 mm) in 2 (0.7%) patients. CT-based assessment detected residual LAA patency in 38 (18.8%) of 202 patients. The presence of device-related thrombus was detected in 21 (5.0%) patients. These results are consistent with reported outcomes in the literature [17]. Importantly, patients who underwent pre-procedural imaging with 3D TEE or CT had a higher technical success rate (100% vs. 95%), highlighting the need for advanced pre-procedural imaging when lower temporal/spatial resolution intra-procedural imaging modalities are used.

Table 2 Key studies on TEE-related complications and minitee use in SHD

Current commercially available minitee probes

In a retrospective multi-center study, the current miniTEE probe 9VT-D (GE Healthcare) was evaluated for image quality and feasibility of use for SHD procedures (Table 1, 2; Fig. 1) [14]. Excellent image quality (equivalent to standard TEE) was seen in 22 (73%) of patients. Only 3 patients had direct comparison between a standard TEE probe and miniTEE probe with parameters of 2D imaging, 2D Color Doppler, pulsed and continuous wave Doppler receiving equivalent scores of 5 out of 5 (excellent) but 3D imaging of the miniTEE probe received a score of 4 out of 5 in 2 of the patients. The probe was used to guide 8 SHD procedures performed without general anesthesia: transseptal puncture only (prior to cryoablation), LAAO and interatrial communication closure [14]. Other case reports support the use of this probe for LAAO [18]. However, the short duration of these procedures does not currently support the use of this imaging modality in more lengthy or complex procedures without general anesthesia.

Fig. 1

Transesophageal echocardiography probes. The relative sizes of the transesophageal echocardiography (TEE) probe head are shown

The X11-4T probe (Philips Healthcare) has recently become commercially available (Table 1; Figure 1)

This novel probe has the same number of piezo-electric elements as the larger X8-2T due to the PureWave (second generation of Single Crystal PureWave– technology which enables improved penetration in difficult patients, the ability to image a wide array of patients with a single transducer, and reduced clutter for a better detail endocardium) and the new xMatrix improved three matching layer technology provide a very wide bandwidth frequency response. With 2500 elements, imaging characteristics are similar to the X8-2T. (Fig. 2). The probe has been used in conscious sedation patients and can be used with echo-fluoro fusion technology with a recent case report showing its functionality in the successful performance of bioprosthetic mitral valve paravalvular leak closure without the use of general anesthesia [19].

Fig. 2

Intraprocedural imaging with the miniTEE probe during left atrial appendage occlusion (LAAO). Panel A shows the biplane image of the LAA for sizing the device. Panel B shows the implantation of a Watchman FLX device with the final 3D imaging of the device (panel C)

Operator training and image acquisition for miniTEE

The successful adoption of miniTEE technology in SHD procedures extends beyond hardware availability and patient tolerance and depends also on operator expertise. Although the smaller probe size improves patient comfort under conscious sedation, miniTEE presents unique technical nuances in image acquisition and interpretation. Compared with standard TEE, the miniTEE probe has a more flexible shaft and a smaller footprint, which can affect probe stability and fine control during complex imaging maneuvers. These physical differences necessitate deliberate training in handling techniques to achieve optimal acoustic windows, particularly in procedures that demand high-resolution, real-time guidance. Additionally, 3D imaging with miniTEE, while technologically feasible, may have a lower signal-to-noise ratio or narrower spatial resolution depending on probe generation and user technique. Operators must be proficient in adjusting gain, depth, and multiplanar reconstruction settings to compensate for these differences. Furthermore, image orientation and spatial relationships can be subtly altered with the miniaturized transducer, requiring recalibration of anatomical landmarks and interpretation strategies [20].

To address these challenges, formalized operator training is essential. This may include simulation-based instruction, proctored procedural experience, and dedicated didactics focused on the specific handling, imaging protocols, and interpretative skills unique to miniTEE. The development of standardized imaging checklists, procedural workflows, and quality benchmarks will be instrumental in reducing inter-operator variability and ensuring safe, high-quality outcomes. As adoption increases, incorporating miniTEE training into cardiology and echocardiography fellowships or certification programs may be warranted.

Expanded clinical utility of miniaturized TEE in pediatric and critical care settings

MiniTEE probes have significantly expanded the capabilities of perioperative and bedside cardiac imaging in patients for whom standard TEE probes are not feasible—particularly neonates, small infants, critically ill adults and patients with narrowing of the esophagus. In pediatric cardiac surgery, traditional pediatric TEE probes often cannot be used in patients < 5 kg due to concerns regarding airway compression, esophageal trauma, or hemodynamic instability [21, 22]. Initial attempts to address this limitation included the analysis of 22 successful intraoperative studies using a miniaturized ultrasound-tipped catheter in infants weighing 1.5–4.8 kg. Although diagnostic accuracy was limited by single-plane imaging and lack of thermal sensing, the study demonstrated feasibility and safety [23].

Subsequent advances in probe design have enabled multiplane imaging in very small patients. Toole et al. compared microTEE with standard pediatric multiplane TEE in infants < 5 kg, finding comparable diagnostic accuracy despite modestly reduced image quality, thereby supporting the use of microTEE in this fragile population [24]. Adding to this body of evidence, a prospective study evaluated the safety and utility of microTEE in 42 infants weighing ≤ 5 kg undergoing cardiac surgery [25]. The probe was successfully inserted in all patients without any adverse events or significant hemodynamic or ventilatory changes. Importantly, intraoperative TEE findings led to surgical revision in 6 patients (14%), emphasizing the clinical impact of this imaging modality. These results reinforce the role of miniTEE in enhancing intraoperative decision-making and safety in the smallest and most vulnerable surgical patients.

The miniTEE has also demonstrated increasing value in adult critical care and structural interventions. In one of the first adult applications, the ClariTEE probe helped avoid unnecessary surgical re-exploration in a hemodynamically unstable post-cardiac surgery patient by accurately identifying a non-tamponade fluid collection. Additional studies have confirmed the utility of miniTEE in diagnosing causes of circulatory collapse, guiding inotrope and fluid management, and optimizing care for patients on mechanical circulatory support such as VADs—where continuous esophageal imaging (up to 72 h) enables dynamic monitoring of right heart function and septal position. Moreover, the Philips microTEE has been used transnasally during transcatheter structural heart procedures under conscious sedation, offering adequate anatomic imaging without the need for general anesthesia [20, 26, 27].

Together, these findings underscore the versatility of miniTEE technology across a spectrum of clinical settings—from neonatal cardiac surgery to adult ICU care—offering high-value, low-risk imaging in patients previously excluded from transesophageal echocardiography due to size, tolerance, or hemodynamic instability.

Future directions and conclusion

With the rapid growth of SHD procedures and increasingly standardized procedural techniques, there is growing acceptance of minimalist strategies using conscious sedation. Because intra-procedural imaging guidance is essential for technical and procedural success, developing tools which may allow complex procedures to be guided without the need for general anesthesia has become a major focus of ultrasound manufacturers. This evolution requires imaging modalities that offer a balance of safety, efficiency, and diagnostic precision, with patient comfort during conscious sedation.

The current commercially available miniTEE probes, particularly those equipped with phased array technology and 3D capabilities, represent a promising advancement. However, although these devices have demonstrated procedural feasibility, and safety in select SHD procedures using conscious sedation, there are many limitations that should be emphasized (Graphical abstract). First, the published data comparing image quality and procedural feasibility against standard TEE probes have been primarily evaluated a narrow range of anatomic structures, the LAA and interatrial septum, with authors noting the inadequate acoustic penetration of the probes for more complex or far-field procedures such as mitral or tricuspid interventions. Second, studies have suggested that the image resolution may also be limited with underestimation of LAA dimensions that require pre-procedural 3D TEE or CT imaging to improve technical success of LAAO. The greatest utility to date may be in the pediatric population and in adults who cannot tolerate standard TEE probes (critically ill, or esophageal stricture). However, as crystal technology continues to improve and operator experience grows, the utility of the miniTEE probe may continue to expand, potentially providing adequate imaging in a broader range of interventions. In an unpublished case series of the author’s (RTH), the miniTEE probe has been used to evaluate post-transcatheter aortic valve implantation function immediately following a conscious sedation procedure in a patient with renal dysfunction and poor transthoracic imaging windows (Fig. 3) as well as mitral valve transcatheter edge-to-edge repair under general anesthesia in a patient with esophageal stricture (Fig. 4). These cases highlight other possible clinical scenarios in which the miniTEE probe may improve procedural outcomes and expand access to care. Continued research, including prospective trials comparing miniTEE to standard TEE in complex SHD cases, is needed to better define the limits and full potential of this technology.

Fig. 3

Post-implant imaging with the miniTEE probe during transcatheter aortic valve implantation (TAVI). This case shows the use of the X11-4T phased array miniTEE probe during a transcatheter aortic valve implantation procedure under monitored anesthetic care. The patient had baseline renal dysfunction and in order to reduce contrast use, the probe was inserted immediately following the TAVI implantation to a mid-esophageal imaging level. Panel A shows biplane color Doppler showing a non-obstructed left main coronary artery. Panel B shows repositioning of the biplane image to the left ventricular outflow track and trivial paravalvular regurgitation at the site of a calcific nodule posteriorly. The probe was advanced to the deep transgastric (TG) level to image flow across the transcatheter valve. Pulsed wave and continuous wave Doppler (panel D) showed excellent valve hemodynamics

Fig. 4

Imaging for mitral transcatheter edge-to-edge repair (M-TEER). In this case of an 83 year old patient with esophageal stricture, the X11-4T miniTEE probe was used to guide the M-TEER procedure under general anesthesia. Baseline imaging showed adequate mitral valve orifice area (MVOA, panel A) with severely increased effective regurgitant orifice area (EROA, panel B). Three-dimensional (3D) reconstruction could be used to guide introduction of the catheters and positioning of the device (panel C) with grasping of the mitral valve leaflets (panel D) performed using two-dimensional imaging for higher temporal/spatial resolution. After placement of the M-TEER devices, the final MVOA by 3D planimetry of the double orifice was 2.5 cm [2] with EROA of 0.07 cm [2] (panel D) consistent with very mild residual mitral regurgitation