EsoFLIP for Esophageal Dilation: Proposed Advantages

Abstract

Purpose of review:

The EsoFLIP® integrates impedance planimetry technology into a dilator balloon capable of dilating from diameters between 10-30mm via controlled volumetric distension while providing real-time visualization and objective measurement during the dilation procedure, potentially negating the need for fluoroscopy. This review aims to describe the use and application of EsoFLIP® and the potential advantages this novel technology may afford.

Recent findings:

Small pilot and retrospective studies demonstrate EsoFLIP® feasibility and safety, but larger studies are needed to understand its impact on clinical outcomes.

Summary:

EsoFLIP® is an appealing new technology that offers advantages in therapeutic dilation of the lower esophageal sphincter in achalasia or of esophageal strictures due to previous surgery, gastroesophageal reflux disease, or radiation.

Introduction:

Therapeutic dilation performed with sedated upper endoscopy is a safe and effective procedure to improve dysphagia occurring from benign esophageal strictures and rings [1,2]. Various types of esophageal dilators exist, including bougies that are typically passed over a wire with the endoscope removed, and balloons that can be passed through-the-scope (TTS) or over a wire. Standard dilator sizes range from 6 – 20mm. Bougies and some balloons offer a single size per dilator, while multi-size balloons typically provide three different sizes in a range of 2-3mm. Additionally, pneumatic dilation of the lower esophageal sphincter (LES) utilizing larger caliber balloons (30, 35, or 40mm) is an effective treatment modality in achalasia and is also sometimes utilized in post-fundoplication dysphagia [3,4]. Pneumatic dilation balloons are passed over a wire and often positioned using fluoroscopy.

A novel, commercially-available esophageal dilator is the EsoFLIP® (Medtronic Inc, Shoreview, MN, USA). Similar to its diagnostic counterpart the functional luminal imaging probe (FLIP) (EndoFLIP®; Medtronic Inc), the EsoFLIP® utilizes high-resolution impedance planimetry to measure luminal diameters along the length of the balloon, thus providing a real-time graphical depiction of the esophageal lumen and, additionally, performance of the dilation. This review aims to describe the EsoFLIP®, its use and application, and potential advantages it may provide.

The EsoFLIP®

The EsoFLIP® integrates the EndoFLIP® impedance planimetry system technology into a balloon dilation catheter (Figure 1). Impedance planimetry technology applies Ohm’s law to measure luminal cross-sectional area (CSA): voltage = current x resistance and resistance = conductivity/(distance x CSA). Based on the assumption of a circular lumen, the FLIP system converts the measured CSAs to output display in diameters.

Figure 1. The EsoFLIP®.

A. The EsoFLIP® dilator. A wire can be threaded through a hole in the cap at the tip of the catheter (white arrow) to facilitate placement and positioning of the dilator; this wire runs externally to the balloon. B. Positioning of the balloon across and centered at the esophagogastric junction. (EGJ). C. Positioning can be visualized by the real-time display on the EndoFLIP® system via the hour-glass appearance with the waist representing the narrowing at the EGJ. The 14 serial diameter measures are also displayed with estimated diameter measures in mm at the right. The image here represents a 30-ml fill volume in the 30mm maximum diameter balloon (ES-330) in a patient with achalasia immediately prior to a therapeutic dilation – the diameter at the EGJ-waist measures 8.4mm. Original figure used with permission from the Esophageal Center at Northwestern.

While the EsoFLIP® and EndoFLIP® use the same technology and have various similarities, they are different devices with different applications: the EsoFLIP® provides therapeutic dilation while the EndoFLIP® is a diagnostic device (Table 1). Both the EsoFLIP® and the EndoFLIP® are single-use assemblies that consist of a thin catheter with a balloon mounted on the distal end; the balloon is tapered at both ends and assumes a cylindrical shape in the center upon filling. The cylindrical portion of the FLIP balloon houses the multiple impedance planimetry channels that are serially-spaced along the length of the FLIP balloon and provide measurement of the balloon dimensions as the balloon is filled. Filling and emptying of the balloon are controlled through input with the EndoFLIP® system at rates that are adjustable up to 60ml/minute for filling and 30ml/minute for emptying. The EndoFLIP® system also displays the estimated balloon diameters (as well as pressure and distensibility with the EndoFLIP®) in real-time thereby providing a dynamic illustration of the esophagus.

Table 1.

Comparisons of EsoFLIP® and EndoFLIP®

	EsoFLIP®	EndoFLIP®
Use	Therapeutic	Diagnostic
Balloon	Rigid	Compliant
Dimensions (by product number)	ES-330: -7cm length -dilation up to 30mm diameter ES-320: -7cm length -dilation up to 20mm diameter	EF-322: -16cm length EF-325: -8cm length
Resolution (by product number)	ES-330: -5mm spacing of 14 channels ES-320: -5mm spacing of 14 channels	EF-322: -10mm spacing of 16 channels EF-325: -10mm spacing of 16 channels
Pressure sensor	Not included  - Can attach external pressure monitor	Present

The EsoFLIP® consists of a rigid balloon that can perform dilation with volume-controlled filling of the balloon (Figure 1). EsoFLIP dilation balloons are indicated for clinical use in adult patients to dilate the LES in achalasia (hydraulic dilation) and to dilate esophageal strictures due to esophageal surgery, primary gastroesophageal reflux disease, or radiation.

The EsoFLIP® is available in two sizes to facilitate dilation up to a 30mm diameter (ES-330) or up to a 20mm diameter (ES-320) at the maximum fill volumes. However, because the fill volume of the balloon is controlled, dilation to smaller sizes than the maximum dilation size (e.g. 16mm or 25mm) can be achieved with control of the fill volume and visualization of the real-time FLIP display. The tip of the EsoFLIP® catheter is comprised of a plastic cap with an open channel through which a wire can be passed to facilitate passage and positioning of the dilator (Figure 1A); the channel only extends the length of the cap, thus the wire runs externally to the EsoFLIP® catheter and balloon. Differing from the EndoFLIP®, a pressure sensor is not included with the EsoFLIP®, but an external pressure monitor can be attached to the EsoFLIP catheter assembly using a 3-way valve [5*].

On the other hand, the Endophilic® consists of a flimsy, infinitely compliant (within a specified fill range) balloon that also contains a pressure sensor to measure the intraballoon (thus, distensive) pressure associated with the volumetric distension. Hence, the EndoFLIP® provides assessment of the relationship of esophageal dimensions and pressure (i.e. distensibility) and is indicated for use as an adjunctive test in the comprehensive evaluation of patients with symptoms consistent with gastrointestinal motility disorders.

Use of the EsoFLIP®: Dilation technique

Preparation:

Clinical evaluation and endoscopic assessment are performed initially to dictate appropriate indication for balloon dilation similar to other dilation modalties [6]. The use of the EsoFLIP® may facilitate 30mm dilation in achalasia without requiring fluoroscopy (see Advantages below); however, arranging for fluoroscopy availability may still be helpful in some clinical scenarios to complement positioning of the dilator.

If dilation using EsoFLIP® is planned, preparation of the EsoFLIP® assembly prior to the endoscopy should be considered. The manufacturer-recommended external pressure sensor (range of 0 – 5 atm) can be attached to the assembly using a three-way valve. The EsoFLIP® catheter can then be inserted into the EndoFLIP® system and the ‘Pre-Use Check’ (automated preparation process) can be initiated per manufacturer instructions. If performance of EsoFLIP® dilation is not predetermined, the dilator preparation process can be initiated at the time of the endoscopy, though it is worth noting that the automated pre-system check and catheter purge cycles take several minutes to complete.

The ‘Settings’ of the EndoFLIP® system should be adjusted to facilitate balloon filling to the maximum fill volumes: 75-ml for the 30mm dilator, 42ml for the 20mm dilator. Adjustment of filling and emptying rates may also be considered, though setting to the maximum rates of 60ml/minute for filling and 30ml/minute for emptying is typically sufficient.

Additionally, a wire with a floppy, thin tip should be available. As the wire runs external to the dilator balloon, we recommend removal of the wire prior to performing dilation (especially those to 30mm). The end of some spring-tipped wires may be too wide to withdraw and remove through the tip of the EsoFLIP®.

Performance of EsoFLIP® dilation:

During the initial endoscopic assessment, measurement from the incisors to the area of target for dilation [e.g. stricture or esophagogastric junction (EGJ) in achalasia] should be noted. This distance can be marked on the FLIP catheter (measurements on the catheter are referenced to the center of the dilator balloon) to aid initial positioning of the balloon – positioning during dilation will be directed based on the real-time FLIP output (Figure 2). The wire (floppy-end first) should be introduced in the standard fashion through the accessory channel of the endoscope and passed until it is visualized well beyond the end of the endoscope and dilation target. After removal of the endoscope (while maintaining wire positioning), the tip of the wire is threaded through the tip of the EsoFLIP® catheter. The EsoFLIP® balloon should be lubricated and then advanced over the wire through the mouth and into the esophagus to its ultimate position across the dilation target; counter-traction on the wire during advancement may aid with balloon passage. For dilations performed without fluoroscopy, the endoscope should be reintroduced to visually confirm positioning of the EsoFLIP® across the dilation target prior to balloon filling.

Figure 2. EsoFLIP® dilation procedure.

The real-time FLIP images (top) with EsoFLIP® fill volume by time (middle) over the course of the EsoFLIP® dilation procedure during a 30mm dilation performed in a patient with achalasia are displayed. A) Initial positioning and esophagogastric junction (EGJ) waist measurement at the 30-ml fill volume; positioning supplemented here with the fluoroscopy (bottom); the EsoFLIP® balloon is outlined in white dashed line to aid visualization. The impedance planimetry electrodes within the balloon are radiopaque. B) After removal of the wire, the balloon is filled while the positioning is maintained with visualization of the waist. C) The 30mm diameter dilation target is achieved at the maximum fill volume; complete effacement of the balloon is achieved (and thus the waist is no longer visible). The corresponding fluoroscopy image (bottom) demonstrated that the positioning across the EGJ was maintained in this example. Direct visualization with the endoscope should be considered for dilation performed without fluoroscopy. D) The EGJ waist can be measured after dilation to gauge a response to the dilation. Original figure used with permission from the Esophageal Center at Northwestern.

The primary determinant of appropriate positioning of the EsoFLIP® is by identifying the waist that represents the dilation target (e.g. stricture or EGJ in achalasia) on the real-time, 3-D display; Figure 2A. Once positioned across (or slightly distal to) the target, the EsoFLIP® balloon should be partially filled to facilitate visualization of the waist. FLIP balloon filling and emptying are manually controlled via the touch pad on the EndoFLIP® system. This partial filling is typically performed to 30ml for ES-330 balloon or 20ml for ES-320 balloon (though lower fill volumes may be sufficient or necessary depending on the degree of stricture). Diameter and possibly distensibility (if an external pressure monitor is being utilized; distensibility = cross-sectional area divided by pressure) of the waist can be recorded at the preliminary fill volume [5*].

Once appropriate positioning of the balloon relative to the dilation target is achieved, the guidewire should be removed prior to additional balloon filling. During balloon filling, the catheter positioning should be adjusted to center the waist on the dilator balloon (Figure 2B). To perform the dilation, the EsoFLIP® balloon can then be filled to the volume required to achieve the desired dilation size as gauged by the measurement of the waist on the real-time display. Dilations in achalasia to 30mm or for stricture dilation to 20mm typically require filling of the EsoFLIP® to the maximum volume (75ml or 42ml, respectively). There can be a small lag between pressing the stop-filling button on the FLIP system and the increase in diameter at the EsoFLIP® waist (potentially related to fluid flow through the long catheter). Thus, if dilation of a stricture to a predetermined diameter is being performed, the filling should be stopped when the waist is 2-3mm lower than the target dilation size. Once the EsoFLIP® waist achieves a stable measure, additional fluid can be added in small increments until the desired dilation size or effect is achieved.

As the EsoFLIP® is filling, the positioning of the waist should be continually visualized on the FLIP display and tension on the catheter or slight repositioning may be required to maintaining positioning of the waist centered within the balloon. The catheter should be securely held to prevent distal migration of the balloon. When complete effacement of the EsoFLIP® balloon is achieved, the waist utilized for positioning is no longer visible (Figure 2C). Therefore, concurrent endoscopic visualization of dilations to balloon effacement should be considered to confirm maintenance of positioning in dilations performed without fluoroscopy (especially in achalasia).

Once the balloon is filled to the desired dilation size and dilation maintained for the desired duration, the balloon is then emptied while continuing to maintain positioning centered on the dilation target. The balloon emptying can be halted at the same volume as the initial positioning fill-volume (e.g. 30ml for ES330 or 20ml for ES320) and the diameter +/− distensibility of the waist can be reassessed (Figure 2D). These measures may serve as a method to immediately monitor dilation response (see Advantages below) [5*].

Post-procedural monitoring can occur per standard physician or center practices as based on the clinical scenario.

Proposed advantages of dilation with EsoFLIP®

The real-time objective assessment of dilation provided by impedance planimetry with the EsoFLIP®, as well as the controlled volumetric manner in which the dilator balloon is filled, offers several potential advantages over other balloon dilators. While clinical data associated with this novel device remains limited, the safety and feasibility of EsoFLIP® balloon dilation was reported in porcine studies and a study of 10 human patients with achalasia [5*,7]. The latter pilot study investigated the feasibility of 30mm EsoFLIP® dilation and was successful with reduction in symptom scores at 1 week and 3 months after dilation; and no major complications occurred [5*]. A retrospective study also reported the use of EsoFLIP® in 3 pediatric patients with epidermolysis bullosa and esophageal stenosis. They reported cases in which it allowed for larger diameter changes than TTS dilation, longer lasting symptom response, and shortened procedure and fluoroscopy times when compared to EndoFLIP® + TTS dilation [8*].

Potential advantages of EsoFLIP® dilation are listed and discussed below:

Dilation without fluoroscopy

Visualization of the EsoFLIP® waist via the real-time impedance planimetry output may facilitate performing dilation, in particular for 30mm dilations, without the need for fluoroscopy. This reduces radiation exposure and may aid with the logistics associated with performing endoscopy with fluoroscopy (e.g. access to equipment). While the waist is visible, movement of the dilator balloon with relation to the stenosis can be observed and corrected upon in real-time. However, it is worth noting that at complete effacement, the balloon waist is no longer visible on the real-time display (Figure 2C), thus concurrent endoscopic visualization of the balloon may be considered.

Control of dilation sizes

Another advantage is the ability to control the dilation size to any interval dimension via the volumetric control of balloon filling. The real-time output of measurement at the balloon waist allows for controlled dilation to any diameter needed to generate the desired dilation effect (e.g. mucosal disruption at a stricture) ranging from 10 to 20mm with the ES320 balloon. This contrasts with the use of a single-size or even multi-size dilator balloon that may require use of multiple balloons if the initial balloon selection does not achieve the desired effect.

Further, the 30mm EsoFLIP® allows for dilation to a range of diameters including 21 to 29mm; a window between which traditional TTS dilation and pneumatic dilation balloons cannot reliably achieve. While studies on clinical outcomes of dilations to these intermediate ranges are unavailable, this conceptually may be helpful in inconclusive clinical cases in which there is reluctance to fully commit to a 30mm dilation. Examples may include a patient with a manometric diagnosis of EGJ outflow obstruction, representing a suspected (but inconclusive) diagnosis of achalasia, or a patient with post-fundoplication dysphagia that did not respond to 20 mm dilation. In these scenarios, endoscopic assessment after dilation to intermediate sizes (e.g. 22 mm or 25 mm) could be performed and if mucosal injury is observed, dilation could be concluded at that point without additional dilation to a greater degree. This could potentially lower the risk of perforation. Dilation in achalasia to sizes of 21-29 mm could also be very appealing in the treatment of pediatric achalasia; however, at present the EsoFLIP® is only approved for use in adult patients.

Measurement of stricture size and assessment of dilation effect

The EsoFLIP® dilation provides the potential to objectively measure stricture size and additionally, to objectively assess the response to dilation immediately following dilation. Studies utilizing the EndoFLIP® have demonstrated utility in measuring stricture size, particularly in eosinophilic esophagitis [9,10]. Additionally, measurement of EGJ distensibility with the EndoFLIP® in achalasia facilitates evaluation of response to achalasia treatment (myotomy or pneumatic dilation) with associations to clinical outcomes both at the time of treatment [11,12] and upon assessment during follow-up [13, 14, 15*].^1-3 However, while there is likely correlation of EndoFLIP® and EsoFLIP® measurements, there could be some contribution of the rigid therapeutic balloon to EsoFLIP® measures, thus potentially posing a challenge to delineate the line between where measurement ends and dilation begins.

Limitations of EsoFLIP® dilation:

While the EsoFLIP® provides potential advantages for dilation, it also carries some limitations. Some aspects of the device can limit the ease of the procedure, such as the lack of ability to pass through-the-scope, the external guidewire that requires removal prior to dilation, the requirement for an external pressure monitor, and the time required to fill and empty the dilator balloon. Additionally and as expected given the novelty of the device, there are few studies that report on EsoFLIP® utilization or effectiveness. However, with ongoing clinical utilization, future outcome studies, and potential future device modifications, these limitations will likely be addressed.

Conclusions:

The EsoFLIP® is a novel dilation balloon that provides real-time, objective visualization and monitoring of therapeutic dilation as it is being performed via controlled volumetric filling. Therefore, this technical advancement in therapeutic dilation can potentially enhance performance of dilation by confirming appropriate positioning for controlled dilation, while reducing the need for fluoroscopy (and associated radiation). While future studies remain needed to further evaluate its utilization and associated outcomes, the EsoFLIP® represents an appealing addition to the treatment toolbox of esophageal disorders.

Key Points:

• EsoFLIP® is a balloon dilator that incorporates high-resolution impedance planimetry, thus allowing for real-time measurement of luminal diameters as well as performance of therapeutic dilation.

• EsoFLIP® can be used for dilation of the lower esophageal sphincter in achalasia or of esophageal strictures due to previous surgery, gastroesophageal reflux disease, or radiation.

• The potential advantages of EsoFLIP® balloon dilation include the ability to dilate over a larger range of diameters with one balloon (10-30 mm) in a controlled manner, the potential avoidance of fluoroscopy (and radiation), and the ability to assess esophageal dimensions before and after treatment.

• Small studies demonstrate the feasibility and safety of EsoFLIP® balloon dilation, but more robust studies are needed to further evaluate its application and associated clinical outcomes.