Use of Endoflip – Impedance Planimetry System: For Which Indications?

Abstract

Background

The functional lumen imaging probe (EndoFLIP), which utilizes impedance planimetry, has emerged as a valuable tool for a more comprehensive evaluation of esophageal physiology and pathophysiology beyond traditional high-resolution manometry.

Summary

EndoFLIP, including its variations EndoFLIP and EsoFLIP, measures intraluminal distensibility and compliance by assessing diameter and distension pressure using balloon catheters.

Key Messages

This technology is applicable to various organs such as the esophagus, stomach, and anorectal region, and serves in both diagnostic and therapeutic contexts, especially in ambiguous clinical cases.

Introduction

In the last 2 decades, functional gastrointestinal diagnostics, particularly motility testing, have significantly evolved. High-resolution manometry (HRM) has become the gold standard for esophageal motility testing. The evolution of esophageal function testing has led to advanced and complementary techniques like impedance measurements with EndoFLIP, which assesses mechanical properties and distensibility rather than just contractile patterns and bolus transit. Initially tested on the esophago-gastric junction (EGJ), the first commercial EndoFLIP device was introduced in 2009 by Crospon (now Medtronic, Minneapolis, MN, USA) [1–3].

The EndoFLIP high-resolution impedance planimetry device enables dynamic assessment of the biomechanical properties of the gastrointestinal (GI) tract’s sphincters or tubular organs during volume-controlled distention, by providing a three-dimensional image of the esophageal lumen. It uses a balloon catheter with impedance electrodes to calculate luminal diameter, cross-sectional area, and distension pressure, allowing for the evaluation of luminal distensibility and compliance. This provides a more detailed understanding of sphincter function compared to stationary manometry and helps to evaluate esophageal wall stiffness. Initially, EndoFLIP was used to evaluate the EGJ in gastroesophageal reflux disease (GERD) and achalasia patients as well as treatment outcomes after fundoplication or esophageal myotomy. Over the past decade, its use has expanded to other esophageal conditions like eosinophilic esophagitis and other parts of the GI tract, including the stomach, pharyngeal, and anorectal regions.

EsoFLIP, a therapeutic variant, combines diagnostic and therapeutic functions and is used for dilating GI tract stenoses. Emerging evidence supports FLIPs use as a complementary diagnostic tool when standard tests are inconclusive.

This review article aims to summarize the available data in literature and latest advancements on the clinical applications of EndoFLIP in the GI tract.

Methods

Impedance Planimetry Technology

Impedance planimetry was first adapted for gastrointestinal use in the late 1980s, facilitating compliance or distensibility assessment and providing insights into EGJ function in conditions like gastroesophageal reflux disease (GERD) and achalasia. The EndoFLIP system, developed by Crospon and later Medtronic, received FDA approval in 2010 (version 1.0) and 2017 (version 2.0 with FLIP topography) [4] (see Fig. 1). EndoFLIP measurements utilize impedance planimetry, a technique that applies Ohm’s law to determine luminal cross-sectional area (CSA). By measuring the voltage across electrodes within a balloon filled with conductive fluid, CSA is calculated using the known electrode distance and fluid conductivity. For clinical applications, the EndoFLIP system converts CSA [CSA = π × (diameter/2)²] to diameter for real-time 3D imaging. In the esophagus, balloon pressure increases linearly with CSA and exponentially with wall tension, maintaining stable compliance [5].

Fig. 1.

EndoFLIP system.

Endoflip Catheter

The EndoFLIP system comprises a 240-mm long catheter with a 3-mm outer diameter and a highly sensitive balloon at its tip. The balloon contains 16 paired impedance electrodes and a solid-state pressure transducer at the distal end. The catheter is available in two lengths: EF-322 (16 cm) and EF-325 (8 cm), each designed for different clinical applications (see Fig. 2). During an EndoFLIP study, excitation electrodes at both ends of the balloon emit a continuous low electric current, and the voltage is measured to determine the CSA. The ballon is automatically filled with conductive fluid from an 80-mL syringe that is controlled by the Endoflip™ impedance planimetry system. The EF-325 uses a 0.3% NaCl solution, while the EF-322 uses a 0.75% NaCl solution. The EndoFLIP system’s balloon is infinitely compliant within its fill volume limits, conforming to the esophageal lumen and allowing for accurate measurement of distensive properties and esophagogastric junction (EGJ) function.

Fig. 2.

Endoluminal functional lumen imaging probe catheter (filled).

Endoflip^™ Impedance Planimetry System Metrics

Parameters measured by EndoFLIP include distensibility index (DI), CSA, balloon diameter, and intraballoon pressure (IBP). During a typical examination, the balloon is inflated in 10 mL increments up to 70 mL. Measurements of 16 CSA and pressure points are simultaneously recorded at a 10-Hz sampling rate, with CSA values taken at intervals based on electrode spacing. The narrowest area within the 16 recording sites is assessed in real-time using a 3-dimensional (3-D) display, providing both visual and numerical diameter measurements. The EndoFLIP system utilizes a pressure transducer to measure IBP (mm Hg), allowing for the calculation of distensibility, expressed as the DI (mm²/mm Hg). This index represents the ratio of the narrowest CSA to the concurrent distension pressure at each volume increment. These measurements are dynamic, with CSA and pressure fluctuating due to respiratory and vascular artifacts as well as esophageal contractions. This enables the assessment of biomechanical properties such as wall tension, stiffness, and strain, as well as thresholds for inducing secondary peristalsis. The system’s flexibility and real-time imaging capabilities facilitate clinical evaluations of esophageal and EGJ distensibility [3, 5–7].

The former FLIP 1.0 module converted impedance recordings to CSA measurements along the catheter’s length, while the FLIP 2.0 module uses diameter topography to display diameter-pressure changes over time. This allows for the assessment of motility patterns across the tubular esophagus and the EGJ.

The combination of EGJ distensibility and esophageal body contractile response to distention can lead to a EndoFLIP panometry diagnosis, guiding further evaluation and treatment. The DI ranges from 3.1 to 9.0 mm²/mm Hg in normal subjects, with values below 2.0 mm²/mm Hg indicating potential EGJ outflow obstruction (EGJOO). Elevated EGJ-DI values are associated with GERD. The distensibility plateau represents the fixed luminal diameter despite increasing pressure, relevant for assessing esophageal bolus transit [8–10].

The EF-322 catheter with FLIP topography evaluates esophageal body contractile pattern in response to volumetric distention, identifying repetitive antegrade contractions (RACs) in normal subjects. RACs are defined as three or more consecutively and consistently spaced antegrade contractions. Hypercontractile or spastic motor disorders may present as repetitive retrograde contractions (RRCs), which are defined as three or more consecutive retrograde contractions. Absent contractility indicates a lack of esophageal response. Disordered or diminished contractile responses (DDCRs) exhibit patterns that do not meet the criteria for normal, hypercontractile, or absent responses and may suggest ineffective esophageal motility [6].

EndoFLIP Catheter Placement

Prior to conducting an upper gastrointestinal (GI) EndoFLIP study, a standard endoscopy, usually performed in sedated patients or intraoperatively under general anesthesia, is used to visually examine the mucosa and clear any esophageal or gastric contents. After withdrawing the endoscope, the empty balloon catheter is zeroed to atmospheric pressure and introduced trans-orally or trans-nasally into the esophagus or further into the stomach and pylorus. Typically, the catheter can be reliably positioned without endoscopic guidance, but if resistance is encountered, the catheter should be withdrawn and reinserted. Endoscopic guidance is recommended for known esophageal diverticula, but the endoscope should be removed before starting the protocol. Unlike the esophagus, catheter placement in the pyloric sphincter requires endoscopic guidance and sometimes the use of endoscopic forceps or a snare. Optimal positioning is achieved when the balloon straddles the EGJ or the pylorus, appearing as an hourglass shape on the EndoFLIP image at a low fill volume (20–30 mL). Correct positioning depends on the balloon type and the area being examined. The catheter may need adjustment during the study due to esophageal contractions. Visual confirmation of placement can be achieved by reinserting the endoscope, but it should be removed before balloon inflation to avoid affecting distensibility measurements [11].

EndoFLIP Study Protocol

Various EndoFLIP study protocols exist, with differences in patient sedation (conscious sedation or general anesthesia), placement method (oral or nasal), and pressure reference (atmospheric or gastric). The EndoFLip protocol involves the controlled inflation of the balloon, using an electro-hydraulic pump with conductive fluid to achieve a baseline volume of 20–30 mL, contingent upon the specific balloon type being utilized. Following this initial inflation, a stepwise filling process is executed, wherein a proposed protocol is adhered to. In the case of the 16 cm balloon, the initial filling volume is set at 30 mL, with subsequent increments of 10 mL up to 70 mL if required. Conversely, for the 8 cm balloon, the initial volume is set at 20 mL, then incrementally increased to 50 mL. The monitoring system displays a diameter topography image and provides values for various parameters such as diameter, CSA, DI, and IBP at designated filling volumes. CSA and pressure measurements, and consequently distensibility assessments, can vary depending on the degree of volume distension. Hence, measurements are obtained at stable distension volumes at each volume increment over a sufficient period, typically 15–30 s, to account for fluctuations related to respiration and esophageal contractions. It’s noted that normative data is most robust at certain fill volumes, namely 60 mL for the EF-322 catheter and 40 mL for the EF-325 catheter. Fill volumes of 70 mL are recommended in certain situations where adequate distension is required for accurate CSA assessment. Ideally, an assistant operates the EndoFLIP probe and records data, allowing the endoscopist to focus on the scope and adapt balloon placement as needed. At the end of the protocol, the balloon should be emptied to 10 mL or less and then be removed [6, 9].

Use of the Functional Luminal Imaging Probe in Clinical Practice

Use of EndoFLIP in the Esophagus

Assessing the Lower Esophageal Sphincter Function

Early studies on esophageal distensibility mainly focused on EGJ and have since expanded to various esophageal pathologies [3, 12]. By measuring distensibility, EndoFLIP sheds light on both obstructive and reflux-related processes at the lower esophageal sphincter (LES) and complements the assessment of gastrointestinal motility disorders, particularly achalasia, EGJ outflow obstruction and GERD. It is not standalone but enhances the understanding of EGJ dynamics and esophageal wall stiffness. Real-time EndoFLIP interpretation can potentially obviate the need for HRM in specific clinical scenarios, given its sensitivity to detecting conditions like achalasia and helps to confirm true obstructions when manometry indicates EGJ outflow issues. Although previously limited by a lack of normative data, recent studies involving healthy controls have defined normal EGJ distensibility as an EGJ-DI >2.8 mm²/mm Hg and a maximum EGJ diameter >18 mm [8, 13]. EndoFLIP is also effective in guiding real-time therapeutic interventions during procedures.

Achalasia. Achalasia, characterized by LES dysfunction and abnormal tubular peristalsis, is traditionally diagnosed using HRM. Esophageal manometry offers high sensitivity and can identify three distinct achalasia subtypes. However, manometry may yield inconclusive results, especially in cases with borderline pressure values or conflicting findings from other diagnostic modalities. The EndoFLIP has demonstrated high sensitivity in detecting motility abnormalities in patients diagnosed with achalasia [9]. It is also effective in identifying achalasia in patients who do not meet the HRM criteria of the Chicago Classification v4.0 but exhibit decreased EGJ-DI or abnormal esophageal contractions [14–16]. EndoFLIP has been suggested as a reliable diagnostic tool during endoscopy, potentially eliminating the need for HRM [17]. However, HRM remains the gold standard for diagnosing achalasia, with EndoFLIP providing supplementary information. Studies have consistently shown that treatment-naive achalasia patients exhibit significantly reduced EGJ-DI values compared to healthy controls when assessed with EndoFLIP [9]. This metric is particularly useful as it directly correlates the degree of luminal opening with bolus flow, which is conceptually more relevant than LES relaxation alone [14, 18]. EndoFLIP can be used intraoperatively during laparoscopic Heller myotomy (LHM) or peroral endoscopic myotomy (POEM) and helps to assess the adequacy of myotomy in real-time, thus is useful in predicting and assessing treatment outcomes [19–23]. This real-time feedback can help tailor the myotomy and fundoplasty to balance dysphagia relief and GERD prevention. It has been shown that an increase in the EGJ-DI after pneumatic dilation, POEM or LHM predicts clinical response, allowing for appropriate follow-up and scheduling of procedures [24, 25]. In post-treatment evaluations, the EGJ-DI has been identified as the most useful measure of EGJ opening [25]. Research indicates that patients with poor symptomatic outcomes after treatments such as pneumatic dilation or LES myotomy often have lower EGJ-DI values, typically below 2.8–2.9 mm²/mm Hg, compared to those with better outcomes [26, 27]. A multi-center study found that a lower EGJ-CSA at a 30-mL fill volume correlated with poorer symptomatic outcomes, while higher EGJ-CSA was associated with GERD [21]. Another study has shown that a change in EGJ-DI of more than 1.8 mm²/mm Hg after dilation accurately predicted symptomatic improvement [28] and another study found an optimal cut-off value of 272% change in DI for a good clinical response following POEM [29] (see Fig. 3a, b).

Fig. 3.

a EndoFLIP distensibility measurement in the esophagus before and after myotomy in an achalasia patient undergoing POEM (30 mL ballon filling). b EndoFLIP distensibility measurement in the esophagus before and after myotomy in an achalasia patient undergoing POEM (40 mL ballon filling).

Additionally, esophageal dilation balloons incorporating EndoFLIP technology are available, offering a potential alternative to fluoroscopy for achalasia dilation as a therapeutic intervention. A recent study demonstrated the feasibility and short-term effectiveness of using a EndoFLIP-based hydraulic dilation balloon, which can identify the EGJ in real-time to position the balloon accurately [30]. This method holds promise for improving achalasia treatment.

Esophagogastric Junction Outflow Obstruction (EGJOO). EndoFLIP plays a pivotal role in evaluating non-achalasia EGJOO. EGJOO, characterized by elevated integrated relaxation pressure (IRP) and intrabolus pressure on HRM, presents diagnostic and therapeutic challenges due to its heterogenous etiologies including mechanical obstruction, achalasia, or an artifact of the manometry catheter, and often requires additional methods like fluoroscopy or EndoFLIP to confirm clinically relevant EGJ obstruction [15]. In a validation study, EGJ-DI thresholds of 3.0 mm²/mm Hg or 2–3 mm²/mm Hg with maximum EGJ diameter >12 mm were indicative of clinically relevant EGJOO in 93% of patients with EGJOO [13]. Studies comparing EndoFLIP with HRM demonstrate EndoFLIP’s accuracy in detecting EGJOO. In a retrospective study of 34 patients with idiopathic EGJOO, all with a normal EGJ-DI (>3 mm²/mm Hg) who were treated conservatively had symptomatic improvement, although 78% with an abnormal EGJ-DI (<2 mm²/mm Hg) treated with achalasia-type therapy also improved [31]. Values in the borderline range require further evaluation by assessing the maximal diameter attained when pressures are greater than 20 mm Hg [9]. Although data are less robust with the 8-cm catheter, the same values could be extrapolated during the 40 mL distention volume [32]. Adjunct testing, such as a barium esophagogram could provide further clarification.

In conclusion, EndoFLIP offers a dynamic and comprehensive evaluation of the EGJ, it provides significant advantages in the diagnosis and management of achalasia and EGJ outflow obstruction and could provide guidance in therapeutic interventions.

Gastroesophageal Reflux Disease. EndoFLIP has been explored as a diagnostic tool for GERD, but evidence supporting its routine use in GERD diagnosis is still evolving. Impaired EGJ anti-reflux barrier function is implicated in GERD pathogenesis, suggesting potential utility of EndoFLIP in evaluating EGJ distensibility in GERD diagnosis. Initial studies indicated higher EGJ-DIs in symptomatic GERD patients compared to controls [4], but subsequent research contradicted these results [10, 33]. Moreover, EGJ-DI did not consistently correlate with esophageal acid exposure or predict clinical outcomes and studies have not established a definitive diagnostic threshold for EGJ-DI in GERD, nor consistently differentiated between GERD patients and controls based on EGJ-DI values [10, 34]. Nevertheless, data suggest that patients with impaired contractile response on EndoFLIP may have lower acid exposure times, emphasizing the role of esophageal motor function in acid clearance [34]. But still, the role of EndoFLIP in routine GERD diagnosis remains unclear. Therefore, the American Gastroenterological Association (AGA) recommends against the routine use of EndoFLIP in GERD management due to these inconsistencies [32], but interest persists in its application in anti-reflux procedures as a tool to tailor the tightness of the fundoplication wrap. In fundoplication, the EGJ distensibility objectively decreases after surgery with different values reflecting the type of wrap [4, 35]. One study suggested that an intraoperative EGJ-DI value between 2 and 3.5 mm²/mm Hg is associated with lower frequency of post-fundoplication dysphagia and less reflux symptom burden at follow up [36]. On the contrary, postoperative EGJ-DI <2 mm²/mm Hg was associated with development of post-fundoplication dysphagia and the need for intervention [37–39]. However, the ideal EGJ-DI targets for optimal outcomes remain unclear.

In summary, while the diagnostic utility of EndoFLIP in GERD is still under investigation, its potential for evaluating physiological components related to GERD pathophysiology and tailoring anti-reflux procedures is promising. However, due to the current inconsistencies and limited evidence, EndoFLIP should not be routinely used for GERD management until further outcome studies can substantiate its clinical utility.

Assessing the Upper Esophageal Sphincter Function

The upper esophageal sphincter (UES) plays a crucial role in oropharyngeal swallowing, comprising the cricopharyngeal muscle, the proximal cervical esophagus, and the inferior pharyngeal constrictor muscle. Various methods are available to assess UES function, including videofluoroscopy, nasopharyngolaryngoscopy, and pharyngeal manometry. However, these methods have limitations, prompting exploration of alternative approaches such as EndoFLIP. EndoFLIP has demonstrated feasibility and safety in evaluating UES distensibility in post-laryngectomy patients [40], and it has been used to measure UES distensibility and opening patterns during swallowing in healthy control subjects [41, 42]. Further studies are warranted to establish the clinical significance of EndoFLIP findings in assessing UES function and its role in the evaluation of oropharyngeal swallowing.

Assessing Esophageal Body Wall Stiffness

Achalasia. Traditionally, research on impedance planimetry (IP) in conditions like achalasia has primarily focused on the EGJ. However, Carlson et al. [14] pioneered the use of EndoFLIP topography to assess esophageal contractility patterns. Their study revealed distinct contraction patterns across different achalasia subtypes, suggesting the potential of EndoFLIP topography to characterize esophageal dysmotility more comprehensively than conventional manometry. When the esophagus undergoes distension via EndoFLIP, it triggers secondary contractions categorized into three types: RACs, RRCs, and DDCR [][18]. Research on asymptomatic volunteers demonstrated a typical pattern of repetitive, antegrade contractions in response to sustained volumetric dilation of the distal esophagus, likely representing secondary peristalsis [18]. Thresholds and properties of contractile activity induced by distension were evaluated, and in patients with newly diagnosed achalasia, EndoFLIP topography revealed evidence of esophageal contractility even in cases without detectable contractility on HRM, particularly in type I and type II achalasia. Some patients, especially those with type III achalasia, exhibited a distinct pattern of RRCs not observed in controls [14]. The contractility detected by EndoFLIP in achalasia may provide additional prognostic information beyond manometric assessment.

Eosinophilic Esophagitis. Eosinophilic esophagitis (EoE) is characterized by chronic immune-mediated inflammation of the esophagus, leading to fibrous changes, stiffening of the esophageal wall with a decrease in esophageal compliance, luminal narrowing, and the formation of strictures [43, 44]. Traditional monitoring of EoE involves upper endoscopy with biopsies to assess histologic activity and guide treatment [45]. However, endoscopic evaluation can be inconsistent, and the extent of microscopic inflammation often does not correlate with macroscopic structural changes. EndoFLIP technology offers an alternative approach and provides an objective measurement to evaluate esophageal remodeling as well as detection and localization of esophageal narrowing and dominant strictures by measuring the mechanical properties of the esophageal wall [46]. EndoFLIP assesses esophageal distensibility by recording CSA and corresponding intraluminal pressure during volumetric distension. This method identifies the distensibility plateau, which reflects the luminal opening at its narrowest point. Studies have demonstrated that EoE patients have significantly reduced esophageal compliance compared to controls, with lower distensibility plateaus associated with the severity of endoscopic signs such as rings and strictures and increased risks of food impaction and the need for dilation [47]. Importantly, these reductions in distensibility were not correlated with histologic eosinophil counts, suggesting that EndoFLIP provides insights into esophageal remodeling that are not captured by biopsy alone [48]. On the contrary, a distensibility plateau value of 225 mm² is associated with a lower risk of food impaction and the need for dilation in EoE patients [47]. Consequently, EndoFLIP can serve as a valuable tool for diagnostic and therapeutic purposes in patients suspected of having EoE-related strictures, enabling therapeutic interventions, such as dilation, within a single endoscopic session.

Systemic Sclerosis. Most patients with connective tissue diseases experience esophageal symptoms due to the progressive atrophy and collagenous replacement of smooth muscle. Manometric evaluation typically reveals a pattern of aperistalsis associated with a hypotonic LES [49]. IP studies have demonstrated increased CSA in patients with systemic sclerosis compared to controls, along with reduced distensibility. Furthermore, the degree of wall stiffness and impaired muscle function has been shown to correlate with disease duration [50, 51]. Currently, the management implications of these findings are limited due to the lack of effective therapies for this condition. However, IP offers a potential platform for testing the effects of pharmacologic interventions.

EndoFLIP provides a reliable, quantitative measure of esophageal remodeling and biomechanical properties, offering advantages over traditional methods like barium esophagrams, high-resolution manometry and endoscopy, aiding in diagnosis, therapeutic decision-making, and monitoring of disease progression.

Use of EndoFLIP in the Stomach

Over the past decade, increasing attention has been directed toward the distensibility testing of the pylorus, particularly in the context of pylorospasm, which appears to play a significant role in the pathophysiology of a subset of patients with gastroparesis. The pylorus is crucial for regulating gastric emptying (GE), but the correlation between symptom severity and GE is weak. GE primarily occurs during pyloric relaxation, driven by gastric tone and content pressure rather than antral contraction. Pyloric contraction during gastric peristalsis can lead to bolus retention and content mixing [52]. Identifying pylorospasm could facilitate targeted treatments, such as gastric peroral endoscopic myotomy (G-POEM), potentially alleviating symptoms and addressing the limitations of current therapeutic options. However, there is a lack of objective measurement methods and a clear definition of pylorospasm. While the EndoFLIP system shows promise in assessing pyloric distensibility, data on its correlation with gastric emptying and symptoms in gastroparesis patients are inconsistent. Consequently, the European Society of Gastrointestinal Endoscopy (ESGE) has not yet recommended EndoFLIP to select patients for pylorus-targeted therapy [53]. Initial studies using EndoFLIP reported a mean pyloric compliance of 25 ± 2.4 mm²/mm Hg at 40 mL filling volume in healthy volunteers, compared to 16.9 ± 2.1 mm²/mm Hg in gastroparesis patients and 10.9 ± 2.9 mm²/mm Hg in post-esophagectomy patients, with 10 mm²/mm Hg set as the lower normal cutoff [54]. Subsequent studies, including one by Malik et al. [55] observed a mean DI of 10.7 ± 2.57 mm²/mm Hg in patients with idiopathic and diabetic gastroparesis, with a wide range of values. However, other studies demonstrated significant variability, emphasizing the need for prospective validation of current cutoff values for DI or CSA in both healthy individuals and gastroparesis patients. Some studies have suggested an inverse relationship between early satiety/postprandial fullness and pylorus CSA and diameter, representing an association between diagnostic findings and gastroparesis symptoms [55–57]. However, the exact mechanism behind this association remains elusive, necessitating further research. EndoFLIP has also shown promise in predicting clinical response to pylorus-targeted therapies, such as botulinum toxin injection or dilation, with patients exhibiting abnormal pylorus EndoFLIP measurements showing sustained symptom improvement compared to those with normal measurements [58–60]. Lower DI in gastroparesis patients has been linked to better outcomes after G-POEM or dilation [57].

In conclusion, the utilization of EndoFLIP in assessing pyloric sphincter function is expanding, offering promising diagnostic insights and correlating symptoms with GE. Moreover, it identifies patients who may benefit from targeted pylorus therapy, emphasizing its potential in improving treatment outcomes for gastroparesis.

Use of the Dilatation Catheter EsoFLIP for Therapeutic Indications

Dilatation with a bougie or balloon dilator is a well-established method for treating benign strictures throughout the gastrointestinal tract. It is known for its favorable efficacy and safety. Existing randomized trials show no significant outcome differences between wire-guided bougies and through-the-scope balloon dilators [61–63]. Physician preference and availability typically guide the choice of dilation technique. Despite the procedure being performed under fluoroscopic or endoscopic guidance, these techniques do not offer immediate feedback on changes to the luminal structure, and both have inherent limitations. The EsoFLIP (Medtronic, Minnesota, USA) is an advanced device designed for esophageal hydraulic balloon dilation. It utilizes the same hardware and technology as EndoFLIP but features a more robust balloon capable of generating the necessary pressure for effective dilation. This tool provides the advantage of direct visual control during dilation, allowing real-time assessment of the dilated area’s shape and diameter. However, due to its rigid structure, the EsoFLIP balloon does not support real-time distensibility measurements. The EsoFLIP system offers three catheter sizes: 10 mm (ES-310) and 20 mm (ES-320) balloons for esophageal strictures and a 30 mm (ES-330) balloon, mainly used for achalasia and esophago-gastric junction outflow obstruction. Beyond the esophagus, EsoFLIP can potentially be used to dilate the pylorus or other upper GI strictures within its technical scope. The dilation balloon’s diameter is manually controlled via an electro-hydraulic pump, allowing adjustments based on the target diameter and the stricture’s behavior during the procedure. Initial measurements of the diameter or CSA at partial filling volume (20 mL for ES-320 and 30 mL for ES-330) are followed by gradual, stepwise filling to approximately 30 mL/50 mL, with additional increments of 1–3 mL to reach the target diameter. The maximum filling volume of 42 mL/75 mL (ES-320/ES-330) is used to achieve a target diameter of 20/30 mm. The stricture and the surrounding mucosa are visually assessed during the procedure by placing the endoscope tip on the balloon. Post-dilation, the balloon is emptied, and the diameter and CSA are measured to evaluate the treatment response. EndoFLIP measurements can be performed in the same session before and after the procedure. The EsoFLIP system offers several advantages: precise control of the balloon filling allows dilation to the desired diameter with a single balloon, and continuous visualization of the lumen and stricture localization eliminates the need for fluoroscopy, reducing radiation exposure [64]. Although clinical outcome studies on EsoFLIP are limited, small series have demonstrated its technical feasibility, safety, and short-term efficacy. A feasibility study on 10 achalasia patients using the FLIP hydraulic balloon dilator showed successful dilation to 28–30 mm without serious adverse events [65]. The main limitation for achalasia patients is the 30 mm maximum balloon size.

In conclusion, EsoFLIP offers promising advantages in stricture dilation, providing precise diameter measurements and eliminating the need for fluoroscopy. While initial studies show positive outcomes, further research is necessary to establish its efficacy and guide the selection of dilation techniques.

Limitations and Future Directions

Despite the growing evidence supporting the clinical utility of EndoFLIP, several limitations and gaps in the quality of available evidence hinder its widespread adoption. These include high costs, lack of real-time data processing software, and limited data storage solutions. Moreover, the absence of standardized protocols and data analysis methodologies restricts its use to specialized centers. Thirdly, direct comparative studies with other imaging modalities such as barium esophagography and scintigraphy are scarce. On the other hand, EndoFLIP’s potential in clinical practice has extended beyond the esophagus. Increased usage and broader experiences have provided further insights into its promising applications in clinical scenarios. Ongoing and future research, particularly with refined protocols, standardized data collection, and establishing normative data in large cohorts will be crucial for the technology’s advancement and broader adoption of this technology in routine clinical practice.

Conclusion

The EndoFLIP is an advanced diagnostic tool that enhances the evaluation of sphincters and hollow organs by providing real-time dynamic monitoring of distensibility, luminal geometry, and biomechanical properties. Initially used for assessing the esophagogastric junction, its application has expanded to the esophageal body, upper esophageal sphincter, and pylorus. EndoFLIP offers a significant improvement over traditional methods by allowing detailed functional assessment beyond simple pressure measurement. The device's ability to measure distensibility can guide the tailoring of specific endoscopic and surgical therapies, such as dilation, fundoplication, and myotomy, to achieve optimal clinical outcomes and enable therapeutic procedures in one session when dilation is necessary. Future research should focus on standardizing measurement protocols, validating normative values in both healthy and pathological conditions, and further exploring the use of EndoFLIP in therapeutic settings, translating functional results into clinical outcomes. As these technologies evolve, they hold the potential for diagnosis and treatment within a single session.

Conflict of Interest Statement

Prof. Dr. Helmut Messmann: Olympus, Satisfai (Grants); Dr. Falk Pharma, Olympus, Norgine, IPSEN, medupdate, Erbe (Speakers fee); Olympus, Ambu, Boston Scientific, Covidien, Takeda (Consultation fees). Dr. Alanna Ebigbo: Olympus Medical, FujiFilm, Pentax, Ambu, Falk Pharma and Medtronic (Lecture fees). Dr. Sandra Nagl: Falk Pharma, Pfizer and Sanofi (Lecture fees).

Funding Sources

None received.

Author Contributions

Drafting of the manuscript: Sandra Nagl, Alanna Ebigbo; Helmut Messmann. Critical revision of the manuscript: Sandra Nagl, Alanna Ebigbo, Helmut Messmann.

Funding Statement

None received.