Design and Validation of a Surface-Contact Electrode for Gastric Pacing and Concurrent Slow-Wave Mapping

Optimization of pacing parameters to entrain slow wave activity in the pig jejunum

Pacing has been proposed as a therapy to restore function in motility disorders associated with electrical dysrhythmias. The spatial response of bioelectrical activity in the small intestine to pacing is poorly understood due to a lack of high-resolution investigations. This study systematically varied pacing parameters to determine the optimal settings for the spatial entrainment of slow wave activity in the jejunum. An electrode array was developed to allow simultaneous pacing and high-resolution mapping of the small intestine. Pacing parameters including pulse-width (50, 100 ms), pulse-amplitude (2, 4, 8 mA) and pacing electrode orientation (antegrade, retrograde, circumferential) were systematically varied and applied to the jejunum (n = 15 pigs). Pulse-amplitudes of 4 mA (p = 0.012) and 8 mA (p = 0.002) were more effective than 2 mA in achieving spatial entrainment while pulse-widths of 50 ms and 100 ms had comparable effects (p = 0.125). A pulse-width of 100 ms and a pulse-amplitude of 4 mA were determined to be most effective for slow wave entrainment when paced in the antegrade or circumferential direction with a success rate of greater than 75%. These settings can be applied in chronic studies to evaluate the long-term efficacy of pacing, a critical aspect in determining its therapeutic potential.

Optimization of Gastric Pacing Parameters Using High-Resolution Mapping

OBJECTIVE

Abnormal slow-wave activity has been associated with functional motility disorders. Gastric pacing has been investigated to correct slow-wave abnormalities, but clinical therapies are yet to be established. This study aimed to define optimal parameters to advance the application of gastric pacing.

METHODS

High-resolution gastric mapping was utilized to evaluate four pacing parameters in in-vivo pig studies: (i) orientation of the pacing electrodes (longitudinal vs circumferential), (ii) pacing energy (900 vs 10,000 ms mA2), (iii) the pacing location (corpus vs antrum), and (iv) pacing period (between 12 and 36 s).

RESULTS

The probability of slow-wave initiation and entrainment with the pacing electrodes oriented longitudinally was significantly higher than with electrodes orientated circumferentially (86 vs 10%). High-energy pacing accelerated entrainment over the entire mapped field compared to low-energy pacing (3.1±1.5 vs 7.3±2.4 impulses, p < 0.001). Regardless of the location of the pacing site, the new site of slow-wave initiation was always located 4-12 mm away from the pacing site, between the greater curvature and negative pacing electrode. A pacing period between 14-30 s resulted in stable slow-wave initiation and entrainment.

CONCLUSION

These data will now inform effective application of gastric pacing in future studies, including human translation.

Optical Mapping of Virtual Electrode Polarization Pattern and Its Relationship with Pacemaker Location during Gastric Pacing. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2023;2023:1-4. [PMID: 38082999 DOI: 10.1109/embc40787.2023.10340002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Gastric rhythmic contractions are regulated by bioelectrical events known as slow waves (SW). Abnormal SW activity is associated with gastric motility disorders. Gastric pacing is a potential treatment method to restore rhythmic SW activity. However, to date, the efficacy of gastric pacing is inconsistent and the underlying mechanisms of gastric pacing are poorly understood. Optical mapping is widely used in cardiac electrophysiology studies. Its immunity to pacing artifacts offers a distinct advantage over conventional electrical mapping for studying pacing. In the present study, we first found that optical mapping can image pacing-induced virtual electrode polarization patterns in the stomach (adjacent regions of depolarized and hyperpolarized tissue). Second, we found that elicited SWs usually (15 of 16) originated from the depolarized areas of the stimulated region (virtual cathodes). To our knowledge, this is the first direct observation of virtual electrode polarization patterns in the stomach. Conclusions: Optical mapping can image virtual electrode polarization patterns during gastric pacing with high spatial resolution.Clinical Relevance- Gastric pacing is a potential therapeutic method for gastric motility disorders. This study provides direct observation of virtual electrode polarization pattern during gastric pacing and improves our understanding of the mechanisms underlying gastric pacing..

Stomach Geometry Reconstruction Using Serosal Transmitting Coils and Magnetic Source Localization

OBJECTIVE

Bioelectric slow waves (SWs) are a key regulator of gastrointestinal motility, and disordered SW activity has been linked to motility disorders. There is currently a lack of practical options for the acquisition of the 3D stomach geometry during research studies when medical imaging is challenging. Accurately recording the geometry of the stomach and co-registering electrode and sensor positions would provide context for in-vivo studies and aid the development of non-invasive methods of gastric SW assessment.

METHODS

A stomach geometry reconstruction method based on the localization of transmitting coils placed on the gastric serosa was developed. The positions and orientations of the coils, which represented boundary points and surface-normal vectors, were estimated using a magnetic source localization algorithm. Coil localization results were then used to generate surface models. The reconstruction method was evaluated against four 3D-printed anatomically realistic human stomach models and applied in a proof of concept in-vivo pig study.

RESULTS

Over ten repeated reconstructions, average Hausdorff distance and average surface-normal vector error values were 4.7 ±0.2 mm and 18.7 ±0.7° for the whole stomach, and 3.6 ±0.2 mm and 14.6 ±0.6° for the corpus. Furthermore, mean intra-array localization error was 1.4 ±1.1 mm for the benchtop experiment and 1.7 ±1.6 mm in-vivo.

CONCLUSION AND SIGNIFICANCE

Results demonstrated that the proposed reconstruction method is accurate and feasible. The stomach models generated by this method, when co-registered with electrode and sensor positions, could enable the investigation and validation of novel inverse analysis techniques.

A novel framework for the removal of pacing artifacts from bio-electrical recordings

BACKGROUND

Electroceuticals provide clinical solutions for a range of disorders including Parkinson's disease, cardiac arrythmias and are emerging as a potential treatment option for gastrointestinal disorders. However, pre-clinical investigations are challenged by the large stimulation artifacts registered in bio-electrical recordings.

METHOD

A generalized framework capable of isolating and suppressing stimulation artifacts with minimal intervention was developed. Stimulation artifacts with different pulse-parameters in synthetic and experimental cardiac and gastrointestinal signals were detected using a Hampel filter and reconstructed using 3 methods: i) autoregression, ii) weighted mean, and iii) linear interpolation.

RESULTS

Synthetic stimulation artifacts with amplitudes of 2 mV and 4 mV and pulse-widths of 50 ms, 100 ms, and 200 ms were successfully isolated and the artifact window size remained uninfluenced by the pulse-amplitude, but was influenced by pulse-width (e.g., the autoregression method resulted in an identical Root Mean Square Error (RMSE) of 1.64 mV for artifacts with 200 ms pulse-width and both 2 mV and 4 mV amplitudes). The performance of autoregression (RMSE = 1.45 ± 0.16 mV) and linear interpolation (RMSE = 1.22 ± 0.14 mV) methods were comparable and better than weighted mean (RMSE = 5.54 ± 0.56 mV) for synthetic data. However, for experimental recordings, artifact removal by autoregression was superior to both linear interpolation and weighted mean approaches in gastric, small intestinal and cardiac recordings.

CONCLUSIONS

A novel signal processing framework enabled efficient analysis of bio-electrical recordings with stimulation artifacts. This will allow the bio-electrical events induced by stimulation protocols to be efficiently and systematically evaluated, resulting in improved stimulation therapies.

Systematic review of small intestine pacing parameters for modulation of gut function

BACKGROUND AND PURPOSE

The efficacy of conventional treatments for severe and chronic functional motility disorders remains limited. High-energy pacing is a promising alternative therapy for patients that fail conventional treatment. Pacing primarily regulates gut motility by modulating rhythmic bio-electrical events called slow waves. While the efficacy of this technique has been widely investigated on the stomach, its application in the small intestine is less developed. This systematic review was undertaken to summarize the status of small intestinal pacing and evaluate its efficacy in modulating bowel function through preclinical research studies.

METHODS

The literature was searched using Scopus, PubMed, Ovid, Cochrane, CINAHL, and Google Scholar. Studies investigating electrophysiological, motility, and/or nutrient absorption responses to pacing were included. A critical review of all included studies was conducted comparing study outcomes against experimental protocols.

RESULTS

The inclusion criteria were met by 34 publications. A range of pacing parameters including amplitude, pulse width, pacing direction, and its application to broad regional small intestinal segments were identified and assessed. Out of the 34 studies surveyed, 20/23 studies successfully achieved slow-wave entrainment, 9/11 studies enhanced nutrient absorption and 21/27 studies modulated motility with pacing.

CONCLUSION

Small intestine pacing shows therapeutic potential in treating disorders such as short bowel syndrome and obesity. This systematic review proposes standardized protocols to maximize research outcomes and thereby translate to human studies for clinical validation. The use of novel techniques such as high-resolution electrical, manometric, and optical mapping in future studies will enable a mechanistic understanding of pacing.

Localized bioelectrical conduction block from radiofrequency gastric ablation persists after healing: safety and feasibility in a recovery model

Gastric ablation has demonstrated potential to induce conduction blocks and correct abnormal electrical activity (i.e., ectopic slow-wave propagation) in acute, intraoperative in vivo studies. This study aimed to evaluate the safety and feasibility of gastric ablation to modulate slow-wave conduction after 2 wk of healing. Chronic in vivo experiments were performed in weaner pigs (n = 6). Animals were randomly divided into two groups: sham-ablation (n = 3, control group; no power delivery, room temperature, 5 s/point) and radiofrequency (RF) ablation (n = 3; temperature-control mode, 65°C, 5 s/point). In the initial surgery, high-resolution serosal electrical mapping (16 × 16 electrodes; 6 × 6 cm) was performed to define the baseline slow-wave activation profile. Ablation (sham/RF) was then performed in the mid-corpus, in a line around the circumferential axis of the stomach, followed by acute postablation mapping. All animals recovered from the procedure, with no sign of perforation or other complications. Two weeks later, intraoperative high-resolution mapping was repeated. High-resolution mapping showed that ablation successfully induced sustained conduction blocks in all cases in the RF-ablation group at both the acute and 2 wk time points, whereas all sham-controls had no conduction block. Histological and immunohistochemical evaluation showed that after 2 wk of healing, the lesions were in the inflammation and early proliferation phase, and interstitial cells of Cajal (ICC) were depleted and/or deformed within the ablation lesions. This safety and feasibility study demonstrates that gastric ablation can safely and effectively induce a sustained localized conduction block in the stomach without disrupting the surrounding slow-wave conduction capability.NEW & NOTEWORTHY Ablation has recently emerged as a tool for modulating gastric electrical activation and may hold interventional potential for disorders of gastric function. However, previous studies have been limited to the acute intraoperative setting. This study now presents the safety of gastric ablation after postsurgical recovery and healing. Localized electrical conduction blocks created by ablation remained after 2 wk of healing, and no perforation or other complications were observed over the postsurgical period.

A generalized framework for pacing artifact removal using a Hampel filter

Cardiac pacing is a clinical therapy widely used for treating irregular heart rhythms. Equivalent techniques for the treatment of gastric functional motility disorders hold great potential. Accurate analysis of pacing studies is often hindered by the stimulus artifacts which are superimposed on the recorded signals. This paper presents a semi-automated artifact detection method using a Hampel filter accompanied by 2 separate artifact reconstruction methods: (i) an auto-regressive model, and (ii) weighted mean to estimate the underlying signal. The developed framework was validated on synthetic and experimental signals containing large periodic pacing artifacts alongside evoked bioelectrical events. The performance of the proposed algorithms was quantified for gastric and cardiac pacing data collected in vivo. A lower mean RMS difference was achieved by the artifact segment reconstructed using the auto-regression ([Formula: see text]), method compared to the weighted mean ([Formula: see text]) method. Therefore, a more accurate artifact reconstruction was provided by the auto-regression approach. Clinical Relevance- The ability to efficiently and accurately isolate evoked bioelectrical events by eliminating large artifacts is a critical advancement for the analysis of paced recordings. The developed framework allows more efficient analysis of preclinical pacing data and thereby contributes to the advancement of pacing as a clinical therapy.

Gastric pacing response evaluated with simultaneous electrical and optical mapping

Gastric pacing is an attractive therapeutic approach for correcting abnormal bioelectrical activity. While high-resolution (HR) electrical mapping techniques have largely contributed to the current understanding of the effect of pacing on the electrophysiological function, these mapping techniques are restricted to surface contact electrodes and the signal quality can be corrupted by pacing artifacts. Optical mapping of voltage sensitive dyes is an alternative approach used in cardiac research, and the signal quality is not affected by pacing artifacts. In this study, we simultaneously applied HR optical and electrical mapping techniques to evaluate the bioelectrical slow wave response to gastric pacing. The studies were conducted in vivo on porcine stomachs ( n=3) where the gastric electrical activity was entrained using high-energy pacing. The pacing response was optically tracked using voltage-sensitive fluorescent dyes and electrically tracked using surface contact electrodes positioned on adjacent regions. Slow waves were captured optically and electrically and were concordant in time and direction of propagation with comparable mean velocities ([Formula: see text]) and periods ([Formula: see text]). Importantly, the optical signals were free from pacing artifacts otherwise induced in electrical recordings highlighting an advantage of optical mapping. Clinical Relevance- Entrainment mapping of gastric pacing using optical techniques is a major advance for improving the preclinical understanding of the therapy. The findings can thereby inform the efficacy of gastric pacing in treating functional motility disorders.

Targeted ablation of gastric pacemaker sites to modulate patterns of bioelectrical slow wave activation and propagation in an anesthetized pig model

Gastric motility is coordinated by underlying bioelectrical slow waves. Gastric dysrhythmias occur in gastrointestinal (GI) motility disorders, but there are no validated methods for eliminating dysrhythmias. We hypothesized that targeted ablation could eliminate pacemaker sites in the stomach, including dysrhythmic ectopic pacemaker sites. In vivo high-resolution serosal electrical mapping (16 × 16 electrodes; 6 × 6 cm) was applied to localize normal and ectopic gastric pacemaker sites in 13 anesthetized pigs. Radiofrequency ablation was performed in a square formation surrounding the pacemaker site. Postablation high-resolution mapping revealed that ablation successfully induced localized conduction blocks after 18 min (SD 5). Normal gastric pacemaker sites were eliminated by ablation (n = 6), resulting in the emergence of a new pacemaker site immediately distal to the original site in all cases. Ectopic pacemaker sites were similarly eliminated by ablation in all cases (n = 7), and the surrounding mapped area was then entrained by normal antegrade activity in five of those cases. Histological analysis showed that ablation lesions extended through the entire depth of the muscle layer. Immunohistochemical staining confirmed localized interruption of the interstitial cell of Cajal (ICC) network through the ablation lesions. This study demonstrates that targeted gastric ablation can effectively modulate gastric electrical activation, including eliminating ectopic sites of slow wave activation underlying gastric dysrhythmias, without disrupting surrounding conduction capability or tissue structure. Gastric ablation presents a powerful new research tool for modulating gastric electrical activation and may likely hold therapeutic potential for disorders of gastric function.NEW & NOTEWORTHY This study presents gastric ablation as a novel tool for modulating gastric bioelectrical activation, including eliminating the normal gastric pacemaker site as well as abnormal ectopic pacemaker sites underlying gastric dysrhythmias. Targeted application of radiofrequency ablation was able to eliminate these pacemaker sites without disrupting surrounding conduction capability or tissue structure. Gastric ablation presents a powerful new research tool for modulating gastric electrical activation and may likely hold therapeutic potential for disorders of gastric function.

Miniaturized wireless gastric pacing via inductive power transfer with non-invasive monitoring using cutaneous Electrogastrography

BACKGROUND

Gastroparesis is a debilitating disease that is often refractory to pharmacotherapy. While gastric electrical stimulation has been studied as a potential treatment, current devices are limited by surgical complications and an incomplete understanding of the mechanism by which electrical stimulation affects physiology.

METHODS

A leadless inductively-powered pacemaker was implanted on the gastric serosa in an anesthetized pig. Wireless pacing was performed at transmitter-to-receiver distances up to 20 mm, frequency of 0.05 Hz, and pulse width of 400 ms. Electrogastrogram (EGG) recordings using cutaneous and serosal electrode arrays were analyzed to compute spectral and spatial statistical parameters associated with the slow wave.

RESULTS

Our data demonstrated evident change in EGG signal patterns upon initiation of pacing. A buffer period was noted before a pattern of entrainment appeared with consistent and low variability in slow wave direction. A spectral power increase in the EGG frequency band during entrainment also suggested that pacing increased strength of the slow wave.

CONCLUSION

Our preliminary in vivo study using wireless pacing and concurrent EGG recording established the foundations for a minimally invasive approach to understand and optimize the effect of pacing on gastric motor activity as a means to treat conditions of gastric dysmotility.