Gastric ablation as a novel technique for modulating electrical conduction in the in vivo stomach

Power-Controlled, Irrigated Radio-Frequency Ablation of Gastric Tissue: A Biophysical Analysis of Lesion Formation

BACKGROUND

Radio-frequency ablation of gastric tissue is in its infancy compared to its extensive history and use in the cardiac field.

AIMS

We employed power-controlled, irrigated radio-frequency ablation to create lesions on the serosal surface of the stomach to examine the impact of ablation power, irrigation, temperature, and impedance on lesion formation and tissue damage.

METHODS

A total of 160 lesions were created in vivo in female weaner pigs (n = 5) using a combination of four power levels (10, 15, 20, 30 W) at two irrigation rates (2, 5 mL min-1) and with one temperature-controlled (65 °C) reference setting previously validated for electrophysiological intervention in the stomach.

RESULTS

Power and irrigation rate combinations above 15 W resulted in lesions with significantly higher surface area and depth than the temperature-controlled setting. Irrigation resulted in significantly lower temperature (p < 0.001) and impedance (p < 0.001) compared to the temperature-controlled setting. No instances of perforation or tissue pop were recorded for any ablation sequence.

CONCLUSION

Power-controlled, irrigated radio-frequency ablation of gastric tissue is effective in creating larger and deeper lesions at reduced temperatures than previously investigated temperature-controlled radio-frequency ablation, highlighting a substantial improvement. These data define the biophysical impact of ablation parameters in gastric tissue, and they will guide future translation toward clinical application and in silico gastric ablation modeling. Combination of ablation settings (10-30 W power, 2-5 mL min-1 irrigation) were used to create serosal spot lesions. Histological analysis of lesions quantified localized tissue damage.

Anaesthesia by intravenous propofol reduces the incidence of intra-operative gastric electrical slow-wave dysrhythmias compared to isoflurane

Gastric motility is coordinated by bioelectrical slow-wave activity, and abnormal electrical dysrhythmias have been associated with nausea and vomiting. Studies have often been conducted under general anaesthesia, while the impact of general anaesthesia on slow-wave activity has not been studied. Clinical studies have shown that propofol anaesthesia reduces postoperative nausea and vomiting (PONV) compared with isoflurane, while the underlying mechanisms remain unclear. In this study, we investigated the effects of two anaesthetic drugs, intravenous (IV) propofol and volatile isoflurane, on slow-wave activity. In vivo experiments were performed in female weaner pigs (n = 24). Zolazepam and tiletamine were used to induce general anaesthesia, which was maintained using either IV propofol (n = 12) or isoflurane (n = 12). High-resolution electrical mapping of slow-wave activity was performed. Slow-wave dysrhythmias occurred less often in the propofol group, both in the duration of the recorded period that was dysrhythmic (propofol 14 ± 26%, isoflurane 43 ± 39%, P = 0.043 (Mann-Whitney U test)), and in a case-by-case basis (propofol 3/12, isoflurane 8/12, P = 0.015 (Chi-squared test)). Slow-wave amplitude was similar, while velocity and frequency were higher in the propofol group than the isoflurane group (P < 0.001 (Student's t-test)). This study presents a potential physiological biomarker linked to recent observations of reduced PONV with IV propofol. The results suggest that propofol is a more suitable anaesthetic for studying slow-wave patterns in vivo.

High-resolution in vivo monophasic gastric slow waves to quantify activation and recovery profiles

BACKGROUND

Gastric bio-electrical slow waves are, in part, responsible for coordinating motility. Spatial dynamics about the recovery phase of slow wave recordings have not been thoroughly investigated due to the lack of suitable experimental techniques.

METHODS

A high-resolution multi-channel suction electrode array was developed and applied in pigs to acquire monophasic gastric slow waves. Signal characteristics were verified against biphasic slow waves recorded by conventional surface contact electrode arrays. Monophasic slow wave events were categorized into two groups based on their morphological characteristics, after which their amplitudes, activation to recovery intervals, and gradients were quantified and compared. Coverage of activation and recovery maps for both electrode types were calculated and compared.

KEY RESULTS

Monophasic slow waves had a more pronounced recovery phase with a higher gradient than biphasic slow waves (0.5 ± 0.1 vs. 0.3 ± 0.1 mV·s^-1 ). Between the 2 groups of monophasic slow waves, there was a significant difference in amplitude (1.8 ± 0.5 vs. 1.1 ± 0.2 mV), activation time gradient (0.8 ± 0.2 vs. 0.3 ± 0.1 mV·s^-1 ), and recovery time gradient (0.5 ± 0.1 vs. 0.3 ± 0.1 mV·s^-1 ). For the suction and conventional contact electrode arrays, the recovery maps had reduced coverage compared to the activation maps (4 ± 6% and 43 ± 11%, respectively).

CONCLUSIONS AND INFERENCES

A novel high-resolution multi-channel suction electrode array was developed and applied in vivo to record monophasic gastric slow waves. Slow wave recovery phase analysis could be performed more efficiently on monophasic signals compared with biphasic signals, due to the more identifiable recovery phases.

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.

Validation of noninvasive body-surface gastric mapping for detecting gastric slow-wave spatiotemporal features by simultaneous serosal mapping in porcine

Gastric disorders are increasingly prevalent, but reliable noninvasive tools to objectively assess gastric function are lacking. Body-surface gastric mapping (BSGM) is a noninvasive method for the detection of gastric electrophysiological features, which are correlated with symptoms in patients with gastroparesis and functional dyspepsia. Previous studies have validated the relationship between serosal and cutaneous recordings from limited number of channels. This study aimed to comprehensively evaluate the basis of BSGM from 64 cutaneous channels and reliably identify spatial biomarkers associated with slow-wave dysrhythmias. High-resolution electrode arrays were placed to simultaneously capture slow waves from the gastric serosa (32 × 6 electrodes at 4 mm spacing) and epigastrium (8 × 8 electrodes at 20 mm spacing) in 14 porcine subjects. BSGM signals were processed based on a combination of wavelet and phase information analyses. A total of 1,185 individual cycles of slow waves were assessed, out of which 897 (76%) were classified as normal antegrade waves, occurring in 10 (71%) subjects studied. BSGM accurately detected the underlying slow wave in terms of frequency (r = 0.99, P = 0.43) as well as the direction of propagation (P = 0.41, F-measure: 0.92). In addition, the cycle-by-cycle match between BSGM and transitions of gastric slow wave dysrhythmias was demonstrated. These results validate BSGM as a suitable method for noninvasively and accurately detecting gastric slow-wave spatiotemporal profiles from the body surface.NEW & NOTEWORTHY Gastric dysfunctions are associated with abnormalities in the gastric bioelectrical slow waves. Noninvasive detection of gastric slow waves from the body surface can be achieved through multichannel, high-resolution, body-surface gastric mapping (BSGM). BSGM matched the spatiotemporal characteristics of gastric slow waves recorded directly and simultaneously from the serosal surface of the stomach. Abnormal gastric slow waves, such as retrograde propagation, ectopic pacemaker, and colliding wavefronts can be detected by changes in the phase of BSGM.

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.

The Effect of Power-Control and Irrigation Settings on Lesion Size during Radio-Frequency Ablation of Gastric Tissue

Gastric ablation has recently emerged as a promising potential therapy for correcting bioelectrical dysrhythmias that underpin many gastrointestinal motility disorders. Despite similarities to well-developed cardiac radiofrequency (RF) ablation, gastric RF ablation is in its infancy and has thus far been limited to temperature-controlled, non-irrigated settings. The potential benefits of power-controlled and irrigated RF ablation have not been investigated in gastric tissue. In this study, RF ablation was performed in vivo in pigs ( n=5) using a range of power-control (10-30 W, 10s per point) and irrigation (2-5 ml/min) settings and compared to known temperature-controlled (65°C), non-irrigated settings. Excised tissue was stained with H&E. Lesion surface area was calculated and tissue damage was quantitatively ranked by visual assessment. The results demonstrated that irrigation allowed greater energy delivery to tissue with reduced interface temperatures compared to non-irrigated settings. Power settings above 10 W created lesions that extended through the full-thickness of the muscle layer, which suggests the parameter range that can now be used to correct gastric dysrhythmias. Clinical Relevance- This work presents the results of power-controlled, irrigated RF ablation settings applied to the in vivo porcine stomach. The relationships of both lesion area and depth to ablation dose provides an improved insight into which energy doses could provide a safe and effective therapeutic response.

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.

A computational model of radiofrequency ablation in the stomach, an emerging therapy for gastric dysrhythmias

Gastric ablation has recently emerged as a promising potential therapy for bioelectrical dysrhythmias that underpin many gastrointestinal disorders. Despite similarities to well-developed cardiac ablation, gastric ablation is in early development and has thus far been limited to temperature-controlled, non-irrigated settings. A computational model of gastric ablation is needed to enable in silico testing and optimization of ablation parameters and techniques. In this study, we developed a computational model of radio-frequency (RF) gastric ablation. Model parameters and boundary conditions were established based on the current in vivo experimental application of serosal gastric ablation with a non-irrigated RF catheter. The Pennes bioheat transfer equation was used to model the thermal component of RF ablation, and Laplace's equation was used to model the Joule heating component. Tissue, blood, and catheter parameters were obtained from literature. The performance of the model was compared to previously established experimental values of temperature measured from various distances from the catheter tip. The model produced temperature estimations that were within 6% of the maximum experimental temperature at 2.5 mm from the catheter, and within 13% of the maximum temperature change at 4.7 mm. This model now provides a computational basis through which to conduct in silico testing of gastric ablation, and can be usefully applied to optimize gastric ablation parameters. In future, the model can be expanded to include irrigation of the catheter tip and power-controlled RF settings.Clinical Relevance- This work presents a computational model of gastric ablation that can now guide the in silico development of effective ablation parameters and therapeutic strategies, expanding the breadth of this promising therapy.

Transmural recordings of gastrointestinal electrical activity using a spatially-dense microelectrode array

Objective. High-resolution serosal recordings provide detailed information about the bioelectrical conduction patterns in the gastrointestinal (GI) tract. However, equivalent knowledge about the electrical activity through the GI tract wall remains largely unknown. This study aims to capture and quantify the bioelectrical activity across the wall of the GI tract.Approach. A needle-based microelectrode array was used to measure the bioelectrical activity across the GI wallin vivo. Quantitative and qualitative evaluations of transmural slow wave characteristics were carried out in comparison to the serosal slow wave features, through which the period, amplitude, and SNR metrics were quantified and statistically compared.Main results. Identical periods of 4.7 ± 0.3 s with amplitudes of 0.17 ± 0.04 mV versus 0.31 ± 0.1 mV and signal to noise ratios of 5.5 ± 1.3 dB versus 14.4 ± 1.1 dB were observed for transmural and serosal layers, respectively. Four different slow wave morphologies were observed across the transmural layers of the GI wall. Similar amplitudes were observed for all morphology types, and Type 1 and Type 2 were of the highest prevalence, dominating the outer and inner layers. Type 2 was exclusive to the middle layer while Type 4 was primarily observed in the middle layer as well.Significance. This study demonstrates the validity of new methodologies for measuring transmural slow wave activation in the GI wall and can now be applied to investigate the source and origin of GI dysrhythmias leading to dysmotility, and to validate novel therapeutics for GI health and disease.

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

OBJECTIVE

Gastric contractions are, in part, coordinated by slow-waves. Functional motility disorders are correlated with abnormal slow-wave patterns. Gastric pacing has been attempted in a limited number of studies to correct gastric dysmotility. Integrated electrode arrays capable of pacing and recording slow-wave responses are required.

METHODS

New flexible surface-contact pacing electrodes (SPE) that can be placed atraumatically to pace and simultaneously map the slow-wave activity in the surrounding area were developed. SPE were applied in pigs in-vivo for gastric pacing along with concurrent high-resolution slow wave mapping as validation. Histology was conducted to assess for tissue damage around the pacing site. SPE were compared against temporary cardiac pacing electrodes (CPE), and hook-shaped pacing electrodes (HPE), for entrainment rate, entrainment threshold, contact quality, and slow-wave propagation patterns.

RESULTS

Pacing with SPE (amplitude: 2 mA, pulse width: 100 ms) consistently achieved pacemaker initiation. Histological analysis illustrated no significant tissue damage. SPE resulted in a higher rate of entrainment (64%) than CPE (37%) and HPE (24%), with lower entrainment threshold (25% of CPE and 16% of HPE). High resolution mapping showed that there was no significant difference between the initiated slow-wave propagation speed for SPE and CPE (6.8 ± 0.1 vs 6.8 ± 0.2 mm/s, P>0.05). However, SPE had higher loss of tissue lead contact quality than CPE (42 ± 16 vs 13 ± 10% over 20 min).

CONCLUSION

Pacing with SPE induced a slow-wave pacemaker site without tissue damage.

SIGNIFICANCE

SPE offered an atraumatic pacing electrode with a significant reduction of power consumption and placement time compared to impaled electrodes.