How the concept of biochemical response influenced the management of primary biliary cholangitis over time.

BACKGROUND: Criteria assessing biochemical response to ursodeoxycholic acid (UDCA) are established risk stratification tools in primary biliary cholangitis (PBC). We aimed to evaluate to what extent liver tests influenced patient management during a three decade period, and whether this changed over time. METHODS: 851 Dutch PBC patients diagnosed between 1988 and 2012 were reviewed to assess patient management in relation to liver test results during UDCA treatment. To do so, biochemical response at one year was analysed retrospectively according to Paris-1 criteria. RESULTS: Response was assessable for 687/851 (81%) patients; 157/687 non-responders. During a follow-up of 8.8 years (IQR 4.8-13.9), 141 died and 30 underwent liver transplantation. Transplant-free survival of non-responders (60%) was significantly worse compared with responders (87%) (p < 0.0001). Management was modified in 46/157 (29%) non-responders. The most frequent change observed, noted in 26/46 patients, was an increase in UDCA dosage. Subsequently, 9/26 (35%) non-responders became responders within the next two years. Steroid treatment was started in one patient; 19 patients were referred to a tertiary centre. No trend towards more frequent changes in management over time was observed (p = 0.10). CONCLUSION: Changes in medical management occurred in a minority of non-responders. This can largely be explained by the lack of accepted response criteria and of established second-line treatments for PBC. Nevertheless, the observation that response-guided management did not increase over time suggests that awareness of the concept of biochemical response requires further attention,particularly since new treatment options for PBC will soon become available.

Inhomogeneities in the propagation of the slow wave in the stomach.

The propagation of the slow wave in the stomach and its role in inducing sweeping peristaltic contractions toward the pylorus, essential for a proper digestion and emptying, have been studied for many years. Irregularities in the timing or in the pattern of propagation of the slow wave have been known to induce various gastric malfunctions and, recently, several types of gastric dysrhythmias have been described which could lead to gastric contraction abnormalities. In this study, Du et al. have analyzed the disturbances caused by a simple transmural incision in a human stomach, performed to obtain a biopsy of the muscle, on the propagation pattern of the slow wave. In addition, they show that such an incision may by itself also induce new types of gastric dysrhythmias. These results are important in demonstrating that the function of the stomach can easily be disturbed by such procedures. This mini-review describes several ways in which inhomogeneities in propagation may affect the conduction pattern of the slow wave, including the genesis of several dysrhythmias, and what is currently known about their impact on gastric contraction and digestion.

Normal and abnormal electrical propagation in the small intestine.

As in other muscular organs, small intestinal motility is determined to a large degree by the electrical activities that occur in the smooth muscle layers of the small intestine. In recent decades, the interstitial cells of Cajal, located in the myenteric plexus, have been shown to be responsible for the generation and propagation of the electrical impulse: the slow wave. It was also known that the slow waves as such do not cause contraction, but that the action potentials ('spikes') that are generated by the slow waves are responsible for the contractions. Recording from large number of extracellular electrodes simultaneously is one method to determine origin and pattern of propagation of these electrical signals. This review reports the characteristics of slow wave propagation through the intestinal tube, the occurrence of propagation blocks along its length, which explains the well-known decrease in frequency, and the specific propagation pattern of the spikes that follow the slow waves. But the value of high-resolution mapping is highest in discovering and analysing mechanisms of arrhythmias in the gut. Most recently, circus movements (also called 're-entries') have been described in the small intestine in several species. Moreover, several types of re-entries have now been described, some similar to what may occur in the heart, such as functional re-entries, but others more unique to the small intestine, such as circumferential re-entry. These findings seem to suggest the possibilities of hitherto unknown pathologies that may be present in the small intestine.

Macroscopic electrical propagation in the guinea pig urinary bladder.

There is little knowledge about macroscopic electrical propagation in the wall of the urinary bladder. Recording simultaneously from a large number of extracellular electrodes is one technology that could be used to study the patterns of macroscopic electrical propagations. The urinary bladders from 14 guinea pigs were isolated and placed in an organ bath. A 16 × 4-electrode array was positioned at various sites on the serosal bladder surface, and recordings were performed at different intravesical volumes. In four experiments, carbachol (CCH; 10(-6) M), nifedipine (10 mM), or tetrodotoxin (TTX; 10(-6) M) was added to the superfusing fluid. After the experiments, the extracellular signals were analyzed and propagation maps were constructed. Electrical waves were detected at all sites on the bladder surface and propagated for a limited distance before terminating spontaneously. The majority of waves (>90%) propagated in the axial direction (i.e., from dome to base or vice versa). An increase in vesicle volume significantly decreased the conduction velocity (from 4.9 ± 1.5 to 2.7 ± 0.7 cm/s; P < 0.05). CCH increased, nifedipine decreased, while TTX had little effect on electrical activities. In addition, a new electrical phenomenon, termed a "patch," was discovered whereby a simultaneous electrical deflection was detected across an area of the bladder surface. Two types of electrical activities were detected on the bladder surface: 1) electrical waves propagating preferentially in the axial direction and 2) electrical patches. The propagating electrical waves could form the basis for local spontaneous contractions in the bladder during the filling phase.

Arrhythmic substrate, slowed propagation and increased dispersion in conduction direction in the right ventricular outflow tract of murine Scn5a+/- hearts.

AIM: To test a hypothesis attributing arrhythmia in Brugada Syndrome to right ventricular (RV) outflow tract (RVOT) conduction abnormalities arising from Nav 1.5 insufficiency and fibrotic change. METHODS: Arrhythmic properties of Langendorff-perfused Scn5a+/- and wild-type mouse hearts were correlated with ventricular effective refractory periods (VERPs), multi-electrode array (MEA) measurements of action potential (AP) conduction velocities and dispersions in conduction direction (CD), Nav 1.5 expression levels, and fibrotic change, as measured at the RVOT and RV. Two-way anova was used to test for both independent and interacting effects of anatomical region and genotype on these parameters. RESULTS: Scn5a+/- hearts showed greater arrhythmic frequencies during programmed electrical stimulation at the RVOT but not the RV. The Scn5a+/- genotype caused an independent increase of VERP regardless of whether the recording site was the RVOT or RV. Effective AP conduction velocities (CV†s), derived from fitting regression planes to arrays of observed local activation times were reduced in Scn5a+/- hearts and at the RVOT independently. AP conduction velocity magnitudes derived by averaging MEA results from local vector analyses, CV*, were reduced by the Scn5a+/- genotype alone. In contrast, dispersions in conduction direction, were greater in the RVOT than the RV, when the atrioventricular node was used as the pacing site. The observed reductions in Nav 1.5 expression were attributable to Scn5a+/-, whereas increased levels of fibrosis were associated with the RVOT. CONCLUSIONS: The Scn5a+/- RVOT recapitulates clinical findings of increased arrhythmogenicity through reduced CV† reflecting reduced CV* attributable to reduced Nav 1.5 expression and increased CD attributable to fibrosis.

Arrhythmias in the gut.

In recent years, it has become possible to record, from a large number of extracellular electrodes, the electrical activities of smooth muscle organs. These recordings, after proper processing and analysis, may reveal origin and propagation of normal and abnormal electrical activities in these organs. Several publications have appeared in the past 5 years describing origin and propagation of slow waves in the stomach of experimental animals and in humans. Furthermore, publications are now starting to appear that describe pathophysiological patterns of propagation and these studies provide us with novel concepts regarding potential mechanisms of arrhythmias in the gut, crucial information if we are ever going to successfully treat patients suffering from such arrhythmias. In this issue of Neurogastroenterology & Motility, Angeli et al. have mapped the slow wave propagation in the porcine small intestine and discovered two types of reentry; functional reentry and circumferential reentry. Next to the descriptions of arrhythmias in the stomach, the fact that reentrant arrhythmias may also occur in the small intestine further extends this new emerging field of gastrointestinal (GI) arrhythmias. In this viewpoint, the relevance of these arrhythmias is further discussed and a few ideas for future research in this field, not necessarily constrained to the GI system, proposed.

Rapid high-amplitude circumferential slow wave propagation during normal gastric pacemaking and dysrhythmias.

BACKGROUND: Gastric slow waves propagate aborally as rings of excitation. Circumferential propagation does not normally occur, except at the pacemaker region. We hypothesized that (i) the unexplained high-velocity, high-amplitude activity associated with the pacemaker region is a consequence of circumferential propagation; (ii) rapid, high-amplitude circumferential propagation emerges during gastric dysrhythmias; (iii) the driving network conductance might switch between interstitial cells of Cajal myenteric plexus (ICC-MP) and circular interstitial cells of Cajal intramuscular (ICC-IM) during circumferential propagation; and (iv) extracellular amplitudes and velocities are correlated. METHODS: An experimental-theoretical study was performed. High-resolution gastric mapping was performed in pigs during normal activation, pacing, and dysrhythmia. Activation profiles, velocities, and amplitudes were quantified. ICC pathways were theoretically evaluated in a bidomain model. Extracellular potentials were modeled as a function of membrane potentials. KEY RESULTS: High-velocity, high-amplitude activation was only recorded in the pacemaker region when circumferential conduction occurred. Circumferential propagation accompanied dysrhythmia in 8/8 experiments was faster than longitudinal propagation (8.9 vs 6.9 mm s(-1) ; P = 0.004) and of higher amplitude (739 vs 528 µV; P = 0.007). Simulations predicted that ICC-MP could be the driving network during longitudinal propagation, whereas during ectopic pacemaking, ICC-IM could outpace and activate ICC-MP in the circumferential axis. Experimental and modeling data demonstrated a linear relationship between velocities and amplitudes (P < 0.001). CONCLUSIONS & INFERENCES: The high-velocity and high-amplitude profile of the normal pacemaker region is due to localized circumferential propagation. Rapid circumferential propagation also emerges during a range of gastric dysrhythmias, elevating extracellular amplitudes and organizing transverse wavefronts. One possible explanation for these findings is bidirectional coupling between ICC-MP and circular ICC-IM networks.

High-resolution spatial analysis of slow wave initiation and conduction in porcine gastric dysrhythmia.

BACKGROUND: The significance of gastric dysrhythmias remains uncertain. Progress requires a better understanding of dysrhythmic behaviors, including the slow wave patterns that accompany or promote them. The aim of this study was to use high-resolution spatiotemporal mapping to characterize and quantify the initiation and conduction of porcine gastric dysrhythmias. METHODS: High-resolution mapping was performed on healthy fasted weaner pigs under general anesthesia. Recordings were made from the gastric serosa using flexible arrays (160-192 electrodes; 7.6mm spacing). Dysrhythmias were observed to occur in 14 of 97 individual recordings (from 8 of 16 pigs), and these events were characterized, quantified and classified using isochronal mapping and animation. KEY RESULTS: All observed dysrhythmias originated in the corpus and fundus. The range of dysrhythmias included incomplete conduction block (n=3 pigs; 3.9±0.5cpm; normal range: 3.2±0.2cpm) complete conduction block (n=3; 3.7±0.4cpm), escape rhythm (n=5; 2.0±0.3cpm), competing ectopic pacemakers (n=5, 3.7±0.1cpm) and functional re-entry (n=3, 4.1±0.4cpm). Incomplete conduction block was observed to self-perpetuate due to retrograde propagation of wave fragments. Functional re-entry occurred in the corpus around a line of unidirectional block. 'Double potentials' were observed in electrograms at sites of re-entry and at wave collisions. CONCLUSIONS & INFERENCES: Intraoperative multi-electrode mapping of fasted weaner healthy pigs detected dysrhythmias in 15% of recordings (from 50% of animals), including patterns not previously reported. The techniques and findings described here offer new opportunities to understand the nature of human gastric dysrhythmias.

Origin, propagation and regional characteristics of porcine gastric slow wave activity determined by high-resolution mapping.

BACKGROUND: The pig is a popular model for gastric electrophysiology studies. However, its normal baseline gastric activity has not been well characterized. High-resolution (HR) mapping has recently enabled an accurate description of human and canine gastric slow wave activity, and was employed here to define porcine gastric slow wave activity. METHODS: Fasted pigs underwent HR mapping following anesthesia and laparotomy. Flexible printed-circuit-board arrays were used (160-192 electrodes; spacing 7.62 mm). Anterior and posterior surfaces were mapped simultaneously. Activation times, velocities, amplitudes and frequencies were calculated, and regional differences evaluated. KEY RESULTS: Mean slow wave frequency was 3.22 ± 0.23 cpm. Slow waves propagated isotropically from the pacemaker site (greater curvature, mid-fundus). Pacemaker activity was of higher velocity (13.3 ± 1.0 mm s(-1)) and greater amplitude (1.3 ± 0.2 mV) than distal fundal activity (9.0 ± 0.6 mm s(-1), 0.9 ± 0.1 mV; P < 0.05). Velocities and amplitudes were similar in the distal fundus, proximal corpus (8.4 ± 0.8 mm s(-1), 1.0 ± 0.1 mV), distal corpus (8.3 ± 0.8 mm s(-1), 0.9 ± 0.2 mV) and antrum (6.8 ± 0.6 mm s(-1), 1.1 ± 0.2 mV). Activity was continuous across the anterior and posterior gastric surfaces. CONCLUSIONS & INFERENCES: This study has quantified normal porcine gastric slow wave activity at HR during anesthesia and laparotomy. The pacemaker region was associated with high-amplitude, high-velocity slow wave activity compared to the activity in the rest of the stomach. The increase in distal antral slow wave velocity and amplitude previously described in canines and humans is not observed in the pig. Investigators should be aware of these inter-species differences.

High-resolution mapping of in vivo gastrointestinal slow wave activity using flexible printed circuit board electrodes: methodology and validation.

High-resolution, multi-electrode mapping is providing valuable new insights into the origin, propagation, and abnormalities of gastrointestinal (GI) slow wave activity. Construction of high-resolution mapping arrays has previously been a costly and time-consuming endeavor, and existing arrays are not well suited for human research as they cannot be reliably and repeatedly sterilized. The design and fabrication of a new flexible printed circuit board (PCB) multi-electrode array that is suitable for GI mapping is presented, together with its in vivo validation in a porcine model. A modified methodology for characterizing slow waves and forming spatiotemporal activation maps showing slow waves propagation is also demonstrated. The validation study found that flexible PCB electrode arrays are able to reliably record gastric slow wave activity with signal quality near that achieved by traditional epoxy resin-embedded silver electrode arrays. Flexible PCB electrode arrays provide a clinically viable alternative to previously published devices for the high-resolution mapping of GI slow wave activity. PCBs may be mass-produced at low cost, and are easily sterilized and potentially disposable, making them ideally suited to intra-operative human use.

Mapping slow waves and spikes in chronically instrumented conscious dogs: implantation techniques and recordings.

Myoelectric recordings from the intestines in conscious animals have been limited to a few electrode sites with relatively large inter-electrode distances. The aim of this project was to increase the number of recording sites to allow high-resolution reconstruction of the propagation of myoelectrical signals. Sets of six unipolar electrodes, positioned in a 3x2 array, were constructed. A silver ring close to each set served as the reference electrodes. Inter-electrode distances varied from 4 to 8 mm. Electrode sets, to a maximum of 4, were implanted in various configurations allowing recording from 24 sites simultaneously. Four sets of 6 electrodes each were implanted successfully in 11 female Beagles. Implantation sites evaluated were the upper small intestine (n=10), the lower small intestine (n=4) and the stomach (n=3). The implants remained functional for 7.2 months (median; range 1.4-27.3 months). Recorded signals showed slow waves at regular intervals and spike potentials. In addition, when the sets were positioned close together, it was possible to re-construct the propagation of individual slow waves, to determine their direction of propagation and to calculate their propagation velocity. No signs or symptoms of interference with normal GI-function were observed in the tested animals. With this approach, it is possible to implant 24 extracellular electrodes on the serosal surface of the intestines without interfering with its normal physiology. This approach makes it possible to study the electrical activities of the GI system at high resolution in vivo in the conscious animal.

Electrical activity in the rectum of anaesthetized dogs.

There is limited data available on the electrical activity of the rectum. An in vivo canine model was developed to record 240 extracellular electrograms simultaneously from the serosal surface of the rectum thereby enabling an off-line reconstruction of the behaviour of the electrical signals. Serosal rectal electrical activity is characterized by brief bursts of action potentials (=spikes) with a frequency of 22 cycles min(-1). High-resolution mapping of these signals revealed predominant propagation of these spikes in the longitudinal direction, originating from any site and conducted for a limited time and length before stopping spontaneously, thereby describing a patch of activity. The dimension of the patches in the longitudinal direction was significantly longer than the transversal width (13.6 vs 2.4 mm; P < 0.001). Spike propagation could occur in the aboral (46% of cases), in the oral (34%) or in both directions (20%). A bolus of betanechol (i.v., 0.5 mg kg(-1)) increased the frequency of the spikes without affecting size, shape or orientation of the patches. As in other parts of the gastrointestinal system, individual spike propagation in the rectum is limited to small areas or patches. The contractile activity of the organ could possibly reflect this underlying pattern of electrical behaviour.

Spatiotemporal electrical and motility mapping of distension-induced propagating oscillations in the murine small intestine.

Since the development of knockout animals, the mouse has become an important model to study gastrointestinal motility. However, little information is available on the electrical and contractile activities induced by distension in the murine small intestine. Spatiotemporal electrical mapping and mechanical recordings were made from isolated intestinal segments from different regions of the murine small intestine during distension. The electrical activity was recorded with 16 extracellular electrodes while motility was assessed simultaneously by tracking the border movements with a digital camera. Distension induced propagating oscillatory contractions in isolated intestinal segments. These propagating contractions were dictated by the underlying propagating slow wave with superimposed spikes. The frequencies, velocities, and direction of the propagating oscillations strongly correlated with the frequencies (r = 0.86), velocities (r = 0.84), and direction (r = 1) of the electrical slow waves. N(omega)-nitro-L-arginine methyl ester decreased the maximal diameter of the segment and reduced the peak contraction amplitude of the propagating oscillatory contractions, whereas atropine and verapamil blocked the propagating oscillations. Tetrodotoxin had little effect on the maximal diameter and peak contraction amplitude. In conclusion, distension in the murine small intestine does not initiate peristaltic reflexes but induces a propagating oscillatory motor pattern that is determined by propagating slow waves with superimposed spikes. These spikes are cholinergic and calcium dependent.

Spatial determination of successive spikes in the isolated cat duodenum.

In seven isolated segments of the feline duodenum, the timings of all spikes and the locations of all spike patches that occurred after 12-16 successive slow waves were analysed. Simultaneous recordings were performed during 1-min periods using 240 extracellular electrodes (24 x 10 array; interelectrode distance 2 mm) positioned onto the serosal surface. In all seven preparations, spikes always occurred during the first half of the slow wave cycle. From preparation to preparation, and within 1-min periods in each preparation, there was limited variation in the spike-spike intervals, in the times between the spikes and the preceding slow wave and in the number of spikes at each electrode site. In contrast, the number of electrode sites that recorded spikes and the number of spike patches both showed great variability between preparations and sometimes within a single preparation. In addition, the location of spikes and spike patches was not random but was significantly concentrated in certain areas, often located along the anti-mesenteric border, while other sites showed little or no spike activity. In conclusion, spikes and spike patches tend to occur significantly in some areas and not in others. This spatial heterogeneity will play a role in intestinal motility.

Anisotropic propagation in the small intestine.

Abstract Measuring propagation anisotropy may help in determining the tissue layers involved in the propagation of electrical impulses in the intestine. We used 240 extracellular electrograms recorded from the isolated feline duodenum. The conduction velocities of slow waves and of individual spikes were measured from their site of origin into all directions. Both slow waves and spikes propagate anisotropically in the small intestine but in different directions and to a different degree. Slow waves propagated anisotropically faster in the circumferential (1.7 +/- 0.8 cm s(-1)) than in the axial direction (1.3 +/- 0.5 cm s(-1); P < 0.001). Spikes, on the other hand, propagated faster in the longitudinal direction (7.8 +/- 4.5 cm s(-1)) than in the circumferential direction (3.3 +/- 4.3 cm s(-1); P < 0.001). Furthermore, the average conduction velocity of spikes (6.3 +/- 4.5 cm s(-1)) was significantly higher than that of slow waves (1.5 +/- 1.1 cm s(-1); P < 0.001). The anisotropic propagation of spikes supports the argument that these propagate in the longitudinal muscle layer. The anisotropic propagation of slow waves may be the result of the interaction between the myenteric layer of interstitial cells of Cajal and their electrotonic connection to both the longitudinal and the circular muscle layer.

Two-dimensional high-resolution motility mapping in the isolated feline duodenum: methodology and initial results.

Several types of electrical events occur in the small intestine but their spatial and temporal contributions to overall motility are not clear. In order to quantify local motility in greater detail, a new technique of recording and analysing movements at multiple sites was developed. Use was made of isolated segments of feline duodenum superfused in a tissue bath. Multiple marker dots (20-75) were placed on the serosal surface by applying fine spots of candle soot in rectangular arrays (1-2 mm dot separation). A digital video camera was used to record spontaneous movements of the dots for periods of 10-30 min. After each experiment, 4-6 periods (10-60 s each) of video frames were transferred to a computer (25 fps, 720 x 576 pixels) and the movements of the dots was tracked every 40 ms using custom-made software. Initial results (eight experiments) show that spontaneous motility is remarkably variable, both in space and time. Three types of movement could be discerned: (i) periodic, rolling or pendular movements, with a frequency of approximately 15 min-1 occurring predominantly in the longitudinal direction; (ii) twitches, wherein a subset of dots were suddenly displaced longitudinally; and (iii) drifts of most of the dots in a circular or oblique direction. All three types of movement occurred throughout every recording session although their relative magnitudes differed greatly from moment to moment. Occasionally, it was possible to detect propagated 'contractions' with an apparent velocity of 10 mm s(-1). Immobilizing the preparation at one point by inserting a needle through the middle of the array of markers had a negligible effect on the displacements, whereas application of verapamil (10(-5) mol L(-1)) reduced or abolished motility. In summary, we present a new technique to map in detail two-dimensional motility at the surface of the intestine. Initial results seem to suggest that motility at the serosal surface is not uniform and highly anisotropic.

Of slow waves and spike patches.

In the small intestines, the major task of the slow wave is to induce mechanical movements in the intestinal wall by generating local calcium spikes. High resolution electrical mapping reveals fundamental differences in propagation between slow waves and calcium spikes. These differences suggest that slow waves and spikes are propagated by different mechanisms through different cell networks.