Introduction
Endoscopic submucosal dissection (ESD) has become the standard procedure for en bloc
resection of gastrointestinal tract tumors [1]
[2]
[3]
[4]
[5]
[6]
[7]. ESD requires advanced skills and a long learning curve to achieve consistent and
complete procedures [8]
[9]. In addition, ESD has the disadvantage of high complication rates [10]. Specifically, since the esophageal wall is thin and its lumen is narrow, esophageal
ESD complications such as perforation and active bleeding can be frequent and difficult
to treat [1]
[11]
[12]
[13]
[14]
[15].
HybridKnife is a unique ESD device that provides high pressure water flow on the top
of the stainless steel tube. It has an outer diameter of 2.1 mm and a length of 2.2 m.
The tip of the stainless steel tube incorporates a microcapillary lumen with a diameter
of 150 µm [16]
[17]
[18]
[19]
[20]. When used with the waterjet generator ERBEJET 2 System, HybridKnife enables needleless
infusion for submucosal elevation as well as electrical cutting and coagulation of
visible vessels without changing devices [21]
[22]
[23]
[24]. The combination of HybridKnife and ERBEJET 2 can attain water pressures of up to
80 bar in the endoscopy field. Recent experimental studies of other prototype waterjet
dissectors showed less damage to the gastrointestinal muscular layer [9]
[25]
[26]. Thus, we hypothesized that the high pressure waterjet generated by HybridKnife
and ERBEJET 2 might enable dissection of the submucosal layer with less tissue damage
and improve the safety of esophageal ESD. The primary aims are to find the appropriate
water pressure for waterjet ESD and to evaluate the safety and feasibility of warterjet
dissection using HybridKnife in an anesthetized porcine model.
Materials and methods
Animals
Two healthy 3-month-old domestic pigs weighing 50 kg were used. The pigs were deprived
of food, but water consumption was allowed for 24 hours before the procedure. All
procedures were performed with the animals placed in the left lateral decubitus position
on the operating table under general anesthesia. The pigs were premedicated with intramuscular
ketamine (10 mg/kg) and xylazine hydrochloride (2 mg/kg). Isofluorane gas (1.5 L/min)
was used to maintain anesthesia under mechanical respiratory assistance. Vital signs
and physiological parameters were monitored during the procedures. The endoscope was
inserted through a flexible sterile overtube (MD48618, Sumitomo Bakelite, Tokyo, Japan).
At the end of procedure, the pigs were euthanized, and necropsy was performed immediately.
This study was approved by the Institutional Animal Care and Use Committee of the
University of Tsukuba.
Endoscope, ESD devices, and other equipment
A forward-viewing single channel gastrointestinal endoscope (GIF-Q260J; Olympus Medical
Systems, Tokyo, Japan) with a conical transparent cap attached to the tip was used
for all procedures. We used a HybridKnife T-Type (Erbe Elektromedizin, Tübingen, Germany)
for waterjet dissection and DualKnife with a 1.5-mm long needle (KD-650U, Olympus
Medical Systems, Tokyo, Japan) for circumferential cutting and conventional dissection.
The modular VIO generator (VIO 300D; Erbe Elektromedizin, Tübingen, Germany) was used
as the radiofrequency surgical system. The VIO was set to modes ENDO CUT Q 2-3-2 for
circumferential cutting and SWIFT COAG E2 40 W for DualKnife dissection. The argon
plasma coagulation (APC) mode used to mark pseudo-esophageal lesions was FORCED APC
40 W, and the vessel coagulation mode was SOFT COAG E2 60 W.
The cartridge in the waterjet generator, ERBEJET 2 (Erbe Elektromedizin, Tübingen,
Germany), was filled with 0.9 % saline solution with 0.5 % Indigo Carmine. For initial
mucosal lifting, a mixture with hyaluronic acid (MucoUp; Seikagaku Co., Tokyo, Japan)
was injected with a 23-gauge injection needle (MD-47393; Olympus Medical Systems,
Tokyo, Japan). Endoclips (HX-610-135 L, Olympus Medical Systems, Tokyo, Japan) with
string were used for countertraction. The ERBEJET 2 was attached to the VIO 300 D.
To find the appropriate water pressure for dissection, we performed preliminary experiments
in one pig. Water pressures of 30, 50, and 70 bar were tested for dissection in four
virtual esophageal lesions. To further confirm safety, we applied water pressures
of 50 and 70 bar directly to the resection bed at an angle of 45° for 1 minute.
Preparation of the pseudo-lesions and circumferential cutting
The locations of pseudo-esophageal lesions per pig were as follows: one each left
side in the lower, middle, and upper esophagus per technique. This sample number was
determined referring to a previous report [25]. The lesions were resected alternately from lower to upper esophagus, i. e. lower
and upper esophagus for waterjet ESD (WJ-ESD) and middle esophagus for conventional
ESD (C-ESD) in one pig and vice versa in another pig. The distance between each lesion
was at least 20 mm. These lesions were marked by APC in an oval shape with an approximately
30-mm longitudinal diameter. The size of each lesion was estimated by the distance
marker imprinted on the APC probe. This 30-mm size was decided upon because it was
technically easy to treat and it was used in another experimental study [26]. After marking with APC, we injected a mixture of hyaluronic acid with 0.5 % Indigo
Carmine around the pseudo-lesion to form an initial elevation. The injections were
repeated to secure appropriate mucosal layer lifting and separation from the muscle
layer. After a sufficiently high mucosal elevation, a circumferential incision outside
the markers was performed as deeply as possible using the DualKnife. Before submucosal
dissection, the clip with string was attached to the oral edge of the lesion, and
the string was pulled in the oral direction to move the submucosal surface to the
front.
Esophageal submucosal dissection using two dissection methods
A single endoscopist who had extensive experience in therapeutic endoscopy performed
all procedures. All procedures were recorded on video. Two techniques, conventional
dissection with DualKnife (C-ESD) and waterjet dissection with HybridKnife (WJ-ESD),
were performed on three lesions each. In C-ESD, the procedure was initiated from the
oral side using Swift Coagulation mode in the usual manner. A mixture of hyaluronic
acid was injected as often as needed. In WJ-ESD, the surface of the submucosal layer
was dissected by waterjet only, and electrocautery was not used other than at fibrosis-rich
sites. During WJ-ESD, the distance to the submucosal surface from the HybridKnife
tip was always less than 5 mm ([Video 1]).
Outcome evaluation in two methods
The sizes of ESD samples and dissection times were measured. The dissection speeds
were calculated as sample area divided by dissection time [27]
[28]. When blood vessels were encountered and bleeding occurred, coagulation was performed
with each knife in the SOFT COAG mode (E4, 60 W). When initial coagulation did not
work, the bleeding was stopped with additional hemostatic tools, such as coagulation
forceps. After the pig had been euthanized, the esophagus was removed and opened with
scissors. The esophageal resection beds were checked from the outer side for macroscopic
perforations. The ESD specimens and resection beds were stretched and pinned on a
cork board immersed in 15 % formalin, and these samples were cut to 2-mm widths to
mount for preparation. Thermal damage to the muscle layer was defined as resection
bed muscle fiber degeneration, such as laceration, disruption, or vaporization. The
percentages of thermal damage were calculated as the total length of thermal damage
divided by the length of the dissected mucosal layer. This was calculated for all
2-mm specimen preparations from each location.
Statistical analysis
Data were collected and described in actual numbers and percentages. No statistical
analysis of significance was performed between the treatment groups because of the
small sample sizes.
Results
Determination of water pressure for dissection
First we applied 30, 50, and 70 bar water pressures to assess the dissection abilities
on one pseudo-lesion. Thirty bar water pressure was too low to dissect submucosa.
Then, we performed 70 bar WJ-ESD in two pseudo-lesions and 50 bar WJ-ESD in one pseudo-lesion.
Both 70 and 50 bar of water pressure made it possible to dissect submucosa similarly.
Intense water backflow, which disturbed the endoscopic front view, occurred more frequently
when using 70 bar compared with 50 bar. The 50 bar waterjet was appropriate for WJ-ESD
because it balanced proper dissection and endoscopic view. No muscle injury was observed
when using a water pressure of 50 bar directly to the muscle layer of a resection
bed for 1 minute ([Fig. 1a, b]), but a perforation occurred at 70 bar ([Fig. 1c]). Based on these results, 50 bar of water pressure was considered optimal for WJ-ESD
of porcine esophagus and was used in subsequent experiments.
Fig. 1 Macroscopic and microscopic findings after application of a water pressure of 50 bar
(a, b) and 70 bar (c) directly to the muscle layer of a resection bed for 1 minute. No perforation was
observed when using 50 bar, but a small perforation occurred when using 70 bar (arrow).
This was observed with transmitted light behind the resected bed. * A blood clot.
Outcomes of the two methods
The planned ESDs were all successfully performed. The en bloc resection rate was 100 %.
A total of six ESD samples and six resection beds were obtained (three using C-ESD
and three using WJ-ESD). The results are presented in [Table 1]. Resected mucosa sizes were similar in both procedures. Dissection times were longer
in the WJ-ESD procedure and dissection speed was slower in the WJ-ESD procedure.
Table 1
Outcomes of the two ESD procedures.
|
Conventional ESD
(n = 3)
|
Waterjet ESD
(n = 3)
|
|
Dissected specimen size, cm2
|
10/8/5
|
8/6/7
|
|
Dissection time, min
|
9/15/5
|
36/7/32
|
|
Dissection speed, cm2/min
|
1.1/0.5/1.0
|
0.2/0.9/0.2
|
|
Minor bleeding events treated with electrocoagulation, n
|
1/1/1
|
6/4/8
|
|
Device change for hemostasis, n
|
1/2/0
|
0/0/0
|
|
Thermally damaged area in the muscle layer[*], %
|
14/16/7
|
4/6/8
|
ESD, endoscopic submucosal dissection.
All values are presented according to the site of ESD: lower/middle/upper esophagus.
* (sum of the lengths of thermal damage in the muscle layer/sum of the lengths of the
dissected beds) × 100. Each length was calculated in all specimens for histological
examination, which were sliced in 2-mm lengths.
Minor bleeding, which was easily stopped by electrocoagulation using the same knife,
was more frequent in the WJ-ESD procedure. Neither uncontrollable bleeding nor perforation
occurred, and the use of coagulation forceps was not required in either procedure.
No microscopic perforation was observed in either procedure. The thermally damaged
areas in the muscle layer were smaller in the lesions of the WJ-ESD procedure as expected
([Fig. 2]).
Fig. 2 Dissected bed specimens from conventional ESD (C-ESD) with DualKnife (a, b) and waterjet ESD (WJ-ESD) with HybridKnife (c, d). a A bed dissected using conventional ESD appears reddish and edematous, and some coagulation
is observed. b Dotted lines indicate microscopic thermal damage to the muscle layer in the dissected
bed (solid line) in C-ESD. c A bed dissected using waterjet appears reddish and edematous, but coagulation is
not observed. d Dotted line indicates microscopic thermal damage to the muscle layer in the dissected
bed (solid line) in WJ-ESD. Hematoxylin-eosin staining.
Discussion
In this experimental study, we safely completed waterjet submucosal dissection using
the HybridKnife in porcine esophagus. Waterjet could be used for tissue-sparing blunt
submucosal dissection in the esophagus. Bleeding was easily managed using coagulation
mode, and no perforation was observed. Much more time was required to complete the
procedure with WJ-ESD, but thermal damage to the muscle layer was much milder.
We used 50 bar water pressure in WJ-ESD for porcine esophagus. Higher water pressure
enables faster dissection, but it increases the risk of perforation and bleeding.
Although a water pressure of 20 – 30 bar was reported to be feasible for porcine tissue
dissection [25]
[26], we tested higher pressures to speed up dissection as much as was safely feasible.
A water pressure of 70 bar caused a macroscopic perforation and additionally intense
water backflow, which disturbed the endoscopic front view, and was not considered
applicable. Given the harder porcine esophagus, a water pressure of 50 bar is considered
appropriate for WJ-ESD. When performing WJ-ESD in patients, the most appropriate waterjet
pressure under 50 bar should be determined in a carefully and safely designed clinical
trial.
In Japan, esophageal ESD is a widely accepted treatment for early squamous cell carcinoma
or high grade intraepithelial neoplasia [2]. However, esophageal ESD is associated with a higher rate of complications, such
as perforation or bleeding, than that for other gastrointestinal organs. The esophageal
ESD perforation rate is approximately 5.2 % [2], and delayed perforation can occur from thermal damage several days after the procedure.
In addition, thermal damage to the muscle layer may cause a scar stenosis even if
the resected tissue is small. These esophageal ESD complications could be more serious
than those of gastric ESD. To minimize these complications, less electrocautery device
usage is reasonable. In this study, we showed that thermal damage to the muscle layer
was essentially mild and minor in WJ-ESD. This method may reduce the risk not only
of esophageal perforation but also stenosis.
Recently, the efficacy of the Thread-Traction method (T-T method) with clips was reported
for esophageal ESD, and this procedure has become widespread in Japan [29]
[30]
[31]. Since the T-T method with clips tenses the submucosal tissue in front of the endoscope,
we used this method to transmit the power of the waterjet directly to the edge of
dissection and successfully completed the procedure.
WJ-ESD is safe, but it takes more time, even with the T-T method. For future clinical
development, WJ-ESD should be combined with conventional methods. For example, after
removing soft tissue using the waterjet with the T-T method, hard tissue, e. g. fibrosis,
should be treated using electrocoagulation, making the dissection time shorter. Additional
injections were not needed for mucosal lifting because the waterjet elevated the submucosal
layer concurrently, and this allowed the operator to lighten the work load of needle
exchange ([Video 1]). We are now planning prospective clinical studies to assess the combination of
electrocoagulation and WJ-ESD.
There are some limitations to this study. First, the sample size was small. Recently,
it has become difficult to use many animals from an ethical standpoint. However, we
can confirm that three WJ-ESD procedures were safely completed. Second, the porcine
esophagus had some fibrosis, and it was somewhat difficult to dissect using only the
waterjet. Since the submucosal layer of the human esophagus would be softer than that
of a pig, dissection with only the waterjet may be easier in humans. Third, evaluation
of healing after WJ-ESD is lacking in the present study because it is impossible to
feed pigs for a long time after ESD at our institution. However, the milder pathological
changes in dissected specimens suggest better healing after WJ-ESD.
In conclusion, WJ-ESD using the HybridKnife and ERBEJET 2 System is safe with lower
thermal damage, and can be combined with conventional submucosal dissection. Clinical
trials of WJ-ESD are warranted based on these findings.
Video 1: Waterjet submucosal dissection using the HybridKnife with ERBEJET 2 system.
