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Keywords:

  • ureteric physiology;
  • ureteric stent;
  • electromyography

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

OBJECTIVE

To test a novel ‘ribbon stent’ (RS) design using an extraluminal bipolar electromyographic (EMG) and giant magnetoresistive (GMR) sensor system to characterize ureteric responses.

MATERIALS AND METHODS

In all, 11 female domestic pigs were divided into three groups to evaluate ureteric physiology: group 1 (two pigs) with an unstented ureter, group 2 (three) with a standard 6 F ureteric stent, and group 3 (six) with the RS. For all groups EMG/GMR evaluation was performed at baseline, immediately after stenting, and at 3 and 7 days after stenting. All pigs underwent standardized retrograde ureteropyelogram evaluation at these time points, and after the final evaluation the pigs were killed and the urinary tract was harvested for histopathological evaluation.

RESULTS

One stent in group 3 could not be deployed due to a problem with ureteric access. For groups 1, 2 and 3 the ureteric peristaltic activity was 109, 63, 72 events/h at baseline (P = 0.49); 61, 70, and 66 events/h immediately after stenting (P = 0.97); 66, 0, 8 events/h at 3 days after stenting (P = 0.002); and 61, 12, 0 events/h at 7 days after stenting, respectively (P = 0.049).

CONCLUSION

The RS was deployed easily and safely in the porcine model using a standard technique. As with a standard stent, there was significant ureteric dilation and decrease in peristalsis with the RS.


Abbreviations
RS

ribbon stent

EMG

extraluminal bipolar electromyography/ic

GMR

giant magnetoresistive (sensor).

INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

Ureteric stenting remains an important technique in urological practice [1]. Together with its widespread use, stenting is associated with significant morbidity, which is manifested in various urinary symptoms including haematuria, and a reduction in quality of life that can even affect sexual health [2–5].

In an effort to minimize adverse effects and morbidity of ureteric stenting, numerous attempts for stent modifications have been made, including alteration of surface coatings, insertion techniques, length, and altering the composition material [1]. Despite all these improvements little progress has been made in understanding the ureteric physiology of a stented ureter and improving the associated morbidity [1,6].

Until recently, all physiological measurements of ureteric stent response were performed by intraluminal measuring devices (a device measuring ureteric response within the lumen of the ureter). Intraluminal testing is of very limited utility as the presence of a foreign body within the lumen of the ureter is known to dramatically alter the normal physiological function of this structure [7,8]. Few extraluminal techniques for ureteric physiological evaluation have been described. Cox et al.[9] evaluated peristalsis by using colour Doppler ultrasonography. Although the technique was viable, the results were limited as the stented ureter lacked wall opposition, the ability of the anterior and posterior ureteric wall to efficiently propel the urinary bolus, which diminished ureteric jet observation under ultrasonography [10]. Similarly, Chew et al.[11] assessed ureteric movement in patients with stents. However, this technique is limited by the two-dimensional nature of plain radiography and by the requirement for significant radiation exposure.

Recently, Venkatesh et al.[12] developed a novel tool using extraluminal bipolar electromyographic (EMG) and giant magnetoresistive (GMR) sensors to measure ureteric electrical impulses and ureteric mechanical motion, respectively. These sensors can measure ureteric response to varying conditions in an extraluminal manner and can be deployed using a minimally invasive technique (laparoscopy). This new technology enables minimal collateral damage and an increased understanding of stented ureteric physiology. Using the EMG/GMR system to evaluate new stent materials and characteristics will possibly allow Urologist to reduce stent-associated morbidity in patients. However, correlation of ureteric physiological changes and clinical response has not been reported.

We have recently developed a novel stent design in the hope of minimizing changes to ureteric physiology. The ‘ribbon stent’ (RS) design has a reduced surface area and therefore the physical contact between the ureter and stent is reduced. The present study was a preclinical evaluation to compare the ureteric response between the RS and a standard stent design.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

The Columbia University Institutional Animal Care Usage Committee approved the protocol. In all, 11 female domestic pigs, weighing ≈25 kg were used. The pigs were divided into three groups to evaluate ureteric physiology: group 1 (two pigs) with an unstented ureter, group 2 (three) with a standard 18 cm 6 F JJ stent (Boston Scientific, Natick, MA, USA), and group 3 (six) with the RS. All the pigs were kept alive for 1 week. In all, four ureteric EMG/GMR evaluations were conducted at specific time points: before ureteric stenting, immediately after ureteric stenting, and at 3 and 7 days after stenting. Ureteric evaluations consisted of both EMG/GMR electro-physical measurements and visual assessment of peristaltic activity on the right ureter as previously described [12].

The RS design used in the present study is a flat stent design with an inner and outer diameter of 0.71 and 1.02 mm. In addition to this small diameter tube, two flat wings are affixed in opposition to each other measuring a distance of 2.34 mm from wing to wing (Fig. 1). The RS design does incorporate drainage holes.

image

Figure 1. The RS was developed with an inner and outer diameter of 0.71 and 1.02 mm. In addition to this small diameter tube, two wings are affixed in opposition to each other measuring a distance of 2.34 mm from wing to wing. The largest diameter wire this stent will accept is a 0.64 mm diameter glide wire. The stent will not accept a 0.64 mm PTFE wire.

Download figure to PowerPoint

Anaesthetic procedures and laparoscopic access were performed as previously described [12]. The ureter was identified and three small incisions were made in the peritoneum above the ureter at the renal pelvis, mid and distal ureter. At the mid-ureteric site, additional dissection underneath the ureter was performed. Development of this space was needed for deployment of the GMR sensor. At both the renal pelvis and distal ureter, EMG electrodes were placed into the muscular coat of the ureter. A 1 h baseline ureteric evaluation was performed. Upon completion of the baseline ureteric evaluation, the pig was placed supine and a rigid cystoscope was inserted, and either the standard stent or RS was deployed. The pig was then repositioned into the flank position for additional ureteric monitoring for 1 h. Ureteric monitoring was repeated in the same manner at 3 and 7 days after stenting.

After the ureteric evaluation at 7 days after stenting, the pig underwent bilateral retrograde ureteropyelography and the diameter of the ureter was quantified by digital measurements at the proximal, mid and distal ureter. The pig was then killed with a sodium pentobarbital overdose. Both ureters were harvested and splayed open down to the ureteric orifices. The circumference of the ureter was quantified by measurement of the flat splayed open ureter. The ureters were then fixed with formalin for 24 h. The ureteric specimens were imbedded in paraffin wax, sectioned and stained with haematoxylin and eosin for histological evaluation. An experienced histopathologist with extensive experience of porcine ureters performed all histopathological evaluations. Histological evaluations assessed the kidney, ureter and ureteric orifice for both inflammation and fibrosis. A 4-point scale assessed the degree of change, with 0 indicating no change and 3 indicating severe changes.

anova analysis was used to compare ureteric peristaltic events, and differences in ureter circumferences and diameters. The Kruskal–Wallis test was used to assess differences between the various stented ureters subjective histological scores.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

Stent placement was successfully performed in 10 pigs. Due to a challenging anatomy with a very tortuous ureter, we were unable to place a wire in one pig in the RS group and thus the stent was not deployed. The inability to deploy was related only to wire access and not the stent design. There were no complications during or after the procedures. All the pigs completed the necessary observation period for the study, before being killed. The baseline ureteric peristaltic activities in groups 1, 2 and 3 are shown in Table 1.

Table 1.  Ureteric peristalsis (events/h) before and after stent placement
Ureteric peristalsisExperimental group
123
Events/h at:
 Baseline1096372
 Immediately after stenting 617066
 3 days after stenting 66 0 8
 7 days after stenting 6112 0
P  0.097 0.002 0.049

The retrograde ureteropyelogram evaluations of both ureteric diameters for groups 1, 2 and 3 showed a change of 0, +4.8 and +7.1 mm (P = 0.67) in the proximal ureter; 0, +8.6 and +7.5 mm (P = 0.79) in the mid-ureter; and 0, +12.5, and +12.7 mm (P = 0.96) in the distal ureter, respectively.

The gross ureteric circumferential measurements of both ureters for groups 1, 2 and 3 changed by +1, +2 and +6 mm (P = 0.58) in the proximal ureter; by 0, +4.6 and +2.8 mm (P = 0.64) in the mid-ureter; and by +0.5, +4.3, and +5.0 mm (P = 0.92) in the distal ureter, respectively.

Histological grading assessing inflammation was performed on the kidney, ureter and ureteric orifice. The mean inflammation scores for groups 1, 2 and 3 were 0, 0.3 and 0 in the kidney (P = 0.83); 0, 1.2 and 1.6 in the ureter (P = 0.044); and 0, 0.6 and 1.6 in the ureteric orifice (P = 0.04), respectively. Additionally, histological grading assessing fibroses was performed on the kidney, ureter and ureteric orifice. The mean fibrosis scores for groups 1, 2 and 3 were 0, 0.66 and 0.16 in the kidney (P = 0.20); 0, 1 and 1.2, in the ureter (P = 0.024); 0, 1.0 and 1.0 in the ureteric orifice, respectively (P = 0.85).

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

Ureteric stenting with a standard ureteric stent design continues to be a mainstay of urological practice and the application of ureteric stents continues to increase. Ureteric stents are a source of significant morbidity and discomfort to patients. Vega et al.[13] evaluated 100 patients with ureteric stents inserted for various indications, and described an 89% rate of complaints related to stent placement and a significant diminishment in patient quality of life.

Many studies evaluating possible causative factors to stent-related symptoms have been conducted. Attention has focussed on factors including stent material, length, coating, and diameter. However, to date, no strong and direct causative relationship has been found to post-stenting symptoms [14–16]. El-Nahas et al.[17] studied risk factors for the development of stent-related symptoms and reported that a positive urine culture, crossing of the lower coil to the other side of the bladder, calyceal position of the upper coil, longer stents, larger stent diameter and presence of Percuflex® stents, as being significant factors for patient discomfort.

In theory, the characteristics of an ideal ureteric stent would include biocompatibility, ability to allow intra- and extra-luminal flow, stability after placement, radiopacity, stability in contact with urine, resistance to encrustation and infection, maintenance of long-term flow, no causative relation to irritative symptoms, and cost efficiency [18]. Despite many efforts to alter stent technology, no such ideal stent is available, and the information on stent-related physiology is confined to a few studies, based mainly on symptoms other than working mechanisms [13,19].

To date, most studies to evaluate ureteric peristalsis consisted of invasive procedures using intraluminal transductors [20] or ultrasound-based evaluation that lacks accuracy, as it is subjective to both the ability of the person who is performing it and the ability of the technology to detect peristalsis [10].

The present study is the first to evaluate ureteric peristalsis in a extraluminal setting and minimally invasive way, acquiring direct measures by using bipolar EMG and GMR sensors, since its description by Venkatesh et al. in 2005 [12]. This new technology enables more accurate evaluation of ureteric peristalsis and therefore a better understanding of the stents influence on it.

The present findings showed an increase in ureteric peristalsis after regular 6 F stenting, possibly an effect of ureteric stimulation from the larger contact surface between the stent and the ureteric wall compared with the RS. The new RS showed little immediate interference on peristalsis, probably reflecting its smaller contact surface. This finding is in accordance to Venkatesh et al.[12] who reported an increase in peristalsis in the first 2 h after ureteric stenting. The RS-stented pigs maintained baseline peristalsis after stenting, reinforcing our theory of there being less inflammation caused on ureteric wall with the flat-shape RS.

At 3 days after stenting, peristalsis was markedly reduced in both stented groups, possibly due to ureteric dilation and inflammation. However, in group 3 (RS-stented group) there was a smaller reduction in peristalsis, possibly reflecting its lesser interaction with ureteric tissue due to its shape. Diminishment of ureteric peristalsis persisted to 7 days after stenting in groups 2 and 3, reflecting maintained ureteric dilation and inflammation due to stent presence reducing the force of contractions. These findings are consistent to those from Kinn and Lykkeskov-Andersen [20] that describe a lack of ureteric peristalsis at 7 days after stenting and support the recommendation of maintenance of a ureteric stent for as short a period as clinical features allow.

In conclusion, the flat-shaped RS was easily deployed in the porcine model using a standard stenting technique over a 0.64 mm glide wire. The RS maintained normal active ureteric peristalsis immediately after stenting. We were able to detect no difference between the RS and the regular 6 F JJ stent at 3 and 7 days after stenting.

CONFLICT OF INTEREST

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES

None declared. Source of funding: departmental.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. CONFLICT OF INTEREST
  8. REFERENCES