Transperineal ultrasound to assess the effect of tension-free vaginal tape position on flow rates

Ultrasound Obstet Gynecol 2010; 36: 379 383 Published online 3 August 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/uog.7640 Transperineal ultrasound to assess the effect of tension-free vaginal tape position on flow rates J. DUCKETT*, M. BASU and N. PAPANIKOLAOU* *Department of Obstetrics and Gynaecology, Medway Maritime Hospital, Gillingham and Department of Obstetrics and Gynaecology, William Harvey Hospital, Ashford, UK KEYWORDS: sling; transperineal; TVT; ultrasound; urethra; voiding dysfunction ABSTRACT Objective To determine whether the position of the tension-free vaginal tape (TVT) has an effect on postoperative flow rates and voiding function in women successfully cured of urodynamic stress incontinence. Methods Postoperatively 72 women who had undergone TVT surgery had a transperineal ultrasound examination to assess the position of the TVT on the urethra. The tape was categorized as proximal, mid or distal urethral. The effect on voiding was assessed using the maximum flow rate (MFR) centiles corrected for voided volume and detrusor pressure at maximum flow. Results Forty-six women had distal tapes and 26 midurethral tapes. A tape lying on the mid urethra was associated with a fall in MFR centile (P = 0.04) while a tape lying on the distal urethra did not cause a fall in the MFR centile (P = 0.52). There was no significant change in the detrusor pressure at maximum flow between mid and distally placed tapes. Conclusions Distally placed tapes cause less alteration in flow rates than do mid-urethrally placed tapes. This may be beneficial in certain patient groups. Copyright 2010 ISUOG. Published by John Wiley & Sons, Ltd. INTRODUCTION Urinary incontinence is a common condition affecting many women 1. The tension-free vaginal tape (TVT) operation is one of the commonest operations performed for urodynamic stress incontinence (USI), and was originally described in 1995 by Ulmsten and Petros 2. Many studies have documented a good outcome for this operation 3,4. The TVT is thought to act by compression of the urethra against the symphysis or sling 5 7. The urethra is not a uniform tube with identical properties throughout its length. The distal urethra is thought to be relatively fixed while the proximal urethra is more mobile 8. Although the tape is designed to be tension free, its insertion in TVT operations usually results in a reduction in flow 9 11. Therefore it could be postulated that placement of the TVT at different positions along the urethra might have different effects for both the resolution of USI and the effect on flow rates and voiding. Voiding and outlet resistance may be important in the etiology of detrusor overactivity (DO) and in the outcome of TVT surgery 12.Different centers have reported markedly different rates of voiding dysfunction following TVT surgery; one study described only 1.2% of patients reporting voiding dysfunction beyond 6 weeks 13, but this is in contrast to other reports with up to 8% of women self catheterizing at 6 months 14. Although this may be due to differences in intraoperative tensioning, it is also plausible that some of the variation might be due to different positioning of the tape on the urethra. In women, voiding is achieved by a rise in detrusor pressure usually accompanied by a rise in intra-abdominal pressure (rectal pressure). Very few women empty by pure pelvic relaxation. The rise in intra-abdominal pressure will compress the urethra and affect voiding. A TVT placed on the distal urethra lies further from the symphysis and might be expected to be less effective at compressing the urethra. The distal urethra is also surrounded by dense connective tissue and may be more difficult to compress and less affected by rises in intra-abdominal pressure. A TVT placed on the mid urethra (which is closest to the symphysis) might be more likely to compress the urethra during voiding. Correspondence to: Mr J. Duckett, Medway Maritime Hospital, Windmill Road, Gillingham, Kent ME7 5NY, UK (e-mail: jraduckett@hotmail.com) Accepted: 2 March 2010 Copyright 2010 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER

380 Duckett et al. A different mechanism may be important during coughing, when a rapid, high rise in pressure causes dynamic kinking of the urethra across the sling. This effect might produce equally positive results that depend more on the mobility of the urethra than on the precise placement of the tape. Hence USI may be cured largely irrespective of tape position, but tape position may affect voiding. It has previously been shown that a lower fall in flow rate is associated with better outcome following TVT surgery in women with mixed DO and USI 9. Therefore a sling that results in less change in flow rate might be more beneficial for some women. Women with disordered voiding prior to a TVT insertion are also more likely to benefit from a sling that causes a lower fall in flow rate. An internal audit of our department suggested that mid-urethral tapes result in a higher fall in flow rates, but the numbers were insufficient to make firm conclusions (unpublished data). A properly powered study was designed to test this hypothesis. In this study we aimed to assess whether a mid-urethral TVT is more likely to cause a fall in the maximum flow rate (MFR) than is a distally placed tape. METHODS This was a single-center, single-surgeon prospective observational study of women undergoing TVT surgery without concomitant prolapse surgery. The study was performed between August 2005 and August 2008. Patients with persistent urinary symptoms after TVT surgery were investigated with repeat cystometry and pressure-flow studies; this group included 20% of the population undergoing TVT surgery. Preoperatively, 56% of the women had coexistent DO, and persistent overactive bladder was the commonest indication for repeat postoperative cystometry. Seventy-eight women with pre- and postoperative pressure-flow studies underwent a transperineal ultrasound scan to assess tape position. The sling was inserted in a standard fashion by the experienced senior author (who had performed more than 300 such procedures prior to the start of the study) or a suitably trained member of the team. No attempt was made to place the tape on any particular position on the urethra. A 1-cm skin incision was made 1 cm below the external urethral orifice and the tape inserted as previously described 2. All procedures were performed under spinal anesthesia and the sling was adjusted sufficiently tightly so that leakage was abolished using a cough test with 350 ml in the bladder. The sling was positioned to lie flat under the urethra without causing distortion or elevation. A pair of scissors could easily be passed between the sling and the urethra. Women having additional prolapse procedures were excluded, as the effects of a colporrhaphy might itself alter urinary symptoms and flow rates and thus introduce bias 15. Women with neurological disease or abnormalities at cystoscopy were also excluded. All women were examined in the supine position using a GE Logiq 400 (GE Medical Systems, Waukesha, WI, USA) ultrasound machine and a linear array 5.0-MHz probe applied to the external urethral meatus 6 18 (mean, 9.2) months after surgery. The women were instructed to empty their bladders prior to scanning and any residual was measured. An empty bladder was used to avoid different bladder volumes potentially affecting urethral length. The urethral longitudinal smooth muscle and mucosa can be identified as a hypoechoic tube (Figure 1). The urethral length was measured from the introitus to the bladder. The distance of the proximal and distal ends of the sling from the introitus was measured and the position of the sling was defined. The urethra was arbitrarily divided into thirds, with the sling position classified as proximal, mid or distal urethra. A sling lying partially in different thirds was classified according to the position of the majority of the sling. More precise measurements of sling position were not used as these have not been adequately validated. All perineal scans were performed by the senior author. Only women successfully treated for USI were included in the final analysis, as women with persistent USI were unlikely to have sufficiently tight tapes. MFRs are dependent on the voided volume 16. Flow rate centiles were used to correct MFR for voided volume as previously described 17. Continuous variables were analyzed using a t-test (paired t-test for paired data) with standard deviations stated. The change in detrusor pressure at maximum flow was compared in those women with mid and distal tapes. The primary outcome indicator was the fall in MFR centile after surgery. Using a 5% significance level and a required power of 80% gave a sample size of 76 (38 in each arm), based on our own internal audit data. All definitions of symptoms, signs and urodynamic observations used in the study conform to the terminology recommended by the International Continence Society 18. Ethical approval for Figure 1 Transperineal ultrasound image showing tension-free vaginal tape (arrow) lying over the urethra (arrowhead).

TVT position related to flow rates 381 the study was obtained from West Kent Ethics Committee (UK). Table 1 Mean maximum flow-rate centiles for distally and mid-placed tension-free vaginal tapes pre- and postoperatively Sling position RESULTS Seventy-eight women were enrolled in the study and underwent evaluation of sling position on ultrasonography as well as pre- and postoperative pressure-flow studies. Six of the women (7.7%) had sling failures and 72 (93.6%) were cured of their stress incontinence. Sling failures resulted in no change in the MFR and these are excluded from the analysis. One of the patients excluded because of sling failure had a proximally placed sling. No patient developed de novo symptoms. The selection of this study population is outlined in Figure 2. The median urethral length was 29 (range, 17 41) mm. The sling was lying distally in 46/72 (63.9%) women and mid urethrally in 26 (36.1%) women. A sling lying on the mid urethra was associated with a fall in MFR centile (P = 0.04), but there was no fall in MFR centile when the sling was lying on the distal urethra (P = 0.52) (Table 1.). There was no difference in the change in detrusor pressure at maximum flow postoperatively, with a small non-significant fall for distal tapes (38 to 36.6) and a non-significant rise in mid-urethral slings (35.1 to 43) (Table 2). Of the sling failures one was proximally positioned, with three mid and two distal. The figures are Tape failures: excluded from analysis (n = 6) TVT inserted (n = 832) Women without prolapse surgery (n = 560) Repeat urodynamics for persistent symptoms (n = 112) Postoperative ultrasound to assess sling position (n = 78) Final study population (n = 72) Excluded because of concomitant prolapse surgery (n = 272) Figure 2 Flow diagram illustrating selection of the study population. TVT, tension-free vaginal tape. Distal (n = 46) Mid (n = 26) P Preoperative 15.5 ± 20.8 19.4 ± 24.8 0.47 Postoperative 12.5 ± 18.1 8.97 ± 9.1 0.35 P 0.52 0.04* Data are expressed as mean ± SD. *Statistically significant Table 2 Detrusor pressure (in cmh 2 O) at maximum flow in women after insertion of tension-free vaginal tapes pre- and postoperatively Sling position Distal (n = 46) Mid (n = 26) P Preoperative 38.0 ± 15.9 35.1 ± 13.3 0.51 Postoperative 36.6 ± 12.1 43.0 ± 15.4 0.078 P 0.67 0.05 Data are expressed as mean ± SD. too small to analyze statistically. The residual was less than 100 ml in all the women. DISCUSSION This study suggests that there is an association between a mid-urethrally placed sling and a fall in MFR centile, with no such association for distally placed slings. No alterations in cure or complication rates were noted but the study was not powered to look at these endpoints. There was a trend towards an increase in detrusor pressure at maximum flow in the mid-urethral slings (P = 0.05). Placement of the sling at the distal urethra may be advantageous if minimal alterations in flow rate are thought to be beneficial. The TVT procedure is an operation performed in many different ways but it produces good results with different techniques. Slings have been reported to lie variously at the proximal 19, mid or distal urethra 19 21. A recent report suggests that tapes lying in the upper or lower quarter of the urethra were more likely to fail 20. These tapes are more distant from the symphysis and may be less compressible. The original technique describes the placement of a mid-urethral tape 2. Most studies assessing tape position have related tape position to success. However they are commonly small studies 19,21,22 involving 20 40 women, with an even smaller number of failures and no power calculations 20, which makes statistical analysis uncertain. Tape position may be only one factor in the resolution of stress incontinence postoperatively. Other factors such as characteristics of the tape, e.g. elasticity, may be important 23. We have been unable to find any other papers that document the effect of voiding and relate this to tape position.

382 Duckett et al. Our study has certain limitations. It is possible that tapes were inserted with different degrees of tightness at different places on the urethra. Although a standard method was used for sling tensioning this may be impossible to standardize in practice and could lead to bias. However, no conscious effort was made to do this and the tapes were adjusted to abolish leakage under spinal anesthetic, the same technique being used for all women. The study was not a randomized controlled trial and the results should be interpreted in the context of observational research. It is unknown whether these results are generalizable to all surgeons who insert slings, but other surgeons should consider repeating the study to ascertain whether the results are reproducible. It might be possible to repeat the study by randomizing between distal- and mid-tape position, but it remains to be seen whether accurate tape placement can be achieved. Although mid-urethral tapes were associated with a fall in MFR centile this was not translated into a different clinical outcome. A much larger study would be needed to assess the effect of flow rates on clinical outcome. Prior to the study we expected the tapes to be split equally between the mid and distal urethra but there was an excess of tapes on the distal urethra (46 vs. 26). This has the potential to leave the study underpowered. A larger sample size in the mid-urethral group may have resulted in lower standard deviations overall and a more certain interpretation of the results. There are no flow-rate centiles based on intubated flows in women. Flows are generally slower when intubated. The Liverpool nomograms and flow-rate centile calculations refer to non-intubated flow, and this resulted in all our centiles falling in the lower reference range. However, the statistical power calculation was based on this premise. The study was based on pressureflow data with the intention of assessing whether flow-rate changes resulted in other changes in voiding parameters, such as an alteration in the detrusor pressure at maximum flow. Unfortunately we were unable to demonstrate any alteration in other flow variables although previous studies have shown changes 9. No free-flow data were collected. Free-flow data would have been useful for confirming the flow-rate findings identified in the pressureflow studies, and would have increased the power of our study. More recently voiding has been related to the tape position (closeness) in relation to the urethral lumen 20.A tape lying closer to the urethral lumen was more likely to result in complications but a distinction regarding voiding dysfunction was not made. Tape position can be assessed as proximal, mid, or distal, or as a percentage point along the urethra from the external meatus or bladder neck 20. The method that we used may be less precise, but we chose to use this method as our validation study in a small number of women showed good reproducibility. We do not know whether using a percentage point to define urethral position is accurate or reproducible. When the tape failed to control stress incontinence there was no change in the MFR. Although distally placed tapes may be less obstructive, this may result in a lower cure rate. Kociszewski et al. 20 documented an increased failure rate in distal and proximal tapes, which lie further from the symphysis and are probably less compressible. Our study was insufficiently powered to study failure rate related to tape position. A mid-urethral tape is more likely to be associated with a fall in the postoperative flow-rate centile than is a distally placed tape. There was also a trend towards higher detrusor pressure at maximum flow in midurethral tapes, which may indicate a higher degree of urethral resistance. 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