Hypothesis / aims of study
The aim of this study was to assess whether the opening detrusor pressure (ODP) may be a predictor of long-term outcomes for TVT (tension-free vaginal tape) in patients with urodynamic stress incontinence (USI) and mixed urinary incontinence (MUI).
A high opening detrusor pressure is associated with detrusor overactivity (1). A lower opening detrusor pressure in the MUI group is likely to signify a predominant stress incontinence component.
Previous work has shown that a low opening detrusor pressure is predictive of persistent stress incontinence after Burch colposuspension (2). There are a wide range of techniques available for the surgical management of stress incontinence, including autologous fascial slings, Burch colposuspension, TVT, TOT and injectables. The differences in the mechanics of the procedures lead to different side-effect profiles, and therefore a difference in urodynamics predictive values.
Study design, materials and methods
Long-term follow up of patients that underwent TVT between 2005 to 2017.
All patient that underwent TVT were identified by reviewing hospital logbooks. Their pre-operative urodynamic records and KHQs (King’s Health Questionnaires) were reviewed. Patients were followed up with a postal KHQ and 24-hour pad test. A low KHQ score reflects fewer symptoms and bother, therefore better quality of life. A poor outcome was defined as a urine loss of more than 4g per day, as advised by ICS (International Continence Society).
Predictive factors investigated included age, parity, diagnosis, opening detrusor pressure, flow pressure, flow rate, previous TVT, prolapse, TVT at the time of prolapse repair.
A power calculation for a p<0.05 significance suggested a minimum of 30 patients required. SPSS v24 was used for analysis.
The response rate was 47% (111/235). Median follow-up was 41 months. Pre-operatively, USI had a lower total mean KHQ score than MUI (48.2 vs 62.2; t-test, p=0.002). Post-operatively, USI also had a lower total KHQ score than MUI (37.4 vs 47.8; t-test, p=0.002). However, the mean change was not significant (USI 6.2 vs MUI 7.5; t-test, p=0.8).
The opening detrusor pressure (AUC 0.73, p<0.001) and history of previous TVT (AUC 0.79, p=0.01) were found to be significant predictive factors.
When the pad test was negative, the ODP in the SUI group was 17.1cmH2O (95%CI9.5), compared with 13.3cmH2O (95%CI4.5) when the pad test was positive; Mann-Whitney test, p=0.8). When the pad test was negative, the ODP in the MUI group was 7.4cmH2O (95%CI7.0), compared with 19.1cmH2O (95%CI4.7) when the pad test was positive; Mann-Whitney test, p=0.01).
The prediction of TVT success at an ODP threshold of 19cmH2O has sensitivity 80%, specificity 42%, positive predictive value 62%, negative predictive value 63%.
The ROC curve of ODP predicting urine loss of less than 4g in 24 hours area under the curve is 0.73, with a standard error 0.06, p<0.001, 95%CI 0.62-0.85, p<0.001.
Interpretation of results
Both patients with SUI and MUI experienced a long-term benefit in their objective and subjective quality of life from a TVT. Drier patients reported a better quality of life.
Patients with a negative pad test had a lower pre-operative ODP in the MUI group. This means that the opening detrusor pressure is an important pre-operative predictor of long-term outcomes.
Therefore, according to this data, the presence of detrusor overactivity on pre-operative urodynamics should not discourage us from performing a TVT. However, it is a higher opening detrusor pressure that is a pre-operative predictor of poor long-term outcomes.
This data is supportive of the ICS-RS 2017 expert opinion that recommended further research into pre-operative predictors in order to improve surgical outcomes (3). Currently, there is a large number of procedures available for stress incontinence being used in practice. A detailed pre-operative assessment pre-operatively prior to all continence procedures would contribute towards our understanding of whether different patient sub-groups may benefit more or less from the choices available.