The MIETHKE GAV® is a unique gravitational valve for the treatment of adult hydrocephalus. It automatically varies its opening pressure as soon as this becomes necessary due to alterations in the patient’s body position. Thus it effectively prevents symptoms of overdrainage. Thanks to the physiological drainage and its variable concept, the MIETHKE GAV® is well suited for the treatment of NPH patients, as well as for extreme forms of hydrocephalus in adults. The MIETHKE GAV® is made from titanium, a material that guarantees outstanding precision, reliability and biocompatibility.
The use of adjustable pressure valves with gravity-assisted units in shunt therapy of children with hydrocephalus was reported to be feasible and promising as a way to avoid chronic shunt overdrainage.
Two common valve types used to treat hydrocephalus include gravity assisted valves (GAV) and medium pressure valves (MPV). Despite their different mechanism of action, differentiated surgical indications per type are not well defined. One could assume that due to a higher complexity of the GAV system, it may be more prone to valve-related malfunction.
All data were collected from a cohort of infants (93 patients [37 girls and 56 boys], less than 1 year of age [mean age 4.1 ± 3.1 months]) who received their first adjustable pressure hydrocephalus shunt as either a primary or secondary implant between May 2007 and April 2012. Rates of valve and shunt failure were recorded for a total of 85 months until the end of the observation period in May 2014.
During a follow-up of 54.2 ± 15.9 months (range 26-85 months), the Kaplan-Meier rate of shunt survival was 69.2% at 1 year and 34.1% at 85 months; the Kaplan-Meier rate of valve survival was 77.8% at 1 year and 56% at 85 months. Survival rates of the shunt were significantly inferior if the patients had previous shunt surgery. During follow-up, 44 valves were exchanged in cases of infection (n = 19), occlusion (n = 14), dysfunction of the adjustment unit (n = 10), or to change the gravitational unit (n = 1).
Although a higher shunt complication rate is observed in infant populations compared with older children, reasonable survival rates demonstrate the feasibility of using this sophisticated valve technology. The gravitational unit of this valve is well tolerated and its adjustability offers the flexible application of opening pressure in an unpredictable cohort of patients. This may adequately address overdrainage-related complications from early in treatment 1).
The purpose of a retrospective study was to compare the valve-related complication rates of GAV and MPV in patients with communicating hydrocephalus.
Patients aged 16 years or older undergoing their first shunt implantation using GAV or MPV were included. We recorded demographic data, implantation diagnosis, outcome, complications, valve type and valve adjustments. Symptoms were documented at discharge and follow-up. Valve-related malfunctions were distinguished from other shunt complications.
N = 252 patients (range 16.6-88.4, mean 65.0 years, 116 male and 136 female) underwent shunt placement for the first time. N = 122 GAV (48.4 %) and n = 130 MPV were implanted (51.6 %) over a period of 5 years. The most frequent diagnoses were normal pressure hydrocephalus (NPH) in 86 cases (34.1 %) and posthemorrhagic hydrocephalus in 114 cases (45.2 %). About two thirds of patients were free of hydrocephalus-related symptoms at follow-up. N = 66 subjects (26.2 %) underwent at least one shunt revision. N = 29 revisions (11.5 %) were due to valve-related malfunction. Valve-related revisions were the main cause for revision in 18/37 cases (48.6 %) in the GAV group and in 11/29 (37.9 %) in the MPV group. Neither clinical improvement nor valve-related malfunctions were found to be statistically different among groups 2).
From January 2002 to December 2009, 111 patients underwent ventriculoperitoneal (VP) shunting.
Overall shunt survival time was 268 weeks. Mean survival time of gravity-assisted valve (GAV) was 222 weeks versus 286 weeks for other shunts. Survival time of programmable valves (264 weeks) was longer than that of pressure-controlled valves (186 weeks). The most common cause for shunt revision was underdrainage (13 valves). The revision rate due to underdrainage in patients with GAV (7 of 10 patients) was higher than that for other valve types. Of 7 patients requiring revision for GAV underdrainage, 6 patients were bedridden. The overall infection rate was 3.6%, which was lower than reported series. Seven patients demonstrating overdrainage had cranial defects when operations were performed (41%), and overdrainage was improved in 5 patients after cranioplasty.
Although none of the differences was statistically significant, some of the observations were especially notable. If a candidate for VP shunting is bedridden, GAV may not be indicated because it could lead to underdrainage. Careful procedure and perioperative management can reduce infection rate. Cranioplasty performed prior to VP shunting may be beneficial 3)
The performance of GAV may be affected by its inclination as a tantalum sphere in the valve, which generates a downhill force in proportion to the sine of the angle with respect to level. Accordingly, the aim of this study was to evaluate the effect of valve inclination relative to the vertical on shunt performance.
In 24 adult patients who underwent ventriculoperitoneal shunting using a GAV for hydrocephalus, valve inclination relative to the vertical was measured using AP and lateral projections of skull x-rays that were taken in a standing position, and the relationship between valve inclination and ventricular volume change after ventriculoperitoneal shunting in CT scans was evaluated.
The Pearson correlation coefficient between valve inclination in a sagittal plane and ventricular volume change was -0.768 (P < .01), whereas lateral valve inclination had no correlation with ventricular volume change. Eleven patients with a posterior valve inclination relative to the vertical exhibited a greater ventricular volume reduction of 34.1% +/- 8.2% compared to the volume reduction of 13.4% +/- 9.2 % in 13 other patients with an anterior valve inclination (P = .000). Two (40%) of 5 patients with a severe anterior valve inclination of more than 20 degrees relative to the vertical underwent shunt revision for underdrainage.
A severe anterior inclination of the valve by more than 20 degrees relative to the vertical can lead to underdrainage owing to an increased OP in a lying position, especially in patients who are nonambulatory at the time of GAV implantation 4).
For a minimum of 2 years the authors monitored 169 of 182 hydrocephalic children who received a pediatric GAV at their first CSF shunt insertion (61.5%) or as a substitute for any differential pressure valve (38.5%) at 1 of 7 European pediatric hydrocephalus centers. Outcomes were categorized as valve survival (primary outcome) or shunt survival (secondary outcome). The end point was defined as valve explantation.
Within a follow-up period of 2 years, the valve remained functional in 130 (76.9%) of 169 patients. One hundred eight of these patients (63.9%) had an uncomplicated clinical course without any subsequent surgery, and 22 (13%) were submitted to a valve-preserving catheter revision without any further complications during the follow-up period. Thirty-nine patients (23.1%) reached an end point of valve explantation: 13 valve failures from infection (7.7%), 8 (4.7%) from overdrainage, and 18 (10.6%) from underdrainage.
Compared with nongravitational shunt designs, a GAV does not substantially affect the early complication rate. Valve-preserving shunt revisions do not increase the risk of subsequent valve failure and therefore should not be defined as an end point in studies on valve design. A significant impact of any well-established valve design on the early complication rate in shunt surgery is not supported by any current data; therefore, this correlation should be dismissed. As overdrainage-related complications have been shown to occur late, the presumed advantages of a pediatric GAV remain to be shown in a long-term study 5).
123 patients with idiopathic NPH were surgically treated by implanting a hydrostatic shunt at the Departments of Neurosurgery of the Unfallkrankenhaus Berlin and the University Homburg/Saar. As part of a prospective randomized study, all patients were examined preoperatively, postoperatively, and 1 year after the intervention. Forty-three percent of the patients showed a very good outcome, 25% good outcome, 20% fair outcome, and 12% poor outcome 1 year after the shunt implantation. Patients treated with an opening pressure rating of 50 mmH2O in the low-pressure stage of the gravitational valve showed a better outcome than those with an opening pressure of 100 or 130 mmH2O. According to present knowledge, hydrostatic shunts with an opening pressure of 50 mmH2O for the low-pressure stage are the best option for patients with idiopathic NPH. Due to the prompt switching function when the patient changes posture (lying down, standing, sitting, slanting etc.), the Miethke gravity-assisted valve (GAV) is more suitable in such cases than the Miethke Dual-Switch valve (DSV) 6).
A total of 32 patients were enrolled onto the study, with 2 undergoing first shunt insertion after failed ventriculostomy and 30 undergoing shunt revisions. On average, the patients had had 3.3 shunt procedures prior to insertion of a Paedi-Gav valve.
During a follow-up interval of minimum 52 weeks and a median of 24 months after the first implantation on-study, shunt revisions were required in 17 (53.1%) of the 32 patients. The 12-month shunt-survival rate without revision of any component was 53%, with a median shunt-survival time of 388 days. The most common reasons for shunt revision were shunt obstructions (12/17) and overdrainage (3/17). Shunt obstructions were caused by valve-related failures (9/12) and distal obstructions (3/12).
Although the small number of patients enrolled in this study warrants cautious conclusions, the overall results are comparable to those reported for primary shunt insertions with conventional valves in pediatric patients with hydrocephalus. Although this study provides a rationale for examining the Paedi-Gav gravity-assisted shunt valve in a larger prospective randomized controlled trial, the shunt failure pattern, with a rather high frequency of valve-related failures, may indicate potential for further improvements in the valve design and/or manufacturing 7).