Surgery Section - Wireless Pressure Monitoring in Endovascular Aneurysm

IMPORTANT REMINDER

This Medical Policy has been developed through consideration of medical necessity, generally accepted standards of medical practice, and review of medical literature and government approval status.

Benefit determinations should be based in all cases on the applicable contract language. To the extent there are any conflicts between these guidelines and the contract language, the contract language will control.

The purpose of medical policy is to provide a guide to coverage. Medical Policy is not intended to dictate to providers how to practice medicine. Providers are expected to exercise their medical judgment in providing the most appropriate care.

Description

The goal of abdominal aortic aneurysm (AAA) repair is to reduce pressure in the aneurysm sac and thus prevent rupture.  Failure to completely exclude the aneurysm from the systemic circulation results in continued pressurization.  An endoleak (persistent perfusion of the aneurysmal sac) may be primary (within the first 30 days) or secondary (after 30 days).  Endoleaks are reported to vary from 10%–50% of cases, and there are 5 types of endoleaks. (2)  Type I endoleaks result from ineffective fixation at either end of the graft; while these can seal spontaneously, risk of rupture is high and intervention is often indicated.  Type II endoleaks result from retrograde filling of the aneurysm mainly from lumbar and/or inferior mesenteric arteries.  Risk of rupture is less than with types I and III and type II endoleaks can often be monitored when the aneurysm is shrinking.  Type III endoleaks are caused by failure of the implanted graft and include development of holes, which need to be treated aggressively.  Type IV endoleaks are caused by the porosity of the graft fabric.  Type V endoleaks are referred to as endotension and correspond to continued aneurysm expansion in the absence of a confirmed endoleak.  Endoleaks, particularly types I and III, lead to continued sac pressurization and therefore may be considered technical failures of endovascular aneurysm repair (EVAR).

The completeness of exclusion or absence of endoleaks is evaluated by intraoperative angiography.    However, interpretation of images can be problematic and it can also cause patient morbidity due to the dye load from repeated injections of contrast material.  Direct measurement of sac pressure provides a physiologic assessment of success.  Studies have used direct sac pressure measurements with a catheter; the drawback of this approach is the interference by the catheter during endovascular repair and the inability to leave it in place.  Since endoleaks may also develop subsequent to the time of surgery, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound are used in monitoring the aneurysmal sac.  Percutaneous catheter-based approaches can also be used to measure intrasac pressures postoperatively.

Several factors determine aneurysm sac pressure after EVAR.  These include graft-related factors such as endoleak, graft porosity, and graft compliance and anatomic factors such as patency of aneurysm side branches, aneurysm morphology, and the characteristics of aneurysm thrombus.

Given this situation, wireless implantable pressure-sensing devices are being evaluated to monitor pressure in the aneurysm sac.  These implanted devices use various mechanisms to wirelessly transmit pressure readings to devices for measuring and recording pressure.  These devices have the potential to improve outcomes for patients who have had endovascular repair.  They may change the need for or the frequency of monitoring of the aneurysm sac using contrast-enhanced CT scans.  They may improve postoperative monitoring.  However, the accuracy of these devices must be determined, and potential benefits and risks must be considered and evaluated.  At present, two types of systems are being evaluated: radiofrequency and ultrasound-based systems.

In October 2006, the U.S. Food and Drug Administration (FDA) cleared the CardioMEMS EndoSure™ (radiofrequency based) system through the 510(k) process. (3)  The favorable FDA review indicated only that the device was substantially equivalent to legally marketed predicate devices.  The FDA labeling indications noted that the device is intended for measuring intrasac pressure during endovascular abdominal aortic aneurysm repair.  It also noted that it may be used as an adjunctive tool in the detection of intraoperative endoleaks.  The ImPressure™ system (ultrasound-based) is used in Europe and is being used as part of an investigation device exemption (IDE) trial of stent grafts.

Policy/Criteria

Use of wireless pressure sensors is considered investigational in the management (intraoperative and/or postoperative) of patients having endovascular aneurysm repair.

Position Summary

While multiple factors (see above) influence aneurysm sac pressure after endovascular aneurysm repair (EVAR), models have demonstrated that with exclusion of the sac after EVAR, sac pressures diminish significantly.  Using direct translumbar puncture in ten patients after EVAR with sac shrinkage and no evidence of endoleak, Sonesson demonstrated that mean intrasac pressure diminishes to 20% of mean arterial pressure. (4)  Dias and colleagues reported on 46 percutaneous intrasac pressure readings in 37 patients following EVAR. (5)  In these patients, they calculated the mean pressure index (MPI)—the percentage of mean intra-aneurysm pressure relative to the simultaneous mean intra-aortic pressure.  Median MPI was 19% in 11 patients with shrinking sacs, 30% in ten  patients with unchanged sacs, and 59% in 9 expanding aneurysms.  Type II endoleaks (six  patients) were associated with a wide range of MPI (22%–92%).  The authors comment that the findings from this small series do not imply that imaging follow-up can be replaced by pressure measurements.  They also note that a definitive pressure threshold using direct measurement for subsequent intervention needs to be defined by further studies.

For the wireless devices, Ohki and colleagues reported initial results from the APEX study—acute pressure measurement to confirm aneurysm sac exclusion. (6)  They reported 30-day results on 76 of 90 enrolled patients at 12 sites worldwide who received the CardioMEMS wireless pressure sensor during EVAR.  Of the patients enrolled, results were not reported on 14 patients due to “protocol deviations, typically a missed measurement.”  In one  patient, the device could not be deployed because there was inadequate space (less than 10 mm) within the aneurysm sac after graft deployment.  In all 76 patients, there was close agreement between the wireless sensor and angiographic catheter for a type I endoleak equivalent.  As defined in the study, a reduction in pulse pressure of 30% or more from the initial pressure measurement would be associated with a sealed sac and a less than 30% reduction in pulse pressure would indicate a type I or III endoleak.  With angiography as the standard, for detection of type I or III endoleak at the completion of the procedure, the sensor detected four  of five  (80%) of the leaks.  The authors comment that the case that was not detected was not clinically significant, i.e., no intervention was required.  The wireless sensor indicated no endoleak in 66 of 71 (93%) cases without an angiographic endoleak.  Deployment of the device was noted to add 10 minutes to the EVAR procedure; the average operative time for those in the study was 205 +/- 87 minutes.  No complications were felt due to the wireless sensor, although the authors did comment that there was a learning curve associated with deployment and using the device.  This report also notes that these patients will be followed up for five  years, and that long-term data will provide information to evaluate the value of the sensor for postoperative follow-up surveillance.  The value of the device will need to consider not only benefit but also any potential complications due to the implanted device.  A clinical trial is being initiated to assess the safety and efficacy of the Endosure device in comparison to CT angiography for long-term follow-up after EVAR.

Ellozy reported results with a mean follow-up of 11 months of 21 patients using the Impressure AAA Sac Pressure Transducer. (7)  This device was studied as part of an IDE examining use of an endovascular stent-graft in the repair of infrarenal AAAs in high-risk patients.  This transducer is hand-sewn into the outside of the stent-graft and then packaged as part of the delivery sheath.  During follow-up, pressures could be obtained at all visits in 15 of the 21 patients.  There were problems with readings from four  of the devices that were thought to be due to placement of the devices between the iliac limbs of the stent graft.  For the 14 patients with follow-up of at least six  months, aneurysm sac shrinkage of more than five  mm was seen in seven  patients, and the mean pressure index (MPI) was significantly lower in those with sac shrinkage at six  months.  Two of the patients with shrinking aneurysms had type II endoleaks.

In 2008, two case series were published, both using the EndoSure radiofrequency device, one of intraoperative use and one of postoperative follow-up for 30 days.  The intraoperative series reported the correlation of measurements made during the procedure using the pressure sensor and a catheter inserted into the aneurysm sac among 19 patients. (8)  Although the authors reported that all correlation coefficients were statistically significant, they ranged from 0.50 to 0.96.  Data presented in the paper show marked differences in measurement, suggesting that the accuracy of the measures requires further study.  Of eight sets of measurements, four had more than 50% of patients with at least 10% variation between methods.  A second series was an Ultrasound-based study of postoperative monitoring for endoleaks using the EndoSure sensor in 12 patients with 30-day follow-up. (9)  At 30 days, 2 type-II endoleaks were noted on CT.  Sac pressures were unchanged with 1 patient and had decreased in the other.  One patient with a type-III endoleak on CT had increasing sac pressure.  Delivery of the sensor was complicated in two of 12 patients (17%).

Additional data are needed from larger, randomized trials with long-term follow-up to determine the effectiveness of wireless pressure sensor devices for the management of patients with aneurysm repair.  Unanswered questions include potential long-term, device-related complications, test accuracy  for detecting endoleaks, the type and number of devices that might best be used in monitoring patients, and the extent to which the device can reduce imaging requirements following EVAR (via direct comparison with CT).  Because the impact of this technology on clinical outcomes is not known, the TEC criteria are not met and use of wireless pressure sensors for monitoring endovascular aneurysm repair is considered investigational.

References

1. BlueCross BlueShield Association Medical Policy Reference Manual, Policy No. 7.01.111
2. Golzarian J, Valenti D.  Endoleakage after endovascular treatment of abdominal aortic aneurysms:  diagnosis, significance and treatment.  Eur Radiol 2006; 16(12):1849-57
3. www.fda.gov/cdrh/pdf6/K061046.pdf
4. Sonesson B, Dias N, Malina M et al.  Intra-aneurysm pressure measurement in successfully excluded abdominal aortic aneurysm after endovascular repair.  J Vasc Surg  2003; 37:733-8
5. Dias NV, Ivancev K, Malina M et al.  Intra-aneurysm sac pressure measurements after endovascular aneurysm repair” differences between shrinking, unchanged, and expanding aneurysms with and without endoleaks.  J Vasc Surg  2004; 39:1229-35
6. Ohki T, Ouriel K, Silveira PG et al.  Initial results of wireless pressure sensing for endovascular aneurysm repair: the APEX Trial--Acute Pressure Measurement to Confirm Aneurysm Sac EXclusion. J Vasc Surg 2007; 45(2):236-42
7. Ellozy SH, Carroccio A, Lookstein RA et al.  Abdominal aortic aneurysm sac shrinkage after endovascular aneurysm repair: correlation with chronic sac pressure measurement.  J Vasc Surg 2006; 43(1):2-7
8. Silveira PG, Miller CW, Mendes RF et al.  Correlation between intrasac pressure measurements of a pressure sensor and an angiographic catheter during endovascular repair of abdominal aortic aneurysm. Clinics 2008; 63(1):59-66
9. Hoppe H, Segall JA, Liem TK et al.  Aortic aneurysm sac pressure measurements after endovascular repair using an implantable remote sensor: initial experience and short-term follow-up.  Eur Radiol 2008; 18(5):957-65

Cross References

Endovascular Grafts for Abdominal Aortic Aneurysms, Regence Medical Policy Manual,  Surgery  Policy No. 98

Endovascular Stent Grafts for Thoracic Aortic Aneurysms or Dissections, Regence Medical Policy Manual, Surgery Policy No. 124

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