Description:
Wireless sensors implanted in an aortic aneurysm sac after endovascular repair are being investigated to measure postprocedural pressure. It is thought that low pressures may correlate with positive prognoses and high pressures may indicate the need for revision.

For individuals who have received endovascular aneurysm repair who are monitored with wireless pressure sensors, the evidence consists of case series. Relevant outcomes are test accuracy and validity, resource utilization and treatment-related morbidity. Evidence from small case series is insufficient to indicate whether use of this device improves clinical outcomes. Device performance over time, including the accuracy of the device in patients with various types of endoleaks, needs to be assessed. Work is also needed to determine the type and number of devices that might best for monitoring because sac compartmentalization might lead to a pressure-sensing device missing an endoleak. It also is not known whether there are serious long-term complications from this implanted device. Furthermore, the extent to which the device can reduce imaging requirements following endovascular aneurysm repair (which can be established using direct comparison to computed tomography) is undetermined. The evidence is insufficient to determine the effects of the technology on health outcomes.

Background 
The goal of abdominal aortic aneurysm (AAA) repair is to reduce pressure in the aneurysm sac and thus to prevent rupture. Failure to exclude the aneurysm completely 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% to 50% of cases, and there are 5 types of endoleaks.¹ Type I endoleaks result from ineffective fixation at either end of the graft; while the leaks 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 leaks, 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. Because endoleaks may also develop subsequent to the time of surgery, magnetic resonance imaging 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. They include graft-related factors (e.g., endoleak, graft porosity, graft compliance) and anatomic factors (e.g., patency of aneurysm side branches, aneurysm morphology, characteristics of aneurysm thrombus).

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 that measure and record pressure data. 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 computed tomography scans and they may improve postoperative monitoring. However, the accuracy of these devices must be determined, and potential benefits and risks must be evaluated. At present, 2 types of systems are being evaluated: radiofrequency and ultrasound-based systems.

Regulatory Status
In October 2006, the U.S. Food and Drug Administration (FDA) cleared the CardioMEMS EndoSure^™ (radiofrequency-based) system through the 510(k) process. 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 AAA repair. It also noted that it may be used as an adjunctive tool in the detection of intraoperative endoleaks. In March 2007, additional language was added, stating that the CardioMEMS device may be used to measure intrasac pressure during thoracic aortic aneurysm repair.

The ImPressure^™ system (ultrasound-based) is used in Europe and is being used as part of an investigational device exemption trial of stent grafts (see Rationale section).

Related Policies
20224 Cardiac Hemodynamic Monitoring for the Management of Heart Failure in the Outpatient Setting
70167 Endovascular Grafts for Abdominal Aortic Aneurysms
70186 Endovascular Stent Grafts for Disorders of the Thoracic Aorta

Policy:
Use of wireless pressure sensors is considered INVESTIGATIONAL in the measurement (intraoperative and/or postoperative) of patients having endovascular repair.

Policy Guidelines
Effective in 2008, there are CPT category I codes specific to the use of this device:

34806: Transcatheter placement of wireless physiologic sensor in aneurysmal sac during endovascular repair, including radiological supervision and interpretation, instrument calibration and collection of pressure data (List separately in addition to code for primary procedure.)

93982: Noninvasive physiologic study of implanted wireless pressure sensor in aneurysmal sac following endovascular repair, complete study including recording, analysis of pressure and waveform tracings, interpretation and report

CPT code 34806 is not to be reported in conjunction with 93982, as any study done at the time of insertion is included in 34806. Code 34806 includes deployment of the sensor, intraoperative calibration and any repositioning required.

Benefit Application:
BlueCard/National Account Issues
State or federal mandates (e.g., FEP) may dictate that all devices approved by the U.S. Food and Drug Administration (FDA) may not be considered investigational, and, thus, these devices may be assessed only on the basis of their medical necessity.

For these FEP reviews of the CardioMEMS EndoSure^™ system, it is important to note that the FDA language comments only on intraoperative use of the device.

Rationale
While multiple factors (see above) influence aneurysm sac pressure after endovascular aneurysm repair (EVAR), data from small case series suggest that, with exclusion of the sac after EVAR, sac pressures diminish significantly.^2,3 For example, Dias et al. reported on percutaneous intrasac pressure readings in 37 patients following EVAR.² 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 percent in 11 patients with shrinking sacs, 30 percent in 10 patients with unchanged sacs and 59 percent in nine expanding aneurysms. Type II endoleaks (six patients) were associated with a wide range of MPI (22 – 92 percent). 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 et al. reported on results from the APEX study — acute pressure measurement to confirm aneurysm sac exclusion.⁴ 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 space was inadequate (< 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 percent or more from the initial pressure measurement would be associated with a sealed sac, and a less than 30 percent 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 percent) 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 percent) 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 deploying 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 include not only benefit but also any potential complications due to the implanted device.  

Ellozy et al. reported results with a mean follow-up of 11 months of 21 patients using the ImPressure^™ AAA (abdominal aortic aneurysm) Sac Pressure Transducer.⁵ This device was studied as part of an investigational device exemption 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 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 5 mm was seen in seven patients, and the MPI was significantly lower in those with sac shrinkage at six months. Two 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.⁶ Although the authors reported that all correlation coefficients were statistically significant, they ranged from 0.50 to 0.96. Data presented in the article 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 percent of patients with at least 10 percent variation between methods. A second series was a U.S.-based study of postoperative monitoring for endoleaks using the EndoSure^™ sensor in 12 patients with 30-day follow-up.⁷ At 30 days, two type II endoleaks were noted on computed tomography (CT). Sac pressures were unchanged in one 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 percent). Additional data are needed for these devices with larger patient series and longer duration of follow-up. 

In 2010, Parsa et al. reported on a single-center case series of 43 patients undergoing thoracic EVAR.⁸ Each patient’s aneurysm was implanted with the EndoSure^™ device. Aneurysm sac pressures were taken predischarge and at follow-up visits. In three patients, pressure measurements prompted imaging that confirmed leakage, which was corrected with further procedures. However, the study was not designed to evaluate how the device contributes to clinical utility. 

Ongoing and Unpublished Clinical Trials
An ongoing trial is assessing the safety and efficacy of the EndoSure^™ device in comparison to CT angiography for long-term follow-up after EVAR (NCT00831870). This trial, sponsored by CardioMEMS, is officially titled: Pressure and Imaging — Using the CardioMEMS EndoSure Sensor for Long-term follow-up after EVAR with Standard Surveillance (PRICELESS). As of November 2014, the study is enrolling participants by invitation. 

Summary of Evidence
Wireless sensors implanted in an aortic aneurysm sac after endovascular repair are being investigated to measure postprocedural pressure. It is thought that low pressures may correlate with positive prognoses, and high pressures may indicate the need for revision.

Data are currently insufficient to indicate if use of this device improves clinical outcomes. The accuracy of the device in those with various types of endoleaks needs to be determined with larger numbers of patients. Also, the performance over time needs to be addressed. Work is also needed to determine the type and number of devices that might best be used in monitoring, given that sac compartmentalization might lead to a pressure-sensing device missing an endoleak. It also is not known whether there might be important long-term complications from this implanted device. Furthermore, the extent to which the device can reduce imaging requirements following endovascular aneurysm repair (via direct comparison with computed tomography) is undetermined. The evidence to date, which consists of small case series, is insufficient to permit conclusions concerning the effect of this device on health outcomes. Therefore, the use of wireless pressure sensors in detecting endoleaks in aneurysm repair is considered investigational.

Practice Guidelines and Position Statements
No relevant practice guidelines or position statements were identified.

U.S. Preventive Services Task Force Recommendations
Not applicable

References:       

1. Golzarian J, Valenti D. Endoleakage after endovascular treatment of abdominal aortic aneurysms: Diagnosis, significance and treatment. Eur Radiol. Dec 2006;16(12):2849-2857. PMID 16607497
2. 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. Jun 2004;39(6):1229-1235. PMID 15192561
3. Sonesson B, Dias N, Malina M, et al. Intra-aneurysm pressure measurements in successfully excluded abdominal aortic aneurysm after endovascular repair. J Vasc Surg. Apr 2003;37(4):733-738. PMID 12663970
4. 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. Feb 2007;45(2):236-242. PMID 17263995
5. 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. Jan 2006;43(1):2-7. PMID 16414379
6. 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. Feb 2008;63(1):59-66. PMID 18297208
7. 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. May 2008;18(5):957-965. PMID 18094972
8. Parsa CJ, Daneshmand MA, Lima B, et al. Utility of remote wireless pressure sensing for endovascular leak detection after endovascular thoracic aneurysm repair. Ann Thorac Surg. Feb 2010;89(2):446-452. PMID 20103319

Coding Section

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