The Clinical Rationale for the Sentry Bioconvertible Inferior Vena Cava Filter for the Prevention of Pulmonary Embolism

Abstract

The Sentry inferior vena cava (IVC) filter is designed to provide temporary protection against pulmonary embolism (PE) during transient high-risk periods and then to bioconvert after 60 days after implantation. At the time of bioconversion, the device's nitinol arms retract from the filtering position into the caval wall. Subsequently, the stable stent-like nitinol frame is endothelialized. The Sentry bioconvertible IVC filter has been evaluated in a multicenter investigational-device-exemption pivotal trial (NCT01975090) of 129 patients with documented deep vein thrombosis (DVT) or PE, or at temporary risk of developing DVT or PE, and with contraindications to anticoagulation. Successful filter conversion was observed in 95.7% of patients at 6 months (110/115) and 96.4% at 12 months (106/110). Through 12 months, there were no cases of symptomatic PE. The rationale for development of the Sentry bioconvertible device includes the following considerations: (1) the period of highest risk of PE for the vast majority of patients occurs within the first 60 days after an index event, with most of the PEs occurring in the first 30 days; (2) the design of retrievable IVC filters to support their removal after a transitory high-PE-risk period has, in practice, been associated with insecure filter dynamics and time-dependent complications including tilting, fracture, embolization, migration, and IVC perforation; (3) most retrievable IVC filters are placed for temporary protection, but for a variety of reasons they are not removed in any more than half of implanted patients, and when removal is attempted, the procedure is not always successful even with advanced techniques; and (4) analysis of Medicare hospital data suggests that payment for the retrieval procedure does not routinely compensate for expense. The Sentry device is not intended for removal after bioconversion. In initial clinical use, complications have been limited. Long-term results for the Sentry bioconvertible IVC filter are anticipated soon.

Figure 1

The Sentry bioconvertible IVC filter in filtering (above) and bioconverted (below) configurations, with corresponding axial views on the right.

Figure 2

Time course to pulmonary embolism (PE) in patients at level 1 trauma centers. AIS = Abbreviated Injury Scale. Adapted from Brakenridge et al. [19] and Coleman et al. [17]

Figure 3

Median days to pulmonary embolism (PE) in large surgery populations. IQR = Interquartile range. Data from Jordan et al. [25], Thomas et al. [26], Parvizi et al. [31], and Bjornara et al. [29].

Figure 4

Computed tomography imaging of the Sentry bioconvertible IVC filter for a single patient. (a) Coronal image acquired as part of helical dataset 1 month after filter placement, showing the Sentry device in filtering configuration. (b) Coronal image at 6-month follow-up showing the device in bioconverted configuration. ((c), (d), (e)) Axial views of the bioconverted device at 6-month follow-up, with the images keyed to the coronal view in (b). Reprinted with permission from Dake et al. [60]

Figure 5

Histological images of the integration of the Sentry filter arms into the wall of the inferior vena cava. Above: section cut through the tips of the filter arms stained with hematoxylin and eosin. Below (dark red box in image above): residual filament material surrounding chronic inflammatory cells adjacent to the fully incorporated tip of a filter arm. Reprinted with permission from Gaines et al. [59]