The Greenfield Vena Cava Filter: Recurrent Pulmonary Embolism

The Greenfield Vena Cava Filter: Recurrent Pulmonary EmbolismRecurrent Pulmonary Embolism
The purpose of caval filtration is to prevent pulmonary embolism. One of the arguments against the use of the Mobin-Uddin umbrella, and indeed, all other devices which can lead to caval occlusion, is that future embolization may take pace through extensive venous collateral circulation. In addition, the presence of a foreign surface in the blood stream may activate clotting, and the “protector” may then become the seed from which future embolic episodes grow.

Recurrent pulmonary embolism is an uncommon event following Greenfield filter insertion. Published data on 289 patients’ disclosed seven pulmonary emboli after insertion (2.4 percent). An additional patient died from pulmonary embolism after a filter was misplaced into the right iliac vein, leaving a left proximal iliac DVT uncovered. The low incidence of embolic recurrence (whether or not anticoagulant was used) had been attributed to the geometry of the device and its excellent record of longterm patency. At odds with these data are three patients reported from the University of Pittsburgh, all of whom had pulmonary emboli arising from proximally propagating clot on top of the filter. Others had reported the risk of clot formation in an obliquely lodged filter, but those patients had a benign course. The Pittsburgh series is unique in that two of the three filters were in apparently good position. All three cavae were patent, although two filters contained thrombus. Unfortunately, the total number of patients was not reported; thus, their overall incidence of recurrence is unknown.
Venous stasis complications are a significant concern in any patient with deep vein thrombosis. While the primary obstructing thrombi usually lie in the distal veins of the legs, caval occlusion may markedly exaggerate stasis complications. Long-term caval patency has proven to be a unique advantage of this device. In nine series comprising 257 patients with varying degrees of follow-up, only eight cases (3.1 percent) of caval thrombosis were documented.’ When commented upon, the occlusions occurred within one month of insertion. New venous stasis complications have not been seen postoperatively unless caval occlusion or recurrent deep venous thrombosis developed. Indeed, patients with lower extremity edema related to venous thrombosis have resolved their stasis phenomena after filter placement. The role of anticoagulation in conditioning the long-term patency of the device remains uncertain. Whether subclinical clot formation takes place intermittently on the filter is not known. It has been postulated that some venograms revealing clot “trapped” within a filter may in reality represent in-situ thrombosis, and thus a source for future embolus.

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