Lazar J. Greenfield is an honors graduate of Baylor College of Medicine in 1958 and completed his surgical training at the Johns Hopkins Hospital. He began his academic career as Assistant Professor of Surgery at the University of Oklahoma Medical Center and rapidly ascended the ladder to Professor of Surgery in 1971. After a successful 13 year appointment as Stuart McGuire Professor and Chair at the Medical College of Virginia, he was appointed as the F.A. Coller Distinguished Professor of Surgery and Chairman of the Department of Surgery at the University of Michigan. After 15 years as Chair, he retired from that responsibility in 2004 to devote his efforts to research and teaching. Dr. Greenfield is best known for his development of an intracaval filter device to prevent pulmonary embolism that bears his name – the Greenfield filter.
The Greenfield filter is placed in the vena cava of patients who have contraindications to anticoagulation, but who would otherwise be at risk of pulmonary embolism without such anticoagulation. Those IVC filters are placed endovascularly, meaning that they are inserted via the blood vessels.
Most filters are placed for the following reasons.
- Failure of anticoagulation; e.g. development of deep vein thrombosis (DVT) or pulmonary emboli (PE) despite adequate anticoagulation.
- Contraindications to anticoagulation; e.g. a patient at risk of PE who has another condition that puts them at risk of bleeding, such as a recent bleed into the brain, or a patient about to undergo major surgery
- Large clots in the vena cava or iliac veins
- Patients at high risk of having a PE
Greenfield introduced a new stainless steel filter in 1973. The Greenfield filter has been on the market the longest, it is the most extensively evaluated filter, and it has become the criterion standard with which other IVC filters are compared.
The original Greenfield filter is conical, and it consists of 6 strands of 0.015-in, zigzag-shaped, 316L-grade stainless steel legs in a radial array, each with a hook at the end that anchors the filter to the IVC. The steel struts are 4.6 cm in length and are fitted to an apical hub, which is directed cephalad in the patient. The base is 3.0 cm in diameter with the legs separated by 11 mm in the deployed position. The filter is loaded into a 24F carrier with a 29.5F external diameter.
The design of the Greenfield filter made it possible for thrombi to fill and occlude 70% of the filter cone, representing a volume of thrombus of approximately 4 cm3 (34.3% of total volume) without reducing the cross-sectional area by 50%. If the cone is filled to 80% of total volume, the reduction of cross-sectional area is 64%. The ability of this filter to trap clinically significant emboli has been demonstrated in several in vitro and in vivo studies.
There are also titanium Greenfield filter and percutaneous steel Greenfield filter (PSGF) or also called the stainless steel Greenfield filter.