John C. Hoak

Management of Deep Vein Thrombosis and Pulmonary Embolism A Statement for Healthcare Professionals From the Council on Thrombosis (in Consultation With the Council on Cardiovascular Radiology), American Heart Association

Deep vein thrombosis (DVT) is a common but elusive illness that can result in suffering and death if not recognized and treated effectively. DVT occurs in ≈2 million Americans each year. Death can occur when the venous thrombi break off and form pulmonary emboli, which pass to and obstruct the arteries of the lungs. DVT and pulmonary embolism (PE) most often complicate the course of sick, hospitalized patients but may also affect ambulatory and otherwise healthy persons.1 2 3 4 It is estimated that each year 600 000 patients develop PE and that 60 000 die of this complication.5 6 7 This number exceeds the number of American women who die each year from breast cancer. PE is now the most frequent cause of death associated with childbirth.8 Women are a prime target for PE, being affected more often than men. Deep vein thrombosis is a major complication in orthopedic surgical patients and patients with cancer and other chronic illnesses. DVT can be a chronic disease. Patients who survive the initial episode of DVT are prone to chronic swelling of the leg and pain because the valves in the veins can be damaged by the thrombotic process, leading to venous hypertension. In some instances skin ulceration and impaired mobility prevent patients from leading normal, active lives. In addition, patients with DVT are prone to recurrent episodes. In those instances in which DVT and PE develop as complications of a surgical or medical illness, in addition to the mortality risk, hospitalization is prolonged and healthcare costs are increased. Over the past 20 years results of clinical trials have provided information that has revolutionized the approach to management of venous thromboembolic disease. New diagnostic modalities and therapeutic agents have been developed that are more effective, less expensive, and more …

An improved method for the addition of long-chain free fatty acid to protein solutions☆

Abstract FFA is transferred rapidly from fatty acid coated Amberlite, Celite, or Microthene particles into aqueous media containing protein. Solutions that contain a relatively high ratio of FFA to protein can be prepared by this technique.

MASSIVE THROMBOSIS PRODUCED BY FATTY ACID INFUSION

Previous investigations have shown that fatty acids affect the coagulation of blood (2-4). In particular, certain fatty acids greatly accelerated the formation of thrombi from rat or human blood in the Chandler apparatus 1 (6, 7). Long-chain, saturated fatty acids, such as stearic and palmitic, shortened the time of thrombus formation, whereas the unsaturated fatty acids of similar chain length (oleic, linoleic, linolenic, and arachidonic) did not influence the thrombus formation time. Shortchain, saturated fatty acids of chain length less than C12 were likewise without effect. The mechanism whereby thrombus formation was accelerated by long-chain, saturated fatty acids probably resulted from the activation of the Hageman or contact factor of plasma (7). These observations relating fatty acids to thrombus formation in vitro have prompted additional investigations designed to test the effects of different fatty acids given intravenously to anesthetized dogs. Many previous workers have infused fatty acids (or their sodium salts) into animals. As early as 1889, Munk had noted that dogs developed hypotension and asystole after the intravenous injection of oleate or palmitate (8). Others have documented that fatty acids or their sodium salts, when given to animals intravenously, produced hemolysis (9, 10), capillary damage (11), and death (10-13). In none of these re-

Effect of Aspirin on Thrombin-Induced Adherence of Platelets to Cultured Cells from the Blood Vessel Wall

An in vitro method was used to detect adherence of (51)Cr-labeled platelets to monolayers of cultured human endothelial, fibroblast, and smooth muscle cells. Washed platelets did not adhere to untreated or aspirin-treated endothelial monolayers in the absence of thrombin. In contrast, thrombin-induced platelet aggregates adhered to all of the monolayers but adherence to endothelium was significantly less than to the other cells. Additional evidence for adherence of platelets to the endothelium was provided by scanning and transmission electron microscopy. Thrombin-induced platelet adherence to endothelium was inhibited by hirudin. Platelet adherence induced by thrombin was enhanced significantly by treatment of the endothelial monolayer with 1-2 mM aspirin. This increase in adherence was seen even when aspirin-treated platelets were used; adherence values approached those seen with fibroblasts and smooth muscle cells. An aspirin concentration of 0.1 mM was sufficient to block thrombin-induced malonaldehyde production in platelets but it did not interfere with the inhibitory effect of the endothelium against platelet adherence. The effect of aspirin on the endothelium was temporary and inhibitory activity of the endothelium was restored 1 h after aspirin had been removed from the incubation system. The ability of thrombin to cause adherence of platelets to undamaged endothelium, and the potential for aspirin to enhance this adherence have implications for mechanisms which operate in platelet interaction with the blood vessel wall.

Utilization of arachidonic and linoleic acids by cultured human endothelial cells.

When cultured human umbilical vein endothelial cells are supplemented with linoleic acid, the arachidonic acid content of the cellular phospholipids is reduced approximately 35%. Most of the fatty acid compositional change occurs during the first 24 h. One factor responsible for this effect is the inability of the endothelial cells to convert appreciable amounts of linoleic to arachidonic acid, due to a fatty acid delta 6-desaturase deficiency. By contrast, these endothelial cultures contain delta 5- and delta 9-desaturase activity and are able to elongate long-chain polyunsaturated fatty acids. The other factor that contributes to the decrease in arachidonic acid is that high concentrations of linoleic acid reduce the incorporation of arachidonate into cellular phospholipids. Stearic acid, a long-chain saturate, does not produce any reduction, whereas eicosatrienoic acid is an even more effective inhibitor than linoleic acid. In spite of the fact that high concentrations of these polyunsaturates produced inhibition, the endothelial cells were found to efficiently incorporate exogenous arachidonic acid into cellular phospholipids and triglycerides. This may serve to compensate for the inability of these cells to synthesize arachidonic acid from linoleic acid. These findings suggest that the endothelium obtains arachidonic acid from an extracellular source, that this cannot be provided in the form of linoleic acid and, in fact, that high concentrations of linoleic acid actually may interfere with the ability of the endothelium to maintain an adequate supply of intracellular arachidonic acid.

Effect of fatty acid modification on prostacyclin production by cultured human endothelial cells.

We have investigated whether changes in cellular fatty acid saturation can influence prostacyclin (PGI2) production by cultured human umbilical vein endothelial cells. As compared to control cells, those enriched with linoleic acid released 60--75% less PGI2 in response to thrombin or the calcium ionophore A23187. A similar but considerably smaller effect was observed when the cells were enriched with oleic or linolenic acid, but no reduction occurred with palmitic or linoelaidic acids. Some reduction in PGI2 release was noted as early as 1 h after exposure to linoleic acid. When the culture medium was supplemented with linoleic acid, the cell phospholipids contained four to five times more linoleate and 25--40% less arachidonate. These changes were most marked in the choline and serine plus inositol phosphoglyceride fractions. When the fatty acid composition of the cells enriched with linoleic acid was allowed to revert, there was a progressive increase in the capacity of the cells to release PGI2 in response to thrombin. The increase correlated with a reduction in linoleate content of the cell lipids, but there was no change in arachidonate content. This suggests that linoleic acid may act as an inhibitor of PGI2 production. The cultured endothelial cells were also able to produce PGI2 directly from added arachidonic acid. As the arachidonic acid concentration of the medium was raised, PGI2 formation by the linoleate-enriched cells increased relative to control cells, suggesting that the inhibition produced by linoleic acid may be competitive.

Increased Platelet Aggregates in Patients With Transient Ischemic Attacks

In order to evaluate the pathogenetic importance of platelet aggregates in cerebrovascular disease, a platelet count ratio method was used to study 66 patients with transient ischemic attacks (TIAs). Thirty normal subjects and 22 patients without thromboembolic disorders were also included as controls. The mean platelet aggregate ratio of the TIA group was 0.75 ± 0.03 SEM which was significantly lower than that of normal subjects (0.90 ± 0.02) or patient controls (0.88 ± 0.01) (P < 0.01). Seventeen patients with TIA were then treated with aspirin (1,200 mg) and dipyridamole (200 mg) daily. The platelet aggregate ratios were normalized in 13 patients. Of four patients who did not respond to this regimen, one did respond to sulfinpyrazone. When sulfinpyrazone was discontinued, recurrence of symptoms was preceded by an increase in platelet aggregates. These findings suggest that platelet aggregates may play an important role in the pathogenesis of cerebrovascular insufficiency. The determination of platelet aggregates appears useful in selecting patients for antiplatelet therapy.

Replication of Human Endothelial Cells in Culture

Investigative studies dealing with the properties and functions of endothelial cells have been hampered because there has been little or no success in the isolation, growth, and passage of individual cells in large numbers. We have developed a system whereby pure cultures of endothelial cells derived from umbilical veins can be subcultured for at least five serial passages. Many facets of endothelial function and interaction can be evaluated with the use of this new adaptive system of isolation and culture.

Inhibition of prostacyclin by treatment of endothelium with aspirin. Correlation with platelet adherence.

Aspirin treatment of cultured endothelial cells from the umbilical vein increased the adherence of 51Cr-platelets when thrombin was present. If the cyclooxygenase activity of endothelium was inhibited by aspirin, as it is in the platelet, reduction of endogenous prostacyclin (PGI2) production could have been responsible. By correlating thrombin-induced adherence of platelets to endothelial monolayers with PGI2 release (as measured by radioimmunoassay for 6-keto-prostaglandin FI1 alpha [6-keto-PGF1 alpha]), we have demonstrated an inverse relationship between platelet adherence and PGI2 levels. Untreated endothelial monolayers exposed to thrombin and platelets resulted in 4% platelet adherence and 107 nM 6-keto-PGF1 alpha. With 0.1 mM aspirin treatment, which is known to block platelet cyclooxygenase, adherence was 5% and 6-keto-PGF1 alpha decreased to 45 nM. Increasing the aspirin concentration to 1 mM resulted in 44% adherence and less than 3 nM 6-keto-PGF1 alpha. When 25 nM exogenous PGI2 was added to 1 mM aspirin-treated endothelium, adherence returned to 5%. The increase in thrombin-induced platelet adherence to 1 mM aspirin-treated monolayers was reversed 2 h after removal of the aspirin solution. 6-Keto-PGF1 alpha returned to 37% of the untreated monolayer value. Recovery from the aspirin effect did not occur when cycloheximide, an inhibitor of protein synthesis, was present during the 2-h period.

Utilization of long-chain free fatty acids by human platelets

There was a rapid net uptake of free fatty acid (FFA) by human platelets when long-chain FFA, bound to human serum albumin, were incubated with platelet suspensions. Results from experiments in which both palmitate and albumin were labeled indicated that the fatty acid dissociated from the protein during uptake. Much of the FFA taken up by the platelet in short-term incubations remained in unesterified form, i.e., it was recovered as platelet FFA. As the incubation continued, increasing amounts of FFA were oxidized to CO(2) and incorporated into platelet lipid esters, particularly lecithin. Essentially all of the fatty acid that was incorporated into the platelet FFA fraction was released rapidly from the cells when they were exposed to a medium containing FFA-free albumin. The magnitude of uptake into the platelet FFA fraction was similiar at 0 degrees and 37 degrees C. Likewise, the rate and magnitude of FFA release from the platelet were similar at 0 degrees and 37 degrees C. Therefore, it is likely that both FFA uptake and FFA release occur by energy-independent mechanisms. The major effect of increasing the FFA concentration of the incubation medium was increased fatty acid uptake into the platelet FFA fraction. Similar results occurred when platelets were incubated in human plasma containing increasing amounts of added palmitate. At a given extracellular FFA concentration, considerably more of the saturated fatty acids, palmitate and stearate, were taken up as platelet FFA than either oleate or linoleate.