Management of heparin therapy: Controlled prospective trial

Anticoagulation therapy for venous thromboembolism in patients with gynecologic malignancy

Anticoagulation therapy in 74 patients with gynecologic malignancy and venous thromboembolism was evaluated as to hemorrhagic complications, recurrent thrombosis, and completion of prescribed course. Clinically significant bleeding complications occurred in 25 patients and the course of anticoagulant therapy was not completed in 29 patients because of bleeding complications or death within 3 months. Venous thromboembolism recurred in 11% of patients. Risk factors associated with hemorrhagic complications and unsuccessful completion of anticoagulation therapy include advanced age, advanced stage of malignancy, incomplete surgical resection of tumor, and systemic chemotherapy. Complications of anticoagulant therapy were found to be excessive when compared to those in reports dealing with noncancer patients and may exceed the benefits of therapy in certain patients. Alternative methods of management for this group of high-risk patients are discussed.

Pulmonary vascular disease--overview

Some intriguing advances in the diagnosis of pulmonary vascular diseases have been made in the past decade. Moreover, developments in treatment of recurrent thromboembolic disease have come to the forefront, with a considerable reduction in morbidity and mortality rates in the past few years.

Adjusting heparin infusion rates from the initial response to activated coagulation time

A mathematical description of the dose-response curve of heparin to the activated coagulation time is applied retrospectively to 20 patients treated with continuous heparin infusion. The adjusted heparin dose was compared with a calculated prediction using the theoretical mathematical model. The main actual dose was 28 U/kg/h, and the mean predicted dose was 25.8 U/kg/h. The correlation coefficient was 0.862 (p3 0.05). These data are used to develop a dosing adjustment chart. Special considerations prior to using the calculation or dosing adjustment chart are discussed. The use of this model may allow the clinician to determine more rapidly a therapeutic heparin dosage than previous empiric approaches.

Anticoagulation in cerebral ischemia

Anticoagulation clearly benefits patients at risk of stroke from cerebral embolism. Conversely, patients with completed ischemic stroke are not benefited, and may show a higher mortality and morbidity because of hemorrhagic complications. Technical advances in the early, accurate diagnosis of cerebral hemorrhage, the constant infusion of heparin, and closer monitoring of anticoagulation have continued to reduce the risk of hemorrhage in treated patients. In patients with TIA, alternative therapy with anti-platelet agents, which appears to prevent stroke at less bleeding risk, is under study. Current results show no differences between the two therapies, but only historical controls are available for evaluation of benefit. Whether or not anticoagulation prevents progression of neurologic deficit in patients with strokes-in-evolution remains an unanswered question, which can be resolved only by prospective, randomized, controlled trials.

Anticoagulation. Current approach to heparin and warfarin therapy

Anticoagulant therapy is required for a variety of indications. Heparin, usually administered intravenously, is the drug of choice for acute anticoagulation, with the infusion monitored by partial thromboplastin time. For long-term therapy the standard regimen includes heparin given via intravenous infusion for 7 to 14 days followed by oral warfarin therapy, monitored by prothrombin time. The duration of anticoagulant therapy depends on the indication for its use. The most serious complication with the anticoagulants is bleeding. Physicians should be aware of the risk factors for bleeding and of the measures capable of reversing the effects of the drugs.

Value of postoperative heparin therapy in peripheral arterial thromboembolism

The experience with 359 patients with arterial thromboembolism from 1963 to 1982 has been reported. Combined operative and anticoagulant therapy appears the most beneficial form of treatment. Treatment with heparin after catheter embolectomy was associated with a decrease in mortality (7.6 percent), number of amputations (5 percent), and recurrent emboli (6 percent). Serious wound complications occurred less frequently than anticipated (8 percent). We advocate prompt arteriography and revascularization procedures to ensure long-term limb function after initial embolectomy for salvage, if the result is less than optimal or expected. Postoperative heparin seems to buy time in marginal cases, enabling secondary operations to ensure a satisfactory outcome in most patients.

Screening and treatment of pulmonary embolism after total hip replacement

The effect of anticoagulative treatment of pulmonary embolism was studied in 63 patients out of 348 operated on with total hip replacement. Screening diagnosis of pulmonary embolism was obtained from 99mTc perfusion scintigraphy in combination with 99mTc-microaerosol ventilation scintigraphy and chest radiogram. The administration of heparin and warfarin was associated with hemorrhagic side effects in 7 per cent. The final outcome of surgery, however, was not interfered with. Fatal pulmonary embolism occurred in one patient (0.3 per cent) in whom the diagnosis had been missed.

Subcutaneous administration of heparin. A randomised comparison with intravenous administration of heparin to patients with deep-vein thrombosis

One-hundred and forty-one patients with clinical signs of acute deep venous thrombosis (DVT) in the legs were randomly allocated to receive heparin either as two daily subcutaneous injections (s.c.) or as continuous intravenous infusion (i.v.). The thrombi extended into the popliteal or femoral veins in 83% of the patients. Verification of diagnosis and evaluation of therapy was performed by phlebography, plethysmography and thermography. The results showed that heparin administered s.c. twice daily was as efficient as continuous i.v. infusion in preventing extension of the thrombus. In two patients the s.c. administration was stopped due to local haematomas at the injection sites. Retroperitoneal or intramuscular bleedings occurred in four patients, two in each group. Two major, non-fatal pulmonary emboli occurred, one in each group.

Comparison of the in vivo hemorrhagic and antithrombotic effects of a low antithrombin-III affinity heparin fraction

Antithrombin III (ATIII) affinity chromatography of commercial grade heparin yields fractions of high and low affinity for ATIII. In vitro, the high affinity fraction accounts for most of the anticoagulant effect while there is evidence that the low affinity material interferes with platelet function. We have studied the relative antithrombotic and hemorrhagic effects of low affinity heparin. The low affinity heparin fraction, specific activity 43 USP units/mg, was compared with standard heparin (150 USP units/mg) in rabbit experimental models. A residual 12.5% by weight of this low affinity heparin showed high affinity for ATIII. Inhibition of thrombosis in a stasis-hypercoagulability model was directly related to the weight (mg) of high affinity material in each of the heparins. In the bleeding model, when similar weights (mg) of high affinity material were infused, significantly more bleeding was demonstrated with the low affinity fraction which contained a 5-fold excess by weight of low affinity material. We have demonstrated that a low affinity heparin depleted of in vitro anticoagulant and in vivo antithrombotic activity significantly contributes to hemorrhage.

Anticoagulant therapy by continuous heparinization in newborn and older infants

In order to evaluate the metabolism and anticoagulant effect of heparin in the newborn infant and young child, 15 babies were monitored during continuous intravenous heparinization for documented large vessel thromboses. Infants with the most significant thromboses had the highest clearance rates for heparin. Plasma heparin levels in the therapeutic range (0.3 to 0.5 U/ml) and clinical resolution of the thrombi were associated with heparin doses of 16 to 35 U/kg/hour (mean = 27 U/kg/hour). A micro whole blood clotting time was evaluated and shown to be a useful guide to heparin effect in these infants. With the exception of excessive oozing from puncture sites in one infant, no complications of heparin therapy were noted. The newborn infant appears to require a larger amount of heparin than adults in order to achieve adequate heparinization.

Indium-111-labeled platelets: effects of heparin on uptake by venous thrombi and relationship to the activated partial thromboplastin time

The goal of heparin therapy in deep vein thrombosis is to prevent thrombus extension. The relationship between thrombus extension and the results of coagulation tests used to monitor heparin therapy is unclear. To explore this relationship, we studied the effect of several heparin regimens on the accretion of indium-111-labeled platelets on fresh venous thrombi, as detected by gamma imaging, and monitored the activated partial thromboplastin time (APTT). Six dogs were treated with a 300-U/kg bolus of heparin followed by a 90-U/kg/hour heparin infusion, a dose of heparin sufficient to increase the APTT to levels greater than eight times baseline (APTT ratio); platelet accretion (thrombus imaging) occurred only after the heparin effect was reversed with protamine sulfate. Nineteen dogs were treated with a 150-U/kg bolus of heparin followed by a 4-hour, 45-U/kg/hour heparin infusion; a thrombus was demonstrated only after protamine injection in 12 (mean APTT ratio 1.3 +/- 0.19) and before protamine injection in seven. In thirteen of these 19 dogs, 30 minutes separated the platelet injection from heparin therapy, while in six this duration was less than 30 minutes. In four of these six dogs, thrombi were demonstrated before protamine therapy and at APTT ratios greater than 3.0. Finally, 10 dogs were treated with a 100-U/kg bolus followed by a 3-hour, 50-U/kg/hour heparin infusion, after which the APTT was allowed to return to baseline values spontaneously. In all 10 dogs, a thrombus was demonstrated only after cessation of the heparin infusion, and at a mean APTT ratio of 1.4 +/- 0.15 times baseline. These results suggest that, except with very early platelet injection, platelet accretion by thrombi is consistently inhibited by heparin at APTT ratios greater than 2.5. Platelet accretion by venous thrombi occurs within narrow limits of heparin effect as reflected by the APTT.

A novel anti-thrombotic heparinoid (Org 10172) devoid of bleeding inducing capacity: a survey of its pharmacological properties in experimental animal models

The pharmacological profile of Org 10172, a mixture of sulphated glycosaminoglycorunans derived from hog intestinal mucosa, has been assessed in experimental thrombosis and bleeding models in rats and compared with heparin USP. Org 10172 inhibited thrombus formation in arterio-venous shunts dose dependently, the dose required for 50% inhibition (ID50) of thrombus formation was 40 anti-Xa units/kg i.v. The ID50 for heparin USP was 70 anti-Xa units/kg i.v. Org 10172 hardly increased bleeding in doses upto 1600 anti-Xa units/kg i.v., whereas heparin USP dose dependently increased bleeding from 90 anti-Xa units/kg i.v. onwards. The benefit (anti-thrombotic)/risk (bleeding) ratio of Org 10172 was therefore considerably better than that of heparin USP. The improved profile of Org 10172 towards bleeding might be caused by differences in the interaction with blood platelets in comparison with heparin USP. Org 10172 had less effect on the platelet content in thrombi than heparin USP. Org 10172 did not inhibit collagen induced release of serotonin in contrast to heparin USP. Org 10172 inhibited factor Xa induced aggregation of rabbit platelets but only at anti-Xa levels which were fifteen times higher than for heparin USP. In contrast to heparin USP Org 10172 had only a very weak effect on the activated partial thromboplastin time (APTT) ex vivo.

Transvenous vena caval filtration and pulmonary embolectomy

The diagnosis of deep vein thrombosis or pulmonary embolism can be made accurately using angiographic and radioisotopic techniques. Utilizing hemodynamic data, it is possible to classify patients with pulmonary embolism into five groups, which is helpful for planning therapy and assessing prognosis. Surgery for pulmonary embolism has evolved to include intraluminal methods of vena caval filtration for prevention of recurrent pulmonary embolism and transvenous extraction of pulmonary emboli. Though the majority of patients surviving pulmonary embolism can be managed medically with anticoagulation, a significant number will require surgical intervention. The development of transvenous methods allows effective emergency management of major pulmonary embolism, even in hospitals that do not have the capability for cardiopulmonary bypass.

Current status of anticoagulant therapy

Anticoagulant therapy has stood the test to time. Full-dose heparin and warfarin prevent recurring pulmonary embolism and deep venous thrombosis. Their use is indicated in patients who have experienced venous thromboembolism unless contraindications are compelling. Low-dose heparin is successful in preventing the initial episode of venous thrombosis in most patients at high risk for the development of thrombophlebitis. Warfarin reduces the incidence of systemic embolization in patients with heart disease and atrial fibrillation and in patients with artificial heart valves. Evidence is accumulating to suggest that warfarin may still retain an important role in the management of patients with myocardial infarction. However, bleeding remains an inevitable risk in patients receiving anticoagulant therapy. The risk, however, can be diminished when both the physician and patient understand the mechanism of action of the drugs and the factors that predispose to bleeding.

Adjusted subcutaneous heparin versus warfarin sodium in the long-term treatment of venous thrombosis

Previously, we compared fixed low doses of heparin with adjusted doses of warfarin for the long-term treatment of venous thrombosis; in that study low-dose heparin was ineffective in preventing recurrence in patients with proximal-vein thrombosis. We have now completed a randomized trial comparing adjusted doses of heparin and of warfarin for prevention of recurrent venous thromboembolism in patients with proximal-vein thrombosis. One hundred six consecutive patients with acute proximal-vein thrombosis confirmed by venography were treated with intravenous heparin and then randomized to secondary prophylaxis. Two of 53 patients receiving heparin, as compared with one of 53 receiving warfarin, had new episodes of objectively documented venous thromboembolism. Nine patients taking warfarin had bleeding complications (which were major in three patients), as compared with one patient taking heparin (P = 0.008). Our data indicate that adjusted-dose subcutaneous heparin therapy provides an effective alternative to warfarin sodium and is associated with a lower risk of bleeding.

Intersubject variability in the anticoagulant response to heparin in vitro

The significance of baseline coagulation times and plasma concentrations of serine protease inhibitors as determinants of the relationship between heparin activity and its anticoagulant effect has been investigated in vitro. Citrated plasma was prepared from blood obtained from 20 normal subjects, and heparin added to yield concentrations ranging from 0.05 to 1.5 units/ml. The anticoagulant effect was determined by the activated partial thromboplastin time (APTT) and thrombin time (TT). An excellent linear relationship was observed between the natural logarithms (ln) of the coagulation times and heparin activity. Baseline APTT values ranged from 28.4 to 59.7 s and the slope values for the ln APTT vs heparin curves ranged from 1.488 to 3.427 ml/unit. Similar range was observed in the slope values for the ln TT vs heparin curves. There was a highly significant positive correlation between the ln APTT vs heparin slope values and the baseline APTT values (r: 0.905; p less than 0.001). There was also a weak but statistically significant positive correlation between plasma concentrations of alpha 2 macroglobulin and baseline APTT values (0.02 greater than 0 greater than 0.01) and slope values of the ln APTT vs heparin curves (0.02 greater than p greater than 0.01). Furthermore, there was a statistically significant positive correlation between plasma concentrations of alpha 1 antitrypsin and baseline TT values (0.05 greater than p greater than 0.02) and slope values of the 1n TT vs heparin (0.02 greater than p greater than 0.01). Neither baseline APTT and TT values nor slope values of the ln APTT and TT vs heparin curves were statistically significantly related to plasma concentrations of antithrombin III, fibrinogen, or alpha 1 acid glycoprotein. This study has demonstrated that baseline APTT is a major determinant of the anticoagulant response to heparin in vitro, as determined by that same coagulation test, and it illustrates that there is a wide intersubject variation in the anticoagulant response to heparin in vitro.

A comparison of prostacyclin and heparin on hemodialyses in dogs

A comparison of the efficacy of prostacyclin and heparin as anticoagulants during hemodialysis in uremic dogs was evaluated. Prostacyclin was infused continuously into the arterial limb of the dialyzer (100 ng/kg/min) while heparin was administered as a 5000 unit bolus at the beginning of dialysis. Prostacyclin and heparin were alternated and a total of 4 dialyses/dog were performed. Parameters followed to assess the efficacy of dialyses included: dialysance (ml/min) of urea, creatinine, ultrafiltration rate (ml/hr), residual volume and platelet count (% of baseline). A lesser degree of hemodialysis associated thrombocytopenia, and a higher ultrafiltration rate were observed with prostacyclin. These studies demonstrate that prostacyclin can be used alone as an anticoagulant in a uremic dog model, and in contrast to heparin it maintains the platelet count and improves the ultrafiltration rate during hemodialysis.

Heparin therapy in venous thromboembolism

Patients with pulmonary embolism or deep venous thrombosis were randomly assigned to receive either intermittent or continuous intravenous heparin therapy. In patients with an enhanced risk of bleeding, major bleeding was significantly more common during the intermittent use of heparin; in patients without these risk factors, hemorrhage occurred with equal frequency during intermittent and continuous heparin therapy. Recurrent thromboembolism was seen significantly more often in patients receiving continuous heparin therapy. Controlling the dose of heparin with coagulation tests resulted in the administration of significantly larger daily doses of heparin with intermittent injections than with continuous infusion. Therefore, the bleeding complications of intermittent heparin therapy could have been due to the higher dose, and the recurrences associated with continuous heparin therapy may have resulted from lower doses rather than from differences in the method of administration. In a small trial, arbitrary lower doses of heparin given intermittently similar to the doses of heparin given continuously resulted in fewer bleeding complications and more recurrences. In patients without risk factors for bleeding, the intermittent administration of heparin in the higher dose is preferable because of fewer recurrences and no increase in hemorrhagic complications. In patients with a high risk of bleeding, conventional doses of heparin given continuously can reduce the rate of hemorrhagic complications but will result in more recurrences.

A practical approach to disorders of hemostasis

Simple screening tests are available to detect abnormalities in the plasma coagulation system and platelet function. Prothrombin time reflects the integrity of the extrinsic system, while activated partial thromboplastin time indicates whether the intrinsic system is intact. Thrombin clotting time is a measure of the integrity of the end stage of clotting. Prothrombin time is also helpful in monitoring warfarin therapy; either of the latter two tests can perform a similar function in patients receiving heparin. Ivy bleeding time is the best screening test of platelet function. If bleeding time is prolonged but results of plasma coagulation tests are normal, specialized platelet function tests may be necessary.

The role of noninvasive tests versus pulmonary angiography in the diagnosis of pulmonary embolism

We studied 243 patients in whom 248 pulmonary angiograms were performed because of suspected pulmonary embolism. Ventilation and perfusion lung scanning in 140 of them revealed 38 to be in low and high probability groups. Of 19 patients with subsegmental and nonsegmental perfusion defects that were matched with ventilation defects, none had pulmonary embolism. Conversely, angiography was positive in 17 of 19 patients with multiple segmental or lobar perfusion defects in areas of normal ventilation. Doppler flow examinations of the veins of the legs showed normal flow in 61 of 79 (77 percent) patients with pulmonary emboli and, therefore, were insensitive indicators of embolism. There was no mortality from angiography, and serious complications occurred in 2 percent of the patients. Anticoagulation in 83 patients was associated with bleeding in 25, two of whom died. The data indicate that ventilation-perfusion lung scanning can be used to separate many of the patients suspected of having pulmonary embolism who need anticoagulant treatment from those who do not. However, there is a considerable number of patients with nonspecific abnormalities on lung scan. For this group of patients with nonspecific abnormalities, the risk of complications from empiric treatment with anticoagulant drugs is probably greater than the risk of complications from pulmonary angiography. Further, our data show that patients with negative angiography have a very low risk of subsequent pulmonary embolism. In this group of patients, therefore, pulmonary embolism should be demonstrated by angiography before long-term anticoagulant therapy is prescribed.

Stability of heparin in intravenous fluids

Images

Heparin therapy for deep venous thrombosis

One hundred fifty-six cases of deep venous thrombosis were reviewed. A previous episode of thrombosis, seen in 47 percent of the patients, was the most common predisposing factor. Medical illness, operation and local trauma were other important predisposing factors. Treatment consisted of continuous intravenous heparin therapy monitored by the activated coagulation time of whole blood (ACT). Thirty-three patients with an average ACT greater than 180 seconds had a more rapid recovery and had no recurrent deep venous thrombosis, embolism or failure to improve. Recurrent thrombosis, embolism or failure to improve was seen in 7 of 65 patients with an average ACT below 180 seconds. Major bleeding, defined as life-threatening bleeding or bleeding requiring transfusion, was not increased when the ACT was over 180 seconds, although minor bleeding was increased. Bleeding was also increased in women, elderly and postoperative patients. We advocate the use of higher doses of heparin to treat most patients with deep venous thrombosis because of the more rapid and complete recovery.

Defibrinogenation as an alternative to heparinization in prolonged extracorporeal circulation

Complications arising from difficulty controlled bleeding and thrombus formation during procedures which require extracorporeal circulation with heparin as anticoagulant motivate the search for better hemostasis and anticoagulant technology. An enzyme (Defibrase), having a specific interaction with fibrinopeptide A such as to cause fibrin depletion in a soluble form, has been proposed as an alternative to heparin. Defibrase, in contrast to heparin, does not affect blood platelet function. Heparin and Defibrase as anticoagulants were compared in 8 h perfusion studies using arterio-venous extracorporeal blood circuits in dogs; the circuitry included pumps, membrane oxygenators and filters serially. Thrombus formation, in the filters and the oxygenators as well as pathology of the perfused animal were investigated. The results suggest that defibrase-like enzymes have potential for enhanced control of hemorrhagic and thrombotic phenomena. Although impeded by a latency of several hours before the full anticoagulant properties are developed in vivo, it appears that enzymatically mediated defibrinogenation of blood may be a valuable alternative to heparinization in extracorporeal circulation procedures.

Current status of ventilation-perfusion imaging

The major clinical use of ventilation-perfusion (V/Q) scintigraphy is for the diagnosis of pulmonary embolism (PE). Accurate diagnosis of PE is essential since effective treatment is available but involves some risk to the patient. The scintigraphic characteristics of PE are segmental perfusion defects in lung that is normally ventilated and normal on the radiograph. The inherent shortcoming of perfusion scintigraphy is its lack of specificity. Combining a ventilation study with perfusion imaging improves the diagnostic specificity of lung scintigraphy. Xenon-133 is currently the most commonly used radionuclide for routine ventilation studies; a long washout technique is more sensitive than single-breath imaging when this radionuclide is used. We obtain preperfusion xenon-133 ventilation studies with a 4-min rebreathing equilibrium phase and a long 5-min washout phase to obtain maximum information. It is imperative that V/Q studies be interpreted with a current high quality chest radiograph. Interpretation of V/Q studies for PE is perhaps best done by assigning a probability diagnosis, since rarely is absolute specificity possible. This article details the criteria we use for these probability determinations.

Pulmonary thromboembolism. 2. New trends in prophylaxis and therapy

Although low-dose heparin therapy is the technique most commonly used for prophylaxis of pulmonary thromboembolism, its usefulness is being questioned. Platelet deaggregation prophylaxis with either aspirin or dipyridamole, or both, apparently is a reasonable alternative, but further studies are needed. For treatment of pulmonary thromboembolism, continuous conventional-dose heparin therapy is the approach of choice. It has the highest therapeutic/toxic ratio and is the most effective technique for prevention of clot propagation. The patient's fibrinolytic network must be intact, however, if clot degradation is to occur. Fibrinolytic therapy with urokinase or streptokinase should be restricted to use in patients with massive pulmonary embolism in whom hemodynamics are unstable. Caval interruption and pulmonary embolectomy have lower benefit/risk ratios than do the medical alternatives and are rarely used for pulmonary thromboembolism.

Clinical pharmacokinetics of heparin

Heparin binds reversibly to its target sites of action, antithrombin and the other serine proteases involved in coagulation, especially activated factor X. It also binds to other plasma proteins, including fibrinogen, plasmin, albumin, and lipases. The volume of distribution of heparin is then, under most circumstances, limited to the plasma volume. Heparin has a very short half-life, about 1.5 hours, which is dose-dependent and varies with the assay method employed for its measurements. It is not eliminated enzymatically nor by glomerular filtration or renal tubular secretion. In all likelihood, the anticoagulant is transferred to reticuloendothelial cells, which may also provide the means for its degradation. Many of the difficulties inherent in assessing the kinetic properties of heparin, as well as its clinical efficacy, may be attributed to: (1) its molecular heterogeneity; (2) its wide spectrum of binding sites and their respective kinetic properties and dissociation constants; (3) differences among methods for measuring heparin effect and concentration; (4) the dose dependence of the drug's half-life; (5) variation in patient response to heparin; (6) the specific cation associated with it; and (7) the presence of hypercoagulation syndromes associated with deficits of antithrombin. Neither renal nor hepatic disease, nor the biological tissues from which heparins are extracted commercially, seem to influence the drug's kinetic properties as much as variations in clearance and response to heparin among individual patients. Many comparisons among available studies are difficult because of the wide variation in the assay methods employed in them. It would appear that optimum therapy with heparin can be achieved only when the individual patient's response to, and rate of elimination of, heparin are taken into account concurrently.