Lepirudin is a safe and effective anticoagulant for patients with heparin-associated antiplatelet antibodies

OBJECTIVE

The purpose of this study was to determine whether lepirudin, a direct thrombin inhibitor, is a safe and effective anticoagulant for patients with heparin-associated antiplatelet antibodies (HAAbs).

METHODS

The charts of HAAb-positive patients who received lepirudin were reviewed. Lepirudin use was analyzed for indication, duration, and effectiveness of anticoagulation, and for adverse events. HAAb presence was determined by platelet aggregation.

RESULTS

Eighteen HAAb-positive patients received lepirudin: 9 had previous documentation of HAAb, 6 had thrombocytopenia while receiving heparin; and 3 had HAAb after a thrombotic event. The indications for lepirudin anticoagulation included thromboembolism prophylaxis (5), arterial thromboses (5), pulmonary embolus (3) or deep venous thrombosis (1), and one each for atrial fibrillation, myocardial infarction, artificial heart valves, and hemodialysis access. The average duration of therapy was 4.04 days. Fifteen patients achieved adequate anticoagulation (activated partial thromboplastin time [aPTT] ratio > 2.0) with lepirudin. Seven patients had aPTTs that were sometimes supratherapeutic (aPTT > 100 seconds) but did not bleed. In all patients who had heparin-induced thrombocytopenia, platelet counts were normalized while they received lepirudin. There were two complications: one patient fell and had a calf hematoma (aPTT ratio 3.24), and one patient who received lepirudin during nine separate hospitalizations had epistaxis (aPTT ratio 2.86) during her ninth hospitalization. Another patient received lepirudin during two hospitalizations without an adverse event.

CONCLUSION

Lepirudin is a safe and effective anticoagulant for patients with HAAbs. The platelet counts of all patients with heparin-induced thrombocytopenia were normalized while they received lepirudin. Careful monitoring of the aPTT and avoidance of trauma while patients are receiving lepirudin are recommended.

The role of type I collagen in aortic wall strength with a homotrimeric

PURPOSE

Elastin and collagen (types I and III) are the primary load-bearing elements in aortic tissue. Deficiencies and derangements in elastin and type III collagen have been associated with the development of aneurysmal disease. However, the role of type I collagen is less well defined. The purpose of this study was to define the role of type I collagen in maintaining biomechanical integrity in the thoracic aorta, with a mouse model that produces homotrimeric type I collagen [alpha1(I)]3, rather than the normally present heterotrimeric [alpha1(I)]2 alpha2(I) type I collagen isotype.

METHODS

Ascending and descending thoracic aortas from homozygous (oim/oim ), heterozygous (oim /+), and wildtype (+/+) mice were harvested. Circumferential and longitudinal load-extension curves were used as a means of determining maximum breaking strength (Fmax) and incremental elastic modulus (IEM). Histologic analyses and hydroxyproline assays were performed as a means of determining collagen organization and content.

RESULTS

Circumferentially, the ascending and descending aortas of oim /oim mice demonstrated significantly reduced Fmax, with an Fmax of only 60% and 23%, respectively, of wildtype mice aortas. Oim/oim descending aortas demonstrated significantly greater compliance (decreased IEM), and the ascending aortas also exhibited a trend toward increased compliance. Reduced breaking strength was also demonstrated with longitudinal extension of the descending aorta.

CONCLUSION

The presence of homotrimeric type I collagen isotype (absence of alpha2(I) collagen) significantly weakens the aorta. This study demonstrates the integral role of type I collagen in the biomechanical and functional properties of the aorta and may help to elucidate the role of collagen in the development of aneurysmal aortic disease or dissection.

The role of heparin-associated antiplatelet antibodies in the outcome of arterial reconstruction

PURPOSE

This study was designed to determine the incidence rate of heparin-associated antiplatelet antibodies (HAAb) in patients who require major vascular reconstruction and to determine whether the HAAb were associated with perioperative thrombotic events.

METHODS

One hundred six patients who underwent elective arterial reconstruction for cerebrovascular occlusive disease (n = 48), aortoiliac occlusive disease (n = 13), aortoiliac aneurysm (n = 17), mesenteric arterial occlusive disease (n = 1), or infrainguinal arterial occlusive disease (n = 28) prospectively underwent evaluation from July 1, 1996, to June 30, 1997. Heparin-associated antibody tests (with a two-point platelet aggregation assay) and platelet counts (via Coulter counter) were performed before surgery and on or after the 4th day after vascular reconstruction. Arterial reconstruction thromboses were established by means of duplex ultrasound scanning or angiography. Acute myocardial infarction (AMI) and venous thromboses were diagnosed with clinical criteria and duplex ultrasound scanning, respectively. A significant decrease in platelet count was defined as a platelet count of less than 100, 000/mm3 or as a more than 30% drop in the platelet count.

RESULTS

Twenty-two patients (21%) had at least one positive HAAb assay: one assay was positive before surgery only (after angiography), six were positive both before and after surgery, and 15 were positive after surgery only. There were three perioperative deaths-one in the HAAb-positive group and two in the HAAb-negative group. Ten thrombotic events occurred in the perioperative period. Four thrombotic events (three operative site thromboses and one AMI) occurred in the HAAb-positive group (18.2%). All of these patients were undergoing heparin therapy. Of the six patients (with three operative site thromboses, two deep venous thromboses, and one AMI) in the HAAb-negative group (7%; P =.21), three were undergoing heparin therapy. No patient who was HAAb positive with a thrombotic event had thrombocytopenia or a significant decrease in platelet count.

CONCLUSION

The frequent exposure to heparin by patients with peripheral vascular disease is associated with a high incidence rate (21%) of HAAb formation, which makes it one of the more common hypercoagulable conditions in these patients. The patients who were HAAb positive had a 2.6-fold increase in perioperative thrombotic events. Thrombocytopenia or decreasing platelet counts were not reliable clinical markers for identifying patients who were HAAb positive. It is suggested that all patients who have undergone heparin therapy and who have an unexplained perioperative thrombotic event develop should undergo testing for HAAb.

Heparin-bonded grafts induce platelet aggregation in the presence of heparin-associated antiplatelet antibodies

PURPOSE

Thromboresistant synthetic grafts should decrease the frequency of graft thromboses and could be useful in bypasses to small arteries and to arteries with compromised flow. Heparin-bonded grafts (HBG) have been developed. Studies were done to determine whether the heparin bond is permanent and whether the HBG would aggregate platelets in the presence of heparin-associated antiplatelet antibodies (HAAbs).

METHODS

We studied an 8 mm HBG from company A (HBGA) and 8 mm and 6 mm HBGs from company B (HBGB-8 and HBGB-6), none of which is available for clinical use in the United States. Five 1 cm long segments of HBGA, HBGB-8, and HBGB-6 were incubated for 24 hours in 5 ml of plasma, 10 ml of saline, or 10 ml of Ringer's lactate. After incubation, 1 ml was obtained from each solution and assayed for heparin. Segments of each graft that leached off an equivalent of 1 U of heparin/ml (i.e., 1 mm2 of HBGA, 5 mm2 of HBGB-8, and 20 mm2 of HBGB-6) were incubated with 0.15 ml of plasma with HAAbs (six samples per graft) for 30 minutes at 25 degrees C. The grafts were removed, and 0.1 ml of normal-donor, platelet-rich plasma was added. The samples were placed in an aggregometer and allowed to react until positive aggregation occurred or 27 minutes had elapsed. Segments of non-heparin-bonded polyester grafts served as controls.

RESULTS

Heparin leached off all grafts in plasma (mean values: HBGA, 83.4 U of heparin/ml; HBGB-8, 4 U of heparin/ml; HBGB-6, 6.2 U of heparin/ml). In normal saline, the mean heparin concentrations were lower (HBGA, 10.8 U of heparin/ml; HBGB-8, 0 U of heparin/ml; HBGB-6, 0.01 U of heparin/ml. The mean heparin concentration after incubation in Ringer's lactate were 10 U of heparin/ml for HBGA, 0 U of heparin/ml HBGB-8, and 0.22 U of heparin/ml HBGB-6. All of the HBGs induced platelet aggregation inHAAb-positive plasma. None of the control grafts induced platelet aggregation in HAAb-positive plasma.

CONCLUSIONS

All HBGs leached heparin into plasma, and all induced platelet aggregation in the presence of HAAbs. The possibility of sensitizing patients to heparin leeching from a HBG with the activation of platelets and secondary thrombosis strongly suggests that HBG be used with great caution. Other methods for inducing graft thromboresistance should be developed.

Reduced morbidity and mortality rates of the heparin-induced thrombocytopenia syndrome

PURPOSE

We reported a 61% morbidity rate and a 23% mortality rate for the heparin-induced thrombocytopenia (HIT) syndrome in 1983. We subsequently reported in 1987 that with early recognition, immediate cessation of the administration of heparin, and platelet function inhibition, the morbidity rate could be reduced to 23% and the mortality rate to 12%. One hundred recent cases of patients with heparin-associated antiplatelet antibodies (HAAb) have been reviewed to determine whether aggressive screening, early diagnosis, and alternate management could further reduce morbidity and mortality rates.

METHODS

The consecutive records of 100 patients with positive platelet aggregation tests were reviewed. Sixty-six patients were male. The patients' ages ranged from 23 days to 92 years. The patients were from vascular (28), cardiothoracic (42), and other (30) services. HIT was suspected in patients who received heparin and had falling platelet counts, platelet counts less than 100,000/mm3, or new thromboembolic or hemorrhagic events.

RESULTS

Heparin was not offered to six patients with known HAAb. Twelve patients were successfully treated with antiplatelet therapy and limited reexposure to heparin, and 75 patients were successfully treated with early diagnosis and prompt cessation of heparin. Alternate forms of anticoagulation therapy were used selectively. Seven patients had 11 complications. Three of the seven patients were treated successfully with warfarin anticoagulation and aspirin (2) or with aspirin alone (1). A fourth patient was treated with thrombectomy, hematoma evacuation, and aspirin. A fifth patient underwent thrombolysis and coronary angioplasty in addition to receiving warfarin and aspirin. The sixth patient required two thrombectomies and warfarin. A seventh patient required two thrombectomies and aspirin. HIT was responsible for one of 17 deaths.

CONCLUSION

A 7.4% morbidity rate and a 1.1% mortality rate have been achieved in patients with HAAb by aggressive screening, early recognition of HIT, and prompt cessation of the administration of heparin. Platelet function inhibitors and other anticoagulants, including nonreacting low molecular weight heparin, are important adjuncts in the management of the thromboembolic disorders associated with HIT.

The glycoprotein IIb/IIIa antagonist c7E3 inhibits platelet aggregation in the presence of heparin-associated antibodies

PURPOSE

Heparin-associated antibodies (HAAb), in the presence of heparin, can cause platelet activation and aggregation. The purpose of this study was to assess whether a platelet glycoprotein (GP) IIb/IIIa receptor antagonist, c7E3, would inhibit platelet aggregation in the presence of HAAb. If aggregation is inhibited by c7E3, enzyme-linked immunosorbent assays (ELISA) would be done to determine whether c7E3 interfered with the binding of heparin and the HAAb.

METHODS

HAAb-positive plasmas from 21 patients (determined by platelet aggregation assays) were studied. Normal donor platelet-rich plasmas (PRP) were incubated (1 minute) with either saline solution or 3 microg/ml of c7E3. Platelet-poor plasma from patients with HAAb and one of three sources of heparin (25 microl, 10 U/ml; porcine heparin, bovine heparin, and low molecular weight heparin [enoxaparin]) were added to the PRP mixture. Aggregation was determined using a platelet aggregometer by measuring time to aggregation, the slope of the aggregation curve, and the percent change in optical density.

RESULTS

Platelet aggregation occured in 100%, 100%, and 95% of the saline solution incubations exposed to porcine heparin, bovine heparin, and enoxaparin, respectively. Incubation with c7E3 caused 100% inhibition of platelet aggregation in plasma exposed to porcine heparin, bovine heparin, and enoxaparin. The optical density curves obtained from the ELISA, which were dependent on the binding of HAAb to heparin, were not significantly different when c7E3 was compared to buffer alone.

CONCLUSIONS

The GP IIb/IIIa receptor antagonist, c7E3, inhibits HAAb-induced platelet aggregation via a mechanism that does not appear to interfere with the binding between heparin and HAAb. Clinical trials are warranted to assess whether GP IIb/IIIa antagonists may allow patients with HAAb to safely receive heparin.

Coumadin: principles of use

Numerous clinical trials have been performed to identify the optimal therapeutic range for various indications in patients receiving warfarin. Other studies have identified risk factors for hemorrhage and thromboembolism to decrease the risk of these complications. A more consistent approach, using guidelines presented in this article, toward initiation, monitoring, and reversal of anticoagulation should further decrease the incidence of complications.

A comparison of the hemodynamic and ventilatory effects of abdominal insufflation with helium and carbon dioxide in young swine

Abdominal CO2 insufflation has been shown to cause hypercarbia, acidemia, and decreased oxygenation in a pediatric animal model. Such metabolic derangements have prompted a search for alternative insufflation gases. This study compares the hemodynamic and ventilatory changes that occur during pneumoperitoneum with CO2 and helium. Four juvenile swine were intubated and given general anesthesia. Minute ventilation was adjusted to obtain a baseline Pco2 of between 32 and 36 mm Hg, and was kept constant for the duration of the experiment. The subjects initially were insufflated with CO2 or helium at a pressure of 10 mm Hg. Peak ventilatory pressure, end-tidal CO2 (ETCO2) arterial pH, Pco2, Po2, and right atrial and inferior vena caval pressures were measured before and during a 1-hour insufflation period. After desufflation, Pco2 and pH were restabilized. The same parameters were then measured during reinsufflation with the alternate gas. CO2 insufflation caused significant decreases in pH, from 7.51 +/- 0.03 to 7.32 +/- 0.06, and Po2 increased from 261 +/- 49 to 189 +/- 33 mm Hg. Pco2 increased from 35.0 +/- 1.4 to 57.9 +/- 6.3 mm Hg. ETCO2 also increased, from 29.0 +/- 2.2 to 47.2 +/- 5.0 mm Hg. Helium insufflation caused pH to decrease from 7.51 +/- 0.01 to 7.42 +/- 0.04. Pco2 increased from 32.8 +/- 0.8 to 43.5 +/- 3.9 mm Hg, and ETCO2 increased from 27.8 +/- 0.5 to 36.8 +/- 3.1 mm Hg. These alterations were significantly less than those with CO2 pneumoperitoneum. Po2 decreased as well-from 266 +/- 30 to 212 +/- 21 mm Hg. During insufflation with both gases, peak ventilatory pressure and right atrial pressure increased significantly. Abdominal insufflation with CO2 or helium causes hypercarbia, acidemia, and increased ETCO2 in this juvenile animal model. These derangements are significantly less with helium. This gas may prove to be the more suitable insufflation agent for pediatric patients.

Flow measurements in a highly curved atherosclerotic coronary artery cast of man

Flow visualization and wall pressure measurements were made in a polyurethane cast of a cadaver coronary artery with a significant "s" shaped reverse curvature. A sucrose solution was used to simulate the kinematic viscosity of blood, with flow rates in the physiologic range. Flow visualization demonstrated significant secondary flow patterns in the wall vicinity, which increased with increasing Reynolds number. Random dye dispersion was observed at a Reynolds number of about 400, but not at 200. Dye filament patterns in the transition between the first and second curved region were predominantly influenced by the second curved region at lower Reynolds numbers, and by the first curved region at higher Re. Local wall pressure measurements demonstrated a significant centrifugal effect with large radial pressure differences across the casting. Flow resistances for the casting were considerably greater than reference Poiseuille flow values, and increased further with pulsatile flow.