David A. Tate

Effect of heparin on coronary arterial patency after thrombolysis with tissue plasminogen activator in acute myocardial infarction

Infarct artery patency rates at 90 minutes after coronary thrombolysis using recombinant tissue-type plasminogen activator (rt-PA) with and without concurrent heparin anticoagulation have been shown to be comparable. The contribution of heparin to efficacy and safety after thrombolysis with rt-PA is unknown. In this pilot study, 84 patients were treated within 6 hours of onset of acute myocardial infarction (mean of 2.7 hours) with the standard dose of 100 mg of rt-PA over 3 hours. Forty-two patients were randomized to receive additionally immediate intravenous heparin anticoagulation (5,000 U of intravenous bolus followed by 1,000 U/hour titrated to a partial thromboplastin time of 1.5 to 2.0 times control) while 42 patients received rt-PA alone. Coronary angiography performed on day 3 (48 to 72 hours, mean 57) after rt-PA therapy revealed infarct artery patency rates of 71 and 43% in anticoagulated and control patients, respectively (p = 0.015). Recurrent ischemia or infarction, or both, occurred in 3 (7.1%) anticoagulated patients and 5 (11.9%) control patients (difference not significant). Mild, moderate and severe bleeding occurred in 52, 10 and 2% of the group receiving anticoagulation, respectively, and 34, 2 and 0% of patients in the control group, respectively (p = 0.006). These data indicate that after rt-PA therapy of acute myocardial infarction, heparin therapy is associated with substantially higher coronary patency rates 3 days after thrombolysis but is accompanied by an increased incidence of minor bleeding complications.

Von Willebrand factor and occlusive arterial thrombosis: A study in normal and von Willebrand's disease pigs with diet-induced hypercholesterolemia and atherosclerosis

The thrombotic response of atherosclerotic arteries to stenosis and injury was studied in 14 pigs, eight normal and six with von Willebrands disease (vWD). Atherosclerosis was produced by feeding a 1% to 2% cholesterol diet for 24 weeks. Both groups of pigs developed severe hypercholesterolemia, greater than five times baseline values. Coronary atherosclerosis was detected in all vWD pigs and in all but one normal pig and was not significantly different between groups. At sacrifice under general anesthesia, a Goldblatt clamp (GC) was positioned around the left anterior descending coronary (LAD) and carotid arteries to produce a stenotic segment, which was pinch-injured with needle holders. A 20 MHz Doppler velocity crystal was placed distal to the GC to detect cyclic flow reductions or permanent cessation of flow velocity indicative of occlusive thrombosis. In the phenotypically normal pigs with diet-induced atherosclerosis, occlusive thrombosis was detected in seven of seven LAD and seven of seven carotid arteries. In atherosclerotic vWD pigs, occlusive thrombosis failed to form in six LAD and 10 carotid arteries (p less than 0.003, Wilcoxon rank sum test). Scanning electron micrographs demonstrated platelet-fibrin microthrombi in both groups of pigs; only phenotypically normal pigs had occlusive thrombi. Von Willebrand factor is essential for the development of occlusive thrombosis and appears to support the progression of a mixed microthrombus to an occlusive thrombus.

Reversal of Heparin Anticoagulation by Recombinant Platelet Factor 4 in Humans

BACKGROUND Protamine is used to reverse the anticoagulant effects of heparin, but it can have important side effects. Platelet factor 4 (PF4) is a protein found in platelet alpha granules that binds to and thereby neutralizes heparin. We evaluated the safety and effectiveness of intravenous recombinant PF4 to neutralize heparin anticoagulation after cardiac catheterization in a phase 1, open-label trial. METHODS AND RESULTS The study group consisted of 18 patients having diagnostic cardiac catheterization. Heparin (5000 U) was given after vascular access was obtained. In the first 12 patients, additional heparin was given at the conclusion of the procedure so that all patients had activated coagulation times > 300 seconds before rPF4 was given. Three patients each received 0.5, 1.0, 2.5, or 5.0 mg/kg rPF4 over a period of 3 minutes at the conclusion of the catheterization procedure. In 6 additional patients, extra heparin was not given at the conclusion of the procedure, and 1.0 mg/kg rPF4 was given. Hemodynamic measurements, cardiac output, and serial blood tests were performed 5, 10, 20, and 30 minutes after rPF4 and then into the next 24 hours. There were no serious side effects in any patient, despite transient rPF4 levels as high as 14,870 ng/mL in the patients receiving 5.0 mg/kg. One patient receiving 2.5 mg/kg had a slight transient rise in liver enzymes possibly related to the rPF4. There were no important hemodynamic effects of rPF4 administration at any dose used. Doses of 2.5 and 5.0 mg/kg were uniformly effective in reversing the anticoagulant effect of heparin. At lower doses, rPF4 neutralized the effects of heparin in most but not all patients. Pharmacokinetic analysis suggested a monophasic and one-compartment clearance of the PF4-heparin complex. No neutralizing factors to rPF4 were detected in the samples collected 7 days after dosing. CONCLUSIONS rPF4, in doses ranging from 0.5 to 5.0 mg/kg over 3 minutes, had no serious side effects. Given in sufficient amounts, rPF4 can completely and rapidly reverse the anticoagulant effects of heparin.

Assessment of platelet activation by coronary sinus blood sampling during balloon angioplasty and directional coronary atherectomy

Three markers of platelet activation (platelet-derived microparticles, fibrinogen binding and expression of P-selectin) were assessed by flow cytometry during diagnostic coronary angiography and therapeutic coronary interventions. In 24 patients undergoing diagnostic angiography, blood was collected to determine if our sampling techniques or coronary angiography caused platelet activation. Changes during diagnostic angiography were used to establish baseline values and interpret changes during coronary interventions. In 21 patients, blood samples were obtained at 5 time points during percutaneous transluminal coronary angioplasty (PTCA) (n = 17) or directional coronary atherectomy (DCA) (n = 4). During coronary interventions, mean values for the percentage of platelets expressing P-selectin or binding fibrinogen increased, but with considerable variation among patients. Individual responses for platelet activation markers in each patient were characterized using a twofold increase to indicate elevation related to the intervention. Patients were classified as having complicated or uncomplicated procedures based on the presence of acute closure, dissection, or thrombus observed by angiography. There were no differences in the percentage of elevated markers between patients with uncomplicated (12.5%) and complicated (19%) PTCA procedures. However, patients treated with DCA had more elevated markers (38%) than those treated with PTCA (15%) (p = 0.04). Our data suggest that the extent of platelet activation in individual patients cannot be predicted by common angiographic findings or complications. More markers of platelet activation were present after DCA and may reflect a greater degree of vascular trauma associated with this procedure.

Impairment of fibrinolysis by streptokinase, urokinase and recombinant tissue-type plasminogen activator in the presence of radiographic contrast agents

OBJECTIVES The purpose of this study was to determine whether an adverse interaction exists between radiographic contrast agents and thrombolytic drugs. BACKGROUND Coronary thrombosis may occur in the setting of unstable angina and after coronary angioplasty. However, the use of thrombolytic drugs in the setting of unstable angina has not been beneficial and, in one large trial of angioplasty in patients with unstable angina, was associated with an increased incidence of ischemic complications and abrupt closure. The reasons for these results are not clear. Coronary arteriography was performed in many of these trials, and it is known that fibrin structure and assembly are altered by radiographic contrast agents. METHODS Blood samples were obtained from patients before (n = 25) and after (n = 20) angiography using iohexol. Blood samples obtained before angiography were tested for response to streptokinase (10 and 100 IU/ml), urokinase (100, 200 and 500 IU/ml) and recombinant tissue-type plasminogen activator (rt-PA) (100 and 1,000 IU/ml) and the results measured. Iohexol, diatrizoate or ioxaglate (4% by volume) was added to separate aliquots of the baseline sample, and the test was repeated. Blood samples obtained after angiography were tested in a similar manner. RESULTS The onset of lysis at baseline by rt-PA at 1,000 IU/ml occurred at 72 +/- 8.2 s (mean +/- SD) and was markedly delayed in the presence of diatrizoate (527 +/- 181.7 s, p < 0.001) or iohexol (460 +/- 197.0 s, p < 0.001) but not ioxaglate. At 100 IU/ml, there was no lysis detected with rt-PA after the addition of any contrast agent. The addition of a contrast agent caused similar delays in the onset of lysis by urokinase and streptokinase; similar to rt-PA, the effect was smaller at higher concentrations of drug. In vivo blood samples obtained from the patient after angiography showed delays in the onset of lysis by rt-PA and urokinase but not streptokinase. CONCLUSIONS These data demonstrate that radiographic contrast agents impede fibrinolysis. This previously undescribed interaction was demonstrated using an in vitro test system, but these findings may have clinical relevance when thrombolytic drugs are used at the time of angiography.

Effects of an ionic and nonionic contrast agent on von Willebrand factor assessed during coronary angiography

This study shows an increase in von Willebrand factor antigen in blood collected from the coronary sinus shortly after coronary angiography with an ionic contrast agent (diatrizoate), but not a nonionic contrast agent (iohexol). These findings suggest that ionic contrast agents may cause more endothelial injury than nonionic contrast agents.

Absence of Human Herpesvirus 8 Genomes in Coronary Atherosclerosis in Immunocompetent Patients

Human herpevirus 8 (HHV8) has been localized to the endothelial and spindle cells of KS, suggesting a role for HHV8 in atherosclerosis. None of the 38 coronary atherectomy specimens contained HHV8 with both sensitive nested PCR assays, making it unlikely that persistent viral infection with HHV8 plays a role in coronary atherogenesis in the general population of the United States.

VARIABLE INFLUENCE OF HEPARIN AND CONTRAST AGENTS ON PLATELET FUNCTION AS ASSESSED BY THE IN VITRO BLEEDING TIME

Both heparin and contrast agents have anticoagulant effects which are well-documented but their effects on platelets are not well-characterized. The purpose of the present study was to evaluate the sequential effects of heparin and then a contrast agent on platelet function during an angiographic procedure. Blood samples from 54 patients were obtained at baseline, after a 5000 unit bolus of heparin and after administration of a contrast agent (iohexol, n = 30: diatrizoate, n = 24) during angiography. The in vitro bleeding time (IVBT) was determined on nonanticoagulated whole blood using a hollow fiber device under physiological flow conditions. Mean IVBT at baseline was 3.6 +/- 2.7 minutes and increased to 17.0 +/- 12.3 minutes after heparin (p < 0.01). After heparin, 44.5% of the patients still had a normal IVBT (< 9.0 minutes), 11% of the patients had a moderately increased IVBT and the remaining patients had a large increase in their IVBT. When contrast was given (167 +/- 52 mls) following heparin, mean IVBT was higher in those who received diatrizoate (23.3 +/- 9.4 minutes) compared with iohexol (15.0 +/- 10.9 minutes, p < 0.05). However, 15 patients (28%) continued to have a normal IVBT after contrast and of these 80% had received iohexol.

Differences in clot lysis among patients demonstrated in vitro with three thrombolytic agents (tissue-type plasminogen activator, streptokinase and urokinase)☆

This study compares the ability of 3 thrombolytic drugs to promote clot lysis using a new in vitro testing procedure. Whole blood samples from 132 patients were tested using 5 different concentrations of tissue-type plasminogen activator (t-PA), streptokinase (SK) and urokinase. A mixture of blood and thrombolytic drug was placed on a dry-reagent test card containing reptilase, buffers and paramagnetic particles where clot formation occurred. Analysis of the motion of the clot-embedded paramagnetic particles caused by an oscillating magnetic field was used to define the lysis onset time. The slope of the linear regression plot of lysis onset time versus 1/[drug concentration] defined the kinetic rate constant (k) for each drug in each patient. Higher values of k indicated greater resistance to in vitro clot lysis. In the patients studied, there was a large range of k values for t-PA and SK (coefficient of variation 143 and 137%, respectively) but a smaller range of k for urokinase (coefficient of variation 32%). The coefficients of variation for t-PA and SK observed in the study group were five- to 10-fold greater than the coefficients of variation determined for replicate test measurements. Resistance to all SK concentrations tested was found in 9% of the patients. In vitro sensitivity to thrombolysis was compared among the drugs by correlating the derived k values. These comparisons indicated no relation for any of the drugs; many patients had a relatively low k value for 1 drug, while having a relatively high k value for a different drug.(ABSTRACT TRUNCATED AT 250 WORDS)

New Challenges for Thrombolytic Therapy

Excerpt A survey of recent medical literature might suggest that the major challenges in the field of coronary thrombolysis have been met. Several large, randomized trials have now established that...