Role of thrombin compared with factor Xa in the procoagulant activity of whole blood clots.

BACKGROUND: Thrombi are known to induce activation of the coagulation system, which may be a mechanism for progression of thrombosis and its recurrence after thrombolysis. This study was designed to characterize the relative role of thrombin and activated factor X (factor Xa) as mediators of procoagulant activity of whole blood clots in blood and plasma. METHODS AND RESULTS: Clots formed from human blood were incubated in recalcified (25 mmol/L CaCl2) citrated plasma or nonanticoagulated blood with increasing concentrations of recombinant desulfatohirudin (hirudin) to inhibit thrombin activity, recombinant tick anticoagulant peptide (TAP) or recombinant tissue factor pathway inhibitor (TFPI) to inhibit factor Xa, or heparin. Fibrinopeptide A (FPA) was assayed serially as an index of procoagulant (thrombin) activity. FPA generation was greatly accelerated by addition of clots to recalcified plasma (from 1251 +/- 211 ng/mL after 15 minutes without clot to 5916 +/- 1412 ng/mL with clot, n = 7, P < .01) or whole blood (4803 +/- 761 ng/mL with clot compared with 546 +/- 233 without clot, n = 5, P < .05) and was attenuated by inhibitors of thrombin (> 90% inhibition of FPA with 0.05 mumol/L hirudin and 1.0 U/mL heparin) and factor Xa (> 90% inhibition of FPA with 1.0 mumol/L TAP and 0.15 mumol/L TFPI) in a concentration-dependent manner. Preincubation of clots with tissue-type plasminogen activator sufficient to induce partial clot lysis increased the rate of thrombin-induced FPA generation by increasing the surface area of clot exposed to plasma. However, procoagulant activity induced by partially lysed clots was attenuated by lower concentrations of both thrombin and Xa inhibitors, presumably because access of the inhibitors to bound procoagulant molecules was facilitated. Comparable results were obtained with incubations in nonanticoagulated blood. CONCLUSIONS: These results indicate that factor Xa is primarily responsible for the procoagulant activity of clots in vitro and suggest a potential molecular mechanism for the observed efficacy of inhibitors of factor Xa in preventing recurrent thrombosis after coronary thrombolysis.

Maintenance of patency after thrombolysis in stenotic coronary arteries requires combined inhibition of thrombin and platelets.

OBJECTIVES: This study was designed to determine whether maintenance of patency in coronary arteries with high grade stenosis after thrombolysis with tissue-type plasminogen activator requires inhibition of thrombin or platelets, or both. BACKGROUND: Activation of both thrombin and platelets has been implicated in delaying coronary recanalization induced with fibrinolytic drugs and in predisposing to reocclusion. METHODS: Hirudin (1.5 mg/kg body weight) or aspirin (5 mg/kg), or both, was given conjunctively with tissue-type plasminogen activator in 28 conscious dogs with coronary thrombosis induced by electrical stimulation of the vessel wall in the presence of a previously placed high grade distal stenosis (85 +/- 12% [SEM] area reduction). RESULTS: Among 22 dogs exhibiting coronary recanalization, hirudin plus aspirin, but neither agent alone, modestly shortened the interval to recanalization (31 +/- 4 min with saline solution, n = 6; 29 +/- 4 min with aspirin, n = 5; 23 +/- 9 min with hirudin, n = 6; 21 +/- 7 min with hirudin+aspirin, n = 5). Reocclusion occurred promptly and persisted in five of six dogs given only saline solution plus tissue-type plasminogen activator, in four of six dogs given hirudin and five of five dogs given aspirin; however, reocclusion was prevented in all five of the dogs given both hirudin and aspirin with tissue-type plasminogen activator (p < 0.05 compared with saline-treated dogs). In dogs given both hirudin and aspirin, the partial thromboplastin time was 2.4 +/- 0.3 times baseline, and the template bleeding time was prolonged only modestly (1.6 +/- 0.3 times baseline). CONCLUSIONS: Thus, the combination of hirudin and aspirin in doses that do not markedly perturb hemostasis prevents early reocclusion after thrombolysis despite the presence of severe stenosis. Accordingly, conjunctive administration of both anti-thrombin and antiplatelet agents appears to be necessary for optimal maintenance of patency after thrombolysis induced in the presence of high grade coronary stenosis.

Long-term effectiveness of surgical treatment of ectopic atrial tachycardia.

OBJECTIVES: The purpose of this study was to determine the long-term clinical outcome of patients with ectopic atrial tachycardias treated surgically. BACKGROUND: Ectopic atrial tachycardia is an uncommon arrhythmia that can be symptomatic and is associated with the development of a cardiomyopathy. Management strategies are not well defined because of the paucity of data on the long-term effectiveness of pharmacologic and nonpharmacologic therapies. METHODS: The long-term clinical impact of medical and surgical therapy was determined in 15 consecutive patients with ectopic atrial tachycardia. All 15 patients were initially treated with antiarrhythmic drugs (mean 5.7 +/- 2.2 drugs/patient). An effective drug regimen was identified in only 5 (33%) of the 15 patients; the remaining 10 patients were treated surgically. In each, individualized surgical procedures were guided by computer-assisted intraoperative mapping, with atrial plaques comprising up to 156 electrodes. Focal ablation was performed in four patients and atrial isolation procedures in six. RESULTS: The 10 patients treated surgically were followed up a mean of 4 +/- 3.2 years. Ectopic atrial tachycardia recurred in one patient. A permanent pacemaker was implanted in two patients, one of whom also required reoperation for constrictive pericarditis. There were no operative deaths. Ectopic atrial tachycardia recurred in three (60%) of the five patients discharged on antiarrhythmic drug therapy during a mean follow-up interval of 6.4 +/- 4.3 years. There was one nonarrhythmic death. CONCLUSIONS: Map-guided surgery demonstrated long-term efficacy in abolishing symptoms in 9 of the 10 patients with ectopic atrial tachycardia. Results demonstrate that surgery is effective for patients with ectopic atrial tachycardias who are not easily treated with antiarrhythmic drugs.

Nature and time course of generation of isoforms of creatine kinase, MB fraction in vivo.

OBJECTIVES: This study was designed to characterize the nature and time course of carboxy-terminal lysine cleavages from the tissue isoform of MB creatine kinase (CK) in vivo. BACKGROUND: Rapid conversion of the tissue isoform of MM CK to two additional circulating isoforms with one or both carboxy-terminal lysines cleaved facilitates early detection of new tissue isoform release after acute myocardial infarction and coronary recanalization. Characterization of changes in plasma MB CK isoform profiles, potentially enhancing specificity even further, has been hindered by difficulties in separating the isoform products and elucidation of carboxy-terminal lysine cleavages underlying their formation. METHODS: Isoform species with carboxy-terminal lysine present on B-monomers were separated from those from which lysine had been cleaved by anion exchange chromatography. Carboxy-terminal lysine on M-monomers was assayed with the use of a monospecific antibody. RESULTS: MB CK in four pooled plasma samples from among 77 normal subjects exhibited carboxy-terminal lysine on 48 +/- 21% (mean +/- SEM) of B-monomers and 82 +/- 12% of M-monomers. Within the 1st 16 h after the onset of acute myocardial infarction, virtually all M- and B-monomers exhibited carboxy-terminal lysine, indicating release into plasma and the lack of rapid cleavage of lysine from the tissue isoform. After 20 to 30 h, 43 +/- 9% (three pools from 19 patients) of B-monomers and 95 +/- 10% of M-monomers exhibited lysine at the carboxyl terminus. After 40 to 50 h, 13 +/- 13% (four pools from 34 patients) of B-monomers and 46 +/- 19% of M-monomers still retained carboxy-terminal lysine. CONCLUSIONS: In contrast to MM CK, the tissue isoform of MB CK undergoes slow cleavage of lysine from both monomers in vivo. Sequential cleavage of lysine first from the carboxyl terminus of B-monomers and subsequently from M-monomers is consistent with generation of at least two additional isoforms. Development of assays capable of resolving all of the isoforms of MB CK that can occur in vivo might increase sensitivity for early detection of new tissue isoform release associated with acute myocardial infarction and coronary recanalization compared with currently available assays that resolve only two species.

Relative efficacy of antithrombin compared with antiplatelet agents in accelerating coronary thrombolysis and preventing early reocclusion.

BACKGROUND: Optimal coronary thrombolysis should be prompt and persistent. Although activation of platelets and increased thrombin activity have been associated with clinical thrombolysis, the role of each in delaying thrombolysis or inducing early coronary reocclusion has been difficult to define. METHODS AND RESULTS: In conscious dogs with coronary thrombosis induced by electrical current, we assessed the impact on the rapidity of thrombolysis and the incidence of reocclusion of two types of adjunctive treatment given concomitantly with intravenous tissue-type plasminogen activator (t-PA): 1) inhibition of platelet function with a peptide mimetic antagonist of platelet glycoprotein IIb/IIIa receptors or with lysine acetylsalicylic acid (ASA) and 2) inhibition of thrombin activity with recombinant hirudin or with heparin. ASA but not the receptor antagonist shortened the time to thrombolysis with t-PA (20 +/- 13 [mean +/- SD] minutes with ASA, 36 +/- 15 minutes with receptor antagonist, and 43 +/- 16 minutes with the saline control). Reocclusion occurred promptly after completion of the infusion of t-PA in all seven dogs given saline. Reocclusion was delayed and prevented in some dogs within 90 minutes after the end of the infusion of t-PA by both antiplatelet agents but still occurred in 42% despite continued inhibition of platelet function (i.e., three of six dogs given ASA and two of six given receptor antagonist). In contrast, inhibition of thrombin activity with recombinant hirudin in a dose that prolonged the partial thromboplastin time modestly (1.5-2-fold) resulted in accelerated lysis (19 +/- 10 minutes) and prevention of reocclusion in each of six dogs. Heparin given in doses that elicited similar prolongation of the partial thromboplastin time did not accelerate lysis nor prevent reocclusion, which occurred in five of six dogs. CONCLUSIONS: Inhibition of thrombin by recombinant hirudin facilitates thrombolysis and maintains patency of coronary arteries recanalized with t-PA particularly effectively. The benefit conferred may reflect direct anticoagulant effects plus diminished activation of platelets secondary to decreased thrombin activity.