A new thrombolytic regimen for acute myocardial infarction using combination half dose tissue-type plasminogen activator with full dose streptokinase: a pilot study. KAMIT Study Group

Understanding haemorrhagic risk following thrombolytic therapy in patients with intermediate-risk and high-risk pulmonary embolism: a hypothesis paper

While systemic intravenous thrombolysis decreases mortality in patients with high-risk pulmonary embolism (PE), it clearly increases haemorrhagic risk. There are many contraindications to thrombolysis, and efforts should aim at selecting those patients who will benefit most, without suffering complications. The current review summarises the evidence for the use of thrombolytic therapy in PE. It clarifies the pathophysiological mechanisms in PE and acute cor pulmonale that increase the risk of bleeding following thrombolysis. It discusses future management challenges, namely tailored drug administration, new treatment monitoring techniques and catheter-directed thrombolysis.

Angiographic study of mutant tissue-type plasminogen activator versus urokinase for acute myocardial infarction

The effects and problems of intravenous thrombolytic therapy with a bolus injection of mutant tissue plasminogen activator (t-PA) were investigated in 34 patients with first acute myocardial infarction (AMI). In contrast, 114 patients were selected from 1,003 patients with AMI for treatment using intravenous infusion urokinase (UK). Angiography of these 148 patients revealed a complete occlusion of infarct-related artery with no clear contraindications to the study treatment. With the exception of thrombolysis in myocardial infarction (TIMI-3) recanalization 60 min after a bolus injection of mutant t-PA, the patients were given intracoronary UK in addition to mutant t-PA. The study comparisons were assessed using the following criteria: (1) 60-min assessment of recanalization rates, mutant t-PA vs UK; (2) time interval from initiation of thrombolysis to recanalization, mutant t-PA vs UK; (3) angiographic reocclusion rates within 1 month, mutant t-PA alone vs UK vs mutant t-PA plus UK; and (4) intracerebral hemorrhage rates, mutant t-PA alone vs UK vs mutant t-PA plus UK. There were no significant differences in the recanalization rates between mutant t-PA and UK, but there was a significant reduction in the time to recanalization with mutant t-PA (31.8 +/- 12.7 min) compared with UK (56.5 +/- 6.3 min). There was a significant difference in the reocclusion rates among the 3 treatment groups (20% mutant t-PA alone vs 4% UK vs 0% mutant t-PA plus UK). On the other hand, no significant differences in intracerebral hemorrhage rates among the 3 treatments were observed. In conclusion, thrombolytic therapy with a bolus injection of mutant t-PA achieved more rapid recanalization, but treatment with mutant t-PA led to a high rate of reocclusion.

A chemiluminescent detection of superoxide radical produced by adherent leucocytes to the subendothelium following thrombolysis: studies with a photochemically induced thrombosis model in the guinea pig femoral artery

Reocclusion following thrombolysis is a major limitation of thrombolytic therapy with recombinant tissue-type plasminogen activator (rt-PA) because denuded vessel wall exposed to blood following thrombolysis is a favourable surface for platelet and leucocyte deposition. We have applied a chemiluminescence technique to detect superoxide radical (0(-2)) produced by leucocytes adherent to the femoral artery 24 h after photochemically induced thrombogenesis in the guinea pig in vivo and subsequent thrombolysis by rt-PA. Intravenous administration of MCLA, a specific chemiluminescence reagent for detecting O(-2), markedly increased photon emission. the photon emission was markedly potentiated by phorbol myristate acetate and was suppressed by superoxide dismutase. Reocclusion 24 h after rt-PA induced thrombolysis was observed in 10 of 16 animals. Histological observations revealed extensive polymorphonuclear leucocytes adherent to the vessel wall at the site of thrombogenesis and thrombolysis. A higher level of 0(-2) could be detected from the arteries in which thrombolysis was induced compared with those without thrombolysis. Further, the level 0(-2) detected was greater in reoccluded arteries compared with those in which reflow was established. These observations suggest that 0(-2) is produced by adherent leucocytes at the site of thrombolysis and that leucocytes are involved in reocclusion after thrombolysis.

Enhancement of thrombolytic efficacy of tissue-type plasminogen activator by adjuvants in the guinea pig thrombosis model

Reocclusion following thrombolysis is a major limitation of thrombolytic therapy with recombinant tissue-type plasminogen activator (rt-PA). We investigated the effects of vapiprost ((1R-(1 alpha(Z),2 beta,3 beta,5 alpha))-7-(5-((1,1'-biphenyl)-4-yl-methoxy)- 3-hydroxy-2-(1-piperidinyl)cyclopentyl)-4-heptenoic acid, a thromboxane A2 receptor antagonist); argatroban ((2R,4R)-4-methyl-1-[N2-(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl)sulfon yl] - L-arginyl)]-2-piperidine-carboxylic acid, a specific thrombin inhibitor) and MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2- dimethylpropanoic acid, a specific leukotriene biosynthesis inhibitor) on the thrombolytic efficacy of rt-PA. The guinea pig femoral artery was thrombotically occluded by photochemical reaction between rose bengal and green light. Thirty min after the occlusion, rt-PA was administered and the time (T1) for reopening of the vessel and the frequency of reocclusion (Fro) 24 h after thrombolysis were monitored. With rt-PA alone, T1 was 28 +/- 7 min (n = 10) and Fro was 70%. T1 was reduced to 9 and 20 min by a combination of rt-PA with vapiprost and argatroban respectively. Fro was reduced by all three adjuvants. Histological observations revealed extensive adherence of polymorphonuclear leucocytes to the damaged endothelium at the site of thrombolysis. It is concluded that thromboxane A2, thrombin and leucocytes are involved in reocclusion after thrombolysis.

Prevention of arterial reocclusion after thrombolysis with activated protein C. Comparison with heparin in a canine model of coronary artery thrombosis

BACKGROUND

Reocclusion of recanalized coronary arteries often limits the efficacy of coronary thrombolytic therapy in patients with acute myocardial infarction. Activated protein C (APC) is an important regulatory enzyme in hemostasis. In view of the potential of human APC as an anticoagulant and profibrinolytic agent, the effect of APC on thrombolysis with recombinant tissue-type plasminogen activator (rTPA) was studied in a canine model of coronary artery thrombosis.

METHODS AND RESULTS

Continuous artery flow monitoring in the left anterior descending coronary artery of 30 anesthetized adult beagles was performed by a magnetic flowmeter. Localized thrombosis was produced in the left anterior descending coronary artery and administration of rTPA (alteplase, 0.45 mg/kg IV) was done for 30 minutes. The dogs were randomly assigned to receive one of the following intravenous adjunctive therapies: (1) control group (n = 10): human albumin at a rate of 0.83 mL/min; (2) APC group (n = 10): human plasma-derived APC (0.6 mg/kg) with human albumin as a vehicle at a rate of 0.83 mL/min; and (3) heparin group (n = 10): heparin (200 U/kg) with saline at a rate of 0.83 mL/min. Each adjunctive therapy was started simultaneously with rTPA and lasted for 60 minutes. Coronary recanalization occurred in all dogs of each adjunctive treatment group in 19.1 +/- 1.9 minutes (mean +/- SEM). In a 120-minute observation after the termination of rTPA, reocclusion developed in all the dogs in the control and heparin groups but in only 3 of the 10 dogs in the APC group (P < .002 versus control and heparin). Time from recanalization to reocclusion (minutes, mean +/- SEM) was prolonged in the APC group (103.2 +/- 14.2) as compared with the control (10.2 +/- 2.3, P < .001) and heparin (30.3 +/- 11.8, P < .002) groups. Activated partial thromboplastin time was prolonged similarly in each group after thrombolytic therapy. On the other hand, bleeding time was prolonged in only the heparin group after the treatment. Serious hemorrhagic side effects were not observed in all three groups.

CONCLUSIONS

APC prevents coronary artery reocclusion after recanalization with rTPA in a canine model of coronary artery thrombosis. This finding suggests that APC may be useful as an adjunctive treatment to enhance the effects of thrombolytic therapy in patients with acute myocardial infarction.

Thrombolytic retreatment with tissue plasminogen activator for threatened reinfarction and thrombotic coronary reocclusion

Following successful coronary arterial thrombolysis, thrombogenic substrate persists, increasing the risk of recurrent thrombosis, reocclusion, and reinfarction. The preferred treatment in this setting has not been established. Although many patients receive mechanical revascularization, it is conceivable that repeat thrombolysis, primarily with tissue plasminogen activator, represents the most readily available and effective alternative.

Validation of the early open infarct vessel hypothesis

The insights from the Global Utilization of Streptokinase and t-PA for Occluded Arteries (GUSTO) trial have paved the way for further refinement in myocardial reperfusion strategies. For the moment, there is a better pharmacologic approach for achieving rapid and complete coronary thrombolysis. However, for the future, the legacy from this project is much more meaningful, providing clear-cut validation of the "early open vessel hypothesis" while at the same time exemplifying how deficient our strategies for reperfusion are today. There are explicit signals for persistent, meaningful improvement in the years ahead.

Combination of inhibition of thrombin and blockade of thromboxane A2 synthetase and receptors enhances thrombolysis and delays reocclusion in canine coronary arteries

BACKGROUND

The efficacy of thrombolytic therapy in treating patients with acute myocardial infarction is limited by failure to achieve reperfusion in some patients, by the prolonged time required to achieve reperfusion, and by reocclusion of some coronary arteries. We designed this study to examine the effect of combined inhibition of thrombin and thromboxane synthesis and blockade of thromboxane A2 receptors in addition to tissue-type plasminogen activator (t-PA) on thrombolysis and reocclusion in an experimental canine model with coronary thrombosis.

METHODS AND RESULTS

Blood flow velocity in the left anterior descending coronary artery (LAD) of 32 anesthetized mongrel dogs was monitored by a pulsed Doppler flow probe. Coronary thrombosis was induced by applying electrical stimulation to the LAD at the site where an external constrictor was used to narrow the artery. Three hours after the formation of occlusive thrombus, animals were randomly assigned to receive one of the following: 1) t-PA (80 micrograms/kg + 8 micrograms.kg-1.min-1 i.v.) and saline; 2) t-PA and hirulog, a hirudin-based synthetic peptide and specific thrombin inhibitor (2 mg/kg + 2 mg.kg-1.hr-1 i.v.); 3) t-PA and ridogrel, a combined thromboxane A2 synthetase inhibitor and receptor antagonist (5 mg/kg + 2.5 mg.kg-1.hr-1 i.v.); or 4) t-PA, hirulog, and ridogrel. Reperfusion developed in 14% (one of seven) of dogs treated with t-PA alone at an average of 86 +/- 4 minutes after treatment, in 78% (seven of nine) of dogs treated with t-PA plus hirulog at 53 +/- 11 minutes, in 13% (one of eight) of dogs treated with t-PA plus ridogrel at 85 +/- 5 minutes, and in 88% (seven of eight) of dogs treated with t-PA, hirulog, and ridogrel at 37 +/- 10 minutes (comparison of the frequency of and the time to reperfusion, both p < 0.01). Among the dogs with reestablished coronary blood flow, reocclusion developed in the one treated with t-PA alone at 36 minutes after reperfusion, in seven of the seven treated with t-PA plus hirulog at 66 +/- 15 minutes, and in two of the seven treated with t-PA, hirulog, and ridogrel at 151 +/- 21 minutes (comparison of the frequency of and time to reocclusion, both p < 0.05). Reocclusion was not detected in the one dog treated with t-PA and ridogrel or in the other five dogs treated with t-PA, hirulog, and ridogrel within 180 minutes after reperfusion. Hirulog prolonged and maintained activated clotting times at a level twice that of baseline values. Hirulog inhibited ex vivo platelet aggregation induced by thrombin, and ridogrel inhibited platelet aggregation induced by U46619, a thromboxane mimetic.

CONCLUSIONS

Inhibition of thrombin in addition to treatment with t-PA enhances thrombolysis. A combination of inhibition of thrombin and thromboxane synthetase and blockade of thromboxane A2 receptor enhances thrombolysis and delays or may prevent reocclusion of the recanalized coronary arteries.

Mechanism of benefit of combination thrombolytic therapy for acute myocardial infarction: a quantitative angiographic and hematologic study

OBJECTIVES

The goal of this study was to lend insight into the mechanisms responsible for the beneficial effects of combination thrombolytic therapy.

BACKGROUND

Combination thrombolytic therapy for acute myocardial infarction has been associated with less reocclusion and fewer in-hospital clinical events than has monotherapy.

METHODS

Infarct-related quantitative coronary dimensions and hemostatic protein levels were evaluated in 287 patients with acute myocardial infarction during the early (90-min) and convalescent (7-day) phases after administration of recombinant tissue-type plasminogen activator (rt-PA), urokinase or combination rt-PA and urokinase.

RESULTS

Minimal lumen diameter was similar in the 90-min and 7-day phases after treatment with rt-PA, urokinase and combination rt-PA and urokinase (0.72 +/- 0.45 mm, 0.62 +/- 0.53 mm and 0.75 +/- 0.58 mm, respectively, at 90 min, p = 0.16; and 1.05 +/- 0.56 mm, 1.12 +/- 0.72 mm and 0.94 +/- 0.54 mm, respectively, at 7 days, p = 0.22). In-hospital clinical event and reocclusion rates were less frequent in patients receiving combination therapy than in those receiving monotherapy (25% vs. 38% and 32% for rt-PA and urokinase, respectively, p = 0.084; and 3% vs. 13% and 9% for rt-PA and urokinase, respectively, p = 0.03), but these events were unrelated to early or late coronary dimensions. Patients receiving combination therapy or urokinase monotherapy had significantly higher peak fibrin degradation products (1,307 +/- 860 and 1,285 +/- 898 micrograms/ml vs. 435 +/- 717 micrograms/ml, respectively, p < 0.0001) and lower nadir fibrinogen levels (0.85 +/- 1.00 and 0.75 +/- 0.53 g/liter vs. 1.90 +/- 0.86 g/liter, respectively, p < 0.0001) than did those receiving rt-PA monotherapy. Peak fibrinogen degradation products indirectly correlated (p = 0.004) and baseline (p = 0.026) and nadir (p = 0.089) fibrinogen levels directly correlated with reocclusion.

CONCLUSIONS

Lower in-hospital clinical event and reocclusion rates observed with combination thrombolytic therapy may relate to systemic hematologic factors rather than to the residual lumen obstruction after thrombolysis.

Confronting the issues of patient safety and investigator conflict of interest in an international clinical trial of myocardial reperfusion. Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO) Steering Committee

The Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO) trial is a large scale international trial of new myocardial reperfusion strategies. The primary hypothesis is that early and sustained coronary artery recanalization will be associated with a significant reduction in mortality. The four regimens that are being tested are 1) streptokinase with subcutaneous heparin; 2) streptokinase with intravenous heparin; 3) accelerated recombinant tissue-type plasminogen activator (rt-PA) with intravenous heparin; and 4) combination streptokinase, rt-PA and intravenous heparin. The planned recruitment of 41,600 patients in 1,500 sites from 15 countries is expected to be completed by December 1992 and will enable detection of a 15% reduction or 1% absolute difference in mortality compared with that associated with standard therapy (streptokinase and subcutaneous heparin). In designing the trial, two important issues were directly addressed. First, a strategy was developed to provide assurance of patient safety during large scale investigational use of an aggressive thrombolytic regimen. This includes fascimile transmission of a one-page safety summary form to the Data Coordinating Center within 24 h of death or discharge, acceptance of the concept of "net clinical benefit" and close surveillance of the trial's progress by the independent Data and Safety Monitoring Committee. Second, to avoid potential conflict of interest beyond elimination of any position of financial equity, the Steering Committee unanimously voted to prohibit any honoraria for speaking engagements, payment for consultancy or travel or reimbursement of any kind from any of the five corporate sponsors until 1 year after publication of the results. Incorporation of these approaches may facilitate the design of future large scale randomized trials in cardiovascular medicine.

Advances in thrombolytic therapy

Alteplase and saruplase are more fibrin-specific thrombolytic drugs than anistreplase. These and the thrombolytic drugs of the first generation (streptokinase and urokinase) have shortcomings and limitations. The prolonged intravenous maintenance infusions have been replaced by a bolus injection, accelerated infusions, or the combined intravenous administration of thrombolytic agents. Numerous truncated alteplase or saruplase molecules have been constructed by deletion and domain substitution or hybrids made of the two molecules without gaining in thrombolytic potency. Recombinant staphylokinase and plasminogen activator from bat saliva have some interesting properties and are being investigated. Thrombus-targeted thrombolytic drugs were constructed using monoclonal antibodies against fibrin fragments or against epitopes of activated platelets. Fibrin-specific thrombolytic drugs require the concomitant use of a potent antithrombotic drug to prevent reocclusion. Whether hirudin or synthetic thrombin inhibitors are superior to heparin and whether novel antiplatelet agents, including monoclonal antibodies to platelet receptors and disintegrins, are more effective than aspirin is under clinical investigation. The place of stable analogues of prostacyclin during thrombolytic treatment is still unsettled.

Present status of rescue coronary angioplasty: current polarization of opinion and randomized trials

Whereas coronary angioplasty has been demonstrated to be unnecessary and perhaps harmful for most patients after successful thrombolytic treatment of acute myocardial infarction, the clinical benefit of rescue angioplasty after failed thrombolysis remains untested in a randomized clinical trial. However, in the clinical judgment of many physicians it is unethical to withhold such treatment, whereas a nearly equal number of physicians believe that such treatment cannot be justified. A review of reported nonrandomized data from a limited number of patients suggests that 1) coronary angioplasty is successful in only 80% of patients after failed thrombolysis, 2) later reocclusion rates may depend on the thrombolytic agent used, 3) left ventricular ejection fraction is seldom improved, and 4) mortality rates after successful angioplasty approximate those after successful thrombolysis alone but mortality rates after failed angioplasty are remarkably high. The arguments for and against rescue angioplasty are reviewed, and it is concluded that results of randomized trials are needed to replace disparate clinical opinion on whether this potentially costly form of therapy should be widely implemented.

Thrombolytic therapy: adjuvant mechanical intervention for acute myocardial infarction

Following successful pharmacologic thrombolysis, early coronary angiography frequently shows a tight residual stenosis in the infarct-related artery at the site of recent occlusion. Approaches to the management of the residual stenosis have undergone a gradual evolution from an aggressive strategy of immediate balloon dilation to a more conservative approach. Randomized, controlled trials have indicated that immediate percutaneous transluminal coronary angioplasty (PTCA) is associated with no greater recovery in regional or global left ventricular function, and a tendency toward an increased incidence of complications, including the need for emergency coronary artery surgery and blood transfusion. The role of immediate rescue PTCA for failed thrombolysis has not been as rigorously investigated, but selected patients, including those with evidence of ongoing myocardial ischemia or hemodynamic instability, may benefit from this approach. A major source of current controversy is the value of routine coronary angiography after uncomplicated myocardial infarction. Two carefully conducted trials have indicated that a conservative strategy of clinically indicated, predischarge cardiac catheterization may be associated with an increased need for readmission and late, elective cardiac catheterization when compared with a more invasive strategy of routine coronary angiography, but that the conservative approach is not associated with an increased incidence of death or reinfarction. Provision was not made in these studies, however, for evaluating the positive economic and psychologic impact of early coronary angiography, early hospital discharge, and early return to work of patients with a favorable postinfarction prognosis. It is concluded that early mechanical revascularization following thrombolysis should be considered for ongoing myocardial ischemia, but should otherwise be deferred pending the results of predischarge functional studies. For most patients, routine coronary angiography is likely to remain an important diagnostic tool and an integral component of the management of the convalescent phase of acute myocardial infarction.

Clinical risks of thrombolytic therapy

Understanding the clinical risks of intravenous thrombolytic therapy is critical to appropriate patient selection. The major risks can be classified into 5 major categories: intracranial hemorrhage, systemic hemorrhage, immunologic complications, hypotension, and myocardial rupture. Although theoretical concern exists about thromboembolic complications, they rarely occur. Although cardiac rhythm disturbances are somewhat more likely to occur at the time of reperfusion, the clinical significance of "reperfusion arrhythmias" is minimal. Intracranial hemorrhage, the most devastating complication, occurs in 0.2-1% of patients treated with thrombolytic therapy. Factors associated with incremental risk are now being identified from large clinical trials. Systemic hemorrhage is uncommon in patients without major vascular punctures and seldom leads to serious adverse outcomes. Immunologic complications--including anaphylaxis, which is rare, and immune complex disease, which is more common--occur only with streptokinase or agents with a streptokinase moiety, including anistreplase (anisoylated plasminogen--streptokinase activator complex, APSAC). Hypotension, which can be managed easily in most patients, is also observed much more frequently with streptokinase and anistreplase. Myocardial rupture is increasingly being recognized as a possible complication of late thrombolysis. A proper perspective on clinical risk can only be gained in the context of potential benefit of therapy. In many cases individual patients considered to be at highest risk for complications also stand to gain the most from treatment. Many of the questions raised by currently available data about bleeding risk are being addressed in the ongoing Global Utilization of t-PA and Streptokinase (GUSTO) Trial. A paradigm for considering this decision making problem is presented.

Clinical benefits of thrombolytic therapy in acute myocardial infarction

The value of coronary artery reperfusion resulting from pharmacologically induced fibrinolysis in patients with evolving myocardial infarction has been rigorously evaluated. Improved left ventricular function and even more impressive improvements in survival rates have been demonstrated consistently in controlled studies. Benefit is related to the restoration of myocardial blood flow. Maximal benefit is achieved with early and sustained restoration of coronary artery patency. Benefits observed during initial hospitalization are sustained for at least 1 year in the majority of patients, even without subsequent mechanical revascularization. To date, analysis of subgroups has not identified a population of patients with evolving infarction that should routinely be excluded from consideration for thrombolysis. As with many potent pharmacologic agents, activators of the fibrinolytic system are associated with a degree of risk whenever they are administered to a patient. Therefore, patients must be assessed carefully prior to initiating treatment, especially for potential bleeding hazards, and appropriate follow-up evaluation and concomitant therapy needs to be planned. However, given the overwhelming body of data now available regarding its benefits and relative safety, thrombolysis should be considered as conventional therapy for patients with acute evolving myocardial infarction (AMI).

New developments in thrombolytic therapy

Pharmacologic lysis of occlusive, ischemia-producing thrombi has become widely accepted during the past decade. New developments in this field have centered around increasing the efficacy of the known plasminogen activators while employing methods to minimize the risk of hemorrhage and decrease the incidence of rethrombosis. Such methods have included the use of thrombus-directed antibodies linked to plasminogen activators, increased plasminogen (substrate) concentration at the thrombus site, anticoagulant and antiplatelet therapy to prevent thrombus propagation and reformation following lysis, and combination plasminogen activator therapy designed to increase efficacy and safety. These new strategies have been extensively tested in vitro and in a variety of animal models. As we have indicated, extrapolation of such results to human patients cannot be done with confidence. However, the strategies are based on sound rationale and the reported findings should serve as the basis for controlled human trials.

Clot-selective coronary thrombolysis with low-dose synergistic combinations of single-chain urokinase-type plasminogen activator and recombinant tissue-type plasminogen activator. The Pro-Urokinase for Myocardial Infarction Study Group

The effect of simultaneous infusions of low-dose recombinant tissue-type plasminogen activator (t-PA) and single-chain urokinase-type plasminogen activator (scu-PA, pro-urokinase) on coronary arterial thrombolysis was investigated in 23 patients treated within 6 hours (mean 2.6 +/- 1.1, range 1.2 to 5.9) of symptoms of an acute myocardial infarction. Infarct artery patency at 90 minutes was achieved in 16 (70%, 95% confidence limits of 0.47 to 0.87) of 23 patients after a 1-hour intravenous infusion of 20 and 16.3 mg of t-PA and scu-PA, respectively. At 90 minutes, the fibrinogen concentration decreased from 369 +/- 207 to 316 +/- 192 mg/dl (p = not significant), while plasminogen decreased to 69 +/- 24% (p = 0.001) and alpha-2-antiplasmin to 77 +/- 24% (p = 0.001) of pretreatment values. Although no bleeding requiring termination of drug infusion or transfusion occurred, 1 patient with cerebrovascular amyloidosis had a fatal intracerebral hemorrhage. These findings suggest that combination therapy may allow substantial reductions in total thrombolytic doses while still achieving effective fibrin-specific coronary thrombolysis.

Thrombolysis, anticoagulation, and reocclusion

Based on apparent higher recanalization rates of the infarct-related artery, preferential use of thrombolytic agents with high clot specificity has been proposed for treating patients with acute myocardial infarction. In the Thrombolysis in Myocardial infarction (TIMI-I) and European Cooperative Group studies, higher reperfusion rates were observed with alteplase compared with streptokinase, causing many to assume that the former would achieve a greater reduction in early hospital mortality. However, the Gruppo Italiano per lo Studio della Streptochinasi nell'Infarto Miocardico (GISSI-2) and its associated International Study Group failed to show any differences in 15-day mortality between these agents in more than 20,000 patients. This apparent lack of correlation between reperfusion rates and early mortality may be explained in part when one considers that recanalization or patency rates measured at a given point in time, such as 90 minutes after onset of therapy, fail to define the subsequent vessel status. Early reocclusion is the major reason for this and is a major limitation to the clinical efficacy of thrombolytic drugs. Following recanalization, residual fibrin-bound thrombin adherent to the site of arterial injury from plaque rupture strongly promotes rethrombosis. Although antiplatelet and antithrombin agents such as aspirin and heparin help to decrease rethrombosis, these agents are far from ideal. Thrombolytic agents that produce a significantly prolonged systemic thrombolytic state, such as streptokinase and anistreplase, are likely to result in less rethrombosis. Therefore, a systemic fibrinolytic state would appear to be an advantage rather than a disadvantage, particularly because the incidence of intracerebral hemorrhage does not appear to be greater with their use compared with agents producing less systemic fibrinolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Creation of the recombinant tissue plasminogen activator (rt-PA) image and its influence on practice habits

American physicians have commonly practiced thrombolytic therapy for acute myocardial infarction with the recombinant form of tissue plasminogen activator (rt-PA), although its cost is much higher than that of streptokinase. The greater popularity of rt-PA is based on the belief that it is a more effective and a safer drug for achieving myocardial salvage and mortality reduction. However, a series of studies testing this assumption have not substantiated its greater efficacy or safety with respect to not only streptokinase but also urokinase and anisoylated plasminogen-streptokinase activator complex (APSAC). This editorial reviews the sequence of events that led to the creation of the rt-PA image, the mistaken premises on which it was based and the questions that need to be addressed if we are to strengthen the scientific method for evaluating similar types of drugs and its influence on practice habits including the costs to the health system.

A prospective, randomized trial comparing combination half-dose tissue-type plasminogen activator and streptokinase with full-dose tissue-type plasminogen activator. Kentucky Acute Myocardial Infarction Trial (KAMIT) Group

BACKGROUND

The potential benefits of combination thrombolytic agents in the treatment of myocardial infarction remain uncertain. In a small pilot study, we demonstrated that combining half-dose tissue-type plasminogen activator (t-PA) with streptokinase (SK) achieved a high rate of infarct vessel patency and a low rate of reocclusion at half the cost of full-dose t-PA.

METHODS AND RESULTS

We designed a prospective trial in which 216 patients were randomized within 6 hours of myocardial infarction to receive either the combination of half-dose (50 mg) t-PA with streptokinase (1.5 MU) during 1 hour or to the conventional dose of t-PA (100 mg) during 3 hours. Acute patency was determined by angiography at 90 minutes, and angioplasty was reserved for failed thrombolysis. Heparin and aspirin regimens were maintained until follow-up catheterization at day 7. Acute patency was significantly greater after t-PA/SK (79%) than with t-PA alone (64%, p less than 0.05). After angioplasty for failed thrombolysis, acute patency increased to 96% in both groups. Marked depletion of serum fibrinogen levels occurred after t-PA/SK compared with t-PA alone at 4 hours (37 +/- 36 versus 199 +/- 66 mg/dl, p less than 0.0001) and persisted 24 hours after therapy (153 +/- 66 versus 252 +/- 75 mg/dl, p less than 0.0001). Reocclusion (3% versus 10%, p = 0.06), reinfarction (0% versus 4%, p less than 0.05), and need for emergency bypass surgery (1% versus 6%, p = 0.05) tended to be less in the t-PA/SK group. Greater myocardial salvage was apparent in the t-PA/SK group as assessed by infarct zone function at day 7 (-1.9 SD/chord versus -2.3 SD/chord after t-PA alone, p less than 0.05). In-hospital mortality (6% versus 4%) and serious bleeding (12% versus 11%) were similar between the two groups.

CONCLUSIONS

These results suggest that a less expensive regimen of half-dose t-PA with SK yields superior 90-minute patency and left ventricular function and a trend toward reduced reocclusion compared with the conventional dose of t-PA.

Combination thrombolytic therapy: a comparison of simultaneous and sequential regimens of tissue plasminogen activator and urokinase

Coronary angioplasty following unsuccessful tissue plasminogen activator (t-PA) therapy for acute myocardial infarction has been associated with a high incidence of subsequent reocclusion of the infarct-related artery, and a relatively high in-hospital mortality. In contrast, the combination of t-PA and urokinase, when given intravenously prior to coronary angiography, appears to be associated with a low incidence of post-rescue angioplasty reocclusion. In order to determine whether intraprocedural urokinase, given at the time of rescue coronary angioplasty for failed t-PA therapy, improves long-term patency of the infarct vessel to the same extent as preangiographic, combination t-PA/urokinase therapy, three thrombolytic treatment strategies were retrospectively compared. The first group included 86 patients undergoing rescue angioplasty after t-PA monotherapy (t-PA alone). The clinical and angiographic outcomes of these patients were compared with those of 24 patients who received intravenous or intracoronary urokinase during rescue angioplasty following unsuccessful t-PA therapy (sequential t-PA/urokinase therapy), and with those of 34 patients undergoing rescue coronary angioplasty following unsuccessful therapy with the combination of intravenous t-PA and urokinase (simultaneous therapy). There was no difference in postangioplasty patency rate of the infarct-related artery between the three groups. However, the sequential t-PA/urokinase regimen was associated with a subsequent reocclusion rate that was lower than the rate that occurred in the t-PA monotherapy group but higher than the rate in the simultaneous t-PA/urokinase group (13 versus 29 versus 2%, respectively; p = 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of combination thrombolytic therapy and timing of cardiac catheterization in acute myocardial infarction. Results of thrombolysis and angioplasty in myocardial infarction--phase 5 randomized trial. TAMI Study Group

Recent trials of myocardial reperfusion using single-agent thrombolytic therapy and sequential cardiac catheterization have supported a conservative approach to the patient with acute myocardial infarction. To evaluate combination thrombolytic therapy and the role of a previously untested strategy for the aggressive use of cardiac catheterization, we performed a multicenter clinical trial with a 3 x 2 factorial design in which 575 patients were randomly allocated to one of three drug regimens--tissue-type plasminogen activator (t-PA) (n = 191), urokinase (n = 190), or both (n = 194) - and one of two catheterization strategies--immediate catheterization with angioplasty for failed thrombolysis (n = 287) or deferred predischarge catheterization on days 5-10 (n = 288). Patients with contraindications to thrombolytic therapy, cardiogenic shock, or age of more than 75 years were excluded. Global left ventricular ejection fraction was well preserved and almost identical at predischarge catheterization (54%), regardless of the catheterization or thrombolytic strategy used (p = 0.98). Combination thrombolytic therapy was associated with a less complicated clinical course, most clearly documented by a lower rate of reocclusion (2%) compared with urokinase (7%) and t-PA (12%) (p = 0.04) and a lower rate of recurrent ischemia (25%) compared with urokinase (35%) and t-PA (31%). When a composite clinical end point (e.g., death, stroke, reinfarction, reocclusion, heart failure, or recurrent ischemia) was examined, combination thrombolytic therapy was associated with greater freedom from any adverse event (68%) compared with either single agent (urokinase, 55%; t-PA, 60%) (p = 0.04) and with a less complicated clinical course when the composite clinical end points were ranked according to clinical severity (p = 0.024). Early patency rates were greater with combination therapy, although predischarge patency rates after considering interventions to maintain patency were similar among drug regimens. No difference in bleeding complication rates was observed with any thrombolytic regimen. The aggressive catheterization strategy led to an overall early patency rate of 96% and a predischarge patency rate of 94% compared with a 90% predischarge patency in the conservative strategy (p = 0.065). The aggressive strategy improved regional wall motion in the infarct region (-2.16 SDs/chord) compared with deferred catheterization (-2.49 SDs/chord) (p = 0.004). More patients treated with the aggressive strategy were free from adverse outcomes (67% versus 55% in the conservative strategy, p = 0.004), and the clinical course was less complicated when the adverse outcomes were ranked according to severity (p = 0.016). No significant increase in use of blood products resulted from the aggressive strategy.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute effects of parenteral beta-blockade on regional ventricular function of infarct and noninfarct zones after reperfusion therapy in humans

Although the mechanism is unknown, clinical trials have suggested that intravenous beta-adrenergic blockade may prevent early cardiac rupture after myocardial infarction. Previous studies have examined effects of beta-blockers on global left ventricular function after myocardial infarction; however, few data exist regarding their immediate effects on regional function or in patients after successful reperfusion. Therefore, 65 patients in whom thrombolysis with or without coronary angioplasty achieved reperfusion at 4.6 +/- 1.7 h from symptom onset were studied. Low osmolarity contrast ventriculograms were obtained immediately before and after administration of 15 mg of intravenous metoprolol (n = 54) or placebo (n = 11). Intravenous metoprolol immediately decreased heart rate (from 92 to 76 beats/min, p less than 0.0001), increased left ventricular diastolic volume (from 150 to 163 ml, p less than 0.001) and systolic volume (from 72 to 77 ml, p less than 0.0005) but did not change systolic and diastolic pressures. Although there was no difference in ejection fraction after metoprolol, centerline chord analysis revealed reduced noninfarct zone motion (from 0.41 to 0.12 SD/chord, p less than 0.05), improved infarct zone motion (from -3.1 to -2.9 SD/chord, p less than 0.01) and smaller circumferential extent of hypokinesia (from 30 to 27 chords, p less than 0.05). Patients with dyskinesia of the infarct zone had the most striking improvement in infarct zone wall motion. Because these changes occurred immediately after beta-blockade, they could not be attributed to myocardial salvage. No significant changes in heart rate, left ventricular volumes or regional wall motion were apparent in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant tissue-type plasminogen activator: current concepts and guidelines for clinical use in acute myocardial infarction. Part II

The extraordinarily high prevalence of coronary heart disease, coupled with the alarming incidence of MI in Western society, has encouraged the investigation and development of pharmacologic agents that can be employed widely, quickly, effectively, and safely. Recombinant t-PA has played a vital role in the treatment of MI, restoring coronary arterial patency, limiting infarct size, preserving ventricular function, and improving patient survival. It has been shown to be safe when given to carefully selected patients and, although indications for clinical use have been relatively restricted, they appear to be expanding considerably. Future investigations must continue to focus on patient selection to allow treatment for all patients who would derive benefit and to establish dosing regimens and adjuvant therapies that will maximize coronary reperfusion while concomitantly limiting reocclusion and hemorrhagic complications.

Multicenter patency trial of intravenous anistreplase compared with streptokinase in acute myocardial infarction. The TEAM-2 Study Investigators

Thrombolytic therapy has been shown to improve clinical outcome when administered early after the onset of symptoms of acute myocardial infarction; the mechanism of benefit is believed to be reestablishment and maintenance of coronary artery patency. Anistreplase is a second generation thrombolytic agent that is easily administered and has a long duration of action. To compare anistreplase (30 units/2-5 min) and therapy with the Food and Drug Administration-approved regimen of intravenous streptokinase (1.5 million units/60 min), a randomized, double-blind, multicenter patency trial was undertaken in 370 patients less than 76 years of age with electrocardiographic ST segment elevation who could be treated within 4 hours of symptom onset. Coronary patency was determined by reading, in a blinded fashion, angiograms obtained early (90-240 minutes; mean, 140 minutes) and later (18-48 hours; mean, 28 hours) after beginning therapy. Early total patency (defined as Thrombolysis in Myocardial Infarction grade 2 or 3 perfusion) was high after both anistreplase (132/183 = 72%) and streptokinase (129/176 = 73%) therapy, and overall patency patterns were similar, although patent arteries showed "complete" (grade 3) perfusion more often after anistreplase (83%) than streptokinase (72%) (p = 0.03). Similarly, residual coronary stenosis, determined quantitatively by a validated computer-assisted method, was slightly less in patent arteries early after anistreplase (mean stenosis diameter, 74.0%) than streptokinase (77.2%, p = 0.02). In patients with patent arteries without other early interventions, reocclusion risk within 1-2 days was defined angiographically and found to be very low (anistreplase = 1/96, streptokinase = 2/94). Average coronary perfusion grade was greater, and percent residual stenosis was less, at follow-up than on initial evaluation and did not differ between treatment groups. Enzymatic and electrocardiographic evolution was not significantly different in the two groups. Despite rapid injection, anistreplase was associated with only a small (4-5 mm Hg), transient (at 5-10 minutes) mean differential fall in blood pressure. In-hospital mortality rates were comparable for anistreplase and streptokinase (5.9%, 7.1%). Stroke occurred in one (0.5%) and three (1.6%) patients, respectively; one stroke was hemorrhagic. Other serious bleeding events and adverse experiences occurred uncommonly and with similar frequency in the two groups. Thus, for the end points of our study (patency, safety), anistreplase and streptokinase showed overall favorable and relatively comparable outcomes, with a few differences.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Fate of patients with acute myocardial infarction with patency of the infarct-related vessel achieved with successful thrombolysis versus rescue angioplasty

Patients with failure of infarct-related artery recanalization after thrombolytic therapy have a poor clinical outcome. These patients have been considered for rescue angioplasty 90 min after thrombolytic therapy at the time of emergency catheterization in the course of five Thrombolysis and Angioplasty in Myocardial Infarction (TAMI) trials. The outcome of 776 patients with patent infarct-related vessels after emergency catheterization was analyzed--607 with thrombolysis-mediated patency of the infarct-related vessel and 169 with patency achieved by angioplasty. Baseline characteristics of the thrombolysis and angioplasty patency groups were similar except for a higher acute left ventricular ejection fraction (51.3% versus 48.2%) in the thrombolysis group (p = 0.003). Seven to 10 day left ventricular ejection fraction was higher (52.3% versus 48.1%), infarct zone functional recovery was greater (0.44 versus 0.21 standard deviation/chord, or 18% versus 7%, p = 0.001) and reocclusion was less (11% versus 21%) in the thrombolysis compared with the angioplasty group. Despite these differences, angioplasty patency was associated with the same low in-hospital mortality rate (5.9% versus 4.6%) and long-term mortality rate (3% versus 2%) as thrombolysis patency. Reocclusion adversely affected the mortality rate and ventricular functional recovery. Technical failure of rescue angioplasty was associated with a much higher mortality rate than was technical success (39.1% versus 5.9%). Thrombolysis patency was preferable to angioplasty patency after thrombolytic therapy in acute myocardial infarction, but both were associated with the same low in-hospital and long-term mortality rates, suggesting that rescue angioplasty is beneficial in some patients with failure of infarct-related artery recanalization after thrombolytic therapy.

Optimal utilization of thrombolytic therapy for acute myocardial infarction: concepts and controversies

Timely administration of thrombolytic therapy decreases myocardial infarct size, lessens the incidence of congestive heart failure and improves survival. However, available data suggest that only 10% of patients with acute infarction in the United States receive thrombolytic drugs. Given the benefits of thrombolytic therapy, all patients with myocardial infarction would likely be treated were it not for associated risks. Several groups exist in which the risk/benefit ratio of thrombolytic therapy continues to be controversial, including those with inferior infarction, absence of ST segment elevation or presentation greater than 6 h from symptom onset, elderly patients and those with hypertension. Three recent thrombolytic trials reported a reduction in mortality that was entirely independent of infarct location. Pooled data from trials involving 12,000 patients with inferior infarction have demonstrated a reduction in mortality rate (6.8% versus 8.7%, p less than 0.0001). Furthermore, improvement in regional and global left ventricular function occurred after reperfusion therapy of inferior infarction. Pooled data indicate that patients treated between 6 and 24 h after symptom onset have a lower mortality rate than do those who receive placebo (11.1% versus 13.1%, p less than 0.001). Improved survival occurs after thrombolytic therapy in patients with ST segment elevation or left bundle branch block, but not in those with isolated ST depression or a normal electrocardiogram. Age should not be considered an absolute contraindication because the lifesaving potential of thrombolytic therapy in the elderly may be two to three times that of the overall group of patients with myocardial infarction. Finally, recent studies demonstrated that patients who present with hypotension or hypertension or who have undergone cardiopulmonary resuscitation may also benefit.(ABSTRACT TRUNCATED AT 250 WORDS)

New approaches to treatment of myocardial infarction

Survival of patients with acute transmural infarction is largely related to the size of the myocardial infarction. The goal of thrombolytic therapy in acute myocardial infarction is maximal salvage of myocardium by reestablishment of flow in the occluded infarct-related artery and the establishment and maintenance of a patent infarct-related artery. Results of randomized trials show a significant reduction in mortality in patients who have undergone thrombolysis. A patent infarct-related artery, even in the absence of a change in left ventricular function, is associated with reduced mortality. The Thrombolysis in Myocardial Infarction Trial and the European Cooperative Trial showed that recombinant tissue-type plasminogen activator is superior to streptokinase in reestablishing flow in a totally occluded artery. Experimental and clinical evidence suggests that thrombolysis and thrombosis occur simultaneously, and that lysis appears to increase both thrombin and platelet activity. Effective reduction of thrombosis accelerates thrombolysis. Rethrombosis after thrombolysis is due to anchored residual thrombus, which alters the hemorrheology of blood flow and produces a highly thrombogenic substrate that is largely due to residual fibrin-bound thrombin. Platelet deposition is directly related to severity of residual stenosis and shear rate. Thrombin appears to be the most potent of the 5 potential stimulators of platelet activation during arterial thrombosis. Proper anticoagulation can play an important role in reducing thrombosis. Experimental evidence strongly supports the use of heparin during and after thrombolysis. A recently reported study shows continued reduction of residual stenosis after 1 month of vigorous anticoagulation with intravenous heparin and subsequent oral anticoagulation.(ABSTRACT TRUNCATED AT 250 WORDS)