Intravenous and intracoronary fibrinolytic therapy in acute myocardial infarction: overview of results on mortality, reinfarction and side-effects from 33 randomized controlled trials

Medical therapy of acute myocardial infarction: Part I. Role of thrombolytic and antithrombotic therapy

Thrombolytic therapy has been established as a safe and effective therapeutic strategy in acute myocardial infarction (MI). Its efficacy is improved with early administration, although modest benefits can be demonstrated for up to 12 hours. Tissue plasminogen activator (TPA) appears to offer benefits over streptokinase when administered to patients who present within 4 hours, those with an anterior MI, and who are less than 75 years old. Age alone is not a contraindication for thrombolysis because the risk of bleeding complications in the elderly is outweighed by a significant improvement in mortality. One of the major limitations of thrombolytic therapy in acute MI is reocclusion. Use of adjunctive antithrombotic therapy can reduce the rate of reocclusion following successful thrombolysis. The beneficial role of aspirin is well established. Use of intravenous heparin in conjunction with streptokinase offers no clinical benefit. The efficacy of heparin when administered with other thrombolytic agents remains to be established. These issues and the role of newer antiplatelet and antithrombin agents are being examined in ongoing clinical trials. The objective of this review is to provide the information needed for careful and appropriate judgment in the use of thrombolytic agents and antithrombotic therapy. General principles are emphasized, and specific recommendations are included as guidelines.

Causes of delay in seeking treatment for heart attack symptoms

With the advent of thrombolytic therapy and other coronary reperfusion strategies, rapid identification and treatment of acute myocardial infarction greatly reduces mortality. Unfortunately, many patients delay seeking medical care and miss the benefits afforded by recent advances in treatment. Studies have shown that the median time from onset of symptoms to seeking care ranges from 2 to 61/2 hours, while optimal benefit is derived during the first hour from symptom onset. The phenomenon of delay by AMI patients and those around them needs to be understood prior to the design of education and counseling strategies to reduce delay. In this article the literature is reviewed and variables that increase patient delay are identified. A theoretical model based on the health belief model, a self regulation model of illness cognition, and interactionist role theory is proposed to explain the response of an individual to the signs and symptoms of acute myocardial infarction. Finally, recommendations are made for future research.

A statistician looks at met-analysis

I begin by considering origins and meanings for the term met-analysis/meta-analysis. The underlying ideas have a long history, not only in medical but also in the agricultural and social sciences. Met-analysis is a form of critical review of research on a stated topic, distinctive for its emphasis on producing quantitative conclusions. It is not in itself a specific technique, but rather an approach to aggregating information with the aid of critical deployment of standard statistical techniques. I shall discuss types of data on which met-analysis may be practised. These may be published papers or reports on past research, or the complete data on which such publications were based, whether from well-designed experiments or from other sources, or even--least satisfactorily--from spontaneously submitted information. Particular dangers are bias arising from the manner in which component studies are chosen, possibly affected by publication bias, and the pernicious influence of the modern tendency to deify the statistical significance test. A further important issue is that of the scale to be used as a measure of the effect of the treatment (or treatments) under study. I end with general comments on the conduct of met-analyses.

The rational use of therapeutic drugs in the 21st century. Important lessons from cumulative meta-analyses of randomized control trials

The use of randomized control trials to assess the usefulness of therapeutic drugs over the last half century has brought significant benefits to patient care. The full potential benefits, however, have been only partially fulfilled because available data are frequently poorly used. Meta-analysis has emerged as an important tool for combining clinical evidence. Several examples are presented that compared the results of cumulative meta-analysis of randomized control trials with clinical expert recommendations. These comparisons demonstrated that clinical expert recommendations are often not synchronized with accumulating evidence, and this lack of recognition often resulted in delays in the acceptance of effective drugs and the slow abandonment of possibly harmful therapeutic practices. The problems of inappropriate therapeutic drug use will only intensify as new drugs are introduced and new uses for established drugs are proposed. The rational use of therapeutic drugs can be achieved only through the routine use of meta-analysis on high-quality clinical data. Some suggestions are made to improve the quality of the original research and the ways of assembling meta-analyses and disseminating their results.

The miracle of DICE therapy for acute stroke: fact or fictional product of subgroup analysis?

OBJECTIVE

To determine whether inappropriate subgroup analysis together with chance could change the conclusion of a systematic review of several randomised trials of an ineffective treatment.

DESIGN

44 randomised controlled trials of DICE therapy for stroke were performed (simulated by rolling different coloured dice; two trials per investigator). Each roll of the dice yielded the outcome (death or survival) for that "patient." Publication bias was also simulated. The results were combined in a systematic review.

SETTING

Edinburgh.

MAIN OUTCOME MEASURE

Mortality.

RESULTS

The "hypothesis generating" trial suggested that DICE therapy provided complete protection against death from acute stroke. However, analysis of all the trials suggested a reduction of only 11% (SD 11) in the odds of death. A predefined subgroup analysis by colour of dice suggested that red dice therapy increased the odds by 9% (22). If the analysis excluded red dice trials and those of poor methodological quality the odds decreased by 22% (13, 2P = 0.09). Analysis of "published" trials showed a decrease of 23% (13, 2P = 0.07) while analysis of only those in which the trialist had become familiar with the intervention showed a decrease of 39% (17, 2P = 0.02).

CONCLUSION

The early benefits of DICE therapy were not confirmed by subsequent trials. A plausible (but inappropriate) subset analysis of the effects of treatment led to the qualitatively different conclusion that DICE therapy reduced mortality, whereas in truth it was ineffective. Chance influences the outcome of clinical trials and systematic reviews of trials much more than many investigators realise, and its effects may lead to incorrect conclusions about the benefits of treatment.

Acute myocardial infarction. Reperfusion strategies

Acute myocardial infarction is the result of an acute interruption of myocardial blood flow resulting in ischemic myocardial necrosis. The pathogenesis of this phenomenon nearly always involves acute thrombosis superimposed on a disrupted atherosclerotic plaque. Thrombolytic agents have been conclusively shown to reduce mortality in many patient subgroups with myocardial infarction, including the elderly, patients with inferior myocardial infarction, and patients with systolic hypertension. Nearly all patients with acute myocardial infarction of less than 6 h in duration with S-T segment elevation should receive thrombolysis unless significant contraindications exist and outweigh the potential benefits. Aspirin should be given to almost all patients regardless of whether they receive thrombolysis. Angioplasty and coronary artery bypass surgery are useful as primary or secondary modes of reperfusion in selected patients with infarction.

The potential impact of the thrombolytic era on cardiac rupture complicating acute myocardial infarction

Cardiac rupture complicating acute myocardial infarction (AMI) remains a serious diagnostic and therapeutic challenge. The authors present 27 consecutive patients who died from cardiac rupture following AMI. These included 22 patients from 1975 through 1983 (prethrombolytic era) and 5 patients from 1984 through 1992 (postthrombolytic era) and all had postmortem examination. There were 16 men and 11 women with a mean age of seventy-two years. Myocardial infarction was anterior/anterolateral in 10 and inferior/inferoposterior in 17. Cardiac rupture followed AMI within one day in 14 (52%), two to five days in 8 (30%), and six to fourteen days in 5 (18%). Chest pain followed by sudden hypotension leading to electromechanical dissociation was the common terminal event. Cardiopulmonary resuscitation was unsuccessful in all patients. Postmortem findings showed three-vessel coronary disease in 21 (78%) and two-vessel disease in 6 (22%). Isolated free left ventricular wall rupture was found in 22 (81%), was anterior/anterolateral in 13 (48%), posterior in 9 (33%), and in conjunction with interventricular septum or papillary muscle in 5 (18%). Patients encountered in this series were mostly elderly hypertensives with multivessel coronary disease and postinfarction angina. Furthermore, cardiac rupture commonly occurred within the first five days of AMI and cardiopulmonary resuscitation was uniformly unsuccessful. During the thrombolytic era at their institution, this complication is now being seen much less often. These observations suggest that such interventions are expected to have a favorable impact on reducing the incidence of this catastrophic event.

Reporting, updating, and correcting systematic reviews of the effects of health care

The recent growth in the numbers of published systematic reviews reflects growing recognition of their importance for improving knowledge about the effects of health care. In Britain the NHS R&D Programme has established two centres to prepare systematic reviews of existing information, and the Cochrane Collaboration--an international network of individuals and institutions--evolved to produce systematic, periodically updated reviews of randomised controlled trials. The large amount of existing evidence that needs to be considered creates a problem for the reporting of systematic reviews: the need to ensure that methods and results of systematic reviews are adequately described has to be reconciled with the limited space available in printed journals. A possible solution is the use of electronic publications: reviews could be published simultaneously in a short, printed form and in a more detailed electronic form. Electronic publications also have the advantage of the ease with which reviews may be updated as new evidence becomes available or mistakes are identified.

Effect of nitrates on the frequency of left ventricular free wall rupture complicating acute myocardial infarction: a case-controlled study

Although up to 33% of all deaths from acute myocardial infarction are attributable to left ventricular free wall rupture, data showing a beneficial effect of drugs on this complication are scarce and contradictory. The aim of our study was to investigate the effect of nitrate therapy (intravenous or oral) during the first days after acute myocardial infarction on the frequency of free wall rupture in human beings. In a retrospective case-controlled study, 91 patients with free wall rupture complicating acute myocardial infarction demonstrated on autopsy or operation were compared with 182 control patients with acute myocardial infarction without rupture. The risk of sustaining free wall rupture was approximately 30% lower in patients receiving nitrates: (crude odds ratio 0.62; adjusted odds ratio 0.73 p 0.038). The data analysis demonstrates a possible association between nitrate use and frequency of left ventricular free wall rupture in patients with acute myocardial infarction. Nitrates seem to reduce the risk of rupture by approximately 30%.

Temporal trends and factors associated with extent of delay to hospital arrival in patients with acute myocardial infarction: the Worcester Heart Attack Study

Factors associated with delay to hospital arrival after the onset of symptoms suggestive of acute myocardial infarction (AMI) were examined in the late 1960s and 1970s, but recent data concerning these characteristics are limited. The purpose of the present study was to examine overall and temporal distributions of the extent of patients' delay from the time of onset of AMI symptoms to hospital arrival and factors associated with delay in seeking medical care from a multihospital, population-based perspective. Review of medical records was undertaken of patients hospitalized with a discharge diagnosis of AMI in 16 teaching and community hospitals in Worcester, Mass. in 1986, 1988, and 1990. The study sample comprised 1279 patients hospitalized with validated AMI in whom data concerning extent of patient delay from onset of symptoms suggestive of AMI to hospital arrival were available. The average delay between onset of symptoms suggestive of AMI and arrival at local emergency departments did not change significantly with time (average of 4.1 hours in 1986, 4.0 hours in 1988, and 4.6 hours in 1990). The median delay was 2.0 hours during each of these years. Fifty percent of patients with AMI went to area-wide emergency departments within 2 hours of the onset of acute symptoms, 22% between 2 and 4 hours, and 28% delayed > 4 hours. Results of a multivariable regression analysis showed that older age, history of diabetes, type of medical insurance coverage and previous AMI were significantly associated with delays in hospital arrival of > 2 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

911 and emergency department use for chest pain: results of a media campaign

STUDY OBJECTIVE

We evaluated the effects of a community public education campaign that encouraged patients to quickly call 911 after the onset of acute myocardial infarction (AMI) symptoms.

SETTING AND PARTICIPANTS

The media campaign focused on residents 50 years of age or older in King County, Washington, which has a population of 1.5 million (1990 census).

DESIGN

We determined 911 responses for chest pain, emergency department visits for AMI symptoms, the number of patients admitted to a CCU with an admitting diagnosis of rule-out MI, and the number of confirmed AMIs before and after the campaign.

RESULTS

The number of emergency medical services (EMS) responses (911 runs) for patients 50 years of age or older experiencing AMI symptoms increased significantly during the media campaign. ED visits for chest pain also increased significantly during the campaign, as did the number of patients 50 years of age or older admitted to a King County CCU with an admitting diagnosis of rule-out MI. Each of the above increases tapered--with time after the media campaign but remained above baseline.

CONCLUSION

An intense public education campaign can significantly increase EMS use, ED visits, and CCU admissions for AMI symptoms. However, these effects taper off with time after the campaign.

Alterations of coronary flow velocity during intervention for acute myocardial infarction: responses to complications of intracoronary thrombolysis and angioplasty

Alterations, either an increase or decrease, in the distal flow velocity over time are associated with alterations in vessel diameter and/or unstable flow velocity. Unexplained unstable flow velocity patterns should act as early warning signs to prompt the interventionalist to assess continued coronary patency and need for renewed interventions.

Treatment strategies for acute myocardial infarction complicated by cardiogenic shock in a community hospital

The risk and benefits of three treatment strategies were examined in 64 consecutive patients with acute myocardial infarction and cardiogenic shock. Thirteen patients received thrombolytic therapy (group 1), 29 patients received intra-aortic balloon pump counterpulsation support (group 2), and 22 patients were treated with combined thrombolytic therapy and intra-aortic balloon pump counterpulsation support (group 3). The groups were similar in regard to age, sex, medical history, hemodynamic data, and extent of coronary artery disease. Survival was improved in patients treated with combined thrombolytic therapy and intra-aortic balloon pump counterpulsation support (group 1, 23 percent; group 2, 28 percent; and group 3, 68 percent; p = 0.0049). Seven percent of the patients who remained at the community hospital survived vs 69 percent who were transferred to a tertiary care center (p < 0.001), and 17 percent survived who were treated medically vs 71 percent who received revascularization (p < 0.001). These findings suggest that patients who present to a community hospital in cardiogenic shock can have their conditions stabilized, and they can then be transferred to a tertiary care hospital for revascularization and have the same outcome as patients who initially present to tertiary care hospitals.

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)

Indications for fibrinolytic therapy in suspected acute myocardial infarction: collaborative overview of early mortality and major morbidity results from all randomised trials of more than 1000 patients. Fibrinolytic Therapy Trialists' (FTT) Collaborative Group

Large randomised trials have demonstrated that fibrinolytic therapy can reduce mortality in patients with suspected acute myocardial infarction (AMI). The indications for, and contraindications to, this treatment in some categories of patient are disputed, examples being late presentation, elderly patients, and those in cardiogenic shock. This overview aims to help resolve some of the remaining uncertainties. From all trials of fibrinolytic therapy versus control that randomised more than 1000 patients with suspected AMI, information was sought and checked on deaths during the first 5 weeks and on major adverse events occurring during hospitalisation. The nine trials included 58,600 patients, among whom 6177 (10.5%) deaths, 564 (1.0%) strokes, and 436 (0.7%) major non-cerebral bleeds were reported. Fibrinolytic therapy was associated with an excess of deaths during days 0-1 (especially among patients presenting more than 12 h after symptom onset, and in the elderly) but this was outweighed by a much larger benefit during days 2-35. This "early hazard" should not obscure the very clear overall survival advantage that is produced by fibrinolytic therapy. Benefit was observed among patients presenting with ST elevation or bundle-branch block (BBB)--irrespective of age, sex, blood pressure, heart rate, or previous history of myocardial infarction or diabetes--and was greater the earlier treatment began. Among the 45,000 patients presenting with ST elevation or BBB the relation between benefit and delay from symptom onset indicated highly significant absolute mortality reductions of about 30 per 1000 for those presenting within 0-6 h and of about 20 per 1000 for those presenting 7-12 h from onset, and a statistically uncertain benefit of about 10 per 1000 for those presenting at 13-18 h (with more randomised evidence needed in this latter group to assess reliably the net effects of treatment). Fibrinolytic therapy was associated with about 4 extra strokes per 1000 during days 0-1: of these, 2 were associated with early death and so were already accounted for in the overall mortality reduction, 1 was moderately or severely disabling, and 1 was not. This overview indicates that fibrinolytic therapy is beneficial in a much wider range of patients than is currently given such treatment routinely.

Plasminogen acceleration of urokinase thrombolysis

PURPOSE

A relative deficiency of plasminogen within the thrombus may be the rate limiting factor in clot lysis.

METHODS

To investigate this hypothesis, we used an in vitro perfusion system and expanded polytetrafluoroethylene graft segments filled with radiolabeled human thrombus. Three groups of five perfusions were compared: (1) urokinase infusion (333 IU/min) into clots laced with buffer, (2) urokinase infusion (333 IU/min) into clots laced with plasminogen (44 CU), and (3) control, D5W infusion into clots laced with buffer. Two end points were measured over time: the amount of lysed thrombus and the flow through the graft.

RESULTS

Urokinase infusion resulted in augmented flow through the graft when compared with control (p < 0.05). Lacing with plasminogen resulted in more rapid restoration of flow when compared with urokinase infusion alone (p < 0.05). Similarly, the rate of clot dissolution was significantly greater in plasminogen-laced thrombi (p < 0.05) when compared with the control and urokinase groups. Embolization of particles of thrombus was uniformly observed in the urokinase group, resulting in a temporary decrease in flow through the thrombosed graft. This event characteristically occurred after 60 minutes of infusion but was never seen in the urokinase/plasminogen treatment group.

CONCLUSIONS

These results suggest that plasminogen supplementation of urokinase thrombolysis may result in significant clinical benefits with respect to the rate of clot lysis and the uniformity of clot dissolution with a lower likelihood of secondary embolization.

Long-term prognosis of medically treated patients with acute myocardial infarction and one-vessel coronary artery disease

Long-term prognosis was studied in 156 patients with acute myocardial infarction (AMI) with 1-vessel coronary artery disease (CAD). During a mean follow-up period of 110 months, 19 patients (14%) had reinfarction, 15 (9.6%) died (including 7 deaths of cardiac origin) and 15 (9.6%) were hospitalized for worsening of angina. A coronary arteriogram was obtained twice in 54 patients. The coronary arteriogram revealed multivessel CAD in all cases with reinfarction (n = 14). Ten percent of the patients with multivessel disease experienced a reinfarction during the initial 3 years after the onset of the first AMI. The recurrence rate of AMI in patients with 1-vessel disease increased gradually from the third year after the onset of their first AMI, reaching 10% in 6.7 years. The recurrence of AMI at the same region as the original infarction was detected in only 1 patient. Six of 19 patients (32%) with recurrence of AMI died and 13 survived after the reinfarction. It was difficult to predict future progression from the outcome of the comparison between the first and second coronary arteriograms. Thus, in patients with uncomplicated AMI with 1-vessel CAD, the prognosis is relatively good and the frequency of reinfarction is very low with conservative treatment.

History of drugs for thrombotic disease. Discovery, development, and directions for the future

The history of the antithrombotic agents--aspirin, heparin, warfarin, and the thrombolytics--is a rich and lively odyssey of serendipity, perseverance, vision, and conflict involving a number of striking personalities. The history of aspirin spans ages and continents from Hippocrates' analgesic for women in labor to the rediscovery of the white willow bark by English country scholar Reverend Edward Stone. Bayer chemist Felix Hoffmann reinvented aspirin for his ailing father; suburban physician L.L. Craven pioneered the prophylactic antithrombotic uses of aspirin; and Sir John Vane elucidated aspirin's mechanism of action as the inhibition of prostaglandin synthetase. Heparin was discovered by McLean, working as a medical student in 1915 in search of a pure procoagulant in dog liver. His original impure material differed somewhat from today's heparin, but purified heparin was rapidly accepted for a myriad of clinical uses; to this day, diverse new properties of this complex glycosaminoglycan continue to be elucidated. The oral anticoagulants emerged from veterinary research in the 1920s on a hemorrhagic disorder afflicting cattle that consumed spoiled sweet clover hay. Several chance encounters led Karl Link and his University of Wisconsin team to the identification of dicumarol as the offending agent in 1939 and its widespread therapeutic use by Wright and others in the 1940s. Link later developed warfarin as a rodenticide, but its use in humans soon followed in the 1950s. Vitamin K was discovered in the 1930s; its involvement in the mechanism of the anticoagulant agents was not delineated until the 1970s. The intrinsic ability of clotted blood to liquify and the fibrinolytic properties of normal urine were noted in the 1800s. Tillett and Sherry's group stumbled on the fibrinolytic properties of streptokinase in the 1930s and pioneered the therapeutic use of streptokinase in the 1940s and of urokinase in the 1960s. Several teams found tissue-type plasminogen activator in various body sites beginning in the 1940s, leading to its cloning and widespread use in the 1980s; anisoylated plasminogen-streptokinase activator complex is an example of rational drug design. The discoverers of these diverse agents have not only provided physicians with a potent armamentarium of antithrombotic drugs but also helped elucidate much basic science and vividly demonstrated the merits of perseverance, independent thought, and adherance to the scientific method.

Maximizing benefits of therapies in acute myocardial infarction

Major advances in the management of acute myocardial infarction have been achieved by a combination of careful experimental work and development of effective pharmacologic and interventional strategies in conjunction with the conduct of large, reliable randomized trials. Current trials indicate that a combination of thrombolytic therapy, aspirin, and intravenous followed by oral beta blockers reduces mortality. There are a number of additional promising interventions, such as intravenous magnesium, nitrates, and the newer antithrombin agents. However, before these agents are used widely in clinical practice, clear proof of benefit and adequate safety should be available from the ongoing randomized trials. Following discharge from the hospital, long-term therapy with aspirin and beta blockers should be considered in all patients. In patients with heart failure and low ejection fraction, angiotensin-converting enzyme (ACE) inhibitors have been shown to reduce mortality, reinfarction, and the need for further hospitalizations for heart failure. Therefore, these therapies, in conjunction with risk factor modification (cessation of cigarette smoking, treatment of hypercholesterolemia, treatment of hypertension), should be considered in all appropriate patients. A number of new strategies for the prevention of atherosclerosis and its complications are currently being evaluated in prospective randomized trials. These include the natural antioxidant vitamins, estrogen replacement therapy, tamoxifen therapy, and ACE inhibitors in patients without evidence of heart failure or left ventricular dysfunction.

Is there an age limit for thrombolytic therapy?

Thrombolytic therapy has revolutionized the treatment of acute myocardial infarction. The mortality of infarction increases very steeply with increasing age > 65 years. One-month mortality in such patients is in the range of 20-30%. The proportional benefit of lytic treatment is somewhat less in these older patients, but since mortality is high, the absolute benefit is as large or larger than that in younger patients. The risks of stroke due to thrombolysis are balanced between increased risk of cerebral hemorrhage but decreased risk for ischemic/embolic stroke. This trade-off results, overall, in a slightly increased stroke rate of about 1-2 per 1,000 nonfatal strokes, but with about 20 fewer deaths per 1,000 myocardial infarctions. In addition to these striking mortality benefits, there are also important reductions in infarct size, leading to decreased morbidity from heart failure or arrhythmias.

Thrombolytic Therapy in Acute Myocardial Infarction: A Review with Current Recommendations

Thrombolytic therapy has clearly become an established therapeutic modality to treat patients with acute myocardial infarction. Since there is no ideal agent at this time, we must evaluate the advantages and disadvantages of current therapy based on major clinical studies. Thrombolysis is the body's natural response to dissolving clots after they have served their purpose. Thrombolytic agents accelerate fibrinolysis by overwhelming the system. There are 4 thrombolytic agents currently available: streptokinase urokinase, anistreplase (APSAC), and rt-PA. Tissue plasminogen activator is a naturally occurring protein that can be created with genetic recombinant technology (rt-PA). It establishes higher patency rates (70–90%) than the other available thrombolytic agents. Recently published results of accelerated rt-PA infusion during acute myocardial infarction demonstrate that the infarct-related artery seems to open more quickly and provide greater blood flow. The use of intravenous heparin as adjunctive therapy along with aspirin seems to maintain patency at comparable levels to streptokinase. Not only is mortality reduced in the accelerated rt-PA group, but complications from myocardial infarction such as arrhythmia and heart failure are significantly reduced. rt-PA remains the drug of choice in the hypotensive patient and, because of potential allergy, in patients with previous exposure to streptokinase. Percutaneous transluminal coronary angioplasty is frequently needed to improve long-term patency and reduce ischemic episodes. Recent studies show that it may provide some advantage over thrombolytic therapy, because the artery can be opened faster, with higher flow rates.

Bedside cardiology and thrombolysis

The study by Christian et al. (37) provides useful clinical information for the management of the patient with myocardial infarction with thrombolytic therapy. 1) Complete resolution of chest pain during the infusion of an intravenous thrombolytic agent suggests reperfusion and myocardial salvage. Initial conservative medical management should be considered in these patients especially if serial ECGs show a progressive and rapid downward defection of the ST segment. 2) Patients presenting within 6 h after the onset of infarction, who are pain free, may still benefit from thrombolysis if their ECGs show persistent ischemia. 3) In the remaining patients in whom chest pain does not resolve completely during thrombolytic therapy, management, whether continued medical or invasive strategy, should be individualized and dictated by the extent of myocardium at risk (i.e., by the number of ECG leads showing ST segment elevation), the response of the ST segment to thrombolysis and, most important, the clinical status of the patient.

Clinical course and left ventricular function in patients with acute myocardial infarction following delayed recanalization of infarct-related artery

The effect of delayed recanalisation of the infarct related artery on clinical course and left ventricular functions was studied in 23 patients with acute myocardial infarction (Group 2). Another 82 patients with acute myocardial infarction served as controls: 48 patients with immediate recanalisation of the infarct related artery following intracoronary thrombolytic therapy (Group 1) and 34 patients with unsuccessful thrombolysis with the artery remaining occluded on repeat angiography (Group 3). Baseline clinical characteristics and left ventricular ejection fractions in the three groups did not differ statistically. Following intracoronary thrombolysis the clinical features and left ventricular functions in the three groups, respectively were as follows: post infarction angina--45.8%, 13.1% and 11.8% (1 vs. 2 and 3, P < 0.05); reinfarction--29.2%, 8.7% and 11.8% (1 vs. 2 and 3, P < 0.05); mortality--0%, 0% and 11.8% (1 and 2 vs. 3; P < 0.05); aneurysm--16.7%, 21.7% and 52.9% (1 and 2 vs. 3, P < 0.05); heart failure--20.8%, 21.7% and 47.1% (1 and 2 vs. 3, P < 0.05). Left ventricular ejection fractions on the second and on days 10-14 were, respectively, 47.6 +/- 1.1%, 42.8 +/- 1.1% and 39.2 +/- 1.6% (1 vs. 2 and 3, P < 0.05) and --52.1 +/- 1.0%, 48.9 +/- 1.1% and 44.3 +/- 1.5% (1 and 2 vs. 3, P < 0.05). Thus following delayed recanalisation of the infarct related artery the clinical course and left ventricular function improved significantly in comparison to patients without recanalisation.

Long-term follow-up of global and regional left ventricular function by two-dimensional echocardiography after thrombolytic therapy in acute myocardial infarction

In order to evaluate changes in left ventricular volumes and regional left ventricular function after thrombolytic therapy in acute myocardial infarction serial two-dimensional echocardiography was performed during a follow-up of 2 years in 206 consecutive patients treated with streptokinase and adjunctive angioplasty in a randomized group of patients. Unexpected progressive left ventricular enlargement was detected both with and without angioplasty. In anterior wall infarction, end-diastolic volume index increased from 55 +/- 14 to 91 +/- 28 ml/m2 (+65%, P < 0.01) and end-systolic volume index increased from 31 +/- 11 to 55 +/- 23 ml/m2 (+79%, P < 0.01), whereas ejection fraction decreased from 45 +/- 9 to 41 +/- 7% (-9%, P = NS). Averaged regional anterior wall motion improved during the first 4 weeks (11 +/- 10 to 16 +/- 12%), but subsequently deteriorated (16 +/- 12 to 10 +/- 6, P < 0.05). The number of segments with pathological wall motion increased. Similar volumetric and regional wall motion data were demonstrated in inferior wall infarction. We believe this reflects a chronic ventricular remodelling phenomenon. This process takes place predominantly during the first 3 months, but continues over the whole follow-up period. Forty percent of the patients suffered symptoms of heart failure on long-term follow-up. Attenuation of progressive ventricular enlargement remains a therapeutic challenge in the long-term care of these patients. Angiotensin-converting enzyme inhibitors are promising agents in this regard.

The logic and role of meta-analysis in clinical research

The term meta-analysis refers to the quantitative combination of data from independent trials. Where the result of such combination is a descriptive summary of the weight of the available evidence, the exercise is of undoubted value. Attempts to apply inferential methods, however, are subject to considerable methodological and logical difficulties. The selection and quality of the trials included, population bias, and the specification of the population to which inference may properly be made are problems to which no satisfactory solutions have been proposed. Insightful quantitative description ought not to differ materially from inferential conclusions; where discrepancies exist the inferential techniques should be regarded with extreme caution.

Continuous 12-lead ST-segment recovery analysis in the TAMI 7 study. Performance of a noninvasive method for real-time detection of failed myocardial reperfusion

BACKGROUND

If a practical, reliable, noninvasive marker of failed reperfusion was available in real time, the benefits of further therapy in this patient subgroup could be tested. We developed a method of 12-lead ST-segment recovery analysis using continuously updated reference points to provide such a marker.

METHODS AND RESULTS

In this study, our method was prospectively tested in 144 patients given thrombolytic therapy early in myocardial infarction. All patients had 12-lead continuous ST-segment monitoring and acute angiography, each analyzed in an independent, blinded core laboratory. ST-segment recovery and re-elevation were analyzed up to the moment of angiography, at which time patency was predicted. Predictions were correlated to angiographic infarct artery flow, with TIMI flow 0 to 1 as occluded and TIMI flow 2 to 3 as patent. Infarct artery occlusion was seen on first injection in 27% of patients. The positive predictive value of incomplete ST recovery or ST re-elevation by our method was 71%, negative predictive value 87%, with 90% specificity and 64% sensitivity for coronary occlusion. ST recovery analysis predicted patency in 94% of patients with TIMI 3 flow versus 81% of patients with TIMI 2 flow and predicted occlusion in 57% of patients with collateralized occlusion versus 72% of patients with non-collateralized occlusion. In a regression model including other noninvasive clinical descriptors, ST recovery alone contained the vast majority of predictive information about patency.

CONCLUSIONS

In a blinded, prospective, angiographically correlated study design, 12-lead continuous ST-segment recovery analysis shows promise as a practical noninvasive marker of failed reperfusion that may contribute substantially to currently available bedside assessment. Our data also suggest that patients with TIMI 2 flow or with collateralized occlusions may represent a physiological spectrum definable with ST-segment recovery analysis.

Enhancement of thrombolysis by external ultrasound

The purpose of our study was to assess the efficacy of external ultrasound to enhance in vitro thrombolysis with urokinase or streptokinase. One-hour-, 1-day-, 4-day-, and 6-day-old human blood thrombi (n = 366) were incubated in normal saline solution with three different concentrations of streptokinase (50, 250, and 2000 mu/ml) or urokinase (200, 2000, and 5000 mu/ml). Thrombi were exposed to pulsed ultrasound of 1 MHz at 1.0, 1.5 and 2.2 W/cm2 at different exposure times. The combination of ultrasound (2.2 W/cm2, 30 min) and urokinase or streptokinase enhanced lysis rate by an average of 25% compared with lysis with thrombolytic agents alone (p < 0.05). The enhancement was greater at higher ultrasound power outputs (2.2 W/cm2 > 1.5 W/cm2 > 1.0 W/cm2). At higher-power outputs there was no increase of temperature in the solution containing the thrombus. The extent of lysis was higher with longer ultrasound exposure time and with fresh thrombi. These data suggest that use of external ultrasound has the potential to increase both efficacy and rate of thrombolysis.

Intravenous thrombolytic therapy in myocardial infarction: an analytical review

The properties and physiological effects of three currently FDA-approved thrombolytic agents, streptokinase (SK), tissue plasminogen activator (tPA), and anisoylated plasminogen activator complex (APSAC) are reviewed. All thrombolytic agents have been shown to reduce mortality postmyocardial infarction (MI). Comparative trials have failed to demonstrate a difference between the effects of tPA, SK, and APSAC on mortality. In addition, no consistent difference between the three agents on ejection fraction (EF) has been found despite a superior reperfusion rate with tPA at 90 min. Furthermore, reinfarction and interventional procedure rates were significantly higher after thrombolytic treatment, and the incidence of total strokes was higher with tPA than SK in some comparative studies. Based on analysis of the published megatrials, SK is a more cost-effective thrombolytic agent for patients with acute MI than tPA or APSAC.

Interim analyses, stopping rules and data monitoring in clinical trials in Europe

A survey was carried out to identify the current policies of European cooperative groups with respect to interim analyses, stopping rules and data monitoring of ongoing clinical trials. The policies differ widely, from informal interim analyses distributed among all participating investigators, to planned interim analyses carried out by an independent statistician and scrutinized by a data monitoring committee. Different situations clearly call for different policies: for instance, trials of new drugs in AIDS need to be monitored more closely than trials of non-toxic adjuvant therapies for cancer. Likewise, trials with an immediately measurable end-point (such as the large-scale trials in myocardial infarction) need more intensive monitoring than those in which the outcome assessment requires prolonged follow-up. In all cases, however, it seems useful to articulate explicit data monitoring procedures in the trial protocol. In general, an independent data monitoring committee is essential to advise on the desirability to continue accrual into the trial, or to stop it early.

Lack of impact of early catheterization and fibrin specificity on bleeding complications after thrombolytic therapy. The TAMI Study Group

OBJECTIVES

The aim of this study was to assess the hemorrhagic risk associated with fibrin-specific thrombolytic therapy and invasive procedures with acute myocardial infarction.

BACKGROUND

Successful coronary artery reperfusion has important prognostic implications. Because immediate coronary angiography is the only method proved to differentiate early fibrinolytic success from failure, its use may be important for selected patients.

METHODS

Five hundred seventy-five patients were evaluated with six combined thrombolytic and catheterization strategies. Patients were randomized to intravenous urokinase alone, recombinant tissue-type plasminogen activator (rt-PA) alone, or both; simultaneously they were randomized to an immediate versus a deferred catheterization strategy. Hemorrhagic events were assessed. The correlation of hemorrhage with clinical and hemostatic variables was evaluated. Prespecified transfusion criteria were employed.

RESULTS

No difference in baseline characteristics or in hemorrhagic complications was noted among the three thrombolytic regimens. Although mild (< 250 ml) bleeding was more common in the group with immediate catheterization, no clinically significant difference among catheterization groups was seen in moderate to life-threatening hemorrhagic events. Most bleeding occurred at vascular access sites, yet severe and life-threatening hemorrhage occurred in < 1% of patients. Baseline and nadir fibrinogen levels, change in baseline fibrinogen levels and peak fibrin and fibrinogen degradation products did not correlate with bleeding risk. A clinical predisposition for bleeding was observed in women as well as older (> or = 65 years) and lighter (< or = 70 kg) patients. With prespecified transfusion criteria, only a minimal increase in blood product usage was noted with immediate catheterization.

CONCLUSIONS

Immediate cardiac catheterization can be accomplished without a clinically significant difference in bleeding risk. Fibrin specificity offers no clear advantage in reducing hemorrhagic risk. Bleeding risk correlates best with baseline patient characteristics. Finally, the amount of blood transfused can be reduced with lower transfusion criteria.

Free radical activity and left ventricular function after thrombolysis for acute infarction

BACKGROUND

Experimental data suggest that reperfusion injury involving free radicals contributes to the impairment of left ventricular function after successful thrombolysis.

METHODS

In 72 patients presenting with acute myocardial infarction, markers of free radical activity were measured before streptokinase and two hours later. Thiobarbituric acid reactive material (TBA-RM) reflects lipid peroxidation by free radicals, and the concentration of plasma total thiols (34 patients) reflects oxidative stress. Coronary arteriography was performed at 18-72 hours after thrombolysis to determine coronary patency, and left ventricular function was assessed by ventriculography and from QRS scoring of the electrocardiogram.

RESULTS

The infarct related artery was patent (Thrombolysis In Myocardial Infarction Trial grade 2 or better) in 60 (83%) and occluded in 12. In the 60 with a patent artery, the concentration of TBA-RM increased after streptokinase by (mean (SD)) 9.2 (14.0) nmol/g albumin, whereas in the 12 with an occluded artery TBA-RM decreased by 7.0 (11.3) nmol/g albumin (p < 0.01 between groups). In those with a patent artery the rise in TBA-RM associated with thrombolysis correlated with left ventricular ejection fraction (R = -0.41, p < 0.002), and with the QRS score (R = +0.38, p = 0.003). Plasma total thiol concentrations decreased by 12.7 (31.1) mumol/l in those with a patent artery, and this decrease associated with thrombolysis correlated with left ventricular ejection fraction (R = +0.39, p < 0.02) but not with the QRS score (R = -0.2, NS).

CONCLUSIONS

These findings suggest that reperfusion injury mediated by free radicals may be of clinical importance in humans.

An association between collateral blood flow and myocardial viability in patients with recent myocardial infarction

BACKGROUND

We hypothesized that successful reperfusion of an occluded infarct-related coronary artery even late after acute myocardial infarction would result in improved regional wall motion and that such improvement might be related to the presence of collateral blood flow within the infarct bed.

METHODS

We assessed regional wall motion by two-dimensional echocardiography at base line and one month after angioplasty was attempted in the occluded infarct-related artery in 43 patients who had had a myocardial infarction two days to five weeks earlier. A wall-motion score was assigned to each patient on a five-point scale (from 1 [normal function] to 5 [dyskinesia]). The percentage of the infarct bed perfused by collateral flow was assessed with myocardial contrast echocardiography.

RESULTS

In the 41 patients who had abnormal wall motion at base line, improvement in function was noted in 25 (78 percent) of the 32 in whom angioplasty was successful, as compared with only 1 (11 percent) of the 9 in whom it was unsuccessful (P < 0.001). The percentage of the infarct bed supplied by collateral flow at base line was directly correlated with wall function and inversely correlated with the wall-motion score one month after successful angioplasty (r = -0.64, P < 0.001). Among the patients in whom angioplasty was successful, the 23 in whom > 50 percent of the infarct bed was supplied by collateral flow had better wall motion (P < 0.001) and greater improvement in wall motion at one month (P = 0.004) than the 9 in whom < or = 50 percent of the bed was supplied by collateral flow. The degree of improvement in function was not influenced by the length of time between the infarction and the attempted angioplasty.

CONCLUSIONS

The myocardium remains viable for a prolonged period in many patients with acute infarction and an occluded infarct-related artery. Viability appears to be associated with the presence of collateral blood flow within the infarct bed.

Thrombolysis in acute ischemic stroke: does it work?

BACKGROUND

This article is presented to provoke further discussion regarding the use of thrombolytic drugs to treat acute ischemic stroke.

SUMMARY OF REVIEW

Overview analysis of the six randomized trials of thrombolysis in acute ischemic stroke available in the world literature shows a 20% increase in the odds of death and a 30% reduction in the odds of death or deterioration (both with wide confidence intervals, neither result significant) after thrombolytic treatment for acute ischemic stroke. Exclusion of the two trials conducted without the benefit of computed tomographic scanning shows a 37% reduction in the odds of death (95% confidence interval, 74% reduction to 40% excess) and a significant reduction of 56% in the odds of death or deterioration after thrombolytic treatment (95% confidence interval, 20-76% reduction; 2p = 0.007). Analysis of all published studies (randomized and nonrandomized) shows that there does not appear to be an excess risk of hemorrhagic transformation of the cerebral infarct or of severe edema formation.

CONCLUSIONS

We believe the present evidence is sufficiently encouraging to warrant proper testing of thrombolysis in sufficiently large and well-designed randomized clinical trials to influence clinical practice.