Overcoming thrombolytic resistance: rationale and initial clinical experience combining thrombolytic therapy and glycoprotein IIb/IIIa receptor inhibition for acute myocardial infarction

Plasminogen activator inhibitor type 1 in platelets induces thrombogenicity by increasing thrombolysis resistance under shear stress in an in-vitro flow chamber model

INTRODUCTION

Despite the proven benefits of thrombolytic therapy with tissue plasminogen activator (t-PA) for peripheral thromboembolism, perfusion failure frequently occurs, particularly in arterial circulation. We evaluated how the modification of fibrinolytic activity affects thrombus formation under flow and static conditions.

MATERIALS AND METHODS

t-PA-treated human whole-blood samples (n=6) were perfused over a microchip coated with collagen and tissue thromboplastin at different shear rates, and thrombus formation was quantified by measuring flow pressure changes. For comparison, rotational thromboelastometry (ROTEM) was used to evaluate fibrinolytic activity under static conditions.

RESULTS

At a shear rate of 240s^-1, t-PA (200-800IU/ml) concentration-dependently delayed capillary occlusion, whereas at 600s^-1, capillary occlusion was significantly faster and t-PA had limited effects, even at a supra-pharmacological concentration (800IU/ml). In contrast, 200IU/ml t-PA efficiently prevented clot formation in the ROTEM assay. The combined treatment of blood with a specific PAI-1 inhibitor (PAI-039) moderately enhanced the efficacy of t-PA, but only under flow conditions. In addition, 1:1-diluted blood samples of PAI-1-deficient (-/-) mice showed a significant delay of capillary occlusion at 240s^-1, compared with those from wild-type mice (1.55 fold; P<0.001). This delayed occlusion was reproduced in samples containing platelets from PAI-1-/- and plasma from wild type, but was not observed by the opposite combination of blood components.

CONCLUSIONS

The present results suggest that the anti-thrombotic efficacy of t-PA is sensitive to arterial shear flow, and that PAI-1 secreted from activated platelets plays an essential role in thrombolytic resistance.

Successful medical management of a left ventricular thrombus and aneurysm following failed thrombolysis in myocardial infarction

We report the case of a patient with an extensive anterior myocardial infarction complicated by left ventricular systolic dysfunction, left ventricular apical thrombus and an apical left ventricular aneurysm following failed thrombolysis. We obtained serial two-dimensional echocardiograms at short intervals in the acute phase and also during the months of recovery and follow up. The patient was successfully and exclusively medically managed.

Plasma fibrinolysis inhibitor levels in acute stroke patients with thrombolysis failure

BACKGROUND AND PURPOSE

Thrombolytics-induced recanalization fails in a significant portion of patients with ischemic stroke, which is partly due to the resistance of clots to lysis by thrombolytic agents. The pretreatment level of endogenous fibrinolysis inhibitors may affect such thrombolysis failure.

METHODS

We studied 43 stroke patients whose arterial recanalization had been evaluated by angiography, and whose blood had been obtained prior to the administration of thrombolytic agents. Plasma samples from 34 healthy volunteers were used as normal controls. Plasminogen activator inhibitor type 1 (PAI-1) and thrombin-activatable fibrinolysis inhibitor (TAFI) levels were quantified using an enzyme-linked immunosorbent assay.

RESULTS

Arteries were recanalized [Thrombolysis in Myocardial Infarction (TIMI) grade 2 or 3] in 30 patients, but not (TIMI grade 0 or 1) in the other 13. The plasma PAI-1 level was significantly higher in patients without recanalization (nonrecanalization) than in those with recanalization and in normal controls. The TAFI levels did not differ among the groups.

CONCLUSIONS

The pretreatment PAI-1 levels are increased in acute stroke patients with thrombolysis failure.

Repeat thrombolysis for acute myocardial infarction

BACKGROUND

Thrombolysis is still the first line of treatment for acute myocardial infarction in the United Kingdom. In a significant proportion of these patients thrombolytic therapy fails to restore patency of the occluded artery or is followed by early re-infarction. The best management of this group of patients is not clear although repeat doses of thrombolysis are commonly administered especially in the district general hospitals that do not have access to invasive facilities. We performed a retrospective clinical study to determine the outcome of repeat thrombolysis for acute myocardial infarction in patients with failed initial thrombolysis or early re-infarction.

METHODS

Ninety-two patients who received two or more doses of thrombolysis for acute myocardial infarction were compared with 98 contemporary similar patients who received only one dose of thrombolysis. Case notes of all patients were examined for retrospective analysis. Main outcome measures were death, heart failure and need for in-hospital revascularization.

RESULTS

Compared to the group thrombolysed once, in the rethrombolysed group there were significantly more deaths at 30 days (p=0.0016), more heart failure (with lower mean ejection fraction), more cardiac arrests as well as more frequent coronary angiography and percutaneous coronary interventions (PCIs). The incidence of haemorrhage in the two groups did not differ.

CONCLUSIONS

The need for repeat thrombolysis identifies a group of patients with a high risk of early complications. Although repeat thrombolysis is safe, these patients then need close monitoring with a view to early intervention. For such patients admitted to district general hospitals without interventional facilities early referral to a tertiary center should be considered.

The platelet-related effects of tenecteplase versus alteplase versus reteplase

Clinical studies have investigated the combination of glycoprotein (GP) IIb/IIIa inhibitors and thrombolytic agents for acute myocardial infarction. However, thrombolytic agents alone may possess direct antiplatelet properties that could affect reperfusion. Blood from 11 patients with coronary disease and five healthy subjects was incubated for 30 min with tenecteplase (4, 12, and 24 microg/ml), alteplase (1, 4, and 10 microg/ml), reteplase (1, 5, and 10 microg/ml) or control buffer. Platelet aggregation induced by 1, 20 and 50 micromol/l adenosine diphosphate (ADP), the stimulated expression of GP IIb/IIIa and P-selectin, and plasma fibrinogen levels were determined. Platelet aggregation in patients was inhibited by medium and high concentrations of alteplase when induced by 1 micromol/l ADP [1.6 +/- 0.5%, P = 0.001 and 0.9 +/- 0.2%, P = 0.002 versus 8.3 +/- 1.6% (control)] and 20 micromol/l ADP [46.9 +/- 3.9%, P = 0.001 and 46.2 +/- 4.8%, P = 0.001 versus 65.7 +/- 2.7% (control)]. High concentration tenecteplase was associated with lower aggregation by 20 micromol/l ADP (58 +/- 2.1% versus control, P = 0.033). There were no changes in GP IIb/IIIa activation or P-selectin expression in patients or healthy subjects. Platelet aggregation (1 micromol/l ADP) in healthy subjects was inhibited only by high doses of alteplase (P = 0.001). Plasma fibrinogen levels were significantly decreased after treatment with reteplase at 1 microg/ml(1.53 +/- 0.21 versus 2.65 +/- 0.31, P = .009) and 5 microg/ml(1.55 +/- 0.16 versus 2.65 +/- 0.31, P = .005). Alteplase inhibits platelet aggregation more than tenecteplase and reteplase. The attenuation of platelet aggregation by alteplase is dissociated from the expression of activated GP IIb/IIIa and P-selectin, and by fibrinogen degradation. These results suggest that alteplase exerts its antiplatelet effect independent of GP IIb/IIIa and P-selectin expressions and fibrinogen degradation. These findings may be directly relevant to the effect of alteplase on reperfusion and to future studies using combined platelet inhibitors and thrombolytic therapy.

Considerations in combination therapy: fibrinolytics plus glycoprotein IIb/IIIa receptor inhibitors in acute myocardial infarction

The combined use of a fibrinolytic and a platelet glycoprotein (GP) IIb/IIIa receptor inhibitor to target the fibrin and platelet components of occlusive thrombi offers the potential for more rapid and complete reperfusion in patients with acute myocardial infarction (MI), although there have been concerns about the safety of this combination therapy. Data from the recent GUSTO-V and the ASSENT-3 trials support the use of this regimen in that the 30-day death or nonfatal reinfarction rate (7 days) in GUSTO-V and death or in-hospital reinfarction or in-hospital refractory ischemia rate in ASSENT-3 were reduced (p = 0.001 and p = 0.0001, respectively). The need for revascularization in both these trials was also reduced significantly. There was no increased risk of intracranial hemorrhage or stroke with the combination therapy, but an increased rate of nonintracranial severe or major bleeding was observed. At present, patients aged > 75 years should not receive combination therapy. Further studies in subgroup patient populations are warranted.

Reteplase with or without Abciximab for Peripheral Arterial Occlusions: Efficacy and Adverse Events

PURPOSE

To retrospectively evaluate reteplase in thrombolysis of peripheral arterial occlusion (PAO).

MATERIALS AND METHODS

Forty limbs in 36 patients were treated with reteplase (0.5 U/h) with or without abciximab (bolus and 12-hour infusion). Twenty-four occlusions were in bypass grafts and 16 were in native arteries. Nineteen patients were treated with reteplase alone and 21 patients were treated with reteplase and abciximab. Chart review provided data from procedures and follow-up at 30 days and 6 months. Multivariable, analysis of variance, and Student t test comparisons of results and complications were performed.

RESULTS

Reteplase infusions averaged 31 hours in duration (range, 12-72 hours). The technical success rate was 80%. The clinical success rates were: immediate, 80%; 30-day, 65%; and 6-month, 45%. Major bleeding complications occurred in 20% of cases and intracranial hemorrhage occurred in 2.5%. The 6-month amputation-free survival rate was 78%. Major, minor, and lack of complications were statistically associated with mean decreases in fibrinogen levels from baseline of 72%, 46%, and 15%, respectively (P =.000013). Complications were not associated with length of infusion or use of abciximab (P =.77). Patients with grafts accounted for 89% of the major complications (eight of nine; P =.009) and had worse clinical success immediately (71%), at 30 days (50%), and at 6 months (21%; P =.002, P =.003, P =.00001).

CONCLUSIONS

There was significant fibrinogen depletion with use of reteplase for PAO. The percent decrease in fibrinogen level correlates with lack of complications and incidence of minor and major complications. Abciximab use did not increase the complication rate. Thrombolysis of grafts is associated with increased incidence of complications and worse outcomes compared with thrombolysis of native arteries.

Comparison of reperfusion regimens with or without tirofiban in ST-elevation acute myocardial infarction

There is continued debate as to whether a combined reperfusion regimen with platelet glycoprotein IIb/IIIa inhibitors provides additional benefit in optimal myocardial reperfusion of patients with a ST-elevation acute myocardial infarction (AMI). In addition, the best angiographic method to evaluate optimal myocardial reperfusion is still controversial. Patients (n = 144) with a first AMI presenting <6 hours from onset of symptoms were randomized to receive a conjunctive strategy (n = 72) with low-dose alteplase (50 mg) and tirofiban (0.4 microg/kg/min/30 minute bolus; infusion of 0.1 microg/kg/minute), or tirofiban plus stenting percutaneous coronary intervention (PCI). Control patients (n = 72) received standard strategy with either full-dose alteplase (100 mg) or stenting PCI [correction]. All patients were submitted to coronary angiographic study at 90 minutes. The primary end point was Thrombolysis In Myocardial Infarction (TIMI) grade 3 flow at 90 minutes. Secondary end points were TIMI myocardial perfusion (TMP) rates, a composite end point at 30 days (death, reinfarction, refractory ischemia, stroke, heart failure, revascularization procedures, or pulmonary edema), and bleeding or hematologic variables. The rate of TIMI 3 flow at 90 minutes for patients treated with alteplase alone was 42% compared with 64% for those who received low-dose alteplase and tirofiban. Standard stenting PCI achieved 81% of TIMI 3 flow compared with 92% when tirofiban was used. Significantly higher rates of TMP grade 3 were observed when tirofiban was used as the adjunctive treatment in both alteplase (66% vs 47%) and stenting PCI (73% vs 55%). Higher rates of the composite end point were observed in standard regimens compared with conjunctive regimens (hazard ratio 5.8, 95% confidence interval 1.27 to 26.6, p = 0.023). Regardless of reperfusion regimen, better outcomes were observed when a combination of TIMI 3 flow and TMP grade 3 was achieved. Beyond TIMI 3 flow rate, the TMP grade was an important determinant. The rates of major bleeding were similar (2.8%) for standard versus conjunctive regimens with tirofiban. Thus, tirofiban as a conjunctive therapy for lytic and stenting regimens not only improves TIMI 3 flow rates, but also the TMP3 rates, which are related to a better clinical outcome without an increase in the risk of major bleeding. This study supports the hypothesis that platelets play a key role not only in the atherothrombosis process, but also in the disturbances of microcirculation and tissue perfusion.

Facilitated percutaneous coronary intervention in acute myocardial infarction: attractive concept but difficult to prove!

Facilitated percutaneous coronary intervention (PCI) refers to a strategy of immediate PCI following the administration of pharmacological therapies in acute myocardial infarction. It has evolved primarily from the time delays (due to geography or logistics) in getting acute myocardial infarction patients to the catheterization laboratory and the associated irreversible loss of myocardial muscle that occurs as door-to-balloon time increases. Facilitated PCI provides an opportunity to start treating many of these patients before they reach the catheterization laboratory and provides an ability to open the infarct-related artery before PCI, which is associated with better outcomes for AMI patients. Pharmacological strategies before PCI include: thrombolytic therapy, glycoprotein IIb/IIIa inhibitor alone, or a combination of thrombolytic therapy plus glycoprotein IIb/IIIa inhibitor. Initial results of angiographic studies show better patency with the latter strategy but at the expense of higher bleeding event rates. Ongoing trials are evaluating different combinations of thrombolytic and glycoprotein IIb/IIIa inhibitor therapy.

Combination pharmacotherapy with reduced-dose fibrinolytic and platelet GP IIb/IIIa inhibition

Combination fibrinolytic and antiplatelet therapy regimens may provide a means of inducing rapid reperfusion in patients requiring myocardial salvage after an acute myocardial infarction (AMI). This article describes case histories and a therapeutic regimen combining reteplase (5 U + 5 U double bolus) and abciximab (0.25 mg/kg bolus + 0.125 microg/kg/min infusion to a maximum of 10 microg/min for 12 h) for AMI patients before percutaneous coronary intervention (PCI). This medication regimen was used in the Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) V clinical trial, for the medical treatment of AMI, resulting in decreased reinfarction rates with similar mortality and intracranial hemorrhage rates as compared to standard fibrinolytic therapy.

Safety and tolerability of abciximab in patients with acute miocardial infarction and failed thrombolysis

AIM

The aim of this study was to evaluate glycoprotein IIb/IIIa receptor inhibitor effectiveness in AMI patients with unsuccessful thrombolysis.

METHODS

Eighty-four patients hospitalised within 4 h of symptom onset were randomised (single blind) into two groups. Regardless of the group, placebo or GP IIb/IIIa inhibitors were administered to patients who did not present with reperfusion signs 30 min after starting thrombolysis and 30-60 min after the end of full thrombolysis in patients with pain recurrence and ST-segment elevation. Reperfusion was assessed by the creatine kinase peak occurring within 12 h, by the observation of rapid ST-segment reduction (50-70% within 1 h) in 12-lead ECG continuous monitoring, by the rapid regression of pain and by the development of early ventricular arrhythmias. Group 1 (GP IIb/IIIa) (42 patients) received treatment with GP IIb/IIIa inhibitors i.v., heparin according to TIMI-14 trial and aspirin during failed thrombolysis or after 30-60 min effective thrombolysis because of pain recurrence and ST segment elevation. Group 2 (placebo) (42 patients) received a full dose of rtpA (100 mg) and placebo either during failed thrombolysis or after 30-60 min effective thrombolysis because of pain recurrence and ST segment elevation and standard heparin treatment and aspirin.

RESULTS

Thirty-nine group 1 (GP IIb/IIIa) patients showed rapid reperfusion (6 +/- 4 min) after abciximab treatment; 22 patients received rtpA 65 mg and 20 patients received rtpA 100 mg and subsequent GP IIb/IIIa inhibitor treatment. Coronarography, performed after 3-12 h, showed patency of infarct related artery (IRA) in 39 patients whose clinical picture was suggestive of rapid reperfusion during administration of a bolus of GP IIb/IIIa inhibitors. No group 2 (placebo) patients showed reperfusion and they were submitted to rescue PTCA.

SIDE EFFECTS

Four cases in the GP IIb/IIIa group and two cases in placebo group (major bleeding). Patients receiving GIIb/IIIa inhibitors showed a reduced incidence of stent treatment (ns) and a significant reduction of events (angina) within 30 days of treatment.

CONCLUSION

Our data suggest the possibility of using IIb/IIIa glycoprotein receptor inhibitors in patients with AMI and failed thrombolysis. The increased risk of bleeding was acceptable. The most important results were the safety of this combination.

Power thrombectomy in acute ischemic coronary syndromes

Intracoronary thrombi are commonly found in patients with acute coronary syndromes. A large thrombus burden or a platelet-rich thrombus frequently resists pharmacologic therapy ("thrombolytic ceiling"). In such cases restoration of adequate antegrade coronary flow necessitates application of a mechanical force. Power thrombectomy is a revascularization strategy incorporating a mechanical device for removal of occlusive coronary thrombi in conjunction with or following administration of either platelet glycoprotein IIb/IIIa receptor inhibitors or thrombolytic agents, or both. Mechanical devices for power thrombectomy include ultrasound sonication, rheolytic thrombectomy (Angiojet), laser, transluminal extraction catheter, aspiration catheter, and to a limited extent, balloon angioplasty. In acute coronary syndromes the strategy of power thrombectomy aims to achieve the clinical advantages of more nearly complete vessel patency, improved antegrade flow, and enhanced preservation of myocardial tissue.

Increase in plasma matrix metalloproteinase-9 in acute stroke patients with thrombolysis failure

BACKGROUND AND PURPOSE

Platelet-rich thrombi are resistant to thrombolytics. Matrix metalloproteinases (MMPs) may be involved in platelet aggregation and contribute to thrombolysis failure in stroke patients.

METHODS

Plasma samples from 23 stroke patients who had received thrombolytics and from 47 healthy volunteers were examined for MMP-2 and MMP-9 by both enzyme-linked immunosorbent assays and zymography.

RESULTS

The arteries were recanalized in 15 patients but not in the other 8. The MMP-9 plasma level was significantly higher in patients whose arteries were not recanalized.

CONCLUSIONS

MMP-9 may be associated with the formation of a thrombolytics-resistant thrombus.

Combination reperfusion therapy with eptifibatide and reduced-dose tenecteplase for ST-elevation myocardial infarction: results of the integrilin and tenecteplase in acute myocardial infarction (INTEGRITI) Phase II Angiographic Trial

OBJECTIVES

The goal of this study was to evaluate combinations of eptifibatide with reduced-dose tenecteplase (TNK) in ST-elevation myocardial infarction (STEMI).

BACKGROUND

Glycoprotein IIb/IIIa inhibitors enhance thrombolysis. The role of combination therapy in clinical practice remains to be established.

METHODS

Patients (n = 438) with STEMI <6 h were enrolled. In dose-finding, 189 patients were randomized to different combinations of double-bolus eptifibatide and reduced-dose TNK. In dose-confirmation, 249 patients were randomized 1:1 to eptifibatide 180 microg/kg bolus, 2 microg/kg/min infusion, and 180 microg/kg bolus 10 min later (180/2/180) plus half-dose TNK (0.27 mg/kg) or standard-dose (0.53 mg/kg) TNK monotherapy. All patients received aspirin and unfractionated heparin (60 U/kg bolus; infusion 7 U/kg/h [combination], 12 U/kg/h [monotherapy]). The primary end point was Thrombolysis In Myocardial Infarction (TIMI) grade 3 epicardial flow at 60 min.

RESULTS

In dose-finding, TIMI grade 3 flow rates were similar across groups (64% to 68%). Arterial patency was highest for eptifibatide 180/2/180 plus half-dose TNK (96%, p = 0.02 vs. eptifibatide 180/2/90 plus half-dose TNK). In dose-confirmation, this combination, compared with TNK monotherapy, tended to achieve more TIMI 3 flow (59% vs. 49%, p = 0.15), arterial patency (85% vs. 77%, p = 0.17), and ST-segment resolution (median 71% vs. 61%, p = 0.08) but was associated with more major hemorrhage (7.6% vs. 2.5%, p = 0.14) and transfusions (13.4% vs. 4.2%, p = 0.02). Intracranial hemorrhage occurred in 1.0%, 0.6%, and 1.7% of patients treated with any combination, eptifibatide 180/2/180 and half-dose TNK, and TNK monotherapy, respectively.

CONCLUSIONS

Double-bolus eptifibatide (180/2/180) plus half-dose TNK tended to improve angiographic flow and ST-segment resolution compared with TNK monotherapy but was associated with more transfusions and non-cerebral bleeding. Further study is needed before this combination can be recommended for general use.

Facilitated primary percutaneous transluminal coronary angioplasty for acute ST segment elevation myocardial infarction: rationale for reuniting pharmacologic and mechanical revascularization strategies

The primary goal of therapy for acute ST segment elevation myocardial infarction is to preserve left ventricular systolic function and to decrease mortality by achieving rapid, complete, and sustained restoration of blood flow in the infarct-related artery. Early studies assessing the safety and efficacy of combining full-dose thrombolytic therapy with primary percutaneous transluminal coronary angioplasty (PTCA) were disappointing due to an increased incidence of abrupt closure, reinfarction, emergent coronary bypass surgery, and mortality. The observation that the presence of normal coronary blood flow at the time of primary PTCA is an independent predictor of survival coupled with interest in the patency of the downstream microvasculature has prompted investigators to revisit the concept of combining pharmacologic and mechanical strategies. The adjunctive use of pharmacologic therapy with mechanical reperfusion has been coined facilitated primary PTCA and involves the use of reduced-dose thrombolytics, platelet glycoprotein IIb/IIIa inhibitors, or both. The primary goal is to achieve pharmacologic reperfusion before performing definitive mechanical reperfusion. While the preliminary data presented is promising, we must await the results of ongoing large, randomized trials that have been specifically designed to address this question.

Snare retrieval of intracranial thrombus in patients with acute stroke

Intravenous or intraarterial thrombolysis of intracranial emboli is becoming an accepted clinical treatment modality for acute ischemic stroke, but not all emboli respond to the lytic drug regimens available today. If drug therapy fails, mechanical retrieval seems warranted. Four patients whose condition was resistant to intravenous and intraarterial thrombolytic drug treatment underwent at least partial clot removal with use of a snare, and almost immediate clinical improvement was noted. A fifth patient's clot was removed before lytic drugs were administered. All five patients, who presented with a sudden onset of stroke, were evaluated by arterial angiography; then, after a failed trial of intraarterial fibrinolytic drugs, they were treated by passing a 2- or 4-mm snare through a microcatheter. The snare wire was guided around the thrombus, gently brought back toward the microcatheter-but not into it-and the entire microcatheter and snare assembly was then removed. In four of the five cases, follow-up angiography performed immediately after the retrieval showed wider distal branches than normal. Follow-up computed tomography results were abnormal in all cases, showing hyperdense material in the territory that was previously ischemic. This hyperdensity subsided within 48 hours in all but one patient who developed small parenchymal hemorrhages; however, he remained asymptomatic. The snare device offers an additional or alternative therapy until completely effective thrombolytic agents become available. Although use of a snare is not ideal, device improvements should make the retrieval less technically challenging and more effective. There is a need for improved mechanical extraction devices, especially in light of the patient improvement that occurred. This experience also suggests that immediate removal of a mature clot could reduce the total time of brain ischemia more quickly than administration of thrombolytic drugs.

Plasminogen activators in inflammation and sepsis

Mortality of severe sepsis remains at 40% to 50%. Intensive efforts over the past two decades have only marginally improved outcome. Improving outcome in sepsis depends on understanding its pathophysiology, which involves triggers, responses of the organism, and dysfunction. Stress, injury, or infection trigger host responses, including local and systemic orchestrated mechanisms. Dysfunction and outcome depend on both trigger and response. Blood coagulation, inflammation, immunity, and fibrinolysis are critical components of the organism's responses. Understanding their role in sepsis pathophysiology is the key to effective treatment. Relevant studies were identified by a systematic literature search, complemented by manual search of individual citations. Using PubMed, 'sepsis' yields more than 62,000 references, 'plasminogen activators' more than 21,000. The selection of citations was guided by preference for reviews that expand important threads of argumentation. Single original studies were included when relevant to critical points. This analytical review describes the essential elements of pathophysiology and the current status of sepsis treatment. Based on this context, an emerging therapeutic option will be discussed: plasminogen activators.

Pharmacotherapeutic options for the management of myocardial infarction

The pharmacological treatment of acute coronary syndrome (ACS), including unstable angina, non-ST- and ST-segment elevation myocardial infarction (MI) is dynamic and continues to evolve. Expert guidelines based on the results of clinical trials for the management of different types of ACS have been published. In both ST-segment elevation and non-ST-segment elevation MI, aspirin/clopidogrel, heparin/low molecular weight heparin/direct thrombin inhibitors, beta-blockers and angiotensin converting enzyme inhibitors are part of the routine regimens. In patients with ST-segment elevation MI, eligibility for thrombolytic therapy needs to be determined and utilised as soon as possible. In patients with non-ST-segment elevation MI, the risks of thrombolytic therapy outweigh the benefits. The use of glycoprotein IIb/IIIa inhibitors has become increasingly important. The use of antihyperlipidaemic agents for the prevention of secondary events in both types of patients continue to be essential and the early aggressive use of lipid-lowering therapy also plays a role in improving endothelial function and stabilising atherosclerotic plaques.

Platelet aggregation inhibitors for use in peripheral vascular interventions: what can we learn from the experience in the coronary arteries?

During the last decade, an enormous amount of information has been gathered about the function of the platelet and its impact on percutaneous vascular interventions. With the discovery of the GP IIb/IIIa receptor, which is responsible for platelet aggregation, new drug antagonists have been developed to prevent platelet aggregation that may result in arterial thrombosis or platelet microembolization. These drugs include the three GP IIb/IIIa receptor antagonists approved by the Food and Drug Administration: abciximab (ReoPro), eptifibatide (Integrilin), and tirofiban (Aggrastat). These drugs have been used in several large studies to improve the outcome of coronary interventions and in conjunction with plasminogen activators to accelerate thrombolysis. In addition, because no oral GP IIb/IIIa inhibitor exists, other oral regimens have been developed with use of the thienopyridines, ticlopidine (Ticlid) and clopidogrel (Plavix), in combination with aspirin to prevent platelet aggregation and thrombosis. Because the majority of investigations have been performed in patients undergoing coronary interventions, knowledge of these data is necessary to attempt to translate the use of these antiplatelet drugs to peripheral vascular interventions. The goal of this article is to review the use of these agents in the percutaneous treatment of coronary artery disease and give insight to their potential utility in noncoronary interventions.

New recommendations from the 1999 American College of Cardiology/American Heart Association acute myocardial infarction guidelines

OBJECTIVE

To review literature relating to significant changes in drug therapy recommendations in the 1999 American College of Cardiology (ACC)/American Heart Association (AHA) guidelines for treating patients with acute myocardial infarction (AMI).

DATA SOURCES

1999 ACC/AHA AMI guidelines, English-language clinical trials, reviews, and editorials researching the role of drug therapy and primary angioplasty for AMI that were referenced in the guidelines were included. Additional data published in 2000 or unpublished were also included if relevant to interpretation of the guidelines.

STUDY SELECTION

The articles selected influence AMI treatment recommendations.

DATA SYNTHESIS

Many clinicians and health systems use the ACC/AHA AMI guidelines to develop treatment plans for AMI patients. This review highlights important changes in AMI drug therapy recommendations by reviewing the results of recent clinical trials. Insights into evolving drug therapy strategies that may impact future guideline development are also described.

CONCLUSIONS

Several changes in drug therapy recommendations were included in the 1999 AMI ACC/AHA guidelines. There is emphasis on administering fibrin-specific thrombolytics secondary to enhanced efficacy. Selection between fibrin-specific agents is unclear at this time. Low response rates to thrombolytics have been noted in the elderly, women, patients with heart failure, and those showing left bundle-branch block on the electrocardiogram. These patient groups should be targeted for improved utilization programs. The use of glycoprotein (GP) IIb/IIIa receptor inhibitors in non-ST-segment elevation MI was emphasized. Small trials combining reduced doses of thrombolytics with GP IIb/IIIa receptor inhibitors have shown promise by increasing reperfusion rates without increasing bleeding risk, but firm conclusions cannot be made until the results of larger trials are known. Primary percutaneous coronary intervention (PCI) trials suggest lower mortality rates for primary PCI when compared with thrombolysis alone. However, primary PCI, including coronary angioplasty, is only available at approximately 13% of US hospitals, making thrombolysis the preferred strategy for most patients. Clopidogrel has supplanted ticlopidine as the recommended antiplatelet agent for patients with aspirin allergy or intolerance following reports of a better safety profile. The recommended dose of unfractionated heparin is lower than previously recommended, necessitating a separate nomogram for patients with acute coronary syndromes. Routine use of warfarin, either alone or in combination with aspirin, is not supported by clinical trials; however, warfarin remains a choice for antithrombotic therapy in patients intolerant to aspirin. Beta-adrenergic receptor blockers continue to be recommended, and emphasis is placed on improving rates of early administration (during hospitalization), even in patients with moderate left ventricular dysfunction. New recommendations for drug treatment of post-AMI patients with low high-density lipoprotein cholesterol and/or elevated triglycerides are included, with either niacin or gemfibrozil recommended as an option. Supplementary antioxidants are not recommended for either primary or secondary prevention of AMI, with new data demonstrating lack of efficacy vitamin E in primary prevention. Estrogen replacement therapy or hormonal replacement therapy should not be initiated solely for prevention of cardiovascular disease, but can be continued in cardiovascular patients already taking long-term therapy for other reasons. Bupropion has been added as a new treatment option for smoking cessation. As drug therapy continues to evolve in treating AMI, more frequent updates of therapy guidelines will be necessary.

Exploring the issues of appropriate dosing in the treatment of acute myocardial infarction: potential benefits of bolus fibrinolytic agents

The Institute of Medicine report on the frequency and consequences of medical errors in clinical practice has stimulated physicians to evaluate current practice and means of improving medical care. In the treatment of patients with acute myocardial infarction, previous studies have found that dosing of fibrinolytic therapy is closely related to outcomes, with too low a dose associated with lower rates of infarct-related artery patency and higher doses associated with increased intracranial hemorrhage. Thus there is a narrow "therapeutic window" for fibrinolytic-antithrombotic regimens, and the potential for adverse outcomes is high if incorrect doses are administered. The first demonstration of this concept came from the GUSTO-I trial, in which 13.5% of patients treated with streptokinase and 11.5% of patients treated with tissue plasminogen activator (t-PA) had a dosing regimen that deviated from the protocol, that is, an incorrect total dose or infusion length. In patients with protocol deviations, 24-hour and 30-day mortality rates were significantly higher compared with those of patients with per-protocol dosing: for t-PA, patients who received incorrect dosing had a 30-day mortality rate of 7.7% versus 5.5% for patients who received correct t-PA dosing (P <.001), with similar findings for streptokinase. More recent data from the InTIME-II trial have shown that the use of a bolus fibrinolytic agent significantly increases the percentage of patients who receive complete and optimally dosed fibrinolysis. Thus use of the simpler bolus fibrinolytic agents may reduce medication errors and thus may optimize clinical outcomes.

Reducing medication errors: potential benefits of bolus thrombolytic agents

A recent Institute of Medicine report highlighted the high incidence of medical errors in clinical practice, and the important fact that errors are associated with increased mortality. The administration of thrombolytic therapy for acute myocardial infarction is a particularly high-risk situation for emergency physicians. The combination of extreme time pressure with a narrow "therapeutic window" increases the potential for adverse outcomes due to dosing errors. Numerous trials have found that the dose of thrombolytic therapy is closely related to outcomes, with too low a dose associated with lower rates of infarct-related artery patency and higher doses associated with increased bleeding and intracranial hemorrhage. In the GUSTO-I trial, 13.5% of patients treated with streptokinase and 11.5% of patients treated with tissue plasminogen activator (t-PA) had a medication error (i.e., incorrect dose or infusion length). Most importantly, 30-day mortality was significantly higher in patients with medication errors: for t-PA dosing errors mortality was 7.7% vs 5.5% for patients who received the correct t-PA dose (p < 0.001), with similar findings for streptokinase. More recent data from the InTIME2 trial and other studies showed that use of a bolus thrombolytic agent reduced the rate of medication errors. Thus, use of the simpler bolus thrombolytic agents may reduce emergency department medication errors, and thus improve overall clinical outcome.

Multimodality reperfusion therapy for acute myocardial infarction

With the strong and direct relation between early reperfusion in acute myocardial infarction (AMI) and improved clinical outcomes, attention has focused on new means of improving rates of reperfusion and accelerating every stage of AMI evaluation and management, from the onset of symptoms of myocardial infarction to the achievement of reperfusion. Critical pathways to streamline the evaluation and management of AMI have cut minutes and even hours off in-hospital treatment times for patients with AMI; public health initiatives focus on educational efforts to shorten time to hospital arrival. The latest advance in fibrinolytic therapy is the availability of bolus fibrinolytic agents with safety and efficacy in large phase III trials comparable to accelerated intravenous infusion regimens. Faster and simpler fibrinolytic regimens may shorten door-to-needle time, reduce medication errors, and facilitate prehospital thrombolysis. Bolus fibrinolytic agents are being evaluated for use in combination with other interventions to open occluded coronary arteries, including acute percutaneous coronary intervention, the glycoprotein IIb/IIIa platelet inhibitors, or both. The goal of this "multimodality" approach to AMI management is to minimize time to reperfusion and maximize the percentage of patients who achieve complete arterial patency and myocardial perfusion without bleeding complications.

Triple therapy for acute myocardial infarction: combining fibrinolysis, platelet IIb/IIIa inhibition, and percutaneous coronary intervention

Reperfusion for acute myocardial infarction (MI) has generally been approached in 1 of 2 ways-fibrinolysis or primary angioplasty. Although fibrinolysis is widely available and has been shown to reduce mortality and improve left ventricular function, its disadvantages include hemorrhage, failure to reperfuse in up to 40% of patients, and early reocclusion in up to 10% of patients. Alternatively, primary angioplasty offers the advantages of anatomic definition, the potential for higher rates of reperfusion, and a lower rate of intracranial hemorrhage. Recently, a better understanding of platelet physiology and its inhibition, and advances in mechanical revascularization with stents have led to combined approaches (fibrinolytic agents, glycoprotein IIb/IIIa inhibitors, and percutaneous coronary interventions [PCI]). Faciliated PCI, the use of planned PCI after pharmacologic reperfusion therapy, has the best potential to fuse the best aspects of thrombolysis and primary angioplasty. This article reviews recent advances and trials studying use of these combinations.

Thrombolysis medication errors: benefits of bolus thrombolytic agents

A recent report has highlighted the high incidence of medical errors in clinical practice and the important fact that errors are associated with increased mortality. This issue is now being examined closely in the field of thrombolytic therapy for acute myocardial infarction. Numerous trials have found that the dose of the thrombolytic agent is closely related to outcome, with too low a dose associated with lower rates of infarct-related artery patency and higher doses associated with increased bleeding and intracranial hemorrhage. Thus, the "therapeutic window" for thrombolytic therapy is small, and the potential for adverse outcome from dosing errors is high. In the Global Use of Strategies To Open occluded arteries (GUSTO)-I trial, 13.5% of patients treated with streptokinase and 11.5% of patients treated with tissue plasminogen activator (t-PA) were subjected to a medication error (e.g., incorrect dose or infusion length). Most importantly, 30-day mortality was significantly higher in patients with medication errors: For t-PA dosing errors, mortality was 7.7% versus 5.5% for patients who received the correct t-PA dose (p<0.001); findings were similar for streptokinase. More recent data from the Intravenous n-PA for Treatment of Infarcting Myocardium Early (InTIME)-II trial and other studies showed that use of a bolus thrombolytic agent reduced the rate of medication errors. Thus, use of the simpler bolus thrombolytic agents may improve overall clinical outcome.