Factors influencing reocclusion after coronary thrombolysis for acute myocardial infarction

Chronic antithrombotic therapy in post-myocardial infarction patients

Because 1.1 million myocardial infarctions occur in the United States alone each year, and 450,000 of them are recurrent infarctions, which carry an inherently greater risk of death and disability than first events, the importance of secondary prevention strategies that can be implemented widely is unparalleled in health care. Antithrombotic therapies, both antiplatelet and anticoagulant, have become the mainstays of these strategies. This article covers the use of chronic antiplatelet and anticoagulation agents after myocardial infarction. It does not include the management of these patients in the acute phase.

Enoxaparin versus unfractionated heparin with fibrinolysis for ST-elevation myocardial infarction

BACKGROUND

Unfractionated heparin is often used as adjunctive therapy with fibrinolysis in patients with ST-elevation myocardial infarction. We compared a low-molecular-weight heparin, enoxaparin, with unfractionated heparin for this purpose.

METHODS

We randomly assigned 20,506 patients with ST-elevation myocardial infarction who were scheduled to undergo fibrinolysis to receive enoxaparin throughout the index hospitalization or weight-based unfractionated heparin for at least 48 hours. The primary efficacy end point was death or nonfatal recurrent myocardial infarction through 30 days.

RESULTS

The primary end point occurred in 12.0 percent of patients in the unfractionated heparin group and 9.9 percent of those in the enoxaparin group (17 percent reduction in relative risk, P<0.001). Nonfatal reinfarction occurred in 4.5 percent of the patients receiving unfractionated heparin and 3.0 percent of those receiving enoxaparin (33 percent reduction in relative risk, P<0.001); 7.5 percent of patients given unfractionated heparin died, as did 6.9 percent of those given enoxaparin (P=0.11). The composite of death, nonfatal reinfarction, or urgent revascularization occurred in 14.5 percent of patients given unfractionated heparin and 11.7 percent of those given enoxaparin (P<0.001); major bleeding occurred in 1.4 percent and 2.1 percent, respectively (P<0.001). The composite of death, nonfatal reinfarction, or nonfatal intracranial hemorrhage (a measure of net clinical benefit) occurred in 12.2 percent of patients given unfractionated heparin and 10.1 percent of those given enoxaparin (P<0.001).

CONCLUSIONS

In patients receiving fibrinolysis for ST-elevation myocardial infarction, treatment with enoxaparin throughout the index hospitalization is superior to treatment with unfractionated heparin for 48 hours but is associated with an increase in major bleeding episodes. These findings should be interpreted in the context of net clinical benefit. (ClinicalTrials.gov number, NCT00077792.).

Chronic Antithrombotic Therapy in Post–Myocardial Infarction Patients

Recent advances in the acute treatment of myocardial infarction (MI) have allowed more to survive the initial event in coronary artery disease. Increasing importance has been placed on secondary-prevention strategies, with more attention directed toward an optimal therapeutic regimen for post-MI patients. When it comes to the subpopulation of the elderly who have had an MI, however, current practice relies less on population-specific evidence and more on extrapolation of current data. This article reviews the pathogenesis of coronary heart disease and MI, and highlights recent major trials that have explored antiplatelet and anticoagulant medications in the chronic treatment of the post-MI population. Special consideration is given to the geriatric community and its unique challenge regarding chronic antithrombotic therapy.

Adding clopidogrel to aspirin improves outcome in ST-elevation myocardial infarction patients receiving fibrinolytic therapy

Acute coronary syndromes result from the rupture of an atherosclerotic plaque with superimposed thrombosis. In an ST-elevation myocardial infarction, the thrombus occludes the coronary vessel, leading to an abrupt decrease in myocardial perfusion. The focus of initial management is the timely restoration of flow in the infarct-related artery via fibrinolytic therapy or percutaneous coronary intervention. Adjunctive therapy aimed at inhibition of platelets and the coagulation cascade is critical to establish and maintain vessel patency. Clopidogrel, an oral antiplatelet agent, has recently been shown to offer significant clinical benefit in STEMI (ST-elevation myocardial infarction) and is a welcome addition to standard fibrinolytic therapy.

High-grade infarct-related stenosis after successful thrombolysis: strong predictor of reocclusion, but not of clinical reinfarction

BACKGROUND

After successful thrombolysis, a high-grade stenosis at 24-hour angiography is strongly predictive of reocclusion and is often believed to result in high reinfarction rates. However, routine angioplasty did not reduce death or reinfarction in past trials. Systematic angiographic follow-up shows that reocclusion often occurs without clinical reinfarction. This study investigates whether the increased risk for reocclusion associated with a high-grade lesion translates into impaired clinical outcome.

METHODS

In the ischemia-guided Antithrombotics in the Prevention of Reocclusion in COronary Thrombolysis (APRICOT-1) trial, 240 patients with ST-elevation MI who had an open infarct artery 24 hours after thrombolysis had 3-month repeat angiography to assess reocclusion, with clinical follow-up at 3 months and 3 years.

RESULTS

On the basis of the optimal discriminative stenosis severity, the reocclusion rate was 40% (47/118) in patients with a high-grade residual stenosis and 16% (20/122) in patients with a low-medium-grade lesion (risk ratio [RR], 2.43; 95% CI, 1.54-3.84; P <.01). Three-month death and reinfarction rates did not differ: 6% (7/118) versus 9% (11/122; RR, 0.66; 95% CI, 0.26-1.64; P = not significant). Systematic angiographic follow-up revealed that reocclusion of a high-grade lesion occurred in the absence of clinical reinfarction in 85% (40/47) of patients, as compared with 45% (9/20) in patients with a low-medium-grade stenosis (RR, 1.89; 95% CI, 1.15-3.12; P <.01). Despite an independent association with reocclusion, a high-grade stenosis was not predictive of either short- or long-term death and reinfarction.

CONCLUSIONS

After successful thrombolysis and adopting an ischemia-guided revascularization strategy, patients with a high-grade stenosis experience death/reinfarction rates similar to that of patients with a low-medium-grade lesion. This is true despite a 2- to 3-fold higher risk for reocclusion. The finding that reocclusion of a high-grade lesion often occurs without clinical reinfarction explains the absence of a relationship between a severe stenosis and death/reinfarction. Appreciation of these observations may contribute to an optimal design of a future randomized trial to re-evaluate the impact of a routine invasive strategy.

Routine invasive strategy within 24 hours of thrombolysis versus ischaemia-guided conservative approach for acute myocardial infarction with ST-segment elevation (GRACIA-1): a randomised controlled trial

BACKGROUND

In patients with ST-segment elevated myocardial infarction (STEMI), early post-thrombolysis routine angioplasty has been discouraged because of its association with high incidence of events. The GRACIA-1 trial was designed to reassess the benefits of an early post-thrombolysis interventional approach in the era of stents and new antiplatelet agents.

METHODS

500 patients with thrombolysed STEMI (with recombinant tissue plasminogen activator) were randomly assigned to angiography and intervention if indicated within 24 h of thrombolysis, or to an ischaemia-guided conservative approach. The primary endpoint was the combined rate of death, reinfarction, or revascularisation at 12 months. Analysis was by intention to treat.

FINDINGS

Invasive treatment included stenting of the culprit artery in 80% (199 of 248) patients, bypass surgery in six (2%), non-culprit artery stenting in three, and no intervention in 40 (16%). Predischarge revascularisation was needed in 51 of 252 patients in the conservative group. By comparison with patients receiving conservative treatment, by 1 year, patients in the invasive group had lower frequency of primary endpoint (23 [9%] vs 51 [21%], risk ratio 0.44 [95% CI 0.28-0.70], p=0.0008), and they tended to have reduced rate of death or reinfarction (7% vs 12%, 0.59 [0.33-1.05], p=0.07). Index time in hospital was shorter in the invasive group, with no differences in major bleeding or vascular complications. At 30 days both groups had a similar incidence of cardiac events. In-hospital incidence of revascularisation induced by spontaneous recurrence of ischaemia was higher in patients in the conservative group than in those in the invasive group.

INTERPRETATION

In patients with STEMI, early post-thrombolysis catheterisation and appropriate intervention is safe and might be preferable to a conservative strategy since it reduces the need for unplanned in-hospital revascularisation, and improves 1-year clinical outcome.

Incidence, determinants, and clinical course of reinfarction in-hospital after index acute myocardial infarction (results from the pooled data of the maximal individual therapy in acute myocardial infarction [mitra], and the myocardial infarction registry [MIR])

There are few data about the incidence, determinants, and clinical course of in-hospital repeat acute myocardial infarction (RE-AMI) after an index AMI. From June 1994 to June 1998, 22,613 patients with AMI as an index event were registered by the Maximal Individual Therapy in Acute Myocardial Infarction (MITRA) and Myocardial Infarction Registries (MIR). Of these, 1,071 (4.7%) had a RE-AMI. For the index event, 9,143 patients (40.5%) were treated with thrombolysis, 1,707 (7.5%) with primary angioplasty, and 443 (2.0%) with a combination of both. Multivariate analysis showed that previous AMI (odds ratio [OR] 1.59; 95% confidence intervals [CI] 1.35 to 1.86), age >70 years (OR 1.57; 95% CI 1.36 to 1.81), diagnostic first electrocardiogram (OR 1.37; 95% CI 1.19 to 1.59), and female gender (OR 1.14; 95% CI 1.05 to 1.32) were independently associated with a higher incidence of RE-AMI. The incidence of RE-AMI was higher when patients received thrombolysis (OR 1.36; 95% CI 1.15 to 1.61), and it was lower when they underwent primary angioplasty (OR 0.74; 95% CI 0.53 to 1.03) or received beta blockers (OR 0.84; 95% CI 0.72 to 0.97). Patients with RE-AMI had higher hospital mortality compared with those without RE-AMI (OR 4.35; 95% CI 3.83 to 4.95). Multivariate logistic regression analysis showed an independent association of RE-AMI with in-hospital death (OR 6.60; 95% CI 5.61 to 7.70), repeat revascularization (OR 2.91; 95% CI 2.42 to 3.50), low workload capacity on the bicycle ergometry test (OR 2.17; 95% CI 1.71 to 2.76), and ejection fraction <40% (OR 1.72; 95% CI 1.38 to 2.14) at discharge. Thus, RE-AMI occurs in 4.7% of patients after an AMI. Previous AMI, age >70 years, diagnostic first electrocardiogram, and female gender are independent determinants for RE-AMI. Thrombolysis is associated with a higher and beta blockers with a lower incidence of RE-AMI. Once a RE-AMI occurs, it is a strong predictor of in-hospital mortality and morbidity.

Long-term arterial patency after coronary reperfusion

Coronary reocclusion is a frequent event after reperfusion and may be responsible for the deterioration of left ventricular function. It may occur early as well as in the chronic phase after hospital discharge. Current, evidence based, strategies to prevent reocclusion include antiplatelet and anticoagulant agents as well as the use of intracoronary stenting in those patients who are treated by PTCA. The combination of aspirin and ticlopidine adds on the results of stenting. Further treatments are currently investigated and may significantly improve the long-term coronary patency.

Thrombin: Structure, Biochemistry, Measurement, and Status in Clinical Medicine

Thrombin remains a molecule of great interest to scientists and clinicians alike because of its important role in hemostasis, thrombosis, inflammation and vascular remodeling. Yet one of the great challenges has been the inhibition of thrombin generation to a degree that minimizes intravascular thrombosis while preserving physiologic hemostasis. It has become increasingly clear that high levels of anticoagulation with either direct or indirect thrombin antagonists are not beneficial and, in fact, are quite detrimental. Despite the overwhelming shift of interest toward the platelet in clinical trials of acute coronary syndromes, much can be gained through further investigation of coagulation processes responsible for thrombin generation and activity.

Thrombosis and cardiovascular disease

The early stages of venous thrombosis originate at selective sites of reduced blood flow in the apices of venous valves. Stagnation of venous flow results in the formation of a platelet-fibrin thrombus, which serves as the nidus for thrombus propagation. Stasis alone, however, does not result in thrombosis necessarily. The presence of activated coagulation factors is essential. The major predisposing factors to venous thrombus are activation of blood coagulation and venous stasis. In contrast to venous thrombus formation, vascular abnormalities are the most important causative factor in arterial thrombosis.

Abnormal coronary flow in infarct arteries 1 year after myocardial infarction is predicted at 4 weeks by corrected Thrombolysis in Myocardial Infarction (TIMI) frame count and stenosis severity

Because 24% to 30% of patent infarct-related arteries occlude in the year following thrombolytic therapy for acute myocardial infarction, angiographic factors including corrected Thrombolysis in Myocardial Infarction (TIMI) frame count which may predict abnormal infarct-artery flow, require definition. We examined changes in coronary flow and infarct-artery lesion severity by computerized quantitative angiography over 1 year in 154 patients with a patent infarct-related artery 4 weeks after myocardial infarction. These patients were randomized to receive either ongoing daily therapy of 50 mg aspirin and 400 mg dipyridamole, or placebo. All angiograms were interpreted blind in our core angiographic laboratory. Infarct-artery flow, assessed by corrected TIMI frame counts, was normal (< or = 27) in 46% and 45% of patients at 4 weeks and 1 year, respectively. At 4 weeks, patients with corrected TIMI frame counts < or = 27 had higher ejection fractions (60+/-11% vs 56+/-12%; p = 0.04) than those with corrected TIMI frame counts >27. On multivariate analysis, corrected TIMI frame count and stenosis severity were predictive of late abnormal infarct-artery flow (TIMI 0 to 2 flow, both p <0.01). Only stenosis severity at 4 weeks predicted reocclusion at 1 year (p <0.0001). Aspirin and dipyridamole had no effect on flow or reocclusion. Thus, corrected TIMI frame count and stenosis severity at 4 weeks was highly correlated with infarct-artery flow at 1 year.

Continuous ST-segment monitoring during coronary angioplasty using orthogonal ECG leads

In order to characterize ST-segment shifts during transient coronary artery occlusion, 24 patients with single-vessel disease were continuously monitored during percutaneous transluminal coronary angioplasty by use of a computerized orthogonal lead system. Changes of ST-segment (J + 60 ms) in leads X, Y, and Z and of the ST vector magnitude were analyzed by using 20 microV as a threshold for significant ST-segment shift. The sensitivity and magnitude of this shift were compared among the left anterior descending, right coronary, and circumflex artery groups (11, 8, and 5 patients, respectively) during balloon inflation. Significant ST-segment shifts were seen in 22 patients (92%) in ST-VM, Y, and Z leads and all patients in lead X (100%). There was no significant difference in sensitivity of either the ST vector magnitude or the most sensitive lead for occlusion detection among the three groups. There was a significantly greater magnitude of ST shift during left anterior descending artery occlusion than during right coronary artery and circumflex artery occlusions in ST-VM. Analysis of the direction of ST shifts in the X, Y, and Z leads showed a characteristic pattern, which could distinguish among the three coronary groups in 21 patients (88%). The presence of collaterals was significantly associated with ST-segment depression in leads oriented toward ischemia (3 of 6 patients) as compared with ST-segment elevation in the absence of collaterals (all of 15 patients), P > .01. It is concluded that ST-segment shift in the orthogonal leads is a reliable marker for myocardial ischemia. It is equally sensitive to occlusion of each of the three major coronary arteries and can thus identify the occluded coronary. An ST-segment depression instead of an elevation was related to the presence of collaterals, which may reflect a lesser degree of ischemia.

Vertebrobasilar thrombosis: diagnosis, management, and the use of intra-arterial thrombolytics

OBJECTIVES

To review the diagnosis and management of vertebrobasilar thrombosis and to discuss the use of thrombolytics in the treatment of this disease.

DATA SOURCES

Selected references discussing epidemiology, anatomy, pathophysiology, diagnosis, therapy, and rehabilitation of vertebrobasilar occlusive disease.

STUDY SELECTION

Studies addressing acute intervention and outcome in the therapy of vertebrobasilar thrombosis were reviewed.

DATA EXTRACTION

Only those studies with angiographic documentation of arterial thrombosis and, in the case of thrombolysis, recanalization, were considered valid.

DATA SYNTHESIS

Thrombosis of the vertebrobasilar system is a highly fatal disease and should be treated as a neurologic emergency. The key to effective management depends on early recognition of the symptom complex and a thorough understanding of the anatomy and pathophysiology of the disease process.

CONCLUSIONS

A timely, integrated, multidisciplinary approach to the patient with vertebrobasilar thrombosis can improve outcome. The use of thrombolytics in the treatment of vertebrobasilar occlusion holds promise but the benefits have not yet been proven in a controlled, randomized study.

Coronary stenting for failed angioplasty in acute myocardial infarction

Intracoronary stents were implanted in 15 patients after unsuccessful PTCA in the setting of acute myocardial infarction (AMI). The stented vessel was the left anterior descending (LAD) in 11 patients, the right coronary artery (RCA) in 3 patients, and a venous bypass graft to the LAD in a single patient. A total of 16 stents were implanted (15 Palmaz Schatz, Johnson and Johnson; and 1 Wiktor, Medtronic).

FOLLOW-UP

1 patient died 10 days after stent implantation as a result of renal failure and cardiogenic shock. Subacute thrombosis occurred in 2 patients, 5 and 15 days after stent implantation; both underwent successful emergency coronary artery bypass grafting (CABG). The remaining 12 patients were free from major ischemic events (death, AMI, and further revascularization) after a mean follow-up of 18.7 +/- 4.1 months. We conclude that the long-term results of intracoronary stenting in AMI after failed PTCA are favourable.

Thrombin-induced platelet aggregation is inhibited by the heptapeptide Leu271-Ala277 of domain 3 in the heavy chain of high molecular weight kininogen

The ability of kininogens to modulate thrombin-induced aggregation of human platelets has been assigned to domain 3 (D3) in the common heavy chain coded for by exons 7, 8, and 9 of kininogen gene. We expressed each of the exons 7, 8, and 9, and various combinations as glutathione S-transferase fusion proteins in Escherichia coli. Each of the exon products 7 (Lys236-Gln292), 9 (Val293-Gly328), and 8 (Gln329-Met357), and their combinations were evaluated for the ability to inhibit thrombin induced platelet aggregation. Only products containing exon 7 inhibited platelet aggregation induced by thrombin with an IC50 of > 20 microM. A deletion mutant of exon 7 product, polypeptide 7A product (Lys236-Lys270) did not block thrombin-induced platelet aggregation, while 7B product (Thr255-Gln292) and 7C product (Leu271-Gln292) inhibited aggregation. These findings indicated that the inhibitory activity is localized to residues Leu271-Gln292. Peptides Phe279-Ile283 and Phe281-Gln292 did not block thrombin, and Asn275-Phe279 had only minimal inhibitory activity. A heptapeptide Leu271-Ala277 inhibited thrombin-induced aggregation of platelets with an IC50 of 65 microM. The effect is specific for the activation of platelets by thrombin but not ADP or collagen. No evidence for a thrombin-kininogen complex was found, and neither HK nor its derivatives directly inhibited thrombin activity. Knowledge of the critical sequence of kininogen should allow design of compounds that can modulate thrombin activation of platelets.

Reocclusion: the flip side of coronary thrombolysis

Since the introduction of thrombolytic therapy for acute myocardial infarction, the incidence of coronary artery reocclusion has been intensively studied. Also, the prediction and diagnosis of reocclusion by angiographic and clinical variables, as well its invasive and pharmacologic prevention, have gained much attention. By angiographic definition, reocclusion requires three angiographic observations: one with an occluded artery, one with a reperfused artery and a third for the assessment of subsequent occlusion (true reocclusion). Since the introduction of early intravenous reperfusion therapy, most studies use only two angiograms: one with a patent and one with a nonpatent infarct-related artery. A search for all published reocclusion studies revealed 61 studies (6,061 patients) with at least two angiograms. The median time interval between the first angiogram after thrombolysis and the second was 16 days (range 0.1 to 365). Reocclusion was observed in 666 (11%) of 6,061 cases. Interestingly, the 28 true reocclusion studies showed an incidence of reocclusion of 16 +/- 10% (mean +/- SD), and the 33 studies with only two angiograms 10 +/- 8% (p=0.04), suggesting that proven initial occlusion of the infarct-related artery is a risk factor for reocclusion after successful thrombolysis. The other predictors for reocclusion are probably severity of residual stenosis of the infarct-related artery after thrombolysis and perhaps the flow state after lysis. Reocclusion is most frequently seen in the early weeks after thrombolysis. The clinical course in patients with reocclusion is more complicated than in those without this complication. Left ventricular contractile recovery after thrombolysis is hampered by reocclusion. Routine invasive strategies have not been proven effective against reocclusion. In the prevention of reocclusion, both antiplatelet and antithrombin strategies have been tested, including hirudin and hirulog, but the safety of these agents in thrombolysis is still questionable. Thus, reocclusion after thrombolysis is an early phenomenon and is more frequent after proven initial occlusion of the infarct-related artery. Reocclusion can be predicted by angiography after thrombolysis. Because reocclusion is detrimental, strategies to prevent it should be developed and carried out after thrombolytic therapy for acute myocardial infarction as soon as they are deemed safe.

Fibrinolytic mechanism, biochemistry, and preclinical pharmacology of recombinant prourokinase

The purpose of this review is to provide a biochemical characterization of recombinant prourokinase (r-ProUK [ABT-187]), including a description of its clot-specific fibrinolytic mechanism. In addition, the preclinical data will be briefly reviewed, demonstrating the efficacy of r-ProUK as a potent therapeutic plasminogen activator. r-ProUK was purified to homogeneity from the culture medium of SP2/0 mouse hybridoma cells. The fibrinolytic potency of r-ProUK was characterized by both in vitro clot lysis experiments in human plasma and a canine femoral artery thrombosis model. In the in vitro clot lysis system, with use of clots prepared from fresh frozen human plasma, r-ProUK exhibits a lag phase to the onset of lysis and a concentration-dependent threshold effect due to the presence of the inhibitors alpha 2-antiplasmin and plasminogen activator inhibitor (PAI-1). Effective clot lysis can be achieved without degradation of the fibrinogen in the surrounding plasma. Over a dose range of 50,000-220,000 IU, the canine femoral artery thrombosis model shows a dose-dependent relationship for r-ProUK and effective clot lysis. The lytic activity of r-ProUK is significantly enhanced in this model by the concomitant administration of heparin as an adjunctive agent for thrombolytic treatment. Fibrinogen, plasminogen, and alpha 2-antiplasmin levels in the systemic circulation were unaltered during the 30-minute infusion period and a 4-hour observation period, in which 85% lysis was achieved with r-ProUK (100,000 IU) and heparin. Moreover, restoration of blood flow in the previously fully occluded femoral artery was achieved within minutes of the start of the r-ProUK infusion. The experimental findings presented here are consistent with the clot-specific fibrinolytic mechanism of r-ProUK. Effective clot lysis can be achieved without alteration of the systemic coagulation and fibrinolytic parameters.

Finger-like lysing patterns of blood clots

One-dimensional modeling of fibrinolysis (Senf, 1979; Zidansek and Blinc, 1991; Diamond and Anand, 1993) has accounted for the dissolution velocity, but the shape of the lysing patterns can be explained only by two- or three- drug-induced blood clot dissolution patterns obtained by proton nuclear magnetic resonance imaging, which can be described by the enzyme transport-limited system of fibrinolytic chemical equations with diffusion and perfusion terms (Zidansek and Blinc, 1991) in the reaction time approximation if the random character of gel porosity is taken into account. A two-dimensional calculation based on the Hele-Shaw random walk models (Kadanoff, 1985; Liang, 1986) leads to fractal lysing patterns as, indeed, is observed. The fractal dimension of the experimental lysing patterns changes from 1.2 at the beginning of the experiments to a maximum of approximately 1.3 in the middle and then decreases toward one when the clot is recanalized.

Maintenance of coronary patency after fibrinolysis with tissue factor pathway inhibitor

BACKGROUND

Pharmacological coronary fibrinolysis induces procoagulant effects that contribute to delayed recanalization and early reocclusion. This study was designed to determine whether brief inhibition of activation of the coagulation cascade with tissue factor pathway inhibitor, a physiological inhibitor of activated factor X and its activation by the tissue factor/factor VII complex, would facilitate fibrinolysis, sustain patency of recanalized arteries, or both.

METHODS AND RESULTS

Platelet-rich coronary thrombi were induced with anodal current that elicited intimal injury in 21 conscious dogs. Each was randomized to human recombinant tissue-type plasminogen activator (rTPA 1.0 mg/kg IV over 1 hour) with infusion of 50 micrograms.kg-1.min-1 of human recombinant tissue factor pathway inhibitor (rTFPI, n = 7), 100 micrograms.kg-1.min-1 of rTFPI (n = 8), or 300 mmol/L arginine phosphate buffer as a control (n = 6) concomitant with and for 1 hour after infusion of the plasminogen activator. Recanalization, verified with proximal Doppler flow probes, occurred in all but 1 dog given the high dose of rTFPI. It was not accelerated by conjunctive rTFPI. Reocclusion occurred within 90 minutes after infusion of rTPA in all 6 control dogs. However, reocclusion was delayed and patency was sustained for the entire 24-hour observation interval in 2 of 6 dogs (excluding 1 that did not survive) given the low dose and in 4 of 6 dogs (excluding 1 that did not receive the desired amount) given the high dose of rTFPI (P < .05 compared with controls). Cyclic flow variations indicative of platelet aggregation and disaggregation locally were virtually eliminated by rTFPI (3 +/- 4[SD]/h in dogs given the low dose and 2 +/- 2/h in those given the high dose of rTFPI compared with 13 +/- 12/h in controls, P < .05). In addition, rTFPI increased activated partial thromboplastin time and prothrombin time only at the high dose (1.4 +/- 0.3 and 2.1 +/- 0.9 times baseline) and had no effects on platelet aggregation assayed ex vivo and only minimal effects on bleeding time assayed in vivo.

CONCLUSIONS

Brief inhibition of the coagulation system by administration of rTFPI sustains patency of arteries recanalized by pharmacological fibrinolysis without markedly perturbing hemostatic mechanisms.

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

BACKGROUND

Thrombi are known to induce activation of the coagulation system, which may be a mechanism for progression of thrombosis and its recurrence after thrombolysis. This study was designed to characterize the relative role of thrombin and activated factor X (factor Xa) as mediators of procoagulant activity of whole blood clots in blood and plasma.

METHODS AND RESULTS

Clots formed from human blood were incubated in recalcified (25 mmol/L CaCl2) citrated plasma or nonanticoagulated blood with increasing concentrations of recombinant desulfatohirudin (hirudin) to inhibit thrombin activity, recombinant tick anticoagulant peptide (TAP) or recombinant tissue factor pathway inhibitor (TFPI) to inhibit factor Xa, or heparin. Fibrinopeptide A (FPA) was assayed serially as an index of procoagulant (thrombin) activity. FPA generation was greatly accelerated by addition of clots to recalcified plasma (from 1251 +/- 211 ng/mL after 15 minutes without clot to 5916 +/- 1412 ng/mL with clot, n = 7, P < .01) or whole blood (4803 +/- 761 ng/mL with clot compared with 546 +/- 233 without clot, n = 5, P < .05) and was attenuated by inhibitors of thrombin (> 90% inhibition of FPA with 0.05 mumol/L hirudin and 1.0 U/mL heparin) and factor Xa (> 90% inhibition of FPA with 1.0 mumol/L TAP and 0.15 mumol/L TFPI) in a concentration-dependent manner. Preincubation of clots with tissue-type plasminogen activator sufficient to induce partial clot lysis increased the rate of thrombin-induced FPA generation by increasing the surface area of clot exposed to plasma. However, procoagulant activity induced by partially lysed clots was attenuated by lower concentrations of both thrombin and Xa inhibitors, presumably because access of the inhibitors to bound procoagulant molecules was facilitated. Comparable results were obtained with incubations in nonanticoagulated blood.

CONCLUSIONS

These results indicate that factor Xa is primarily responsible for the procoagulant activity of clots in vitro and suggest a potential molecular mechanism for the observed efficacy of inhibitors of factor Xa in preventing recurrent thrombosis after coronary thrombolysis.

Implications of recurrent ischemia after reperfusion therapy in acute myocardial infarction: a comparison of thrombolytic therapy and primary angioplasty

OBJECTIVES

The purpose of this study was to examine the incidence and implications of recurrent ischemia after different reperfusion strategies in acute myocardial infarction.

BACKGROUND

The rates and effects of recurrent ischemia after reperfusion with thrombolytic therapy and with primary percutaneous transluminal coronary angioplasty have not been compared.

METHODS

At 12 centers 395 patients presenting within 12 h of the onset of acute myocardial infarction were prospectively randomized to receive recombinant tissue-type plasminogen activator (rt-PA) or primary coronary angioplasty. Sixteen clinical variables were examined by using univariate and multiple logistic regression analysis to identify the predictors of recurrent ischemia. The relation of recurrent ischemic events to patient outcome was analyzed.

RESULTS

Recurrent ischemia developed in 76 patients (19.2%) before hospital discharge, resulting in reinfarction in 18 patients (4.6%) and death in 5 (2.6%). Recurrent ischemia occurred in 56 patients (28.0%) after rt-PA but in only 20 patients (10.3%) after coronary angioplasty (p < 0.0001), directly contributing to a higher rate of death or reinfarction (7.5% vs. 3.1%, p = 0.05), catheterization and revascularization procedures and prolonged hospital stay after thrombolysis. By multivariate analysis, treatment with coronary angioplasty rather than rt-PA was the strongest predictor of freedom from recurrent ischemia. Although the incidence of recurrent ischemia after angioplasty and after rt-PA was similar within the 1st 2 days of admission (9.2% vs. 14.5%, p = 0.11), after hospital day 2 recurrent ischemia occurred in only 2 patients who received primary angioplasty compared with 27 patients who received rt-PA (1.1% vs. 13.5%, p < 0.0001).

CONCLUSIONS

The development of recurrent ischemia adversely affects patient outcome, increasing morbidity, mortality and resource utilization. The much lower rate of recurrent ischemia after primary coronary angioplasty than after rt-PA results in improved survival without reinfarction and allows a shorter, less complicated hospital stay. Given the extremely low rate of recurrent ischemia after hospital day 2, safe early discharge on day 3 after primary coronary angioplasty should be feasible in selected patients with acute myocardial infarction.

Angiographic predictors of reocclusion after thrombolysis: results from the Thrombolysis in Myocardial Infarction (TIMI) 4 trial

OBJECTIVES

This study attempted to determine which lesion characteristics are associated with reocclusion by 18 to 36 h.

BACKGROUND

Reocclusion of the infarct-related artery after successful reperfusion is associated with significant morbidity and up to a threefold increase in mortality.

METHODS

Two hundred seventy-eight patients with acute myocardial infarction were randomized to receive either anisoylated plasminogen streptokinase activator complex (APSAC) or recombinant tissue-type plasminogen activator (rt-PA) or their combination. Culprit arteries were assessed for Thrombolysis in Myocardial Infarction (TIMI) flow grade, lesion ulceration, thrombus, collateral circulation and eccentricity. Minimal lumen diameter, percent diameter stenosis and lesion irregularity (power) were calculated using quantitative angiography.

RESULTS

Reocclusion was observed more frequently in arteries with TIMI 2 versus TIMI 3 flow (10.4% vs. 2.2%, p = 0.003), in ulcerated lesions (10.7% vs. 3.0%, p = 0.009) and in the presence of collateral vessels (18.2% vs. 5.6%, p = 0.03). Similar trends were observed for eccentric (7.3% vs. 2.3%, p = 0.06) and thrombotic (8.4% vs. 3.3%, p = 0.06) lesions. Reocclusion was associated with more severe mean percent stenosis (77.9% vs. 73.9%, p = 0.04). Lesion length, reference segment diameter and Fourier measures of lesion irregularity were not associated with reocclusion.

CONCLUSIONS

Several simply assessed angiographic variables, such as the presence of TIMI grade 2 flow, ulceration, collateral vessels and greater percent diameter stenosis at 90 min after thrombolytic therapy, are associated with significantly higher rates of infarct-related artery reocclusion by 18 to 36 h and may aid in identifying the subset of patients who are at significantly higher risk of early reocclusion and who potentially warrant further early pharmacologic or mechanical intervention.

Predictors of in-hospital and 6-month outcome after acute myocardial infarction in the reperfusion era: the Primary Angioplasty in Myocardial Infarction (PAMI) trail

OBJECTIVES

This study examined the predictors of in-hospital and 6-month outcome after different reperfusion strategies in acute myocardial infarction.

BACKGROUND

Thrombolytic therapy and primary angioplasty are both widely applied as reperfusion modalities in patients with myocardial infarction. Although it is accepted that restoration of early patency of the infarct-related artery can reduce mortality and salvage myocardium, the optimal reperfusion strategy remains controversial, and the predictors of outcome in the reperfusion era have been incompletely characterized.

METHODS

At 12 centers, 395 patients presenting within 12 h of onset of acute transmural myocardial infarction were prospectively randomized to receive tissue-type plasminogen activator (t-PA) or undergo primary angioplasty without antecedent thrombolysis. Sixteen clinical variables were examined with univariate and multiple logistic regression analysis to identify the predictors of clinical outcome.

RESULTS

By univariate analysis, in-hospital mortality was increased in the elderly, women, patients with diabetes and in patients treated with t-PA as opposed to angioplasty. Only advanced age and treatment by t-PA versus angioplasty independently correlated with increased in-hospital mortality (6.5% vs. 2.6%, respectively, p = 0.039 by multiple logistic regression analysis). Similarly, the only variables independently related to in-hospital death or nonfatal reinfarction were advanced age and treatment by t-PA versus angioplasty (12.0% vs. 5.1%, p = 0.02). The reduction in in-hospital death or reinfarction with angioplasty versus t-PA was particularly marked in patients > or = 65 years of age (8.6% vs. 20.0%, p = 0.048). Furthermore, primary management with angioplasty versus t-PA was the most powerful multivariate correlate of freedom from recurrent ischemic events (10.3% vs. 28.0%, p = 0.0001). The independent beneficial effect of angioplasty on freedom from death or reinfarction was maintained at 6-month follow-up (8.2% vs. 17.0%, p = 0.02).

CONCLUSIONS

In the reperfusion era, the two most powerful determinants of freedom from death, reinfarction and recurrent ischemia after myocardial infarction are young age and treatment by primary angioplasty.

Early angiography cannot predict postthrombolytic coronary reocclusion: observations from the GUSTO angiographic study. Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries

OBJECTIVES

The purpose of this study was to determine whether early qualitative or quantitative angiographic features can predict reocclusion after initially successful coronary thrombolysis.

BACKGROUND

Although both the benefits of early reperfusion and the consequences of subsequent reocclusion after thrombolysis for acute myocardial infarction have been well described, efforts to describe angiographic markers of lesions at high risk for reocclusion have produced conflicting results. The Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries (GUSTO) angiographic trial provides the opportunity to examine these relations in the largest single, prospective patient cohort studied to date.

METHODS

We studied 559 patients undergoing follow-up angiography at 90 min and 5 to 7 days after thrombolysis in the GUSTO trial. Patients received one of four thrombolytic regimens: 1) streptokinase with intravenous heparin; 2) streptokinase with subcutaneous heparin; 3) accelerated-dose recombinant tissue-type plasminogen activator (rt-PA) with intravenous heparin; or 4) a combination of streptokinase and conventionally dosed rt-PA with intravenous heparin. Qualitative variables examined at 90-min angiography included Thrombolysis in Myocardial Infarction (TIMI) flow grade, visible thrombus and lesion morphology. Quantitative variables included percent diameter stenosis, percent area stenosis, minimal lumen diameter and lesion length. The study contained a power > 0.85 to detect clinically important differences in percent diameter stenosis, percent area stenosis and minimal lumen diameter between the groups with subsequent reocclusion and sustained patency at the p = 0.05 level.

RESULTS

At follow-up, 33 patients (5.9%) had reocclusion. The reocclusion rate for patients with early TIMI grade 2 flow was 6.3% versus 5.6% for TIMI grade 3 flow (p = NS). When the group with reocclusion was compared with the group with continued patency, there were no differences in presence of early visible thrombus, complex lesion morphology, percent diameter stenosis, percent area stenosis, minimal lumen diameter or lesion length.

CONCLUSIONS

Our findings demonstrate that neither qualitative nor quantitative angiographic variables at 90 min after initiation of thrombolytic therapy can be used to predict subsequent coronary reocclusion.

Early T wave inversion after thrombolytic therapy predicts better coronary perfusion: clinical and angiographic study

OBJECTIVES

This study was undertaken to test the hypothesis that early inversion of T waves after thrombolytic therapy for acute myocardial infarction predicts patency of the infarct-related artery with high Thrombolysis in Myocardial Infarction (TIMI) perfusion flow and better in-hospital outcome.

BACKGROUND

Although numerous studies have demonstrated a strong association between early resolution of ST segment elevation after acute myocardial infarction and successful thrombolysis, little is known about early changes in T waves after thrombolytic therapy.

METHODS

Ninety-four consecutive patients with acute myocardial infarction treated with recombinant tissue-type plasminogen activator (rt-PA) were studied with admission and predischarge radionuclide ventriculography and with coronary angiography within 72 h of admission. Patient stratification was based on the presence or absence of early (within 24 h) T wave inversion.

RESULTS

Early T wave inversion was associated with a higher patency rate of the infarct-related artery (90% vs. 65%, p < 0.02) and less severe residual stenosis ([mean +/- SD] 73 +/- 27 vs. 83 +/- 22, p = 0.06), and when only TIMI perfusion grade 3 was considered, the difference was even greater (77% vs. 41%, p < 0.001). Patients with early inversion of T waves had a lower peak creatine kinase value ([mean +/- SD] 678 +/- 480 vs. 1,076 +/- 620, p < 0.01), and although a similar percent of patients with and without early T wave inversion had a normal ejection fraction (> or = 55%) on admission, a higher percent of patients with early inversion had a normal ejection fraction at hospital discharge (71% vs. 44%, p < 0.03). Early T wave inversion anticipated a more benign in-hospital clinical course with a lower incidence of adverse cardiac events (10% vs. 33%, p < 0.02).

CONCLUSIONS

Early inversion of T waves in patients with acute myocardial infarction treated with thrombolytic therapy suggests patency of the infarct-related artery, better perfusion grade and left ventricular function and a more benign in-hospital course.

Activation of the hemostatic system during thrombolytic therapy

Activation of the hemostatic mechanism has been described during thrombolytic therapy. This phenomenon has been detected by new methods of assessing hemostatic system function, based on immunoenzymatic or radioimmunoassays. However, these methods are extremely sensitive and, unless they are performed in expert laboratories, carefully following the recommended procedures, they generate in vitro artifacts. A description of these methods is provided, as well as a critical review of the available studies. The correct use of these methods will provide us with an understanding of the complex response of the hemostatic system to pharmacologic thrombolysis.

Culprit lesion morphology and stenosis severity in the prediction of reocclusion after coronary thrombolysis: angiographic results of the APRICOT study. Antithrombotics in the Prevention of Reocclusion in Coronary Thrombolysis

OBJECTIVES

In the APRICOT study (Antithrombotics in the Prevention of Reocclusion In Coronary Thrombolysis), we sought to determine whether angiographic characteristics of the culprit lesion could predict reocclusion after successful thrombolysis and to analyze the influence of three antithrombotic treatment regimens.

BACKGROUND

After successful thrombolysis, reocclusion is a major problem. Prediction of reocclusion by angiographic data and choice of antithrombotic treatment would be important for clinical management.

METHODS

After thrombolysis, patients were treated with intravenous heparin until initial angiography was performed within 48 h. Patients with a patent infarct-related artery were eligible. Three hundred patients were randomly selected for treatment with coumadin, aspirin (300 mg once daily) or placebo. Patency on a second angiographic study after 3 months was the primary end point of the study.

RESULTS

Reocclusion rate was 25% with aspirin, 30% with coumadin and 32% with placebo (p = NS). Lesions with > 90% stenosis reoccluded more frequently (42%) than did those with < 90% stenosis (23%) (p < 0.01). Reocclusion rate of smooth lesions was higher (34%) than that of complex lesions (23%) (p < 0.05). In lesions with < 90% stenosis, the reocclusion rate was lower with aspirin (17%) than with coumadin (25%) or placebo (30%) (p < 0.01). In complex lesions, the reocclusion rate was lower with aspirin (14%) than with coumadin (32%) or placebo (25%) (p < 0.02). Multivariate analysis showed only stenosis severity > 90% to be an independent predictor of reocclusion (odds ratio 2.31, 95% confidence interval 1.28 to 4.18, p = 0.006).

CONCLUSIONS

Angiographic features of the culprit lesion after successful coronary thrombolysis significantly predict the risk of reocclusion: high grade (> 90%) stenoses reoccluded more frequently. Aspirin was effective only in complex and less severe lesions (< 90% stenosis). These findings should prompt investigation of the effects of an aggressive approach to patients with severe residual stenosis.

Comparison of symptom-limited and low level exercise tolerance tests early after myocardial infarction

OBJECTIVES

This study was conducted to determine the diagnostic yield and risks of a symptom-limited treadmill exercise test before hospital discharge.

BACKGROUND

Currently, predischarge low level and 6-week symptom-limited exercise treadmill tests are recommended for risk stratification after myocardial infarction. However, few data exist on the safety and value of a predischarge symptom-limited exercise test.

METHODS

We utilized a modified Bruce protocol starting at 1.7 mph and 0 grade with 3-min stages in 150 consecutive patients 6.4 +/- 3.1 days after myocardial infarction. Each exercise test was interpreted for duration, symptoms and ST segment changes at the low level (70% of predicted heart rate) and symptom-limited end point.

RESULTS

There were no complications related to the symptom-limited exercise tests. The test results were positive in only 23% of the patients at the low level end point, but were positive in 40% of the patients at the later symptom-limited end point (p < 0.001). During a mean follow-up period of 15 +/- 5 months in 138 patients (92%), 50 patients (36%) had a cardiac event. Of the patients with a cardiac event, significantly more (p < 0.001) had a positive exercise test at the symptom-limited end point (31 vs. 16 patients). Five patients with a negative and 14 patients with a nondiagnostic symptom-limited exercise test had an event.

CONCLUSIONS

In patients with uncomplicated myocardial infarction, we demonstrated the safety of an early symptom-limited treadmill exercise test. Symptom-limited exercise tests will identify more patients with inducible ischemia who are at risk of future cardiac events and who may benefit from early intervention.

Illusion of reperfusion. Does anyone achieve optimal reperfusion during acute myocardial infarction?

Thrombolytic therapy significantly improves the natural history of acute myocardial infarction, but recent data suggest that current reperfusion strategies have yet to realize the maximum potential for reduction of mortality and salvage of ventricular function. Coronary patency rates as high as 85% assessed by angiography 90 minutes after initiation of treatment greatly overestimate the efficacy of thrombolytic regimens, as this conventional angiographic "snapshot" view does not satisfactorily reflect the dynamic processes of coronary artery recanalization and reocclusion or the adequacy of myocardial perfusion. In fact, only the unusual patient appears to achieve optimal reperfusion for acute myocardial infarction, with a substantial deterioration of benefit in many patients due to insufficiently early or rapid recanalization, incomplete patency with TIMI grade 2 flow or critical residual coronary stenoses, absence of myocardial tissue reflow despite epicardial artery patency, intermittent coronary patency, subsequent reocclusion, or reperfusion injury. Recently developed techniques to critically assess the quality of reperfusion, coupled with the introduction of novel pharmacological agents and an improved understanding of the roles and mechanisms of existing thrombolytic and adjunctive drugs, have provided the opportunity to overcome many of the present limitations of reperfusion therapy. Emerging strategies to achieve optimal reperfusion are directed at enhancement of the velocity and quality of thrombolysis, amelioration of the adverse effects of reperfusion, and use of alternative pathways to myocardial salvage.

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

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Value of negative predischarge exercise testing in identifying patients at low risk after acute myocardial infarction treated by systemic thrombolysis

Although thrombolytic therapy reduces mortality in patients with acute myocardial infarction (AMI), it is associated with a greater incidence of successive coronary events, and there is still no ideal diagnostic and therapeutic strategy for such patients. The present study verifies the value of negative predischarge exercise testing in identifying low-risk patients treated with thrombolysis after AMI. One hundred fifty-seven consecutive patients with an uncomplicated clinical course underwent maximal or symptom-limited exercise testing (Bruce treadmill protocol) within 15 days of AMI in the absence of therapy. The location of the AMI was anterior in 51 patients, inferior in 85 and non-Q-wave in 21. All of the patients were followed for 6 months. Death and nonfatal reinfarction were considered as major coronary events, and the recurrence of angina as a minor event. Exercise test results were negative in 105 patients (group 1) and positive for angina or ST depression greater than or equal to 0.1 mV in 52 (group 2). No deaths occurred during follow-up; there were 3 reinfarctions (3%) and 7 cases (7%) of postinfarction angina in group 1, and 2 reinfarctions (4%) and 21 cases (40%) of postinfarction angina in group 2. By the end of follow-up, 90% of the patients with negative exercise test results were event-free (97% in the case of major events). These results show that thrombolytic therapy does not affect the value of negative postinfarction exercise testing in identifying low-risk patients.

Effects of aspirin on coronary reocclusion and recurrent ischemia after thrombolysis: a meta-analysis

Reocclusion of infarct-related coronary arteries within 2 weeks of thrombolytic therapy varies from 5% to 45% and neither clinical nor angiographic variables have been proved to be predictive of reocclusion. The goal of the present study was to evaluate whether aspirin could prevent coronary reocclusion and recurrent ischemia after thrombolysis. For this purpose, a meta-analysis including 32 studies was performed. Although the studies showed very similar demographic data, the reocclusion rate assessed by angiography in 419 patients treated with aspirin was 11% compared with 25% in 513 patients without aspirin therapy (p less than 0.001). Recurrent ischemic events were present in 25% of 2,977 patients treated with aspirin and 41% of 721 patients treated without aspirin (p less than 0.001). The effect of aspirin was similar in trials with either streptokinase or recombinant tissue-type plasminogen activator (rt-PA). Thus, aspirin in the presence of heparin might prevent coronary reocclusion after thrombolysis.

The role of platelets, thrombin and hyperplasia in restenosis after coronary angioplasty

Coronary angioplasty has become a successful and widely used treatment for patients with coronary artery disease since its first clinical application in 1977. The primary success rate has improved despite the increase in procedure and case complexity. However, acute reocclusion and late restenosis, which constitute the most important problems after successful angioplasty, continue to occur in about 5% and 35% of patients within 3 to 6 months, respectively. Angioscopic and pathologic observations have suggested that a multifactorial pathophysiologic process accounts for acute reocclusion, involving marked thrombosis, intimal dissection, medial and subintimal hemorrhage, vascular recoil and vasocontriction. In contrast, chronic restenosis involves the development of fibrocellular intimal hyperplasia within a milieu created by vascular injury, platelet activation, thrombin generation and the release of mitogens. Although current pharmacologic approaches, which involve antithrombotic and anticoagulant therapy, have been largely ineffective in eliminating acute reocclusion and chronic restenosis, recent advances in the research in thrombosis, platelet receptors and smooth muscle growth regulation have allowed new therapeutic options to be tested in the experimental setting, with subsequent potential clinical applications in patients.

Increased thrombin levels during thrombolytic therapy in acute myocardial infarction. Relevance for the success of therapy

BACKGROUND

It has been suggested that thrombolysis in a feedback reaction may generate pro-coagulant activities.

METHODS AND RESULTS

Fifty-five patients were treated with urokinase-preactivated prourokinase (n = 35) or tissue-type plasminogen activator (n = 20) for acute myocardial infarction and underwent coronary angiography at 90 minutes and at 24-36 hours into thrombolysis, and fibrinogen (Ratnoff-Menzie), D-dimer (ELISA) and thrombin-antithrombin III complex levels (ELISA) were measured. Primary patency was achieved in 39 patients (70.9%), 13 of whom (33.3%) suffered early reocclusion. Nonsignificant decreases in fibrinogen levels were observed while D-dimer levels increased +3,008 +/- 4,047 micrograms/l (p less than 0.01), differences not being significant in respect to the thrombolytic agents or to the clinical course. In contrast, while thrombin-antithrombin III complex levels decreased -4.4 +/- 13.0 micrograms/l in patients with persistent patency, they increased +7.5 +/- 13.6 micrograms/l in case of nonsuccessful thrombolysis (p less than 0.02) and +11.9 +/- 23.8 micrograms/l in case of early reocclusion (p less than 0.001). For patients with thrombin-antithrombin III complex levels greater than 6 ng/l 120 minutes into thrombolysis, the unfavorable clinical course was predicted with 96.2% sensitivity and 93.1% specificity.

CONCLUSION

Generation of thrombin, occurring during thrombolysis, is a major determinant for the success of therapy and thrombin-antithrombin III levels may serve as predictors for the short-term prognosis.

Sudden appearance of coronary thrombus observed by angiography--a case report

A sudden coronary thrombus formation was documented by chance during cardiac catheterization in a patient with postinfarction angina. The thrombus was successfully treated with intravenous urokinase and heparin infusions, and thereafter, coronary angioplasty was performed without any complication.

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

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

Consequences of reocclusion after successful reperfusion therapy in acute myocardial infarction. TAMI Study Group

To determine the clinical consequences of reocclusion of an infarct-related artery after reperfusion therapy, we evaluated 810 patients with acute myocardial infarction. Patients were admitted into four sequential studies with similar entry criteria in which patency of the infarct-related artery was assessed by coronary arteriography 90 minutes after onset of thrombolytic therapy. Successful reperfusion was established acutely in 733 patients. Thrombolytic therapy included tissue-type plasminogen activator (t-PA) in 517, urokinase in 87, and a combination of t-PA and urokinase in 129 patients. All patients received aspirin, intravenous heparin and nitroglycerin, and diltiazem during the recovery phase. A repeat coronary arteriogram was performed in 88% of patients at a median of 7 days after the onset of symptoms. Reocclusion of the infarct-related artery occurred in 91 patients (12.4%), and 58% of these were symptomatic. Angiographic characteristics at 90 minutes after thrombolytic therapy that were associated with reocclusion compared with sustained coronary artery patency were right coronary infarct-related artery (65% versus 44%, respectively) and Thrombolysis in Myocardial Infarction (TIMI) flow 0 or 1 (21% versus 10%, respectively) before further intervention. Median (interquartile value) degree of stenosis in the infarct-related artery at 90 minutes was similar between groups: 99% for reoccluded (value, 90/100%) compared with 95% for patent (value, 80/99%). Patients with reocclusion had similar left ventricular ejection fractions compared with patients with sustained patency at follow-up. However, patients with reocclusion at follow-up had worse infarct-zone function at -2.7 (value, -3.2/-1.8) versus -2.4 (SD/chord) (value, -3.1/-1.3) (p = 0.016). The recovery of both global and infarct-zone function was impaired by reocclusion of the infarct-related artery compared with maintained patency; median delta ejection fraction was -2 compared with 1 (p = 0.006) and median delta infarct-zone wall motion was -0.10 compared with 0.34 SD/chord (p = 0.011), respectively. In addition, patients with reocclusion had more complicated hospital courses and higher in-hospital mortality rates (11.0% versus 4.5%, respectively; p = 0.01). We conclude that reocclusion of the infarct-related artery after successful reperfusion is associated with substantial morbidity and mortality rates. Reocclusion is also detrimental to the functional recovery of both global and infarct-zone regional left ventricular function. Thus, new strategies in the postinfarction period need to be developed to prevent reocclusion of the infarct-related artery.

Comparison of early exercise treadmill test and oral dipyridamole thallium-201 tomography for the identification of jeopardized myocardium in patients receiving thrombolytic therapy for acute Q-wave myocardial infarction

Thrombolytic therapy has become the treatment of choice for patients with acute myocardial infarction. Researchers are not yet able to identify patients with salvage of myocardium who are at risk for recurrent coronary events. Thus, a prospective trial was performed in 46 patients with myocardial infarction (28 anterior and 18 inferior) who received thrombolytic therapy to determine if early thallium tomography (4.7 days) using oral dipyridamole would identify more patients with residual ischemia than early symptom-limited exercise treadmill tests (5.5 days). There were no complications during the exercise treadmill tests or oral dipyridamole thallium tomography. Mean duration of exercise was 11 +/- 3 minutes and the peak heart rate was 126 beats/min. Thirteen patients had positive test results. After oral dipyridamole all patients had abnormal thallium uptake on the early images. Positive scans with partial "filling in" of the initial perfusion defects were evident in 34 patients. Angina developed in 13 patients and was easily reversed with intravenous aminophylline. Both symptom-limited exercise treadmill tests and thallium tomography using oral dipyridamole were safely performed early after myocardial infarction in patients receiving thrombolytic therapy. Thallium tomography identified more patients with residual ischemia than exercise treadmill tests (74 vs 28%). Further studies are required to determine whether the results of thallium tomography after oral dipyridamole can be used to optimize patient management and eliminate the need for coronary angiography in some patients.

Reinfarction after thrombolytic therapy for acute myocardial infarction followed by conservative management: incidence and effect of smoking

A group of 456 consecutive patients seen less than or equal to 6 h after the onset of acute myocardial infarction associated with ST segment elevation received thrombolytic therapy and were followed up for 12 months. Intravenous streptokinase was given to 315 patients and recombinant tissue-type plasminogen activator (rt-PA) to 141 patients. Reinfarction rate and risk factors for reinfarction were assessed. Management after thrombolysis was conservative; revascularization procedures were reserved for patients with symptoms refractory to medical therapy or for those with left main coronary artery stenosis. Coronary artery surgery or angioplasty was performed in only 3.7% of patients during the first 30 days after thrombolysis and in only 8.6% by 1 year. Most patients (79%) underwent coronary arteriography. Twenty-six patients (5.7%) exhibited signs of threatened reinfarction at 1 month after thrombolytic therapy as did 43 patients (9.4%) by 1 year. Reinfarction was prevented in four of these patients by early readministration of thrombolytic therapy. Multivariate analysis of possible risk factors for reinfarction identified at the time of initial infarction showed current cigarette smoking to be the only predictive factor (reinfarction occurred in 12.5% of smokers versus 6.3% of nonsmokers, p = 0.04). A second analysis of risk factors identified 3 weeks after initial infarction, including the severity of residual stenosis at coronary arteriography and exercise test variables, again showed continued cigarette smoking to be the only factor predictive of reinfarction. Twenty percent of patients who continued to smoke developed reinfarction compared with 5.1% of those who stopped (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Combined mechanical and chemical thrombolysis in an experimental animal model: evaluation by angiography and angioscopy

In an experimental animal model of femoral artery thrombosis, contrast angiography was compared to intravascular angioscopy. Additionally, the effect of mechanical, rotational thrombectomy and the additive benefit of the administration of intravascular streptokinase were assessed by means of both procedures. After external forceps crush injury alone, contrast angiograms were generally normal (6 of 14) or showed minimal luminal irregularity (3 of 14), and 5 of 14 had 30% to 50% stenosis. With angioscopy, none appeared normal, and 14 of 14 showed thrombi layered along the wall, as well as intimal flaps, and 6 of 14 had partially occlusive thrombi (p less than 0.001 angiography vs angioscopy). After 2-hour occlusion and injection of thrombin into the injured segment, angiographic total (5 of 14), subtotal (3 of 14), or partial thrombotic occlusions (5 of 14) were created. Angioscopy showed similar results, except that total occlusions were classed as subtotal occlusions. After rotational thrombectomy, most arteries again appeared normal by contrast angiography (6 of 11) but none were angioscopically normal (p less than 0.006). Streptokinase, administered after rotational thrombectomy in seven arteries, normalized one 30% angiographic stenosis; there were no other angiographic changes. Findings with angioscopy were also unchanged. We conclude that in the diagnosis and treatment of intravascular thrombosis, angioscopy is generally more sensitive in the detection of intravascular thrombi, with the exception of total thrombotic occlusions. Angioscopy was uniquely effective in identifying subintimal flaps, which were never identified by angiography. In this model, streptokinase provided little or no additional thrombolytic benefit to mechanical thrombectomy alone.

Role of platelet inhibitor therapy in myocardial infarction

Atherosclerotic plaque disruption is the predominant pathogenetic mechanism underlying the acute coronary syndromes. Plaque rupture leads to the exposure of collagen and vessel media, resulting in platelet and clotting activation, and occlusive thrombus formation. While drugs that interfere with platelet activation and function have been available for years, more powerful agents with novel mechanisms of action are being developed. Of the available platelet inhibitor drugs, only aspirin, sulfinpyrazone, and dipyridamole have undergone extensive clinical testing in patients with cardiovascular disease. More recently ticlopidine, a new and potent platelet inhibitor, has been successfully tested in patients with coronary and vascular disease. In acute myocardial infarction, aspirin significantly reduces cardiovascular mortality and reinfarction. Furthermore, the combination of aspirin and a thrombolytic agent produces maximal benefit. A role for heparin in the prevention of early mortality and reinfarction is emerging. This drug is effective for the prevention of left ventricular thrombosis in patients with anterior myocardial infarction. In the secondary prevention of reinfarction and cardiovascular mortality, available data support the use of a platelet inhibitor. Trials have shown that aspirin is as effective alone as in combination with dipyridamole, and is probably more effective than sulfinpyrazone. Long-term anticoagulant therapy also appears to be beneficial, but is associated with a high cost, need for extensive monitoring, and potential for hemorrhagic side effects. The role of aspirin in primary prevention is controversial. It may be indicated for patients at high risk for coronary disease in whom the benefit of therapy may outweigh the potential risk of cerebral bleeding. Coronary atherosclerotic plaque rupture, associated with thrombus formation, is fundamental to the development of acute myocardial infarction. Based on this concept, the role of antithrombotic therapy for the prevention or treatment of ischemic events in patients with coronary artery disease has stimulated enormous interest among clinicians and basic investigators. In this review we will examine: a) the pathogenesis of coronary thrombosis, b) the pharmacology of platelet-inhibitor agents, and c) their role in the management of patients with acute myocardial infarction and in primary and secondary prevention of cardiovascular disease. Platelets interact with both the coagulation and fibrinolytic systems in the pathogenesis of thrombosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Recurrent ischemia without warning. Analysis of risk factors for in-hospital ischemic events following successful thrombolysis with intravenous tissue plasminogen activator

Ischemic events after successful thrombolysis have been reported to occur in 18-32% of patients treated for acute myocardial infarction with thrombolytic therapy, and previous studies in which patients received streptokinase suggest that risk of early recurrent ischemia is closely related to the presence of a high-grade residual stenosis. If these events are predictable after intravenous recombinant tissue-plasminogen activator (rt-PA) thrombolytic therapy, then further intervention after its use could be targeted at selected patients. One-hundred ninety-two patients from the Thrombolysis and Angioplasty in Myocardial Infarction (TAMI) I and TAMI III trials had successful rt-PA-mediated thrombolysis without immediate coronary angioplasty (PTCA). One-hundred seventy-four of these patients (92%) had prehospital discharge angiography. The mean age was 56 +/- 11 years; 81% were men; the infarct-related artery was the left anterior descending in 76 (39.8%), the left circumflex in 24 (12.6%), and the right coronary artery in 91 (47.6%). Thrombolysis with rt-PA resulted in a residual 73 +/- 13% diameter and 0.95 +/- 0.51 mm stenosis by quantitative coronary arteriography, and Thrombolysis in Myocardial Infarction (TIMI) flow grade 2 in 59.2% and 3 in 40.8% of stenoses as assessed on angiograms obtained 90 minutes after the initiation of rt-PA therapy. Recurrent ischemic events (ischemia requiring emergency percutaneous transluminal coronary angioplasty or urgent bypass surgery, reocclusion of the infarct-related artery, or cardiac death) occurred in 41 patients (21.3%).(ABSTRACT TRUNCATED AT 250 WORDS)