Acute coronary artery obstruction in myocardial infarction: overview of thrombolytic therapy

Tetranectin levels in patients with acute myocardial infarction and their alterations during thrombolytic treatment

Tetranectin (TN), a new regulator of fibrinolysis, was studied in the plasma of 60 patients with acute myocardial infarction (AMI) and 30 healthy subjects (HS), in relation to D-dimer (DD) and alpha 2-plasmin inhibitor (alpha 2-PI), to investigate its possible involvement in the pathophysiology of AMI. Thirty patients underwent thrombolytic treatment with fibrin-specific plasminogen activator (rt-PA) (group A); the other 30 patients, according to the exclusion criteria, were conventionally treated (group B). Twenty of the thrombolysized patients established early recanalization (subgroup A1), while 10 failed to respond to thrombolytic treatment (subgroup A2). Median (interquartile range), baseline plasma TN levels were lower in AMI patients compared to HS [8.27 (2.75) mg/L versus 12.1 (0.55) mg/L, P < 10(-6)]. In subgroup A1, TN increased at the end of rt-PA infusion and returned to the baseline levels 12 h later. A positive association between DD and TN release (3 h level minus baseline level) was found (rs = 0.48, P = 0.03) in subgroup A1. No significant alterations of TN levels were observed during therapy in subgroup A2 and group B. TN, DD and alpha 2-PI concentrations in group B remained relatively constant during the study period. This study provides evidence of a significant decrease of TN levels in AMI patients compared to healthy subjects and of a remarkable difference in the evolution of TN levels during thrombolytic treatment with rt-PA between recanalized and non-recanalized AMI patients. Thus, an involvement of TN in the formation and dissolution of fibrin clot in AMI patients is worthy of further investigation.

Heparin as adjunctive therapy to coronary thrombolysis in acute myocardial infarction

For many years anticoagulation has played a role in the prevention and management of thromboembolic complications associated with acute myocardial infarction. However, the role of heparin therapy after pharmacologic thrombolysis in myocardial infarction remains controversial. Debate continues regarding the necessity of heparin treatment after thrombolytic therapy as well as the mode by which it is administered. The purpose of this review is to summarize the findings of clinical trials designed to evaluate the effectiveness and safety of heparin as an adjuvant agent to thrombolytic therapy in acute myocardial infarction. Data regarding the clinical effectiveness of heparin are presented. Information and recommendations regarding the optimal dose, route of administration, timing of initiation, and duration of heparin treatment are provided.

Effect of successful angioplasty following thrombolysis on infarct size and left ventricular function

The role of the angioplasty following thrombolysis in acute myocardial infarction has been discussed in several studies, however the effect of successful angioplasty on infarct size and left ventricular function has not been properly evaluated. Successful reperfusion was achieved in 79 out of 104 patients with primary anterior acute myocardial infarction. These patients were classified as follows, according to the type of intervention during the acute phase: 50 patients in which thrombolysis was successful (the thrombolysis group); 12 patients who underwent successful immediate angioplasty following successful thrombolysis (the immediate angioplasty group); and 17 patients in which rescue angioplasty was successful (the rescue angioplasty group). The 25 patients whose infarct-related vessels were not reperfused after intervention were classified as the non-reperfused group. Infarct size, evaluated as defect volume by T1-201 SPECT, 1 month after the onset, was 840 +/- 154 units (mean +/- S.D.) in the immediate angioplasty group and was similar to that in the thrombolysis group (948 +/- 88 units), but significantly smaller than in the non-reperfused group (1759 +/- 108 units). There were no significant differences in left ventricular function in the immediate angioplasty group and the thrombolysis group. Successful rescue angioplasty did not have any beneficial effect on left ventricular functions or infarct size, when compared with the failed thrombolytic group (1105 +/- 169 units vs. 1617 +/- 169 units). End-diastolic volume (52 +/- 3 ml/m2) in the successful rescue angioplasty group, however, was significantly smaller than in the failed thrombolysis group (67 +/- 3 ml/m2).(ABSTRACT TRUNCATED AT 250 WORDS)

A fast Fourier transform analysis of coronary reperfusion-induced ventricular fibrillation and the modification by dibutyryl cyclic AMP in a cat model

To investigate the effect of dibutyryl cyclic AMP (dbcAMP) on ventricular fibrillation after coronary reperfusion, the proximal portion of the anterior descending branch of left coronary artery was reperfused 20 min after ligation in 24 cats. McFee X Y Z electrocardiograms were recorded and ventricular fibrillation was analyzed using a fast Fourier transform analysis (FFT). Ventricular fibrillation occurred in 20 of 24 cases. Sixty seconds after the occurrence of ventricular fibrillation, an intracardiac infusion of dbcAMP was administered. Nine of the 20 were defibrillated and converted to sinus rhythm or junctional rhythm after the administration of dbcAMP. The amplitude and frequency of the main power spectrum of the ventricular fibrillation waves were analyzed by FFT before and after the infusion of saline or dbcAMP. In the saline group there was no significant change in FFT. However, in the dbcAMP group, the amplitude increased significantly from 0.036 +/- 0.015 (MV--2) to 0.054 +/- 0.013 (MV--2) (p < 0.01) and the frequency decreased significantly from 4.22 +/- 1.37 (Hz) to 1.33 +/- 0.91 (Hz) (p < 0.01). Those results indicate that dbcAMP increased the amplitude and decreased the frequency of the main power spectrum of ventricular fibrillation analyzed by FFT. These distinctive changes in FFT analysis were associated with defibrillation in 9 of 20 cases.

Use of left ventricular function as an end point of thrombolytic therapy

In recent acute myocardial infarction, early reperfusion of the infarct-related artery by intracoronary or intravenous thrombolytic therapy induces a significant limitation of infarct size, provided reperfusion occurs within a time frame that myocardial salvage can still be expected. Limitation of infarct size reduces scar tissue formation, aneurysm formation, infarct zone expansion, left ventricular volume enlargement, and eventually results in higher left ventricular ejection fraction. Infarct size limitation and left ventricular function preservation occur with all thrombolytic agents currently in clinical use: streptokinase, alteplase and, more recently, anistreplase. When anistreplase is compared with conventional heparin therapy, a 31% reduction in infarct size is found (estimated from single photon emission computed tomography, or SPECT). This translates into a significant preservation of left ventricular ejection fraction as observed in anistreplase-treated patients compared with heparin-treated patients (0.53 +/- 0.13 vs 0.47 +/- 0.12, p less than 0.002). In comparative trials of 2 thrombolytic agents, anistreplase was demonstrated to be as efficient as alteplase on left ventricular ejection fraction preservation and infarct size limitation.

Preventive strategies in management of acute myocardial infarction

Recent studies on pathogenetic mechanisms, supplemented by findings in clinical trials point the way to a logical approach to acute evolving myocardial infarction. This is designed in the earliest stage to limit infarction through reduction in myocardial oxygen demands, improvement in collateral blood supply and dissolution of coronary thrombus, to prevent in a later stage coronary reocclusion through administration of antiplatelet agents, and then to prevent infarct expansion through reduction in ventricular wall tension throughout the period of repair. Application of such an approach holds the promise of reducing infarct size and all the complications of infarction, as well as short and long-term mortality. The approach is active and aggressive, and contrasts with the approach applied a decade ago, where infarction was accepted as inevitable and therapies were reserved for managing its complications.

After coronary thrombolysis and reperfusion, what next?

Thrombolytic therapy for the removal of intravascular thrombi was introduced when streptokinase was first given to humans 40 years ago, the same year the American College of Cardiology was founded. Streptokinase was first administered to patients with acute myocardial infarction in 1959. Today, thrombolytic therapy has been established to offer significant benefits to patients with acute myocardial infarction provided they are brought to medical attention early enough after the onset of symptoms. The two major agents, streptokinase and recombinant tissue-type plasminogen activator (rt-PA), have been shown to result in reperfusion of infarct-related arteries, to salvage ischemic myocardium, to improve myocardial performance and to reduce mortality. In spite of these impressive gains, this novel therapy has shortcomings. The interval from the start of thrombolytic treatment to coronary reperfusion varies significantly from patient to patient and may, at times, be too long to produce a real benefit in terms of salvage of ischemic myocardium. The rate of reocclusion lies somewhere between 10% and 20% and appears not to be influenced by concomitant heparin anticoagulation. The rate of bleeding complications even with the "fibrin-specific" rt-PA is higher than anticipated and may range from 10% to 30%. As a consequence, intensive efforts are being directed at the development of improved thrombolytic agents and for adjunctive therapy evaluating better anticoagulants than heparin and better antiplatelet agents than aspirin. This review is a status report summarizing where we are in thrombolytic therapy in acute myocardial infarction, where we need to improve treatment results and what is being done mainly at the preclinical level to bring about such improvements.

Evaluation of patients for the need of thrombolytic therapy in the prehospital setting

Maximum benefit from thrombolytic therapy in acute myocardial infarction is obtained with early therapy. The earliest possible time to treat is during the initial evaluation of the patient in the home or ambulance, which requires accurate diagnosis of acute myocardial infarction in the prehospital setting. In our study, paramedics evaluated patients who had chest pain with a 12-lead ECG transmitted by cellular telephone and a checklist for inclusion and exclusion criteria for thrombolytic therapy. This information was transmitted to a hospital-based telemetry physician who diagnosed or excluded acute myocardial infarction and made a mock decision to withhold or administer a thrombolytic agent. Forty-eight patients with chest pain were evaluated. Six were diagnosed as having overt acute myocardial infarction by the hospital-based telemetry physician. All six patients had the diagnosis substantiated by both ECG and enzyme studies on hospital admission. Based on the data supplied by paramedics, two of these six patients were considered eligible for thrombolytic therapy by the physician. Hospital evaluation confirmed the prehospital decision to treat with a thrombolytic agent. In addition, all other patients were appropriately diagnosed as ineligible. Prehospital ECG diagnosis resulted in two patients going directly to the catheterization lab, thereby bypassing the emergency department. Overt acute myocardial infarction can be accurately identified by a prehospital-acquired 12-lead ECG transmitted to a hospital-based physician. Our study demonstrates that in conjunction with specially trained paramedics, the hospital physician can decide whether to administer thrombolytic therapy to such patients in the prehospital setting.

Thrombolytic agents in early myocardial infarction

The current revolution in the treatment of acute myocardial infarction by means of thrombolytic therapy has as its underlying strategy 3 aims: early restoration of the blood flow in order to salvage jeopardized but still viable tissues, limitation of the ultimate infarct size, and preservation, as far as possible, of ventricular function. The hope is that these 3 achievements will result in reduced short- and long-term mortality rates. The techniques used in this overall strategy are still under investigation. Three leading pharmacologic compounds vie for supremacy: streptokinase as well as its anisoylated form, recombinant technique tissue-type plasminogen activator and urokinase with or without prourokinase. In addition, the underlying anatomy may require early, or delayed, percutaneous transluminal coronary angioplasty where needed backed by coronary artery bypass grafting. Thus, the tactics of the intervention may vary from case to case and indeed from center to center depending on experience and facilities, but the conclusion is clearly the same: Early reperfusion is a must if one wishes to save ischemic but viable tissue. This report summarizes the current evidence for this new strategy.

Effects of residual stenosis on infarct size and regional transmural myocardial blood flow after reperfusion

This study in dogs was designed to determine the effects of residual stenosis on infarct size and on the transmural distribution of coronary flow in the central and peripheral ischemic perfusion bed. A plastic shunt containing a Doppler flow probe was inserted between the left anterior descending coronary artery and the subclavian artery. The dogs were divided into two groups. Group 1 (N = 7) underwent total shunt occlusion for 2 hours followed by reperfusion at 50% of control flow for 2 hours. Group 2 (N = 8) underwent 2 hours of total occlusion followed by 2 hours of total reperfusion. Regional blood flow was measured by radiolabeled microspheres, and infarct areas were quantitated with triphenyl tetrazolium chloride staining. Infarct sizes expressed as a percentage of the left ventricle or as a percentage of perfusion territory were significantly (p less than 0.05) smaller in animals with total reperfusion (group 2) than in dogs with partial reperfusion (group 1). Endocardial flows in the central infarct zone were significantly higher in dogs with total reperfusion than was observed with partial reperfusion; epicardial flows were not significantly different. In the peripheral region both endocardial flows and epicardial flows with total reperfusion were significantly higher than with partial reperfusion. These studies suggest that residual stenosis after thrombolysis may increase infarct size and reduce endocardial flow in the central infarct zone and transmural flow in the peripheral zone.

Daily serial evaluation of left ventricular function with equilibrium radionuclide ventriculography following thrombolysis during acute myocardial infarction

The changes in ventricular function after reperfusion by coronary thrombolysis are important when deciding about further definitive treatment necessary to ensure long-term vessel patency. The purpose of this study was to evaluate the early changes in left ventricular function after reperfusion. Left ventricular function was serially evaluated for 10 days in a group of 18 patients receiving intracoronary thrombolytic therapy for an acute myocardial infarction. Comparison of the global ventricular function in the successfully and unsuccessfully reperfused groups of patients showed significantly better function in the successful group than the unsuccessful group after the first day, which was maintained for the entire study period. Global and regional ventricular function in the successfully reperfused patients showed significant early improvement during the initial 72 h with maintenance of this improvement for the study period of 10 days. In the patients in whom reperfusion was unsuccessful, regional ventricular function showed no change, while the global function declined from day 5 to day 8 of the study period. This study then confirms the significant improvement in ventricular function after successful reperfusion. The time course pattern of the change in ventricular function indicates that the most significant improvement occurs within the first 72 h after reperfusion. These changes are similar to those previously reported in experimental animals.

Impact of different reperfusion modalities on ventricular function after acute myocardial infarction

Single-plane contrast ventriculography was performed on admission and before hospital discharge in more than 200 patients with acute myocardial infarction participating in a series of prospective clinical trials including intracoronary streptokinase, percutaneous transluminal coronary angioplasty (PTCA), intravenous tissue plasminogen activator (rt-PA) and thrombolysis (intravenous rt-PA or streptokinase) followed by PTCA. Both global ejection fraction (EF) and regional wall motion of the infarct zone were measured to assess serial changes. Patients treated with intracoronary streptokinase 3.6 +/- 1.8 hours after symptom onset had no increase in EF (mean change 1 +/- 6%, difference not significant [NS]), but patients treated with primary PTCA at 3.0 +/- 1.2 hours did (mean improvement 8 +/- 7%, p less than 0.001). Patients treated with sequential intravenous streptokinase and PTCA 2.6 +/- 1.3 hours after symptom onset showed similar improvement in EF (mean change 6 +/- 12%, p less than 0.002). Patients treated with rt-PA had no change in EF whether treated with rt-PA alone or rt-PA followed by immediate angioplasty (mean change -2 +/- 8% and 0.5 +/- 8%, p = NS, respectively). When angioplasty was used in patients with persistent occlusion after thrombolytic therapy, EF improved in those who had received intravenous streptokinase (mean change 10 +/- 7%, p less than 0.002), but not those who had received rt-PA (+0.5%, p = NS). However, infarct zone regional wall motion improved in patients treated with intracoronary streptokinase (+0.59 +/- 0.79 standard deviation/chord, p less than 0.05), primary PTCA (+1.32 +/- 1.32, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)