The effect of intravenous thrombolytic therapy on left ventricular function: a report on tissue-type plasminogen activator and streptokinase from the Thrombolysis in Myocardial Infarction (TIMI Phase I) trial

Late reperfusion for acute myocardial infarction limits the dilatation of left ventricle without the reduction of infarct size

BACKGROUND

While previous clinical studies have shown a possible beneficial effect of the reperfusion performed at a relatively late phase of acute myocardial infarction ("late reperfusion") in preventing left ventricular enlargement, the mechanism has not been clarified.

METHODS AND RESULTS

Of 89 patients with an initial anterior myocardial infarction, reperfusion was successful in 69. These 69 were divided into three groups according to the time required to achieve reperfusion after the onset of symptoms: early-reperfused (< 3 hours from the onset to reperfusion; n = 22), intermediate-reperfused (3 to 6 hours from the onset to reperfusion; n = 28), and late-reperfused (> 6 hours from the onset to reperfusion; n = 19). The 20 patients whose infarct-related artery were occluded in the acute phase as well as 1 month later was classified as nonreperfused. Infarct size, evaluated as defect volume by 201Tl single-photon emission computed tomography 1 month after the onset, was 1593 +/- 652 units (mean +/- SD) in the late-reperfused group, significantly larger (P < .05) than that of the intermediate-reperfused (1066 +/- 546 U) or the early-reperfused groups (372 +/- 453 U) but not different from that of the nonreperfused group (1736 +/- 562 U). Wall motion abnormality index as well as global ejection fraction evaluated by left ventriculography 1 month after the onset showed that late reperfusion did not preserve the left ventricular wall motion and function. These results indicate that the earlier reperfusion decreased the size of the infarction and preserved left ventricular function, whereas late reperfusion (> 6 hours after onset) did not limit infarct size or preserve left ventricular function. In contrast, the end-diastolic volume index did not differ significantly among the early-reperfused (50 +/- 15 mL/m2), intermediate-reperfused (54 +/- 14 mL/m2), and late-reperfused (53 +/- 19 mL/m2) groups; those were significantly smaller than that of the nonreperfused group (68 +/- 12 mL/m2; P < .05). Left ventriculographic data obtained in both the acute and chronic phase in 39 patients showed that left ventricular volumes increased significantly during the course of myocardial infarction only in the nonreperfused group.

CONCLUSIONS

Late reperfusion appeared to prevent ventricular dilatation acute myocardial infarction independent of the limitation of infarct size.

The effects of tissue plasminogen activator, streptokinase, or both on coronary-artery patency, ventricular function, and survival after acute myocardial infarction

BACKGROUND

Although it is known that thrombolytic therapy improves survival after acute myocardial infarction, it has been debated whether the speed with which coronary-artery patency is restored after the initiation of therapy further affects outcome.

METHODS

To study this question, we randomly assigned 2431 patients to one of four treatment strategies for reperfusion: streptokinase with subcutaneous heparin; streptokinase with intravenous heparin; accelerated-dose tissue plasminogen activator (t-PA) with intravenous heparin; or a combination of both activators plus intravenous heparin. Patients were also randomly assigned to cardiac angiography at one of four times after the initiation of thrombolytic therapy: 90 minutes, 180 minutes, 24 hours, or 5 to 7 days. The group that underwent angiography at 90 minutes underwent it again after 5 to 7 days.

RESULTS

The rate of patency of the infarct-related artery at 90 minutes was highest in the group given accelerated-dose t-PA and heparin (81 percent), as compared with the group given streptokinase and subcutaneous heparin (54 percent, P < 0.001), the group given streptokinase and intravenous heparin (60 percent, P < 0.001), and the group given combination therapy (73 percent, P = 0.032). Flow through the infarct-related artery at 90 minutes was normal in 54 percent of the group given t-PA and heparin but in less than 40 percent in the three other groups (P < 0.001). By 180 minutes, the patency rates were the same in the four treatment groups. Reocclusion was infrequent and was similar in all four groups (range, 4.9 to 6.4 percent). Measures of left ventricular function paralleled the rate of patency at 90 minutes; ventricular function was best in the group given t-PA with heparin and in patients with normal flow through the infarct-related artery irrespective of treatment group. Mortality at 30 days was lowest (4.4 percent) among patients with normal coronary flow at 90 minutes and highest (8.9 percent) among patients with no flow (P = 0.009).

CONCLUSIONS

This study supports the hypothesis that more rapid and complete restoration of coronary flow through the infarct-related artery results in improved ventricular performance and lower mortality among patients with myocardial infarction. This would appear to be the mechanism by which accelerated t-PA therapy produced the most favorable outcome in the GUSTO trial.

The role of the coronary collateral circulation in limiting myocardial ischemia and infarct size

The role of coronary collateral circulation in limiting ischemia and infarction has been studied prospectively. Transient occlusion of a coronary artery angioplasty has provided evidence that collateral circulation decreases wall motion abnormalities, ST segment changes, and lactate production. Patients who have collateral flow also have a better outcome after coronary artery dissection and acute closure than patients without collateral flow. Collateral circulation also limits infarct size during acute myocardial infarction with and without thrombolysis. Although collateral flow may decrease coronary artery bypass graft patency in certain subgroups of patients, the perioperative infarct rate and mortality is decreased. Growth factors have been identified that increase the development collateral circulation and may improve ventricular function in the setting of myocardial infarction.

Effects of streptokinase during acute myocardial infarction on the signal-averaged electrocardiogram and on the frequency of late arrhythmias

Although a number of studies have shown that the incidence of late potentials is lower after thrombolytic therapy, it is not known whether this is paralleled by fewer arrhythmic events during long-term follow-up. In patients with first acute myocardial infarction, filtered QRS duration was significantly shorter when treated with streptokinase (95 +/- 11 ms, n = 53) than when treated with conventional therapy (99 +/- 12 ms, n = 77, p < 0.05). The low-amplitude signal (D40) was shorter after thrombolysis (28 +/- 11 vs 33 +/- 12 ms, p < 0.02). Terminal root-mean-square voltage did not differ significantly (41 +/- 24 vs 35 +/- 23 microV). Irrespective of treatment, late potentials were predictive in the complete group (n = 171) for arrhythmic events during follow-up (13 +/- 6 months, range 6 to 24) (hazard ratio 7.7, p < 0.02, Cox proportional-hazards survival analysis), but treatment (streptokinase vs conventional) did not significantly affect outcome when added to the model. It is concluded that thrombolysis prevents the development of late potentials. However, this study does not confirm the hypothesis that prevention of late potentials leads to a decrease in arrhythmic events.

Effect of thrombolysis on acute mitral regurgitation during evolving myocardial infarction. Experience from the Thrombolysis in Myocardial Infarction (TIMI) Trial

OBJECTIVES

This study was undertaken to determine whether early successful thrombolysis can reverse infarct-associated mitral valve dysfunction.

BACKGROUND

Mitral regurgitation is a common complication of acute myocardial infarction and has been shown to adversely affect both short- and long-term prognosis. Although anecdotal reports have suggested that reperfusion of the infarct-related artery may restore normal function to the mitral valve, this theory has not been subjected to formal investigation.

METHODS

Patients with total or partial obstruction of the infarct-related artery received intravenous thrombolytic therapy with either streptokinase or recombinant tissue-type plasminogen activator within 7 h of symptom onset (mean 4.8 h) as part of the Thrombolysis in Myocardial Infarction (TIMI) Phase I trial. Repeat coronary angiography assessed arterial patency at 90 min and 10 days after attempted reperfusion. The presence and severity of mitral regurgitation were determined by contrast ventriculography both before thrombolysis and before hospital discharge.

RESULTS

Overall, 21 (16%) of the 132 study patients exhibited mitral regurgitation on either their initial or their predischarge ventriculogram. The proportion of infarct-related arteries found to be patent (TIMI flow grade 2 or 3) was statistically similar in patients with and without mitral regurgitation during each angiographic evaluation period (initial, 90 min and 10 days). Although coronary artery perfusion increased overall during sequential measurement (mean TIMI grade was 0.4 +/- 0.6 initially, 1.5 +/- 1.3 at 90 min and 2.2 +/- 1.0 at 10 days), the pattern of reperfusion observed could not predict an increase or decrease in regurgitant severity (p = NS). Early mitral regurgitation resolved in 57% of patients by 10 days, but this resolution appeared independent of the presence or absence of improved coronary perfusion (60% vs. 50%). The development of new regurgitation during the recovery period (6%) was also unrelated to improved perfusion (7% vs. 4%).

CONCLUSIONS

Acute mitral regurgitation developing during myocardial infarction shows frequent changes in its presence or severity during the 1st 10 days, appears independent of coronary artery patency both early and late after thrombolysis and cannot be reliably treated by improving arterial perfusion with thrombolytic agents.

Importance of platelets in myocardial injury after reperfusion in the presence of residual coronary stenosis in dogs

Residual coronary stenosis is common after successful thrombolysis for acute infarction. We investigated the role of platelets and the influence of a residual critical stenosis during early reperfusion in survival of reperfused myocardium. The left anterior descending coronary artery was occluded for 90 minutes and reperfused for 6 hours in 5 groups of dogs, 3 with a residual critical stenosis (groups 1 through 3) and 2 without (groups 4 and 5). Thrombocytopenia was produced by an antiserum in groups 2, 3, and 5; group 3 was also made neutropenic by another antiserum. Platelets (groups 1 and 4) and neutrophils (groups 1, 2, 4, and 5) labeled with indium 111 were reinjected at occlusion. Collateral flow was estimated with radioactive microspheres and was statistically similar among groups. Infarct size (percentage of area at risk), revealed by triphenyltetrazolium, was more severe (49.4% +/- 4.0%; p < 0.05) with stenosis (group 1) than without stenosis (group 4: 29.5% +/- 4.6%). Platelet depletion reduced infarct size in group 2 (28.6% +/- 6.3%; p < 0.05 vs group 1) with stenosis, but not in group 5 without stenosis (24.5% +/- 6.2% vs group 4: 29.5% +/- 4.6%). Neutropenia (group 3) did not decrease infarct size in thrombocytopenic dogs. Neutrophil accumulations in reperfused myocardium were similar among groups, but platelets accumulated in greater numbers in reperfused infarcts with stenosis (group 1: 338,581 +/- 52,857/gm; p < 0.05) than without stenosis (group 4: 153,445 +/- 23,949/gm). Therefore a critical stenosis at reperfusion compromises myocardial salvage and increases infarct size by means of a platelet-mediated mechanism.

The choice of thrombolytic agents in the emergency department

STUDY OBJECTIVE

To assess the choice of thrombolytic agents in emergency departments and whether administrators and third-party payers are influencing choices because of cost differences.

DESIGN

A telephone survey.

TYPE OF PARTICIPANTS

ED medical directors, stratifying for hospital ownership, size, and regions of the United States.

MEASUREMENTS AND MAIN RESULTS

One hundred twenty-three ED medical directors completed the interview. Findings indicate that formularies include recombinant tissue-type plasminogen activator (rt-PA) in 94.3% of surveyed hospitals and streptokinase in 63.4%. Public hospitals were significantly less likely to have rt-PA on the formulary (P = .0001). Based on payer type, 68.9% to 77.5% of patients requiring thrombolysis receive rt-PA, with approximately 15% of EDs using it for 1% to 25% of patients and an additional 15% using it for 26% to 50% of patients. Fourteen medical directors (11%) reported that they delay treatment with rt-PA until authorization is provided by the health maintenance organization, and 40% indicated they would change their choice of agents if rt-PA was denied. Cardiologists were the primary decision makers regarding thrombolytic agents in all types of hospitals.

CONCLUSION

Although rt-PA is the most frequently selected thrombolytic agent, significant practice variations exist among hospitals. To avoid interference from third-party payers and administrators, physicians may need to make decisions regarding such expensive agents in more objective forums (eg, pharmacy and therapeutics committees) and be better prepared to defend the resulting practice guidelines.

Effects of intravenous SM-9527 (double-chain tissue plasminogen activator) on left ventricular function in the chronic stage of acute myocardial infarction

Clinical effects of thrombolytic agent SM-9527 (double-chain tissue plasminogen activator) on left ventricular (LV) function were assessed in patients with acute myocardial infarction (AMI). A dose of 30 x 10(6) IU SM-9527 was given intravenously to patients with AMI within 6 h after onset. Of 159 candidates, 20 were excluded from the trial due to diseases other than myocardial infarction or failure to meet the protocol requirements; 114 of the remaining 139 were subjected to LV function analysis. The following results were obtained: (1) Patients with successful reperfusion in response to SM-9527 in the acute stage without later reocclusion revealed a significant improvement of LV function in the chronic stage. (2) Adverse effects were noted in 15 patients (10.8%), but none were serious; all were bleeding related to catheterization. (3) Hemagglutination fibrinolysis system test revealed no problems. It is concluded that early thrombolytic therapy with intravenous SM-9527 for AMI provides significant improvement of LV function in the chronic stage.

Systolic left ventricular function after reperfusion therapy for acute myocardial infarction. Analysis of determinants of improvement. The TAMI Study Group

BACKGROUND

Contrast ventriculograms of 542 patients treated with intravenous thrombolytic agents for acute myocardial infarction were examined to define changes in left ventricular ejection fraction and regional wall motion that occur during the first week after reperfusion therapy for acute myocardial infarction and define clinical, acute angiographic and treatment variables related to improvement in global and regional left ventricular function.

METHODS AND RESULTS

Intravenous tissue-type plasminogen activator and/or urokinase was administered to 805 patients during acute myocardial infarction. Mean time from symptom onset to thrombolytic therapy was 3 hours (22 patients received therapy within the first hour). Acute and 7-day catheterization were performed. Paired left ventricular ejection fraction and centerline regional wall motion were available in 542 patients (67%). Stepwise, multivariable analysis of clinical, acute angiographic and treatment variables was used to develop two models: One related to improvement in left ventricular ejection fraction, and the second related to improvement in infarct zone regional function. Left ventricular ejection fraction did not change (51.2 +/- 11.1% for acute versus 51.9 +/- 11.0% for 1 week, p = 0.19). Improvement in infarct zone regional function was modest (14%) at 1 week (-2.54 +/- 1.07 standard deviation per chord for acute versus -2.17 +/- 1.24 at 1 week, p < 0.001). Subgroup analysis demonstrated modest improvement in ejection fraction (1.4 +/- 9.5%) and greater improvement in infarct zone function (19%) in patients with successful sustained reperfusion at 1 week. Depressed left ventricular ejection fraction and infarct zone regional wall motion at the acute study were strongly associated with improvement of these parameters at 1 week. Resolution of chest pain before acute catheterization, infarct-related artery flow at acute catheterization, and depressed regional wall motion in the noninfarct zone were associated with improvement in both ejection fraction and regional infarct zone function at 1 week. Notably, the time from the onset of symptoms to initiation of thrombolytic treatment was not related to subsequent improvement in ventricular function.

CONCLUSIONS

Dramatic improvement in left ventricular systolic function is not common after thrombolytic therapy for acute myocardial infarction. Improvement in global and regional systolic function is most closely related to acutely depressed ventricular function and successful acute coronary recanalization. Thus, patients with the most myocardium in jeopardy and successful coronary reperfusion demonstrate the greatest improvement in global and infarct zone ventricular function. Overall, the magnitude of this improvement is modest, suggesting that the benefits of coronary reperfusion are not solely related to improvement in systolic left ventricular function.

Diagnosis of right ventricular infarction by overlap images of simultaneous dual emission computed tomography using technetium-99m pyrophosphate and thallium-201

The validity of dual energy single-photon emission computed tomography (SPECT) with technetium-99m pyrophosphate (Tc-99m PPi) and thallium-201 for the diagnosis of right ventricular (RV) infarction, and the clinical features of RV infarction, were investigated in 190 patients with acute myocardial infarction. Diagnosis of RV infarction was performed by Tc-99m PPi accumulation in the RV myocardium on thallium-201 and Tc-99m PPi over-lay images at the dual SPECT with simultaneous imaging taken 2 to 9 days after the onset of myocardial infarction. Thirty RV infarctions were found among the 190 patients with left ventricular infarction (15.8%): 29 (97%) in association with the inferior and 1 (3%) with the lateral infarction. Tc-99m PPi accumulation was mostly observed in the posterior wall of the right ventricle. A total occlusion or a severe stenosis of the right coronary artery was demonstrated angiographically in 92% of the patients with RV infarction. The prevalence of RV infarctions was significantly lower in patients who achieved successful early reperfusion than in those who did not (26.7 vs 68.4%, respectively, p < 0.01). However, a successful early reperfusion therapy could not significantly decrease the rate of RV involvement in patients without significant collateral flow (p < 0.01). Thus, dual isotope SPECT with Tc-99m PPi and thallium-201 can be used as a reliable method for the diagnosis of RV infarction.

Intravenous thrombolytic therapy in myocardial infarction: an analytical review

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

Hemodynamic, mechanical, and metabolic determinants of thrombolytic efficacy: a theoretic framework for assessing the limitations of thrombolysis in patients with cardiogenic shock

Although thrombolytic therapy has been shown to limit infarct size, preserve left ventricular function, and improve survival in most subgroups of patients with acute MI, a benefit has not been demonstrated in patients with clinical left ventricular dysfunction or overt cardiogenic shock before treatment is initiated. The reason(s) for the lack of benefit derived from thrombolytic therapy in these settings is unclear. Left ventricular dysfunction and overt cardiogenic shock are the result of extensive myocardial necrosis, typically in excess of 30% of the left ventricle, which progresses over time. The available data suggest that thrombolytic efficacy is decreased because of either hemodynamic, mechanical, or metabolic factors. As a result coronary patency is rarely achieved in a timely fashion, and if patency is achieved it typically is not maintained. The ability of mechanical revascularization by means of balloon angioplasty to reduce mortality suggests that reperfusion is a key determinant of outcome even among patients with large infarctions and early signs of left ventricular dysfunction. Thrombolytic therapy, which is widely available and extensively tested, represents the standard of care for patients with acute MI. Its apparent lack of efficacy in patients with congestive heart failure and cardiogenic shock is poorly understood. Further investigation must therefore be undertaken.

Myocardial technetium 99m sestamibi kinetics after reperfusion in a canine model

Clinical sestamibi imaging protocols after reperfusion therapy are based on the premise that redistribution does not occur. However, animal studies that use punch biopsies or imaging have variably reported either some or no redistribution. This study was designed to (1) utilize implantable radiation detectors to determine whether sestamibi is redistributed after reperfusion, (2) accurately determine the time course, extent, and kinetics of the redistribution, and (3) determine whether sestamibi kinetics can be used to document reperfusion and salvage after a single dose of sestamibi. Twenty-five dogs were injected with 5.0 mCi of technetium 99m sestamibi and microspheres during circumflex occlusion, and reperfusion occurred within 5 minutes in group 1 (15-minute occlusion) and group 2 (1-hour occlusion). Group 3 was not reperfused. Sestamibi activities in the normal and occluded zones were monitored with radiation detectors for 2 hours, and serial gamma camera imaging and arterial blood sampling was begun. No dogs in group 1 and all dogs in groups 2 and 3 had infarcts as shown by triphenyltetrazolium chloride stain. The final occluded/normal zone technetium 99m activity ratio was significantly higher than the flow ratio at the time of sestamibi injection only in the group 1 dogs (0.51 +/- 0.05 vs 0.38 +/- 0.06, p = < 0.0001). In addition, the mean 2-hour fractional sestamibi clearance from the occluded/reperfused zone (0.03 +/- 0.02) was significantly slower in the group 1 dogs compared with normal zone clearance (0.09 +/- 0.01, p = 0.03). Gamma camera images demonstrated large posterior wall perfusion defects initially, which persisted 2 hours later with no visual evidence of redistribution in any of the reperfused dogs in groups 1 and 2. Thus in an experimental animal model under ideal conditions, sestambi is redistributed into reperfused viable myocardium; however, the amount of this redistribution is small and could not be perceived by visual image analysis. Sestamibi is not redistributed into reperfused nonviable myocardium or into nonreperfused myocardium. Therefore sestamibi kinetics after a single dose of tracer in an experimental animal model can be used to document reperfusion of viable myocardium but cannot differentiate reperfusion of the infarcted territory from nonreperfused infarcted myocardium.

Time course of functional improvement in stunned myocardium in risk area in patients with reperfused anterior infarction

BACKGROUND

The beneficial effect of coronary reflow on myocardial salvage may be assessed more accurately than in previous studies if the size of risk area is taken into account, particularly because the size of risk area varies significantly among patients. In this study, the risk area was determined with myocardial contrast echocardiography to investigate the time course of functional recovery of postischemic myocardium within the risk area in patients with reperfused anterior myocardial infarction.

METHODS AND RESULTS

The study population consisted of 21 patients with anterior myocardial infarction who achieved coronary reflow within 6 hours of onset by means of thrombolysis or coronary angioplasty. Myocardial contrast echocardiography was performed with the injection of hand-agitated Haemaccel (5 ml) into the right and left coronary arteries before coronary reflow, and the risk area was defined as the area of contrast perfusion defect in the apical long-axis view. The ratio of the endocardial length of abnormal contraction (dyskinesis/akinesis) segment to that of contrast defect segment (AS/CD) was determined at days 1, 2, 3, 7, 14, and 28 of reflow. Before reflow, the length of contrast defect correlated well with the segment length of dyskinesis/akinesis. The values for AS/CD in patients with successful reperfusion significantly and progressively decreased until day 14; 1.00 +/- 0.02 at day 1, 0.93 +/- 0.11 at day 2 (p < 0.05 versus day 1), 0.84 +/- 0.16 at day 3 (p < 0.05 versus day 2), 0.80 +/- 0.13 at day 7 (p < 0.01 versus day 2), 0.73 +/- 0.10 at day 14, and 0.72 +/- 0.10 at day 28. Greater improvement in function was obtained in patients reperfused within 4 hours than in those reperfused at > or = 4 hours (AS/CD at day 28, 0.64 +/- 0.12 versus 0.75 +/- 0.09, p < 0.05).

CONCLUSIONS

Thus, a significant amount of myocardium, an average of 28% in segment length of the risk area, is salvaged in patients with reperfused anterior myocardial infarction. Major functional improvement seems to be achieved within 14 days of reflow.

Thrombolytic, antiplatelet, and antithrombotic agents

The relative efficacy and safety of individual thrombolytic agents, administered alone and with antiplatelet and antithrombotic drugs, in the treatment of acute myocardial infarction are presented. The clinical benefits and risks of treatment choices are discussed in relation to the mechanisms of the formation and prevention of thrombus and thrombolysis. It is concluded that streptokinase, tissue plasminogen activator (t-PA), and anisoylated plasminogen-streptokinase activator complex (APSAC) significantly reduce mortality and improve left ventricular function equally, despite differences in the rate at which they achieve vascular patency, their durations of action, and the extent to which their use is associated with adverse events. The questions of how best to minimize reocclusion/reinfarction, bleeding, and stroke are discussed, with particular focus on the beneficial use of aspirin and the unresolved issue of how best to use heparin.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

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

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Streptokinase resistance: when might streptokinase administration be ineffective?

OBJECTIVE

(a) To develop an assay for streptokinase resistance. (b) To determine the prevalence of streptokinase resistance in patients presenting with acute myocardial infarction for the first time. (c) To determine the prevalence of streptokinase resistance in patients after exposure to streptokinase or streptococcal infection.

DESIGN

Open, prospective.

PATIENTS

30 healthy volunteers. 40 patients admitted to the coronary care unit at Addenbrooke's Hospital with suspected acute myocardial infarction, 12 patients 12 months after streptokinase treatment, eight patients 24 months after streptokinase treatment, and sera from 12 patients with raised anti-streptolysin O (ASO) titres.

METHODS

Three assays were used; a dilution neutralisation assay, an enzyme linked immunosorbent assay (ELISA) for immunoglobulin G (IgG) anti-streptokinase antibodies, and an in vitro fibrin plate lysis assay. All measurements were performed on venous blood samples.

RESULTS

Neutralisation and IgG antibody titres were positively correlated. Mean (SEM) antistreptokinase concentrations in the 30 controls were 87 (10) U/ml (neutralisation assay) and 28 (6.3) U/ml (ELISA). Corresponding concentrations in patients before streptokinase were 68 (6.1) U/ml and 18 (4.5) U/ml with a mean fibrin plate assay 117 (7.1)% that of controls. Resistance to streptokinase was detectable in one patient after 72 hours and in all patients by day 10. By day 10 concentrations were 4388 (919) U/ml, 773 (109) U/ml, and 17 (5.4)%. At both 12 and 24 months resistance was present in 75% of patients. Similarly 66% of high ASO titre sera showed resistance. The fibrin plate lysis assay detected significantly reduced streptokinase dependent fibrinolysis in vitro in the absence of raised total concentrations of antistreptokinase antibodies.

CONCLUSIONS

The prevalence of streptokinase resistance in patients presenting with their first myocardial infarction is low. Resistance develops early after treatment and is still present in 75% of patients after 24 months. Retreatment with streptokinase is likely to be suboptimal even after 24 months. The fibrin plate lysis assay detects resistance in patients with normal concentrations of streptokinase antibodies. Streptococcal infection is associated with a high incidence of streptokinase resistance.

The effect of superoxide dismutase in the myocardium during reperfusion in the dog

The aim of the study was to investigate the pathological role of free radicals during myocardial reperfusion. Low (0.5 mg/kg body weight) and high doses (5 mg/kg) of superoxide dismutase (SOD) were infused into the left atrium of mongrel dogs for 4 min starting 29 min after ligation and 1 min before reperfusion of the left anterior descending coronary artery (LAD). Arterial blood pressure, heart rate, electrocardiogram, and the regional contractile force of the left ventricle were monitored throughout the ligation (30 min) and reperfusion periods (20 min). Concentrations of creatine kinase (CK) and malondialdehyde (MDA) in the coronary sinus blood were determined before (0 min) and during ligation (15 and 25 min) and during reperfusion of the LAD (2, 7, and 20 min). In other groups of dogs, the effect of the two doses of SOD on epicardial blood flow was investigated during ligation and reperfusion by the measurement of epicardial temperature using a thermocardiograph. Experimental subjects were mongrel dogs of either sex (n = 25), weight 10-35 kg. Compared to controls (mean +/- SEM, 43.1 +/- 1.2; n = 7), the number of ventricular extrasystoles during the first 5 min of reperfusion was significantly (p < .001) decreased in dogs treated with the high dose (15.01 +/- 2.14; n = 5), but not in those receiving the low dose of the drug (34.6 +/- 5.66; n = 5). The concentrations of CK increased gradually until the end of reperfusion without differences among the different groups. Plasma MDA was the highest in control dogs 7 min after reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

High Level Expression of Streptokinase in Escherichia Coli

Streptokinase (SK), which activates human plasminogen by promoting its conversion to plasmin, is normally obtained from beta-hemolytic streptococci. Treatment with SK is an effective therapy for improving survival and preserving left ventricular function after coronary thrombosis. We report the cloning, expression in E. coli to levels of 25% of the total cell protein, and characterization of a novel SK (SKC-2) gene, the product of which is functionally equivalent to the naturally-derived protein. The availability of a recombinant streptokinase (rSK) in high yield and purity offers a potentially attractive alternative source of this important therapeutic agent.

Effect of an anterior wall motion abnormality on the results of single-plane and biplane left ventriculography

Although the biplane area-length method would be optimal for all left ventriculograms, 2 contrast injections are needed in laboratories with single-plane imaging equipment. The purpose of this study was to develop practical guidelines to identify the need for biplane left ventriculography in laboratories with single-plane equipment. From a retrospective analysis of 91 consecutive biplane ventriculograms (group 1), guidelines were identified that predicted when the ejection fraction calculated by the biplane method would differ significantly from the single-plane value. These guidelines were derived from information immediately available to the operator in the laboratory at the time of the procedure. Patients in group 1 were divided into 3 subgroups: biplane exceeding single-plane ejection fraction by greater than or equal to 0.05 (n = 20); single-plane exceeding biplane ejection fraction by greater than or equal to 0.05 (n = 14); and ejection fractions within +/- 0.04 by the 2 methods (n = 57). By multivariate analysis, the only predictor of a higher ejection fraction calculated by the biplane method was an anterior wall motion abnormality. This finding was tested prospectively in a separate group of 60 patients (group 2). Left ventriculograms in group 2 patients were stratified before analysis by the presence or absence of an anterior wall motion abnormality. In patients with anterior wall motion abnormalities, the biplane ejection fraction was greater than the single-plane value by 0.05 +/- 0.04 (range -0.03 to +0.15). In contrast, this difference in patients without anterior wall motion abnormalities was -0.01 +/- 0.04 (range -0.09 to +0.06; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant tissue plasminogen activator in acute myocardial infarction in the Chinese in Hong Kong

Eighty-nine consecutive Chinese patients (69 males, 20 females) with acute myocardial infarction treated by 100 mg recombinant tissue plasminogen activator (7 intracoronarily, 82 intravenously) at 3.7 +/- 1.0 h after onset, and intravenous heparin or dipyridamole therapy started at 3 h, were studied prospectively. Their mean age was 59.6 +/- 10.6 yr. Forty-six patients (51.7%) had anterior and 39 patients (43.8%) had inferior infarcts. Clinical evidence of reperfusion were seen in 63 patients (70.8%), while new complications included hypotension (5.6%), heart failure (6.7%), cardiac arrhythmias (76.4%) majority of which are related to reperfusion and self-remitting, haematoma around vascular access sites (23.6%), melaena (3.3%) and cerebral infarction (2.2%). Maximal changes in coagulation profiles were seen at 3 h, including a decrease in fibrinogen by 64.2% and an increase in fibrin degradation products by 47 times. The changes in haemostatic variables were not related to body weight or bleeding complications. Nine patients (10.1%) had recurrence of angina and 6 patients (6.9%) died due to pump failure and reinfarction. Angiogram at 14 days confirmed TIMI 2 or 3 patency of infarct-related arteries in 63 out of 73 (86.3%) patients, with a mean global ejection fraction of 52.5 +/- 12.4%. Nearly all survivors could maintain class I-II functional status after discharge. The safety and promise of recombinant tissue plasminogen activator for acute myocardial infarction in the Chinese were confirmed.

Randomized angiographic trial of recombinant tissue-type plasminogen activator (alteplase) in myocardial infarction. RAAMI Study Investigators

Clot dissolution with restoration of infarct-related artery blood flow is the likely mechanism for the improved prognosis and mortality reduction seen after thrombolytic therapy of acute myocardial infarction. A pilot study has suggested that 100 mg of recombinant tissue-type plasminogen activator (rt-PA) infused over 90 min may lead to higher patency rates than the current standard of 100 mg over 3 h. In this multicenter, randomized, open label trial, 281 patients with acute myocardial infarction receive 100 mg of rt-PA according to either the standard 3-h infusion regimen (an initial 10-mg bolus followed by 50 mg for the 1st h, then 20 mg/h for 2 h) or an accelerated 90-min regimen (15-mg bolus followed by 50 mg over 30 min, then 35 mg over 60 min). All patients also received intravenous heparin and oral aspirin during and after rt-PA infusion. At 60 min after initiation of the rt-PA infusion, the observed angiographic patency rates were 76% (95% confidence intervals 65% to 84%) in the accelerated regimen group and 63% in the control group (52% to 73%, p = 0.03). At 90 min these rates were 81% (73% to 87%) and 77% (68% to 84%), respectively (p = 0.21). Both randomized groups experienced similar rates of recurrent ischemia, reinfarction, angiographic reocclusion, other complications of myocardial infarction (including stroke and death) and bleeding complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of vapiprost, a novel thromboxane receptor antagonist, on thrombus formation and vascular patency after thrombolysis by tissue-type plasminogen activator

1. A thrombus was induced in the rat femoral artery by endothelial damage due to the photochemical reaction between systemically-injected Rose Bengal and transillumination with green light (wavelength: 540 nm). The artery of the control rat was completely occluded in 302.8 +/- 27.0 s after the initiation of the reaction. 2. Pretreatment with vapiprost (0.1, 0.3 and 1.0 mg kg-1, i.v., 5 min before the reaction) prolonged the time required to occlude the femoral artery in a dose-dependent manner. The efficacy of vapiprost on the time required for occlusion was over 10 times higher than that of aspirin which was administered 30 min before the reaction. 3. The thrombolytic effects of tissue-type plasminogen activator (tPA) on the established arterial thrombus in the presence and absence of vapiprost were also studied in the same model. When vapiprost (0.3 mg kg-1, i.v.) was administered just before tPA infusion (100 micrograms kg-1 min-1 for 30 min), the time required to reperfuse the occluded artery was reduced, the incidence of the reperfusion was increased and the arterial blood flow after reperfusion was improved. 4. When vapiprost (1.0 mg kg-1 daily p.o.) was administered for 1 week after the establishment of reperfusion by tPA combined with vapiprost, the patency of the reperfused artery was improved and the femoral arterial blood flow was better preserved than after treatment with only tPA. 5. These findings suggest that this thromboxane receptor antagonist may be a useful adjunct to anti-thrombotic therapy. The combination therapy with tPA may be more effective than treatment with tPA alone and provides greater protection against reocclusion after reperfusion.

Thrombolysis in patients with unstable angina improves the angiographic but not the clinical outcome. Results of UNASEM, a multicenter, randomized, placebo-controlled, clinical trial with anistreplase

BACKGROUND

The value of thrombolytic therapy in unstable angina is unclear.

METHODS AND RESULTS

To study this problem, 159 patients were studied in a double-blind, placebo-controlled multicenter trial. Patients without a previous myocardial infarction, with a typical history of unstable angina, and ECG abnormalities indicative of ischemia were included. After baseline angiography, study medication (anistreplase or placebo) was given. Angiography was repeated after 12-28 hours. A significant decrease occurred in diameter stenosis between the first and second angiogram in the anistreplase group compared with the placebo group (11% versus 3%, p = 0.008). This difference was caused by reopening of occluded vessels in the thrombolytic group. However, no beneficial clinical effects of thrombolytic treatment were found. Bleeding complications were significantly higher in patients who received thrombolytic therapy (21 versus seven patients, p = 0.001).

CONCLUSIONS

Thus, angiographic but no clinical improvement after thrombolytic treatment with anistreplase was found in patients with unstable angina with an excess of bleeding complications. Therefore, thrombolytic treatment cannot be recommended in patients diagnosed as having unstable angina until proven otherwise.

Extraction atherectomy during myocardial infarction in a patient with prior coronary artery bypass surgery

In this case report of a patient presenting with an acute inferior wall myocardial infarction, the infarct conduit was a saphenous vein graft. Extraction atherectomy using the TEC successfully reestablished patency and reversed the patient's clinical symptoms. Extraction atherectomy is a feasible procedure during acute coronary events and deserves further investigation.

Relationship between angiographic infarct size and left ventricular filling

Infarct size may influence left ventricular filling after acute myocardial infarction. Pulsed Doppler transmitral flow velocities were compared in 47 patients at 7 +/- 6 days following acute myocardial infarction and 47 age-matched controls. Patients were stratified by angiographic infarct size into Groups I, II, III (corresponding angiographic hypokinetic scores less than 2; 2-2.99; greater than or equal to 3 SD/cord). Early diastolic transmitral Doppler flow velocities did not differ between infarct groups but atrial transmitral Doppler flow measurements did: peak A velocity (p = 0.001), A velocity time integral (p less than 0.001), and total velocity time integral (p = 0.001). Compared to controls atrial transmitral Doppler flow was augmented in Group I, whilst atrial and total transmitral Doppler flow were depressed in Group III. Peak A velocity and A velocity time integral were inversely related to infarct size (R = -0.44 to -0.54) and directly to left ventricular ejection fraction (R = 0.59 to 0.65). Large infarct size following myocardial infarction is associated with lower atrial and total transmitral Doppler flow velocities.

Improved regional myocardial blood flow, left ventricular unloading, and infarct salvage using an axial-flow, transvalvular left ventricular assist device. A comparison with intra-aortic balloon counterpulsation and reperfusion alone in a canine infarction model

BACKGROUND

It has been suggested that left ventricular unloading at the time of reperfusion provides superior infarct salvage over reperfusion alone. The purpose of this study was to show that the Hemopump transvalvular axial-flow left ventricular assist device provides superior left ventricular unloading, ischemic zone collateral blood flow, and infarct size reduction compared with intra-aortic balloon counterpulsation and reperfusion alone.

METHODS AND RESULTS

Eighteen dogs were instrumented with regional myocardial function sonomicrometers in the ischemic and control zones. The left anterior descending coronary artery just distal to the first diagonal branch was instrumented with a silk snare and Doppler flow probe. Additionally, pressure catheters were placed in the left atrial appendage, left ventricular apex, and ascending aorta for hemodynamic measurements. Regional myocardial blood flow was determined by using 15-microns radioactive microspheres. Measurements were made in the control state, immediately after coronary occlusion, at 1 and 2 hours after coronary occlusion, with reperfusion, and 1 hour after reperfusion. In treated animals, left ventricular assistance was maintained during the entire period of occlusion and reperfusion. The Hemopump was associated with a significant decrease in left ventricular systolic and diastolic pressure, whereas mean arterial pressure was maintained. Intra-aortic balloon counterpulsation resulted in no significant changes in left ventricular systolic pressure and a modest decrease in left ventricular diastolic pressure. Regional unloading as assessed by sonomicrometers was significant in the Hemopump animals and absent in the balloon pump animals. Absolute regional myocardial blood flow in the ischemic zone increased slightly (p = 0.002) in the Hemopump animals and did not change in the balloon pump animals. Infarct size expressed as percentage of the zone at risk was 62.6% in the control animals, 27.22% in the balloon pump animals, and 21.7% in the Hemopump animals.

CONCLUSIONS

Mechanical unloading of the ventricle during ischemia and reperfusion appears to result in significant infarct salvage compared with reperfusion alone. The Hemopump appears to provide superior left ventricular systolic and diastolic unloading compared with intra-aortic counterpulsation in a canine model.

Residual coronary stenoses and calculated transstenotic gradients after intravenous streptokinase versus tissue plasminogen activator

To compare the relative success of intravenous streptokinase (STK) and tissue plasminogen activator (TPA) on the severity of residual infarct-related coronary stenoses, we evaluated 45 patients receiving thrombolytic therapy for acute myocardial infarction. Twenty-three patients (18 men and 5 women) received STK (1.5 million units), while 22 patients (18 men and 4 women) received TPA (100 mg) within 6 hours of chest discomfort. Cardiac catheterization was performed before hospital discharge (8 days) with quantitative coronary arteriography and estimation of transstenotic pressure gradients using fluid dynamic equations. Although angina pectoris was equally common (STK, 7 of 23 [30%] versus TPA, 5 of 22 [23%], p = NS), recurrent infarction (STK, 3 of 23 [13%] versus TPA, 7 of 22 [32%], p less than 0.05) and coronary angioplasty (STK, 2 of 23 [9%] versus TPA, 7 of 22 [32%], p less than 0.05) were more frequent in those receiving TPA. Infarct-related coronary patency was greater in TPA-treated subjects (STK, 15 of 23 [65%] versus TPA, 19 of 22 [86%], p less than 0.05), although minimum stenotic diameter (STK, 0.77 +/- 0.48 mm versus TPA, 0.57 +/- 0.38 mm, p less than 0.05), and calculated transstenotic pressure gradient (STK, 8.7 +/- 17.0 mm Hg versus TPA, 23.7 +/- 30.2 mm Hg, p less than 0.05) suggested severe residual stenosis. These effects were accentuated at elevated coronary flow velocities (8 to 20 cm/sec).(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombolysis: the need for a critical review

The (Thrombolysis in Myocardial Infarction) TIMI-I trial led to the hypothesis that the greater reperfusion rate seen with recombinant tissue-type plasminogen activator (rt-PA) versus streptokinase would result in greater reductions in infarct size and mortality in patients with acute myocardial infarction. Despite extensive investigation, no trial comparing rt-PA with streptokinase (European Cooperative Study Group, Plasminogen Activator Italian Multicenter Study [PAIMS], Gruppo Italiano per lo Studio della Sopravvivenze nell'Infarto Miocardico [GISSI-2], International Study on Infarct Survival [ISIS-3], even TIMI-I itself) nor rt-PA and anisoylated plasminogen-streptokinase activator complex (APSAC or anistreplase) (Bassand, TEAM-3, ISIS-3), have confirmed this hypothesis. In a reversal of traditional scientific method, the studies, rather than the unconfirmed hypothesis, have been rejected. A lack of independent review of this subject may have contributed to this outcome. It is proposed that standards of review and editorial comment mandating true critical distance and independence be followed, permitting greater independence of scientific inquiry, review and debate.

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

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

Demonstration of myocardial reperfusion injury in humans: results of a pilot study utilizing acute coronary angioplasty with perfluorochemical in anterior myocardial infarction

Reperfusion may limit the amount of potentially salvageable myocardium through the introduction of cellular elements into previously ischemic but viable myocardium (reperfusion injury). It has been demonstrated that intracoronary infusion of a 20% intravascular perfluorochemical emulsion (Fluosol) significantly reduces infarct size and results in improved left ventricular function in the canine model. This pilot study was performed to explore the existence of myocardial reperfusion injury in humans. Utilizing Fluosol as a probe in conjunction with emergency coronary angioplasty, 26 patients presenting within 4 h with a first anterior myocardial infarction were randomized to emergency angioplasty or angioplasty followed by a 30-min intracoronary infusion of Fluosol at 40 ml/min. Global and regional ventricular function were assessed immediately and a mean of 12 days after successful angioplasty with contrast ventriculography. Infarct size was semiquantitated with thallium-201 single-photon emission computed tomography (SPECT) images before discharge. Twelve patients (six undergoing angioplasty alone, six treated with angioplasty and Fluosol) had an occluded infarct-related vessel (Thrombolysis in Myocardial Infarction [TIMI] grade 0 to 1) at the time of emergency catheterization and were included in the final analysis. At 12 days after successful angioplasty, the improvement in regional ventricular function was greater in patients receiving adjunctive therapy with intracoronary Fluosol versus those undergoing angioplasty alone utilizing both the radial shortening and centerline method, respectively (23 +/- 3.1% vs. 8 +/- 2.3%, p less than 0.02; and -1.6 +/- 0.4 vs. -2.9 +/- 0.2 SD/chord, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Dipyridamole echocardiography test. A new tool for detecting jeopardized myocardium after thrombolytic therapy

BACKGROUND

We wished to assess whether dipyridamole echocardiography test (DET) can detect jeopardized myocardium after thrombolytic therapy.

METHODS AND RESULTS

Seventy-six consecutive patients with a first acute myocardial infarction (AMI) were treated with 2 million IU urokinase i.v. within 4 hours of the onset of AMI and underwent high-dose (as much as 0.84 mg/kg over 10 minutes) DET 8-10 days after AMI. The results were correlated to the anatomy of the infarct-related vessel (IRV). In patients with positive DET, we evaluated the wall motion score index (WMSI; a semiquantitative integrated estimation of extent and severity of the stress-induced dyssynergy). WMSI was derived by summation of individual segment scores divided by the number of interpreted segments. In a 13-segment model, each segment was assigned a score ranging from 1 (normal) to 4 (dyskinetic). Fifty-three patients had positive results on DET. Of these, 42 had dipyridamole-induced new wall motion abnormalities (WMAs) confined to the infarct zone or adjacent segments. In these patients, mean WMSI increased from 1.46 +/- 0.26 (at resting conditions) to 1.73 +/- 0.35 (at peak dipyridamole) (p less than 0.01), whereas no significant change was detected in negative patients (1.6 +/- 0.34 versus 1.57 +/- 0.34, p = NS). Coronary angiography showed a patent IRV (TIMI grade 2 or 3) in 53 patients and no or minimal reperfusion (TIMI grade 0 or 1) in 23 patients. A patent IRV with critical residual stenosis was found in 35 of 42 patients with dipyridamole-induced WMAs in the infarct zone and in 18 of 34 patients without WMAs (p less than 0.05). Among the 23 patients with occluded IRVs, nine had collateral flow to the distal vessel; six of these had a positive DET. Thus, the sensitivity and specificity for identifying a critically stenotic but patent IRV or the presence of a collateral-dependent zone were 66% and 93%, respectively. In a subset of nine patients with a positive DET in the infarct zone or adjacent segments, DET and a control coronary angiography were repeated 1-3 months after an angiographically successful (residual stenosis, 50% or less) coronary angioplasty in the IRV. The repeat DET was negative in eight patients (all with patent IRV at control angiography) and again positive in one patient, who showed restenosis at angiography. The WMSI, at resting conditions was similar before and after angioplasty, whereas it differed significantly at peak dipyridamole (1.7 +/- 0.2 versus 1.4 +/- 0.2, p less than 0.01).

CONCLUSIONS

DET can identify the anatomy of the IRV, and dipyridamole-induced WMAs within the infarct zone detect regions with jeopardized myocardium that may benefit from intervention.

Comparison of intravenous urokinase plus heparin versus heparin alone in acute myocardial infarction. Urochinasi per via Sistemica nell'Infarto Miocardico (USIM) Collaborative Group

In a randomized trial of the effects on in-hospital mortality of intravenous urokinase plus heparin versus heparin alone, 2,531 patients with acute myocardial infarction in 89 coronary care units were enrolled for greater than 30 months. Patients admitted within 4 hours of the onset of pain were randomized to receive either intravenous urokinase (a bolus dose of 1 million U repeated after 60 minutes) plus heparin (a bolus dose of 10,000 U followed by 1,000 IU/hour for 48 hours) or heparin alone (infused at the same rate). Complete data were obtained in 2,201 patients (1,128 taking urokinase and 1,073 taking heparin). At 16 days, overall hospital mortality was 8% in the urokinase and 8.3% in the heparin group (p = not significant). Among patients with anterior infarction, mortality was 10.3% in the urokinase and 13.9% in the heparin group (p = 0.09; relative risk = 0.73). The incidence of major bleeding (urokinase 0.44%, heparin 0.37%) as well as the overall incidence of stroke (urokinase 0.35%, heparin 0.20%) was similar in the 2 groups. The rates of major in-hospital cardiac complications (reinfarction, postinfarction angina) were also similar.

Comparative effects of APSAC and rt-PA on infarct size and left ventricular function in acute myocardial infarction. A multicenter randomized study

BACKGROUND

Recombinant tissue-type plasminogen activator (rt-PA or alteplase) and anisoylated plasminogen streptokinase activator complex (APSAC or anistreplase) have been demonstrated to limit infarct size significantly and to preserve left ventricular function when injected soon after acute myocardial infarction. However, as yet, the efficacy and safety of these two thrombolytic agents have not been directly compared in one trial; this was the aim of this study.

METHODS AND RESULTS

One hundred eighty-three patients suffering from a first acute myocardial infarction were randomly allocated to either APSAC (30 units over 5 minutes) or single-chain rt-PA (100 mg over a 3-hour period) within 4 hours of the onset of symptoms. Global and regional left ventricular function were assessed from contrast angiography an average of 5.3 +/- 2.3 days after initial therapy. Radionuclide angiography and thallium-201 single-photon emission computerized tomography were performed before hospital discharge. Infarct size was assessed by single-photon emission computerized tomography and expressed in percentage of the total myocardial volume. Ninety patients received APSAC and 93 received rt-PA within a mean period of 172 +/- 52 minutes after the onset of symptoms. The two groups were similar in age, location of the acute myocardial infarction, Killip class, and time of randomization. The patency rate of the infarct-related artery was 72% in the APSAC group and 76% in the rt-PA group (NS). Initial and predischarge left ventricular ejection fraction as well as infarct size were similar in both therapeutic groups (0.50 +/- 0.14 versus 0.52 +/- 0.12 for initial and 0.48 +/- 0.10 versus 0.47 +/- 0.10 for predischarge ejection fraction, 11 +/- 7% versus 9 +/- 7% for infarct size, respectively, for APSAC- and rt-PA-treated patients). Bleeding complications requiring blood transfusion occurred in one APSAC patient and in two rt-PA patients. One patient in the rt-PA group died of a massive intracranial hemorrhage. At the end of the 3-week follow-up period, five APSAC patients (5.5%) and seven rt-PA patients (7.5%) had died.

CONCLUSIONS

The early infusion of APSAC or rt-PA in acute myocardial infarction produced a similar patency rate, limitation of infarct size, and preservation of left ventricular systolic function with an equivalent rate of bleeding complications.

Predictive value of ventricular arrhythmias for patency of the infarct-related coronary artery after thrombolytic therapy

In animal studies reperfusion of coronary arteries is commonly accompanied by ventricular arrhythmias. It is not certain, however, whether ventricular arrhythmias can be used as a reliable non-invasive marker of reperfusion in humans. Two-channel Holter recordings were obtained from the start of an intravenous infusion of streptokinase until coronary angiography (2.8 (2.7) hours (mean SD)) afterwards) in 57 patients with acute myocardial infarction of less than four hours who were generally not treated with antiarrhythmic drugs. Ventricular arrhythmias occurred in 21 (37%) of the 57 patients: accelerated idioventricular rhythm in 13 patients and non-sustained ventricular tachycardia in 15 patients. Seven patients had both accelerated idioventricular rhythm and non-sustained ventricular tachycardia. Coronary angiography showed a patent infarct-related vessel in 12 (92%) of the 13 patients with accelerated idioventricular rhythm (95% confidence interval 66 to 99%), in 22 (50%) of the 44 patients without accelerated idioventricular rhythm (95% CI 34 to 66%), in 11 (73%) of the 15 patients with non-sustained ventricular tachycardia (95% CI 45 to 92%), and in 23 (55%) (95% CI 39 to 71%) of the 42 patients who did not have non-sustained ventricular tachycardia. Seventeen (81%) of the 21 patients with accelerated idioventricular rhythm, or non-sustained ventricular tachycardia, or both, had a patent infarct-related vessel (95% CI 58 to 94%) as did 17 (47%) of the 36 patients with no ventricular arrhythmia (95% CI 29 to 65%). In patients with accelerated idioventricular rhythm after thrombolysis the infarct-related vessel is almost certain to be patent; but the infarct-related coronary artery can still be patent when no arrhythmia is seen.

Technetium 99m sestamibi in the assessment of acute myocardial infarction

Technetium 99m sestamibi is a promising new radiopharmaceutical that can assess myocardium at risk, infarct size, and treatment efficacy in acute myocardial infarction. The minimal redistribution of this radiopharmaceutical makes it ideal for the measurement of myocardium at risk, as demonstrated by several animal studies. The high-count density images are readily quantitated, and techniques have been developed and validated for this purpose. Early clinical studies have shown that myocardium at risk varies widely, even for a coronary occlusion in a similar location, a finding similar to that reported previously in several different animal infarction models. The clinical use of this radiopharmaceutical to measure final infarct size and treatment benefit, or myocardial salvage, has now been demonstrated using both planar and tomographic imaging techniques. Evidence of benefit is often evident by 18 to 48 hours after reperfusion therapy, although the full extent of improvement is not evident until later. The current 6-hour shelf life and 30-minute preparation time are logistical barriers to widespread clinical use. This radiopharmaceutical provides a new, powerful measurement tool for the assessment of treatment efficacy in acute myocardial infarction that is probably superior to other currently available methods.

Late variation in ventricular function after myocardial infarction

To assess the possible role of variables not related to early infarct artery reperfusion in predicting late changes in ventricular function after infarction, paired early (mean 6.6 +/- 3.5 days after admission) and late (12.7 +/- 7.0 months later) cross-sectional echocardiograms from 54 infarction survivors were retrospectively reviewed. Ejection fraction was calculated from digitized biapical echocardiographic views on a graphics tablet. Changes of 0.10 or more in LVEF were correlated with 23 clinical variables. By stepwise regression analysis, Q-wave infarction and low early LVEF independently predicted late improvement in function. Early high LVEF and interval infarction were the only independent predictors of late declines in function. Overall, when patients were indexed by early left ventricular systolic function, a pronounced late "regression to the mean" was noted with initially high values tending to fall and low values to rise (r = -0.44, p less than 0.001). This effect must be accounted for in any acute intervention trial in myocardial infarction. The occurrence of Q-wave infarction does not exclude late improvement in ventricular function.

Intracellular compartmentation of cardiac troponin T and its release kinetics in patients with reperfused and nonreperfused myocardial infarction

In a previous study on the diagnostic efficiency of troponin T measurements in patients with suspected acute myocardial infarction (AMI), the authors found a high variability of troponin T serum concentration changes on day 1 in patients with AMI who underwent thrombolytic treatment. Therefore, the aims of the present study were to investigate the intracellular compartmentation of troponin T and to analyze the effects of AMI reperfusion on the appearance kinetics of cardiac troponin T in serum. Cardiac troponin T was measured with a newly developed bideterminant sandwich assay using cardiospecific, affinity-purified polyclonal antibodies and peroxidase-labeled monoclonal antibody. An unbound cytosolic troponin T pool was found in ultracentrifuged homogenates of myocardial tissue of different species ranging from 0.013 to 0.036 mg/g wet weight. The soluble troponin T molecule had electrophoretic properties identical to troponin T compartmented in the myofibrils. The clinical study group comprised 57 patients with AMI undergoing thrombolytic treatment. Blood flow to the infarct zone and point of time of reperfusion were tested by immediate and late angiography. The appearance of troponin T in serum on day 1 after the onset of AMI depended strongly on reperfusion and on duration of ischemia before reperfusion. Thus, in patients with early reperfused AMI, a marked peak in troponin T serum concentrations was found at 14 hours after the onset of pain. This early troponin T peak was absent in patients with AMI reperfusion occurring greater than 5.5 hours after the onset of pain and in patients with nonreperfused AMI. By contrast, the kinetics of troponin T release after the first day after AMI were unaffected by reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

Effects of time required for reperfusion (thrombolysis or angioplasty, or both) and location of acute myocardial infarction on left ventricular functional reserve capacity several months later

The purpose of this study was to determine whether reperfusion of acute myocardial infarction (AMI) by recombinant tissue-type plasminogen activator (rt-PA) or percutaneous transluminal coronary angioplasty, or both, would improve left ventricular (LV) function when it is measured several months later at rest or maximal bicycle exercise, or both. Radionuclide angiography was performed in 44 patients 5 months (range 6 weeks to 9 months) after AMI to assess function, and tomographic myocardial thallium-201 imaging was performed at maximal exercise and delayed rest to determine whether there was any evidence of myocardial ischemia. As expected, no patient had chest pain or redistribution of a thallium defect during the exercise test, because patients had undergone angioplasty (n = 28) or coronary bypass graft surgery (n = 5) where clinically indicated for revascularization. The LV ejection fraction was plotted as a function of the time elapsed between the onset of chest pain and the time when coronary angiography confirmed patency of the infarct-related artery (achieved in 91% of 44 patients by rt-PA [n = 31] or percutaneous transluminal coronary angioplasty [n = 9] ). Functional responses differed markedly between patients with anterior (n = 20) versus inferior (n = 24) wall AMI. LV ejection fraction during exercise correlated with time to reperfusion in patients with an anterior wall AMI (r = -0.58; standard error of the estimate = 11.9%; p less than 0.02) but not in patients with an inferior AMI (r = 0.10; standard error of the estimate = 13.1%; difference not significant.(ABSTRACT TRUNCATED AT 250 WORDS)