Thrombolytic therapy for patients with myocardial infarction presenting after six hours

Usefulness of the presenting electrocardiogram in predicting successful reperfusion with streptokinase in acute myocardial infarction

The presenting electrocardiogram may contain information indicating the probability of successful reperfusion. The relation between 3 parameters in the presenting electrocardiogram (pathologic Q waves, T-wave inversion, and the slope of ST elevation) and Thrombolysis in Myocardial Infarction trial (TIMI) grade 3 flow in the infarct-related artery was assessed angiographically 90 minutes after beginning streptokinase in 362 patients. TIMI grade 3 flow was more common in patients without Q waves (55%) than in those with Q waves (35%; p <0.001), and more common in patients without T-wave inversion (50%) than in those with T-wave inversion (30%; p <0.002). There was no relation between the slope of the ST segment or the magnitude of its deviation and the achievement of TIMI grade 3 flow. Only 20% of the 59 patients with both Q waves and T-wave inversion had TIMI grade 3 flow, compared with 50% of the remaining patients (p <0.0001). Among patients treated within 3 hours, TIMI grade 3 flow was seen in 68% of those without versus 44% of those with Q waves (p <0.01), and in 62% of those without versus 43% of those with T-wave inversion (p = 0.06). Among patients treated after 3 hours, TIMI grade 3 flow was seen in 38% of those without versus 30% of those with Q waves (p = NS), and in 38% of those without versus 23% of those with T-wave inversion (p <0.05). On multivariate analysis, the absence of Q waves, the time from the onset of chest pain to treatment, and age were independent predictors of TIMI grade 3 flow. Pathologic Q waves in the presenting electrocardiogram provide valuable information as to the probability of achieving successful reperfusion following administration of streptokinase, and may be helpful for triage of patients to alternative reperfusion strategies, including percutaneous revascularization.

Influence of time to treatment on early infarct-related artery patency after different thrombolytic regimens. ALKK-Study Group

BACKGROUND

In an in vitro model, recombinant tissue-type plasminogen activator was significantly more effective than streptokinase in dissolving 24-hour-old human blood clots. Therefore there might be a difference in the effect of time to treatment on the efficacy of these fibrinolytics with different fibrin specificity in patients with acute myocardial infarction.

METHODS AND RESULTS

The effect of the interval between symptom onset and initiation of therapy on the efficacy of 6 different thrombolytic regimens was studied in a retrospective analysis of 6 angiographic trials with similar design. The patency of the infarct-related artery was assessed by angiography 90 minutes after initiation of thrombolysis in patients who were seen within 6 hours after symptom onset. Patency rates of patients with an interval of </=3 hours and >3 hours between symptom onset and start of therapy were compared. There was no difference for Thrombolysis in Myocardial Infarction (TIMI) grade 3 perfusion after front-loaded alteplase (72.5% vs 76. 3%) and reteplase (63.6% vs 63.2% ) between the 2 groups. In contrast, in patients treated with streptokinase (36.8% vs 27.6%, P =.09), anisoylated plasminogen streptokinase activator complex (59. 5% vs 34.8%, P =.004), and urokinase (62.3% vs 41.7%, P =.03), TIMI 3 patency decreased with the increasing interval between symptom onset and initiation of therapy.

CONCLUSIONS

We conclude from our data that the thrombolytic efficacy of recombinant tissue-type plasminogen activator and reteplase does not decrease with the increasing interval between symptom onset and initiation of therapy. In contrast, after anisoylated plasminogen streptokinase activator complex, streptokinase, and urokinase treatment, a decrease in patency, especially TIMI-3 patency in patients treated after >3 hours after symptom onset, was observed. These results may influence the choice of the thrombolytic agent in patients who are seen >3 hours after symptom onset.

ISIS-2: 10 year survival among patients with suspected acute myocardial infarction in randomised comparison of intravenous streptokinase, oral aspirin, both, or neither. The ISIS-2 (Second International Study of Infarct Survival) Collaborative Group

OBJECTIVE

To assess effects of intravenous streptokinase, one month of oral aspirin, or both, on long term survival after suspected acute myocardial infarction.

DESIGN

Randomised, "2 x 2 factorial," placebo controlled trial.

SETTING

417 hospitals in 16 countries.

SUBJECTS

17 187 patients with suspected acute myocardial infarction randomised between March 1985 and December 1987. Follow up of vital status complete to at least 1 January 1990 for 95% of all patients and to mid-1997 for the 6213 patients in United Kingdom.

INTERVENTIONS

Intravenous streptokinase (1.5 MU in 1 hour) and oral aspirin (162 mg daily for 1 month) versus matching placebos.

MAIN OUTCOME MEASURES

Mortality from all causes during up to 10 years' follow up, with subgroup analyses based on 4 year follow up.

RESULTS

After randomisation, 1841 deaths were recorded in days 0-35, 991 from day 36 to end of year 1, 1478 in years 2-4, and 1230 in years 5-10. Allocation to streptokinase was associated with 29 (95% confidence interval 20 to 38) fewer deaths per 1000 patients during days 0-35. This early benefit persisted (death rate ratio 0.98 (0.92 to 1.04) for additional deaths between day 36 and end of year 10), so that there were 28 (14 to 42) and 23 (2 to 44) fewer deaths per 1000 patients treated with streptokinase after 4 years and 10 years respectively. There was no evidence that absolute survival benefit increased with prolonged follow up among any category of patient, including those presenting early after symptoms started or with anterior ST elevation. Nor did the early benefits seem to be lost in any category (including those aged over 70). Allocation to one month of aspirin was associated with 26 (16 to 35) fewer deaths per 1000 during first 35 days, with little further benefit or loss during subsequent years (death rate ratio 0.99 (0.93 to 1.06) between day 36 and end of year 10). The early benefit obtained with combination of streptokinase and one month of aspirin also seemed to persist long term.

CONCLUSIONS

The early survival advantages produced by fibrinolytic therapy and one month of aspirin started in acute myocardial infarction seem to be maintained for at least 10 years.

The Open Artery Hypothesis: Past, Present, and Future

The survival benefit following a reperfusion strategy, be it pharmacologic or mechanical, appears to be due to both full and early reperfusion. While the TIMI Flow Grade classification scheme has been a useful tool to assess coronary blood flow in acute syndromes, it has several limitations. A newer method of assessing coronary blood flow called the Corrected TIMI Frame Count method has the following advantages: (1) it is a continuous quantitative variable rather than a categorical qualitative variable; (2) the flow in the non-culprit artery is not assumed to be normal as it is in the assessment of TIMI Grade 3 Flow; (3) there is simplified reporting of reperfusion efficacy through the use of a single number instead of expressing the data in 2 to 4 categories; (4) because a single number rather than 4 categories is used to report the data, there is more efficient use of the dataset by increasing the statistical power; and finally (5) coronary flow can be expressed in intuitive terms (e.g. time or cm/sec for strategy A versus time or cm/sec for strategy B). This paper reviews the history of the open artery hypothesis and recent advances in the field.

Thrombolysis for acute myocardial infarction

Thrombolytic therapy has been a major advance in the management of acute myocardial infarction. Unfortunately, it continues to be underused or is administered later than is optimal. Thrombolytic therapy works by lysing infarct artery thrombi and achieving reperfusion, thereby reducing infarct size, preserving left ventricular function, and improving survival. The most effective thrombolytic regimens achieve angiographic epicardial infarct-artery patency in only approximately 50% of patients within 90 minutes. Bleeding requiring transfusion occurs in approximately 5% of patients and stroke in approximately 1.8% with these regimens, which include adjunctive aspirin and intravenous heparin. There are several ways in which reperfusion rates and thus patient outcomes might be improved, such as different dosing regimens of established agents; combinations of different agents; improved adjunctive therapy such as direct antithrombin agents, low-molecular-weight heparin, or glycoprotein IIb/IIIa receptor antagonists; or the development of novel thrombolytic agents with enhanced fibrin specificity, resistance to native inhibitors, or prolonged half-lives allowing bolus administration. All of these strategies are being tested in clinical trials. The best approach currently is to administer thrombolytic therapy as soon as possible to all patients without contraindications who present within 12 hours of symptom onset and have ST-segment elevation on the ECG or new-onset left bundle-branch block, unless an alternative reperfusion strategy is planned.

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

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

Factors affecting outcome after recovery from myocardial infarction

Patients surviving acute myocardial infarction are susceptible to heart failure, recurrence of angina, reinfarction, arrhythmias, and sudden cardiac death. Most deaths occur in the first six months after infarction. Advancing age is the most important nonmodifiable prognostic factor for long-term prognosis, whereas left ventricular function assessed clinically or measured as either ejection fraction or end-systolic volume is the most important modifiable factor. Other significant long-term prognostic factors include: postinfarction angina at rest, inducible ischemia during exercise testing with or without radioisotope imaging, severity and extent of coronary artery disease, patency of the infarct-related artery, late ventricular arrhythmias, decreased heart rate variability, cigarette smoking, hypercholesterolemia, and diabetes mellitus. Identification of these adverse prognostic factors permits risk stratification and enables physicians to determine the most appropriate and cost-effective treatment. Most patients should have a stress test for inducible ischemia and a non-invasive (echo or radionuclide) assessment of left ventricular function. For high-risk patients such as those with prior infarction, heart failure, early postinfarction angina, or frequent late ventricular arrhythmias, coronary angiography and ventriculography prior to discharge are recommended. Assessment of late potentials and heart rate variability will help identify a subgroup of patients at risk for ventricular arrhythmias and cardiac death. However, a more accurate prediction of reinfarction is not possible at present, and no reliable test for atherosclerotic plaque instability has been developed.

Hirudin and Hirulog

A brief outline is presented of a proposed trial of Hirulog versus heparin after thrombolytic therapy with streptokinase (SK). The lower patency rates achieved with SK compared with tissue plasminogen activator (t-PA) suggest that a potent thrombin specific agent may be more important for SK than for t-PA therapy. This study will involve more than 400 patients with two dose levels of Hirulog. Endpoints will be angiographic patency, and ST segment monitoring showing evidence of coronary reperfusion.

Remodelling of the heart after myocardial infarction

In the first few hours after the onset of coronary occlusion the infarct zone stretches due to myocyte slippage. Subsequently the noninfarct zone develops volume overload hypertrophy with series addition of new sarcomeres and fibre elongation. Dilatation is detrimental as it increases ventricular wall stress and oxygen demand, and re-entry of electrical impulses may be influenced by stretching of the ischaemic scar resulting in ventricular fibrillation. Left ventricular remodelling and dilatation is a progressive process which begins early and continues in the months after infarction. The major determinants of the extent of remodelling are infarct size and patency of the infarct-related artery. Late reperfusion may reverse initial infarct dilatation and decrease left ventricular volumes by inducing calcium-activated contracture of the actomyosin complex. Expansion may also be inhibited by acceleration of healing, splinting of the infarct zone by salvage of subepicardial cells, and blood in the coronary arteries and veins supporting the infarct zone. End-systolic volume is the strongest predictor of long-term prognosis after infarction. A number of therapies including thrombolysis, angiotensin-converting enzyme (ACE) inhibition and nitrates have been shown to decrease left ventricular dilatation. The optimal time for commencement, dose, duration and the effects of combinations of therapy are yet to be determined.