CLINICAL STUDY
Influence of prehospital administration of aspirin and heparin on initial patency of the infarct-related artery in patients with acute st elevation myocardial infarction
Felix Zijlstra, MD, PhD*,*,
Nicolette Ernst, MD*,
Menko-Jan de Boer, MD, PhD*,
Edwin Nibbering*,
Harry Suryapranata, MD, PhD, FACC*,
Jan C. A. Hoorntje, MD, PhD*,
Jan-Henk E. Dambrink, MD, PhD*,
Arnoud W. J. van’t Hof, MD, PhD* and
Freek W. A. Verheugt, MD, PhD
* Department of Cardiology, Hospital De Weezenlanden, Zwolle, Netherlands
Department of Cardiology, University Hospital, Nijmegen, Netherlands
Manuscript received October 18, 2001;
revised manuscript received February 26, 2002,
accepted March 1, 2002.
* Reprint requests and correspondence: Dr. Felix Zijlstra, Isala Klinieken, Hospital De Weezenlanden, Department of Cardiology, Groot Wezenland 20, 8011 JW Zwolle, Netherlands.
f.zijlstra{at}diagram-zwolle.nl
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Abstract
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OBJECTIVES: The aim of this study was to investigate the influence of prehospital administration of aspirin and heparin on the initial patency of the infarct-related artery (IRA) in patients with acute myocardial infarction (MI).
BACKGROUND: Prehospital diagnosis of acute MI facilitates early pharmacologic intervention on the way to the catheterization laboratory for primary angioplasty.
METHODS: We studied the angiographic data and 30-day clinical outcome of 1,702 patients treated with primary angioplasty; 860 received aspirin and heparin before transportation to our hospital and 842 received aspirin and heparin in our hospital.
RESULTS: The Thrombolysis In Myocardial Infarction (TIMI) 2 or 3 flow in the IRA was higher in the prehospital treated group (31% vs. 20%, relative risk 0.65, 95% confidence interval 0.55 to 0.78, p < 0.001). Patients with TIMI 2 or 3 flow on the initial angiogram had a higher angioplasty success rate (94% vs. 89%, p < 0.001), a smaller enzymatic infarct size, a higher left ventricular ejection fraction and a lower 30-day mortality (1.6% vs. 3.4%, p = 0.04).
CONCLUSIONS: Prehospital administration of aspirin and heparin results in a higher initial patency of the IRA in patients with acute MI.
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Abbreviations and Acronyms
| | HEAP | | Heparin in Early Patency trial | | IRA | | infarct-related artery | | LDHQ48 | | enzymatic infarct size from serial measurements of lactate dehydrogenase | | LVEF | | left ventricular ejection fraction | | MI | | myocardial infarction | | TIMI | | Thrombolysis In Myocardial Infarction |
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Early coronary reperfusion is the primary goal of the initial treatment for patients with acute ST segment elevation myocardial infarction (MI). The delay between symptom onset and effective myocardial reperfusion is one of the determinants of early and late clinical outcome. Primary angioplasty is a highly effective reperfusion therapy, resulting in complete and sustained patency of the infarct-related artery (IRA) in most patients (1–3). The total ischemic time of patients with acute MI treated with primary angioplasty is a combination of patient delay, response delay of the primary care system, transportation delay and the time needed to establish reperfusion in the catheterization laboratory (4). Adjunctive therapy given after diagnosis but before angioplasty may induce reperfusion, thereby limiting myocardial injury. Several types of drugs have been studied for this specific purpose with variable results (5–9).
In a steadily increasing proportion of patients, the diagnosis of ST elevation MI is accomplished out-of-hospital, before transportation, either by general practitioners or by ambulance personnel with 12-lead electrocardiography. This allows very early pretreatment with advantages analogous to prehospital thrombolysis compared with hospital-based thrombolysis (4). Therefore, we studied the initial coronary angiograms of consecutive patients who had received aspirin and heparin before reaching the hospital and compared these findings with a consecutive group of patients who had received aspirin and heparin after arrival in our hospital, all on the way to our catheterization laboratory for primary angioplasty.
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Methods
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Patients with acute MI presenting within 6 h after symptom onset were included. The protocol was approved by our institutional review board. Electrocardiographic criteria were ST segment elevation of  1 mm in two or more contiguous leads. The diagnosis of acute MI and the indication for primary angioplasty was established in 860 patients at the patient’s home by the ambulance crew or at the emergency department of one of the 11 community hospitals who refer patients to our hospital for primary angioplasty. These patients received aspirin (500 mg intravenously) and heparin (5,000 IU intravenously) before transportation to our hospital. During the same period, the diagnosis of acute MI and the indication for primary angioplasty was established in 842 patients in the emergency room of our hospital. These patients received aspirin and heparin intravenously in the emergency room and were transported immediately to the catheterization laboratory. None of these patients received fibrinolytic therapy or glycoprotein IIb/IIIa blockers before angiography.
Data collection.
Demographic and clinical data were recorded at baseline. The primary end point was the patency of the IRA at diagnostic angiography. All angiograms were reviewed by two cardiologists, blinded for treatment allocation and clinical data. At discharge, left ventricular ejection fraction (LVEF) was measured with a radionuclide technique, as previously described (2). All major cardiovascular events during hospital admission were documented. Major bleeding was defined as blood loss, requiring blood transfusion. Enzymatic infarct size was determined by measurements of lactate dehydrogenase as reference enzyme. Cumulative enzyme release was calculated from serial measurements up to 48 h after symptom onset. From these measurements, an area under the curve was calculated from at least five measurements (enzymatic infarct size from serial measurements of lactate dehydrogenase [LDHQ48]). Further details of this method have been described previously (10,11). Complete clinical data were available of all 1,702 patients; LDHQ48 was determined in 890 patients; LVEF was determined in 1,086 patients.
Data analysis
Continuous data are summarized as means and SD. Variables were compared using the Fisher exact test or chi-square test for categorical data. Analysis of variance was utilized for normally distributed continuous variables. A nonparametric (Kruskal-Wallis) test was used to compare continuous variables when the data were not normally distributed.
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Results
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A total of 1,702 patients were included, of whom 860 received aspirin and heparin before transfer to our hospital and 842 received aspirin and heparin after arrival in our hospital. Baseline characteristics are shown in Table 1. With respect to gender, Killip class, previous MI, diabetes, multivessel disease and ischemic time, there were no differences between the two groups. The patients in the prehospital aspirin and heparin group were slightly younger and presented more often with an anterior MI location. The time interval from aspirin and heparin administration to angiography in the prehospital group was measured in 117 patients and was 81 ± 43 min, compared with a time interval from aspirin and heparin administration to angiography in the in-hospital group of 26 ± 39 min (p < 0.001). The prevalence of use of aspirin before their MI was 8% in the prehospital group compared with 9% (p = NS) in the in-hospital group with doses ranging from 38 to 100 mg/day. In 263 of 860 patients (31%) in the prehospital aspirin and heparin group, Thrombolysis In Myocardial Infarction (TIMI) flow grade 2 or 3 was observed compared with 168 of 842 patients (20%) in the group who received aspirin and heparin after arrival in our hospital (relative risk 0.65, 95% confidence interval 0.55 to 0.78, p < 0.001). The TIMI 3 flow was observed in 141 of 860 (17%) in the prehospital group compared with 83 of 842 (10%) in the in-hospital group (relative risk 0.60, 95% confidence interval 0.47 to 0.78, p < 0.001). This effect of prehospital treatment was present in almost all subgroups of patients (Table 2).
Clinical outcome.
Primary angioplasty was successful (TIMI flow grade 3 and residual stenosis <50%) in the prehospital group in 92% of patients compared with 90% in patients of the hospital group. There were four strokes (0.2%), one in the prehospital group (0.1%) and three in the in-hospital group (0.4%). Bleeding necessitating a blood transfusion occurred in 43 of 860 (5%) patients in the prehospital group and 59 of 842 (7%) patients in the in-hospital group. In the prehospital group, 26 of 860 (3.0%) had died at 30 days compared with 24 of 842 (2.9%) of patients in the in-hospital group. Death and nonfatal reinfarction occurred in 34 (4%) prehospital patients and 32 (3.8%) in-hospital patients. Clinical outcome variables are given in Table 3.
The presence or absence of TIMI 2 or 3 flow on the initial diagnostic angiogram was a major determinant of clinical outcome. Patients with initial TIMI 2 or 3 flow in the IRA more often had TIMI 3 flow after the angioplasty procedure and had a smaller LDHQ48. A better LVEF and a lower 30-day mortality was observed in anterior MI. Clinical outcome variables according to TIMI flow on the initial diagnostic angiogram are given in Table 4.
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Discussion
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The prehospital administration of aspirin and heparin is a simple, inexpensive and widely applicable treatment option in patients with suspected or confirmed acute MI. We studied the value of prehospital aspirin and heparin in a large cohort of patients on the way to the catheterization laboratory for primary angioplasty of the IRA, but this strategy can also be used in combination with other pharmacologic therapies, when thrombolytic therapy is contraindicated and angioplasty is not available.
Previous studies with heparin.
Previous observations have shown conflicting results as to the effects of heparin on early patency of the IRA (6,7,12,13). As an adjunct to alteplase, heparin has been shown to result in a higher patency rate in a trial of the European Cooperative study group (14). In the Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries trial, heparin was not effective in combination with streptokinase (15,16). In an observational study, heparin was not associated with an improved 30-day mortality rate (13). The effect of high-dose intravenous heparin on initial patency was promising in a pilot trial (6), but the subsequent randomized Heparin in Early Patency (HEAP) trial did not confirm a benefit of high-dose heparin on early patency (7). However, a large majority of the patients in the HEAP trial received heparin after hospital admission and, therefore, the time available for heparin to induce reperfusion was limited. There are several potential reasons why prehospital intravenous heparin may be more effective in this setting. For instance, pharmacologic treatment during the first 1 h or 2 h may be more effective due to a less organized occluding thrombus. As heparin had its antithrombin effects within minutes after administration, the pretreated patients had been anticoagulated longer compared with the patients who received heparin in our emergency room. Early restoration of flow may reduce the ischemic insult and limit reperfusion injury.
Aspirin and other pharmacologic interventions
The beneficial effects of aspirin in patients with acute MI have been established in the International Study of Infarct Survival-2 (17). Whether this beneficial effect may, in part, be due to a higher early patency rate has not been studied. In the present study, prehospital administration of heparin in combination with aspirin enhanced early patency, but the relative importance of these two components is unknown. A small group of patients (8% to 9%) was using aspirin before their MI, a group too small to analyze separately. Whether the effects of pretreatment with intravenous aspirin and heparin are different in patients already using aspirin is unknown. However, our results did not change when we excluded these patients from our analysis. Compared with other pharmacologic interventions such as low dose thrombolytic drugs (5) or glycoprotein IIb/IIIa receptor blockers (8,9), the effect of prehospital administration of aspirin and heparin may seem modest. Aspirin and heparin result in one additional open IRA on the initial coronary angiogram for every 10 patients treated compared with 1 of 6 patients treated with low-dose lytics (5) or abciximab (8), but aspirin and heparin are comparatively safe and inexpensive.
Study limitations
Treatment (prehospital vs. in-hospital heparin and aspirin) was not allocated by randomization but dependent on the routing of the patient on the way to our catheterization laboratory. Patients diagnosed with acute MI in an emergency room of a referring hospital (4,18) or at home after arrival of an ambulance with 12-lead electrocardiography had prehospital treatment with heparin and aspirin, whereas the other group received these two drugs after arrival in our hospital. The slight difference in age and, in particular, the higher rate of anterior MI location is due to selection bias of referring physicians and ambulance personnel. They refer, preferentially, patients for primary angioplasty with large anterior wall MI (4,18). Therefore, we analyzed the impact of the baseline characteristics on the main results of our study (Table 2). There is no interaction between treatment effect and age, gender, MI location, ischemic time and multivessel disease. With regard to Killip class 2 and diabetes, our results are not conclusive due to the limited number of patients with this characteristic, but this does not interfere with the comparison of the two groups.
Treatment allocation was not blinded, but this will not have influenced our findings, as the angiograms were reviewed without knowledge of allocation or clinical data. We did not find a significant difference in mortality between the prehospital and the in-hospital group. This is probably due to the fact that most patients left the catheterization laboratory with a patent IRA and, as a consequence, mortality in this 1,702 patient cohort was very low (3%). Nevertheless, when we analyzed clinical outcome in patients with TIMI 2 or 3 flow on the initial angiogram and compared that to patients with an initially occluded coronary artery, the benefits of early patency of the IRA are confirmed (Table 4) (5,19,20).
Conclusions
Prehospital compared with in-hospital administration of aspirin and heparin in patients with acute MI results in a higher rate of early patency of the IRA. Patients with antegrade flow in the IRA on the initial angiogram have a better clinical outcome compared with patients with an occluded coronary artery.
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Top
Abstract
Methods