Journal of the American College of Cardiology
Influence of treatment delay on infarct size and clinical outcome in patients with acute myocardial infarction treated with primary angioplasty
Author + information
- Aylee L Liem, MDa,
- Arnoud W.J van ‘t Hof, MDa,
- Jan C.A Hoorntje, MDa,
- Menko-Jan de Boer, MDa,
- Harry Suryapranata, MD, FACCa and
- Felix Zijlstra, MDa,*
- ↵*Address for correspondence: Dr. Felix Zijlstra, Department of Cardiology, Hospital de Weezenlanden, Groot Wezenland 20, 8011 JW Zwolle, The Netherlands
Abstract
Objectives. The purpose of this analysis was to determine the influence of an additional treatment delay inherent in transfer to an angioplasty center for primary angioplasty of patients with acute myocardial infarction who are first admitted to hospitals without angioplasty facilities.
Background. Several randomized trials have demonstrated the benefits of primary angioplasty in acute myocardial infarction. In recent years, increasing numbers of patients with myocardial infarction, initially admitted to hospitals without angioplasty facilities are transported to our hospital for primary angioplasty. However, the additional delay due to the transport may have a deleterious effect on infarct size and clinical outcome.
Methods. In a three-year period (December 1993 to November 1996), 207 consecutive patients who were transferred for primary angioplasty were analyzed in a matched comparison with nontransferred patients. Matching criteria were age, sex, infarct location, presentation delay and Killip class.
Results. Patients who were transferred had an additional median delay of 43 min. This resulted in a more extensive enzymatic infarct size and a lower ejection fraction measured at 6 months. The rate of angioplasty success defined as TIMI grade 3 flow, and the 6-month mortality rate (7%) were comparable in both groups.
Conclusions. The additional delay had a deleterious effect on myocardial salvage, reflected by a larger infarct size and a lower left ventricular function. However, the patency rate and 6-month clinical outcome were not affected by this delay.
The time-related effect of treatment on survival and myocardial salvage in patients with acute myocardial infarction (MI) has been demonstrated in thrombolysis trials (1–6). Besides timing of treatment, the grade of flow achieved with reperfusion is important for the long-term outcome (7–10). Primary angioplasty for patients with acute MI has been shown in randomized trials (11–14)to be a very effective reperfusion therapy, and high rates of complete and sustained patency have been reported. Achieving complete reperfusion as defined by thrombolysis in myocardial infarction (TIMI) grade 3 flow after reperfusion is an important factor in short and long term survival. In patients treated with thrombolytic therapy there is an inverse relationship between time to treatment and patency rate. This relationship is not so evident in patients treated with primary angioplasty (15,16). A previous study in infarct patients who were admitted directly to our hospital and treated with primary angioplasty did demonstrate differences in patency rates with increasing ischemic times, but also found important differences in patient characteristics related to the time from symptom onset to treatment (17). A registry study has shown that transferring patients for primary angioplasty to our hospital is safe and effective, and with an acceptable delay due to transportation (18). In this analysis an attempt is made to quantify the effect of an additional delay inherent in transfer to an angioplasty center.
Methods
Study patients
The study was approved by the committee on ethics and research at our institution. For this analysis we retrospectively evaluated patients who were registered in our infarct database. We included patients with acute MI who were first admitted to a community hospital without angioplasty facilities and were transferred to our hospital for primary angioplasty. Only patients who underwent primary angioplasty were included in the analysis. They were compared to patients admitted directly to our hospital, who were also registered in our database for acute MI patients. In this database, all consecutive patients with acute MI are prospectively registered. The transfer patients and the control patients are contemporaneous. The following definitions of the time intervals were used: the first part between symptom onset and hospital admission (for referral patients admission at the community hospital) is called presentation delay. The second part is called treatment delay, and is defined as time from hospital admission to first balloon inflation. The additional delay due to the interhospital transport is the subject of this analysis. Only patients who underwent primary angioplasty for acute MI were included to allow assessment of the time to reperfusion, defined as time to first balloon inflation. In addition, TIMI flow grade was assessed. To study the influence of treatment delay due to transportation, each of the transferred patients (n = 207) was matched to one nontransferred patient. Criteria for matching were: age, sex, infarct location, presentation delay and Killip class. Time intervals (onset of chest pain, presentation delay, transportation time, first balloon inflation) as well as all clinical and angiographic data have been prospectively recorded in our database. Transfer patients were transferred from 15 community hospitals to our hospital for primary angioplasty from December 1993 to November 1996. Our hospital serves as angioplasty center in the region with approximately 1.5 million inhabitants. Travel distances range from 2 to 43 miles.
Study design
Acute MI was diagnosed if a patient had persistent symptoms of chest pain lasting more than 30 min and had ST segment elevation of ≥1 mm in at least 2 contiguous leads. The indications for transfer were: electrocardiographic evidence of an anterior or large inferior infarction, contraindications for thrombolytic therapy (relative or absolute) or hemodynamic instability (Killip class >1). The cumulative sum of ST elevation was scored on the diagnostic electrocardiogram. The exclusion criteria were identical as previously described (11). All transfer patients underwent immediate coronary angiography followed by primary angioplasty if indicated; patients were not treated with primary angioplasty if they had severe multivessel coronary artery disease or involvement of the left main coronary artery that made subsequent urgent coronary bypass grafting (CABG) necessary. Patients with an open infarct-related vessel (IRV) in whom no reperfusion therapy was indicated were treated conservatively. After primary angioplasty, flow through the IRV was scored according to the TIMI classification. The angiograms were all read by two cardiologists blinded for group allocation and clinical data. Primary angioplasty was considered successful if the residual stenosis in the IRV was less than 50% and TIMI grade 3 flow was present after the procedure.
Enzymatic infarct size
Infarct size was determined by measurements of enzyme concentrations with lactate dehydrogenase as reference enzyme (LDHQ72). A two-compartment model was used, which has been validated in studies on the turnover of radio-labeled plasma proteins and circulating enzymes. Cumulative enzyme release was calculated from serial measurements up to 72 h after symptom onset. Samples were obtained on admission and every 12 h to 72 h thereafter. From these measurements, an area under the curve was calculated, from at least five measurements. Further details of this methods have been described before (11,13,19,20).
Left ventricular function
At 6-month follow-up left ventricular ejection fraction (LVEF) was measured with a radionuclide technique as previously described (11,13). Measurements were done by the multiple-gated equilibrium method after labeling of red blood cells with technetium 99m pertechnetate. A gamma-camera (General Electric, Milwaukee, WI, USA) was used. The global LVEF was calculated with the PAGE program (version 2.3).
Clinical outcome
Follow-up information was obtained for all patients. Hospital records of patients who visited our outpatient clinic were reviewed. Information on transferred patients was obtained from referral cardiologists. If necessary, additional information was gathered by telephone contact with general physicians or patients.
Clinical parameters
In this analysis we compared the following clinical parameters: enzymatic infarct size (LDHQ72), LVEF and TIMI flow after primary angioplasty was scored. At 6-month follow-up mortality (of all causes) and recurrent MI were evaluated in both groups. Recurrent MI was defined as the combination of chest pain, changes in the ST-T segment at rest, and a second increase in the creatine kinase level to more than two times the upper limit of normal, or an increase of more than 200 IU/liter over the previous value if the level had not dropped below the upper limit of normal (11). Recurrent infarction and mortality were assessed at 6-month follow-up.
Statistical methods
Time intervals are presented as medians with 25th and 75th percentiles. Data were analyzed as a matched pairs study. The Wilcoxon signed rank test was used to compare means of continuous variables and the chi-square test or Fischer exact test for discrete variables. Two-sided p values <0.05 were considered to be significant.
Results
During a three-year period, 236 patients with acute MI were transferred from referral hospitals. Of these, 213 patients were treated with primary angioplasty. Eight patients with severe multivessel coronary artery disease or involvement of the left main coronary artery underwent urgent CABG. In another 8 patients, the IRV was open and no reperfusion therapy was indicated. Matching criteria were available for all of the patients who underwent primary angioplasty. No match could be found for 6 (3%) of the transferred patients, so 207 transfer patients were one-to-one matched to nontransferred patients. The matching procedure resulted in an equal distribution of all matched baseline characteristics as shown in Table 1. There were more patients with a contraindication for thrombolysis and with multivessel disease in the transfer patients, but these differences were not significant. The cumulative sum of ST elevation showed no difference between the groups. Also the presence of other baseline characteristics such as previous infarction, previous CABG, multivessel disease and diabetes were equally divided. The transfer patients were slightly younger (58 ± 11 years) than patients who were enrolled in our infarction trials in the past years, and a larger majority had an anterior infarct location (Table 1). For the 207 matched transfer patients, the median treatment delay was 103 min compared to 60 min in the nontransferred patients, so the transfer resulted in an additional delay in time to reperfusion of 43 min (Table 2).
Baseline Characteristics legend
In-Hospital Clinical Outcome legend
In-hospital clinical outcome
TIMI grade 3 flow was obtained in most patients; 86% in the transfer group and in 90% in the nontransfer group (Table 2). During the hospital period, 10 transfer patients (5%) and 7 (3%) nontransfer patients died. Five patients died within the first 48 h, before serial enzyme release could be determined. Cumulative enzyme release during the first 72 h could be calculated in 145 (70%) of the transfer patients (mean enzyme release: 1,544 IU, ± SD 1,106 IU) and in 193 (93%) of the nontransfer patients (mean enzyme release: 1,196 IU, ± SD 1,004 IU). This resulted in 137 matched pairs (66%) in whom enzyme release could be calculated and compared. For 49 (24%) patients in the transfer group and for 16 (8%) patients in the nontransfer group, there were inadequate data for analysis. The enzymatic infarct size was 1,536 IU in the transferred patients, compared to 1,235 IU in the nontransfer patients (p < 0.005) (Table 2).
Six-month follow-up
At 6 months, a total of 15 (7%) patients in the transfer group and 12 patients in the nontransfer group (6%) had died. Reinfarction had occurred in 8 (4%) of the transfer patients and in 6 (3%) of the nontransfer patients (Table 3). LVEF was measured at 6 months in 139 matched pairs (72%) of the survivors. Nontransfer patients had an ejection fraction of 47% versus 43% in the transfer patients (p = 0.003). In 27 (13%) patients in the transfer group and in 17 (8%) patients in the nontransfer group, a LVEF measurement was not available; in a small number of patients the test was performed but inconclusive due to an irregular heart rhythm (3 patients in the transfer group and 2 in the nontransfer group). Reasons for not performing this test were inability to return to our hospital (e.g., travel distance) or patient refusal.
Six-Month Clinical Outcomelegend
Discussion
Treatment delay
In this study we analyzed the treatment delay in patients who were transferred from hospitals without angioplasty facilities to our center for primary angioplasty. In this setting, patients who were transferred had an additional treatment delay of 43 min. Although the time delay had no effect on the patency rate after the angioplasty procedure, there was more extensive myocardial damage. As patency is the major determinant of survival, this results in a comparable 6-month clinical outcome of transferred patients compared to nontransferred patients. However, long-term survival is yet unknown and LVEF may become more important over time. The analysis shows that in this cohort of patients the myocardial damage due to the additional delay inherent to transfer to an angioplasty center in high-risk patients with acute MI may be outweighed by the high rate of early, sustained and complete reperfusion as a result of the primary angioplasty procedure. This high rate of successful angioplasty applies to patients with ischemic times up to 6 h, as most of the transfer patients had short presentation delays (median 90 min) and the additional delay caused by the transfer was limited. Few patients with longer presentation delays were transferred, but it may be expected that procedure success rates will be lower after 6 h (17).
Myocardial salvage
The effects of treatment delay could be measured in enzymatic infarct size as well as LVEF. However, more factors may play a role in the degree of myocardial salvage. The presence or absence of collaterals, the size of the infarct area, history of previous infarction or previous angina will be responsible for a wide range of outcomes in individual patients. Nevertheless, for these patient groups a difference in measured infarct size and LVEF was found in relation with a median treatment delay of 43 min.
Transfer for primary angioplasty
Only a limited number of hospitals have angioplasty facilities and most patients with acute MI will be admitted to hospitals without these facilities. Urgent transfer of infarct patients to angioplasty centers is an alternative option to treatment with thrombolysis administered at the community hospital. By evaluation of this cohort of patients who have been transferred for primary angioplasty to our hospital, it is demonstrated that this treatment strategy is safe and can be done effectively. Interhospital delays are minimized by timely referral by the physician at the referral hospital. On arrival at the angioplasty center the patient can be brought to the catherization laboratory immediately. Measures to prepare the catherization laboratory can be made during the patient transport.
Study limitations
This study population represents a selected group of patients, slightly younger than the usual infarct population and with a short presentation delay. Concerning the high percentage of anterior infarctions the transfer patients are a population at higher risk. This fact has probably contributed to the differences found in enzymatic infarct size and LVEF. In patients with nonanterior infarctions, the area at risk would be smaller, and differences expressed in infarct size and LVEF might not be measurable. Also the fact that the total delay before treatment for both groups was within the period of myocardial salvage may have contributed in the difference between the transported patients and matched controls. A bias might be introduced by the fact that some of the clinically better patients did not return for the LVEF test, but only in 13% of the transported patients and in 8% of the matched controls LVEF measurement was not available. The large majority of patients had completed data for enzymatic infarct size and LVEF, but in a matched comparison the percentage of available results in patient pairs is obviously lower. This analysis does not answer the question whether it would be more beneficial to transfer a patient for primary angioplasty than to treat these patients immediately with thrombolysis. This comparison can only be made by means of a randomized trial.
Conclusions
This analysis demonstrates that the success of primary angioplasty in patients with acute MI is not influenced by an additional delay due to interhospital transfer. Analysis of time intervals showed that in our setting the additional delay is limited and only 43 min longer in patients transferred from community hospitals compared to patients admitted directly to the angioplasty center. Therefore total time from symptom onset to first balloon inflation is within a 6 h time window for most patients. The effect of the additional treatment delay on myocardial salvage measured in enzymatic infarct size and in LVEF at 6 months was estimated by a matched pair analysis. Although the additional delay was limited there was a measurable effect on myocardial salvage, which indicates the need to reduce time to treatment in patients treated with primary angioplasty. In this particular setting and infrastructure, the transfer of patients for primary angioplasty is safe and can be done with a limited loss of time. The high success rate in the transfer patients is encouraging to apply this treatment strategy for patients with high-risk features (contraindications for thrombolysis, anterior infarct location and/or hemodynamic instability). However, in each individual patient it should be clear that an additional delay during the first hours of acute MI results in more extensive myocardial damage. If transfer for primary angioplasty is the treatment strategy of choice then the rule “time is muscle” still holds good.
Clinical implications
The strategy to transfer patients with acute MI admitted to a community hospital without angioplasty facilities to an angioplasty center is safe and effective. If the time from symptom onset to treatment does not exceed the period in which myocardial salvage is possible, the results of primary angioplasty will be comparable to those obtained in patients directly admitted to an angioplasty center. Reductions in time to treatment can result in substantial additional myocardial salvage.
Acknowledgements
We appreciate the complementary advice and critical review by Freek Verheugt, MD, PhD. We thank the referral doctors from the 15 community hospitals in the region for their cooperation.
- Abbreviations
- CABG
- coronary artery bypass grafting
- IRV
- infarct-related vessel
- IU
- international units
- LDH
- lactate dehydrogenase
- LVEF
- left ventricular ejection fraction
- MI
- myocardial infarction
- PTCA
- percutaneous transluminal coronary angioplasty
- TIMI
- thrombolysis in myocardial infarction
- Received December 29, 1997.
- Revision received April 22, 1998.
- Accepted May 11, 1998.
- American College of Cardiology
