Triage and Diagnosis of Chest Pain in Rural Hospitals: Implementation of the ACI-TIPI in the High Plains Research Network

INTRODUCTION

Ischemic heart disease resulting in acute myocardial infarction leads to more than 1 million hospitalizations every year in the United States. Lack of clear diagnosis has been reported as one reason for inadequate use of proven treatments.¹ The Acute Cardiac Ischemia Time-Insensitive Predictive Instrument (ACI-TIPI) assists in the diagnosis of acute cardiac ischemia by printing the probability (0% to 100%) on the electrocardiogram header that the patient is truly suffering acute cardiac ischemia). The ACI-TIPI has been shown to improve the diagnostic accuracy and the triage of patients with chest pain in urban and suburban emergency departments. Specifically, the ACI-TIPI has been shown to decrease unnecessary admissions to the hospital and coronary care unit among patients without true acute ischemia heart disease.²

Because many rural and frontier hospitals have limited resources or no coronary care unit, patients requiring a coronary care unit admission are often transferred to another hospital. Unnecessary transfer from a rural hospital to an urban hospital is disruptive and stressful for patients and their family and generates enormous costs. One study found that 30% to 50% of patients with acute cardiac ischemia are transferred at some point during their care.³ No data exist on the incidence of unnecessary interhospital transfer.

The purpose of this study was to evaluate the impact of the use of ACI-TIPI on triage decisions and diagnostic accuracy for patients coming to rural and frontier emergency departments with chest pain or other symptoms suggestive of acute cardiac ischemia. We hypothesized that the use of the ACI-TIPI score might decrease the rate of interhospital transfer for patients without acute ischemia while not affecting the admission and/or transfer decisions for patients truly suffering acute ischemia.

METHODS

RESULTS

Table 1⇓ displays the patient demographics and compares them between months when ACI-TIPI was on and months when ACI-TIPI was off. No differences in patient demographics were found. Eighty-one percent had chest pain as their chief complaint. Nearly 97% of all patients had serum cardiac markers obtained in the emergency department. Greater than 99% of patients had an ECG in the emergency department. Overall, 45.4% of patients in this study were discharged home from the emergency department, 8% were transferred directly from the emergency department, 10% were admitted to the rural hospital then transferred in the subsequent days, and 36% were admitted to and cared for exclusively in the rural hospital.

Table 2⇓ displays the triage and disposition for patients with various diagnoses. In patients with a final diagnosis of no acute cardiac ischemia, there was no significant change in the rate of discharge home from emergency department when ACI-TIPI was available. For patients with acute cardiac ischemia (ICD-9-CM 410, 411) there was a small, nonsignificant decrease in the percentage of patients inappropriately discharged home (5.2% ACI-TIPI off vs 3.0% ACI-TIPI on, P = .4). Patients with acute ischemia were appropriately hospitalized 97% of the time. By far, the largest group of patients was the group who complained of chest pain but were not having acute ischemia. Nearly one half of these patients were admitted to the hospital. Most patients with an acute myocardial infarction were transferred to a tertiary care hospital, and there was no difference in overall transfer rate associated with the availability of the ACI-TIPI score.

In 8 of the 11 facilities the diagnostic accuracy for acute myocardial infarction improved during months when the ACI-TIPI was used (Table 4⇓). For all hospitals, however, the average diagnostic accuracy was not statistically different (86.8% ACI-TIPI off vs 89.0% ACI-TIPI on, P = .15). The true-positive rate remained essentially the same (3.9% ACI-TIPI off, 4.0% ACI-TIPI on). The true-negative rate increased from 82.9% to 85.0%. As expected from previous research, the false-positive rate decreased from 13.2% to 9.7%. Unfortunately, the false-negative rate increased from 0% to 1.3%. Only 3 (2.3%) patients with an ICD-9-CM diagnosis of acute myocardial infarction (410) were discharged from the emergency department. One additional patient that met clinical criteria for an acute myocardial infarction was discharged home. Because there were only a few cases at each hospital, no change reached statistical significance.

DISCUSSION

The purpose of this study was to determine the impact of providing the ACI-TIPI score on triage and diagnostic accuracy for patients complaining of chest pain to rural and frontier hospitals. We found that the ACI-TIPI score had no statistically significant impact on triage or diagnostic accuracy. The small changes in triage and diagnostic accuracy we noted were consistently in the same direction of improving clinical care. Because of the small sample size for each diagnostic category, however, these changes did not reach statistical significance. Overall, diagnostic and triage accuracy were at or above that reported in previous studies.^2,5

Unfortunately, there was no change in the triage among patients without acute ischemia. Although many patients with chest pain have other diagnoses that require hospitalization (pneumonia, heart failure, upper gastrointestinal bleeding), only a small proportion of patients without acute ischemia were transferred (11%), roughly equivalent to the rate of admission to the coronary care unit among patients without acute ischemia in ACI-TIPI research in urban hospitals (7% to 15%).²

The patients in our study were similar in age, sex, and chief complaint to patients in previous studies on ACI-TIPI.² Nearly all patients had ECG and serum cardiac enzyme testing implying that these patients were indeed considered by the treating physician as potentially having acute ischemic heart disease. Only 4 patients who met clinical criteria for acute myocardial infarction were discharged home from the emergency department, a rate similar to that found in previous research.² Unfortunately, we have no follow-up data on this group of patients to determine final diagnosis and outcome.

In a rural hospital without advanced cardiac services, transfer may be viewed as a treatment option, as is the use of aspirin, β-blockers, and thrombolytics. Although there are evidence-based guidelines for the medical treatments of acute myocardial infarction, there are no guidelines aiding the decision of whether to transfer a patient suffering from acute cardiac ischemia. Transfer appears to be a complex decision and was not dramatically altered by the additional diagnostic information obtained using the ACI-TIPI program. Further research on the relationship of hospital, physician, and patients factors related to transfer may help identify patient groups most likely to benefit from transfer.

There were several limitations to this study. First, the newest version of the ACI-TIPI requires that the ECG machine print 2 complete 12-lead ECG reports, one with a traditional interpretation and a second with the ACI-TIPI score. We found several occasions in which the physician was not seeing the ECG report with the ACI-TIPI score. The ACI-TIPI score could be bypassed by a manual override, and we heard of several occasions where this was done and no score was generated. We suggest that the ACI-TIPI score be part of the standard ECG printout. Second, we have no way of knowing when the ACI-TIPI score was actually used by the physician to help with the diagnosis and triage. Comments about the ACI-TIPI score were not a routine part of the patient record.

Third, because we had so few patients with any specific diagnosis, the changes we found in diagnostic accuracy and triage did not reach statistical significance. We anticipated more patients with each diagnosis and a larger effect size. Our rate of acute cardiac ischemia (13%) was lower than previously reported (17.5%).² For patients without acute ischemia (n = 1,537), we had 90% power to detect a 7.5% absolute change in triage, but we found only a 2% to 3% change in triage in this group. For patients with acute ischemia (n = 233) we needed a 20% absolute change in triage to have 90% power to detect a significant change, but found only a 2% to 8% change in triage. Given the total sample, we had 90% power to detect a 4.4% change in diagnostic accuracy. A larger study or one with prospective data collection and determination on the actual use of the ACI-TIPI score is needed to determine whether ACI-TIPI improves outcomes in rural hospitals. Finally, because we did not abstract the charts at urban hospitals where patients were transferred, we were unable to confirm acute myocardial infarction in some patients. There may have been patients transferred with a diagnosis of acute myocardial infarction who had a different final diagnosis from the urban hospital. From a previous study we found that 83% of patients transferred with a diagnosis of acute myocardial infarction had a final diagnosis of acute myocardial infarction or unstable angina.³

The diagnostic accuracy of acute myocardial infarction has been a concern in previous research.^6–8 We found that because so many patients who appear to have acute myocardial infarction get transferred, the rural hospital data are often insufficient to meet the standard WHO criteria for a formal diagnosis of acute myocardial infarction. We chose a conservative measure for the diagnosis of acute myocardial infarction and found excellent overall agreement between the ICD-9-CM diagnosis of acute myocardial infarction and the clinical diagnosis of acute myocardial infarction. Most disagreement between ICD-9-CM diagnosis and clinical diagnosis was an error in overdiagnosing acute ischemia or infarction even when the patient did not meet clinical criteria. Defining an acute myocardial infarction among transferred patients will continue to be a research dilemma and deserves further investigation.

The benefit of this study is that it was a real-life implementation and effectiveness trial of the ACI-TIPI in rural hospitals. It included only the type and amount of education that would occur in a typical nonresearch setting, which may not be adequate to fully educate physicians about the interpretation and benefit of the use of the ACI-TIPI score. This type of research points to the value of a practice-based research network that can collect and aggregate data on important medical conditions for rural primary care physicians.

Physicians in the HPRN diagnosed acute cardiac ischemia and triaged patients accurately. The use of the ACI-TIPI did not appear to have a significant impact on the triage and diagnosis for patients with chest pain. Inclusion of the ACI-TIPI score into the standard ECG interpretation report may make it easier to use. Conducting this type of study in more rural sites may provide a sample sufficient to detect statistically significant changes in triage and diagnostic accuracy.