Abstract
Patients diagnosed with ST-segment elevation myocardial infarction (STEMI) are occasionally found to have no culprit lesion on coronary angiography and are classified as presenting with false-positive STEMI. The clinical presentation and outcomes of these patients need to be further explored. In this case-controlled study, 259 consecutive patients with true code STEMI were compared to 104 consecutive STEMI patients without culprit lesions on emergent coronary angiography. We compared the clinical presentation, electrocardiographic features, etiology, and outcomes of the two groups. STEMI patients without culprit lesions were less likely to have typical chest pain (46% vs. 79%, P < 0.01). The ST-elevation in the group without culprit lesion was more likely to be concave (56% vs. 31%, P < 0.01), with less reciprocal ST-depression (19% vs. 71%, P < 0.01). The group without culprit lesions had a higher rate of ventilator support requirement (12.4% vs. 5.4%, P = 0.02), and higher rate of 30-day mortality (11.0% vs. 5.9%, P = 0.02). However, after excluding the patients with out-of-hospital cardiac arrests from both groups, the difference was no longer significant (P = 0.40 and 0.34 respectively). The relative poor outcomes of patients with false-positive code STEMI reflect the severity of their underlying medical condition. Careful history and review of ECG may help differentiate this group from true STEMI.
Highlights
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Patients with presumed STEMI by ECG often do not have a culprit lesion.
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These patients can often be identified by ECG.
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Patients with false-positive code STEMI may have relatively poor outcome due to other medical conditions.
1
Introduction
Primary percutaneous coronary intervention (pPCI) is the preferred method of reperfusion in ST-segment elevation myocardial infarctions (STEMIs) . The 2013 ACC/AHA guidelines reiterated the importance of timely transport of patients with STEMI to pPCI-capable hospitals as delays to reperfusion are associated with significantly higher rates of morbidity and mortality .
In an effort to expedite the care of STEMI patients, several centers in Ontario have adopted integrated regional pPCI STEMI programs that enable paramedics and emergency physicians to activate the cardiac catheterization laboratory (CCL) after diagnosing STEMI . The establishment of a 24/7 STEMI program can significantly impact patient flow and resources. STEMI patients who are found to have no culprit lesions may be exposed to unnecessary risk of the procedure and also financially burden the medical system with further effects on human resources, especially if the CCL team is activated during the night. Although a certain rate of false activation is expected, there has been no established acceptable rate in the literature due to discrepancies in defining false-positive CCL activation . Frequent cancellation of CCL due to inappropriate activation may weaken collaboration between the CCL team and emergency response staff and have a negative impact on these programs. Although cancellation of cardiac catheterization may occur prior to patient arrival after reviewing the history and ECG, once the patient arrives to the CCL, it may be reasonable to proceed with cardiac catheterization if the diagnosis of STEMI is questionable or the diagnosis of acute coronary syndrome is likely.
The aim of this study was to describe the etiology, clinical presentation, electrocardiographic features, and outcomes of Code STEMI patients who underwent cardiac catheterization but were found to have no culprit lesion, and compare them to patients with true STEMI.
2
Material and methods
2.1
Data collection
This is a retrospective, case–control analysis of Code STEMI patients that presented to University Hospital of the London Health Sciences Centre (LHSC), a tertiary care hospital with 24/7 PCI capabilities and part of a regional primary PCI program of London-Middlesex County serving a population of 460,000. The study was approved by the Western University Research Ethics Board. The study population included patients who presented directly to University Hospital emergency department either by ambulance or self-transport, patients who were transferred directly to the cardiac catheterization laboratory by paramedics, as well as patients transferred from nearby affiliated non-PCI centers for management of STEMI. The emergency department physician or paramedic who had first contact with the patient called the direct STEMI line and after a brief review by the interventional cardiologist on call, the CCL was activated if deemed appropriate according to the given history. Paramedics in the London-Middlesex County employ the University of Glasgow computer algorithm for interpretation of out-of-hospital ECGs and use that as a basis for calling the STEMI line. Consecutive Code STEMI patients without angiographic culprit lesion collected over a 4-year period were compared to consecutive true Code STEMI patients collected over a 1-year period.
Patients’ paper chart and electronic medical records were used to collect information regarding coronary artery disease risk factors, initial clinical presentation, final diagnosis, length of stay, and 30-day mortality.
2.2
Definitions
The quality of the chest pain was classified as a typical pattern if the patient described retro-sternal tightness or pressure without atypical features such as exacerbation by deep inspiration or lying flat, or tearing pain to the back . ST-elevation (STE) was defined as > 1 mm ST-segment elevation measured 0.04 ms from the J-point in 2 or more contiguous limb leads, or > 2 mm elevation in the precordial leads . The morphology of STE was classified as concave if the ST-segment dipped below a straight line drawn between the J-point to the end of the ST-segment . ST depression was classified as reciprocal if it was in the anterior or lateral territories for an inferior STE pattern, in the inferior territory for an anterior or lateral STE pattern, or in the anterior territory for a posterior STE pattern . A culprit coronary lesion was defined as the presence of an acute total or subtotal occlusion of a coronary artery that correlates with the STE identified on the qualifying ECG . Cardiac biomarkers were considered elevated if the measured Troponin I or T was above the upper limit of normal during the patient’s hospitalization following activation of Code STEMI. The qualifying ECG and the coronary angiogram report were used to classify the patients into two groups: 1) true STEMI: patients who had a final diagnosis of a STEMI and had a culprit coronary lesion on angiography that correlated with the territory of STE on ECG, or 2) false-positive STEMI: patients who had an alternate final diagnosis, and had no culprit coronary lesion for a STEMI on angiography. First medical contact time was defined as the time of EMS arrival or, for patients who presented by self-transport, the time at which patients registered at the triage of a LHSC affiliated hospital or the time of the qualifying ECG if the former is unavailable.
2.3
Data analysis
Comparisons were made between the true STEMI patients and patients without culprit lesions using either student t-tests for continuous variables or chi-square tests for categorical variables. Fisher’s exact test was used for variables with an expected count of less than 5. All analyses were performed using IBM SPSS version 21. P value < 0.05 was considered statistically significant.
2
Material and methods
2.1
Data collection
This is a retrospective, case–control analysis of Code STEMI patients that presented to University Hospital of the London Health Sciences Centre (LHSC), a tertiary care hospital with 24/7 PCI capabilities and part of a regional primary PCI program of London-Middlesex County serving a population of 460,000. The study was approved by the Western University Research Ethics Board. The study population included patients who presented directly to University Hospital emergency department either by ambulance or self-transport, patients who were transferred directly to the cardiac catheterization laboratory by paramedics, as well as patients transferred from nearby affiliated non-PCI centers for management of STEMI. The emergency department physician or paramedic who had first contact with the patient called the direct STEMI line and after a brief review by the interventional cardiologist on call, the CCL was activated if deemed appropriate according to the given history. Paramedics in the London-Middlesex County employ the University of Glasgow computer algorithm for interpretation of out-of-hospital ECGs and use that as a basis for calling the STEMI line. Consecutive Code STEMI patients without angiographic culprit lesion collected over a 4-year period were compared to consecutive true Code STEMI patients collected over a 1-year period.
Patients’ paper chart and electronic medical records were used to collect information regarding coronary artery disease risk factors, initial clinical presentation, final diagnosis, length of stay, and 30-day mortality.
2.2
Definitions
The quality of the chest pain was classified as a typical pattern if the patient described retro-sternal tightness or pressure without atypical features such as exacerbation by deep inspiration or lying flat, or tearing pain to the back . ST-elevation (STE) was defined as > 1 mm ST-segment elevation measured 0.04 ms from the J-point in 2 or more contiguous limb leads, or > 2 mm elevation in the precordial leads . The morphology of STE was classified as concave if the ST-segment dipped below a straight line drawn between the J-point to the end of the ST-segment . ST depression was classified as reciprocal if it was in the anterior or lateral territories for an inferior STE pattern, in the inferior territory for an anterior or lateral STE pattern, or in the anterior territory for a posterior STE pattern . A culprit coronary lesion was defined as the presence of an acute total or subtotal occlusion of a coronary artery that correlates with the STE identified on the qualifying ECG . Cardiac biomarkers were considered elevated if the measured Troponin I or T was above the upper limit of normal during the patient’s hospitalization following activation of Code STEMI. The qualifying ECG and the coronary angiogram report were used to classify the patients into two groups: 1) true STEMI: patients who had a final diagnosis of a STEMI and had a culprit coronary lesion on angiography that correlated with the territory of STE on ECG, or 2) false-positive STEMI: patients who had an alternate final diagnosis, and had no culprit coronary lesion for a STEMI on angiography. First medical contact time was defined as the time of EMS arrival or, for patients who presented by self-transport, the time at which patients registered at the triage of a LHSC affiliated hospital or the time of the qualifying ECG if the former is unavailable.
2.3
Data analysis
Comparisons were made between the true STEMI patients and patients without culprit lesions using either student t-tests for continuous variables or chi-square tests for categorical variables. Fisher’s exact test was used for variables with an expected count of less than 5. All analyses were performed using IBM SPSS version 21. P value < 0.05 was considered statistically significant.
3
Results
3.1
Study sample
The overall patient sample consisted of a total of 363 Code STEMI patients. There were 104 patients without culprit lesions, which were derived from 961 total Code STEMI activations from November 2010 to August 2014. These cases were compared to 259 consecutive cases of true Code STEMI collected from September 2012 to August 2013.
3.2
Patient characteristics and clinical presentations
The baseline characteristics are presented in Table 1 . STEMI patients without culprit lesions were younger than patients in the group with culprit lesions. The two groups were similar in all of their coronary artery disease risk factors. Not surprisingly, patients without culprit lesions were less likely to present with typical chest pain compared to the true STEMI group (45.7 vs. 79.2%) and also less likely to have cardiac biomarker elevation (52.4 vs. 98.8%). 30.4% of the STEMIs without culprit lesions are activated by paramedics compared to 40.2% of those with culprit lesions.
| False STEMI (N = 104) | True STEMI (N = 259) | P value | |
|---|---|---|---|
| Age | 61.0 ± 14.5 | 64.4 ± 12.6 | 0.03 |
| Male gender | 74 (70.5%) | 186 (71.8%) | 0.80 |
| Risk factors | |||
| a) Known CAD | 25 (23.8%) | 60 (23.2%) | 0.29 |
| b) Hypertension | 53 (50.5%) | 144 (55.6%) | 0.57 |
| c) Diabetes | 25 (23.8%) | 49 (18.9%) | 0.16 |
| d) Smoker | 63 (60.0%) | 156 (60.2%) | 0.29 |
| e) Dyslipidemia | 37 (35.2%) | 110 (42.5%) | 0.14 |
| f) Family history of CAD | 27 (25.7%) | 68 (26.3%) | 0.21 |
| g) PVD/stroke | 11 (10.5%) | 27 (10.4%) | 0.29 |
| Presentation | |||
| a) Typical chest pain | 48 (45.7%) | 205 (79.2%) | < 0.01 |
| b) Cardiac biomarker elevation | 55 (52.4%) | 256 (98.8%) | < 0.01 |
| c) Paramedic activation | 31 (30.4%) | 104 (40.2%) | 0.08 |
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