For patients with acute myocardial infarction (AMI), symptoms assessed by emergency medical services (EMS) providers have a critical role in prehospital treatment decisions. The purpose of this study was to evaluate the diagnostic accuracy of EMS provider-assessed cardiac symptoms of AMI.
Patients transported by EMS to 4 study hospitals from 2008 to 2012 were included. Using EMS and administrative emergency department databases, patients were stratified according to the presence of EMS-assessed cardiac symptoms and emergency department diagnosis of AMI. Cardiac symptoms were defined as chest pain, dyspnea, palpitations, and syncope. Disproportionate stratified sampling was used, and medical records of sampled patients were reviewed to identify an actual diagnosis of AMI. Using inverse probability weighting, verification bias-corrected diagnostic performance was estimated.
Overall, 92,353 patients were enrolled in the study. Of these, 13,971 (15.1%) complained of cardiac symptoms to EMS providers. A total of 775 patients were sampled for hospital record review. The sensitivity, specificity, positive predictive value, and negative predictive value of EMS provider-assessed cardiac symptoms for the final diagnosis of AMI was 73.3% (95% confidence interval [CI], 70.8 to 75.7), 85.3% (95% CI, 85.3 to 85.4), 3.9% (95% CI, 3.6 to 4.2), and 99.7% (95% CI, 99.7 to 99.8), respectively.
We found that EMS provider-assessed cardiac symptoms had moderate sensitivity and high specificity for diagnosis of AMI. EMS policymakers can use these data to evaluate the pertinence of specific prehospital treatment of AMI.
In contrast to many studies about the diagnostic accuracy of hospital physician-assessed cardiac symptoms for acute myocardial infarction (AMI), the diagnostic accuracy of emergency medical services (EMS) provider-assessed cardiac symptoms for AMI has not been evaluated in previous studies.
The sensitivity of EMS provider-assessed cardiac symptom for the final diagnosis of AMI was 73.3% (95% confidence interval [CI], 70.8 to 75.7), specificity was 85.3% (95% CI, 85.3 to 85.4), positive predictive value was 3.9% (95% CI, 3.6 to 4.2), and negative predictive value was 99.7% (95% CI, 99.7 to 99.8). We found that EMS provider-assessed cardiac symptoms had moderate sensitivity and high specificity for diagnosis of AMI.
The mortality rate of acute myocardial infarction (AMI) has declined substantially during the past 30 years [
Although prehospital 12-lead ECG is the most studied tool and is a class I recommendation for the prehospital management of AMI [
In contrast to many studies about the diagnostic accuracy of hospital physician-assessed cardiac symptoms for AMI [
Korea established a single-tiered and fire-based public EMS system in 1995. The emergency hotline number in Korea is 119, and emergency medical technicians (EMTs) are dispatched during emergency calls. Detailed information on the education and training of Korean EMTs has been described previously [
This study was a retrospective observational study using an EMS database, administrative databases of participating emergency departments (EDs), and hospital medical records. The records of 4 large tertiary academic EDs located in urban areas with 40,000 to 80,000 annual patients were reviewed. We acquired the EMS database from the National Emergency Management Agency for this study. Using the EMS database from January 1, 2008 to December 31, 2012, we linked the participating hospitals’ administrative data to the EMS database and assessed information on age, sex, visiting date, and visiting time. The hospital medical records of the sampled patients were reviewed by trained researchers. Available ED records, hospital admission records, nursing charts, and coronary angiography reports were reviewed.
We included patients who visited any of the 4 participating hospitals’ EDs by EMS from January 1, 2008 to December 31, 2012. Patients whose EMS data were not linked to the administrative data were excluded. Using the disproportionate stratified sampling method, we planned to enroll 800 patients for our analysis.
Because patients who had EMS-assessed cardiac symptoms and patients whose final diagnosis was AMI were rare in the EMS database, a disproportionate stratified sample design was used to gain an adequate number of those patients. EMS-assessed cardiac symptoms and a discharge diagnosis of AMI in the administrative database were used for stratification. To gain an evenly distributed sample, the hospital and year of visit were also used for stratification. We planned to sample 10 patients in each stratum for a total of 800 patients. The sampled data were weighted to the probability of selection.
Among the 30 predefined categories of symptoms in the EMS database, we defined EMS-assessed cardiac symptoms as chest pain, dyspnea, palpitation, and syncope. Meanwhile, an ED discharge diagnosis of AMI was defined as an International Classification of Diseases 10th revision (ICD-10) code of I21.0 to I21.9 in the administrative ED database.
From the EMS database, we collected data on the patient’s age, sex, symptom to call time, response time, scene time, transport time, hospital arriving time, presenting symptoms, prehospital documented shock (at least 1 event of systolic blood pressure less than 90 mmHg as measured by the EMS), and prehospital management, including oxygen therapy, ECG monitoring, intravenous fluid infusion, nitroglycerin administration, and cardiopulmonary resuscitation (CPR).
From the participating hospital’s administrative database, we collected data regarding patients’ age, sex, hospital arriving time, ICD-10 ED diagnosis, and ED disposition status.
By reviewing hospital medical records, we collected data on the final diagnosis of AMI or not. For AMI patients, we also collected data on the presence of ST segment elevation, cardiogenic shock before reperfusion therapy, performance of CPR before reperfusion therapy, and the type of reperfusion therapy (thrombolysis, percutaneous coronary intervention, or coronary artery bypass grafting). Data on door-to-needle or balloon times were also collected in patients with ST elevation myocardial infarction (STEMI).
Descriptive statistics were used to assess the similarity between the study population and the study sample. The characteristics of patients whose final diagnosis was AMI and STEMI were compared according to EMS provider-assessed cardiac symptoms. Values in the study sample were weighted via the reciprocal of the probability of selection in all analyses. Because we planned to compare weighted values according to EMS provider-assessed cardiac symptoms, design-based statistical tests, including Student’s t-test, Wilcoxon rank-sum test, chi-square test, and Fisher exact test, were used as appropriate using a survey package for R software. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) with 95% confidence interval (CI) of each of the EMS-assessed cardiac symptoms as well as all of the EMS-assessed cardiac symptoms combined were calculated for the final diagnosis of AMI. Verification bias-adjusted estimates were calculated by using stratified sampling to weigh results from patients in the EMS database using CompareTests for R software [
The study protocol was approved by the Institutional Review Board of the Seoul National University Hospital (1509-120-705). Informed consent was waived by the Institutional Review Board.
From January 2008 to December 2012, 121,394 patients who visited the participating hospitals via EMS were identified from the EMS database. Among them, data of 92,353 (76.1%) patients were linked to a participating hospital’s administrative ED database. Although stratified sampling of 800 patients was planned, only 775 patients were sampled because the total number of patients in some strata did not exceed the planned number. The medical records of the sampled 775 patients were reviewed. Among them, 276 patients had a final diagnosis of AMI. Notably, no confirmed AMI was observed in patients who did not have a diagnosis of AMI in the administrative ED database (
Because the timeliness of treatment is critical in AMI patients [
We found that EMS provider-assessed cardiac symptoms had very high NPV. However, because only 0.8% of patients had confirmed AMI, the high NPV of EMS provider-assessed cardiac symptoms was primarily based on the low prevalence of confirmed AMI patients in the EMS database. We also found that the sensitivities of dyspnea, palpitation, and syncope were low. Therefore, the diagnostic value of these symptoms is minimal for identifying AMI.
We found that AMI patients who had EMS provider-assessed cardiac symptoms tend to receive more prehospital management and have low prevalence of shock in the ED phase. Active management in the prehospital setting can be associated with early stabilization of AMI patients [
The mechanism of efficient hospital treatment in patients who had EMS-assessed cardiac symptoms was not directly evaluated in our study. Because patients who had EMS-assessed cardiac symptoms had classic symptoms for AMI, the ease of diagnosis can be associated with efficient treatment in the hospital phase. Other EMS provider activities, including prehospital notification and alerts to ED staff when EMS providers hand over patients, can also be associated with those characteristics. Because prehospital 12-lead ECG was not widely used in our setting, the effect of prehospital 12-lead ECG would be minimal in our study.
To our knowledge, this is the first study to evaluate EMS provider-assessed cardiac symptoms in view of the final diagnosis of AMI. Previously, the concordance of symptoms of myocardial infarction between paramedic and hospital records was evaluated in one study, and they found that the concordance of paramedic prehospital patient care documentation of symptoms was excellent for almost all symptoms, including chest pain [
Compared to previous studies, our study has several strengths. First, rather than include only patients who had chest pain or AMI diagnosis, we included and sampled all patients responded by EMS. Therefore, we could estimate all aspects of diagnostic accuracy, including sensitivity, specificity, and predictive values. If we only included patients who had chest pain and AMI diagnosis, the specificity could not be calculated. Second, because we used disproportionate stratified sampling, we captured a substantial proportion of AMI patients in our sample. Because less than 1% of the total patients had AMI, a sample of more than 27,300 patients would be needed to capture 273 confirmed AMI patients, which is the same number of confirmed AMI patients in our study. Although we captured a substantial proportion of AMI patients using disproportionate stratified sampling, we found that baseline characteristics were similar between all patients and weighted values of sample patients (
EMS provider-assessed symptoms are critical for evaluation and management of AMI patients. The diagnostic accuracy of EMS provider-assessed cardiac symptoms can be used as baseline data for policymakers and quality indicators in prehospital AMI management and AMI education programs for EMS providers. Studies about the association between the diagnostic accuracy of EMS provider-assessed cardiac symptoms, outcomes of AMI patients, and the additional diagnostic value of other tests, including prehospital 12-lead ECG, for the evaluation of AMI in patients with EMS provider-assessed cardiac symptoms would be helpful to evaluate the importance of the EMS system and each EMS intervention in the management of AMI more objectively.
Our study has several limitations. First, it was performed at tertiary hospitals in Korea, and the results may not be generalized to other EMS systems. However, the consistency of findings across five years and four hospitals supports our findings, which may be applicable to different ED settings in these regions. Second, the gold standard of AMI was based on hospital medical review in this study, and there may be some errors. However, many studies on AMI use hospital medical review as the gold standard [
In conclusion, each of the EMS provider-assessed cardiac symptoms showed moderate sensitivity, high specificity, low PPV, and very high NPV. We also found that among AMI patients, those who had EMS-assessed cardiac symptoms received more aggressive prehospital management and more efficient in-hospital treatment for AMI. Studies about the association of diagnostic accuracy of EMS provider-assessed cardiac symptoms and outcomes and additional diagnostic value of other tests, including prehospital 12-lead ECG, for the evaluation of AMI in patients with EMS provider-assessed cardiac symptoms are needed.
No potential conflict of interest relevant to this article was reported.
This study was financially supported by the Woochon Cardio-Neuro-Vascular Research Foundation (2014).
Schematic of data analyses. ED, emergency department; EMS, emergency medical services; EMS Sx+, patients who had EMS provider-assessed cardiac symptoms; ED Dx+, patients diagnosed with AMI in the administrative ED database; ED Dx-, patients who did not have a diagnosis of AMI in the administrative ED database; EMS Sx-, patients who did not have EMS provider-assessed cardiac symptoms; AMI, acute myocardial infarction. a)Hospital and year of visit was also used in stratification.
Prehospital and ED characteristics of the study population and sample
Variable | Total | Sample (unweighted) | Sample (weighted |
---|---|---|---|
n = 92,353 | n = 775 | n = 92,353 | |
Age (yr) | 52.2 ± 22.3 | 58.5 ± 19.4 | 49.2 ± 22.5 |
Sex, male | 48,526 (52.5) | 462 (59.6) | 47,577 (51.5) |
EMS provider-assessed cardiac symptoms | |||
Chest pain | 4,413 (4.8) | 200 (25.8) | 3,470 (3.8) |
Dyspnea | 7,764 (8.4) | 185 (23.9) | 8,494 (9.2) |
Palpitations | 461 (0.5) | 9 (1.2) | 391 (0.4) |
Syncope | 2,175 (2.4) | 45 (5.8) | 2,443 (2.6) |
Any cardiac symptom | 13,971 (15.1) | 375 (51.6) | 13,971 (15.1) |
Prehospital documented shock |
5,319 (5.8) | 76 (9.8) | 8,082 (8.8) |
Prehospital time interval (min) | |||
Response time | 7.0 (5.0–9.0) | 7.0 (5.0–9.0) | 7.0 (5.0–9.0) |
Scene time | 7.0 (4.0–10.0) | 6 (4–10) | 7.0 (4.0–10.0) |
Transport time | 11.0 (7.0–20.0) | 11.0 (7.0–19.0) | 10.0 (7.0–18.0) |
Total prehospital time | 28.0 (21.0–38.0) | 26.0 (20.0–36.0) | 26.0 (20.0–36.0) |
Prehospital management | |||
Oxygen therapy | 22,855 (24.7) | 380 (49.0) | 25,800 (27.9) |
ECG monitoring | 16,016 (17.3) | 266 (34.3) | 13,262 (14.4) |
IV infusion | 1,247 (1.4) | 14 (1.8) | 706 (0.8) |
Nitroglycerin | 295 (0.3) | 16 (2.1) | 216 (0.2) |
Cardiopulmonary resuscitation | 1,361 (1.5) | 28 (3.6) | 817 (0.9) |
ED diagnosis of AMI | 1,001 (1.1) | 375 (48.4) | 1,001 (1.1) |
ED disposition | |||
Discharged | 58,111 (62.9) | 235 (30.3) | 55,852 (60.5) |
Admitted | 25,777 (27.9) | 62.6 (18) | 27,109 (29.4) |
Transferred | 3,504 (3.8) | 28 (3.6) | 5,825 (6.3) |
ED death | 1,811 (2.0) | 18 (2.3) | 1,396 (1.5) |
Others | 1,693 (1.8) | 9 (1.2) | 2,172 (2.4) |
Values are presented as mean±standard deviation, number (%), or median (interquartile range).
ED, emergency department; EMS, emergency medical services; ECG, electrocardiogram; IV, intravenous; AMI, acute myocardial infarction.
Values are weighted in sample.
Patients whose systolic blood pressure was less than 90 mmHg in the EMS database at least once.
Diagnostic performance of EMS-assessed cardiac symptoms for acute myocardial infarction
EMS-assessed symptom | Sensitivity | Specificity | PPV | NPV |
---|---|---|---|---|
Chest pain | 65.1 (62.7−67.4) | 95.9 (95.9−95.9) | 11.5 (10.9−12.3) | 99.7 (99.7−99.7) |
Dyspnea | 12.9 (11.3−14.6) | 91.6 (91.6−91.6) | 1.2 (1.1−1.4) | 99.2 (99.2−99.3) |
Palpitations | 0.3 (0.3−0.3) | 99.9 (99.9−99.9) | 1.9 (1.9−1.9) | 99.2 (99.2−99.3) |
Syncope | 1.0 (0.7−1.6) | 97.9 (97.9−97.9) | 0.4 (0.2−0.6) | 99.2 (99.2−99.3) |
Any cardiac symptom | 73.3 (70.8−75.7) | 85.3 (85.3−85.4) | 3.9 (3.6−4.2) | 99.7 (99.7−99.8) |
Values are presented as % (95% confidence interval).
EMS, emergency medical services; PPV, positive predictive value; NPV, negative predictive value.
Prehospital, ED, and hospital characteristics of confirmed AMI patients according to EMS provider-assessed cardiac symptom in the study sample
Variable | Confirmed AMI |
STEMI |
||||
---|---|---|---|---|---|---|
EMS Sx- n = 196 | EMS Sx+ n = 533 | P-value |
EMS Sx- n = 105 | EMS Sx+ n = 322 | P-value |
|
Age (yr) | 66.9 ± 13.2 | 64.6 ± 11.5 | 0.16 | |||
Sex, male | 134 (68.4) | 362 (67.9) | 0.95 | 80 (76.2) | 225 (69.9) | 0.43 |
Symptom to call time (min) | 47 (4.0−217.0) | 49.0 (12.0−142.5) | 0.99 | 25.8 (1−144) | 35.0 (9.5−93.0) | 0.96 |
Response time (min) | 7.0 (5.0−9.0) | 7.0 (5.0−9.0) | 0.56 | 7.0 (5.0−8.0) | 7.0 (6.0−9.0) | 0.11 |
Scene time (min) | 6.0 (4.0−9.0) | 5.0 (3.0−7.8) | 0.03 | 6.0 (3.8−8.0) | 5.0 (3.0−7.0) | 0.16 |
Transport time (min) | 10.0 (6.0−17.0) | 13.0 (8.0−21.4) | 0.01 | 9.0 (6.0−14.8) | 11.8 (8.0−18.0) | 0.03 |
Total prehospital time (min) | 24.0 (20.0−33.0) | 25.0 (20.0−41.0) | 0.22 | 23.1 (20−29.3) | 24.1 (20.0−34.2) | 0.18 |
Prehospital documented shock |
16 (8.2) | 55 (10.3) | 0.56 | 11 (10.5) | 38 (11.8) | 0.75 |
EMS treatment | ||||||
Oxygen therapy | 85 (43.4) | 353 (66.1) | < 0.01 | 44 (42.3) | 214 (66.5) | < 0.01 |
ECG monitoring | 62 (31.6) | 319 (59.8) | < 0.01 | 33 (31.4) | 193 (59.9) | < 0.01 |
IV line insertion | 3 (1.5) | 20 (3.8) | 0.22 | 2 (1.9) | 10 (3.1) | 0.50 |
Nitroglycerin | 0 (0) | 50 (9.4) | 0.02 | 0 (0) | 29 (9) | 0.11 |
Cardiopulmonary resuscitation | 20 (10.3) | 8 (1.5) | < 0.01 | 12 (11.4) | 6 (1.9) | 0.05 |
ED status | 0.37 | 0.85 | ||||
Discharged | 0 (0) | 0 (0) | 0 (0) | 0 (0) | ||
Admitted | 188 (95.9) | 520 (96.6) | 102 (97.1) | 315 (97.8) | ||
Transferred | 0 (0) | 7 (1.3) | - | 1 (0.3) | ||
Others | 8 (4.1) | 6 (1.1) | 3 (2.9) | 6 (1.9) | ||
ED death | 8 (4.1) | 6 (1.1) | 3 (2.9) | 6 (1.9) | ||
Shock before reperfusion therapy |
20 (10.3) | 15 (2.8) | 0.02 | 11 (10.5) | 5 (1.6) | < 0.01 |
CPR before reperfusion therapy | 34 (17.3) | 15 (2.8) | < 0.01 | 21 (20.2) | 6 (1.9) | < 0.01 |
Reperfusion therapy | ||||||
Thrombolysis | 7 (3.6) | 33 (6.2) | 0.34 | 7 (6.7) | 32 (9.9) | 0.53 |
PCI | 127 (65.1) | 440 (82.6) | < 0.01 | 84 (80.0) | 302 (93.8) | 0.02 |
CABG | 12 (6.15) | 20 (3.7) | 0.42 | 3 (2.9) | 0 (0) | 0.08 |
DtoN time (min) |
NA | NA | 20.0 (20.0−28.3) | 25.3 (16.4−28.0) | 0.96 | |
DtoB time (min) |
NA | NA | 107.1 (68.5−205.3) | 72.4 (27.5−87.7) | < 0.01 |
Values are presented as mean±standard deviation, number (%), or median (interquartile range).
ED, emergency department; AMI, acute myocardial infarction; EMS, emergency medical services; STEMI, ST elevation myocardial infarction; EMS Sx-, patients who did not have EMS provider-assessed cardiac symptoms; EMS Sx+, patients who had EMS provider-assessed cardiac symptoms; ECG, electrocardiogram; IV, intravenous; CPR, cardiopulmonary resuscitation; PCI, percutaneous coronary intervention; CABG, coronary artery bypass graft; DtoN time, door-to-needle time in thrombolysis patients; NA, non applicable; DtoB time, door-to-balloon time in primary PCI patients.
All values are weighted in sample. Because all confirmed AMI patient’s ED diagnosis was AMI, only 2 strata were shown.
P-value was calculated via design-based statistical tests, including Student’s t-test, Wilcoxon rank-sum test, chi-square test, and Fisher exact test, as appropriate.
Prehospital documented shock.
Shock before reperfusion therapy.