A total of 123 patients with symptoms of ACS but without ST-elevation were included in the period from November 30th 2017 to November 30th 2018. The average inclusion rate was 0.8 patients per 12-hour shift. The incidence of NSTEMI in the study population was 13%. The median road distance from point of first medical contact (FMC) to the local hospital was 14 km (IQR 14), and 77 km (IQR 20) to the PCI- hospital. 17 (13%) patients were not admitted to any hospital, but received follow-up by outpatient medical service. None of those were admitted during the next 90 days for cardiac events. Clinical characteristics are further presented in table 2. Exept for age, no statistical significant differences were found between groups.
[Table 2: Baseline characteristics of the study population at first medical contact
Variable | Unit | NSTEMI n = 16 | Without NSTEMI n = 107 | p |
n | %, median (min, max) | Missing n | n | %, median (min, max) | Missing n |
Female | - | 4 | 25% | 0 | 44 | 41% | 0 | 0.28 |
Age | years | - | 72 (46, 86) | 0 | - | 61 (27, 93) | 0 | 0.03 |
Previous MI | - | 4 | 25% | 0 | 22 | 22% | 7 | 0.75 |
Body Mass Index | kg/m2 | - | 27 (20, 36) | 0 | - | 27 (17, 48) | 0 | 0.21 |
Smoking | - | 11 | 73% | 1 | 67 | 68% | 8 | 0.77 |
Hypertension | - | 6 | 40% | 1 | 42 | 42% | 8 | 1.00 |
Previous PCI/cABG | - | 4 | 27% | 1 | 20 | 19% | 3 | 0.50 |
Statin use | - | 3 | 20% | 1 | 41 | 41% | 7 | 0.16 |
Diabetes mellitus (I & II) | - | 3 | 19% | 0 | 19 | 18% | 4 | 1.00 |
COPD | - | 1 | 7% | 1 | 12 | 11% | 1 | 1.00 |
Systolic blood pressure | mmHg | - | 149 (70, 192) | 0 | - | 146 (76, 202) | 1 | 0.72 |
Diastolic blood pressure | mmHg | - | 91 (50, 110) | 0 | - | 85 (44, 120) | 1 | 0.46 |
Heart rate | bpm | - | 71 (35, 103) | 0 | - | 73 (40, 137) | 0 | 0.18 |
30-day mortality | - | 2 | 13% | 0 | 5 | 5% | 0 | 0.23 |
Nomination: percentage, mean, (Standard deviation), median(range). Fisher exact test was used to test for inequality between the non ST- elevation myocardial infarction (NSTEMI) and without NSTEMI groups for categorical variables and t-test for normal distributed continuous variables (Age, Systolic/Diastolic blood pressure) and Mann-Whitney was used for other continuous variables (Body Mass Index and Pulse-rate). MI: Myocardial infarction. PCI: percutaneous coronary intervention. cABG: coronary artery bypass graft. COPD: Chronic obstructive pulmonary disease ] |
In patients discharged with NSTEMI, two (13%) had a normal prehospital ECG. In patients discharged without evidence of NSTEMI, a normal ECG was found in 75 (65%). In five cases (5%) ECG was not fully interpretable due to digital transfer issues or low quality of the recordings.
Prehospital POC Hs-cTnT among NSTEMI patients were in nine cases ranging from 51 ng/L to 416 ng/L. In the remaining seven NSTEMI patients, the prehospital Hs-cTnT were < 50 ng/L, which is below the detection limit of the unit. Hospital admission Hs-cTnT showed clinically comparable test results (see supplemental material). All patients without NSTEMI had negative prehospital POC Hs-cTnT values (< 50 ng/L). Technical issues in measuring prehospital POC Hs-cTnT were registered in seven cases (6%). This was mostly noted as a result of too low ambient temperature. Difficulties in providing venous access were registered in three cases (2%). A total of 113 (93%) Hs-cTnT tests were successfully performed.
A total of 107 (87%) focused TTE examinations were interpretable. Interpretability scoring is presented in table 3.
Table 3: Cardiologist interpretability score of TTE images received from paramedics on scene. The Likert- type scale range from 1 (no useful information) to 5 (full interpretable information) n = 123
Score | Frequency* |
| 1 | 3 | (2%) |
2 | 8 | (7%) |
3 | 42 | (34%) |
4 | 46 | (37%) |
5 | 22 | (18%) |
*two cases (2%) score missing.
Equipment-related technical TTE issues were reported in four (3%) patients, resulting in uncompleted or failed examinations. RWMA were detected in 11 (69%) patients with NSTEMI and in six (6%) patients without NSTEMI. Median time consumption in performing focused prehospital TTE was 11 minutes (IQR 8), counting from “probe- to- skin” until all five images were stored. The cardiologists registered a median time consumption of five minutes (IQR 3) for image interpretation, risk stratification and determining course of action. The individual and combined diagnostic results of utilizing ECG, Hs-cTnT and focused TTE are summarized in table 4 and Fig. 3. RWMA was the most common positive prehospital finding among the NSTEMI patients, while 13% still had no initial findings.
Table 4: Prehospital diagnostic characteristics of individual patients, showing the frequency of positive tests among patients diagnosed NSTEMI.
Test combinations | n = 16 |
RWMA+ | 69% |
TnT+ | 56% |
ECG+ | 31% |
RWMA + and TnT + combined | 38% |
RWMA + and ECG + combined | 25% |
TnT + and ECG + combined | 19% |
TnT + RWMA + and ECG + combined | 13% |
All three prehospital tests negative | 13% |
The combined result illustrates the frequency of individual patients with more than one test suspicious of NSTE-ACS present at the same time. RWMA+: Regional wall motion abnormalities on prehospital transthoracic echocardiogram findings, as interpreted by the cardiologist visual evaluation. TnT+: High sensitive troponin -T point of care test > 50 ng/L. ECG+: ST -depression and/ or T- wave inversion on the prehospital electrocardiogram (ST- elevations were already excluded from the study) ] |
13 of the 16 NSTEMI patients were transported directly to the PCI hospital based on prehospital risk stratification. The median time from FMC to the PCI procedure startup was 93 minutes (IQR 82). Of the remaining three NSTEMI, two patients were admitted to the local (non-PCI) hospital after negative prehospital risk stratification, but later transferred for revascularization because of clinical deterioration and positive cardiac biomarkers. The third patient had prehospital assessment suggestive of high-risk NSTE-ACS, but was due to co-morbidity, age and previously confirmed non-treatable coronary heart disease admitted to the local hospital for palliative care.
Four (4%) patients without a NSTEMI were directly transferred to the PCI-hospital due to suspected high-risk NSTE-ACS, but no acute angiography was performed. Of these four, two had uninterpretable prehospital TTE and negative Hs-cTnT, but the combination of clinical suspicion and ongoing pain led to the admission. The third had suspicious TTE findings, and the last had prehospital TTE findings later confirmed as moderate to severe aortic valvular stenosis.
Coronary angiography was performed in 15 patients diagnosed with NSTEMI, and they all underwent acute coronary revascularization by PCI. Six (38%) of these patients had total coronary occlusion, subdivided into right coronary artery (three patients), circumflex artery (two patients) and left anterior descending artery (one patient). In the remaining nine, established coronary artery disease was noted, and conditions like a major stenosis, plaque rupture or subtotal stenosis were treated.