Early detection of ST-segment elevation myocardial infarction (STEMI) on the prehospital electrocardiogram (ECG) improves patient outcomes. Current software algorithms optimize sensitivity but have a high false-positive rate. The authors propose an algorithm to improve the specificity of STEMI diagnosis in the prehospital setting.

A dataset of prehospital ECGs with verified outcomes was used to validate an algorithm to identify true and false-positive software interpretations of STEMI. Four criteria implicated in prior research to differentiate STEMI true positives were applied: heart rate <130, QRS <100, verification of ST-segment elevation, and absence of artifact. The test characteristics were calculated and regression analysis was used to examine the association between the number of criteria included and test characteristics.

There were 44,611 cases available. Of these, 1,193 were identified as STEMI by the software interpretation. Applying all four criteria had the highest positive likelihood ratio of 353 (95% CI, 201-595) and specificity of 99.96% (95% CI, 99.93-99.98), but the lowest sensitivity (14%; 95% CI, 11-17) and worst negative likelihood ratio (0.86; 95% CI, 0.84-0.89). There was a strong correlation between increased positive likelihood ratio (r2 = 0.90) and specificity (r2 = 0.85) with increasing number of criteria.

Prehospital ECGs with a high probability of true STEMI can be accurately identified using these four criteria: heart rate <130, QRS <100, verification of ST-segment elevation, and absence of artifact. Applying these criteria to prehospital ECGs with software interpretations of STEMI could decrease false-positive field activations, while also reducing the need to rely on transmission for physician over-read. This can have significant clinical and quality implications for Emergency Medical Services (EMS) systems.

Decreasing symptom-to-door (S2D) delay is of vital importance for reducing morbidity and mortality in patients with ST-segment elevation myocardial infarction (STEMI). The factors associated with S2D delay in STEMI patients have not been well-characterized.

The aim of this study was to identify factors associated with S2D delay in patients with STEMI.

The PubMed, CINAHL, and Embase databases were searched for data. References from the selected articles and relevant background papers were also manually searched to identify additional eligible studies. The included articles were reviewed and assessed for risk of bias. The level of evidence for each identified factor was evaluated using a semiquantitative synthesis.

Twelve (12) papers were included in the review. Factors associated with S2D delay were complex and could be divided into sociodemographic, clinical history, and onset characteristics. The level of evidence regarding female sex and diabetes was strong, and the evidence was moderate regarding older age, smoking, history of hypertension, self-transport, or referral.

Female sex, older age, previous diabetes, previous hypertension, smoking, and self-transport are all strong or moderate risk factors for S2D time delay in patients with ST-segment myocardial infarction. More efforts should be made to educate at-risk populations concerning symptoms of STEMI and the importance of seeking early medical assistance.

Fibrinolysis is an acceptable treatment for acute ST-segment elevation myocardial infarction (STEMI) when primary percutaneous coronary intervention (PCI) cannot be performed within 120 minutes. The American Heart Association has recommended Emergency Medical Services (EMS) interventions such as prehospital fibrinolysis (PHF), prehospital electrocardiogram (ECG), and hospital bypass direct to PCI center. Nova Scotia, Canada has incorporated these interventions into a unique province-wide approach to STEMI care. A retrospective cohort analysis comparing the primary outcome of 30-day mortality for patients receiving either prehospital or emergency department (ED) fibrinolysis (EDF) to patients transported directly by EMS from community or regional ED for primary PCI was conducted.

This retrospective, population-based cohort study included all STEMI patients in Nova Scotia who survived to hospital admission from July 2011 through July 2013. Three provincial databases were used to collect demographic, 30-day mortality, hospital readmission, and rescue PCI data. The results were grouped and compared according to reperfusion strategy received: PHF, EDF, patients brought by ambulance via EMS direct to PCI (EMS to PCI), and ED to PCI (ED to PCI).

There were 1,071 STEMI patients included with 145 PHF, 606 EDF, 98 EMS to PCI, and 222 ED to PCI. There were no significant differences in 30-day mortality across groups (n, %): PHF 5(3); EDF 36(6); EHS to PCI <5(2); and ED to PCI 10(4); P = .28. There was no significant difference in patients receiving fibrinolysis who underwent rescue PCI.

Prehospital fibrinolysis incorporated into a province-wide approach to STEMI treatment is feasible with no observed difference in patient 30-day mortality outcomes observed.

ST-segment elevation myocardial infarction (STEMI) is a time-sensitive entity that has been shown to benefit from prehospital diagnosis by electrocardiogram (ECG). Current computer algorithms with binary decision making are not accurate enough to be relied on for cardiac catheterization lab (CCL) activation.

An algorithmic approach is proposed to stratify binary STEMI computerized ECG interpretations into low, intermediate, and high STEMI probability tiers.

Based on previous literature, a four-criteria algorithm was developed to rule out/in common causes of prehospital STEMI false-positive computer interpretations: heart rate, QRS width, ST elevation criteria, and artifact. Prehospital STEMI cases were prospectively collected at a single academic center in Salt Lake City, Utah (USA) from May 2012 through October 2013. The prehospital ECGs were applied to the algorithm and compared against activation of the CCL by an emergency department (ED) physician as the outcome of interest. In addition to calculating test characteristics, linear regression was used to look for an association between number of criteria used and accuracy, and logistic regression was used to test if any single criterion performed better than another.

There were 63 ECGs available for review, 39 high probability and 24 intermediate probability. The high probability STEMI tier had excellent test characteristics for ruling in STEMI when all four criteria were used, specificity 1.00 (95% CI, 0.59-1.00), positive predictive value 1.00 (0.91-1.00). Linear regression showed a strong correlation demonstrating that false-positives increased as fewer criteria were used (adjusted r-square 0.51; P <.01). Logistic regression showed no significant predictive value for any one criterion over another (P = .80). Limiting physician overread to the intermediate tier only would reduce the number of ECGs requiring physician overread by a factor of 0.62 (95% CI, 0.48-0.75; P <.01).

Prehospital STEMI ECGs can be accurately stratified to high, intermediate, and low probabilities for STEMI using the four criteria. While additional study is required, using this tiered algorithmic approach in prehospital ECGs could lead to changes in CCL activation and decreased requirements for physician overread. This may have significant clinical and quality implications.

The aim of this study was to determine what clinically important events occur in ST-elevation myocardial infarction (STEMI) patients transported for primary percutaneous coronary intervention (PCI) via a primary care paramedic (PCP) crew, and what proportion of such events could only be treated by advanced care paramedic (ACP) protocols.

We conducted a health record review of STEMI transports by PCP-only crews and those transferred from PCP to ACP crews (ACP-intercept) from 2011 to 2015. A piloted data collection form was used to extract clinically important events, interventions during transport, and mortality.

We identified 214 STEMI bypass cases (118 PCP-only and 96 ACP-intercept). Characteristics were mean age 61.4 years; 44.4% inferior infarcts; mean response time 6 minutes, 19 seconds; total paramedic contact time 29 minutes, 40 seconds; and, in cases of ACP-intercept, 7 minutes, 46 seconds of PCP-only contact time. A clinically important event occurred in 127 (59.3%) of cases: SBP < 90 mm Hg (26.2%), HR < 60 (30.4%), HR > 100 (20.6%), arrhythmias 7.5%, altered mental status 6.5%, airway intervention 2.3%. Two patients (0.9%) arrested, both survived. Of the events identified, 42.5% could be addressed differently by ACP protocols. The majority related to fluid boluses for hypotension (34.6%). In the ACP-intercept group, ACPs acted on 51.6% of events. There were six (2.8%) in-hospital deaths.

Although clinically important events are common in STEMI bypass patients, a smaller proportion of events would be addressed differently by ACP compared with PCP protocols. The majority of clinically important events were transient and of limited clinical significance. PCP-only crews can safely transport STEMI patients directly to primary PCI.

Limited evidence supports primary care paramedic (PCP) direct transport of ST-segment elevation myocardial infarction (STEMI) patients for percutaneous coronary intervention (PCI). The goal of this study was to evaluate an urban-based PCP STEMI bypass guideline.

We reviewed consecutive Toronto Paramedic Services call reports between April 7, 2015, and May 31, 2016, regarding STEMI patients identified by PCPs. The primary outcome was patient assignment (stable versus unstable) according to guideline criteria. Secondary outcomes were the proportion of PCP-transported patients who had an indication for an advanced care intervention (ACI) or who received an ACI when PCPs rendezvoused with an advanced care paramedic (ACP). Lastly, we reviewed prehospital outcomes of cardiac arrest patients and calculated the difference in transport intervals between direct PCP bypass and a PCI-centre and predicted transport interval to the closest emergency department (ED).

Of 361 patients, 232 were PCP transports and 129 were ACP-rendezvous transports. There was a significant difference in the distribution of stable and unstable patients between PCPs and ACPs (p<0.001). For PCP patients, 21/232 (9.1%) had indications for an ACI, whereas 34/129 (26.4%) ACP patients received an ACI. Eleven patients experienced cardiac arrest; 10 were successfully resuscitated (5 of these by PCPs). The median difference between direct PCP bypass and a PCI-centre versus transport to the closest ED was 5.53 minutes (IQR=6.71).

We found a significant difference in the distribution of stable and unstable patients and fewer patients with indications for an ACI in PCP patients. This PCP STEMI bypass guideline appears feasible.

The time interval from diagnosis to reperfusion therapy for patients experiencing ST-segment elevation myocardial infarction (STEMI) has a significant impact on morbidity and mortality.

It is hypothesized that the time required for interfacility patient transfers from a community hospital to a regional percutaneous coronary intervention (PCI) center using an Advanced Life Support (ALS) transfer ambulance service is no different than utilizing the “911” ALS ambulance.

Quality assurance data collected by a tertiary care center cardiac catheterization program were reviewed retrospectively. Data were collected on all patients with STEMI requiring interfacility transfer from a local community hospital to the tertiary care center's PCI suite, approximately 16 miles away by ground, 12 miles by air. In 2009, transfers of patients with STEMI were redirected to the municipal ALS ambulance service, instead of the hospital's contracted ALS transfer service. Data were collected from January 2007 through May 2013. Temporal data were compared between transports initiated through the contracted ALS ambulance service and the municipal ALS service. Data points included time of initial transport request and time of ambulance arrival to the sending facility and the receiving PCI suite.

During the 4-year study period, 63 patients diagnosed with STEMI and transferred to the receiving hospital's PCI suite were included in this study. Mean times from the transport request to arrival of the ambulance at the sending hospital's emergency department were six minutes (95% CI, 4-7 minutes) via municipal ALS and 13 minutes (95% CI, 9-16 minutes) for the ALS transfer service. The mean times from the ground transport request to arrival at the receiving hospital's PCI suite when utilizing the municipal ALS ambulance and hospital contracted ALS ambulance services were 48 minutes (95% CI, 33-64 minutes) and 56 minutes (95% CI 52-59 minutes), respectively. This eight-minute period represented a 14% (P = .001) reduction in the mean transfer time to the PCI suite for patients transported via the municipal ALS ambulance.

In the appropriate setting, the use of the municipal “911” ALS ambulance service for the interfacility transport of patients with STEMI appears advantageous in reducing door-to-catheterization times.

TennysonJC , QualeMR . Reduction in STEMI Transfer Times Utilizing a Municipal “911” Ambulance Service. Prehosp Disaster Med. 2014;29(1):1-4.