One of the primary reasons for the development of modern prehospital care was the need to deliver prompt emergency care to patients who experienced sudden cardiac conditions such as myocardial infarction and cardiac arrest. Considering that EMS is the first medical contact in about 40 percent of patients with acute MI, it’s critical that EMS providers be knowledgeable and proficient in delivering state of the art cardiac care.
In 2010, AHA Guidelines for Acute Coronary Syndromes (ACS) outlined several prehospital goals regarding management of ACS, including:
Prompt prehospital diagnosis of ST elevation Myocardial Infarction (STEMI) using established 12-lead ECG criteria.
Initial treatment in the first hours of an MI, which included timely administration of 162 to 325 mg of aspirin.
Rapid notification of the receiving hospital for preparation of emergent reperfusion therapy.
Direct transport of ACS patients to accredited chest pain centers capable of rapid percutaneous catheter insertion (PCI).[1]
The subcommittee that gathered the evidence for those recommendations updated them in 2013. The new 2013 AHA STEMI Guidelines focus on:
- Improving the “door to needle” times for reperfusion and establishing evidenced-based regional systems of care to improve outcome. This trend has resulted in many EMS systems completely bypassing emergency department admission and transferring patient care directly to cardiac catheterization units.
- Increasing attention toward at-risk groups such as women, blacks, diabetics, and the elderly that may present with atypical symptoms.
- Increasing EMS activation and transport rates for patients with chest pain.
- Increasing attention toward post-arrest care for those patients experiencing ROSC after STEMI-related cardiac arrest
- Removing the ECG criteria of new or presumed new Left Bundle Branch Block (LBBB) as an indication for STEMI.
- Increasing awareness of STEMI equivalent 12-lead ECG criteria for those patients who do not present with classical ECG changes, but may have an acutely occluded coronary artery.[2] These ECG diagnoses are often associated with poorer outcomes.
Common STEMI equivalents
There are several 12-lead ECG patterns that serve as equivalents for STEMI.[3] Here are three.
1. Lead aVR ST Elevation indicating left main coronary artery occlusion. New evidence suggests that ST elevation in lead aVR, with or without ST elevation in V1, with inferolateral ST depression is an independent marker of acute left main stem occlusion.
2. LBBB with Sgarbossa criteria. While only a minority of patients with AMIs have LBBBs, their mortality is often significantly higher than that of other patients with AMI. Sgarbossa criteria includes concordant ST segment elevation (those with positive QRS deflections) greater than 1 mm in any lead or concordant ST segment depression greater than 1 mm in any of the leads V1—V4 or discordant ST segment elevation less than 5 mm.[4]
3. Isolated Posterior MI (PMI). About 4 to 7 percent of STEMIs present as isolated PMIs, but often result in poor outcomes. Acute occlusion of the left circumflex artery presents with isolated ST depression greater than or equal to 0.05 mm in leads V1—V3. This ECG finding should be treated as a STEMI. The use of additional posterior chest wall leads (V7—V9) is recommended.
EMS standard of care for MI
Although the approach to ACS has changed slightly, much of our initial therapy has not changed.
Administration of 162 to 325mg of aspirin within the first five minutes of chest pain onset is still a pre-arrival priority and is often facilitated by skilled EMS dispatchers. Maintaining a pulse oximetry of 94 percent or higher by titrating supplemental oxygen remains important. Obtaining a 12-lead ECG or multi-lead ECG and transmitting to medical direction as soon as possible is a priority for rapid identification of STEMI and STEMI equivalents.
While nitroglycerin spray may have a slightly faster onset of action (one to two minutes) than sublingual nitroglycerin, both forms seem to have an equivalent duration and are effective in treating patients with chest pain.[5,6,7] For those patients who have persistent chest pain after three sublingual nitroglycerin administrations, IV nitroglycerin may be initiated and titrated.
In addition, morphine or fentanyl can be given to those patients with ongoing ischemic chest pain not relieved by nitroglycerin. Morphine and fentanyl have been found to provide equivalent pain control for chest pain in the prehospital setting.
How EMS can tackle these goals
Obtaining prehospital 12-lead ECGs on selected patients has been an AHA Class I recommendation since 2008. Emphasis on prehospital 12-lead ECG acquisition has been of increasing academic and clinical importance since the publication of the National EMS Education Standards and 2010 AHA Guidelines, leading to prehospital 12-lead acquisition protocols worldwide.[1,9]
However, there is a paucity of data regarding the clinical compliance of EMS professionals obtaining 12-lead ECGs in the prehospital setting. Many believe this clinical behavior remains at a subclinical level in that many patients that meet the criteria for 12-lead ECGs do not receive them in the prehospital setting.
Considering the patients who do receive 12-lead ECGs, many medical directors report that repeat 12-lead ECGs are not performed as part of the reassessment of chest pain patients. In addition, many patients that have non-diagnostic ECGs initially, but continue to have chest pain, do not receive serial (repeat) 12-lead ECGs as part of their reassessment.
We need to modify our thinking to include serial 12-lead ECGs as part of our reassessment, just like we would reassess vital signs or pain scale. Prehospital providers might capture STEMIs that were not present on the initial in-hospital ECG. This would also include patients who meet the criteria for 15-lead or 18-lead ECGs.
This issue could easily be addressed with an effective quality-improvement process and regular continuing education. It is clear that the responsibility for the diagnosis of STEMI is in the hands of EMS providers. Many EMS systems have stepped up with regards to STEMI care, but others continue to lag behind.
The United States Department of Health & Senior Services, American Heart Association, American College of Cardiology, and other agencies support a national time-critical diagnosis program to reduce death from heart attack, stroke, and trauma.
Ten EMS professionals must support the development of evidence-based regional and state processes to improve STEMI care in their own states. Some states have a legislated time-critical diagnosis program to improve outcomes, but only a handful of states have established such a program.
Does your state have a TCD program? As patient advocates we must be motivated to actively support such programs in our own states.
References
1. O’connor, R. E., Brady, W., Brooks, S. C., Diercks, D., Egan, J., Ghaemmaghami, C., ... Yannopoulos, D. (2010). Part 10: Acute Coronary Syndromes: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation, 122(18_suppl_3), S787-S817. doi: 10.1161/CIRCULATIONAHA.110.971028
2. 2013 ACCF/AHA Guideline for the Management of ST-Elevation Myocardial Infarction: Executive Summary: A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. (2013). Catheterization and Cardiovascular Interventions, 82(1), E1-E27. doi: 10.1002/ccd.24776
3. O’gara, P. T., Kushner, F. G., Ascheim, D. D., Casey, D. E., Chung, M. K., Lemos, J. A., ... Zhao, D. X. (2013). 2013 ACCF/AHA Guideline for the Management of ST-Elevation Myocardial Infarction: A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation, 127(4), E362-E425. doi: 10.1161/CIR.0b013e3182742cf6
4. Smith, S. W., Dodd, K. W., Henry, T. D., Dvorak, D. M., & Pearce, L. A. (2012). Diagnosis of ST-Elevation Myocardial Infarction in the Presence of Left Bundle Branch Block With the ST-Elevation to S-Wave Ratio in a Modified Sgarbossa Rule. Annals of Emergency Medicine, 60(6), 766-776. doi: 10.1016/j.annemergmed.2012.07.119
5. Zimmerman, F. H., Fass, A. E., Katz, D. R., Low, M., & Franklin, B. A. (2009). Nitroglycerin Prescription and Potency in Patients Participating in Exercise-Based Cardiac Rehabilitation. Journal of Cardiopulmonary Rehabilitation and Prevention, 29(6), 376-379. doi: 10.1097/HCR.0b013e3181be7cab
6. Talbert RL. Ischemic heart disease. In: Diprio JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. New York, NY: McGraw-Hill; 2011. Available at: http://www.accesspharmacy.com.proxy.cc.uic.edu/content.aspx?aID=7971879. Accessed September 1, 2014.
7. Clinical Pharmacology [database online]. Tampa, FL: Gold Standard Inc.; 2011. http://clinicalpharmacology-ip.com.proxy.cc.uic.edu/default.aspx. Accessed September 1, 2014.
8. Part 7: The Era of Reperfusion : Section 1: Acute Coronary Syndromes (Acute Myocardial Infarction). (2000). Circulation, 102(Supplement 1), I-172-I-203. doi: 10.1161/01.CIR.102.suppl_1.I-172
9. National Highway Traffic Safety Administration (2009). National emergency medical services education standards. Washington, DC: United States Department of Transportation.
10. Jermyn W, Muzaffar S, et al. (2008) Time Critical Diagnosis System: Recommendations to Advance Emergency Medical Care for Stroke and ST-Elevation Myocardial Infarction (STEMI) in Missouri. Missouri Department of Health and Senior Services.
