Review Of: Verbeek PR, Ryan D, Turner L, et al. Serial prehospital 12-lead electrocardiograms increase identification of ST-segment elevation myocardial infarction. Prehosp Emerg Care. 2012;16(1):109–114.
The Science: Investigators from the University of Toronto, using the Toronto EMS system, sought to evaluate the effects of serial 12-leads in capturing more patients experiencing a STEMI. Over a one-year period, data on 325 patients experiencing STEMI identified in the prehospital setting were retrospectively analyzed. Summary statistics show that initial STEMI identification based on the first 12-lead ECG obtained was 84.6%, with cumulative totals of 93.8% on the second, and 100% on the third (or 9.2% and 6.2% increases respectively).
Investigators concluded that prehospital providers who perform a single 12-lead on patients experiencing chest pain or angina are at risk for a missed opportunity to identify STEMI in the field.
Medic Marshall: I applaud the investigators of this study for attempting to improve prehospital recognition and diagnosis of STEMI. We all need to remember that 12-lead ECG acquisition is still relatively new to EMS; and although there are many studies that describe the enormous positive impact it has had, there seems to be a lack of research to improve it beyond what it is now.
I spent some time thinking about 12-leads in the field, and anecdotally, the philosophy on acquiring them is broad: ranging from almost never to almost anyone or everyone. But from my experiences, there really isn’t a systematic approach in assessing 12-lead changes. Perhaps we need to consider the 12-lead similar to vital signs—i.e., any patient with cardiac symptomatology who gets an initial 12-lead should get a 12-lead every 10 minutes after the initial acquisition.
As for the study, one thing that is lacking and would be very interesting to know is how many missed opportunities there were. For example, out of those that received only one 12-lead by EMS and didn’t show STEMI, how many patients developed changes later in the ED? The same can be said for those that received two 12-leads and three 12-leads. Unfortunately, the evaluation of these outcomes is outside the scope of the study.
Dr. Wesley: This extremely important paper validates what emergency medicine physicians have witnessed in the emergency department (ED) for many years. I have all too frequently evaluated a patient with chest pain only to have a non-diagnostic ECG obtained the moment they first arrive. Then after going about the workup for angina and obtaining labs and X-rays, I have repeated the ECG and discovered to my chagrin a STEMI. Had I obtained serial 12-leads during the first 30 minutes of their workup I could have moved them to the cath lab sooner.
Another issue that this paper raises but does not address specifically is the fact that if a patient is having a STEMI, the administration of nitrates will not diminish the value of prehospital 12-leads. Some have proposed that first responders should not give a chest pain patient nitrates before the 12-lead because it may “normalize” the ECG. Although this may occur with the first ECG, obtaining three 12-leads over the ensuing 30 minutes will reveal the underlying STEMI.
This paper should encourage, as the standard of care, the acquisition of serial 12-leads in the prehospital care of patients with chest pain.
Verbeek PR, Ryan D, Turner L, et al. Serial prehospital 12-lead electrocardiograms increase identification of ST-segment elevation myocardial infarction. Prehosp Emerg Care. 2012;16(1):109–114.
Background: Many prehospital protocols require acquisition of a single 12-lead electrocardiogram (ECG) when assessing a patient for ST-segment elevation myocardial infarction (STEMI). However, it’s known that ECG evidence of STEMI can evolve over time.
Objectives: To determine how often the first and, if necessary, second or third prehospital ECGs identified STEMI, and the time intervals associated with acquiring these ECGs and arrival at the emergency department (ED).
Methods: We retrospectively analyzed 325 consecutive prehospital STEMIs identified between June 2008 and May 2009 in a large third-service EMS system. If the first ECG didn’t identify STEMI, then protocol required a second ECG just before transport and, if necessary, a third ECG before entering the receiving ED. Paramedics who identified STEMI at any time bypassed participating local EDs, taking patients directly to the percutaneous coronary intervention (PCI) center. Paramedics used computerized ECG interpretation with STEMI diagnosis defined as an “acute MI” report by GE/Marquette 12-SL software in ZOLL E-series defibrillator/cardiac monitors (ZOLL Medical, Chelmsford, Mass.) We recorded the time of each ECG, and the ordinal number of the diagnostic ECG. We then determined the number of cases and frequency of STEMI diagnosis on the first, second, or third ECG. We also measured the interval between ECGs and the interval from the initial positive ECG to arrival at the ED.
Results: STEMI was identified on the first prehospital ECG in 275 cases, on the second ECG in 30 cases, and on the third ECG in 20 cases (cumulative percentages of 84.6%, 93.8%, and 100%, respectively). For STEMIs identified on the second or third ECG, 90% were identified within 25 minutes after the first ECG. The median times from identification of STEMI to arrival at the ED were 17.5 minutes, 11.0 minutes, and 0.7 minutes for STEMIs identified on the first, second, and third ECGs, respectively.
Conclusions: A single prehospital ECG would have identified only 84.6% of STEMI patients. This suggests caution using a single prehospital ECG to rule out STEMI. Three serial ECGs acquired over 25 minutes is feasible and may be valuable in maximizing prehospital diagnostic yield, particularly where emergent access to PCI exists.