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CE ARTICLE spike depends on the patient's posi- tion, lead's position and type of lead being viewed. A pacemaker spike may be difficult to see in some or even all leads. Anyone who interprets ECGs should develop the habit of deliberately looking for these smaller pacer spikes, which can easily be overlooked. Other than seeing or palpating the implanted pacemaker during a clinical exam, there are no clinical exam find- ings that are specific or even suggestive for an implanted pacemaker. A paced rhythm is an ECG entity without any clinical manifestations. DIFFERENTIATING BETWEEN PACED RHYTHM AND STEMI A ventricular paced rhythm will typi- cally have an LBBB ECG morphology. As is the case with LBBB, it's a common m i s c o n c e p t i o n t h a t y o u c a n n o t identif y a STEMI in a patient with a ventricular paced rhythm. This is not true, and in fact sometimes you can identif y myocardial ischemia, in the form of a STEMI, in the presence of a ventricular paced rhythm using the same Sgarbossa criteria used with LBBB discussed in Part 1. Recall that there are three Sgarbossa criteria, identified as A, B and C: A— Concordant ST elevation of 1 mm or more in any lead with a posi- tive QRS complex (the deflection of the QRS is primarily upward, and there is ST elevation greater than or equal to 1 mm); B— Concordant ST depression of 1 mm or more in V1–V3 (in V1–V3 the deflection of the QRS is primarily down- ward, and there is ST depression greater than or equal to 1 mm); C — E xc e s si v e l y dis c o r d a n t ST elevation (5 mm or more) in any lead with a negative QRS complex. Thirty-two patients in the GUSTO-1 trial (the results from which Sgarbossa an d c olle a gu e s d ete r min e d t h eir criteria) presented with a ventricular paced rhythm, accounting for 0.1% of enrolled patients. Sgarbossa criteria C proved to be the only ECG criteria with a high specificity and statistical significance for the diagnosis of acute myo c ardial infarc tion. 5 S gar b o s s a criteria A and B are considered to have "acceptable" specificity. 6 Patients with a ventricular paced rhythm who meet Sgarbossa C criteria should be considered to have a STEMI, and a c ardiac c atheterization lab should be activated. Patients with who meet Sgarbossa criteria A or B present a diagnostic challenge, and a medical control physician should be contacted. Ideally the ECG would be transmitted to the medical control physician, who could then assist with a determination regarding transport to a STEMI center and activation of a cardiac catheteriza- tion lab. The patient in our opening case presented with ST-segment elevation in leads II, III, aVF and V2–V4, but he does not meet Sgarbossa criteria A, B or C, so should be considered to not be having a STEMI. It is worth reinforcing the concept of serial ECGs in any patient with suspected acute coronary syndrome. Serial ECGs, performed ever y 10–15 minutes at most, should be performed an all patients with suspected ACS. The role of serial ECGs in identifying myocardial ischemia and infarction was reinforced by the Myocardial Infarction Triage and Intervention (MITI) project. 7 The MITI trial had a number of findings directly applicable to EMS: • ECG abnormalities secondary to AMI could be identified on a prehos- pital ECG within 90 minutes of symptom onset; • Serial ECGs were more effective at identifying patients with myocardial ischemia or infarction; • ST-segment changes bet ween serial ECGs improved overall sensitivity from 36% to 46%; • When all ECG abnormalities were considered (ST segment, T-waves, Q-waves, LBBB), the diagnostic sensi- tivity of the ECG increased from 80% to 87%. In summary, perform serial ECGs! Yo ur likelih o o d of id e ntif y in g an evolving STEMI is greater if you do. In addition, serial ECGs can help with the identification of STEMI imitators, which will not show ST-segment evolution over time and multiple ECGs. TREATMENT There is no treatment needed for a normally paced cardiac rhy thm. Prehospital treatment should center on the clinical signs and symptoms presented by the patient. The patient in this case has clinical exam and history findings strongly suggestive of gastro- esophageal reflux disease (GERD); his description of his pain is more charac- teristic of GERD than acute coronary syndrome, and he has a history of risk factors for GERD: smoking, diabetes and obesity. In addition, we have deter- mined that the ST-segment elevation on his 12-lead ECG is normal for his ventricular pacemaker, and he does not meet criteria for STEMI activation. That said, the patient does have a history of AMI as well as risk factors, Cardiac complications are not uncommon immediately following subarachnoid hemorrhage or ischemic stroke. 92 DECEMBER 2014 | EMSWORLD.com