Let’s Get Serial: The Importance of Serial ECGs in the Emergency Department
Author: Lauren Gruffi, MD PGY3
Peer Reviewer: Amy Hembree, MD PGY3
Faculty Editor: Sam Senturia, MD
Introduction:
In patients with suspected acute coronary syndromes (ACS), obtaining serial ECGs is critical both in the prehospital and emergency department (ED) setting. The recently released 2025 American Heart Association/American College of Cardiology Guidelines on ACS management emphasize this point. In their first update in over a decade, the guidelines highlight that serial ECGs should be considered standard of care in emergency medicine. Failure to do so risks missed diagnoses of ACS, including STEMI.
To illustrate why, let’s begin with a case.
Case:
A 72-year-old man with a history of hypertension, hyperlipidemia, diabetes mellitus, and COPD presented with sore throat and chest tightness. High-sensitivity troponins were elevated, with a significant rise on repeat measurement. He was loaded with aspirin and started on heparin for a presumed NSTEMI. His initial ECG is shown below:
One hour later, a repeat ECG was obtained:
This demonstrated complete AV block with a wide-complex, unstable ventricular escape rhythm, prompting immediate cardiology consultation. The patient was taken emergently to the catheterization lab, where angiography revealed a 100% RCA occlusion, and a temporary transvenous pacemaker was placed.
In this case, a repeat ECG identified a life-threatening complication of NSTEMI and directly triggered urgent cath lab activation. Without that additional ECG, the diagnosis might have been delayed, with potentially disastrous consequences.
Evidence for Serial ECGs
The case above reflects a broader body of literature demonstrating the value of repeat ECGs.
Tanguay et al. (2025): In Prehospital Emergency Care, researchers retrospectively studied patients with suspected STEMI transported by EMS. A serial 12-lead system transmitted averaged ECGs every two minutes. In 8% of patients, STEMI was identified only on a subsequent tracing, after the initial ECG appeared nondiagnostic.
Verbeek et al. (2012): This prehospital STEMI study required repeat ECGs if the initial tracing was nondiagnostic. Only 84.6% of STEMIs were detected on the first ECG, meaning roughly 15% would have been missed without additional tracings.
Lehmacher et al. (2020): In patients presenting to the ED with suspected AMI (excluding STEMI at baseline), those with persistent ischemic ECG changes at three hours had worse outcomes, including higher rates of mortality, recurrent MI, and need for revascularization.
Which patients need serial ECGs?
Several patient groups particularly benefit from repeat tracings:
Suspected ACS with a nondiagnostic initial ECG: In these patients, dynamic changes such as new ST elevations or depressions may emerge only over time.
NSTEMI with rising troponins: As infarction progresses, evolving ischemic changes may become apparent. These subtle shifts can strengthen the case for early cath lab activation.
Wellens Syndrome: Wellens Syndrome is characterized by biphasic or deeply inverted T waves in V2-V3 [Figure 1], plus a history of chest pain that has now resolved. Importantly, the classic Wellenoid pattern appears only when the patient is pain-free. During episodes of chest pain, the T waves will pseudonormalize and the ST segments may become elevated. For this reason, if the initial ECG is obtained while the patient is symptomatic, a repeat tracing should be performed once the pain resolves.
Figure 1. Characteristic Wellens patterns seen on ECG. Courtesy of Life in the Fast Lane.
Brugada Syndrome: The characteristic ST-segment elevation pattern in Brugada can be intermittent (Figure 2). Serial ECGs improve diagnostic yield, especially when clinical suspicion remains high. Multiple factors have been shown to influence the ECG appearance such as heart rate, fever, autonomic tone, insulin secretion, and sodium channel blockers.
Figure 2. Brugada syndrome ECG example. Courtesy of Life in the Fast Lane.
How often should ECGs be obtained?
There is no single universal schedule, but a few guiding principles are widely applicable:
Repeat an ECG whenever a serial troponin is obtained.
Repeat an ECG with any change in symptoms—worsening, improvement, or resolution.
If the initial ECG is nondiagnostic and clinical suspicion for ACS remains high, repeat an ECG every 15- to 30-minutes during the first hour.
For example, in our institutions, repeat ECGs are obtained at both hour 2 and 3 in patients requiring multiple troponin draws. This approach ensures that evolving ischemia is not missed between labs.
Takeaway Points:
Serial ECGs are standard of care for patients with suspected ACS and a nondiagnostic initial tracing, per the 2025 AHA/ACC Guidelines.
Failure to obtain repeat ECGs risks missed STEMI.
Dynamic ECG changes provide critical information about evolving infarction and can accelerate appropriate interventions.
Repeat ECGs should be obtained whenever troponins are drawn and whenever there is a clinical change in the patient’s status.
If the initial ECG is nondiagnostic and clinical suspicion for ACS remains high, repeat an ECG every 15- to 30-minutes during the first hour.
References:
Bouzid Z, Faramand Z, Martin-Gill C, Sereika SM, Callaway CW, Saba S, Gregg R, Badilini F, Sejdic E, Al-Zaiti SS. Incorporation of Serial 12-Lead Electrocardiogram With Machine Learning to Augment the Out-of-Hospital Diagnosis of Non-ST Elevation Acute Coronary Syndrome. Ann Emerg Med. 2023 Jan;81(1):57-69. doi: 10.1016/j.annemergmed.2022.08.005. Epub 2022 Oct 15. PMID: 36253296; PMCID: PMC9780162.
Buttner, M. C. (2021, September 8). Wellens syndrome. Life in the Fast Lane • LITFL. https://litfl.com/wellens-syndrome-ecg-library/
John Larkin, Mike Cadogan and Robert Buttner. (2024, October 22). Brugada syndrome. Life in the Fast Lane • LITFL. https://litfl.com/brugada-syndrome-ecg-library/
Lehmacher J, Neumann JT, Sörensen NA, Goßling A, Haller PM, Hartikainen TS, Clemmensen P, Zeller T, Blankenberg S, Westermann D. Predictive Value of Serial ECGs in Patients with Suspected Myocardial Infarction. J Clin Med. 2020 Jul 20;9(7):2303. doi: 10.3390/jcm9072303. PMID: 32698466; PMCID: PMC7408822.
Tanguay A, Lebon J, Lau L, Hébert D, Bégin F. Detection of STEMI Using Prehospital Serial 12-Lead Electrocardiograms. Prehosp Emerg Care. 2018 Jul-Aug;22(4):419-426. doi: 10.1080/10903127.2017.1399185. Epub 2018 Jan 16. PMID: 29336652.
Mitsuhiro Nishizaki, Noriyoshi Yamawake, Harumizu Sakurada, Masayasu Hiraoka, ECG interpretation in Brugada syndrome, Journal of Arrhythmia, Volume 29, Issue 2, 2013, Pages 56-64, ISSN 1880-4276, https://doi.org/10.1016/j.joa.2013.01.001.
Ohlsson M, Ohlin H, Wallerstedt SM, Edenbrandt L. Usefulness of serial electrocardiograms for diagnosis of acute myocardial infarction. Am J Cardiol. 2001 Sep 1;88(5):478-81. doi: 10.1016/s0002-9149(01)01722-2. PMID: 11524053.
Verbeek PR, Ryan D, Turner L, Craig AM. Serial prehospital 12-lead electrocardiograms increase identification of ST-segment elevation myocardial infarction. Prehosp Emerg Care. 2012 Jan-Mar;16(1):109-14. doi: 10.3109/10903127.2011.614045. Epub 2011 Sep 28. PMID: 21954895.
