An electrocardiogram (EKG or ECG) is used in the operating room (OR) to record electrical impulses transmitted across the skin of the patient and translate them—and their differences—into a temporal graph which can be used to interpret aspects of the cardiac electrical circuitry and rhythm.1 These transmitted signals provide information on heart rate, the initiation of electrical impulses, and pathologies related to aberrant conduction and transmission of cardiac electrical impulses.1
One of the most important pieces of data the EKG can convey to the anesthesiologist in the OR is ischemia, or the stress placed on an organ system due to absolute or relatively reduced blood supply and, with that, oxygen content. The American Society of Anesthesiologists (ASA) Committee on Standards and Practice Parameters recommends that every patient receiving anesthesia, whether general anesthesia or monitored anesthesia care, be continuously monitored with an EKG, as the EKG provides information about circulation—one of the four parameters which must be continuously or continually evaluated by the anesthesiologist.2
The most common setup for EKG in the OR is having the leads placed anterior (i.e., across the front of the patient). This setup is similar to that in the intensive care unit, wherein four electrodes are placed on the torso, corresponding to the limb leads, with the fifth electrode placed along the chest. This lead along the chest is usually lead V1, which is best for monitoring arrhythmias.3
However, there are some OR contexts for which anterior placement of EKG leads is not feasible. For example, in some craniotomies, the patient is positioned supine (i.e., face down), at which point anterior lead placement could be difficult to maintain or adjust intraoperatively.4 Additionally, when a posterior myocardial infarction is suspected, posterior placement of EKG leads may help elucidate ischemic changes.5 A 1999 study published in the Journal of the American College of Cardiology suggested that posterior EKG limb lead placement was effective in identifying posterior myocardial infarctions. In the study, 33 patients’ EKGs demonstrated ST elevations in the posterior leads, further confirmed by 97% of these patients demonstrating posterior wall-motion abnormalities within 48 hours of admission.6
EKG is an indispensable tool in the OR which the anesthesiologist can utilize to monitor for arrhythmia, ischemia, and heart rate. Anterior lead placement is most common; however, posterior placement may be pursued when the patient is supine or if there is concern for a posterior myocardial infarction.
References
1. AlGhatrif M, Lindsay J. A brief review: history to understand fundamentals of electrocardiography. J Community Hosp Intern Med Perspect. 2012;2(1):14383. doi:10.3402/jchimp.v2i1.14383
2. Committee on Standards and Practice Parameters. Standards for basic anesthetic monitoring. Am Soc Anesthesiol. Published online 2025. https://www.asahq.org/standards-and-practice-parameters/standards-for-basic-anesthetic-monitoring
3. Francis J. ECG monitoring leads and special leads. Indian Pacing Electrophysiol J. 2016;16(3):92-95. doi:10.1016/j.ipej.2016.07.003
4. Shuer LM, Chang SD, Chaudhary N. Craniotomy for tumor. In: Jaffe RA, Schmiesing CA, Golianu B, eds. Anesthesiologist’s Manual of Surgical Procedures. 6th ed. Wolters Kluwer.
5. Lizzo JM, Chowdhury YS. Posterior myocardial infarction. Natl Libr Med. Published online 2025. https://www.ncbi.nlm.nih.gov/books/NBK553168/
6. Matetzky S, Freimark D, Feinberg MS, et al. Acute myocardial infarction with isolated ST-segment elevation in posterior chest leads V7-9: “hidden” ST-segment elevations revealing acute posterior infarction. J Am Coll Cardiol. 1999;34(3):748-753. doi:10.1016/s0735-1097(99)00249-1