Explore the intriguing world of EKG interpretation with insights on subendocardial ischemia. Discover what the ST segment represents and learn about its significance in recognizing heart conditions. Elevated ST segments may indicate a serious injury, while depressed segments reveal ischemic issues. The importance of patient history is emphasized as a vital component in diagnosing various cardiovascular conditions. Delve into the nuanced details of EKG patterns and their implications for heart health.
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insights INSIGHT
Subendocardial Ischemia vs. STEMI
ST depression suggests reduced blood flow and myocardial stress, a supply-demand mismatch.
Unlike ST elevation, which indicates full occlusion and cell death, depression implies some flow remains.
insights INSIGHT
Reciprocal ST Elevation in aVR
Lead aVR often shows reciprocal ST elevation with diffuse ST depression.
This is due to the heart's vector and doesn't indicate a STEMI in aVR itself.
volunteer_activism ADVICE
Importance of Patient History
Consider the patient's history when seeing ST elevation in aVR with diffuse ST depression.
DKA or shock require different interventions than ACS.
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The ST segment on an ECG represents the interval between the end of ventricular depolarization (QRS) and the beginning of ventricular repolarization (T-wave).
It should appear isoelectric (flat) in a normal ECG.
What if the ST segment is elevated?
This is evidence that there is an injury that goes all the way through the muscular wall of the heart (transmural)
This is very concerning for a heart attack (STEMI) but can be occasionally caused by other pathology, such as pericarditis
What if the ST segment is depressed?
This is evidence that only the innermost part of the muscular wall of the heart is becoming ischemic
This has a much broader differential and includes a partial occlusion of a coronary artery but also any other stress on the body that could cause a supply-and-demand mismatch between the oxygen the coronaries can deliver and the oxygen the heart needs
This is called subendocardial ischemia
What else should you look for in the ECG to identify subendocardial ischemia?
The ST-depressions should be at least 1 mm
The ST depressions should be present in leads I, II, V4-6 and a variable number of additional leads.
There is often reciprocal ST elevation in aVR > 1 mm
The most important thing to remember when you see subendocardial ischemia is…history
Still, keep all cardiac causes on your differential, such as unstable angina, stable angina, Prinzmetal angina, etc.
Also consider a wide array of non-cardiac causes such as severe anemia, severe hypertension, pulmonary embolism, COPD, severe pneumonia, sepsis, shock, thyrotoxicosis, stimulant use, DKA, or any other state that lead to reduced oxygen supply to the subendocardium and/or increased myocardial oxygen demand.
References
Birnbaum, Y., Wilson, J. M., Fiol, M., de Luna, A. B., Eskola, M., & Nikus, K. (2014). ECG diagnosis and classification of acute coronary syndromes. Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc, 19(1), 4–14. https://doi.org/10.1111/anec.12130
Buttà, C., Zappia, L., Laterra, G., & Roberto, M. (2020). Diagnostic and prognostic role of electrocardiogram in acute myocarditis: A comprehensive review. Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc, 25(3), e12726. https://doi.org/10.1111/anec.12726
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