A BRIEF REVIEW
Before attempting to make sense of NSST-T wave changes, a clear understanding of the normal ST segments and T-waves is required. This knowledge will help the clinician to recognize abnormalities that may need to be explained or pursued.
- The ST segment is usually isoelectric.
▪ Elevation <1 mm (one small box on ECG) may be normal
▪ Usually not depressed >0.5 mm
- Primary ST-segment changes (elevations or depressions)
▪ May be associated with ischemia or inflammation
▪ Infarct and pericarditis are the most common etiologies
- Secondary ST-segment changes
▪ Related to conduction abnormalities (e.g., bundle branch blocks)
▪ Ventricular hypertrophy
▪ Effect of drugs or electrolytes
- T-waves represent the recovery period following ventricular depolarization and contraction (referred to as “repolarization”).
- Normally upright in leads I, II, and V3-V6.
▪ Usually inverted in the aVR lead
▪ Variable in all other leads
- T-wave amplitude
▪ Not typically > 5-6 mm (limb leads); 10-12 mm (precordial leads)
- Tall T-waves may represent infarction, hyperkalemia, ischemia, drug effects, brain trauma, or cerebrovascular accident.
CLASSIC ST CHANGES ON ECG
Classic changes of ischemia may be described or explained as follows:
1. ST-segment elevations or depressions that are usually localized (but may be diffuse) and may be associated with such T-wave changes as flattening or inversion.
2. Diffuse ST-segment elevations (seen in most or all limb leads and precordial leads) may be seen in pericarditis.
3. ST elevations seen in conjunction with left ventricular hypertrophy (LVH) are referred to as a “strain” pattern (LVH with strain) but actually may represent repolarization changes attributable to ischemia of the endocardial layer of the myocardium.
4. Patients who are status-post previous MI (with persistent ST-segment elevations on ECG) who may demonstrate such abnormalities due to aneurysm formation around the site of the prior MI.
The ECG interpretation of NSST-T wave changes is not synonymous with normal, normal variant, or benign. Be particularly cautious when these findings are noted in an acutely symptomatic patient. While NSST-T changes may represent a benign finding, other conditions should be considered.
SHOULD CLINICIANS BE CONCERNED ABOUT NSST-T CHANGES?
When treating a patient with NSST-T wave changes on ECG, be aware of the following:
- Know your patient (personal history, family history, current medications, etc.)
- Consider the setting and the “whole picture” (e.g., presentation/symptoms, comorbidities, stable vs. unstable, patient age, CHD risks).
- Is the patient’s presentation concerning based on symptoms, history, risk factors, etc.? If so, then err on the side of caution. Assume serious, treatable, or reversible causes until proven otherwise.
- Are there other conditions, in this particular patient, about which to be concerned? If so, why?
These last two bullets may be the most important because NSST-T wave changes might require specific work-up to rule out ischemia, infarction, electrolyte abnormalities, etc.
In the setting of NSST-T wave changes: (1) proceed with caution; (2) do not dismiss these findings too quickly; (3) reassure yourself (and the patient) with reservation; (4) carefully consider patient presentation and history; and (5) expand the differential diagnosis beyond ischemia or infarction, even if these additional etiologies may not be high on your list.
AN INFORMED APPROACH
The astute clinician uses all available information at his or her disposal in evaluating individuals with chest pain. This initial assessment should include a thorough history and physical exam and careful interpretation of the ECG. Additional workup should arise out of the differential diagnosis.
Exercise caution when faced with nonspecific changes on an ECG. Consider such factors as the patient’s symptoms, comorbidities, and some etiologies of nonspecific ECG findings most relevant for a given patient. This approach may broaden the differential diagnosis, impact the working diagnosis, and enable the clinician to more efficiently diagnose or rule out some less obvious etiologies for the chest pain and ECG abnormalities. A heightened level of awareness and sensitivity may also allow the clinician to communicate medical information and concerns to patients more clearly, appropriately, and effectively.
Understanding the basics regarding ST segments and T-waves, what constitutes abnormalities, and the possible etiologies for these abnormalities will better enable the clinician to thoughtfully, carefully, and methodically approach the patient presenting with chest pain and NSST-T wave changes on ECG.
Finally, once a patient with NSST-T wave changes on ECG has been thoroughly evaluated, including appropriate diagnostic workup as indicated, it is the clinician’s responsibility to explain the situation as clearly as possible.
The better the clinician understands the implications and possible etiologies of nonspecific ECG changes, the better positioned he or she will be to assist the patient in understanding the ECG abnormalities seen, what those abnormalities may suggest, and additional testing that may become necessary.
Lendell Richardson, MD, is the medical director & an assistant professor in the Physician Assistant Program at Midwestern University in Downers Grove, Ill.
- Brady WJ, Roberts D, Morris F. The nondiagnostic ECG in the chest pain patient: normal and nonspecific initial ECG presentations of acute MI. Am J Emerg Med. 1999;17:394-397.
- Madsen T, Bledsoe J, Bossart P. Physician documentation of nonspecific EKG changes predicts hospital admission among observation unit chest pain patients. Crit Pathw Cardiol. 2009;8:34-37.
- Johnson R, Swartz M. A Simplified Approach To Electrocardiography. Philadelphia, Pa.: W.B. Saunders; 1986.
- Philip P. ECG Tutorial: ST and T wave changes. In: UpToDate, Goldberger, AL (Ed), UpToDate, Waltham, Mass.: 2012.
- Dubin D. Rapid Interpretation of EKGs. 6th ed. Fort Meyers, Fla.: Cover Pub Co; 2000.