ECG criteria
- The baseline resting ECG must be suitable for ST evaluation: LBBB, ventricular pacing, WPW syndrome, marked baseline ST depression, LVH with strain, and digoxin therapy limit the diagnostic interpretation of ST changes, but do not render the test useless for assessing functional capacity, symptoms, and blood pressure response.
- Positive ECG test: horizontal or downsloping ST depression ≥ 1 mm (0.1 mV), measured 80 ms after the J point (60–80 ms acceptable depending on heart rate), in two or more contiguous leads, persisting for at least 3 consecutive complexes.
- Slow upsloping ST depression ≥ 1.5 mm at 80 ms after the J point may be considered suspicious but is less specific; fast upsloping depression is generally not a diagnostic criterion for ischemia.
- ST-segment elevation ≥ 1 mm in leads without a preexisting pathological Q wave is a high-risk sign that requires immediate cessation of exercise and clinical evaluation (not automatically equivalent to definitive transmural ischemia: coronary spasm, scar tissue, and other causes are also possible).
- The blood pressure response is also assessed (normal rise, blood pressure drop is an unfavorable sign), along with the appearance of ventricular arrhythmias; achieving approximately 85% of the age-predicted maximum heart rate serves as a guide for adequate workload for diagnostic value rather than an independent test-termination criterion—beta-blocker therapy and chronotropic incompetence lower the achieved heart rate and complicate interpretation.
- Clinical context is taken into account: typical angina during exercise increases the diagnostic significance of ST changes.
- Test termination criteria: marked ST depression/elevation, blood pressure drop, severe arrhythmia, typical anginal pain, severe dyspnea, reaching the patient's maximum workload, patient refusal.
What it looks like on ECG
During graded incremental exercise, 12-lead ECG and blood pressure are recorded at each stage and during the recovery period. The key element is the ST segment relative to the baseline (the TP or PR segment is used as the baseline level).
| ST depression morphology | Diagnostic significance |
|---|---|
| Horizontal | More specific and more suspicious for ischemia than fast upsloping |
| Downsloping | More specific and more suspicious for ischemia; prognosis is often worse |
| Slow upsloping ≥ 1.5 mm | Suspicious, less specific |
| Fast upsloping | Usually a variant of normal during tachycardia |
The prognostic value of ST depression increases with its greater magnitude, early onset at low workload, involvement of multiple leads, and persistence into the recovery period. ST changes are evaluated at the J point + 60–80 ms across all leads, looking for at least 2 contiguous leads with depression ≥ 1 mm persisting for at least 3 consecutive complexes. ST elevation ≥ 1 mm in leads without a pathological Q wave is a sign requiring immediate test termination. Additionally, heart rate and blood pressure are recorded at each stage, along with the appearance of extrasystoles or ventricular tachycardia, and the dynamics of the T wave and QRS complex. ST changes may appear only during the recovery period, so monitoring is continued for at least 6–8 minutes after exercise ends and longer until ischemic changes and symptoms resolve and hemodynamics stabilize.
Mechanism
During physical exertion, myocardial oxygen demand increases due to elevated heart rate, contractility, and blood pressure. If coronary blood flow cannot adequately increase due to stenosing atherosclerosis, induced myocardial ischemia develops. Exercise-induced ST-segment depression is typical of such ischemia and more often reflects subendocardial ischemic imbalance (the subendocardial layer is less well-perfused due to higher intraventricular pressure), but by itself it is not a specific marker of ischemia depth—exercise ECG does not reliably differentiate between subendocardial and transmural injury. ST-segment elevation during exercise is rarer and requires immediate test termination to rule out severe hemodynamically significant stenosis, coronary spasm, as well as scar tissue and left ventricular aneurysm, which can also cause exercise ST elevation.
Causes of a positive test
- Stenosing coronary atherosclerosis (coronary artery disease)
- Multivessel coronary artery disease
- Coronary spasm (vasospastic angina)
- Microvascular dysfunction
- Marked left ventricular hypertrophy (can cause a false-positive result)
- Nonspecific ST changes can occur in various structural heart diseases, including certain cardiomyopathies; they do not prove coronary artery disease
Differential diagnosis
- Fast upsloping ST depression in the setting of marked tachycardia is a variant of normal, not ischemia
- Baseline resting ST-T changes (LVH with strain, digoxin therapy) — the test is uninformative for ST evaluation; imaging stress testing is needed (stress echocardiography, myocardial perfusion scintigraphy)
- LBBB and ventricular pacing — ST cannot be interpreted; an imaging modality is indicated
- WPW syndrome — baseline complex deformation makes ST evaluation unreliable
- Hyperventilation and nonspecific repolarization changes can mimic ischemic changes; results are interpreted only in conjunction with clinical context, baseline ECG, and, if necessary, a stress imaging test.
Clinical significance and management
For suspected chronic coronary syndrome, CT coronary angiography or functional imaging (stress echocardiography, myocardial perfusion scintigraphy, stress MRI) is preferred due to higher diagnostic accuracy. The exercise ECG test is used in suitable patients, especially when imaging methods are unavailable, as well as to assess exercise tolerance, symptoms, prognosis, and treatment efficacy.
Contraindications are divided into absolute and relative. Absolute contraindications include ongoing ischemia and unstable acute phase of ACS, decompensated heart failure, uncontrolled life-threatening arrhythmias, symptomatic severe aortic stenosis, acute myocarditis or pericarditis, acute pulmonary embolism, acute aortic dissection; after clinical stabilization, testing is possible only under a special protocol and in the absence of other contraindications. Relative contraindications: known left main coronary artery stenosis, moderate valvular defects, severe uncontrolled resting hypertension (approximately SBP > 200 mmHg or DBP > 110 mmHg), tachyarrhythmias with uncontrolled ventricular rate, marked bradyarrhythmia, hypertrophic cardiomyopathy, and other conditions limiting cardiac output reserve.
The physician evaluates a combination of factors: clinical presentation (typicality of pain), ST dynamics, blood pressure and heart rate response, workload at which changes occurred (low workload indicates a worse prognosis), and presence of arrhythmias. The test is performed under the supervision of a physician trained in resuscitation, with a defibrillator available.
Common interpretation errors
- Evaluating ST depression without considering its morphology (horizontal/downsloping vs. fast upsloping)
- Measuring at the incorrect point (not 60–80 ms after the J point)
- Ignoring baseline ECG changes that limit ST interpretation (LBBB, WPW, ventricular pacing, digoxin, marked LVH)
- Stopping monitoring immediately after exercise without observation during the recovery period, when ST changes may only just appear
- Interpreting isolated ST depression without considering clinical presentation and hemodynamic response
1. How many ms after the J point is ST depression measured during an exercise test?
The standard measurement point is about 80 ms after the J point (60–80 ms is acceptable depending on heart rate).
2. Which type of exercise-induced ST depression is the least specific for ischemia?
Rapid upsloping ST depression is frequently observed during tachycardia in healthy individuals and is generally not considered a diagnostic criterion for ischemia.
3. What limits the interpretation of the ST segment during an exercise stress test?
In LBBB, baseline ST-T wave abnormalities preclude reliable assessment of ischemic changes during exercise.
Frequently asked questions
What type of ST depression constitutes a positive test?
Horizontal or downsloping ST-segment depression ≥ 1 mm (0.1 mV), measured 60–80 ms (ideally 80 ms) after the J point, in two or more contiguous leads, persisting for at least 3 consecutive complexes. The sensitivity and specificity of this criterion are limited, so results must be interpreted in conjunction with the clinical presentation and pre-test probability of CAD.
Is the exercise ECG stress test dangerous?
The risk of major complications (infarction, life-threatening arrhythmias) is low when indications and contraindications are followed, but the test must be performed exclusively under physician supervision with immediate resuscitation capabilities available.
Why might a stress test be uninformative?
Baseline ECG abnormalities—such as left bundle branch block, ventricular pacing, WPW syndrome, marked left ventricular hypertrophy with strain pattern, or digoxin therapy—limit ST-segment interpretation, rendering ST depression diagnostically non-diagnostic. Nevertheless, the test may retain value for assessing symptoms, functional capacity, and blood pressure response.
What should be done if ST elevation occurs during the test?
ST-segment elevation ≥ 1 mm in leads without a preexisting pathological Q wave is a high-risk finding that mandates immediate exercise cessation and clinical evaluation. It does not automatically prove transmural ischemia, as coronary spasm, scar tissue, and other etiologies are also possible; therefore, evaluation of the baseline ECG, symptoms, and post-exercise dynamics is essential.
What is the difference between cycle ergometry and a treadmill test?
Cycle ergometry uses a progressively loaded stationary bicycle, whereas the treadmill test utilizes a motorized treadmill with protocols such as Bruce. Both methods allow assessment of the ECG response, symptoms, and hemodynamics, but results depend on the protocol and workload achieved, and the methods are not fully interchangeable.
ECG Course
Interpretation from basics to myocardial infarction — learn to read any ECG using a systematic algorithm.
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- Study guide: "All ECGs in 25 minutes"
ECG Strip Simulator
ECG, radiology, histology, pathomorphology, pharmacology — thousands of flashcards with detailed explanations.
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Related terms
More in the section "Ischemia and Myocardial Infarction"
Sources
- Hampton J. The ECG in Practice, 6th ed.
- Goldberger A. Clinical Electrocardiography, 9th ed.
- ESC Guidelines for the management of chronic coronary syndromes
- Orlov V.N. Guide to Electrocardiography
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.