Can a patient with tachycardia develop ST‑segment changes on the electrocardiogram?

Can Tachycardia Cause ST-T Changes on ECG?

Yes, tachycardia commonly produces ST-segment and T-wave changes on the electrocardiogram, even in patients without underlying coronary artery disease, and these changes are frequently nonspecific and do not reliably indicate myocardial ischemia.

Mechanism and Prevalence

ST-segment depression during tachycardia is extremely common and occurs through multiple mechanisms:

• In supraventricular tachycardia (SVT), ST-segment depression occurs in approximately 51% of patients and is nonspecific for coronary disease, with a predictive value for significant coronary artery disease of only 6% 1
• The rapid heart rates normally observed in pediatric patients may produce nonspecific ST-T wave changes, highlighting that rate-related repolarization abnormalities are a physiologic phenomenon 2
• The primary mechanism is overlap of the QRS complex with the preceding T wave during rapid rates, particularly when cycle length drops below 300 milliseconds, rather than true myocardial ischemia 3
• In patients without coronary disease undergoing electrophysiologic testing, myocardial lactate extraction remains normal (28 ± 13%) during SVT despite marked ST depression of 1-8 mm, proving that ST changes do not reflect ischemia in most cases 4

Rate-Dependent ST Changes

Critical heart rate thresholds determine the severity of ST-T abnormalities:

• ST-segment depression correlates negatively with tachycardia cycle length (R = 0.356, P = 0.001), with changes stabilizing at cycle lengths around 270 milliseconds 3
• A critical increase in heart rate above 95 beats per minute can trigger ST-segment depression that resolves when heart rate decreases below this threshold, even in patients with normal coronary arteries 5
• The steeply sloping ST segments in patients with bundle branch block cause ST amplitude to vary with heart rate, leading to frequent false alarms during monitoring 2

Clinical Characteristics

The ST-T changes during tachycardia have distinctive features:

• ST depression during SVT typically affects 1-9 of the 12 ECG leads and ranges from 1-8 mm in depth, often accompanied by chest pain in 64% of patients despite absence of ischemia 4
• ST-segment changes may persist after conversion to sinus rhythm, suggesting global microvascular effects rather than epicardial coronary obstruction 6
• There is no relationship between the presence of significant ST depression and age, sex, mechanism, or rate of tachycardia, making clinical prediction unreliable 1

Distinguishing Ischemic from Rate-Related Changes

Key differentiating features help identify true ischemia:

• Ischemic ST-segment changes preceding arrhythmia are uncommon, occurring in only 12.6% of patients with documented sudden cardiac death during Holter monitoring 2
• In patients with known coronary artery disease, atrial pacing produces net myocardial lactate production (-27 ± 20%) compared to continued lactate extraction during SVT in patients without coronary disease 4
• Dynamic ST-segment changes that evolve over hours to days suggest acute coronary ischemia, whereas stable rate-related changes appear and resolve with tachycardia episodes 2

Monitoring Limitations

Several conditions make ST-segment monitoring unreliable during tachycardia:

• Patients with left bundle branch block should not undergo ST-segment monitoring because of frequent false alarms triggered by rate-dependent ST amplitude variation 2
• Patients with coarse atrial fibrillation or flutter may have fluctuating ST-segment amplitudes because chaotic atrial activity is measured in the ST segment 2
• Intermittent accelerated ventricular rhythm may interfere with ST monitoring, lasting 30-90 seconds—long enough to trigger false alarms 2

Clinical Approach

When evaluating ST-T changes during tachycardia:

• Compare the ECG during tachycardia with a tracing obtained after symptoms resolve or following nitrate administration to assess for dynamic ischemic changes 2
• Measure serial high-sensitivity cardiac troponin at 6-12 hours to distinguish acute coronary syndrome from benign rate-related changes 2
• Perform carotid sinus massage or administer beta-blockers to slow the heart rate below 95 beats per minute; resolution of ST depression with rate control confirms a rate-dependent mechanism 5
• Consider that ST-segment depression during tachycardia has 51% specificity for coronary disease, meaning nearly half of patients without coronary disease will demonstrate these changes 1

Common Pitfalls

• Do not assume ST-segment depression during tachycardia indicates myocardial ischemia, as this finding is common in young healthy individuals without coronary disease 1, 4
• Do not rely on the presence or absence of chest pain to distinguish ischemic from non-ischemic ST changes, since 64% of patients without coronary disease experience chest pain during SVT with ST depression 4
• Avoid initiating ST-segment monitoring in patients with baseline conduction abnormalities (LBBB, ventricular pacing), as these produce secondary ST-T changes that vary with heart rate and generate false alarms 2