What does a stress‑pattern electrocardiogram (ECG) signify and how should it be managed?

What Does a Stress-Pattern ECG Mean?

A "stress pattern" on ECG typically refers to ST-segment and T-wave changes that suggest myocardial ischemia during exercise or pharmacologic stress testing, most commonly horizontal or downsloping ST-segment depression ≥0.1 mV persisting for at least 0.06-0.08 seconds after the J-point. 1

Diagnostic ECG Findings During Stress Testing

The primary diagnostic abnormality consists of:

• Horizontal or downsloping ST-segment depression ≥0.1 mV (1 mm) lasting at least 0.06-0.08 seconds after the J-point in one or more ECG leads 1
• ST-segment elevation may indicate severe transmural ischemia or even simulate patterns seen in acute myocardial infarction 2
• Approximately 15% of diagnostic ST-segment changes appear only during the recovery phase, not during peak exercise 1

Clinical Significance and Risk Stratification

A positive stress pattern indicates:

• Myocardial ischemia due to supply-demand mismatch during increased cardiac workload 1
• Need for hospital admission and further management when accompanied by ongoing pain, positive cardiac markers, new ST-segment deviations, or hemodynamic abnormalities 1
• Diagnostic and prognostic information including heart rate response, blood pressure response, symptoms, and workload achieved 1

When Stress ECG Patterns Are NOT Interpretable

Exercise ECG testing has no diagnostic value and should not be performed in the following baseline conditions: 1

• Complete left bundle branch block (LBBB) - ECG changes are not interpretable
• Electronically paced ventricular rhythm - baseline abnormalities mask ischemic changes
• Wolff-Parkinson-White syndrome (pre-excitation) - abnormal depolarization patterns interfere
• Resting ST-segment depression ≥0.1 mV - cannot reliably detect additional ischemic changes 1
• Left ventricular hypertrophy with repolarization abnormalities - false-positive results are frequent 1
• Digitalis use - causes baseline ST-T wave changes that mimic ischemia 1
• Atrial fibrillation or significant intraventricular conduction abnormalities - false-positive results increase 1

Management Algorithm Based on Stress Pattern Findings

If Positive Stress Pattern (Ischemia Detected):

Patients should be admitted to the hospital and proceed to risk stratification with consideration for invasive coronary angiography, especially if: 1

• Severe symptoms or clinical constellation suggesting high-risk coronary anatomy
• Positive cardiac markers
• New ST-segment deviations or deep T-wave inversions
• Hemodynamic abnormalities during testing
• Low workload tolerance or early onset of ischemia

If Negative or Inconclusive Stress Pattern:

An imaging stress test (echocardiography, SPECT, PET, or CMR) should be performed when: 1

• 85% of maximum heart rate was not achieved without symptoms or signs of ischemia 1
• Exercise was limited by orthopedic or other non-cardiac problems 1
• ECG changes are equivocal 1
• Pre-test probability is 66-85% or left ventricular ejection fraction is <50% without typical angina 1
• Patient has prior revascularization (PCI or CABG) 1

Special Consideration for Women:

Exercise ECG testing is less sensitive and specific in women, though a recent randomized trial showed that standard exercise treadmill testing had similar clinical outcomes compared to the more expensive nuclear myocardial perfusion imaging strategy in symptomatic women who could exercise adequately 1

Critical Pitfalls to Avoid

• Do not interpret a "normal" stress ECG in patients taking anti-ischemic drugs as ruling out significant coronary disease - medications may mask ischemic changes 1
• Do not rely on exercise ECG alone when baseline ECG abnormalities are present - upgrade to stress imaging instead 1
• Remember that false-positive results occur more frequently with electrolyte imbalance 1
• Approximately 15% of ischemic changes manifest only in recovery, so monitoring must continue post-exercise 1

When Pharmacologic Stress Should Replace Exercise:

Pharmacologic stress testing with imaging is preferred over exercise when: 1

• Patient cannot exercise adequately due to physical limitations
• Baseline ECG abnormalities make exercise ECG uninterpretable (LBBB, paced rhythm, WPW, LVH with ST-T changes, resting ST depression ≥0.1 mV, or digitalis use)
• Assessment of myocardial viability is needed (dobutamine stress)
• Patient has complete LBBB or paced rhythm (vasodilator stress mandatory) 3, 4