How do you interpret a treadmill test (TMT)?

How to Interpret a Treadmill Test (TMT)

A treadmill test should be interpreted using an integrated, multi-parameter approach that includes exercise capacity, ST-segment changes, Duke Treadmill Score, hemodynamic response, heart rate recovery, and symptom reproduction—not just ST-segment changes alone. 1

Key Parameters to Assess

1. Exercise Capacity

• Measure in METs (metabolic equivalents): Exercise capacity is one of the strongest prognostic indicators 1
• High-risk threshold: <5 METs or <100% age-predicted METs (calculated as 14.7 - [0.13 × age]) 1
• Normal capacity: Ability to achieve adequate exertional effort with no evidence of ischemia 1

2. ST-Segment Changes

• High-risk findings 1:
  • ST-segment depression ≥2 mm at any time
  • ST-segment depression ≥1 mm occurring at <5 METs or persisting >5 minutes into recovery
  • ST-segment elevation ≥2 mm (not in Q-wave lead or aVR)
• Important caveat: ST-segment changes alone provide inadequate prognostication and should never be interpreted in isolation 1
• Uninterpretable ST segments: Baseline abnormalities (left bundle branch block, >1 mm ST depression at rest, paced rhythm, Wolff-Parkinson-White) make ST-segment analysis unreliable 1, 2

3. Duke Treadmill Score (Primary Risk Stratification Tool)

Formula: Exercise time (minutes) - (5 × ST deviation in mm) - (4 × angina index) 1

• Angina index: 0 = no angina, 1 = non-limiting angina, 2 = limiting angina that stops test 1

Risk Categories 1:

• Low risk: Score ≥5 (4-year survival 99%, annual mortality 0.25%)
• Moderate risk: Score -10 to +4
• High risk: Score ≤-11 (4-year survival 79%, annual mortality 5%)

Sex-specific considerations: Women with high Duke Treadmill Scores have 89% prevalence of obstructive disease and should be referred for angiography; intermediate scores warrant stress imaging 1

4. Hemodynamic Response

• Blood pressure response 1:
  • High-risk: Decrease in systolic BP >10 mm Hg from rest to peak exercise
  • Normal response shows progressive increase in systolic BP with exercise
• Chronotropic response: Failure to achieve ≥85% maximum predicted heart rate suggests chronotropic incompetence or submaximal effort 1

5. Heart Rate Recovery

• Measurement: Difference between peak heart rate and heart rate at 1 minute of recovery (upright cooldown) 1
• High-risk threshold: ≤12 bpm after 1 minute recovery 1
• Prognostic value: Heart rate recovery has substantial independent prognostic value for near- and long-term outcomes 1

6. Symptoms During Exercise

• Reproduction of symptoms: Document whether typical symptoms are reproduced during exercise 1
• Angina occurrence: Note timing and whether angina limits exercise 1
• Limited predictive value: Presence of chest pain alone has limited predictive value, especially in women 1

7. Arrhythmias

• Ventricular arrhythmias: Persistent ventricular tachycardia/fibrillation is high-risk 1
• Exercise-provoked VPCs: Associated with myocardial ischemia, particularly when occurring during exercise phase in patients <65 years 3

Test Result Categories

Normal Test 1

• Adequate exertional effort achieved
• No evidence of ischemia
• No reproduction of symptoms
• Normal hemodynamic response

Inconclusive Test 1

A test that does not provide sufficient confidence for clinical decisions:

• <85% maximum predicted heart rate achieved (submaximal effort)
• ST segments uninterpretable due to baseline abnormalities
• ST-segment changes that resolve rapidly or are nonspecific

Management of inconclusive tests: Proceed to stress imaging for definitive evaluation 1

Positive Test (Abnormal)

• Significant ST-segment changes meeting high-risk criteria
• Abnormal hemodynamic response
• High-risk Duke Treadmill Score
• Next step: Additional diagnostic testing with stress imaging or consideration for angiography based on risk stratification 1

Common Pitfalls and Contraindications

When NOT to Use Standard TMT 1, 2

• Baseline ECG abnormalities: Left bundle branch block, >1 mm ST depression at rest, paced rhythm, pre-excitation syndrome 1, 2
• Digoxin use: Interferes with ST-segment interpretation 1
• Baseline ST elevation: Requires imaging modality added to stress test 2
• Alternative: Use stress imaging (echocardiography or nuclear perfusion) in these patients 1, 2

Medication Effects

• Beta blockers: Significantly decrease sensitivity of TMT (76% vs 90% without beta blockers, false negative rate 24% vs 10%) 4
• Consider cautious withdrawal prior to diagnostic testing if clinically appropriate 4

Sex-Specific Considerations

• Women have lower diagnostic accuracy with standard ECG criteria (sensitivity 61%, specificity 70% vs men 72%/77%) 1
• Integration of Duke Treadmill Score improves accuracy in women 1
• Breast attenuation artifacts can affect interpretation if imaging is added 1

Reporting Requirements

Every TMT interpretation must include 1:

• Exercise capacity (METs achieved)
• ST-segment response with measurements
• Duke Treadmill Score with risk category
• Chronotropic response (% maximum predicted heart rate)
• Heart rate recovery measurement
• Blood pressure response to exercise
• Symptoms during exercise
• Arrhythmias if present