Interpretation of Treadmill Test Results
Key Parameters to Assess
- Exercise capacity is one of the strongest prognic indicators, measured in METs, with a high-risk threshold of <5 METs or <100% age-predicted METs, according to the American Heart Association 1, 3
- A high-risk finding is defined as ST-segment depression ≥2 mm at any time, ST-segment depression ≥1 mm occurring at <5 METs or persisting >5 minutes into recovery, or ST-segment elevation ≥2 mm, as stated by the American College of Cardiology 1
- The Duke Treadmill Score is a primary risk stratification tool, calculated using the formula: exercise time (minutes) - (5 × ST deviation in mm) - (4 × angina index), with risk categories including low risk (score ≥5), moderate risk (score -10 to +4), and high risk (score ≤-11), as recommended by the American Heart Association 2, 3
- Hemodynamic response, including blood pressure and chronotropic response, should be assessed, with a high-risk finding defined as a decrease in systolic BP >10 mm Hg from rest to peak exercise, according to the American College of Cardiology 1
- Heart rate recovery, measured as the difference between peak heart rate and heart rate at 1 minute of recovery, has substantial independent prognostic value, with a high-risk threshold of ≤12 bpm, as stated by the American Heart Association 1, 3
Test Result Categories
- A normal test is defined as adequate exertional effort achieved, no evidence of ischemia, no reproduction of symptoms, and normal hemodynamic response, according to the American College of Cardiology 4
- An inconclusive test is defined as a test that does not provide sufficient confidence for clinical decisions, including submaximal effort, ST segments uninterpretable due to baseline abnormalities, or ST-segment changes that resolve rapidly or are nonspecific, as stated by the American Heart Association 4, 5
Common Pitfalls and Contraindications
- Baseline ECG abnormalities, including left bundle branch block, >1 mm ST depression at rest, paced rhythm, or pre-excitation syndrome, are contraindications for standard TMT, according to the American College of Cardiology 2, 5
- Digoxin use interferes with ST-segment interpretation, and alternative stress testing modalities should be considered, as recommended by the American Heart Association 2
Sex-Specific Considerations
- Women have lower diagnostic accuracy with standard ECG criteria, but integration of the Duke Treadmill Score improves accuracy, according to the American Heart Association 3, 6
- Breast attenuation artifacts can affect interpretation if imaging is added, as stated by the American College of Cardiology 7