Treadmill Stress Test (TMT)

A Treadmill Stress Test records a continuous 12-lead ECG while you walk on a treadmill at progressively increasing speed and incline (Modified Bruce Protocol). The purpose is to detect myocardial ischaemia — reduced blood flow to the heart muscle caused by obstructive coronary artery disease — that is not visible on a resting ECG but becomes apparent when the heart is stressed by exercise. It also measures exercise capacity (METs), heart rate response, and blood pressure response. The result includes a Duke Treadmill Score for risk stratification.

A positive TMT shows evidence of cardiac ischaemia (reduced blood flow) during exercise. The main positive finding is ≥1 mm horizontal or downsloping ST depression in two or more leads during exercise. Other positive findings include chest pain during the test, exercise-induced fall in blood pressure, or significant arrhythmia. A positive TMT does not confirm coronary artery disease with certainty — it indicates probability of significant stenosis, typically requiring further evaluation with coronary CT angiography or invasive coronary angiography.

The Duke Treadmill Score (DTS) is a validated scoring system combining three inputs: exercise capacity in METs (the most heavily weighted component), the magnitude of ST segment depression in millimetres, and an angina index. Formula: DTS = Treadmill time (min) − (5 × ST deviation mm) − (4 × angina index). The score maps to a three-way management fork: a high-risk DTS (≤−11) typically prompts referral for coronary angiography, and when angiography confirms significant obstructive disease, revascularisation (PCI or CABG) may be recommended to treat myocardial ischaemia. An intermediate DTS (−10 to +4) guides initiation or optimisation of guideline-directed medical therapy — antiplatelet agents, high-intensity statins, beta-blockers, and ACE inhibitors. A low-risk DTS (≥+5) supports conservative management. Not every positive test leads to angiography or a procedure.

TMT test preparation starts with screening for contraindications: the ordering clinician reviews your current clinical status, recent investigations, and medication list before confirming the appointment. Once safety is confirmed, eat a light meal 2 hours before the test (do not come fasting), wear comfortable walking shoes and loose clothing, continue all medications unless specifically told to stop beta-blockers, avoid caffeine and smoking for 3 hours before, and do not apply body lotion or powder to your chest. Bring previous TMT reports and your medication list.

Screening for contraindications to TMT is the first step of TMT test preparation — not a bedside judgment made on the day. Absolute contraindications include: acute MI within the preceding 2 days, unstable angina, uncontrolled heart failure or pulmonary oedema, severe symptomatic aortic stenosis, haemodynamically significant arrhythmia, active myocarditis or pericarditis, and resting BP above 200/110 mmHg. Relative contraindications require discussion with the cardiologist. When contraindications are present, a stress echocardiogram (pharmacological) or CT coronary angiography is typically used as the alternative investigation.

If you are unable to complete the full Bruce protocol due to exhaustion, breathlessness, leg fatigue, or other symptoms, the test is still clinically useful. The key metrics recorded — exercise duration in minutes (or METs achieved), maximum ST deviation, and reason for stopping — are all components of the Duke Treadmill Score. Achieving <5 METs (approximately Stage 1) is an independent predictor of increased cardiovascular risk. Your cardiologist will interpret the result in context, and if the test was limited by non-cardiac reasons, alternative stress testing options can be considered.

The exercise ECG has a sensitivity of approximately 68% and specificity of approximately 77% for detecting significant coronary artery disease (>70% stenosis). This means it is moderately accurate but not perfect — false positives (abnormal TMT with normal coronary arteries) and false negatives (normal TMT despite significant CAD) do occur. Accuracy is higher in patients with multi-vessel disease and lower in single-vessel disease. TMT is best used as a risk stratification tool rather than a definitive diagnostic test — an abnormal result indicates intermediate-to-high probability of CAD and guides the need for further imaging.

A TMT records only the ECG during exercise, detecting electrical signs of ischaemia (ST changes). A stress echocardiogram (stress echo) adds ultrasound imaging of the heart before and immediately after exercise, looking for new wall motion abnormalities that indicate ischaemia. Stress echo is significantly more sensitive (approximately 80–85%) and specific (approximately 84–86%) than TMT alone, and can localise the ischaemic territory to a specific coronary artery. However, stress echo requires additional equipment, expertise, and is more expensive. TMT remains the recommended first-line test for intermediate-risk patients with suspected CAD due to its availability, simplicity, and cost-effectiveness.

This depends on the purpose of the test. If the TMT is being performed to diagnose coronary artery disease (diagnostic test), your cardiologist may ask you to stop beta-blockers and rate-limiting calcium channel blockers for 24–48 hours before the test, as these drugs can mask ischaemic changes and prevent you from reaching target heart rate. However, if the test is to assess the effectiveness of your current treatment regimen (on-therapy assessment), continue all medications as usual. Never stop any medication without explicit instruction from your prescribing cardiologist. Bring a complete list of your medications to the appointment.