Cardiac Stress Test: What It Actually Tests For, and What It Misses

A cardiac stress test — usually called a TMT (treadmill test) in India — is the standard next step after a normal resting ECG when heart disease is suspected. It costs ₹1,500-3,500, takes 20-30 minutes, and reveals blockages that a resting ECG cannot. It is also one of the most misunderstood tests: normal does not mean 'no heart disease' and abnormal does not always mean 'blockage'.

What actually happens

• You walk on a treadmill with increasing speed and incline.
• An ECG runs continuously; BP is checked periodically.
• The test continues until you reach target heart rate (85% of predicted max, roughly 220 minus age × 0.85).
• It stops early if you get chest pain, ECG changes suggest ischaemia, BP drops, or you cannot continue.
• A report follows within 24-48 hours with the cardiologist's interpretation.

What the report says and means

• Result: Negative (normal), full heart rate reached · What it means: Low probability of significant coronary disease · Next step: Reassurance; investigate other symptom causes
• Result: Negative, target not reached · What it means: Test inconclusive · Next step: Different test needed (nuclear stress, angiography)
• Result: Equivocal · What it means: Findings suggestive but not definitive · Next step: Further testing
• Result: Positive (ST depression, chest pain, arrhythmia) · What it means: Suggestive of coronary disease · Next step: Angiography usually recommended
• Result: Strongly positive (early, deep changes) · What it means: High probability of significant blockage · Next step: Urgent angiography

The specific limits — where TMT fails

• It's less accurate in women than men (more false positives).
• A normal test in an obese, sedentary person who could only walk 4 minutes doesn't prove much.
• It cannot detect blockages that are stable but critical if they do not restrict flow enough to cause ischaemia.
• It cannot detect vulnerable plaques (soft plaques that might rupture).
• Bundle branch blocks and other ECG abnormalities make interpretation hard.

Alternatives when TMT is not right

• Nuclear stress test (SPECT MPI) — for patients who cannot exercise adequately or have baseline ECG abnormalities.
• Stress echocardiography — real-time cardiac imaging during exercise or dobutamine infusion.
• Coronary CT angiography — non-invasive imaging of the arteries directly.
• Coronary calcium score — a passive test; measures existing calcification, doesn't stress the heart.
• Invasive angiography — the gold standard, but invasive and costly.

When to have one

• Chest pain workup in a patient with intermediate probability of coronary disease.
• Assessment before starting an exercise programme in a high-risk patient.
• Follow-up after coronary intervention (some cardiologists do this at 6-12 months).
• Suspected exertional arrhythmia.

A stress test result is not a lifetime clearance. Coronary disease can develop and progress in the years after a normal test. A negative TMT at 55 does not mean no chest pain at 62 needs investigation. The record — 'TMT negative 2024-06' — is context, not exemption.

References

• AHA — Exercise stress testing
• Cardiological Society of India
• PMC — stress testing in Indian practice