Evaluation

Exercise Stress Test

A treadmill stress test evaluates how the heart responds to exercise

The exercise treadmill stress test assesses cardiovascular function under progressive physical stress — recording heart rate, blood pressure, and 12-lead ECG continuously as workload is incrementally increased. It detects myocardial ischaemia, exercise-induced arrhythmias, abnormal blood pressure responses, and chronotropic incompetence that are absent at rest. It is a widely used, cost-effective first-line investigation for suspected coronary artery disease and functional cardiac assessment.

How the Test Is Performed

The standard protocol is the Bruce protocol — a staged treadmill exercise test in which speed and incline increase every three minutes across seven stages, from a slow walk at 2.7 km/h to a brisk run at 9.6 km/h. The target endpoint is 85% of the age-predicted maximum heart rate (220 minus age), representing adequate cardiac stress for diagnostic purposes. The test is performed with continuous 12-lead ECG monitoring and blood pressure measurement at each stage. Patients are asked to report any chest discomfort, breathlessness, or dizziness during the test. A physician is present throughout. The test is stopped at target heart rate, development of significant symptoms, ST changes meeting diagnostic criteria, haemodynamic instability, or at the patient's request. Total test duration including preparation and recovery monitoring is approximately 45–60 minutes. Patients should fast for three hours, avoid caffeine on the day, wear exercise footwear, and discuss whether cardiac medications — particularly beta-blockers — should be withheld before the test, as they blunt the heart rate response.

What the Test Detects

• Myocardial ischaemia is identified by ST segment changes — horizontal or downsloping ST depression of 1mm or more at 60–80 milliseconds after the J-point is the standard diagnostic criterion for exercise-induced ischaemia, indicating inadequate coronary perfusion under demand. ST elevation during exercise indicates severe ischaemia or vasospasm and warrants urgent further assessment.
• Exercise-induced arrhythmias — including ventricular tachycardia, frequent ventricular ectopy increasing with exercise, and supraventricular arrhythmias — are detected and characterised. Their provocation by exercise suggests arrhythmogenic substrate related to ischaemia or structural heart disease.
• Chronotropic incompetence — failure of heart rate to reach 85% of age-predicted maximum despite adequate effort — indicates sinus node dysfunction or autonomic impairment and is associated with increased cardiovascular mortality independently of ischaemia.
• Abnormal blood pressure response — exaggerated hypertensive response (systolic above 210 mmHg) or hypotensive response (systolic drop below baseline) during exercise — provides prognostic information and guides further investigation.
• Functional capacity — expressed in metabolic equivalents (METs) — is a strong independent predictor of cardiovascular mortality. Achieving above 10 METs is associated with excellent prognosis; below 5 METs indicates significantly elevated risk.

Duke Treadmill Score

The Duke Treadmill Score (DTS) is a validated prognostic tool calculated from three exercise test parameters: exercise duration (in minutes on Bruce protocol), maximum ST deviation (in mm), and an angina index (0 if no angina, 1 if angina occurred, 2 if angina caused test termination). The formula is: DTS = Exercise time − (5 × ST deviation) − (4 × Angina index). A score of +5 or above is low risk (annual mortality below 1%); −10 or below is high risk (annual mortality above 5%) and warrants urgent further investigation. The DTS provides objective risk stratification that guides the urgency and type of further testing.

Contraindications

Absolute contraindications include acute myocardial infarction within two days, unstable angina not yet stabilised, uncontrolled symptomatic arrhythmias, severe symptomatic aortic stenosis, decompensated heart failure, acute pulmonary embolism, and acute aortic dissection. Relative contraindications include left main coronary stenosis, significant hypertension (above 200/110 mmHg at rest), hypertrophic obstructive cardiomyopathy, and high-degree AV block. Clinical assessment before testing identifies contraindications and determines whether stress echocardiography or pharmacological stress testing is safer.

When to Choose Stress Echo or Nuclear Imaging Instead

Exercise treadmill testing has diagnostic limitations in patients with resting ECG abnormalities — left bundle branch block, pre-excitation, paced rhythm, digoxin effect, and significant resting ST changes — where ST analysis during exercise is unreliable. In these patients, stress echocardiography (exercise or dobutamine) or myocardial perfusion imaging (MPI) provides functional ischaemia detection without reliance on ECG criteria. Stress echo and nuclear imaging also offer additional information on wall motion, perfusion territory, and viability that the exercise ECG cannot provide. The choice between modalities is determined by the clinical question, resting ECG, patient's ability to exercise, and local expertise.

Requiring an exercise stress test or cardiac functional assessment in Singapore? Dr. Peter Chang performs treadmill stress testing in-clinic at Paragon Medical Centre, Orchard Road. Book an appointment today.