Exercise Stress Testing
Conduct and interpretation
Know the indications (chest pain evaluation, functional capacity, arrhythmia provocation, chronotropic response) and the absolute contraindications: acute MI within about 48 hours, unstable angina, uncontrolled symptomatic arrhythmia, severe symptomatic aortic stenosis, decompensated heart failure, acute pulmonary embolism or dissection, and resting hypertension above roughly 200/110 mmHg. Preparation includes fasting, baseline supine and standing 12-lead tracings, and medication review - beta-blockers blunt the heart-rate response and digoxin alters ST segments.
The standard Bruce protocol uses 3-minute stages beginning at 1.7 mph and 10% grade, with a target of 85% of the age-predicted maximum (220 − age). Endpoints include reaching target heart rate, ≥2 mm ST depression, ST elevation, sustained ventricular tachycardia, a systolic pressure fall >10 mmHg with signs, and severe symptoms.
Traps: upsloping ST depression and ST change superimposed on LVH or LBBB are weak evidence. Exercise-induced hypotension is a powerful marker of severe disease. Recovery-phase changes count, so continue recording at least 6–10 minutes after peak exercise.
Rule of thumb: Duke Treadmill Score = METs − (5 × maximum ST deviation in mm) − (4 × angina index, where 0 = none, 1 = nonlimiting, 2 = limiting). Scores ≥ +5 are low risk, −10 to +4 intermediate, and ≤ −11 high risk.