Stress Testing and Nuclear Perfusion Imaging

Why rest can hide the problem

A partly narrowed coronary artery may deliver plenty of blood while you sit still. The trouble appears only when the heart works harder and demands more — climbing stairs, running for a bus. That is the whole idea of a stress test: deliberately raise the heart’s workload and watch for signs that some muscle is no longer getting enough blood, a state called coronary ischemia. A resting ECG can look perfectly normal in someone with significant stable angina.

1. Exercise stress: walk a treadmill on a rising slope and speed — the classic exercise tolerance test. Best if you can walk well.
2. Pharmacologic stress: if walking is not possible, a drug speeds the heart or dilates the arteries to mimic exercise.
3. During stress, the heart is watched — by ECG, by echo, or by a nuclear tracer — for signs of starved muscle.

Reading the plain exercise ECG

In the simplest stress test, only the ECG is recorded. The key clue is the ST segment: when muscle is starved of blood, the ST segment tends to sag downward — ST depression — and may bring on the patient’s typical chest pain. The test also records how far the person could exercise and how the blood pressure and heart rate responded, all of which carry prognostic weight.

Reading an exercise (treadmill) ECG — what changes mean

1. Target heart rate (rough) = 220 - age
     age 60 -> aim near 0.85 x (220-60) = ~136 bpm

2. Watch the ST segment in each lead:
     flat/upsloping, no shift ......... reassuring
     >= 1 mm horizontal/downsloping
        ST depression ................. suggests ischemia
     ST elevation (rare on stress) .... alarming, stop test

3. Watch the patient and the numbers:
     reproduces typical chest pain .... supports ischemia
     blood pressure falls with effort . abnormal, stop
     dangerous arrhythmia appears ..... stop test

Result is read together: ECG + symptoms + exercise
capacity + blood-pressure response.

Nuclear perfusion: mapping the fed and the hungry

When the ECG alone is not enough, myocardial perfusion imaging adds a picture. A tiny amount of radioactive tracer is injected; healthy, well-fed muscle soaks it up, while an under-supplied region shows up faint. Images taken at stress and again at rest are compared. A spot that is faint under stress but fills in at rest signals a reversible defect — living muscle starved by a narrowed artery. A spot faint in both signals a fixed defect — often old scar from a prior heart attack.