Exercise treadmill stress testing

What it is

The exercise treadmill test, also called the exercise stress test, is the diagnostic test for stable angina. Stable angina occurs when the myocardium becomes ischemic, typically a substernal pressure lasting 5-15 minutes, improved with rest and GTN, with ST depression on the ECG during an attack. On a rest ECG between attacks, and on cardiac enzymes (CK-MB/troponin), such a patient is normal, so the diagnosis has to be made by putting the heart under load.

Two matters come before the test is ordered:

• Can the patient do the test?
• Can you read the ECG? Bundle branch block, left ventricular hypertrophy, or a pacemaker all make the ECG hard to read.

When either answer is no, another form of stress is used: a nuclear stress test, a dobutamine or adenosine stress test, or a stress echocardiogram.

How it is diagnosed

Which test is chosen follows the pretest probability of CAD.

• Low probability: no additional diagnostic testing.
• Intermediate probability with a normal ECG and able to exercise: exercise treadmill stress test.
• Intermediate probability with an abnormal ECG and able to exercise: exercise nuclear stress test or exercise echocardiography.
• Intermediate probability and not able to exercise: pharmacologic stress test.
• High probability: medical therapy for CAD, moving on to coronary angiography when there is no response to therapy, lifestyle-limiting symptoms, or progression to unstable angina.

A markedly positive test at any of these points leads to coronary angiography, and the criteria differ by test: first, exercise treadmill, where they are a significant ST segment ↓ at a low work load, ST segment ↑, and hypotension; second, exercise nuclear, where they are TID or lung uptake of thallium, ischemia in more than 2 vascular distributions, and EF below 35%; and third, exercise echocardiography, where they are EF below 35% at rest, ischemia in more than 2 vascular distributions, and a fall in EF with stress.

A positive stress ECG shows ST segment depression, and stress echocardiography shows exercise-induced ischemia as wall motion abnormalities. Patients with a positive stress test result should undergo cardiac catheterization; cardiac catheterization with coronary angiography is the definitive test for CAD and the gold standard.