Stress Testing

What Is Stress Testing?

Echocardiography Evaluates Cardiac Function:

• At rest
• During stress evoked by adrenergic (dobutamine) challenge or by dynamic exercise (treadmill)
• Immediately following dynamic exercise

Indications for Stress Testing

• Suspected or known coronary artery disease.
• Myocardial evaluation.
• Evaluation of dyspnea to identify possible cardiac origin.
• Mitral stenosis and regurgitation.
• Aortic stenosis.
• Hypertrophic cardiomyopathy.
• Pulmonary hypertension.

Those with tachyarrhythmias and hypertension should not have stress testing; abdominal aortic aneurysm is a relative contraindication.

Types of Stress Testing

Exercise stress testing is preferred to a pharmacologic challenge due to its predictive superiority for outcomes. Anyone who can tolerate exercise should have this type of stress testing. Use of a treadmill, the most common technique, involves pre-exercise imaging and image acquisition during exercise. Those who cannot perform exercise testing can pharmacologically challenge the myocardium with dobutamine stress, a potent ischemic stressor. A temporary pacemaker can be used for those who cannot exercise. The pacing rate is raised in combination with the pharmacologic dobutamine stress method.

Complementary Imaging Techniques

An important part of stress testing is imaging the heart before, during, and after the challenge. 2D echocardiography is used to make “before-and-after” side-by-side comparisons of both global and left ventricular systolic function. Images at rest, pre-peak, and at peak stress are compared.

Stress Testing Diagnosis and Tests

Coronary Heart Disease

Most stress tests are done to identify coronary heart disease and assess myocardial viability.

Other Cardiac Diagnostics and Testing

It can also be used for other cardiac conditions, such as

• Valvular heart disease
• Hypertrophic cardiomyopathy
• Dyspnea of cardiac origin
• Pulmonary hypertension
• Mitral valve disease (stenosis and regurgitation)
• Aortic stenosis
• Left ventricular outflow resistance

Diagnostic Results

After the following steps, interpretation can follow.

• The maximal heart rate is determined by the formula of Maximal HR = (208 – age). From that, the target heart rate for the stress test is formulated: 85% of Maximal Heart Rate.
• A 12-Lead ECG is done and BP readings incorporated into the tabulations.
• The test is continued until the patient feels it impossible to continue although a patient’s request to stop before this point, should always be respected. The test is stopped by the provider if there is marked ST depression in the absence of Q waves, ventricular tachycardia, a Mobitz 2 second degree atrioventricular heart block, complete heart block, sustained ventricular tachycardia (or fibrillation), ventricular ectopy, or supraventricular tachyarrhythmia.
• ECG is repeated after 15-30 seconds supine if there the test was done due to a suspicion of ischemia. It is repeated every 2 minutes until the HR falls to < 100 bpm or the ECG returns to the character of the resting ECG.

Shifts in the ST segment, T wave, and the U wave can indicate ischemia:

• ST depression, especially horizontal or down sloping.
• Upsloping ST depression can occur during normal recovery. 
• ST segment elevation in association with a resting normal ECG (transmural ischemia and severe multi-vessel coronary artery disease).

As with any ECGs, stress test ECGs can demonstrate bundle branch blocks and other conductive abnormalities.

Treatment Based off Stress Tests

Management and treatment in regard to stress testing is determined according to the type of patient being considered for it:

• If the patient is unable to exercise: An adrenergic challenge (dobutamine) can stimulate stress on the myocardium.
• If the patient is unable to undergo an adrenergic challenge with dobutamine: Due to hypertension, etc., and exercise is contraindicated, other diagnostic approaches should be considered, such as advanced cardiac imaging, such as CMR (cardiac magnetic resonance).
• If the resting ECG prior to the test is abnormal: The provider should consider aborting the test for management of the heart disease specifically indicated on the resting ECG and perhaps re-testing if a normal resting ECG can be achieved.
• If ST changes during the test indicate ischemia: Management of the causes of ischemia can follow.

Prevention of Stress Tests

Very rarely (1 in 10,000), serious complications can occur with stress testing. To minimize this risk, the following are part of a risk-reduction protocol to prevent unforeseeable complications:

• Trained personnel in testing, CPR, and the diagnostic instruments
• A capable healthcare professional, preferably a physician, present during the testing
• Emergency resuscitation equipment and drugs immediately available in a well-supplied, frequently checked supply area 
• An in-depth history and thorough physical exam pre-testing
• Education for the patient in the recognition of limits and signs of jeopardy
• Straightforward exercise and test end-points, including target heart rate
• Avoid showering until complete cool-down

The patient’s non-cardiac health must be considered to prevent complications. Conditions such as insulin-dependent diabetes requires formulating the increased glucose/insulin dynamic in with exercise. Smokers, obese patients, and patients with metabolic syndrome and/or dyslipidemia underscore the value of the resting ECG prior to testing.