Stress testing: a beginner’s guide

Stress testing: a beginner’s guide

Author: Jason Brown, Capt, USAF, MD (EM Resident Physician, University of Maryland) // Editor: Alex Koyfman, MD

Stress tests are aptly named in that the goal is to cause a physiologic stress and to, through a variety of modalities, detect that stress’ impact on the myocardium.

There are three major modes of stressing the patient:

• Exercise – either treadmill or supine bike
• Vasodilation – adenosine, dipyridamole, regadenoson
• Inotropy – dobutamine

There are five different ways to detect stress on the myocardium:

• EKG *all modalities employ
• Echocardiography
• Radionuclide imaging – Thallium²⁰¹, Technetium^99M
• PET
• MRI

Treadmill stress testing is the most common form of stress test that you will see as a direct extension of the ED.  It employs the Bruce protocol (starting at 1.7mph and 10% grade with increases in both every 3 minutes to a maximum heart rate of 85% (220-age)) while the patient wears an EKG.  Tests are positive if the patient has early chest pain, hyper-/hypotension, ST changes, or arrhythmia.

Supine bike exercise testing allows for real-time echocardiography.  This provides an excellent option for patients with valvular disease and are functional but cannot use a treadmill.

The vasodilatory stress tests use agents which increase coronary blood blow.  They work on the principle that diseased arteries are already maximally dilated and that there will be no further perfusion of their vascular territories when under stress.  A variety of detectors can be used to detect the difference between rest and stress phases.

• Vasodilation is contraindicated in patients with hypotension, high AV block, or bronchospasm
• No caffeine (12 hours), Cialis (72 hours), nitrates (48 hours), or calcium channel blockers (48 hours) prior to the test

Dobutamine stress tests use the positive inotropic effects of dobutamine to increase the heart rate and elicit perfusion deficits in lieu of actual exercise.  There are a variety of protocols but the main goal is to achieve 85% of maximal heart rate (220-age) and to use a detector to examine the myocardium.

• Contraindicated in patients with arrhythmias, significant hypertension, or LV outflow obstruction.
• Must hold beta-blockers and calcium channel blockers 24 hours prior.

 Detection of myocardial perfusion deficits

The EKG is the most common modality for detection of ischemic changes. Consistent horizontal or down-sloping ST depressions in contiguous leads is considered positive.

In patients that have known CAD or prior revascularization, an abnormal EKG, or a need for functional examination of the heart structures (valvular function, LVEF, etc) then imaging should be considered.

There are four major imaging modalities: SPECT, ECHO, PET, MRI.

Dobutamine is used in conjunction with echocardiography to evaluate function under stress.  New wall motion abnormalities are considered positive for flow-limiting disease.  Drawbacks include: technologist-dependent images and difficult interpretation in patients with baseline wall motion abnormalities and/or the obese.

All three of the above vasodilators can be used with SPECT, PET, and MRI; deemed myocardial perfusion imaging.  All three of these imaging modalities attempt to detect perfusion deficits between rest and stress states.  These tests are generally used in patients which need investigations which are beyond the scope of the emergency department.

Recommendations:

Personally, when I am evaluating a patient in our clinical decision unit (CDU, observation unit) I use either:

• An EKG treadmill stress for low-intermediate risk ACS patients with normal initial and serial EKGs who can exercise.
• A supine bike ECHO for any patient that is low-intermediate risk who has an abnormal but nonischemic EKG who can exercise.
• A dobutamine stress ECHO for any patient with an abnormal EKG who cannot exercise.
• Any patient with CHF, known CAD, previous PCI/CABG, BBB, or congenital cardiac issue should be evaluated by a staff cardiologist.

REFERENCES

-Anderson KM, Murphy DL, Balaji M. Essentials of noninvasive cardiac stress testing. J Am Assoc Nurse Pract. 2014;26(2):59-69.

-Gibbons RJ, Balady GJ, Bricker JT, et al. ACC/AHA 2002 guideline update for exercise testing: summary article. J Am Coll Cardiol 2002; 40:1531.

-Hendel RC, Berman DS, Di Carli MF, et al. ACCF/ASNC/ACR/AHA/ASE/SCCT/SCMR/SNM 2009 Appropriate Use Criteria for Cardiac Radionuclide Imaging. J Am Coll Cardiol 2009; 53:2201.

-ACCF/ASE/AHA/ASNC/HFSA/HRS/SCAI/SCCM/SCCT/SCMR 2011 Appropriate Use Criteria for Echocardiography. J Am Soc Echocardiogr 2011; 24:229.

-Douglas PS , Khandheria B, Stainback R. et al. ACCF / ASE / ACEP / AHA / ASNC / SCAI / SCCT / SCMR 2008 Appropriateness Criteria for Stress echocardiography. Circulation. 2008;117:1478‐1497

-Fraker TD Jr, Fihn SD, et al. Chronic Stable Angina Writing Committee: focused update of the ACC/AHA 2002 guidelines for the management of patients with chronic stable angina: J Am Coll Cardiol. 2007;50(23):2264.

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