In stress testing, the heart is monitored by electrocardiography (ECG) and often imaging studies Myocardial Perfusion Imaging Radionuclide imaging uses a special detector (gamma camera) to create an image following injection of radioactive material. This test is done to evaluate Cardiac valvular disorders Cardiomyopathy... read more during an induced episode of increased cardiac demand so that ischemic areas potentially at risk of infarction can be identified. In patients with coronary artery disease Overview of Coronary Artery Disease Coronary artery disease (CAD) involves impairment of blood flow through the coronary arteries, most commonly by atheromas. Clinical presentations include silent ischemia, angina pectoris, acute... read more (CAD), a blood supply that is adequate at rest may be inadequate when cardiac demands are increased by exercise or other forms of stress. Heart rate is increased to 85% of age-predicted maximum (target heart rate) or until symptoms develop, whichever occurs first.
Stress testing is used for
Stratifying risk in patients with known CAD
Monitoring patients with known CAD
Stress testing is less invasive and less expensive than cardiac catheterization Cardiac Catheterization Cardiac catheterization is the passage of a catheter through peripheral arteries or veins into cardiac chambers, the pulmonary artery, and coronary arteries and veins. Cardiac catheterization... read more , and it detects abnormalities of blood flow; however, it is less accurate for diagnosis in patients with a low pretest likelihood of CAD. It can define the functional significance of abnormalities in coronary artery anatomy identified with coronary angiography during catheterization. Because coronary artery plaques that are not significantly stenotic (ie, do not result in ischemia during stress testing) may nonetheless rupture and cause an acute coronary syndrome, a normal stress test result does not guarantee future freedom from myocardial infarction.
Risks of stress testing include infarction and sudden death, which occur in about 1/5000 patients tested. Stress testing has several absolute and relative contraindications
Absolute contraindications to exercise stress testing are
Acute coronary syndrome Overview of Acute Coronary Syndromes (ACS) Acute coronary syndromes result from acute obstruction of a coronary artery. Consequences depend on degree and location of obstruction and range from unstable angina to non–ST-segment elevation... read more (myocardial infarction within 48 hours or uncontrolled unstable angina)
Pulmonary infarction if acute
Relative contraindications to exercise stress testing include
Hypertension Hypertension Hypertension is sustained elevation of resting systolic blood pressure (≥ 130 mm Hg), diastolic blood pressure (≥ 80 mm Hg), or both. Hypertension with no known cause (primary; formerly, essential... read more (systolic blood pressure [BP] >200 mm Hg or diastolic BP > 110 mm Hg)
Inability to exercise adequately due to mental or physical impairment
Stenosis of heart valve if moderate or severe
Stenosis of left main coronary artery
Stress Test Methodology
Cardiac demand can be increased by
Drugs (pharmacologic stress)
Patients must fast for 4 to 6 hours before the test. When dipyridamole, adenosine, or regadenoson is used for pharmacologic stress, xanthine compounds (eg, aminophylline, theophylline, caffeine) may produce a false-negative result, so such substances (including tea, coffee, cocoa, chocolate, certain energy supplements and drinks, and caffeinated sodas) should be avoided for 24 hours before testing.
Exercise stress testing
Exercise is preferred to drugs for increasing cardiac demand because it more closely replicates ischemia-inducing stressors. Usually, a patient walks on a conventional treadmill, following the Bruce protocol or a similar exercise schedule, until the target heart rate is reached or symptoms occur. The Bruce protocol (most commonly used) increases treadmill speed and slope incrementally at roughly 3-minute intervals.
Pharmacologic stress testing
Pharmacologic stress testing is usually used when patients cannot walk on a treadmill long enough to reach their target heart rate because of deconditioning, musculoskeletal disorders, obesity, peripheral arterial disease, or other disorders. Drugs used include IV dipyridamole, adenosine, regadenoson, and dobutamine.
Dipyridamole augments endogenous adenosine, causing coronary artery vasodilation. It increases myocardial blood flow in normal coronary arteries but not in arteries distal to a stenosis, creating a “steal” phenomenon from stenosed arteries and an imbalance in perfusion. Dipyridamole-induced ischemia or other adverse effects (eg, nausea, vomiting, headache, bronchospasm) occur in about 10% of patients, but these effects can be reversed by IV aminophylline. Severe reactions occur in < 1% of patients. Contraindications include asthma, acute phase myocardial infarction (MI), unstable angina pectoris, critical aortic stenosis, and systemic hypotension (systolic BP < 90 mm Hg).
Adenosine has the same effect as dipyridamole but must be given in a continuous IV infusion because it is rapidly degraded in the plasma. Adverse effects include transient flushing, chest pain, and tachycardia, which can be reversed by terminating the infusion.
Regadenoson is a more selective adenosine agonist than either dipyridamole or adenosine and is non-inferior for the diagnosis of ischemia with fewer adverse effects and greater ease of administration.
Dobutamine is an inotrope, chronotrope, and vasodilator used mainly when dipyridamole and adenosine are contraindicated (eg, in patients with asthma or 2nd-degree atrioventricular block) and when echocardiography is used to image the heart. Dobutamine must be used with caution in patients who have severe hypertension or arrhythmia, left ventricular outflow tract obstruction, multiple previous MIs, or acute MI.
Diagnostic Stress Test Methodology
Several imaging tests can detect ischemia after exercise or pharmacologic stress:
Radionuclide perfusion imaging
ECG is always used with stress testing to diagnose coronary artery disease and help determine prognosis. Stress ECG alone (ie, without radionuclide imaging or echocardiography) is most useful in patients with
Intermediate likelihood of CAD based on age and sex
Normal ECG at rest
Diagnosis involves assessment of ST-segment response (a measure of global subendocardial ischemia), BP response, and the patient’s symptoms.
Average sensitivity is 67%; average specificity is 72%. Sensitivity and specificity are lower in women partly because incidence of CAD is lower in young and middle-aged women. Prognosis worsens with depth of ST depression.
Radionuclide myocardial perfusion imaging
Radionuclide myocardial perfusion imaging Myocardial Perfusion Imaging Radionuclide imaging uses a special detector (gamma camera) to create an image following injection of radioactive material. This test is done to evaluate Cardiac valvular disorders Cardiomyopathy... read more is more sensitive (85 to 90%) and specific (70 to 80%) than ECG stress testing. Combining findings from both tests increases sensitivity for coronary artery disease.
Myocardial perfusion imaging is particularly useful for patients with
Baseline ECG abnormalities that may interfere with interpretation of ECG changes during a stress test (eg, bundle branch block, fixed-rate pacemakers, digitalis effects).
High probability of false-positive results on exercise ECGs (eg, premenopausal women, patients with mitral valve prolapse)
This imaging test can help determine the functional significance of coronary artery stenosis, identified by coronary angiography, when surgeons are choosing lesions to bypass or dilate via percutaneous transluminal coronary angioplasty.
Echocardiography Echocardiography This photo shows a patient having echocardiography. This image shows all 4 cardiac chambers and the tricupsid and mitral valves. Echocardiography uses ultrasound waves to produce an image of... read more is useful when information about more than just perfusion is needed. Echocardiography detects wall motion abnormalities that are a sign of regional ischemia and, using Doppler techniques, helps evaluate valvular disorders that may contribute to or result from ischemia or valvular disorders unrelated to ischemia but which deserve concomitant evaluation.
The echocardiogram is typically obtained immediately before and after an exercise treadmill test or during dobutamine infusion.
Echocardiography is relatively portable, does not use ionizing radiation, has a rapid acquisition time, and is inexpensive, but it is difficult to carry out in obese patients and in patients with COPD and lung hyperinflation. Done by experts, stress echocardiography has a predictive value similar to that of stress myocardial radionuclide perfusion testing.
Stress hemodynamic echocardiography is considered for selected individuals for diagnosis of heart failure with preserved ejection fraction Heart failure with preserved ejection fraction (HFpEF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more .
Radionuclide ventriculography Radionuclide Ventriculography Radionuclide imaging uses a special detector (gamma camera) to create an image following injection of radioactive material. This test is done to evaluate Cardiac valvular disorders Cardiomyopathy... read more is occasionally used with exercise stress testing instead of echocardiography to assess exercise ejection fraction (EF), the best prognostic indicator in patients with coronary artery disease.
Normally, EF is ≥ 5 percentage points higher during exercise than at rest. Ventricular dysfunction (eg, due to valvular heart disorders, cardiomyopathy, or CAD) can decrease exercise EF below baseline or prevent it from increasing.
In patients with CAD, the 8-year survival rate is 80% with an exercise EF of 40 to 49%, 75% with an exercise EF of 30 to 39%, and 40% with an exercise EF of < 30%.