In stress testing, the heart is monitored by electrocardiography (ECG) and often imaging studies 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 (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
Diagnosing coronary artery disease
Stratifying risk in patients with known CAD
Monitoring patients with known CAD
Stress testing is less invasive and less expensive than cardiac catheterization, 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 (myocardial infarction within 48 hours or uncontrolled unstable angina)
Aortic dissection if acute
Aortic stenosis if symptomatic or severe
Arrhythmias if symptomatic or hemodynamically significant
Heart failure if decompensated
Myocarditis if acute
Pericarditis if acute
Pulmonary embolism if acute
Pulmonary infarction if acute
Relative contraindications to exercise stress testing include
Atrioventricular block if high-degree
Bradyarrhythmias
Electrolyte imbalance
Hypertension (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
Systemic illness
Tachyarrhythmias
Stress Test Methodology
Cardiac demand can be increased by
Exercise
Drugs (pharmacologic stress)
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
augments endogenous adenosine< 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).
is a more selective adenosine
Diagnostic Stress Test Methodology
Several imaging tests can detect ischemia after exercise or pharmacologic stress:
ECG
Radionuclide perfusion imaging
Echocardiography
Electrocardiography (ECG)
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 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 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.
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 patients with obesity 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.
Radionuclide ventriculography
Radionuclide ventriculography 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%.
