Cardiac Stress Testing
Various Procedures to Assess the Integrity of Coronary Circulation
Nov 22, 2008
Cardiac stress testing refers to procedures that determine the risk for a heart attack (unstable angina or myocardial infarction). They are used for patients who do not present with a full-blown heart attack but report symptoms that suggest a risk, such as an individual with chest pain that appears during exercise and fades with rest (stable angina). The results of cardiac stress testing determine if a patient can benefit from intervention to prevent a serious cardiac event.
Components of Stress Testing
There are multiple types of cardiac stress testing for physicians to choose from, but all have the same two basic components. The patient's heart must work harder than normal (stress methodology) while clinical data is being recorded (diagnostic methodology).
Stress methodology utilizes one of the following techniques:
- Exercise: Cardiac stress testing with exercise involves the patient walking on a treadmill whose speed and incline are slightly boosted every few minutes. The patient keeps walking until he or she reaches a goal heart rate or can no longer tolerate the effort.
- Pharmacological: In pharmacological stress testing, the heart is stimulated by dobutamine, dipyridamole, or adenosine. These medications increase the heart's rate and strength of contraction, producing effects similar to those of exercise.
Diagnostic methodology involves one of the following modalities:
- Electrocardiography (EKG): EKG displays a horizontal graphical representation of the heart's rhythm. It can exhibit certain abnormalities related to coronary artery disease and suggest the location of disease in the heart based on the EKG leads showing these anomalies.
- Echocardiography: The modality of echocardiography uses ultrasound to image the anatomy of the heart as it is contracting. This is useful if a physician also suspects an anatomical abnormality, such as valvular heart disease, contributing to the patient's symptoms.
- Myocardial Perfusion Scanning: Myocardial perfusion scanning, performed by a nuclear medicine specialist, involves the administration of thallium-201 or technetium-99 sestamibi. These radioactive markers flow into the heart muscle, indicating which portions of the heart have adequate perfusion of blood.
Choice of Stress Testing
When ordering cardiac stress testing, the physician chooses one stress method and one diagnostic method. The stress method depends mainly on the patient's mobility, and exercise stress testing is always chosen unless the patient has obesity, weakness, musculoskeletal problems, or other conditions that prevent optimal activity on a treadmill. As for the diagnostic method, it depends on what the physician needs to see. In general, EKG is the basic choice, echocardiography is reserved for evaluation of other anatomical structures of the heart if necessary, and myocardial perfusion scanning provides further analysis of impaired blood flow to the heart that is more clear than EKG.
Interpretation of Stress Testing
With any cardiac stress test, the diagnostic measures are taken before, during, and after application of the cardiac stress. The main interpretation of results depends on when abnormalities appear. For example, myocardial perfusion scanning that shows impaired cardiac blood flow during the stress but not before and after means that the heart is deprived of perfusion only with physical activity. However, if impaired cardiac blood flow is seen at all times, it means the affected portion of the heart has a fixed narrowing in a coronary artery.
Progression of Stress Testing
In general, patients at risk for heart attacks begin with EKG or echocardiography stress testing. If the results are worrisome, particularly an abnormality that persists after the cardiac stressor, the patient proceeds to myocardial perfusion scanning. If results on this test show a fixed perfusion defect, the patient undergoes cardiac catheterization to visualize the coronary arteries and, if necessary, receive revascularization treatment.
