The American College of Cardiology and the American Heart Association recognize cardiovascular stress testing as an invaluable diagnostic tool for the determination of the presence and severity of cardiovascular disease. Additionally, stress testing is prescribed for patients who have recently undergone restorative cardiovascular procedures such as stenting and bypass grafting to assess the functionality of the repaired heart. In order to meet the diagnostic needs of each patient, cardiologists have a wide range of testing protocols to choose from.
Commonalities
Common to all stress testing procedures is the acquisition of vital statistics. All testing should include continuous monitoring of blood pressure, heart rate and electrical activity of the heart, via an electrocardiogram, or EKG. These measurements should be recorded prior to testing while the patient is at rest, at least once during each stage of the procedure, and following the testing until the heart rate and blood pressure return to baseline levels.
In addition to these measurements, the American College of Sports Medicine recommends obtaining measurements for oxygen consumption, or VO2, throughout testing. Oxygen consumption provides information regarding the ability of the heart to deliver oxygen to the working muscles.
Graded Exercise Test
The most basic stress test is the graded exercise test, also referred to as a GXT. The GXT involves monitoring the standard vital statistics while the patient exercises on either a treadmill or a cycle ergometer. Regardless of exercise mode, the testing protocol is such that the intensity of exercise will increase every two to three minutes until the patient reaches fatigue. This basic test allows the cardiologist to assess the patient's heart rate, blood pressure and EKG response to increasing workloads.
Nuclear Stress Test
Nuclear stress testing involves the infusion of a radioactive isotope before exercise and again with one minute remaining in the exercise protocol. The heart tissue absorbs the isotope, which is then viewed with a single-photon emission computed tomography camera, similar to a CT scan. This type of stress test, also known as a myocardial perfusion imaging test, utilizes the same exercise protocol as the GXT and uses the images of the heart to discern abnormalities in blood flow to various areas of the heart tissue. The images gained with the nuclear stress test add a higher level of accuracy to the GXT.
Stress Echocardiogram
While myocardial perfusion testing evaluates blood flow to the heart tissue, an echocardiogram evaluates the ability of the heart muscle to contract and relax synchronously. An echocardiogram, a type of sonogram, evaluates the motion of the walls of each of the chambers of the heart to ensure proper functioning. While a patient's heart might appear normal during a resting echocardiogram, abnormalities may appear immediately following exercise as a result of the increased stress placed on the heart. For that reason, stress echocardiograms are a useful tool to diagnose differences in heart wall motion before and after exercise. Similar to the nuclear stress test, the exercise protocol for a stress echocardiogram is generally the same as a GXT.
Pharmacological Stress Test
Occasionally a patient will have limiting factors that render him unable to complete the graded exercise protocol. For these patients, pharmacological stress tests offer similar diagnostic abilities without the need for the patient to use the treadmill or cycle ergometer. To complete this test the patient is administered a drug that mimics the heart's response to exercise. This testing is used in conjunction with either a nuclear scan or an echocardiogram and the required vital measurements to assess cardiovascular function.
References
- "Journal of the American College of Cardiology"; ACC/AHA 2002 Guideline Update for Exercise Testing; Dr. Raymond J Gibbons; 2002
- "ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription"; American College of Sports Medicine; 2010
