Cardiac Stress Imaging

Cardiac stress imaging can assess coronary perfusion, cardiac (including valvular) function, myocardium viability, and exercise capacity. Stress can be induced pharmacologically or through physical exercise. Imaging modalities include echocardiography and nuclear myocardial perfusion imaging with either single-photon emission computed tomography (SPECT) or positron emission tomography (PET) scanning. Electrocardiogram (EKG) exercise stress testing can offer a sufficient ischemic evaluation for select patients, but imaging modalities offer more information and are often preferred. The different imaging modalities and modes of stress each have advantages and disadvantages when selecting the most appropriate test for each patient. The definitive diagnosis of coronary artery disease (CAD) is made by the presence of at least 50 to 70% stenosis of at least one epicardial vessel on coronary angiography. Stress testing is not diagnostic of CAD, as it only implies evidence of stenosis through functional assessments. However, the results can increase or decrease the probability of CAD, termed post-test likelihood, and guide decisions regarding pursuing invasive coronary angiography. Results can further risk stratify, predict prognosis, and guide treatment in various cardiac pathologies.An ischemic evaluation typically is warranted when patients present with clinical concerns for angina or new heart failure suggesting coronary artery disease. Chest pain is categorized as typical angina, atypical angina, or non-cardiac chest pain, depending on the clinical characteristics. These characteristics include 1) substernal chest discomfort, 2) worsened with exertion or stress, and 3) relieved by rest or nitroglycerine. Typical angina pain meets all three characteristics, and atypical meets only two. If the pain has none or only one of the above characteristics, it is considered non-anginal/non-cardiac chest pain. Based on the above clinical chest pain characteristics and patient factors such as age, gender, and comorbidities, each patient can be assigned a pre-test probability, ranging from low ( 90%) pretest-probability of having coronary artery disease according to the American College of Cardiology and American Heart Association (ACC/AHA). Stress testing is ideal for the intermediate-risk patient, as the test outcome has the highest potential to impact CAD post-test likelihood in this group. A positive test result in the high-pretest-risk patient group would not add much to CAD's likelihood, and these patients are often referred directly to an angiography without stress testing.