Cards-Dx Testing Flashcards
What patient is stress testing most useful for?
Intermediate risk patients–it classifies them into higher or lower risk possibilities
High risk… a positive or negative test wouldn’t change what you do
What are the best tests to assess mild stenosis? Diastolic and systolic dysfunction? Significant coronary stenosis?
The earliest changes with mild stenosis are perfusion changes detectable only with highly sensitive modalities, such as nuclear or cardiac magnetic resonance (CMR) imaging. With progressive coronary occlusion, diastolic dysfunction followed by systolic dysfunction may be seen by imaging studies such as echocardiography. Only when there is significant coronary stenosis will electrocardiographic (ECG) changes be seen and symptoms occur.
What are functional or anatomic cardiac studies used for? What are examples?
The many different types of tests to diagnose CAD can be broadly categorized as assessing either functional or anatomic evidence of ischemia. Functional studies evaluate for obstructive CAD from evidence of ECG changes, myocardial perfusion abnormalities, or wall motion abnormalities, usually under stress conditions. Anatomic studies assess percentage stenosis of the coronary vessels at rest, which can be visualized by single-photon emission CT (SPECT), PET/CT scan, or CMR imaging study. These imaging modalities may also be used to quantify infarction size and assess myocardial viability.
What test is best for a patient with intermediate-risk who are able to exercise and have a normal baseline ECG?
The initial type of stress testing should be exercise stress testing.
On an exercise ECG, what is used to assess risk?
- Duke treadmill score, which factors development of symptoms, degree of ST-segment depression, and exercise duration to provide incremental prognostic information for 5-year mortality risk.
- Heart rate recovery is another powerful predictor; patients with a heart rate drop of less than 12/min in the first minute after cessation of exercise have a higher mortality rate.
What is needed to accurately assess ischemia risk (what should HR be? how long exercise for?)
Ischemia is identified on the basis of the development of 1 mm or greater of horizontal or downsloping ST depression with exercise ( Figure 1 ), but the coronary territory involved cannot be localized based on the ECG changes alone. Ideally, patients should exercise for 6 to 12 minutes to provide adequate time for development of maximal metabolic demand. Although achieving 85% of the age-predicted maximal heart rate (PMHR) is considered adequate for diagnosis of ischemia, as heart rate and blood pressure are the major determinants of myocardial oxygen demand, patients should continue to exercise until limited by symptoms.
What is the Bruce protocol? When should stress tests be stopped?
A standard Bruce protocol increases the speed and grade of the treadmill every 3 minutes, and patients who have poor functional capacity and cannot achieve at least the first stage of the Bruce protocol (5 metabolic equivalents [METs]) have significantly higher all-cause mortality. Stress tests should be terminated when the patient has exerted maximal effort and achieved at least 85% PMHR, the patient requests to stop or experiences significant anginal or other physical symptoms, or when other adverse markers develop, such as exertional hypotension, significant hypertension, ST-segment elevation or significant ST-segment depression, or ventricular or supraventricular arrhythmias.
For a stress test what should you do about the patients medications?
The decision about whether to keep a patient on cardiac medications during stress testing should be individualized based on the clinical question being addressed. If the stress test is being performed to establish the diagnosis of CAD, medications such as β-blockers and nitrates should be withheld for at least 24 hours before the test. If the stress test is being performed to evaluate symptoms or to define prognosis in a patient with known disease, the patient should remain on current therapy to determine if ischemia is present on the current regimen.
What are the indications for stress testing with additional imaging?
There are several indications for stress testing with additional imaging with either echocardiography, CMR imaging, or perfusion imaging with SPECT or PET/CT.
These include inability to exercise, baseline ECG abnormalities, and conditions in which exercise is contraindicated. Patients with abnormal baseline ECGs that interfere with the interpretation of the exercise ECG (for example, left bundle branch block [LBBB], left ventricular hypertrophy with ST-segment abnormalities, or a paced rhythm) should undergo stress imaging to identify obstructive CAD. In addition, stress testing with imaging may be helpful to elucidate a diagnosis in patients with indeterminate results on treadmill testing. Patients with right bundle branch block (RBBB), bifascicular block, or who are on digoxin can undergo exercise stress testing, but ST segments may be more difficult to interpret or may produce false-positive results.
When should pharmacological testing be used? What about with imaging?
Patients with severe aortic stenosis, abdominal aortic aneurysm, severe hypertension, or uncontrolled arrhythmias should not exercise; rather, these patients should undergo pharmacologic stress testing with vasodilators.
Patients who are unable to exercise should undergo pharmacologic stress testing with imaging. In addition, in patients with LBBB undergoing nuclear stress testing, a pharmacologic stressor should be used even if the patient is able to exercise because of the potential for a false-positive test owing to a septal perfusion abnormality that may occur with exercise. The choice of imaging modality should be based on local expertise and patient characteristics.
On a stress echo, what do wall motion abnormalities at rest and exercise suggest?
Wall motion abnormalities at rest that do not change with exercise usually indicate infarction. Improvement in regional wall motion with low-dose exercise or dobutamine that worsens at higher levels suggests viable but hibernating myocardium.
What is the benefit of SPECT imaging and how is it used?
SPECT imaging takes advantage of the relative differences in blood flow with stress. Radioactive tracer is injected and taken up by the myocardium with blood flow. Images are obtained at rest. Then, with exercise or vasodilator stress, a second injection is given. Tracer is again distributed with blood flow and, therefore, less tracer is taken up in the left ventricular region supplied by a stenotic vessel. This relative difference in flow between stress and rest tomographic images is seen as a perfusion defect and is indicative of CAD
What is myocardial perfusion imaging and its +s/-s?
Myocardial perfusion imaging can quantify the extent and severity of disease and help direct treatment strategies. High-risk features that may be seen on myocardial perfusion imaging include lack of augmentation of post-stress ejection fraction, cavity dilatation, and new wall motion abnormalities. Unlike stress echocardiography, images are not obtained immediately post stress and are often delayed. If there is evidence of a new wall motion abnormality in these delayed images, it signifies a high degree of stenosis.
When is PET used? What are its +s and -s?
Like SPECT imaging, cardiac PET can be used to detect ischemia. PET imaging provides improved diagnostic accuracy compared with SPECT and can be particularly useful in patients with nondiagnostic imaging stress tests, obese patients, and patients with diabetes mellitus. Cardiac PET also allows for assessment of peak stress ejection fraction, quantitation of myocardial blood flow, and evaluation of myocardial metabolism. Because some PET radiotracers identify metabolically active myocytes, it is an excellent tool to evaluate for viability.
What do you use to assess cardiac inflammatory or infiltrative disease?
CMR imaging can be used for evaluation of myocardial and pericardial disease processes and can be particularly useful for evaluation of infiltrative and inflammatory diseases.
