Stress Tests and Admitting to the Observation Unit for Chest Pain
Here are a few pearls about how to choose stress tests for patients presenting with CP that you’re admitting to the observation unit.
Caveat #1: Much of this is specific to our observation at the Mayo Clinic. We have access to a multiude of provocative tests including EKG treadmills, Adenosine, Dobutamine, and exercise sestamibis, exercise and Dobutamine stress echocardiograms, cardiology consultations, and next day cardiology follow-up appoints.
Caveat #2: This is not a discussion of the utility and evidence or lack-there-of for stress tests in low risk chest pain patients. Rather, during an emergency medicine residency and working in an emergency department with an observation unit, a resident will order a lot of stress tests as it is part of the practice of many Emergency Medicine Attending physicians. Given this, it is important to know some tips / tricks on how to select the most appropriate test.
As EM physicians we are expected to following the 2007 ACC/AHA Guidelines to the Management of Patients With Unstable Angina/ Non–ST-Elevation Myocardial Infarction http://www.ncbi.nlm.nih.gov/pubmed/17692738
For low risk chest pain, this guideline basically says:
- If the patient is deemed to be low risk based on history, a unremarkable EKG and negative serial troponins, the patient should receive provocative testing, i.e. stress test, to further delineate risk stratification, ideally during their initial encounter (in the obs unit if available or as inpatient). This should be performed within 72 hours from the episode of chest pain.
So in essence, if strictly following these guidelines, essentially every patient that we order trops on that isn’t being admitted to the hospital, should have a stress test that follows in the Obs unit or at least have outpatient cardiology or primary care follow up within 72 hours so a stress test can be ordered.
SO YOUR PATIENT IS GOING TO OBS FOR A STRESS TEST. WHAT DO YOU ORDER? A SIMPLIFIED GUIDE:
Step 1: Look to see if they had an old stress test. If there was a stress test done greater than 6 – 12 months ago, your best bet is to repeat it. People love comparing the exact same tests delineated by time. If the test was <6 months ago, safe bet is cardiology consult – as it would be unlikely that you’ll find new information when comparing to a recently completed stress test. If they have never had a stress test, proceed to step 2.
Step 2: Are they young, say less than 65 years old, and able to walk on a treadmill and handle getting tired? (able to walk 5 minutes or more or walk up 2 flights of stairs without stopping). Is they’re EKG essentially normal? NO ST DEPRESSION/ELEVATION. NO QRS >120ms (bundle or other conduction delay or paced rhythm). NO DIGOXIN. Then you can order an Exercise/EKG Treadmill. (Patient walks on a treadmill until they’re HR gets to a calculated rate (based on age), they monitor EKG for ischemic changes as well as BP, symptoms, exercise duration, etc. It’s the cheapest and easiest. Least sensitive of all the tests ~60-75%. Exercise/EKG treadmill is the most common test you’ll order when in a young patient that has never had a stress test before.
Step 3: So they’re not young, and they haven’t had a stress before? Or they had a treadmill years ago and now they’re old and/or can’t walk on a treadmill? Or they’re EKG doesn’t meet criteria for a treadmill stress? Now you’ve got options:
Option A: Adenosine Sestamibi
- This is the most common test you’ll order after Exercise EKG.
- A sestamibi is a study where radioactive dye is injected into a PIV. Dye in the blood will eventually go through the coronaries arteries. Flow is measured in the coronary arteries. The dye is seen with SPECT (fancy word for different kind of CT) and flow can be measured. Bad vessels have bad flow when “stressed". Good vessels have better flow. When this is seen “ischemia” is diagnosed, and they can correlate it to a particular artery.
- Fun fact: Sestamibis often exposure the patient to as much radiation, sometimes more, than a CT scan of the chest.
- How Adenosine Sestamibis works.
- Adenosine is a calcium channel blocker (a vasodilator). It dilates the coronaries. But plaque ridden coronary arteries don’t dilate as well as regular ones. So bad coronaries stay “tight” and there is less flow.
- When to not choose adenosine?
- History of COPD or asthma. Calcium channel blocker can cause bronchospasm.
- History of sick sinus, bradycardia, or AV block. Don’t want to slow them down more!
- Hypotension. Calcium channel blockers to a patient with low blood pressure is obviously not a good idea.
Option B: Dobumatine Sestamibi
- Same sestamibi but with Dobutamine
- How does Dobutamine work.
- Dobutamine is a beta-1 agonist. It increased the HR. Increased HR leads to more overall time in systole and less time in diastole. Remember the coronaries fill in diastole. With limited time in diastole, what dye is able to get into the coronaries will preferentially go to open vessels. So bad coronaries are seen having less flow.
- When to not choose Dobutamine
- History of ventricular arrhythmia. Dobutamine is slightly arrhythmogenic.
- Outflow tract obstruction (i.e. Aortic stenosis). Fast HR may not be compatible with life.
- So why is Dobutamine not chosen more often than Adenosine? It seems to make more physiologic sense.
- Good point. But everyone worries about the possibility of arrhythmias with Dobutamine. The thought is that adenosine is safer. I have never seen any evidence or data to support this. That said, I’ve never seen any data to dismiss this thought either.
Option C: Exercise Sestamibi
- Same as the last two, but now instead of a med, you walk on a treadmill with radioactive dye in your veins.
- Most physiologic "stress" of the sestamibis. But if they can walk on a treadmill, why are you getting the sestamibi? Sure there may be another reason they can’t have an treadmill EKG, but it’s pretty rare. Because of this, this test isn’t ordered very often.
Option D: Exercise Echo
- A really cool test, although not available in many places due to technical difficulties as well as comfort/practice of providers interpreting the imaging and test itself.
- No radiation. And no meds.
- Real physiologic stress walking on a treadmill + echo so they are looking for actual wall-motion abnormalities as the HR increases (less flow in diastole). Wall motion abnormalities equal ischemia. That’s pretty cool (even though it still doesn’t change outcome)
- But the key is they can see other things with Echo. Maybe the chest pain/shortness of breath was from aortic stenosis? They’d see it. Maybe there is a pericardial effusion? They’d see it. Maybe there’s mitral regurg and diastolic dysfunction.
- You can diagnose structural heart disease with stress Echo, even if it’s accidental
- Limitations:
- If they already have wall-motion abnormalities on an old Echo, you can’t necessarily see new ischemia in the same region (this would send you back up to ordering a sestamibi)
- Supposedly more expensive than sestamibi. I don’t know if this is true.
- Harder for the cardiologist to do. Makse sense. You can imagine them trying to do an Echo in the limited amount of the time the HR is fast.
- Again, many hospitals don’t have it… but we do.
Option E: Dobutmaine Echo
- The stress Echo for those that can’t walk.
- Contraindications are the same as Dobutamine sestamibi.
- History of ventricular arrhythmia. Dobutamine is slightly arrhythmogenic.
- Outflow tract obstruction (i.e. Aortic stenosis). Fast HR may not be compatible with life.
Option F: Cards Consult
- If you’re not sure about which stress test. Or you don’t think one is indicated.
- Cards can determine if they want to order a stress tests and which one.
- Argument against this: Slows down the visit by a few hours if you “know” they’re going to order one anyways.
- If they’ve had a recent stress test.
- Probably doesn’t make sense to repeat a test that was just done. Generally considered < 6 months – 12 months as the cutoff for “just done”.
- If they’re decently high risk / good story and you think cards just might take them straight to catheterization to “have a look”.
- Discussion of the evidence for cardiac catheterization in anyone not having a STEMI or refractory pain during an NSTEMI is a discussion for another day. Regardless, "elective" caths happens all the time and if you think cardiology might take the patient straight to cath, then what's the point of ordering a stress test?
Option G: Urgent Outpatient Cards Follow up
- Still follows ACC/AHA Guidelines if patient is deemed “low risk” and they are seen within 72 hours. Cardiology then decides in clinic whether or not to do the stress test in outpatient setting to comply with guidelines.
- Not used very often, because again, the overall practice is to do this in the ED. It is felt that most patient’s are too high risk to go home and that the stress is beneficial. This is a discussion for another day.
Option H: Stress Test and Cards Consult
- Don’t order both. It's not fair to cardiology. They will refer to the stress test which you can do just as well. If you have questions about the results of a stress test, have an inadequate test, or have questions after the test itself, you could ask cardiology for their input.
So there you have it. Hopefully you've found a few helpful pearls to use when choosing a stress tests or lack of a stress test for your patient with chest pain that you're admitting to the observation unit.
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