AttendingDocNJ

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Ordering a right type of stress test

Hey guys, if you are like me, you always get a little flustered when you see many options on deciding what kind of stress test to order in your patient suspicious of CAD. This article will break down the main differences between different types of stress tests and provide you an algorithm next time you are faced with this quandary. So let’s begin:

The two main types of stress tests are exercise and pharmacological. Let’s just start with that and forget about imaging for now. So what kind of patient would be a candidate for an exercise treadmill test? It's a patient that can walk at a hefty pace and well, exercise up to a certain exertion point. By guidelines, it is a patient that can “walk for more than 5 minutes on a flat ground or up to 1 to 2 flights of stairs without needing to stop.”1 So, if our patient has osteoarthritis of the knees and can’t handle this level of exercise workload, he or she wouldn’t be a candidate for an exercise stress test. Naturally, the only remaining choice would be a pharmacological stress test. Sounds easy so far? Good, because we are about to dig deeper.

Now, let’s assume that your patient can exercise and so you should obtain a baseline EKG for that patient. Why? Because if patient has an abnormal baseline EKG, we will need imaging to determine if any ischemic changes are present. Now, a bread-and-butter exercise EKG treadmill test is abnormal when you see a ST-depression > 1 mm in atleast 1 lead during the stress portion of it and within 7 minutes of recovery. That’s all you need: 1 lead! Also, the lead to keep an eye on is V5 which is the most specific and most sensitive.

Quick question: Does ST-depression during exercise EKG treadmill test localize ischemia to a particular coronary artery or region of the heart? No! However, in the instance that you see ST-elevation in leads without prior Q waves present there, that ST-elevation can localize ischemia to that specific region/coronary artery. ST-elevation in areas with prior Q waves does not indicate active ischemia but demonstrates further dysfunction of the infarcted myocardium and as you can imagine, worse prognosis.

Okay so having said that, if a baseline EKG already has any ST depression > 1 mm, then it wouldn’t be helpful to do an exercise EKG stress test on this patient as we will now need imaging. Other baseline EKG abnormalities for which exercise EKG treadmill test is not recommended are LBBB, paced rhythm, nonspecific intraventricular conduction delay > 120 ms, LVH, patient on digoxin, or pts with Wolff-Parkinson-White syndrome (WPW).

So now if your patient can exercise but has one of these aforementioned EKG abnormalities, what are our options? We have to use an imaging modality and it can be either stress echo or nuclear stress test (using technetium or thallium nuclear agents). What are technetium or thallium nuclear agents? They are radioisotopes which “light up” the heart to show the regions of activity and more importantly, inactivity with capture by gamma camera or through SPECT (single-photon emission computed tomography) technology during exercise. For these nuclear type of stress tests, which again can be pharmacological or exercise (we are currently focusing on the exercise aspect), there are two portions which make it a practical test. There is a resting portion where the images are taken during the rest and then during the exercise portion, when patient is put on a treadmill, 2nd set of images are captured. Naturally, these images are compared side-by-side to see what areas of the heart demonstrate ischemia. Makes sense? Great!

Okay, so couple exceptions now (you knew it couldn’t be that easy). For LBBB or paced rhythm, the only appropriate stress test is an adenosine pharmacological nuclear stress test. But why? Because, exercise or dobutamine will lead to septal motion abnormalities and septal defects in the setting of LBBB and can be interpreted as a positive stress test when that is not the case (false-positive!). In an event adenosine nuclear stress test isn’t possible (because patient is actively wheezing and thereby, bronchospastic), we can resort to exercise stress echo or dobutamine stress echo (preferred over dobutamine nuclear testing). We have to interpret it cautiously and focus on septal thickening rather than septal excursion. Another important exception: Patients with prior history of CABG or PCI: we should get stress imaging rather than just stress EKG as we want a test with a better sensitivity to ensure that this patient with already pre-existing history of coronary artery disease doesn't have any new lesions. This concept inherently makes sense as we want to use a stress test modality with relatively high specificity and sensitivity in these particular subset of patients.

*If patient is morbidly obese, best option is stress nuclear imaging with PET scan, which is not an available option at many facilities. Also, if need to assess the myocardial viability, then can do nuclear stress test with PET or cardiac MRI (again not the easiest option available).

Okay, time for an intermission. We covered the stress tests with exercise treadmill involvement. Now it is time to discuss pharmacological stress tests.

There are 2 types of pharmacological stress tests and you can guess them by now:

1) Vasodilator or Dobutamine nuclear stress test imaging

2) Dobutamine stress echo.

Okay, so the most common vasodilators you will see at your institution are: Adenosine [Adenoscan], Dipyridamole [Persantine], and Regadenoson [Lexiscan]. When are these vasodilators contraindicated? When patients are actively wheezing or have bronchospastic airways, hypotension (in which case stress test should be cancelled altogether), or SSS or high-degree AV block (please don’t do a stress test under these circumstances). Another point to keep in mind: Withhold Theophylline 48 hours before this type of stress test and caffeine 12 hours before it as these drugs interfere with the efficacy of vasodilators.

Dobutamine is a sympathomimetic, which stimulates the beta-1 receptors and causes increase of heart rate (chronotropic effect) and increase in myocardial contractility (inotropic effect). Dobutamine is the stress agent used for pharmacological stress echocardiography as remember these patients are not stressing themselves on their own by exercising. It is also a 2nd-line agent for nuclear stress test in the instance when vasodilators are contraindicated. Why is it a 2nd-line agent? Because vasodilators cause great filling of coronary arteries compared to dobutamine and in an instance when vasodilators are contraindicated, atropine is commonly employed with dobutamine to achieve maximal coronary vasodilation. When should you not use dobutamine? You guys guessed it: Uncontrolled arrhythmias (A.fib with RVR, V-tach, etc) is the main contraindication. Other ones are when patient has HTN urgency, unstable angina, aortic dissection, and recent MI but remember all these reasons in themselves are reasons not to do a stress test in first place. One point to keep in mind when using dobutamine is to make sure that patient hasn’t taken his beta-blocker 24 hours prior to the stress test as patient may not achieve the satisfactory heart rate for successful validity of the stress test. Okay, so we covered all the salient points and I have designed the algorithm below to simplify your clinical decision-making. If you like the way this concept was explained, please let me know and I will do other topics. As always, use your clinical judgment in actual circumstances.

References:

  1. Askew, J.W; Chareonthaitawee, P; Arruda-Olson, AM. Selecting the optimal cardiac stress test. In: UpToDate, Post TW (Ed), UptoDate, Waltham, MA.
  2. Hanna, Elias. (2009) Cardiology-Handbook for Clinicians. Arlington, VA: Scrub Hill Press, Inc.
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chessknt87

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I would also point out that recumbent bicycles exist as a form of exercise instead of just treadmills at some places. These allow people with exercise capacity but with bad joints to still get an exercise-based test done.
 
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AttendingDocNJ

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Thanks jdh71 for your kind comments and yeah I agree..asking a cardiologist is always an option. Chessknt87, I wasn't aware that they could use recumbent bicycles and so that's great..will have to look into that.
 

Instatewaiter

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Good review and important information for any internist to know.

I think the most important thing to know are that everyone should exercise unless they cant or shouldn't, when to use imaging and when to use nuclear vs echo as your imaging modality.
 
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PlutoBoy

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**** that. Lexiscan. Next patient. Thank you very much.
 

Instatewaiter

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**** that. Lexiscan. Next patient. Thank you very much.
Or you know, with 2 seconds of though you can get much more information from exercising the appropriate patient than doing a pharm... But you know money, laziness and stupidity are cool too.
 

PlutoBoy

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Or you know, with 2 seconds of though you can get much more information from exercising the appropriate patient than doing a pharm... But you know money, laziness and stupidity are cool too.
NM GXT and call it a day. Or I can consult you.
 
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PlutoBoy

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In all seriousness even if you look at the above algorithm if you combine NM with regadenoson you will be right most of the time, especially if you do at least a low level exercise as well (which we always tried to do).

The sensitivity is also higher than a regular exercise ECG (of course you already know this. I'm just saying.@Instatewaiter
 

viostorm

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Only thing I'd offer is IMO there is no reason to ever do an exercise ECG. If you are ordering this, just do an exercise stress echo. You get better sensitivity / specificity and get to assess for any congenital / valvular heart disease ... still with zero radiation.
 
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sacrament

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Only thing I'd offer is IMO there is no reason to ever do an exercise ECG. If you are ordering this, just do an exercise stress echo. You get better sensitivity / specificity and get to assess for any congenital / valvular heart disease ... still with zero radiation.
Three reasons I can readily think of to do a exercise treadmill test without imaging.
1) The only reason you are doing it is because the patient needs an annual stress test of some type for work purposes (i.e. the firefighters here in town are mandated to get one).
2) It's comparatively cheap. If the patient is self-pay, then it may be all they can afford.
3) You are really only interested in excluding very high risk disease, and your treatment plan would not change in the context of an abnormal but low-risk test. There are numerous clinical scenarios where this is the case. If your patient exercises >10 METs without chest pain or ECG changes, their prognosis is pretty good regardless of whatever the imaging part would show.
 
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Instatewaiter

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In all seriousness even if you look at the above algorithm if you combine NM with regadenoson you will be right most of the time, especially if you do at least a low level exercise as well (which we always tried to do).

The sensitivity is also higher than a regular exercise ECG (of course you already know this. I'm just saying.@Instatewaiter
Low level exercise adds almost nothing other than to limit symptoms from Regadenson. While sure, exercise alone doesn't have perfect sensitivity, exercise + imaging gives you the reliability of imaging plus the significant prognostic value of the exercise. And the prognostic value from exercise is one of the most robust risk stratification methods we have in all of medicine- and it works in all comers.

These stress tests are used most in stable angina and exercise EKGs tend not to miss severe multivessel CAD or LM/prox LAD disease, which quite frankly is the only thing that matters. We know that fixing stable angina doesn't improve outcomes, so missing a little LCx or RCA disease isn't that big of a deal. However, not recognizing the patient's significant mortality risk because of a poor stress test performance is a big deal. Furthermore, regadenason misses multiveesl/balanced CAD, while you are less likely to miss it with exercise + nuc imaging. And the wonderful thing is that if you don't reach heart rate, you just give Regadenason rescue and not only have your diagnostic imaging but also the prognostic information from the stress test.

PlutoBoy and JDH, why don't you guys just consult me next time
 
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jdh71

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I think remember saying elsewhere cardiologists were pendantic. You can't win. They love to tell you you're doing it wrong. So just let THEM do it. I don't GAF. Consult. Cards. Lol. Thanks.
 
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PlutoBoy

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Low level exercise adds almost nothing other than to limit symptoms from Regadenson. While sure, exercise alone doesn't have perfect sensitivity, exercise + imaging gives you the reliability of imaging plus the significant prognostic value of the exercise. And the prognostic value from exercise is one of the most robust risk stratification methods we have in all of medicine- and it works in all comers.

These stress tests are used most in stable angina and exercise EKGs tend not to miss severe multivessel CAD or LM/prox LAD disease, which quite frankly is the only thing that matters. We know that fixing stable angina doesn't improve outcomes, so missing a little LCx or RCA disease isn't that big of a deal. However, not recognizing the patient's significant mortality risk because of a poor stress test performance is a big deal. Furthermore, regadenason misses multiveesl/balanced CAD, while you are less likely to miss it with exercise + nuc imaging. And the wonderful thing is that if you don't reach heart rate, you just give Regadenason rescue and not only have your diagnostic imaging but also the prognostic information from the stress test.

PlutoBoy and JDH, why don't you guys just consult me next time
I will.

Reason for consult: Pick stress test.

Can't wait to see if I can pull this off! :D
 
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Raryn

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I will.

Reason for consult: Pick stress test.

Can't wait to see if I can pull this off! :D
Reason for consult: Risk stratification
Reason for consult: Preop evaluation
Reason for consult: Chest pain
Reason for consult: Troponin 0.12 in setting of <omfg badness>

All of them amount to the same question :p
 

Instatewaiter

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Reason for consult: Risk stratification
Reason for consult: Preop evaluation
Reason for consult: Chest pain
Reason for consult: Troponin 0.12 in setting of <omfg badness>

All of them amount to the same question :p
Thank you for this interesting consult. We appreciate being involved in this patient's care.
 

Raryn

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Thank you for this interesting consult. We appreciate being involved in this patient's care.
One of my interns actually included "Thank you for this interesting consult" as part of his template on various services. He had it in there for a few months before anyone actually told him the implications of the phrase.
 
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Siggy

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Reason for consult: Risk stratification
Reason for consult: Preop evaluation
Reason for consult: Chest pain
Reason for consult: Troponin 0.12 in setting of <omfg badness>

All of them amount to the same question :p
Preop eval? We can cath that.
Troponin of 0.12 in HF and ESRD? We can cath that.
Chest pain? We can cath you.
 
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Then yea.. cards love lexiscan. Want to see card's hate lexiscan? Have rads read it.

my rules as a practicing cardiologist

1- if pt can walk, do treadmill +/- imaging

2- get imaging component in nearly everyone (unless low low risk or super young and u just need a stress for liability reasons (post ER, ect)

3- if u want to cath get nuclear treadmill... If u don't want to cath get stress echo- I usually always get Nuc unless younger woman as easier and quicker to interpret.. Unless it's someone I want to reassure that their stress was completely normal in which case will get stress echo

4- if the pt can't walk or u suspect that they'll whine that they can't walk get lexiscan

5- never get a dobutamine stress echo

6- have radiology read if u really want to cath. They will over call everything..
 
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any good guides out there for interpreting unique features of a stress ECG? Wondering how to identify motion artifacts and differentiate from true abnormalities in particular as it is my understanding artifact can mimic diagnostic ST changes.
 
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nlax30

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