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A 45-year-old man presents to your emergency department (ED) with a 2-hour history of chest pain.  It was localized to the left side of his chest, began while he was sitting at his desk at work and did not radiate to his arms, back or neck.  He denies any shortness of breath, nausea, vomiting or diaphoresis.  He is a non-smoker and states he walks regularly in the evenings after work.  He has never needed to stop walking due to chest pressure or shortness of breath.  You make note that he has a history of controlled hypertension for which he takes perindopril and that his father suffered a “heart attack” when he was 72 years old. 

He is brought in to the department where he undergoes an electrocardiogram (ECG) and has basic bloodwork drawn, including a highly-sensitive troponin (hsTrop).  The physician elects to send the patient for a Chest X-ray (CXR) as well.  He is given 2 ASA 81 mg to chew and some sublingual nitroglycerin (NTG) in an attempt to relieve his pain.

His ECG shows a normal sinus rhythm (NSR) with a heart rate (HR) of 72 beats per minute (bpm) and no signs of ischemia.  Two hsTrops drawn at 0 and 3 hours are normal.  His baseline bloodwork is also normal and his CXR is identified has having no acute processes.  His pain did not improve with NTG but seems to be alleviated at the moment.  He appears well and is anxious to be discharged. 

In the midst of a busy shift, you ask yourself should this patient be discharged from the ED or should he be admitted to hospital?  You look at the information in front of you and feel that the patient is at low-risk of having an acute coronary syndrome (ACS) and is well enough to be discharged.  But just to be safe, you grab the outpatient requisition for early follow-up through the Cardiac Assessment Clinic (CAC) – meaning you plan for low-risk patient to receive an exercise stress test (EST) soon after discharge “just to make sure everything is OK.” 

But, does the use of ESTs truly benefit our patients?  Should we be performing ESTs on all our low-risk chest pain patients?  Could we be causing harm by doing so?  Is there something that we can use at the bedside to help us differentiate our low-risk from our moderate-to-high risk chest pain patients?  I think we all need to take a step back and think about these important questions before we blindly reach for that EST requisition.  

It’s important to ask ourselves what we actually mean when we say, “just to make sure everything is OK.”  In most cases, this translates into “I don’t want to miss something.” During most of our training, we were taught that the miss rate for acute myocardial infarction (MI) in patients presenting to the ED was in the vicinity of 2%¹.  Certainly, this number makes us uncomfortable.  Most of us are not keen on missing this many MIs in our patient population.  However, when you look into this evidence further, you realize this 2% miss rate was based on patients who were actually already diagnosed with an MI.  It did not encompass all-comers to the ED with undifferentiated chest pain.  When you look more closely you see the miss rate of MI in undifferentiated chest pain patients was closer to 0.1-0.2%.  That’s a big difference.

This data seems very consistent when you look at other studies.  For example, Foy et. al in 2015 found a 0.1% miss rate of acute MI in a database consisting of roughly 420,000 patients presenting to the ED with chest pain².  Another trial³ found even lower numbers of miss rates than that of 0.1% when it looked at 3,543 patients admitted to hospital with chest pain.  These authors found a 0% miss rate of death and MI despite all patients being admitted to hospital. 

But let’s say for arguments sake we happen to send a patient home and miss the fact that patient is having an MI.  What happens then?  Does our patient do worse?  Not necessarily as patients that had missed MIs tended to do just as well as those who didn’t^1,4.   

With this in mind, wouldn’t it be fantastic to have a tool to help us evaluate risk in our chest pain patients that present to our departments?  And if we had it, would this tool potentially help us get patients at, or at least close to those above numbers of roughly 0.2% risk?  Is this helpful tool in the form of an EST or is there something even more readily available to us in the ED that is as accurate or even better? 

Certain tools have been used in the past to help us risk stratify our chest pain patients.  One such tool is the TIMI risk score⁵.  TIMI was first developed to look at a patient population that was already deemed to be high risk (patients already diagnosed with ACS) to see if they’d benefit from invasive medical therapies such as angiography.  However, does it meet the needs of our patients presenting to the ED with undifferentiated chest pain?  Well, it depends.  But the likely answer is no!  To try to use the TIMI risk score to evaluate low risk chest pain patients in the ED is like trying to use a hammer to insert a screw.  It uses a tool, but not the right tool for the job.⁶   So, the question is, do we have a proper, more accurate tool to assess these patients? 

Well actually, we do!  Enter the HEART score.  First created by Backus in 2008⁷, the heart score is a prediction model designed specifically to assess short term risk stratification of patients with possible ACS. This scoring system assesses important risk factors surrounding the patient (i.e. History, ECG, Age, Risk Factors, and Troponin) as predictors of Major Adverse Cardiac Events (MACE) which is defined as death, MI or the need for revascularization. 

The HEART score is an incredibly important tool as it has been externally validated across numerous studies.^8,9,10 Moreover, it outperforms other prediction models (such as TIMI) in comparison studies.¹¹ So, what can the HEART score actually tell us about our patients.  Well, it not only accurately predicts patients with low risk chest pain, but it also, based on the data the score collects, determines our patient’s risk of MACE.  Why is this important?  Well, as per the HEART score, a patient categorized as being low risk means he/she has a risk of MACE of less than 1%.  That’s less than that equivocal number of 2% quoted by Pope in 2000.    

But what if we dove deeper into the HEART score literature.  Can the HEART score do even better?

A meta-analysis¹² of 25,000 patients found that if you happened to live in North America, your risk of MACE dropped to 0.7%.  And, if you happened to use the HEART pathway,⁸ meaning you combined the HEART score with an hsTrop at 0 and 3 hours (and it was negative), the risk of MACE for said patient would become 0.3%.  Therefore, you have an externally validated tool that, if used correctly reduces the patient’s risk of MACE to less than/equal to 0.3%.  That is, your patient’s pretest probability (likelihood of having ACS prior to even considering an EST) is 0.3%. 

Let’s use our patient from the case above to highlight the use of the heart pathway.  For any of us working at the bedside in the emergency department I’d highly encourage you to download the Heart Pathway App onto your mobile device (available on the App store).  With this app, you can easily work through the pathway to determine a result.  Our patient above would score a 1 due to his history of hypertension.  We know that a HEART score of 0-3 deems patients to be low risk and results in a less than a 1% (more like 0.3% with the 0 and 3-hour hsTrop) chance of MACE within 30 days.     

Knowing this, we can say that this particular patient has a 0.3% likelihood of death, MI or the need for revascularization in the next 30 days!  But, as mentioned previously, should we then follow-up with an exercise stress test to “just make sure everything is ok?”  And, more importantly, does it actually help us risk stratify our patients even more (i.e. get the number lower than 0.3%)?

Let’s start with the accuracy of stress tests.  Are they actually good medical tools at identifying MI, death and the need for revascularization?  Justin Morgenstern from First10EM has an excellent summary of the literature on this very topic.¹³ In brief, the accuracy of ESTs actually plays out like this – they have a sensitivity of 45% and a specificity of 85% for coronary artery disease (CAD).  What does this mean for our above patient?  Well, if we send him for an exercise stress test, the test will be able to rule out CAD 45% of the time and rule in CAD 85% of the time.  Those are pretty poor numbers.  Moreover, if the test is negative, it won’t change the patient’s overall risk of roughly 0.3% (i.e. we are no further ahead after the stress test). 

But what about if he has a positive stress test?  Well, he still only has a 1% chance of MI over the short term.  Again, not much change from the HEART score’s calculation of less than 1%. Furthermore, we do need to understand that for every positive test, we will be left with 150 false positives.  Wow!  Let’s reiterate this point.  Every time we find a patient with a true positive test, the test will also yield 150 false positive tests!!!  That’s 150 patients with no significant CAD that will be sent onward for more invasive and more risky tests, such as angiography.    

Should this worry us?  Of course it should!  Although technology has inevitably reduced certain complications of angiography, this is still an invasive test that comes with inherent risks, some of which are life-threatening.  And what if a coronary lesion is found in a patient with low risk chest pain and a positive stress test?  Well, stenting the lesion does not appear to reduce mortality or MI.¹⁴ What?!?!  Yes, that’s what the evidence seems to show.  We know stenting saves lives in STEMI patient’s (that’s a bit of a no brainer) but how many STEMI patients are we sending for exercise stress tests?⁴

So, if we can fairly accurately predict which patients are low risk via a tool like the HEART pathway and we know that ESTs do not help further evaluation of our patients with low risk chest pain, then why do we continue to do them? 

The title “The Death of CAC” does not mean I completely believe in abolishing cardiac assessment clinics.  It simply implies abandoning the use of exercise stress tests for our low risk chest pain patients.  I would actually advocate for the opposite – that cardiac assessment clinics are maintained as long as they encompass a more comprehensive approach to patient care. 

Rather than tying up resources in a test that doesn’t get us any further ahead with respect to risk stratifying our chest pain patients discharged from the ED, perhaps we could look at a more integrated approach.  An approach that intertwines cardiac disease on multiple levels.  Rapid follow-up for our more moderate risk patients perhaps?  A means for rapid assessment of our heart failure patients who are teetering in the balance of possible admission?  Or perhaps the patient with atrial fibrillation who could receive rapid follow-up and potential delayed cardioversion (if warranted)?

Imagine the patient care possibilities that would exist for our cardiac patients in a multidisciplinary cardiac assessment clinic that, via a team approach, could assist in complex management plans moving forward.  Couple this with good follow up with patients family physicians in order to help manage their chronic diseases such as hypertension, diabetes and dyslipidemia as well as counselling around smoking cessation, diet and exercise, the system would create a powerhouse of resource utilization that would benefit our entire cardiac patient population.

So, where does this leave us?  In summary:

1. We miss very few MI’s in the ED.  Only 0.1-0.3% of our low risk chest pain patients go on to have an MI, not the 2% that was once quoted.
2. The HEART score/pathway is an extremely accurate tool to use when it comes to detecting these low-risk chest pain patients.  It is simple to use and can be done at the patient’s bedside.
3. Exercise stress tests are not accurate at predicting coronary artery disease let alone MI.  A negative test does not translate to lowering a patient’s risk any more than the HEART score does.
4. Exercise stress tests can cause harm for our patients.  For every positive test there will be 150 false positives!  These patients will likely be sent on for further, more invasive and riskier testing such as angiography. 
5. Together, beside nurses and physicians can encourage one another to take thorough histories from our patients and remind each other to use the HEART score to help predict risk in our chest pain patients.  Moreover, we can continually (and cordially) question the ordering of outpatient ESTs just to make sure “everything is OK.”
6. Cardiac Assessment Clinics are not necessarily dead.  They simply need reviving.  Reallocation of resources away from ESTs for our low-risk patients and placed towards a more comprehensive care approach only benefits all of our cardiac patients.  Just another example of how we can all keep working better, together!

References

1. Pope JH, Aufderheide TP, Ruthazer R, et al. Missed diagnoses of acute cardiac ischemia in the emergency department. N Engl J Med. 2000;342:(16)1163-70.
2. Foy AJ, Liu G, Davidson WR, Sciamanna C, Leslie DL. Comparative effectiveness of diagnostic testing strategies in emergency department patients with chest pain: an analysis of downstream testing, interventions, and outcomes. JAMA internal medicine. 2015; 175(3):428-36.
3. Napoli AM. The association between pretest probability of coronary artery disease and stress test utilization and outcomes in a chest pain observation unit. Academic emergency medicine: official journal of the Society for Academic Emergency Medicine. 2014; 21(4):401-7.
4. Helman, A. Morgenstern, J., Spiegel R. Cardiac Stress Testing After Negative Workup for MI. Emergency Medicine Cases. April, 2019. https://emergencymedicinecases.com/cardiac-stress-testing/. Accessed October 2019.
5. Antman EM, Cohen M, Bernink PJ, et al.  The TIMI risk score for unstable angina/non-ST elevation MI: A method for prognostication and therapeutic decision making.  JAMA. 2000;284(7)835-42.
6. Salim Rezaie, “Management and Disposition of Low Risk Chest Pain”, REBEL EM blog, February 18, 2016. Available at: https://rebelem.com/management-and-disposition-of-low-risk-chest-pain/.
7. Six AJ, Backus BE and Kelder JC.  Chest pain in the emergency room: value of the HEART score.  Netherlands Heart Journal. 2008;16(6)191-96.
8. Mahler SA, Riley RF, Hiestand BC, et al.  The HEART pathway randomized trial.  Circulation. 2015;8:195-203.
9. Poldervaart JM, Reitsma JB, Backus BE, et al.  Effect of using the HEART score in patients with chest pain in the emergency department; a stepped-wedge, cluster randomized trial. Ann Intern Med. 2017;166(10)689-97.
10. Backus BE, Six AJ, Kelder JC, et al.  A prospective validation of the HEART score for chest pain patients at the emergency department.  Int J Cardiol. 2013;168(3):2153-8.
11. Sun BC et al. Comparison of the HEART and TIMI Risk Scores for Suspected Acute Coronary Syndrome in the Emergency Department. Crit Pathw Cardiol 2016;15(1): 1-5
12. Laureano-Phillips J, Robinson RD, Aryal S, et al.  HEART score risk stratification of low-risk chest pain patients in the emergency department: a systematic review and meta-analysis. Ann Emerg Med. 2018;74(2)187-203.
13. Justin Morgenstern, “Stress Tests Part 3: Stress test accuracy”, First10EM blog, March 13, 2019. Available at: https://first10em.com/stress-test-accuracy/.
14. Justin Morgenstern, “Stress Tests Part 4: Revascularization and the Value of Stenting”, First10EM blog, March 14, 2019. Available at: https://first10em.com/revascularization-evidence/.

Cite this article as: Angus MacDonald, “The Death of CAC”, EMcenterED blog. October 31, 2019. Available at: https://emcentered.com/the-death-of-cac/.

Be sure to check out our other posts such as the use of the Zero Point Survey to better prepare for complex resuscitations.