Evaluation of Low Risk Chest Pain

Background for the residents: You will be seeing chest pain every day for the rest of your career, and need a straightforward & systematic approach to these patients. The easiest approach is to divide them into 2 or 3 risk categories. Two category system = discharge or admission. Three category system = discharge, chest pain unit, or admission.

If you have a tremendous amount of clinical experience, categorization can be done by clinical gestalt. Otherwise, consider using a decision aid. The HEART score is one of many; expect "new & improved" CP decision aids in the future.

Article 1: Mahler SA, Hiestand BC, Goff DC et at. Can the HEART Score Safely Reduce Stress Testing and Cardiac Imaging in Patients at Low Risk for Major Adverse Cardiac Events? Crit Pathways in Cardiol. 2011;10:128-133.

In this study of registry data, 1070 low-risk ED chest pain patients defined as “low risk CP” by physician assessment and TIMI score < 2 were dichotomized into low vs. high risk “HEART” (History, ECG, Age, Risk factors, Troponin) score groups. Primary outcome was major adverse cardiac events (MACE = death, MI, revascularization) occurring by 30 days. MACE occurred in 0.6% patients with low risk HEART scores compared with 4.2% of patients with high risk scores (odds ratio 8, significant). High risk score was 58% sensitive and 85% specific for MACE. Authors also looked at adding serial troponins to the HEART score. Abnormal serial troponins + high risk HEART = 100% sensitivity to pick up MACE (95%CI 72-100%).

Author conclusion: in low risk chest pain patients, low HEART scores can be used to guide stress testing/cardiac imaging and significantly reduce cardiac testing.

Issues: These are already really low risk patients; only 1.1% of entire cohort had MACE. Low risk HEART score reduces MACE to 0.6%, eg you will still miss 0.5%. Unless you admit everyone, you’ll never get to zero misses. Important societal question concerns our acceptable miss rate. Important to include patient in discussion of risk stratification; personal “acceptable miss rate” will vary among patients. Logistical issues; retrospective registry trial, and 30% of patients were lost to follow-up.

Although serial troponins weren’t part of initial study design, only 2 patients with negative serial troponins had MACE; one went to CABG and the other had sudden cardiac death; could argue that neither of these are true “misses”. Reaffirms importance of serial troponins.

An important caveat about this study: it looked at patients already stratified as low risk, THEN applied the HEART score to help predict MACE and decide who needs stress/cardiac imaging. It was NOT a study of all-comers to an ED who present with chest pain. Authors think of the HEART score like PERC; to be used for additional risk stratification in low risk patients. Finally, this doesn’t address the question of who needs a troponin (low risk vs. no risk).

Bottom line: HEART score useful for new clinicians to help further risk stratify low risk CP patients and decrease ordering of stress tests. Experienced clinicians will likely use gestalt + 2 troponins to reach the same conclusions.

Additional Harwood comments: HEART score of 0-3 = less than 1% chance of MACE with 2 year F/U. HEART score of 0-3 along with a second negative troponin = MACE of 0%. Although it has not been validated prospectively, a heart score of 0 or 1, seems to be safe for discharge with a single negative troponin. HEART score of 4-6 = death/MI risk of 12% in 2 years. These patients would be a candidate for a chest pain unit protocol that accepts intermediate risk patients. HEART score of 7-10 = 65% chance of death/MI (Backus: 2010). Obviously, these patients generally are admitted and will often end up in the cath lab.

Article 2: Ely S, Chandra A, Mani G et al. Utility of Observation Units for Young Emergency Department Chest Pain Patients. JEM 2013;44:306-312.

This retrospective observational study evaluated outcomes of 239 patients ≤ 40 yr old enrolled in an ED observation unit due to suspected ACS. Enrollment required ECG without ST changes, negative trop, normal VS and no dysrhythmias. Primary outcome: to evaluate the rate of abnormal stress tests associated with significant CAD. Five patients had positive stress tests. One additional patient had troponin elevation and a negative cath, but was labeled as +MI. Stress testing identified one patient with intervenable ACS. There was an 80% false positive stress test rate. At one year followup, 2 MI and 1 PCI for overall adverse cardiac outcome rate of 0.8% (95% CI 0.1-2.5%). Author conclusion: observation and stress testing should not be routinely performed in this demographic unless other high-risk features are present.

Issues: didn’t consider cocaine, also didn’t identify why 1/3 of patients didn’t receive stress tests. Nine stress tests were “indeterminate”, without further testing or good followup. Overall lost to followup = 21%.

Bottom line: due to limitations/lack of followup, may not be practice changing, but reinforces results from other studies that stress testing in young CP patients has very low diagnostic utility, with high false positive stress test rates (leading to more unnecessary testing, cost, complications).

Article 3:Shah BN, Balaji G, Alhajiri A, et al. Incremental Diagnostic and Prognostic Value of Contemporary Stress Echocardiography in a Chest Pain Unit Mortality and Morbidity Outcomes From a Real-World Setting. Circ Cardiovasc Imaging. 2013;6:202-209.

Last and least. This retrospective study evaluated outcomes in 811 patients admitted to a chest pain unit with ≥ 2 cardiac risk factors and suspected ACS but nondiagnostic ECG and negative 12 hour troponin who received stress echocardiogram (SE) within 24 hours. Primary outcome was the accuracy of SE for predicting mortality/MI. At one year, 2% rate of death or MI; 0.5% of patients in normal SE vs. 6.6% of patients in abnormal SE group died or had MI. No difference in 30 day re-admission rates between normal/abnormal SE groups. Author conclusions: stress echos are awesome.

Interesting that these were not low risk patients (had cardiac risk factors). 50% of patients received ultrasound contrast agents (not typical practice). Excellent followup (97% followed up at least one year)

Harwood comment: Shah found if patient had normal SE, they had 0 deaths @ 6 month & about 1%/yr for the next 3 yrs. Remember, in Shah's study his pts with a (+) stress ECHO had a 16% death rate after 3 yrs. Mean age was 63 this was a sicker population that is seen in most USA CT angio studies. In Litt's study of 1400 pts, (NEJM 2012) mean age was 49. There were zero deaths @ 30 days.

Big question and fatal flaw: how does this study help us? As Erik stated, for any test, you want to know what information it provides above and beyond what we already know. No demographic information is provided in order to compare patients with abnormal and normal stress tests, and therefore we can’t know if the SE is providing any additional prognostic information. Erik contacted the senior author, who responded but stated that the requested information was not available. Hmmmm.

Additional Harwood comments:

--If the patient has a normal coronary CT angiogram, it appears as though the only a 1% chance of having a MACE the next 5 years. (see March journal club)

--Traditional teaching is that Stress ECHO has 15% False (+) rate & 15% False (-) rate. This is based on studies where all Pt's get Stress & caths (i.e., a very high pretest prob group of CP pts)

CTA for low risk chest pain

Use of coronary CT Angiography in the evaluation of low-risk CP 

For starters, important to remember that the discussion is restricted to low-risk CP patients (our typical CPEP).  Tests will always have different performance characteristics in different patient populations.  Also, as discussed by CK,  our goal was to emphasize the prognostic/clinical strength of the test (how will these patients do once they are discharged from the ED?, can we pick up the 3-5% “missed ACS” cases?) rather than simply the diagnostic efficacy of the test (do the number of 50% blocked lesions match the number of lesions seen on invasive angiography?).   This is important, as EK mentioned in passing, because there is a whole other discussion out there about whether or not lesions seen on invasive angiography should be stented.   The COURAGE trial (April 12, 2007 NEJM) took patients with “stable” CP and documented 70% blockages on angiography or abnormal stress tests, and showed that mortality/MI rates were the same with maximal medical management or stenting.  So, our articles:

1.    Goldstein J, et al:  A Randomized Controlled Trial of Multi-Slice Coronary Computed Tomography for Evaluation   of Acute Chest Pain.  JACC 2007; 49(8):863-8712.     

197 low-risk patients, really compared 2 protocols; either 0/4 hour ECG/CIP then CTA, or 0/4/8 hour ECG/CIP then nuclear med (SPECT) stress testing.   No test complications in the CT group, and no major adverse cardiac events at 6 months in any of the patients sent home from either group.  Ultimately, accuracy was  equivalent for the two approaches.  Twenty-four % of the CTA group had intermediate disease on CTA or nondiagnostic CTA; these patients all required a second test (SPECT).  There were also 11% false positive CTAs.   The article emphasized the shorter ED length of stay for the CTA patients, but this was largely because of the additional time built into the SPECT protocol (a shorter rule-out time would have cut out much of the difference), and there was a several hundred dollar difference in “cost of care”, and as SA and CM pointed out, “cost of care” determinations are pretty much hand-waving.  Also, only a 4% rate of disease in the whole group- in this small study of only 200 patients, safety conclusions will have wide confidence intervals.

2.  Hollander J et al:  Coronary Computed Tomographic Angiography for Rapid Discharge of Low-Risk Patients With Potential Acute Coronary Syndromes.  Annals of Emergency Medicine, In Press.  

568 patients evaluated with coronary CTA, low TIMI score, either receiving CTA without serial CIP (some received one set) or CTA after observation period (if they came to the ED at night).  Everybody did great (except for the guy who died in a car crash).  No major adverse cardiac events at 30 days (0%, 95% CI 0% to 0.8%).   Again, a very low risk population (6 patients out of 568 received stents).   Conclusion that CTA can be used to safely send home low risk patients (<1% risk of MI/death at 30 days).   One large issue with the study-patients were enrolled in part because emergency physicians had decided to order a coronary CTA on them, introducing a significant selection bias.

 3. Takakuwa K,  Halpern E:  Evaluation of a “Triple Rule-Out” Coronary CT Angiography Protocol:  Use of 64-Section CT in Low-to-Moderate Risk ED Patients Suspected of Having Acute Coronary Syndrome.  Radiology 2008;248(2):438-446. 

This study had the same primary outcome of adverse clinical outcomes at 30 days, 197 low risk patients, but used the “Triple Rule-out” protocol, which involves higher radiation but evaluates the rest of the thorax.  Negative predictive value for CTA 99.4%, but small study, low risk population, so CI 96.9%-100%.  They did find other stuff;  PEs, dissections, pancreatic and pulmonary masses, among others.  Unfortunately, no clinically information was reported about the patients, so impossible to say if clinicians were already worried about these other diseases or not (serendipitous finds vs. clinically suspected).  AN made the excellent point that in his case, a MRI (like a CT would have) diagnosed his constrictive pericarditis and gave him a new lease on life.  As a counterpoint, CK related how a CT with a ?tumor finding led to her unnecessary surgery.   Always a balance.

Other things to remember about coronary CTA:  

-Static rather than Functional (stress test) study.

-For now, you need to be in normal sinus rhythm, and usually need betablockers/NTG to slow the HR and max. open the vessels to get good pictures.  Stents and high calcium scores muck up the pictures.
-Think about the potential complications/patient exclusions.  The radiation dose is substantial (10-20 mSv), which is estimated to increased overall cancer risk by 1 in 200 to 1 in several thousand.  Doesn’t mean not to do it, but easily ordered technologies tend to be overused-just something to think about.  Along the same line, what happens when the patient returns the next year with similar pain?  Another CT and more radiation?  How long are they “good for”?  Unknown.

-In these studies, no renal issues from the dye load, but they (and all studies so far) have been small-no more than several hundred patients.

Can I wrap it up already?  The room was pretty evenly split at the end of the night on whether they would advocate for this test in the vignette patient.  I think the potential speed of the test (at least compared to our current CPEP) was appealing to some.  To others, the potential to find other disease/explanations for the pain is an important selling point (“triple rule-out).  Remember, in these low risk patients, there is such a small chance of a poor outcome that you could just send them all home without any testing and be right 90-95% of the time, so we really need much larger studies in this low risk group to be happy about safety  (CIs for adverse cardiac outcomes are just too wide in studies 1 and 3.   Study 2 with <1% risk of adverse event at 30 days but significant selection bias).  For now, based on available data, coronary CTA is probably safe in low risk CP patients (similar performance to stress echo or nuclear stress/SPECT), and if you are trying to get more “bang for your buck” (thinking cardiac vs. PE, or cardiac vs. dissection), this might be the way to go.   SA also brought up the excellent point that depending on where you practice, if it’s a small hospital, this test can be tele-radiologied to someone to read even if you don’t have a CTA radiologist on-site, and you might not have a cardiologist available to do stress echoes.   So it comes down to patient selection (is CTA safe for your patient, and how clear is their clinical presentation) and what are the available resources/alternative strategies at your institution.