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)