Perspective: Acute MI “Yes” or “No”- Still more art than science

By Charles A. Pilcher MD FACEP
August, 2015

A recent article in BMJ Emergency Medicine got considerable press suggesting a new “high-sensitivity troponin T” test would predict who is and who is not having a heart attack – with 100% certainty.

Hopefully our skepticism rises whenever we see “100% certainty,” “foolproof,” “game-changer,” “breakthrough” or other such words.

Here’s what the report says. See if you can spot the “not so fast” language in this abstract of the article by Body et al. Here’s the abstract:

Objective To determine the diagnostic accuracy of emergency physician gestalt in emergency department (ED) patients with suspected cardiac chest pain, both alone and in combination with initial troponin level and ECG findings.
Methods We prospectively included patients presenting to the ED with suspected cardiac chest pain. Clinicians recorded their ‘gestalt’ at the time of presentation using a five-point Likert scale, blinded to outcome. Troponin T and high-sensitivity troponin T (hs-cTnT; both Roche Diagnostics Elecsys) levels were measured in admission blood samples. All patients underwent troponin testing at least 12 h after peak symptoms. The primary outcome was acute myocardial infarction (AMI).
Results 458 patients were included in this study, 81 (17.7%) of whom had AMI. Clinician gestalt alone had an area under the receiver operating characteristic curve of 0.76 (95% CI 0.70 to 0.82) for AMI. Immediately discharging patients with normal initial troponin and ECG in whom the clinician felt the diagnosis was ‘probably not’ or ‘definitely not’ acute coronary syndrome (ACS) would have avoided admission for 23.1% (95% CI 19% to 28%) patients with 100% sensitivity (95% CI 95.6% to 100%). With hs-cTnT, 100% sensitivity could have been achieved even if only patients with ‘probable’ or ‘definite’ ACS were investigated further, which would have allowed 41.7% patients to be discharged immediately.
Conclusions Gestalt alone cannot be used to ‘rule in’ or ‘rule out’ ACS. By combining clinician gestalt with the admission ECG and troponin level, we found 100% sensitivity without the need for serial troponin testing. These findings have the potential to reduce unnecessary hospital admissions for suspected ACS but must be prospectively validated before considering clinical implementation.

And here’s what I read – and why I’m skeptical:

  1. Clinical gestalt was accurate in 76% of the patients. That leaves only 24% of patients in whom the diagnosis remained in question. Not a very big sample size.
  2. Less than 18% actually had a heart attack. So just a random guess would make you right 82% of the time.
  3. The test was done 12 hours or more after onset of symptoms. Patients surviving 12 hours after their heart attack probably don’t have “the big one.” And by then whatever heart muscle has been injured will probably not recover, i. e., it doesn’t really matter – in most cases.
  4. 76% of patients could be admitted or sent home based on clinical gestalt alone. The remaining 24% (n=112) needed tests. A normal ECG and a normal standard troponin test plus clinical gestalt would have allowed safe discharge of 23% (n=26) of those 112 patients who were truly not having an MI. By finding a normal “high-senstivity troponin test,” that figure rises to about 48% (n=54), leaving 52% of the negative patients still in limbo. This is a 25% improvement, but the difference of 28 out of of the total of 458 patients, is only 6%, the number of additional patients who could be safely discharged through the use of the “high-sensitivity test” compared to clinical gestalt.
  5. Finally, ruling in or ruling out an MI is not the be-all and end-all of a chest pain evaluation. Too many physicians have discharged too many patients, telling them “I have some good news. You’re not having a heart attack.” Only to have the patient die hours to days later of a pulmonary embolus, an aortic dissection or even from a subsequent MI because the angina of an acute coronary syndrome was missed.

I guess if you’re one of that 6% and you didn’t need to be in the hospital, you might find the “fancy” (read “expensive”) test worth it. On the other hand, maybe you’d rather be one of those who were treated the old fashioned way: Stay in the hospital and have another test or two until we’re SURE you aren’t having a heart attack.

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