Winston Salem, NC - Doctors are doing a good job identifying patients with evolving MI presenting to the emergency department with chest pain but without ST-segment elevation or an initial positive troponin test, a new study suggests [1].

The study, published in the August 1, 2008 issue of Emergency Medicine Journal, was conducted by a group led by Dr Chadwick Miller (Wake Forest University Baptist Medical Center, Winston Salem, NC).

He explained to heartwire that some patients who are having an MI might not always show a positive troponin when first presenting because it can take six to eight hours for troponins to rise after the start of an MI. And there is concern that, among patients without ST elevation or a positive initial troponin test, those with evolving MI might not be identified and therefore might not be treated as aggressively as they should be.

To look at this further, the researchers conducted an observational study using data from the Internet Tracking Registry for Acute Coronary Syndromes, a registry of patients presenting with undifferentiated chest pain. This analysis included patients without ST-segment elevation with at least two troponin assay results less than 12 hours apart. Patients were stratified into three groups: those with an initial negative but a second positive troponin assay (classified as evolving MI); those with an initial positive troponin assays (NSTEMI); and those with two negative troponin assays (no MI). Miller explained that the first two groups had similar conditions but different time frames; the first group was at an earlier stage in the course of their MI than the second group.

Of the 4136 patients studied, 5% were found to be having an evolving MI, 8% had NSTEMI, and 87% had no MI. Patients with evolving MI were more similar, with respect to demographic characteristics, presentation, admission patterns, and revascularization, to those with NSTEMI than to those with no MI, and 76% of the time, physicians' initial impressions suggested heightened concern for cardiac risk in the evolving-MI patients.

"Our results show that, on the whole, emergency physicians are doing a good job in picking up the patients with evolving MI before conclusive troponin tests are in," Miller commented to heartwire. "It was hard to tell from this study which factors are the most important in identifying these patients. It was a combination of findings from the patient's history, clinical examination, and ECG. But what we have shown is that the emergency doctor's best guess is usually right in finding these patients."

One of the symptoms of interest was chest pain described as burning. "We showed a strong association between burning chest pain and evolving MI. Burning chest pain is often taken as a symptom of GI reflux, but I think one message from our study is that we should not be discounting burning pain as reflux, as actually there is quite a high likelihood that it could be an ACS," Miller commented to heartwire.

He added that these results have implications for how a chest-pain triage system is managed. "There are places where the triage system could be improved. But on the whole, I am happy with what we saw here. It is reassuring to see that the admission patterns among the evolving-MI patients were more aggressive than with the patients found not to be having an MI, even though in both these groups the initial troponin results were not elevated. This suggests that clinicians are not allowing the initial negative troponin results to overshadow their clinical impression," he said.

Miller explained that one of the issues is that chest-pain patients thought not to be having an MI are sometimes sent for stress tests to rule out further cardiac causes before the second troponin test is back, but this would not be advisable for a patient who is having an evolving MI because it could induce ventricular arrhythmias. "If patients with evolving MI are lumped in with this group, then we could have a problem. But our results suggest that this is relatively unlikely to happen. In our study, of 4136 patients, just 187 were found to be having an evolving MI on the basis of the second troponin test. Because 76% of these were initially thought to be having an MI, unstable angina, or high-risk chest pain, only about 40 of these patients were not flagged after the initial examination," he noted.