Unstable angina still exists. Beware.

A middle aged male with h/o one stent 5 years prior presented with 7 hours of continuous vague chest pressure.  During this, while he got up to walk, he had some elbow pressure bilaterally.   He took some nitro without any relief.  By the time he arrived in the ED, he stated that it was gone.

He appeared very comfortable and had a normal exam.

Here is his initial ECG:

Normal

The patient and his wife were surprised that the physicians recommended hospitalization.

An initial sensitive contemporary (not high sensitive, as these are not yet FDA-approved in the United States) troponin I drawn at 8 hours ofter onset of discomfort returned at 0.025 ng/mL (99% reference is 0.30 ng/mL; thus this level was detectable, but normal).

2.5 hours later another ECG was recorded. It is not certain whether there was any chest discomfort at this time.

What do you see?

There is now extremely subtle ST elevation in II, III, and aVF.   Even more important, there is reciprocal ST depression in aVL.  This is diagnostic of inferior MI, especially when compared with the first one.  It was read as normal.

This was not seen.

The patient was admitted for a "rule out".

At 10.5 hours after pain onset, the second troponin returned at 0.42 ng/mL. This is above the 99% reference range and indicated myocardial infarction.  At this point, another ECG was recorded:

All diagnostic findings have resolved.

These dynamic findings were not noticed.   

The patient was interviewed by the admitting physician, and stated that he had some chest pressure again.  Another ECG was recorded:

Diagnostic of inferior STEMI

The patient went for prompt and successful angiography and PCI of inferior STEMI.

Learning Points

1. This patient had angina (unstable angina) for 7 hours without developing any hint of ACS on either his ECG or his troponin.  A measurable but negative troponin is a common finding in patients without ACS, though patients with a measurable troponin do have a higher incidence of adverse outcomes than patients with undetectable levels.  See paper below.

2.  Serial ECGs are essential for patients with ACS who have persistent or recurrent symptoms, or are at high risk.

3.  The findings on the serial ECGs must be scrutinized carefully.  The change from ECG 1 to ECG 2 was real, but subtle and not noticed by very fine and well-informed emergency physicians.

4. There are those who have pronounced a requiem for unstable angina, who believe that there is no longer any such thing as unstable angina. Here are many examples to contradict this notion.

5. You may rule out MI only if all 3 of these variables are negative: a 6 hour undetectable troponin, a truly normal serial ECG, and a low risk patient, but if any one of these variables is positive, it is insufficient.  In this case. all 3 were positive: troponin was detectable, patient was high risk (h/o CAD), and the 2nd ECG was not truly normal. 

See this paper: 

         Apple FS, Smith SW, Pearce LA, et al.  Use of the Centaur TnI-Ultra Assay for Detection of Myocardial Infarction and Adverse Events in Patients Presenting With Symptoms Suggestive of Acute Coronary Syndrome

         Here is a quote from the abstract: "The event rate in those with cTnI less then 0.006 g/L (undetectable) was significantly lower than in groups with cTnI 0.006 –0.04 g/L (detectable but in the normal range), 0.04 –0.10 g/L (slightly above normal), or 0.10 g/L (greater than 2.5 x the upper limit of normal)  (2.8% vs 11.1%, 24.1%, 55.1%, respectively; P 0.0001). Relative risks for the increasing cTnI cutoff groups were 3.9 (95% CI 1.2–13), 8.9 (2.4 – 34), and 25 (7.3–82) after adjustment for age, diabetes, history of hypertension, previous MI, and estimated glomerular filtration rate."