After 16 years of trying, just when I thought I was starting to get the hang of the interpretation of an ECG in the context of chest pain, They move the goalposts. In this case “They” are the Writing Group on behalf of the Joint ESC/ACCF/AHA/WHF Task Force for the Universal Definition of Myocardial Infarction. So the goalposts are really theirs to move, but it is still makes me cross!

“They” did this a year ago (on 24th August 2012 to be precise) and I only just found out. Many of you will be scoffing at my lack of perspicacity (but some of those will have to look up the definition of perspicacity, so I feel a bit better) and I agree. I don’t know how I missed it. For those of you in the same boat as me I have summarised the paper below:

For those who don’t want to read it all, the difference is outlined at the end; for the rest of you…

Reference:

Kristian Thygesen, Joseph S. Alpert, Allan S. Jaffe, Maarten L. Simoons, Bernard R. Chaitman and Harvey D. White: theWriting Group on behalf of the Joint ESC/ACCF/AHA/WHF Task Force for the Universal Definition of Myocardial. Infarction European Heart Journal (2012) 33, 2551–2567. August 2012.

Definition:

The term acute myocardial infarction (MI) should be used when there is evidence of myocardial necrosis in a clinical setting consistent with acute myocardial ischaemia. Under these conditions any one of the following criteria meets the diagnosis for MI:

• Detection of a rise and/or fall of cardiac biomarker values [preferably cardiac troponin (cTn)] with at least one value above the 99th percentile upper reference limit (URL) and with at least one of the following:

     -Symptoms of ischaemia.

     -New or presumed new significant ST-segment–T wave (ST–T) changes or new left bundle branch block (LBBB).

     -Development of pathological Q waves in the ECG.

     -Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality.

     -Identification of an intracoronary thrombus by angiography or autopsy.

• Cardiac death with symptoms suggestive of myocardial ischaemia and presumed new ischaemic ECG changes or new LBBB, but death occurred before cardiac biomarkers were obtained, or before cardiac biomarker values would be increased.

• Percutaneous coronary intervention (PCI) related MI is arbitrarily defined by elevation of cTn values (>5 x 99th percentile URL) in patients with normal baseline values (≤99th percentile URL) or a rise of cTn values >20% if the baseline values are elevated and are stable or falling. In addition, either:

      i.         Symptoms suggestive of myocardial ischaemia or

     ii.         new ischaemic ECG changes or

   iii.         angiographic findings consistent with a procedural complication or

    iv.         imaging demonstration of new loss of viable myocardium or new regional wall motion abnormality are required.

• Stent thrombosis associated with MI when detected by coronary angiography or autopsy in the setting of myocardial ischaemia and with a rise and/or fall of cardiac biomarker values with at least one value above the 99th percentile URL.

• Coronary artery bypass grafting (CABG) related MI is arbitrarily defined by elevation of cardiac biomarker values (>10 x 99th percentile URL) in patients with normal baseline cTn values (≤99th percentile URL). In addition, either:

      i.         new pathological Q waves or new LBBB, or

     ii.         angiographic documented new graft or new native coronary artery occlusion, or

   iii.         imaging evidence of new loss of viable myocardium or new regional wall motion abnormality.

So there is no change there from the Universal Definition of Myocardial Infarction published in November 2007 (Circulation. 2007; 116: 2634-2653).

Nor is there any change in the clinical classifications of MI either, they remain:

Type 1: Spontaneous myocardial infarction

Type 2: Myocardial infarction secondary to an ischaemic imbalance

Type 3: Myocardial infarction resulting in death when biomarker values are unavailable

Type 4a: Myocardial infarction related to percutaneous coronary intervention (PCI)

Type 4b: Myocardial infarction related to stent thrombosis

Type 5: Myocardial infarction related to coronary artery bypass grafting (CABG)

In the emergency department we are primarily concerned with the first two types and the differences are summarised below:

Type 1 MI

Type 2 MI

Spontaneous myocardial infarction related to atherosclerotic plaque rupture, ulceration, fissuring, erosion, or dissection with resulting intraluminal thrombus in one or more of the coronary arteries leading to decreased myocardial blood flow or distal platelet emboli with ensuing myocyte necrosis. The patient may have underlying severe CAD but on occasion non-obstructive or no CAD.

In instances of myocardial injury with necrosis where a condition other than CAD contributes to an imbalance between myocardial oxygen supply and/or demand, e.g. coronary endothelial dysfunction, coronary artery spasm, coronary embolism, tachy-/brady-arrhythmias, anaemia, respiratory failure, hypotension, and hypertension with or without LVH. 

The differences occur when we get to the ECG manifestations of myocardial infarction, the 2012 definition states:

ECG manifestations of acute myocardial ischaemia (in absence of LVH and LBBB)

ST elevation

New ST elevation at the J point in two contiguous leads with the cut-points: ≥0.1 mV in all leads other than leads V2–V3 where the following cut points apply: ≥0.2 mV in men ≥40 years; ≥0.25 mV in men <40 years, or ≥0.15 mV in women.

ST depression and T wave changes

New horizontal or down-sloping ST depression ≥0.05 mV in two contiguous leads and/or T inversion ≥0.1

The criteria highlighted in red are the new additions. Younger men are now allowed greater degree of ST elevation at the J point than in previous years without having an MI on ECG.

The 2007 paper is 22 pages long, the 2012 paper is 18 pages long. As far as my reading tells me, this is the only significant difference in the definitions that is applicable to the non-cardiologist dealing with patients with ischaemic chest pain.

Will Davies