It is another weary on call night, where annoyingly everyone has decided to have chest pain. As you sit down to scrutinise probably your tenth ECG, some ST elevation in lead AVR catches your eye. This jolts you from your torpor. Real pathology? You get your registrar to swing by and have a look. He furrows his brow as he looks down his nose at you, saying;
“ Remember, young padawan, one lead is no lead.” He reminds you of the STEMI criteria (1), which must be present in at least 2 anatomically contiguous leads:
- ≥1 mm (0.1 mV) of ST segment elevation in the limb leads
- ≥ 2 mm elevation in the precordial leads
- New LBBB
It turns out this teaching is not quite complete and will eventually cause you to miss some significant coronary occlusions. For you see, the classification of MIs into STEMI and NSTEMI is not some random division based on the aesthetic s of the ECG waveform. STEMI represents total occlusion of a coronary artery, therefore high risk of cardiogenic shock and death, and therefore benefit of immediate revascularisation. NSTEMI, on the other hand, an incomplete blockage, has failed to show benefit from immediate angiography (2).
The key point is that there are other ECG patterns that are also indicative of coronary occlusion which are simply not taught, mostly because they have only been described in the last decade or two, and unfortunately medicine can be slow to catch up. These “STEMI equivalents” cannot just be sat on, waiting for the troponin.
To start with, new LBBB is not even considered a STEMI criterion anymore (3). You can however interpret ST segments in a LBBB, despite what you might have been told, by utilising the ‘Scarbossi Criteria’. These will be covered in a separate post.
De Winter’s Waves
ST depression indicating NSTEMI? Think again.
A decade ago, De Winter et al described the above ECG pattern consisting of “1-to 3-mm upsloping ST-segment depression at the J point in leads V1 to V6 that continued into tall, positive symmetrical T waves. In most patients there was a 1- to 2-mm ST-elevation in lead aVR” (4). Continue reading