Horizontal ST depression in V1-V3 with tall R waves and upright T waves, and ST elevation in the posterior leads V7-V9.
The posterior wall faces away from the chest leads, so V1-V3 see its injury upside down. That's why it shows up there as horizontal ST depression, tall broad R waves (the mirror image of posterior Q waves) with R/S over 1 in V2, and upright T waves. The posterior leads V7 (left posterior axillary line), V8 (tip of the scapula) and V9 (left paraspinal), placed in V6's horizontal plane, show the elevation directly, and in those leads 0.5 mm counts. It usually comes with an inferior or lateral STEMI, and is isolated in 5-10% of infarcts. An early ECG may not show the tall R yet.
Each is a standard 12-lead: 2.5 seconds of each lead in four columns, with 10 seconds of lead II along the bottom, drawn to scale (25 mm a second, 10 mm a millivolt). The measurements are under each one.
ST elevation in II, III and aVF, with reciprocal ST depression in aVL.
ST elevation in I, aVL, V5 and V6, with reciprocal depression in III and aVF.
A QRS of 0.12 s or more with rSR' (an 'M') in V1-V3 and a wide, slurred S in I, aVL, V5 and V6.
A short PR (under 0.12 s), a slurred upstroke at the start of the QRS (the delta wave) and a QRS over 0.11 s.
The ECG tool in the app gives you a new 12-lead every time and walks you through reading it: rate, QRS, axis, then where the ST is up and down. It's part of the Paramedic level, and you can try 5 ECGs a day free.
Try the 12-lead drill
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