Flattened T waves, ST depression and prominent U waves (best in V2-V3) that can merge with the T to look like a long QT.
Low potassium flattens the T wave first. Then the ST sags, the P grows a little and the PR lengthens, and U waves appear: a second hump after the T, best in V2-V3. When the U is big and runs into the T, the QT looks long, but what you're really measuring is a QU interval. Think of it in anyone with vomiting, diarrhea or diuretics, and remember low magnesium usually travels with it. Together they set up torsades.
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.
Sinus rhythm with a QT too long for the rate: the T wave ends late, a QTc of 500 ms or more here, where the risk of torsades climbs.
A sagging, scooped ST depression (the reverse tick) where the R waves are tall, flattened T waves and a short QT. It means the patient takes digoxin, not that they're toxic.
Horizontal ST depression across many leads, deepest in V4-V6, I and II, with ST elevation in aVR (bigger than any in V1): global subendocardial ischemia, not a territory.
A long QT made by a long, flat ST segment, with a normal-looking T wave at the end of it.
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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