T waves that are tall, narrow at the base and peaked, best seen in the chest leads. As potassium rises, the P wave flattens, the PR lengthens and the QRS widens.
The earliest change is a taller T wave: peaked, narrow-based and symmetric, best seen in V2-V4. As potassium climbs, the P wave widens and flattens and the PR lengthens. Bradycardia follows (sinus, AV block, junctional or ventricular escapes), then a widening QRS of bizarre shape, and bundle branch and fascicular blocks. After that the QRS merges into the T wave (the sine wave), then VF, PEA or asystole. The serum potassium may not track closely with the ECG, so a near-normal ECG doesn't rule out a dangerous level.
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.
Upsloping ST depression of more than 1 mm at the J point in the chest leads, running into tall, symmetric T waves, with no ST elevation there and slight ST elevation in aVR.
ST elevation across V1-V4, from an occluded left anterior descending artery.
Sinus rhythm, a normal axis, normal intervals, R waves growing from V1 to V5, and no ST elevation or depression.
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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