A normal P wave is positive (upright) in leads I and II, but negative (inverted) in aVR. It should be less than 3 small squares wide (120 ms), and less than 2.5 mm tall (or <1.5 mm in the chest leads V1-V6) at standard settings.
See also: P wave
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This ECG is from a man in his 60s who presented with intermittent shortness of breath and chest pressure over the past few days. This was his repeat ECG after the rhythm changed.
This ECG shows a sinus tachycardia with ST elevation in inferior leads and ST depression in anterior leads and aVL. He underwent angiography and had stents inserted to the left circumflex and right coronary arteries.
This ECG is from a man in his 60s who presented with sudden onset severe chest pain and dyspnoea. He had no medical history or medications. On arrival he was in extremis with altered mentation, cyanosis and diaphoresis . There was no palpable radial pulse. Pulse oximetry read HR 170 and saturation 53%. This was the repeat ECG after unsynchronised cardioversion.